Commit 3c2c41e63608f63085f36bd31ec16bc90d76cbbb - swi-prolog

New upstream version 7.6.3+dfsg Lev Lamberov 6 years ago

231 changed file(s) with 20470 addition(s) and 11810 deletion(s). Raw diff Collapse all Expand all

-1

VERSION less more

0		7.6.2
	0	7.6.3

+11

-3

library/MANUAL less more

5	5
6	6	SWI-Prolog 7.6
7	7	Reference Manual
8		_U_p_d_a_t_e_d _f_o_r _v_e_r_s_i_o_n _7_._6_-_2_, _N_o_v_e_m_b_e_r _2_0_1_7
	8	_U_p_d_a_t_e_d _f_o_r _v_e_r_s_i_o_n _7_._6_-_3_, _N_o_v_e_m_b_e_r _2_0_1_7
9	9
10	10	_J_a_n _W_i_e_l_e_m_a_k_e_r
11	11	J.Wielemaker@vu.nl

30357	30357	ignores the first _C_o_u_n_t solutions.
30358	30358
30359	30359
30360		oorrddeerr__bbyy((_S_p_e_c_, _G_o_a_l))
	30360	ccaallll__nntthh((_:_G_o_a_l_, _?_N_t_h))
	30361	True when _G_o_a_l succeeded for the _N_t_h time. If _N_t_h is bound on
	30362	entry, the predicate succeeds deterministically if there are at
	30363	least _N_t_h solutions for _G_o_a_l.
	30364
	30365
	30366	oorrddeerr__bbyy((_+_S_p_e_c_, _:_G_o_a_l))
30361	30367	Order solutions according to _S_p_e_c. _S_p_e_c is a list of terms, where
30362	30368	each element is one of. The ordering of solutions of _G_o_a_l that
30363	30369	only differ in variables that are _n_o_t shared with _S_p_e_c is not

34144	34150
34145	34151	1188..22..3344 lliibbrraarryy((ssoolluuttiioonn__sseeqquueenncceess))
34146	34152
	34153	call_nth/2 True when Goal succeeded for the Nth time.
34147	34154	distinct/1 True if Goal is true and no previous solution of Goal bound Witness to the same value.
34148	34155	distinct/2 True if Goal is true and no previous solution of Goal bound Witness to the same value.
34149	34156	group_by/4 Group bindings of Template that have the same value for By.

34151	34158	offset/2 Ignore the first Count solutions.
34152	34159	order_by/2 Order solutions according to Spec.
34153	34160	reduced/1 Similar to distinct/1, but does not guarantee unique results in return for using a limited amount of memory.
	34161
34154	34162	reduced/3 Similar to distinct/1, but does not guarantee unique results in return for using a limited amount of memory.
34155	34163
34156	34164

34440	34448	_A_r_t _o_f _P_r_o_l_o_g. MIT Press, Cambridge,
34441	34449	Massachusetts, 1986.
34442	34450
34443		1966
	34451	1967

+167

-165

library/helpidx.pl less more

1123	1123	predicate(reduced,3,'Similar to distinct/1, but does not guarantee unique results in return for using a limited amount of memory.',30335,30347).
1124	1124	predicate(limit,2,'Limit the number of solutions.',30349,30353).
1125	1125	predicate(offset,2,'Ignore the first Count solutions.',30355,30359).
1126		predicate(group_by,4,'Group bindings of Template that have the same value for By.',30374,30380).
1127		predicate(table,1,'Declare predicate to be tabled',30656,30674).
1128		predicate(abolish_all_tables,0,'Abolish computed tables',30676,30683).
1129		predicate(abolish_table_subgoals,1,'Abolish tables for a goal',30685,30687).
1130		predicate(thread_pool_create,3,'Create a pool of threads.',30781,30798).
1131		predicate(thread_pool_destroy,1,'Destroy the thread pool named Name.',30800,30804).
1132		predicate(current_thread_pool,1,'True if Name refers to a defined thread pool.',30806,30808).
1133		predicate(thread_pool_property,2,'True if Property is a property of thread pool Name.',30810,30831).
1134		predicate(thread_create_in_pool,4,'Create a thread in Pool.',30833,30847).
1135		predicate(create_pool,1,'Hook to create a thread pool lazily.',30849,30863).
1136		predicate(vertices_edges_to_ugraph,3,'Create unweighted graph',30894,30912).
1137		predicate(vertices,2,'Find vertices in graph',30914,30920).
1138		predicate(edges,2,'Find edges in graph',30922,30929).
1139		predicate(add_vertices,3,'Add vertices to graph',30931,30939).
1140		predicate(del_vertices,3,'Delete vertices from graph',30941,30953).
1141		predicate(add_edges,3,'Add edges to graph',30955,30967).
1142		predicate(del_edges,3,'Delete edges from graph',30969,30979).
1143		predicate(transpose_ugraph,2,'Invert the direction of all edges',30981,30992).
1144		predicate(neighbours,3,'Find neighbors of vertice',30994,31003).
1145		predicate(neighbors,3,'Find neighbors of vertice',31005,31007).
1146		predicate(complement,2,'Inverse presense of edges',31009,31019).
1147		predicate(compose,3,'',31021,31029).
1148		predicate(ugraph_union,3,'Union of two graphs',31031,31038).
1149		predicate(top_sort,2,'Sort graph topologically',31040,31050).
1150		predicate(top_sort,3,'Sort graph topologically',31052,31055).
1151		predicate(transitive_closure,2,'Create transitive closure of graph',31057,31065).
1152		predicate(reachable,3,'Find all reachable vertices',31067,31075).
1153		predicate(global_url,3,'Translate a possibly relative URL into an absolute one.',31098,31102).
1154		predicate(is_absolute_url,1,'True if URL is an absolute URL.',31104,31107).
1155		predicate(http_location,2,'Construct or analyze an HTTP location.',31109,31120).
1156		predicate(parse_url,2,'Construct or analyse a URL.',31122,31179).
1157		predicate(parse_url,3,'Similar to parse_url/2 for relative URLs.',31181,31184).
1158		predicate(www_form_encode,2,'En/decode to/from application/x-www-form-encoded.',31186,31187).
1159		predicate(www_form_encode,2,'En/decode to/from application/x-www-form-encoded.',31189,31200).
1160		predicate(set_url_encoding,2,'Query and set the encoding for URLs.',31202,31209).
1161		predicate(url_iri,2,'Convert between a URL, encoding in US-ASCII and an IRI.',31211,31212).
1162		predicate(url_iri,2,'Convert between a URL, encoding in US-ASCII and an IRI.',31214,31218).
1163		predicate(parse_url_search,2,'Construct or analyze an HTTP search specification.',31220,31224).
1164		predicate(file_name_to_url,2,'Translate between a filename and a file:Sidiv{} URL.',31226,31227).
1165		predicate(file_name_to_url,2,'Translate between a filename and a file:Sidiv{} URL.',31229,31234).
1166		predicate(numbervars,1,'Number variables in Term using $VAR(N).',31260,31265).
1167		predicate(varnumbers,2,'Inverse of numbervars/1.',31267,31269).
1168		predicate(varnumbers,3,'Inverse of numbervars/3.',31271,31282).
1169		predicate(max_var_number,3,'True when Max is the max of Start and the highest numbered $VAR(N) term.',31284,31291).
1170		predicate(varnumbers_names,3,'If Term is a term with numbered and named variables using the reserved term \'$VAR\'(X), Copy is a copy of Term where each \'$VAR\'(X) is consistently replaced by a fresh variable and Bindings is a list `X = Var`, relating the `X` terms with the variable it is mapped to.',31293,31302).
1171		predicate(>>,2,'Calls a copy of Lambda.',31377,31378).
1172		predicate(>>,3,'Calls a copy of Lambda.',31380,31381).
1173		predicate(>>,4,'Calls a copy of Lambda.',31383,31384).
1174		predicate(>>,5,'Calls a copy of Lambda.',31386,31387).
1175		predicate(>>,6,'Calls a copy of Lambda.',31389,31390).
1176		predicate(>>,7,'Calls a copy of Lambda.',31392,31393).
1177		predicate(>>,8,'Calls a copy of Lambda.',31395,31396).
1178		predicate(>>,9,'Calls a copy of Lambda.',31398,31415).
1179		predicate(/,2,'Shorthand for `Free/[]Srshift{}Lambda`.',31417,31418).
1180		predicate(/,3,'Shorthand for `Free/[]Srshift{}Lambda`.',31420,31421).
1181		predicate(/,4,'Shorthand for `Free/[]Srshift{}Lambda`.',31423,31424).
1182		predicate(/,5,'Shorthand for `Free/[]Srshift{}Lambda`.',31426,31427).
1183		predicate(/,6,'Shorthand for `Free/[]Srshift{}Lambda`.',31429,31430).
1184		predicate(/,7,'Shorthand for `Free/[]Srshift{}Lambda`.',31432,31433).
1185		predicate(/,8,'Shorthand for `Free/[]Srshift{}Lambda`.',31435,31436).
1186		predicate(/,9,'Shorthand for `Free/[]Srshift{}Lambda`.',31438,31461).
1187		predicate(is_lambda,1,'True if Term is a valid Lambda expression.',31463,31465).
1188		predicate(lambda_calls,2,'Goal is the goal called if call/N is applied to LambdaExpression, where ExtraArgs are the additional arguments to call/N.',31467,31468).
1189		predicate(lambda_calls,3,'Goal is the goal called if call/N is applied to LambdaExpression, where ExtraArgs are the additional arguments to call/N.',31470,31475).
1190		predicate(prolog_current_frame,1,'Reference to goal\'s environment stack',31490,31496).
1191		predicate(prolog_current_choice,1,'Reference to most recent choice point',31498,31502).
1192		predicate(prolog_frame_attribute,3,'Obtain information on a goal environment',31504,31587).
1193		predicate(prolog_choice_attribute,3,'Examine the choice point stack',31589,31611).
1194		predicate(deterministic,1,'Test deterministicy of current clause',31613,31620).
1195		predicate(prolog_cut_to,1,'Realise global cuts',31625,31638).
1196		predicate(prolog_trace_interception,4,'library(user) Intercept the Prolog tracer',31643,31756).
1197		predicate(prolog_skip_frame,1,'Perform `skip\' on a frame',31758,31765).
1198		predicate(prolog_skip_level,2,'Indicate deepest recursion to trace',31767,31774).
1199		predicate(break_hook,6,'Hook (prolog) Debugger hook',31786,31863).
1200		predicate(prolog_exception_hook,4,'Rewrite exceptions',31873,31917).
1201		predicate(exception,3,'Hook (user) Handle runtime exceptions',31932,31958).
1202		predicate(prolog_list_goal,1,'Hook (user) Intercept tracer \'L\' command',31970,31976).
1203		predicate(debug_control_hook,1,'Hook (prolog) Extend spy/1, etc.',31978,32004).
1204		predicate(help_hook,1,'Hook (prolog) User-hook in the help-system',32006,32021).
1205		predicate(prolog_load_file,2,'Hook (user) Program load_files/2',32030,32041).
1206		predicate(comment_hook,3,'Hook (prolog) handle comments in sources',32043,32062).
1207		predicate(expects_dialect,1,'For which Prolog dialect is this code written?',32105,32131).
1208		predicate(exists_source,1,'Check existence of a Prolog source',32133,32137).
1209		predicate(source_exports,2,'Check whether source exports a predicate',32139,32142).
1210		predicate(license,0,'Evaluate licenses of loaded modules',32690,32697).
1211		predicate(license,2,'Define license for named module',32699,32717).
1212		predicate(license,1,'Define license for current file',32719,32722).
1213		predicate(known_licenses,0,'Print known licenses',32729,32733).
	1126	predicate(call_nth,2,'True when Goal succeeded for the Nth time.',30361,30365).
	1127	predicate(order_by,2,'Order solutions according to Spec.',30367,30378).
	1128	predicate(group_by,4,'Group bindings of Template that have the same value for By.',30380,30386).
	1129	predicate(table,1,'Declare predicate to be tabled',30662,30680).
	1130	predicate(abolish_all_tables,0,'Abolish computed tables',30682,30689).
	1131	predicate(abolish_table_subgoals,1,'Abolish tables for a goal',30691,30693).
	1132	predicate(thread_pool_create,3,'Create a pool of threads.',30787,30804).
	1133	predicate(thread_pool_destroy,1,'Destroy the thread pool named Name.',30806,30810).
	1134	predicate(current_thread_pool,1,'True if Name refers to a defined thread pool.',30812,30814).
	1135	predicate(thread_pool_property,2,'True if Property is a property of thread pool Name.',30816,30837).
	1136	predicate(thread_create_in_pool,4,'Create a thread in Pool.',30839,30853).
	1137	predicate(create_pool,1,'Hook to create a thread pool lazily.',30855,30869).
	1138	predicate(vertices_edges_to_ugraph,3,'Create unweighted graph',30900,30918).
	1139	predicate(vertices,2,'Find vertices in graph',30920,30926).
	1140	predicate(edges,2,'Find edges in graph',30928,30935).
	1141	predicate(add_vertices,3,'Add vertices to graph',30937,30945).
	1142	predicate(del_vertices,3,'Delete vertices from graph',30947,30959).
	1143	predicate(add_edges,3,'Add edges to graph',30961,30973).
	1144	predicate(del_edges,3,'Delete edges from graph',30975,30985).
	1145	predicate(transpose_ugraph,2,'Invert the direction of all edges',30987,30998).
	1146	predicate(neighbours,3,'Find neighbors of vertice',31000,31009).
	1147	predicate(neighbors,3,'Find neighbors of vertice',31011,31013).
	1148	predicate(complement,2,'Inverse presense of edges',31015,31025).
	1149	predicate(compose,3,'',31027,31035).
	1150	predicate(ugraph_union,3,'Union of two graphs',31037,31044).
	1151	predicate(top_sort,2,'Sort graph topologically',31046,31056).
	1152	predicate(top_sort,3,'Sort graph topologically',31058,31061).
	1153	predicate(transitive_closure,2,'Create transitive closure of graph',31063,31071).
	1154	predicate(reachable,3,'Find all reachable vertices',31073,31081).
	1155	predicate(global_url,3,'Translate a possibly relative URL into an absolute one.',31104,31108).
	1156	predicate(is_absolute_url,1,'True if URL is an absolute URL.',31110,31113).
	1157	predicate(http_location,2,'Construct or analyze an HTTP location.',31115,31126).
	1158	predicate(parse_url,2,'Construct or analyse a URL.',31128,31185).
	1159	predicate(parse_url,3,'Similar to parse_url/2 for relative URLs.',31187,31190).
	1160	predicate(www_form_encode,2,'En/decode to/from application/x-www-form-encoded.',31192,31193).
	1161	predicate(www_form_encode,2,'En/decode to/from application/x-www-form-encoded.',31195,31206).
	1162	predicate(set_url_encoding,2,'Query and set the encoding for URLs.',31208,31215).
	1163	predicate(url_iri,2,'Convert between a URL, encoding in US-ASCII and an IRI.',31217,31218).
	1164	predicate(url_iri,2,'Convert between a URL, encoding in US-ASCII and an IRI.',31220,31224).
	1165	predicate(parse_url_search,2,'Construct or analyze an HTTP search specification.',31226,31230).
	1166	predicate(file_name_to_url,2,'Translate between a filename and a file:Sidiv{} URL.',31232,31233).
	1167	predicate(file_name_to_url,2,'Translate between a filename and a file:Sidiv{} URL.',31235,31240).
	1168	predicate(numbervars,1,'Number variables in Term using $VAR(N).',31266,31271).
	1169	predicate(varnumbers,2,'Inverse of numbervars/1.',31273,31275).
	1170	predicate(varnumbers,3,'Inverse of numbervars/3.',31277,31288).
	1171	predicate(max_var_number,3,'True when Max is the max of Start and the highest numbered $VAR(N) term.',31290,31297).
	1172	predicate(varnumbers_names,3,'If Term is a term with numbered and named variables using the reserved term \'$VAR\'(X), Copy is a copy of Term where each \'$VAR\'(X) is consistently replaced by a fresh variable and Bindings is a list `X = Var`, relating the `X` terms with the variable it is mapped to.',31299,31308).
	1173	predicate(>>,2,'Calls a copy of Lambda.',31383,31384).
	1174	predicate(>>,3,'Calls a copy of Lambda.',31386,31387).
	1175	predicate(>>,4,'Calls a copy of Lambda.',31389,31390).
	1176	predicate(>>,5,'Calls a copy of Lambda.',31392,31393).
	1177	predicate(>>,6,'Calls a copy of Lambda.',31395,31396).
	1178	predicate(>>,7,'Calls a copy of Lambda.',31398,31399).
	1179	predicate(>>,8,'Calls a copy of Lambda.',31401,31402).
	1180	predicate(>>,9,'Calls a copy of Lambda.',31404,31421).
	1181	predicate(/,2,'Shorthand for `Free/[]Srshift{}Lambda`.',31423,31424).
	1182	predicate(/,3,'Shorthand for `Free/[]Srshift{}Lambda`.',31426,31427).
	1183	predicate(/,4,'Shorthand for `Free/[]Srshift{}Lambda`.',31429,31430).
	1184	predicate(/,5,'Shorthand for `Free/[]Srshift{}Lambda`.',31432,31433).
	1185	predicate(/,6,'Shorthand for `Free/[]Srshift{}Lambda`.',31435,31436).
	1186	predicate(/,7,'Shorthand for `Free/[]Srshift{}Lambda`.',31438,31439).
	1187	predicate(/,8,'Shorthand for `Free/[]Srshift{}Lambda`.',31441,31442).
	1188	predicate(/,9,'Shorthand for `Free/[]Srshift{}Lambda`.',31444,31467).
	1189	predicate(is_lambda,1,'True if Term is a valid Lambda expression.',31469,31471).
	1190	predicate(lambda_calls,2,'Goal is the goal called if call/N is applied to LambdaExpression, where ExtraArgs are the additional arguments to call/N.',31473,31474).
	1191	predicate(lambda_calls,3,'Goal is the goal called if call/N is applied to LambdaExpression, where ExtraArgs are the additional arguments to call/N.',31476,31481).
	1192	predicate(prolog_current_frame,1,'Reference to goal\'s environment stack',31496,31502).
	1193	predicate(prolog_current_choice,1,'Reference to most recent choice point',31504,31508).
	1194	predicate(prolog_frame_attribute,3,'Obtain information on a goal environment',31510,31593).
	1195	predicate(prolog_choice_attribute,3,'Examine the choice point stack',31595,31617).
	1196	predicate(deterministic,1,'Test deterministicy of current clause',31619,31626).
	1197	predicate(prolog_cut_to,1,'Realise global cuts',31631,31644).
	1198	predicate(prolog_trace_interception,4,'library(user) Intercept the Prolog tracer',31649,31762).
	1199	predicate(prolog_skip_frame,1,'Perform `skip\' on a frame',31764,31771).
	1200	predicate(prolog_skip_level,2,'Indicate deepest recursion to trace',31773,31780).
	1201	predicate(break_hook,6,'Hook (prolog) Debugger hook',31792,31869).
	1202	predicate(prolog_exception_hook,4,'Rewrite exceptions',31879,31923).
	1203	predicate(exception,3,'Hook (user) Handle runtime exceptions',31938,31964).
	1204	predicate(prolog_list_goal,1,'Hook (user) Intercept tracer \'L\' command',31976,31982).
	1205	predicate(debug_control_hook,1,'Hook (prolog) Extend spy/1, etc.',31984,32010).
	1206	predicate(help_hook,1,'Hook (prolog) User-hook in the help-system',32012,32027).
	1207	predicate(prolog_load_file,2,'Hook (user) Program load_files/2',32036,32047).
	1208	predicate(comment_hook,3,'Hook (prolog) handle comments in sources',32049,32068).
	1209	predicate(expects_dialect,1,'For which Prolog dialect is this code written?',32111,32137).
	1210	predicate(exists_source,1,'Check existence of a Prolog source',32139,32143).
	1211	predicate(source_exports,2,'Check whether source exports a predicate',32145,32148).
	1212	predicate(license,0,'Evaluate licenses of loaded modules',32696,32703).
	1213	predicate(license,2,'Define license for named module',32705,32723).
	1214	predicate(license,1,'Define license for current file',32725,32728).
	1215	predicate(known_licenses,0,'Print known licenses',32735,32739).
1214	1216
1215	1217
1216	1218	% Predicate section/4

1352	1354	section([4,17,1],'Predefined stream aliases',8024,8060).
1353	1355	section([4,17,2],'ISO Input and Output Streams',8062,8585).
1354	1356	section([4,17,3],'Edinburgh-style I/O',8587,8705).
1355		section([],'Compatibility notes',8635,34444).
	1357	section([],'Compatibility notes',8635,34452).
1356	1358	section([4,17,4],'Switching between Edinburgh and ISO I/O',8707,8731).
1357	1359	section([4,17,5],'Write onto atoms, code-lists, etc.',8733,8786).
1358	1360	section([4,17,6],'Fast binary term I/O',8788,8829).

1574	1576	section([12,3,2],'The swipl-rc program',23837,23866).
1575	1577	section([12,4],'Finding Application files',23868,23913).
1576	1578	section([12,4,1],'Specifying a file search path from the command line',23900,23913).
1577		section([13],'THE SWI-PROLOG LIBRARY',23915,31475).
	1579	section([13],'THE SWI-PROLOG LIBRARY',23915,31481).
1578	1580	section([13,1],'library(aggregate): Aggregation operators on backtrackable',23939,24105).
1579	1581	section([13,2],'library(apply): Apply predicates on a list',24107,24219).
1580	1582	section([13,3],'library(assoc): Association lists',24221,24384).

1668	1670	section([13,33,4,1],'Example 1',30116,30149).
1669	1671	section([13,33,4,2],'Example 2',30151,30211).
1670	1672	section([13,33,4,3],'Example 3',30213,30261).
1671		section([13,34],'library(solution_sequences): Modify solution sequences',30263,30380).
1672		section([13,35],'library(tabling): Tabled execution (SLG)',30382,30743).
1673		section([13,35,0,1],'Example 1: using tabling for memoizing',30412,30497).
1674		section([13,35,0,2],'Example 2: avoiding non-termination',30499,30560).
1675		section([13,35,0,3],'Mode directed tabling',30562,30651).
1676		section([13,35,1],'Tabling predicate reference',30653,30743).
1677		section([13,35,1,1],'About the tabling implementation',30689,30723).
1678		section([13,35,1,2],'Status of tabling',30725,30743).
1679		section([13,36],'library(thread_pool): Resource bounded thread management',30745,30863).
1680		section([13,37],'library(ugraphs): Unweighted Graphs',30865,31075).
1681		section([13,38],'library(url): Analysing and constructing URL',31077,31234).
1682		section([13,39],'library(varnumbers): Utilities for numbered terms',31236,31302).
1683		section([13,40],'library(yall): Lambda expressions',31304,31475).
1684		section([14],'HACKERS CORNER',31477,32062).
1685		section([14,1],'Examining the Environment Stack',31487,31620).
1686		section([14,2],'Ancestral cuts',31622,31638).
1687		section([14,3],'Intercepting the Tracer',31640,31774).
1688		section([14,4],'Breakpoint and watchpoint handling',31776,31863).
1689		section([14,5],'Adding context to errors: prolog_exception_hook',31865,31917).
1690		section([14,6],'Hooks using the exception predicate',31919,31958).
1691		section([14,7],'Hooks for integrating libraries',31960,32021).
1692		section([14,8],'Hooks for loading files',32023,32062).
1693		section([15],'COMPATIBILITY WITH OTHER PROLOG DIALECTS',32064,32260).
1694		section([15,1],'Some considerations for writing portable code',32144,32260).
1695		section([16],'GLOSSARY OF TERMS',32262,32606).
1696		section([17],'SWI-PROLOG LICENSE CONDITIONS AND TOOLS',32608,32769).
1697		section([17,1],'Contributing to the SWI-Prolog project',32668,32677).
1698		section([17,2],'Software support to keep track of license conditions',32679,32733).
1699		section([17,3],'License conditions inherited from used code',32735,32769).
1700		section([17,3,1],'Cryptographic routines',32738,32769).
1701		section([18],'SUMMARY',32771,34353).
1702		section([18,1],'Predicates',32774,33628).
1703		section([18,2],'Library predicates',33630,34200).
1704		section([18,2,1],'library(aggregate)',33633,33641).
1705		section([18,2,2],'library(apply)',33643,33664).
1706		section([18,2,3],'library(assoc)',33666,33683).
1707		section([18,2,4],'library(broadcast)',33685,33695).
1708		section([18,2,5],'library(charsio)',33697,33714).
1709		section([18,2,6],'library(check)',33716,33733).
1710		section([18,2,7],'library(clpb)',33735,33743).
1711		section([18,2,8],'library(clpfd)',33745,33794).
1712		section([18,2,9],'library(clpqr)',33796,33808).
1713		section([18,2,10],'library(csv)',33810,33823).
1714		section([18,2,11],'library(debug)',33825,33838).
1715		section([18,2,12],'library(error)',33840,33856).
1716		section([18,2,13],'library(iostream)',33858,33859).
1717		section([18,2,14],'library(summaries.d/iostream/tex)',33861,33862).
1718		section([18,2,15],'library(lists)',33864,33902).
1719		section([18,2,16],'library(main)',33904,33908).
1720		section([18,2,17],'library(option)',33910,33919).
1721		section([18,2,18],'library(optparse)',33921,33928).
1722		section([18,2,19],'library(ordsets)',33930,33954).
1723		section([18,2,20],'library(persistency)',33956,33965).
1724		section([18,2,21],'library(predicate_options)',33967,33981).
1725		section([18,2,22],'library(prologpack)',33983,33999).
1726		section([18,2,23],'library(prologxref)',34001,34013).
1727		section([18,2,24],'library(pairs)',34015,34023).
1728		section([18,2,25],'library(pio)',34025,34037).
1729		section([18,2,25,1],'library(pure_input)',34028,34037).
1730		section([18,2,26],'library(random)',34039,34056).
1731		section([18,2,27],'library(readutil)',34058,34066).
1732		section([18,2,28],'library(record)',34068,34071).
1733		section([18,2,29],'library(registry)',34073,34085).
1734		section([18,2,30],'library(simplex)',34087,34101).
1735		section([18,2,31],'library(ugraphs)',34103,34124).
1736		section([18,2,32],'library(url)',34126,34139).
1737		section([18,2,33],'library(www_browser)',34141,34144).
1738		section([18,2,34],'library(solution_sequences)',34146,34156).
1739		section([18,2,35],'library(thread_pool)',34158,34166).
1740		section([18,2,36],'library(varnumbers)',34168,34175).
1741		section([18,2,37],'library(yall)',34177,34200).
1742		section([18,3],'Arithmetic Functions',34202,34286).
1743		section([18,4],'Operators',34288,34353).
1744		section([19],'Bibliography',34355,34444).
	1673	section([13,34],'library(solution_sequences): Modify solution sequences',30263,30386).
	1674	section([13,35],'library(tabling): Tabled execution (SLG)',30388,30749).
	1675	section([13,35,0,1],'Example 1: using tabling for memoizing',30418,30503).
	1676	section([13,35,0,2],'Example 2: avoiding non-termination',30505,30566).
	1677	section([13,35,0,3],'Mode directed tabling',30568,30657).
	1678	section([13,35,1],'Tabling predicate reference',30659,30749).
	1679	section([13,35,1,1],'About the tabling implementation',30695,30729).
	1680	section([13,35,1,2],'Status of tabling',30731,30749).
	1681	section([13,36],'library(thread_pool): Resource bounded thread management',30751,30869).
	1682	section([13,37],'library(ugraphs): Unweighted Graphs',30871,31081).
	1683	section([13,38],'library(url): Analysing and constructing URL',31083,31240).
	1684	section([13,39],'library(varnumbers): Utilities for numbered terms',31242,31308).
	1685	section([13,40],'library(yall): Lambda expressions',31310,31481).
	1686	section([14],'HACKERS CORNER',31483,32068).
	1687	section([14,1],'Examining the Environment Stack',31493,31626).
	1688	section([14,2],'Ancestral cuts',31628,31644).
	1689	section([14,3],'Intercepting the Tracer',31646,31780).
	1690	section([14,4],'Breakpoint and watchpoint handling',31782,31869).
	1691	section([14,5],'Adding context to errors: prolog_exception_hook',31871,31923).
	1692	section([14,6],'Hooks using the exception predicate',31925,31964).
	1693	section([14,7],'Hooks for integrating libraries',31966,32027).
	1694	section([14,8],'Hooks for loading files',32029,32068).
	1695	section([15],'COMPATIBILITY WITH OTHER PROLOG DIALECTS',32070,32266).
	1696	section([15,1],'Some considerations for writing portable code',32150,32266).
	1697	section([16],'GLOSSARY OF TERMS',32268,32612).
	1698	section([17],'SWI-PROLOG LICENSE CONDITIONS AND TOOLS',32614,32775).
	1699	section([17,1],'Contributing to the SWI-Prolog project',32674,32683).
	1700	section([17,2],'Software support to keep track of license conditions',32685,32739).
	1701	section([17,3],'License conditions inherited from used code',32741,32775).
	1702	section([17,3,1],'Cryptographic routines',32744,32775).
	1703	section([18],'SUMMARY',32777,34361).
	1704	section([18,1],'Predicates',32780,33634).
	1705	section([18,2],'Library predicates',33636,34208).
	1706	section([18,2,1],'library(aggregate)',33639,33647).
	1707	section([18,2,2],'library(apply)',33649,33670).
	1708	section([18,2,3],'library(assoc)',33672,33689).
	1709	section([18,2,4],'library(broadcast)',33691,33701).
	1710	section([18,2,5],'library(charsio)',33703,33720).
	1711	section([18,2,6],'library(check)',33722,33739).
	1712	section([18,2,7],'library(clpb)',33741,33749).
	1713	section([18,2,8],'library(clpfd)',33751,33800).
	1714	section([18,2,9],'library(clpqr)',33802,33814).
	1715	section([18,2,10],'library(csv)',33816,33829).
	1716	section([18,2,11],'library(debug)',33831,33844).
	1717	section([18,2,12],'library(error)',33846,33862).
	1718	section([18,2,13],'library(iostream)',33864,33865).
	1719	section([18,2,14],'library(summaries.d/iostream/tex)',33867,33868).
	1720	section([18,2,15],'library(lists)',33870,33908).
	1721	section([18,2,16],'library(main)',33910,33914).
	1722	section([18,2,17],'library(option)',33916,33925).
	1723	section([18,2,18],'library(optparse)',33927,33934).
	1724	section([18,2,19],'library(ordsets)',33936,33960).
	1725	section([18,2,20],'library(persistency)',33962,33971).
	1726	section([18,2,21],'library(predicate_options)',33973,33987).
	1727	section([18,2,22],'library(prologpack)',33989,34005).
	1728	section([18,2,23],'library(prologxref)',34007,34019).
	1729	section([18,2,24],'library(pairs)',34021,34029).
	1730	section([18,2,25],'library(pio)',34031,34043).
	1731	section([18,2,25,1],'library(pure_input)',34034,34043).
	1732	section([18,2,26],'library(random)',34045,34062).
	1733	section([18,2,27],'library(readutil)',34064,34072).
	1734	section([18,2,28],'library(record)',34074,34077).
	1735	section([18,2,29],'library(registry)',34079,34091).
	1736	section([18,2,30],'library(simplex)',34093,34107).
	1737	section([18,2,31],'library(ugraphs)',34109,34130).
	1738	section([18,2,32],'library(url)',34132,34145).
	1739	section([18,2,33],'library(www_browser)',34147,34150).
	1740	section([18,2,34],'library(solution_sequences)',34152,34164).
	1741	section([18,2,35],'library(thread_pool)',34166,34174).
	1742	section([18,2,36],'library(varnumbers)',34176,34183).
	1743	section([18,2,37],'library(yall)',34185,34208).
	1744	section([18,3],'Arithmetic Functions',34210,34294).
	1745	section([18,4],'Operators',34296,34361).
	1746	section([19],'Bibliography',34363,34452).
1745	1747
1746	1748
1747	1749	% Predicate function/3

1975	1977	function('PL_malloc_atomic_uncollectable',23407,23413).
1976	1978	function('PL_malloc_stubborn',23415,23416).
1977	1979	function('PL_end_stubborn_change',23418,23421).
1978		function('PL_license',32724,32727).
	1980	function('PL_license',32730,32733).
1979	1981
1980	1982

+83

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 2.21</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 2.21</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
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7	7	<link rel="summary" href="summary.html">

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191	232	<a class="nav" href="limits.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:64bits"><a name="sec:2.21"><span class="sec-nr">2.21</span> <span class="sec-title">SWI-Prolog
	235	<h2 id="sec:64bits"><a id="sec:2.21"><span class="sec-nr">2.21</span> <span class="sec-title">SWI-Prolog
195	236	and 64-bit machines</span></a></h2>
196	237
197		<a name="sec:64bits"></a>
198
199		<p><a name="idx:bits64:285"></a>Most of today's 64-bit platforms are
	238	<a id="sec:64bits"></a>
	239
	240	<p><a id="idx:bits64:285"></a>Most of today's 64-bit platforms are
200	241	capable of running both 32-bit and 64-bit applications. This asks for
201	242	some clarifications on the advantages and drawbacks of 64-bit addressing
202	243	for (SWI-)Prolog.
203	244
204		<p><h3 id="sec:64bitsplatforms"><a name="sec:2.21.1"><span class="sec-nr">2.21.1</span> <span class="sec-title">Supported
	245	<p><h3 id="sec:64bitsplatforms"><a id="sec:2.21.1"><span class="sec-nr">2.21.1</span> <span class="sec-title">Supported
205	246	platforms</span></a></h3>
206	247
207		<a name="sec:64bitsplatforms"></a>
208
209		<p><a name="idx:64bitsplatforms:286"></a>SWI-Prolog can be compiled for
210		a 32- or 64-bit address space on any system with a suitable C compiler.
	248	<a id="sec:64bitsplatforms"></a>
	249
	250	<p><a id="idx:64bitsplatforms:286"></a>SWI-Prolog can be compiled for a
	251	32- or 64-bit address space on any system with a suitable C compiler.
211	252	Pointer arithmetic is based on the type (u)intptr_t from <code>stdint.h</code>,
212	253	with suitable emulation on MS-Windows.
213	254
214		<p><h3 id="sec:32vs64bits"><a name="sec:2.21.2"><span class="sec-nr">2.21.2</span> <span class="sec-title">Comparing
	255	<p><h3 id="sec:32vs64bits"><a id="sec:2.21.2"><span class="sec-nr">2.21.2</span> <span class="sec-title">Comparing
215	256	32- and 64-bits Prolog</span></a></h3>
216	257
217		<a name="sec:32vs64bits"></a>
	258	<a id="sec:32vs64bits"></a>
218	259
219	260	<p>Most of Prolog's memory usage consists of pointers. This indicates
220	261	the primary drawback: Prolog memory usage almost doubles when using the

233	274
234	275	<p>Multi-threaded applications profit much more because every thread has
235	276	its own set of stacks. The Prolog stacks start small and are dynamically
236		expanded (see <a class="sec" href="limits.html">section 2.20.1</a>). The
237		C stack is also dynamically expanded, but the maximum size is <em>reserved</em>
238		when a thread is started. Using 100 threads at the maximum default C
239		stack of 8Mb (Linux) costs 800Mb virtual memory!<sup class="fn">35<span class="fn-text">C-recursion
	277	expanded (see <a class="sec" href="limits.html#sec:2.20.1">section
	278	2.20.1</a>). The C stack is also dynamically expanded, but the maximum
	279	size is <em>reserved</em> when a thread is started. Using 100 threads at
	280	the maximum default C stack of 8Mb (Linux) costs 800Mb virtual memory!<sup class="fn">35<span class="fn-text">C-recursion
240	281	over Prolog data structures is removed from most of SWI-Prolog. When
241	282	removed from all predicates it will often be possible to use lower
242	283	limits in threads. See <a class="url" href="http://www.swi-prolog.org/Devel/CStack.html">http://www.swi-prolog.org/Devel/CStack.html</a></span></sup>
243	284
244		<p><a name="idx:IA32:287"></a><a name="idx:AMD64:288"></a>The
245		implications of theoretical performance loss due to increased memory
246		bandwidth implied by exchanging wider pointers depend on the design of
247		the hardware. We only have data for the popular IA32 vs. AMD64
	285	<p><a id="idx:IA32:287"></a><a id="idx:AMD64:288"></a>The implications
	286	of theoretical performance loss due to increased memory bandwidth
	287	implied by exchanging wider pointers depend on the design of the
	288	hardware. We only have data for the popular IA32 vs. AMD64
248	289	architectures. Here, it appears that the loss is compensated for by an
249	290	instruction set that has been optimized for modern programming. In
250	291	particular, the AMD64 has more registers and the relative addressing

252	293	degradation when placing the SWI-Prolog kernel in a Unix shared object,
253	294	we cannot find a measurable difference on AMD64.
254	295
255		<p><h3 id="sec:32vs64bitschoice"><a name="sec:2.21.3"><span class="sec-nr">2.21.3</span> <span class="sec-title">Choosing
	296	<p><h3 id="sec:32vs64bitschoice"><a id="sec:2.21.3"><span class="sec-nr">2.21.3</span> <span class="sec-title">Choosing
256	297	between 32- and 64-bit Prolog</span></a></h3>
257	298
258		<a name="sec:32vs64bitschoice"></a>
	299	<a id="sec:32vs64bitschoice"></a>
259	300
260	301	<p>For those cases where we can choose between 32 and 64 bits, either
261	302	because the hardware and OS support both or because we can still choose

280	321	of 32-bit hardware is 4GB, but in many cases the operating system
281	322	provides less to user applications.
282	323
283		<p><a name="idx:RDFmemoryusage:289"></a>The only standard SWI-Prolog
	324	<p><a id="idx:RDFmemoryusage:289"></a>The only standard SWI-Prolog
284	325	library adding significantly to this calculation is the RDF database
285	326	provided by the <em>semweb</em> package. It uses approximately 80 bytes
286	327	per triple on 32-bit hardware and 150 bytes on 64-bit hardware. Details

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194	235
195		<h1><a name="sec:G"><span class="sec-nr">G</span> <span class="sec-title">Bibliography</span></a></h1>
	236	<h1><a id="sec:G"><span class="sec-nr">G</span> <span class="sec-title">Bibliography</span></a></h1>
196	237
197	238	<dl class="bib">
198		<dt class="bib"><a name="Bowen:83"><strong>Bowen <em>et al.</em>, 1983</strong></a></dt>
	239	<dt class="bib"><a id="Bowen:83"><strong>Bowen <em>et al.</em>, 1983</strong></a></dt>
199	240	<dd class="bib">
200	241	D. L. Bowen, L. M. Byrd, and WF. Clocksin. A portable Prolog
201	242	compiler. In L. M. Pereira, editor, <em>Proceedings of the Logic
202	243	Programming Workshop 1983</em>, Lisabon, Portugal, 1983. Universidade
203	244	nova de Lisboa.</dd>
204		<dt class="bib"><a name="Bratko:86"><strong>Bratko, 1986</strong></a></dt>
	245	<dt class="bib"><a id="Bratko:86"><strong>Bratko, 1986</strong></a></dt>
205	246	<dd class="bib">
206	247	I. Bratko.
207	248	<em>Prolog Programming for Artificial Intelligence</em>. Addison-Wesley,
208	249	Reading, Massachusetts, 1986.</dd>
209		<dt class="bib"><a name="Butenhof:1997:PPT"><strong>Butenhof, 1997</strong></a></dt>
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210	251	<dd class="bib">
211	252	David R. Butenhof.
212	253	<em>Programming with POSIX threads</em>. Ad d i s on-Wes l ey, Reading,
213	254	MA, USA, 1997.</dd>
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	255	<dt class="bib"><a id="Byrd:80"><strong>Byrd, 1980</strong></a></dt>
215	256	<dd class="bib">
216	257	L. Byrd. Understanding the control flow of Prolog programs.
217	258	<em>Logic Programming Workshop</em>, 1980.</dd>
218		<dt class="bib"><a name="Clocksin:87"><strong>Clocksin & Melish,
219		1987</strong></a></dt>
	259	<dt class="bib"><a id="Clocksin:87"><strong>Clocksin & Melish, 1987</strong></a></dt>
220	260	<dd class="bib">
221	261	W. F. Clocksin and C. S. Melish.
222	262	<em>Programming in Prolog</em>. Springer-Verlag, New York, Third, Revised
223	263	and Extended edition, 1987.</dd>
224		<dt class="bib"><a name="Demoen:CW350"><strong>Demoen, 2002</strong></a></dt>
	264	<dt class="bib"><a id="Demoen:CW350"><strong>Demoen, 2002</strong></a></dt>
225	265	<dd class="bib">
226	266	Bart Demoen.
227	267	Dynamic attributes, their hProlog implementation, and a first
228	268	evaluation. Report CW 350, Department of Computer Science, K.U.Leuven,
229	269	Leuven, Belgium, oct 2002. URL =
230	270	http://www.cs.kuleuven.ac.be/publicaties/rapporten/cw/CW350.abs.html.</dd>
231		<dt class="bib"><a name="DBLP:journals/tplp/DesouterDS15"><strong>Desouter <em>et
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233	273	<dd class="bib">
234	274	Benoit Desouter, Marko van Dooren, and Tom Schrijvers. Tabling as a
235	275	library with delimited control.
236	276	<em>TPLP</em>, 15(4-5):419--433, 2015.</dd>
237		<dt class="bib"><a name="oai:CiteSeerPSU:36493"><strong>Freire <em>et
238		al.</em>, 1997</strong></a></dt>
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	278	1997</strong></a></dt>
239	279	<dd class="bib">
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241	281	and Terrance Swift.
242	282	XSB: A system for efficiently computing well-founded semantics. In <em>Proceedings
243	283	of LPNMR 97</em>, pages 430--440, Berlin, Germany, jan 1997. Springer
244	284	Verlag. LNCS 1265.</dd>
245		<dt class="bib"><a name="chrSite"><strong>Frühwirth,</strong></a></dt>
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246	286	<dd class="bib">
247	287	T. Frühwirth. Thom Fruehwirth's constraint handling rules
248	288	website. http://www.constraint-handling-rules.org.</dd>
249		<dt class="bib"><a name="Freuhwirth:2009"><strong>Frühwirth, 2009</strong></a></dt>
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250	290	<dd class="bib">
251	291	T. Frühwirth.
252	292	<em>Constraint Handling Rules</em>. Cambridge University Press, 2009.</dd>
253		<dt class="bib"><a name="graham82gprof"><strong>Graham <em>et al.</em>,
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254	294	1982</strong></a></dt>
255	295	<dd class="bib">
256	296	Susan L. Graham, Peter B. Kessler, and Marshall K.
257	297	McKusick. gprof: a call graph execution profiler. In <em>SIGPLAN
258	298	Symposium on Compiler Construction</em>, pages 120--126, 1982.</dd>
259		<dt class="bib"><a name="stdprolog:98"><strong>Hodgson, 1998</strong></a></dt>
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260	300	<dd class="bib">
261	301	Jonathan Hodgson. validation suite for conformance with part 1 of the
262	302	standard, 1998,
263	303	<a class="url" href="http://www.sju.edu/~jhodgson/pub/suite.tar.gz">http://www.sju.edu/~jhodgson/pub/suite.tar.gz</a>.</dd>
264		<dt class="bib"><a name="holzbaur:1992"><strong>Holzbaur, 1992</strong></a></dt>
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265	305	<dd class="bib">
266	306	Christian Holzbaur. Metastructures versus attributed variables in the
267	307	context of extensible unification. In <em>PLILP</em>, volume 631, pages
268	308	260--268. Springer-Verlag, 1992. LNCS 631.</dd>
269		<dt class="bib"><a name="Kernighan:78"><strong>Kernighan & Ritchie,
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270	310	1978</strong></a></dt>
271	311	<dd class="bib">
272	312	B. W. Kernighan and D. M. Ritchie.
273	313	<em>The C Programming Language</em>. Prentice-Hall, Englewood Cliffs,
274	314	New Jersey, 1978.</dd>
275		<dt class="bib"><a name="Neumerkel:93"><strong>Neumerkel, 1993</strong></a></dt>
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276	316	<dd class="bib">
277	317	Ulrich Neumerkel. The binary WAM, a simplified Prolog engine. Technical
278	318	report, Technische Universität Wien , 1993.
279	319	http://www.complang.tuwien.ac.at/ulrich/papers/PDF/binwam-nov93.pdf.</dd>
280		<dt class="bib"><a name="Keefe:90"><strong>O'Keefe, 1990</strong></a></dt>
	320	<dt class="bib"><a id="Keefe:90"><strong>O'Keefe, 1990</strong></a></dt>
281	321	<dd class="bib">
282	322	R. A. O'Keefe.
283	323	<em>The Craft of Prolog</em>. MIT Press, Massachussetts, 1990.</dd>
284		<dt class="bib"><a name="CPROLOG:manual"><strong>Pereira, 1986</strong></a></dt>
	324	<dt class="bib"><a id="CPROLOG:manual"><strong>Pereira, 1986</strong></a></dt>
285	325	<dd class="bib">
286	326	F. Pereira.
287	327	<em>C-Prolog User's Manual</em>. EdCaad, University of Edinburgh, 1986.</dd>
288		<dt class="bib"><a name="QUINTUS:manual"><strong>Qui, 1997</strong></a></dt>
	328	<dt class="bib"><a id="QUINTUS:manual"><strong>Qui, 1997</strong></a></dt>
289	329	<dd class="bib">
290	330	AI International ltd., Berkhamsted, UK.
291	331	<em>Quintus Prolog, User Guide and Reference Manual</em>, 1997.</dd>
292		<dt class="bib"><a name="logicalloops:2002"><strong>Schimpf, 2002</strong></a></dt>
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293	333	<dd class="bib">
294	334	Joachim Schimpf. Logical loops. In PeterJ. Stuckey, editor, <em>Logic
295	335	Programming</em>, volume 2401 of
296	336	<em>Lecture Notes in Computer Science</em>, pages 224--238. Springer
297	337	Berlin Heidelberg, 2002.</dd>
298		<dt class="bib"><a name="DBLP:journals/tplp/SchrijversDDW13"><strong>Schrijvers <em>et
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299	339	al.</em>, 2013</strong></a></dt>
300	340	<dd class="bib">
301	341	Tom Schrijvers, Bart Demoen, Benoit Desouter, and Jan Wielemaker.
302	342	Delimited continuations for prolog.
303	343	<em>TPLP</em>, 13(4-5):533--546, 2013.</dd>
304		<dt class="bib"><a name="Sterling:86"><strong>Sterling & Shapiro,
305		1986</strong></a></dt>
	344	<dt class="bib"><a id="Sterling:86"><strong>Sterling & Shapiro, 1986</strong></a></dt>
306	345	<dd class="bib">
307	346	L. Sterling and E. Shapiro.
308	347	<em>The Art of Prolog</em>. MIT Press, Cambridge, Massachusetts, 1986.</dd>
309		<dt class="bib"><a name="DBLP:conf/coordination/Tarau11"><strong>Tarau,
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310	349	2011</strong></a></dt>
311	350	<dd class="bib">
312	351	Paul Tarau. Coordination and concurrency in multi-engine prolog. In

315	354	COORDINATION 2011, Reykjavik, Iceland, June 6-9, 2011. Proceedings</em>,
316	355	volume 6721 of <em>Lecture Notes in Computer Science</em>, pages
317	356	157--171. Springer, 2011.</dd>
318		<dt class="bib"><a name="clpb:Triska2016"><strong>Triska, 2016</strong></a></dt>
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319	358	<dd class="bib">
320	359	Markus Triska. The Boolean constraint solver of SWI-Prolog: System
321	360	description. In <em>FLOPS</em>, volume 9613 of <em>LNCS</em>, pages

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	236	<h1><a id="document-contents">Table of Contents</a></h1>
196	237
197	238	<div class="toc">
198	239	<div class="toc-h1"><a class="sec" href="intro.html"><span class="sec-nr">1</span> <span class="sec-title">Introduction</span></a></div>

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193	234	</div>
194		<h2 id="sec:DCG"><a name="sec:4.13"><span class="sec-nr">4.13</span> <span class="sec-title">DCG
	235	<h2 id="sec:DCG"><a id="sec:4.13"><span class="sec-nr">4.13</span> <span class="sec-title">DCG
195	236	Grammar rules</span></a></h2>
196	237
197		<a name="sec:DCG"></a>
198
199		<p><a name="idx:DCG:777"></a><a name="idx:serialize:778"></a><a name="idx:deserialize:779"></a>Grammar
	238	<a id="sec:DCG"></a>
	239
	240	<p><a id="idx:DCG:777"></a><a id="idx:serialize:778"></a><a id="idx:deserialize:779"></a>Grammar
200	241	rules form a comfortable interface to <em>difference lists</em>. They
201	242	are designed both to support writing parsers that build a parse tree
202	243	from a list of characters or tokens and for generating a flat list from

204	245
205	246	<p>Grammar rules look like ordinary clauses using <code><code>--></code>/2</code>
206	247	for separating the head and body rather than <code><code>:-</code>/2</code>.
207		Expanding grammar rules is done by <a name="idx:expandterm2:780"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>,
	248	Expanding grammar rules is done by <a id="idx:expandterm2:780"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>,
208	249	which adds two additional arguments to each term for representing the
209	250	difference list.
210	251

239	280	}.
240	281	</pre>
241	282
242		<p>Grammar rule sets are called using the built-in predicates <a name="idx:phrase2:781"></a><a class="pred" href="DCG.html#phrase/2">phrase/2</a>
243		and <a name="idx:phrase3:782"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>:
	283	<p>Grammar rule sets are called using the built-in predicates <a id="idx:phrase2:781"></a><a class="pred" href="DCG.html#phrase/2">phrase/2</a>
	284	and <a id="idx:phrase3:782"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>:
244	285
245	286	<dl class="latex">
246		<dt class="pubdef"><a name="phrase/2"><strong>phrase</strong>(<var>:DCGBody,
	287	<dt class="pubdef"><a id="phrase/2"><strong>phrase</strong>(<var>:DCGBody,
247	288	?List</var>)</a></dt>
248	289	<dd class="defbody">
249	290	Equivalent to <code>phrase(<var>DCGBody</var>, <var>InputList</var>, [])</code>.
250	291	</dd>
251		<dt class="pubdef"><a name="phrase/3"><strong>phrase</strong>(<var>:DCGBody,
	292	<dt class="pubdef"><a id="phrase/3"><strong>phrase</strong>(<var>:DCGBody,
252	293	?List, ?Rest</var>)</a></dt>
253	294	<dd class="defbody">
254	295	True when <var>DCGBody</var> applies to the difference

257	298	<em>callable</em> term that denotes a grammar rule, it can be any term
258	299	that is valid as the body of a DCG rule.
259	300
260		<p>The example below calls the rule set <a name="idx:integer1:783"></a><span class="pred-ext">integer/3</span>
261		defined in <a class="sec" href="DCG.html">section 4.13</a> and available
262		from <code>library(library(dcg/basics))</code>, binding <var>Rest</var>
	301	<p>The example below calls the rule set <a id="idx:integer1:783"></a><span class="pred-ext">integer//1</span>
	302	defined in <a class="sec" href="DCG.html#sec:4.13">section 4.13</a> and
	303	available from <code>library(library(dcg/basics))</code>, binding <var>Rest</var>
263	304	to the remainder of the input after matching the integer.
264	305
265	306	<pre class="code">

271	312	</pre>
272	313
273	314	<p>The next example exploits a complete body. Given the following
274		definition of digit_weight1, we can pose the query below.
	315	definition of digit_weight//1 , we can pose the query below.
275	316
276	317	<pre class="code">
277	318	digit_weight(W) -->

288	329	Minor = 4.
289	330	</pre>
290	331
291		<p>The SWI-Prolog implementation of <a name="idx:phrase3:784"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>
	332	<p>The SWI-Prolog implementation of <a id="idx:phrase3:784"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>
292	333	verifies that the <var>List</var> and <var>Rest</var> arguments are
293	334	unbound, bound to the empty list or a list
294	335	<em>cons cell</em>. Other values raise a type error.<sup class="fn">71<span class="fn-text">The
295	336	ISO standard allows for both raising a type error and accepting any term
296	337	as input and output. Note the tail of the list is not checked for
297		performance reasons.</span></sup> The predicate <a name="idx:calldcg3:785"></a><a class="pred" href="DCG.html#call_dcg/3">call_dcg/3</a>
	338	performance reasons.</span></sup> The predicate <a id="idx:calldcg3:785"></a><a class="pred" href="DCG.html#call_dcg/3">call_dcg/3</a>
298	339	is provided to use grammar rules with terms that are not lists.
299	340
300	341	<p>Note that the syntax for lists of codes changed in SWI-Prolog version 7
301		(see <a class="sec" href="strings.html">section 5.2</a>). If a DCG body
302		is translated, both <code>"text"</code> and <code>`text`</code> is a
303		valid code-list literal in version 7. A version 7 string (<code>"text"</code>)
304		is <b>not</b> acceptable for the second and third arguments of <a name="idx:phrase3:786"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>.
	342	(see <a class="sec" href="strings.html#sec:5.2">section 5.2</a>). If a
	343	DCG body is translated, both <code>"text"</code> and <code>`text`</code>
	344	is a valid code-list literal in version 7. A version 7 string
	345	(<code>"text"</code>) is <b>not</b> acceptable for the second and third
	346	arguments of <a id="idx:phrase3:786"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>.
305	347	This is typically not a problem for applications as the input of a DCG
306	348	rarely appears in the source code. For testing in the toplevel, one must
307	349	use double quoted text in versions prior to 7 and back quoted text
308	350	in version 7 or later.
309	351
310		<p>See also <a name="idx:portraytext1:787"></a><span class="pred-ext">portray_text/1</span>,
	352	<p>See also <a id="idx:portraytext1:787"></a><span class="pred-ext">portray_text/1</span>,
311	353	which can be used to print lists of character codes as a string to the
312	354	top level and debugger to facilitate debugging DCGs that process
313		character codes. The library <code>library(apply_macros)</code> compiles <a name="idx:phrase3:788"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>
	355	character codes. The library <code>library(apply_macros)</code> compiles <a id="idx:phrase3:788"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>
314	356	if the argument is sufficiently instantiated, eliminating the runtime
315	357	overhead of translating <var>DCGBody</var> and meta-calling.</dd>
316		<dt class="pubdef"><a name="call_dcg/3"><strong>call_dcg</strong>(<var>:DCGBody,
	358	<dt class="pubdef"><a id="call_dcg/3"><strong>call_dcg</strong>(<var>:DCGBody,
317	359	?State0, ?State</var>)</a></dt>
318	360	<dd class="defbody">
319		As <a name="idx:phrase3:789"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>,
	361	As <a id="idx:phrase3:789"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>,
320	362	but without type checking <var>State0</var> and <var>State</var>. This
321	363	allows for using DCG rules for threading an arbitrary state variable.
322	364	This predicate was introduced after type checking was added to
323		<a name="idx:phrase3:790"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>.<sup class="fn">72<span class="fn-text">After
	365	<a id="idx:phrase3:790"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>.<sup class="fn">72<span class="fn-text">After
324	366	discussion with Samer Abdallah.</span></sup>
325	367
326	368	<p>A portable solution for threading state through a DCG can be

339	381
340	382	<p>As stated above, grammar rules are a general interface to difference
341	383	lists. To illustrate, we show a DCG-based implementation of
342		<a name="idx:reverse2:791"></a><a class="pred" href="lists.html#reverse/2">reverse/2</a>:
	384	<a id="idx:reverse2:791"></a><a class="pred" href="lists.html#reverse/2">reverse/2</a>:
343	385
344	386	<pre class="code">
345	387	reverse(List, Reversed) :-

+77

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193	234	</div>
194		<h2 id="sec:DDE"><a name="sec:4.43"><span class="sec-nr">4.43</span> <span class="sec-title">Windows
	235	<h2 id="sec:DDE"><a id="sec:4.43"><span class="sec-nr">4.43</span> <span class="sec-title">Windows
195	236	DDE interface</span></a></h2>
196	237
197		<a name="sec:DDE"></a>
	238	<a id="sec:DDE"></a>
198	239
199	240	<p>The predicates in this section deal with MS-Windows `Dynamic Data
200	241	Exchange' or DDE protocol.<sup class="fn">141<span class="fn-text">This

212	253	error(dde_error(Operation, Message), Context)
213	254	</pre>
214	255
215		<p><h3 id="sec:dde-client"><a name="sec:4.43.1"><span class="sec-nr">4.43.1</span> <span class="sec-title">DDE
	256	<p><h3 id="sec:dde-client"><a id="sec:4.43.1"><span class="sec-nr">4.43.1</span> <span class="sec-title">DDE
216	257	client interface</span></a></h3>
217	258
218		<a name="sec:dde-client"></a>
	259	<a id="sec:dde-client"></a>
219	260
220	261	<p>The DDE client interface allows Prolog to talk to DDE server
221	262	programs. We will demonstrate the use of the DDE interface using the

242	283	setup scripts in Prolog.
243	284
244	285	<dl class="latex">
245		<dt class="pubdef"><a name="open_dde_conversation/3"><strong>open_dde_conversation</strong>(<var>+Service,
	286	<dt class="pubdef"><a id="open_dde_conversation/3"><strong>open_dde_conversation</strong>(<var>+Service,
246	287	+Topic, -Handle</var>)</a></dt>
247	288	<dd class="defbody">
248	289	Open a conversation with a server supporting the given service name and
249	290	topic (atoms). If successful, <var>Handle</var> may be used to send
250	291	transactions to the server. If no willing server is found this predicate
251	292	fails silently.</dd>
252		<dt class="pubdef"><a name="close_dde_conversation/1"><strong>close_dde_conversation</strong>(<var>+Handle</var>)</a></dt>
	293	<dt class="pubdef"><a id="close_dde_conversation/1"><strong>close_dde_conversation</strong>(<var>+Handle</var>)</a></dt>
253	294	<dd class="defbody">
254	295	Close the conversation associated with <var>Handle</var>. All opened
255	296	conversations should be closed when they're no longer needed, although
256	297	the system will close any that remain open on process termination.</dd>
257		<dt class="pubdef"><a name="dde_request/3"><strong>dde_request</strong>(<var>+Handle,
	298	<dt class="pubdef"><a id="dde_request/3"><strong>dde_request</strong>(<var>+Handle,
258	299	+Item, -Value</var>)</a></dt>
259	300	<dd class="defbody">
260	301	Request a value from the server. <var>Item</var> is an atom that
261	302	identifies the requested data, and <var>Value</var> will be a string (<code>CF_TEXT</code>
262	303	data in DDE parlance) representing that data, if the request is
263	304	successful.</dd>
264		<dt class="pubdef"><a name="dde_execute/2"><strong>dde_execute</strong>(<var>+Handle,
	305	<dt class="pubdef"><a id="dde_execute/2"><strong>dde_execute</strong>(<var>+Handle,
265	306	+Command</var>)</a></dt>
266	307	<dd class="defbody">
267	308	Request the DDE server to execute the given command string. Succeeds if
268	309	the command could be executed and fails with an error message otherwise.</dd>
269		<dt class="pubdef"><a name="dde_poke/4"><strong>dde_poke</strong>(<var>+Handle,
	310	<dt class="pubdef"><a id="dde_poke/4"><strong>dde_poke</strong>(<var>+Handle,
270	311	+Item, +Command</var>)</a></dt>
271	312	<dd class="defbody">
272	313	Issue a <code>POKE</code> command to the server on the specified <var>Item</var>.

274	315	</dd>
275	316	</dl>
276	317
277		<p><h3 id="sec:dde-server"><a name="sec:4.43.2"><span class="sec-nr">4.43.2</span> <span class="sec-title">DDE
	318	<p><h3 id="sec:dde-server"><a id="sec:4.43.2"><span class="sec-nr">4.43.2</span> <span class="sec-title">DDE
278	319	server mode</span></a></h3>
279	320
280		<a name="sec:dde-server"></a>
	321	<a id="sec:dde-server"></a>
281	322
282	323	<p>The <code>library(dde)</code> defines primitives to realise simple
283	324	DDE server applications in SWI-Prolog. These features are provided as of

286	327	provided by this interface, please study <code>library(dde)</code>.
287	328
288	329	<dl class="latex">
289		<dt class="pubdef"><a name="dde_register_service/2"><strong>dde_register_service</strong>(<var>+Template,
	330	<dt class="pubdef"><a id="dde_register_service/2"><strong>dde_register_service</strong>(<var>+Template,
290	331	+Goal</var>)</a></dt>
291	332	<dd class="defbody">
292	333	Register a server to handle DDE request or DDE <code>execute</code>

303	344	to version 3.4.5 this was a list of character codes. As recent versions
304	345	have atom garbage collection there is no need for this anymore.</span></sup>
305	346
306		<p>The example below registers the Prolog <a name="idx:currentprologflag2:1585"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
	347	<p>The example below registers the Prolog <a id="idx:currentprologflag2:1585"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
307	348	predicate to be accessible from other applications. The request may be
308	349	given from the same Prolog as well as from another application.
309	350

327	368	requests either succeed or fail. If <var>Goal</var> fails, a `not
328	369	processed' is passed back to the caller of the DDE request.
329	370	</dd>
330		<dt class="pubdef"><a name="dde_unregister_service/1"><strong>dde_unregister_service</strong>(<var>+Service</var>)</a></dt>
	371	<dt class="pubdef"><a id="dde_unregister_service/1"><strong>dde_unregister_service</strong>(<var>+Service</var>)</a></dt>
331	372	<dd class="defbody">
332	373	Stop responding to <var>Service</var>. If Prolog is halted, it will
333	374	automatically call this on all open services.
334	375	</dd>
335		<dt class="pubdef"><a name="dde_current_service/2"><strong>dde_current_service</strong>(<var>-Service,
	376	<dt class="pubdef"><a id="dde_current_service/2"><strong>dde_current_service</strong>(<var>-Service,
336	377	-Topic</var>)</a></dt>
337	378	<dd class="defbody">
338	379	Find currently registered services and the topics served on them.
339	380	</dd>
340		<dt class="pubdef"><a name="dde_current_connection/2"><strong>dde_current_connection</strong>(<var>-Service,
	381	<dt class="pubdef"><a id="dde_current_connection/2"><strong>dde_current_connection</strong>(<var>-Service,
341	382	-Topic</var>)</a></dt>
342	383	<dd class="defbody">
343	384	Find currently open conversations.

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194	235
195	236	<dl>
196	237	<dt class="index-sep">?</dt>

216	257	<dt><a class="idx" href="tabling.html#abolish_table_subgoals/1">abolish_table_subgoals/1</a></dt>
217	258	<dt><a class="idx" href="toplevel.html#abort/0">abort/0</a></dt>
218	259	<dd>
219		<a class="idx" href="cmdline.html#idx:abort0:45">2.4.4</a> <a class="idx" href="debugoverview.html#idx:abort0:66">2.9</a> <a class="idx" href="exception.html#idx:abort0:710">4.11</a> <a class="idx" href="exception.html#idx:abort0:712">4.11.1</a> <a class="idx" href="exception.html#idx:abort0:717">4.11.1</a> <a class="idx" href="exception.html#idx:abort0:720">4.11.1</a> <a class="idx" href="exception.html#idx:abort0:721">4.11.1</a> <a class="idx" href="IO.html#idx:abort0:976">4.17.2</a> <a class="idx" href="IO.html#idx:abort0:984">4.17.2</a> <a class="idx" href="IO.html#idx:abort0:1018">4.17.2</a> <a class="idx" href="debugging.html#idx:abort0:1817">8.4.2</a> <a class="idx" href="foreigninclude.html#idx:abort0:2064">11.4.16</a> <a class="idx" href="foreigninclude.html#idx:abort0:2068">11.4.19</a> <a class="idx" href="foreigninclude.html#idx:abort0:2069">11.4.19</a> <a class="idx" href="tracehook.html#idx:abort0:2194">B.3</a></dd>
	260	<a class="idx" href="cmdline.html#idx:abort0:45">2.4.4</a> <a class="idx" href="debugoverview.html#idx:abort0:66">2.9</a> <a class="idx" href="exception.html#idx:abort0:710">4.11</a> <a class="idx" href="exception.html#idx:abort0:712">4.11.1</a> <a class="idx" href="exception.html#idx:abort0:717">4.11.1</a> <a class="idx" href="exception.html#idx:abort0:720">4.11.1</a> <a class="idx" href="exception.html#idx:abort0:721">4.11.1</a> <a class="idx" href="IO.html#idx:abort0:976">4.17.2</a> <a class="idx" href="IO.html#idx:abort0:984">4.17.2</a> <a class="idx" href="IO.html#idx:abort0:1018">4.17.2</a> <a class="idx" href="debugging.html#idx:abort0:1821">8.4.2</a> <a class="idx" href="foreigninclude.html#idx:abort0:2068">11.4.16</a> <a class="idx" href="foreigninclude.html#idx:abort0:2072">11.4.19</a> <a class="idx" href="foreigninclude.html#idx:abort0:2073">11.4.19</a> <a class="idx" href="tracehook.html#idx:abort0:2198">B.3</a></dd>
220	261	<dt><a class="idx" href="files.html#absolute_file_name/2">absolute_file_name/2</a></dt>
221	262	<dd>
222		<a class="idx" href="acknowledge.html#idx:absolutefilename2:5">1.6</a> <a class="idx" href="consulting.html#idx:absolutefilename2:397">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename2:473">4.3</a> <a class="idx" href="files.html#idx:absolutefilename2:1513">4.36</a> <a class="idx" href="files.html#idx:absolutefilename2:1519">4.36</a> <a class="idx" href="useresource.html#idx:absolutefilename2:2124">12.3.1</a></dd>
	263	<a class="idx" href="acknowledge.html#idx:absolutefilename2:5">1.6</a> <a class="idx" href="consulting.html#idx:absolutefilename2:397">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename2:473">4.3</a> <a class="idx" href="files.html#idx:absolutefilename2:1513">4.36</a> <a class="idx" href="files.html#idx:absolutefilename2:1519">4.36</a> <a class="idx" href="useresource.html#idx:absolutefilename2:2128">12.3.1</a></dd>
223	264	<dt><a class="idx" href="files.html#absolute_file_name/3">absolute_file_name/3</a></dt>
224	265	<dd>
225		<a class="idx" href="flags.html#idx:absolutefilename3:113">2.11</a> <a class="idx" href="flags.html#idx:absolutefilename3:134">2.11</a> <a class="idx" href="hooks.html#idx:absolutefilename3:171">2.12</a> <a class="idx" href="hooks.html#idx:absolutefilename3:172">2.12</a> <a class="idx" href="packs.html#idx:absolutefilename3:208">2.14</a> <a class="idx" href="xref.html#idx:absolutefilename3:324">3.7</a> <a class="idx" href="consulting.html#idx:absolutefilename3:363">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename3:365">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename3:464">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename3:469">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename3:495">4.3</a> <a class="idx" href="system.html#idx:absolutefilename3:1474">4.35.1</a> <a class="idx" href="files.html#idx:absolutefilename3:1504">4.36</a> <a class="idx" href="files.html#idx:absolutefilename3:1506">4.36</a> <a class="idx" href="foreigninclude.html#idx:absolutefilename3:2055">11.4.14.3</a> <a class="idx" href="foreigninclude.html#idx:absolutefilename3:2056">11.4.14.3</a> <a class="idx" href="readutil.html#idx:absolutefilename3:2158">A.30</a> <a class="idx" href="readutil.html#idx:absolutefilename3:2159">A.30</a> <a class="idx" href="readutil.html#idx:absolutefilename3:2162">A.30</a> <a class="idx" href="readutil.html#idx:absolutefilename3:2163">A.30</a></dd>
	266	<a class="idx" href="flags.html#idx:absolutefilename3:113">2.11</a> <a class="idx" href="flags.html#idx:absolutefilename3:134">2.11</a> <a class="idx" href="hooks.html#idx:absolutefilename3:171">2.12</a> <a class="idx" href="hooks.html#idx:absolutefilename3:172">2.12</a> <a class="idx" href="packs.html#idx:absolutefilename3:208">2.14</a> <a class="idx" href="xref.html#idx:absolutefilename3:324">3.7</a> <a class="idx" href="consulting.html#idx:absolutefilename3:363">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename3:365">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename3:464">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename3:469">4.3</a> <a class="idx" href="consulting.html#idx:absolutefilename3:495">4.3</a> <a class="idx" href="system.html#idx:absolutefilename3:1474">4.35.1</a> <a class="idx" href="files.html#idx:absolutefilename3:1504">4.36</a> <a class="idx" href="files.html#idx:absolutefilename3:1506">4.36</a> <a class="idx" href="foreigninclude.html#idx:absolutefilename3:2059">11.4.14.3</a> <a class="idx" href="foreigninclude.html#idx:absolutefilename3:2060">11.4.14.3</a> <a class="idx" href="readutil.html#idx:absolutefilename3:2162">A.30</a> <a class="idx" href="readutil.html#idx:absolutefilename3:2163">A.30</a> <a class="idx" href="readutil.html#idx:absolutefilename3:2166">A.30</a> <a class="idx" href="readutil.html#idx:absolutefilename3:2167">A.30</a></dd>
226	267	<dt>absolute_file_name/[2,3]</dt>
227	268	<dd>
228	269	<a class="idx" href="flags.html#idx:absolutefilename23:155">2.11</a> <a class="idx" href="consulting.html#idx:absolutefilename23:468">4.3</a> <a class="idx" href="files.html#idx:absolutefilename23:1508">4.36</a></dd>

236	277	<dt><a class="idx" href="ugraphs.html#add_edges/3">add_edges/3</a></dt>
237	278	<dt><a class="idx" href="importmodule.html#add_import_module/3">add_import_module/3</a></dt>
238	279	<dd>
239		<a class="idx" href="importmodule.html#idx:addimportmodule3:1719">6.9</a> <a class="idx" href="modulecompat.html#idx:addimportmodule3:1757">6.15</a></dd>
	280	<a class="idx" href="importmodule.html#idx:addimportmodule3:1723">6.9</a> <a class="idx" href="modulecompat.html#idx:addimportmodule3:1761">6.15</a></dd>
240	281	<dt><a class="idx" href="nb_set.html#add_nb_set/2">add_nb_set/2</a></dt>
241	282	<dt><a class="idx" href="nb_set.html#add_nb_set/3">add_nb_set/3</a></dt>
242	283	<dd>
243		<a class="idx" href="nb_set.html#idx:addnbset3:2146">A.17</a> <a class="idx" href="nb_set.html#idx:addnbset3:2147">A.17</a></dd>
	284	<a class="idx" href="nb_set.html#idx:addnbset3:2150">A.17</a> <a class="idx" href="nb_set.html#idx:addnbset3:2151">A.17</a></dd>
244	285	<dt><a class="idx" href="ugraphs.html#add_vertices/3">add_vertices/3</a></dt>
245	286	<dt>agent</dt>
246	287	<dd>
247		<a class="idx" href="broadcast.html#idx:agent:2135">A.4</a></dd>
	288	<a class="idx" href="broadcast.html#idx:agent:2139">A.4</a></dd>
248	289	<dt><a class="idx" href="aggregate.html#aggregate/3">aggregate/3</a></dt>
249	290	<dd>
250		<a class="idx" href="db.html#idx:aggregate3:793">4.14</a> <a class="idx" href="metapred.html#idx:aggregate3:1695">6.4</a></dd>
	291	<a class="idx" href="db.html#idx:aggregate3:793">4.14</a> <a class="idx" href="metapred.html#idx:aggregate3:1699">6.4</a></dd>
251	292	<dt><a class="idx" href="aggregate.html#aggregate/4">aggregate/4</a></dt>
252	293	<dd>
253		<a class="idx" href="metapred.html#idx:aggregate4:1696">6.4</a></dd>
	294	<a class="idx" href="metapred.html#idx:aggregate4:1700">6.4</a></dd>
254	295	<dt><a class="idx" href="aggregate.html#aggregate_all/3">aggregate_all/3</a></dt>
255	296	<dd>
256	297	<a class="idx" href="db.html#idx:aggregateall3:813">4.14</a></dd>

259	300	<dt><a class="idx" href="clpfd.html#all_distinct/1">all_distinct/1</a></dt>
260	301	<dt>anonymous variable</dt>
261	302	<dd>
262		<a class="idx" href="glossary.html#idx:anonymousvariable:2266">D</a></dd>
	303	<a class="idx" href="glossary.html#idx:anonymousvariable:2270">D</a></dd>
263	304	<dt>anonymous,variable</dt>
264	305	<dd>
265	306	<a class="idx" href="syntax.html#idx:anonymousvariable:223">2.16.1.9</a></dd>

268	309	<a class="idx" href="exception.html#idx:ansiformat3:760">4.11.4</a></dd>
269	310	<dt>answer subsumption,tabling</dt>
270	311	<dd>
271		<a class="idx" href="tabling.html#idx:answersubsumptiontabling:2174">A.35.3</a></dd>
	312	<a class="idx" href="tabling.html#idx:answersubsumptiontabling:2178">A.35.3</a></dd>
272	313	<dt><a class="idx" href="IO.html#append/1">append/1</a></dt>
273	314	<dd>
274	315	<a class="idx" href="IO.html#idx:append1:1033">4.17.3</a></dd>
275	316	<dt><a class="idx" href="lists.html#append/2">append/2</a></dt>
276	317	<dd>
277		<a class="idx" href="import.html#idx:append2:1678">6.3</a></dd>
	318	<a class="idx" href="import.html#idx:append2:1682">6.3</a></dd>
278	319	<dt><a class="idx" href="lists.html#append/3">append/3</a></dt>
279	320	<dd>
280	321	<a class="idx" href="examineprog.html#idx:append3:939">4.16</a> <a class="idx" href="manipatom.html#idx:append3:1273">4.22</a></dd>
281	322	<dt><a class="idx" href="metacall.html#apply/2">apply/2</a></dt>
282	323	<dt><a class="idx" href="help.html#apropos/1">apropos/1</a></dt>
283	324	<dd>
284		<a class="idx" href="help.html#idx:apropos1:49">2.6</a> <a class="idx" href="help.html#idx:apropos1:50">2.6</a> <a class="idx" href="hooks.html#idx:apropos1:188">2.12</a> <a class="idx" href="intlibs.html#idx:apropos1:2235">B.7</a> <a class="idx" href="predsummary.html#idx:apropos1:2345">F.1</a></dd>
	325	<a class="idx" href="help.html#idx:apropos1:49">2.6</a> <a class="idx" href="help.html#idx:apropos1:50">2.6</a> <a class="idx" href="hooks.html#idx:apropos1:188">2.12</a> <a class="idx" href="intlibs.html#idx:apropos1:2239">B.7</a> <a class="idx" href="predsummary.html#idx:apropos1:2349">F.1</a></dd>
285	326	<dt><a class="idx" href="manipterm.html#arg/3">arg/3</a></dt>
286	327	<dd>
287	328	<a class="idx" href="manipterm.html#idx:arg3:1192">4.21</a></dd>
288	329	<dt><a class="idx" href="main.html#argv_options/3">argv_options/3</a></dt>
289	330	<dt>arithmetic_function/1</dt>
290	331	<dd>
291		<a class="idx" href="foreigninclude.html#idx:arithmeticfunction1:2047">11.4.12</a></dd>
	332	<a class="idx" href="foreigninclude.html#idx:arithmeticfunction1:2051">11.4.12</a></dd>
292	333	<dt>arity</dt>
293	334	<dd>
294		<a class="idx" href="glossary.html#idx:arity:2268">D</a></dd>
	335	<a class="idx" href="glossary.html#idx:arity:2272">D</a></dd>
295	336	<dt>assert</dt>
296	337	<dd>
297		<a class="idx" href="glossary.html#idx:assert:2269">D</a></dd>
	338	<a class="idx" href="glossary.html#idx:assert:2273">D</a></dd>
298	339	<dt><a class="idx" href="db.html#assert/1">assert/1</a></dt>
299	340	<dd>
300		<a class="idx" href="consulting.html#idx:assert1:371">4.3</a> <a class="idx" href="db.html#idx:assert1:831">4.14.1</a> <a class="idx" href="db.html#idx:assert1:837">4.14.1</a> <a class="idx" href="db.html#idx:assert1:862">4.14.5</a> <a class="idx" href="dynamic.html#idx:assert1:880">4.15</a> <a class="idx" href="dynamic.html#idx:assert1:885">4.15</a> <a class="idx" href="dynamic.html#idx:assert1:886">4.15</a> <a class="idx" href="examineprog.html#idx:assert1:913">4.16</a> <a class="idx" href="gvar.html#idx:assert1:1411">4.33</a> <a class="idx" href="modules.html#idx:assert1:1659">6</a> <a class="idx" href="metapred.html#idx:assert1:1686">6.4</a> <a class="idx" href="threadcom.html#idx:assert1:1917">9.3.3</a></dd>
	341	<a class="idx" href="consulting.html#idx:assert1:371">4.3</a> <a class="idx" href="db.html#idx:assert1:831">4.14.1</a> <a class="idx" href="db.html#idx:assert1:837">4.14.1</a> <a class="idx" href="db.html#idx:assert1:862">4.14.5</a> <a class="idx" href="dynamic.html#idx:assert1:880">4.15</a> <a class="idx" href="dynamic.html#idx:assert1:885">4.15</a> <a class="idx" href="dynamic.html#idx:assert1:886">4.15</a> <a class="idx" href="examineprog.html#idx:assert1:913">4.16</a> <a class="idx" href="gvar.html#idx:assert1:1411">4.33</a> <a class="idx" href="modules.html#idx:assert1:1663">6</a> <a class="idx" href="metapred.html#idx:assert1:1690">6.4</a> <a class="idx" href="threadcom.html#idx:assert1:1921">9.3.3</a></dd>
301	342	<dt><a class="idx" href="db.html#assert/2">assert/2</a></dt>
302	343	<dd>
303	344	<a class="idx" href="flags.html#idx:assert2:99">2.11</a> <a class="idx" href="db.html#idx:assert2:849">4.14.2</a> <a class="idx" href="examineprog.html#idx:assert2:937">4.16</a></dd>
304	345	<dt><a class="idx" href="predicate_options.html#assert_predicate_options/4">assert_predicate_options/4</a></dt>
305	346	<dt><a class="idx" href="db.html#asserta/1">asserta/1</a></dt>
306	347	<dd>
307		<a class="idx" href="cmdline.html#idx:asserta1:37">2.4.2</a> <a class="idx" href="cyclic.html#idx:asserta1:254">2.17</a> <a class="idx" href="jitindex.html#idx:asserta1:256">2.18</a> <a class="idx" href="consulting.html#idx:asserta1:461">4.3</a> <a class="idx" href="compare.html#idx:asserta1:636">4.7.2</a> <a class="idx" href="db.html#idx:asserta1:794">4.14</a> <a class="idx" href="db.html#idx:asserta1:829">4.14.1</a> <a class="idx" href="db.html#idx:asserta1:834">4.14.1</a> <a class="idx" href="db.html#idx:asserta1:835">4.14.1</a> <a class="idx" href="overrule.html#idx:asserta1:1702">6.5</a> <a class="idx" href="overrule.html#idx:asserta1:1704">6.5.1</a> <a class="idx" href="glossary.html#idx:asserta1:2270">D</a></dd>
	348	<a class="idx" href="cmdline.html#idx:asserta1:37">2.4.2</a> <a class="idx" href="cyclic.html#idx:asserta1:254">2.17</a> <a class="idx" href="jitindex.html#idx:asserta1:256">2.18</a> <a class="idx" href="consulting.html#idx:asserta1:461">4.3</a> <a class="idx" href="compare.html#idx:asserta1:636">4.7.2</a> <a class="idx" href="db.html#idx:asserta1:794">4.14</a> <a class="idx" href="db.html#idx:asserta1:829">4.14.1</a> <a class="idx" href="db.html#idx:asserta1:834">4.14.1</a> <a class="idx" href="db.html#idx:asserta1:835">4.14.1</a> <a class="idx" href="overrule.html#idx:asserta1:1706">6.5</a> <a class="idx" href="overrule.html#idx:asserta1:1708">6.5.1</a> <a class="idx" href="glossary.html#idx:asserta1:2274">D</a></dd>
308	349	<dt><a class="idx" href="db.html#asserta/2">asserta/2</a></dt>
309	350	<dd>
310	351	<a class="idx" href="db.html#idx:asserta2:850">4.14.2</a></dd>
311	352	<dt><a class="idx" href="debug.html#assertion/1">assertion/1</a></dt>
312	353	<dd>
313		<a class="idx" href="breakpoint.html#idx:assertion1:2203">B.4</a></dd>
	354	<a class="idx" href="breakpoint.html#idx:assertion1:2207">B.4</a></dd>
314	355	<dt><a class="idx" href="db.html#assertz/1">assertz/1</a></dt>
315	356	<dd>
316		<a class="idx" href="quickstart.html#idx:assertz1:8">2.1.2</a> <a class="idx" href="consulting.html#idx:assertz1:460">4.3</a> <a class="idx" href="db.html#idx:assertz1:795">4.14</a> <a class="idx" href="db.html#idx:assertz1:822">4.14.1</a> <a class="idx" href="db.html#idx:assertz1:830">4.14.1</a> <a class="idx" href="db.html#idx:assertz1:832">4.14.1</a> <a class="idx" href="db.html#idx:assertz1:836">4.14.1</a> <a class="idx" href="examineprog.html#idx:assertz1:927">4.16</a> <a class="idx" href="examineprog.html#idx:assertz1:944">4.16</a> <a class="idx" href="manipmodule.html#idx:assertz1:1750">6.14</a> <a class="idx" href="clp.html#idx:assertz1:1766">7</a> <a class="idx" href="engine-examples.html#idx:assertz1:1971">10.1.2</a> <a class="idx" href="glossary.html#idx:assertz1:2271">D</a></dd>
	357	<a class="idx" href="quickstart.html#idx:assertz1:8">2.1.2</a> <a class="idx" href="consulting.html#idx:assertz1:460">4.3</a> <a class="idx" href="db.html#idx:assertz1:795">4.14</a> <a class="idx" href="db.html#idx:assertz1:822">4.14.1</a> <a class="idx" href="db.html#idx:assertz1:830">4.14.1</a> <a class="idx" href="db.html#idx:assertz1:832">4.14.1</a> <a class="idx" href="db.html#idx:assertz1:836">4.14.1</a> <a class="idx" href="examineprog.html#idx:assertz1:927">4.16</a> <a class="idx" href="examineprog.html#idx:assertz1:944">4.16</a> <a class="idx" href="manipmodule.html#idx:assertz1:1754">6.14</a> <a class="idx" href="clp.html#idx:assertz1:1770">7</a> <a class="idx" href="engine-examples.html#idx:assertz1:1975">10.1.2</a> <a class="idx" href="glossary.html#idx:assertz1:2275">D</a></dd>
317	358	<dt><a class="idx" href="db.html#assertz/2">assertz/2</a></dt>
318	359	<dd>
319	360	<a class="idx" href="db.html#idx:assertz2:851">4.14.2</a></dd>

327	368	<a class="idx" href="chario.html#idx:atendofstream1:1107">4.19</a></dd>
328	369	<dt>at_end_of_stream/[0,1]</dt>
329	370	<dd>
330		<a class="idx" href="IO.html#idx:atendofstream01:985">4.17.2</a> <a class="idx" href="readutil.html#idx:atendofstream01:2155">A.30</a></dd>
	371	<a class="idx" href="IO.html#idx:atendofstream01:985">4.17.2</a> <a class="idx" href="readutil.html#idx:atendofstream01:2159">A.30</a></dd>
331	372	<dt><a class="idx" href="consulting.html#at_halt/1">at_halt/1</a></dt>
332	373	<dd>
333		<a class="idx" href="flags.html#idx:athalt1:108">2.11</a> <a class="idx" href="consulting.html#idx:athalt1:501">4.3</a> <a class="idx" href="toplevel.html#idx:athalt1:1530">4.37</a> <a class="idx" href="threadcreate.html#idx:athalt1:1865">9.1</a> <a class="idx" href="foreigninclude.html#idx:athalt1:2070">11.4.19</a> <a class="idx" href="foreigninclude.html#idx:athalt1:2071">11.4.19</a> <a class="idx" href="foreigninclude.html#idx:athalt1:2072">11.4.19</a> <a class="idx" href="foreigninclude.html#idx:athalt1:2083">11.4.21</a> <a class="idx" href="predsummary.html#idx:athalt1:2352">F.1</a></dd>
	374	<a class="idx" href="flags.html#idx:athalt1:108">2.11</a> <a class="idx" href="consulting.html#idx:athalt1:501">4.3</a> <a class="idx" href="toplevel.html#idx:athalt1:1530">4.37</a> <a class="idx" href="threadcreate.html#idx:athalt1:1869">9.1</a> <a class="idx" href="foreigninclude.html#idx:athalt1:2074">11.4.19</a> <a class="idx" href="foreigninclude.html#idx:athalt1:2075">11.4.19</a> <a class="idx" href="foreigninclude.html#idx:athalt1:2076">11.4.19</a> <a class="idx" href="foreigninclude.html#idx:athalt1:2087">11.4.21</a> <a class="idx" href="predsummary.html#idx:athalt1:2356">F.1</a></dd>
334	375	<dt>atom</dt>
335	376	<dd>
336		<a class="idx" href="glossary.html#idx:atom:2272">D</a></dd>
	377	<a class="idx" href="glossary.html#idx:atom:2276">D</a></dd>
337	378	<dt><a class="idx" href="typetest.html#atom/1">atom/1</a></dt>
338	379	<dd>
339		<a class="idx" href="typetest.html#idx:atom1:604">4.6</a> <a class="idx" href="coroutining.html#idx:atom1:1795">7.2</a> <a class="idx" href="foreigninclude.html#idx:atom1:2016">11.4.3</a></dd>
	380	<a class="idx" href="typetest.html#idx:atom1:604">4.6</a> <a class="idx" href="coroutining.html#idx:atom1:1799">7.2</a> <a class="idx" href="foreigninclude.html#idx:atom1:2020">11.4.3</a></dd>
340	381	<dt><a class="idx" href="manipatom.html#atom_chars/2">atom_chars/2</a></dt>
341	382	<dd>
342		<a class="idx" href="chars.html#idx:atomchars2:345">4.2</a> <a class="idx" href="IO.html#idx:atomchars2:1059">4.17.5</a> <a class="idx" href="chario.html#idx:atomchars2:1084">4.19</a> <a class="idx" href="manipatom.html#idx:atomchars2:1246">4.22</a> <a class="idx" href="manipatom.html#idx:atomchars2:1247">4.22</a> <a class="idx" href="manipatom.html#idx:atomchars2:1249">4.22</a> <a class="idx" href="manipatom.html#idx:atomchars2:1251">4.22</a> <a class="idx" href="manipatom.html#idx:atomchars2:1253">4.22</a> <a class="idx" href="chartype.html#idx:atomchars2:1298">4.24</a> <a class="idx" href="ext-issues.html#idx:atomchars2:1656">5.6</a></dd>
	383	<a class="idx" href="chars.html#idx:atomchars2:345">4.2</a> <a class="idx" href="IO.html#idx:atomchars2:1059">4.17.5</a> <a class="idx" href="chario.html#idx:atomchars2:1084">4.19</a> <a class="idx" href="manipatom.html#idx:atomchars2:1246">4.22</a> <a class="idx" href="manipatom.html#idx:atomchars2:1247">4.22</a> <a class="idx" href="manipatom.html#idx:atomchars2:1249">4.22</a> <a class="idx" href="manipatom.html#idx:atomchars2:1251">4.22</a> <a class="idx" href="manipatom.html#idx:atomchars2:1253">4.22</a> <a class="idx" href="chartype.html#idx:atomchars2:1298">4.24</a> <a class="idx" href="ext-issues.html#idx:atomchars2:1660">5.6</a></dd>
343	384	<dt><a class="idx" href="manipatom.html#atom_codes/2">atom_codes/2</a></dt>
344	385	<dd>
345		<a class="idx" href="chars.html#idx:atomcodes2:343">4.2</a> <a class="idx" href="chars.html#idx:atomcodes2:346">4.2</a> <a class="idx" href="IO.html#idx:atomcodes2:1058">4.17.5</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1240">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1243">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1248">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1250">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1252">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1257">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1263">4.22</a> <a class="idx" href="chartype.html#idx:atomcodes2:1299">4.24</a> <a class="idx" href="ext-issues.html#idx:atomcodes2:1655">5.6</a></dd>
	386	<a class="idx" href="chars.html#idx:atomcodes2:343">4.2</a> <a class="idx" href="chars.html#idx:atomcodes2:346">4.2</a> <a class="idx" href="IO.html#idx:atomcodes2:1058">4.17.5</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1240">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1243">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1248">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1250">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1252">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1257">4.22</a> <a class="idx" href="manipatom.html#idx:atomcodes2:1263">4.22</a> <a class="idx" href="chartype.html#idx:atomcodes2:1299">4.24</a> <a class="idx" href="ext-issues.html#idx:atomcodes2:1659">5.6</a></dd>
346	387	<dt><a class="idx" href="manipatom.html#atom_concat/3">atom_concat/3</a></dt>
347	388	<dd>
348	389	<a class="idx" href="strings.html#idx:atomconcat3:1602">5.2.1</a></dd>

355	396	<dt><a class="idx" href="manipatom.html#atom_prefix/2">atom_prefix/2</a></dt>
356	397	<dt>atom_result/2</dt>
357	398	<dd>
358		<a class="idx" href="ctxmodule.html#idx:atomresult2:1741">6.13</a></dd>
	399	<a class="idx" href="ctxmodule.html#idx:atomresult2:1745">6.13</a></dd>
359	400	<dt><a class="idx" href="strings.html#atom_string/2">atom_string/2</a></dt>
360	401	<dt><a class="idx" href="charsio.html#atom_to_chars/2">atom_to_chars/2</a></dt>
361	402	<dt><a class="idx" href="charsio.html#atom_to_chars/3">atom_to_chars/3</a></dt>

378	419	<dt><a class="idx" href="strings.html#atomics_to_string/3">atomics_to_string/3</a></dt>
379	420	<dt><a class="idx" href="thutil.html#attach_console/0">attach_console/0</a></dt>
380	421	<dd>
381		<a class="idx" href="thutil.html#idx:attachconsole0:1938">9.5</a> <a class="idx" href="thutil.html#idx:attachconsole0:1940">9.5.1</a> <a class="idx" href="foreigninclude.html#idx:attachconsole0:2066">11.4.16</a></dd>
	422	<a class="idx" href="thutil.html#idx:attachconsole0:1942">9.5</a> <a class="idx" href="thutil.html#idx:attachconsole0:1944">9.5.1</a> <a class="idx" href="foreigninclude.html#idx:attachconsole0:2070">11.4.16</a></dd>
382	423	<dt><a class="idx" href="packs.html#attach_packs/0">attach_packs/0</a></dt>
383	424	<dd>
384	425	<a class="idx" href="packs.html#idx:attachpacks0:209">2.14</a></dd>

391	432	<a class="idx" href="termrw.html#idx:attrportrayhook2:1120">4.20</a></dd>
392	433	<dt><a class="idx" href="attvar.html#attr_unify_hook/2">attr_unify_hook/2</a></dt>
393	434	<dd>
394		<a class="idx" href="attvar.html#idx:attrunifyhook2:1771">7.1</a> <a class="idx" href="attvar.html#idx:attrunifyhook2:1773">7.1</a></dd>
395		<dt>attribute_goals//1</dt>
396		<dd>
397		<a class="idx" href="attvar.html#idx:attributegoals1:1774">7.1</a> <a class="idx" href="attvar.html#idx:attributegoals1:1780">7.1.2</a> <a class="idx" href="attvar.html#idx:attributegoals1:1785">7.1.2</a> <a class="idx" href="attvar.html#idx:attributegoals1:1786">7.1.3</a></dd>
398		<dt><a class="idx" href="attvar.html#attribute_goals/1">attribute_goals/1</a></dt>
	435	<a class="idx" href="attvar.html#idx:attrunifyhook2:1775">7.1</a> <a class="idx" href="attvar.html#idx:attrunifyhook2:1777">7.1</a></dd>
	436	<dt><a class="idx" href="attvar.html#attribute_goals//1">attribute_goals//1</a></dt>
	437	<dd>
	438	<a class="idx" href="attvar.html#idx:attributegoals1:1778">7.1</a> <a class="idx" href="attvar.html#idx:attributegoals1:1784">7.1.2</a> <a class="idx" href="attvar.html#idx:attributegoals1:1789">7.1.2</a> <a class="idx" href="attvar.html#idx:attributegoals1:1790">7.1.3</a></dd>
399	439	<dt><a class="idx" href="attvar.html#attvar/1">attvar/1</a></dt>
400	440	<dt><a class="idx" href="runtime.html#autoload/0">autoload/0</a></dt>
401	441	<dd>
402		<a class="idx" href="autoload.html#idx:autoload0:207">2.13</a> <a class="idx" href="consulting.html#idx:autoload0:453">4.3</a> <a class="idx" href="runtime.html#idx:autoload0:2100">12</a> <a class="idx" href="runtime.html#idx:autoload0:2104">12</a></dd>
	442	<a class="idx" href="autoload.html#idx:autoload0:207">2.13</a> <a class="idx" href="consulting.html#idx:autoload0:453">4.3</a> <a class="idx" href="runtime.html#idx:autoload0:2104">12</a> <a class="idx" href="runtime.html#idx:autoload0:2108">12</a></dd>
403	443	<dt><a class="idx" href="autoload.html#autoload_path/1">autoload_path/1</a></dt>
404	444	<dt><a class="idx" href="clpfd.html#automaton/3">automaton/3</a></dt>
405	445	<dt><a class="idx" href="clpfd.html#automaton/8">automaton/8</a></dt>

409	449	<dt><a class="idx" href="dicts.html#b_set_dict/3">b_set_dict/3</a></dt>
410	450	<dt><a class="idx" href="gvar.html#b_setval/2">b_setval/2</a></dt>
411	451	<dd>
412		<a class="idx" href="flags.html#idx:bsetval2:140">2.11</a> <a class="idx" href="db.html#idx:bsetval2:809">4.14</a> <a class="idx" href="gvar.html#idx:bsetval2:1414">4.33</a> <a class="idx" href="gvar.html#idx:bsetval2:1415">4.33</a> <a class="idx" href="dicts.html#idx:bsetval2:1641">5.4.2.1</a> <a class="idx" href="engine-examples.html#idx:bsetval2:1973">10.1.2</a> <a class="idx" href="exception3.html#idx:bsetval2:2218">B.6</a></dd>
	452	<a class="idx" href="flags.html#idx:bsetval2:140">2.11</a> <a class="idx" href="db.html#idx:bsetval2:809">4.14</a> <a class="idx" href="gvar.html#idx:bsetval2:1414">4.33</a> <a class="idx" href="gvar.html#idx:bsetval2:1415">4.33</a> <a class="idx" href="dicts.html#idx:bsetval2:1645">5.4.2.1</a> <a class="idx" href="engine-examples.html#idx:bsetval2:1977">10.1.2</a> <a class="idx" href="exception3.html#idx:bsetval2:2222">B.6</a></dd>
413	453	<dt>backtracking</dt>
414	454	<dd>
415		<a class="idx" href="glossary.html#idx:backtracking:2273">D</a></dd>
	455	<a class="idx" href="glossary.html#idx:backtracking:2277">D</a></dd>
416	456	<dt><a class="idx" href="allsolutions.html#bagof/3">bagof/3</a></dt>
417	457	<dd>
418		<a class="idx" href="cyclic.html#idx:bagof3:233">2.17</a> <a class="idx" href="allsolutions.html#idx:bagof3:1362">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1363">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1369">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1370">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1371">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1372">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1373">4.30</a> <a class="idx" href="metapred.html#idx:bagof3:1694">6.4</a> <a class="idx" href="engine-examples.html#idx:bagof3:1967">10.1.1</a> <a class="idx" href="predsummary.html#idx:bagof3:2347">F.1</a></dd>
	458	<a class="idx" href="cyclic.html#idx:bagof3:233">2.17</a> <a class="idx" href="allsolutions.html#idx:bagof3:1362">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1363">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1369">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1370">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1371">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1372">4.30</a> <a class="idx" href="allsolutions.html#idx:bagof3:1373">4.30</a> <a class="idx" href="metapred.html#idx:bagof3:1698">6.4</a> <a class="idx" href="engine-examples.html#idx:bagof3:1971">10.1.1</a> <a class="idx" href="predsummary.html#idx:bagof3:2351">F.1</a></dd>
419	459	<dt><a class="idx" href="clpqr.html#bb_inf/3">bb_inf/3</a></dt>
420	460	<dt><a class="idx" href="clpqr.html#bb_inf/4">bb_inf/4</a></dt>
421	461	<dt><a class="idx" href="clpqr.html#bb_inf/5">bb_inf/5</a></dt>

424	464	<a class="idx" href="arith.html#idx:between3:1321">4.27.1</a></dd>
425	465	<dt>binding</dt>
426	466	<dd>
427		<a class="idx" href="glossary.html#idx:binding:2274">D</a></dd>
	467	<a class="idx" href="glossary.html#idx:binding:2278">D</a></dd>
428	468	<dt>bits, 64</dt>
429	469	<dd>
430	470	<a class="idx" href="64bits.html#idx:bits64:285">2.21</a></dd>
431	471	<dt>blackboard</dt>
432	472	<dd>
433		<a class="idx" href="broadcast.html#idx:blackboard:2134">A.4</a></dd>
	473	<a class="idx" href="broadcast.html#idx:blackboard:2138">A.4</a></dd>
434	474	<dt><a class="idx" href="typetest.html#blob/2">blob/2</a></dt>
435	475	<dd>
436	476	<a class="idx" href="typetest.html#idx:blob2:608">4.6</a> <a class="idx" href="IO.html#idx:blob2:970">4.17.2</a></dd>
437	477	<dt>body</dt>
438	478	<dd>
439		<a class="idx" href="glossary.html#idx:body:2277">D</a></dd>
	479	<a class="idx" href="glossary.html#idx:body:2281">D</a></dd>
440	480	<dt><a class="idx" href="toplevel.html#break/0">break/0</a></dt>
441	481	<dd>
442		<a class="idx" href="cmdline.html#idx:break0:44">2.4.4</a> <a class="idx" href="debugoverview.html#idx:break0:67">2.9</a> <a class="idx" href="flags.html#idx:break0:91">2.11</a> <a class="idx" href="flags.html#idx:break0:143">2.11</a> <a class="idx" href="debugging.html#idx:break0:1816">8.4.2</a> <a class="idx" href="foreigninclude.html#idx:break0:2065">11.4.16</a></dd>
	482	<a class="idx" href="cmdline.html#idx:break0:44">2.4.4</a> <a class="idx" href="debugoverview.html#idx:break0:67">2.9</a> <a class="idx" href="flags.html#idx:break0:91">2.11</a> <a class="idx" href="flags.html#idx:break0:143">2.11</a> <a class="idx" href="debugging.html#idx:break0:1820">8.4.2</a> <a class="idx" href="foreigninclude.html#idx:break0:2069">11.4.16</a></dd>
443	483	<dt>broadcast</dt>
444	484	<dd>
445		<a class="idx" href="broadcast.html#idx:broadcast:2132">A.4</a></dd>
	485	<a class="idx" href="broadcast.html#idx:broadcast:2136">A.4</a></dd>
446	486	<dt><a class="idx" href="broadcast.html#broadcast/1">broadcast/1</a></dt>
447	487	<dd>
448		<a class="idx" href="broadcast.html#idx:broadcast1:2137">A.4</a> <a class="idx" href="broadcast.html#idx:broadcast1:2138">A.4</a></dd>
	488	<a class="idx" href="broadcast.html#idx:broadcast1:2141">A.4</a> <a class="idx" href="broadcast.html#idx:broadcast1:2142">A.4</a></dd>
449	489	<dt><a class="idx" href="broadcast.html#broadcast_request/1">broadcast_request/1</a></dt>
450	490	<dt>built-in predicate</dt>
451	491	<dd>
452		<a class="idx" href="glossary.html#idx:builtinpredicate:2275">D</a></dd>
	492	<a class="idx" href="glossary.html#idx:builtinpredicate:2279">D</a></dd>
453	493	<dt><a class="idx" href="streamstat.html#byte_count/2">byte_count/2</a></dt>
454	494	<dd>
455	495	<a class="idx" href="IO.html#idx:bytecount2:1002">4.17.2</a></dd>
456	496	<dt><a class="idx" href="metacall.html#call/1">call/1</a></dt>
457	497	<dd>
458		<a class="idx" href="xref.html#idx:call1:322">3.7</a> <a class="idx" href="typetest.html#idx:call1:612">4.6</a> <a class="idx" href="typetest.html#idx:call1:614">4.6</a> <a class="idx" href="typetest.html#idx:call1:617">4.6</a> <a class="idx" href="control.html#idx:call1:646">4.8</a> <a class="idx" href="metacall.html#idx:call1:649">4.9</a> <a class="idx" href="exception.html#idx:call1:693">4.11</a> <a class="idx" href="exception.html#idx:call1:697">4.11</a> <a class="idx" href="exception.html#idx:call1:699">4.11</a> <a class="idx" href="debugger.html#idx:call1:1553">4.39</a> <a class="idx" href="statistics.html#idx:call1:1565">4.40</a> <a class="idx" href="profile.html#idx:call1:1570">4.41.1</a> <a class="idx" href="profile.html#idx:call1:1573">4.41.3</a> <a class="idx" href="profile.html#idx:call1:1574">4.41.3</a> <a class="idx" href="modules.html#idx:call1:1658">6</a> <a class="idx" href="coroutining.html#idx:call1:1804">7.2</a> <a class="idx" href="foreigninclude.html#idx:call1:2040">11.4.9</a> <a class="idx" href="breakpoint.html#idx:call1:2202">B.4</a></dd>
	498	<a class="idx" href="xref.html#idx:call1:322">3.7</a> <a class="idx" href="typetest.html#idx:call1:612">4.6</a> <a class="idx" href="typetest.html#idx:call1:614">4.6</a> <a class="idx" href="typetest.html#idx:call1:617">4.6</a> <a class="idx" href="control.html#idx:call1:646">4.8</a> <a class="idx" href="metacall.html#idx:call1:649">4.9</a> <a class="idx" href="exception.html#idx:call1:693">4.11</a> <a class="idx" href="exception.html#idx:call1:697">4.11</a> <a class="idx" href="exception.html#idx:call1:699">4.11</a> <a class="idx" href="debugger.html#idx:call1:1553">4.39</a> <a class="idx" href="statistics.html#idx:call1:1565">4.40</a> <a class="idx" href="profile.html#idx:call1:1570">4.41.1</a> <a class="idx" href="profile.html#idx:call1:1573">4.41.3</a> <a class="idx" href="profile.html#idx:call1:1574">4.41.3</a> <a class="idx" href="modules.html#idx:call1:1662">6</a> <a class="idx" href="coroutining.html#idx:call1:1808">7.2</a> <a class="idx" href="foreigninclude.html#idx:call1:2044">11.4.9</a> <a class="idx" href="breakpoint.html#idx:call1:2206">B.4</a></dd>
459	499	<dt><a class="idx" href="metacall.html#call/2">call/2</a></dt>
460	500	<dd>
461	501	<a class="idx" href="typetest.html#idx:call2:613">4.6</a></dd>

467	507	<a class="idx" href="metacall.html#idx:call28:650">4.9</a></dd>
468	508	<dt><a class="idx" href="metacall.html#call_cleanup/2">call_cleanup/2</a></dt>
469	509	<dd>
470		<a class="idx" href="metacall.html#idx:callcleanup2:674">4.9</a> <a class="idx" href="metacall.html#idx:callcleanup2:675">4.9</a> <a class="idx" href="metacall.html#idx:callcleanup2:677">4.9</a> <a class="idx" href="IO.html#idx:callcleanup2:1057">4.17.5</a> <a class="idx" href="manipstack.html#idx:callcleanup2:2186">B.1</a> <a class="idx" href="portabilitystrategies.html#idx:callcleanup2:2256">C.1</a></dd>
	510	<a class="idx" href="metacall.html#idx:callcleanup2:674">4.9</a> <a class="idx" href="metacall.html#idx:callcleanup2:675">4.9</a> <a class="idx" href="metacall.html#idx:callcleanup2:677">4.9</a> <a class="idx" href="IO.html#idx:callcleanup2:1057">4.17.5</a> <a class="idx" href="manipstack.html#idx:callcleanup2:2190">B.1</a> <a class="idx" href="portabilitystrategies.html#idx:callcleanup2:2260">C.1</a></dd>
471	511	<dt><a class="idx" href="metacall.html#call_cleanup/3">call_cleanup/3</a></dt>
472	512	<dt><a class="idx" href="DCG.html#call_dcg/3">call_dcg/3</a></dt>
473	513	<dd>
474	514	<a class="idx" href="DCG.html#idx:calldcg3:785">4.13</a></dd>
	515	<dt><a class="idx" href="solutionsequences.html#call_nth/2">call_nth/2</a></dt>
475	516	<dt><a class="idx" href="coroutining.html#call_residue_vars/2">call_residue_vars/2</a></dt>
476	517	<dd>
477		<a class="idx" href="coroutining.html#idx:callresiduevars2:1798">7.2</a> <a class="idx" href="coroutining.html#idx:callresiduevars2:1809">7.2</a> <a class="idx" href="coroutining.html#idx:callresiduevars2:1810">7.2</a></dd>
	518	<a class="idx" href="coroutining.html#idx:callresiduevars2:1802">7.2</a> <a class="idx" href="coroutining.html#idx:callresiduevars2:1813">7.2</a> <a class="idx" href="coroutining.html#idx:callresiduevars2:1814">7.2</a></dd>
478	519	<dt><a class="idx" href="foreignlink.html#call_shared_object_function/2">call_shared_object_function/2</a></dt>
479	520	<dt><a class="idx" href="metacall.html#call_with_depth_limit/3">call_with_depth_limit/3</a></dt>
480	521	<dd>

487	528	<a class="idx" href="metacall.html#idx:callwithtimelimit2:665">4.9</a> <a class="idx" href="metacall.html#idx:callwithtimelimit2:666">4.9</a> <a class="idx" href="exception.html#idx:callwithtimelimit2:718">4.11.1</a></dd>
488	529	<dt><a class="idx" href="typetest.html#callable/1">callable/1</a></dt>
489	530	<dd>
490		<a class="idx" href="typetest.html#idx:callable1:616">4.6</a> <a class="idx" href="foreigninclude.html#idx:callable1:2018">11.4.3.1</a> <a class="idx" href="prolog_xref.html#idx:callable1:2153">A.27</a></dd>
	531	<a class="idx" href="typetest.html#idx:callable1:616">4.6</a> <a class="idx" href="foreigninclude.html#idx:callable1:2022">11.4.3.1</a> <a class="idx" href="prolog_xref.html#idx:callable1:2157">A.27</a></dd>
491	532	<dt><a class="idx" href="consulting.html#cancel_halt/1">cancel_halt/1</a></dt>
492	533	<dd>
493		<a class="idx" href="consulting.html#idx:cancelhalt1:499">4.3</a> <a class="idx" href="toplevel.html#idx:cancelhalt1:1531">4.37</a> <a class="idx" href="foreigninclude.html#idx:cancelhalt1:2084">11.4.21</a></dd>
	534	<a class="idx" href="consulting.html#idx:cancelhalt1:499">4.3</a> <a class="idx" href="toplevel.html#idx:cancelhalt1:1531">4.37</a> <a class="idx" href="foreigninclude.html#idx:cancelhalt1:2088">11.4.21</a></dd>
494	535	<dt><a class="idx" href="exception.html#catch/3">catch/3</a></dt>
495	536	<dd>
496		<a class="idx" href="delcont.html#idx:catch3:682">4.10</a> <a class="idx" href="exception.html#idx:catch3:691">4.11</a> <a class="idx" href="exception.html#idx:catch3:696">4.11</a> <a class="idx" href="exception.html#idx:catch3:698">4.11</a> <a class="idx" href="exception.html#idx:catch3:701">4.11</a> <a class="idx" href="exception.html#idx:catch3:702">4.11</a> <a class="idx" href="exception.html#idx:catch3:703">4.11</a> <a class="idx" href="exception.html#idx:catch3:705">4.11</a> <a class="idx" href="exception.html#idx:catch3:706">4.11</a> <a class="idx" href="exception.html#idx:catch3:707">4.11</a> <a class="idx" href="exception.html#idx:catch3:708">4.11</a> <a class="idx" href="exception.html#idx:catch3:722">4.11.1</a> <a class="idx" href="exception.html#idx:catch3:725">4.11.2</a> <a class="idx" href="exception.html#idx:catch3:726">4.11.2</a> <a class="idx" href="exception.html#idx:catch3:727">4.11.2</a> <a class="idx" href="termrw.html#idx:catch3:1167">4.20</a> <a class="idx" href="files.html#idx:catch3:1494">4.36</a> <a class="idx" href="toplevel.html#idx:catch3:1527">4.37</a> <a class="idx" href="profile.html#idx:catch3:1572">4.41.1</a> <a class="idx" href="threadcreate.html#idx:catch3:1844">9.1</a> <a class="idx" href="thmonitor.html#idx:catch3:1872">9.2</a> <a class="idx" href="thmonitor.html#idx:catch3:1877">9.2</a> <a class="idx" href="engine-examples.html#idx:catch3:1978">10.1.2</a> <a class="idx" href="manipstack.html#idx:catch3:2184">B.1</a> <a class="idx" href="excepthook.html#idx:catch3:2207">B.5</a> <a class="idx" href="exception3.html#idx:catch3:2212">B.6</a> <a class="idx" href="exception3.html#idx:catch3:2215">B.6</a> <a class="idx" href="predsummary.html#idx:catch3:2370">F.1</a></dd>
	537	<a class="idx" href="delcont.html#idx:catch3:682">4.10</a> <a class="idx" href="exception.html#idx:catch3:691">4.11</a> <a class="idx" href="exception.html#idx:catch3:696">4.11</a> <a class="idx" href="exception.html#idx:catch3:698">4.11</a> <a class="idx" href="exception.html#idx:catch3:701">4.11</a> <a class="idx" href="exception.html#idx:catch3:702">4.11</a> <a class="idx" href="exception.html#idx:catch3:703">4.11</a> <a class="idx" href="exception.html#idx:catch3:705">4.11</a> <a class="idx" href="exception.html#idx:catch3:706">4.11</a> <a class="idx" href="exception.html#idx:catch3:707">4.11</a> <a class="idx" href="exception.html#idx:catch3:708">4.11</a> <a class="idx" href="exception.html#idx:catch3:722">4.11.1</a> <a class="idx" href="exception.html#idx:catch3:725">4.11.2</a> <a class="idx" href="exception.html#idx:catch3:726">4.11.2</a> <a class="idx" href="exception.html#idx:catch3:727">4.11.2</a> <a class="idx" href="termrw.html#idx:catch3:1167">4.20</a> <a class="idx" href="files.html#idx:catch3:1494">4.36</a> <a class="idx" href="toplevel.html#idx:catch3:1527">4.37</a> <a class="idx" href="profile.html#idx:catch3:1572">4.41.1</a> <a class="idx" href="threadcreate.html#idx:catch3:1848">9.1</a> <a class="idx" href="thmonitor.html#idx:catch3:1876">9.2</a> <a class="idx" href="thmonitor.html#idx:catch3:1881">9.2</a> <a class="idx" href="engine-examples.html#idx:catch3:1982">10.1.2</a> <a class="idx" href="manipstack.html#idx:catch3:2188">B.1</a> <a class="idx" href="excepthook.html#idx:catch3:2211">B.5</a> <a class="idx" href="exception3.html#idx:catch3:2216">B.6</a> <a class="idx" href="exception3.html#idx:catch3:2219">B.6</a> <a class="idx" href="predsummary.html#idx:catch3:2374">F.1</a></dd>
497	538	<dt><a class="idx" href="clpfd.html#chain/2">chain/2</a></dt>
498	539	<dt><a class="idx" href="manipatom.html#char_code/2">char_code/2</a></dt>
499	540	<dd>

523	564	<dt><a class="idx" href="check.html#checker/2">checker/2</a></dt>
524	565	<dt>choice point</dt>
525	566	<dd>
526		<a class="idx" href="glossary.html#idx:choicepoint:2278">D</a></dd>
	567	<a class="idx" href="glossary.html#idx:choicepoint:2282">D</a></dd>
527	568	<dt><a class="idx" href="practical.html#chr_constraint/1">chr_constraint/1</a></dt>
528	569	<dd>
529		<a class="idx" href="practical.html#idx:chrconstraint1:1811">8.3.2</a> <a class="idx" href="sicstus-chr.html#idx:chrconstraint1:1823">8.6.1</a></dd>
	570	<a class="idx" href="practical.html#idx:chrconstraint1:1815">8.3.2</a> <a class="idx" href="sicstus-chr.html#idx:chrconstraint1:1827">8.6.1</a></dd>
530	571	<dt><a class="idx" href="debugging.html#chr_leash/1">chr_leash/1</a></dt>
531	572	<dt><a class="idx" href="debugging.html#chr_notrace/0">chr_notrace/0</a></dt>
532	573	<dd>
533		<a class="idx" href="debugging.html#idx:chrnotrace0:1815">8.4.2</a></dd>
	574	<a class="idx" href="debugging.html#idx:chrnotrace0:1819">8.4.2</a></dd>
534	575	<dt><a class="idx" href="SyntaxAndSemantics.html#chr_option/2">chr_option/2</a></dt>
535	576	<dd>
536		<a class="idx" href="sicstus-chr.html#idx:chroption2:1824">8.6.1</a></dd>
	577	<a class="idx" href="sicstus-chr.html#idx:chroption2:1828">8.6.1</a></dd>
537	578	<dt><a class="idx" href="debugging.html#chr_show_store/1">chr_show_store/1</a></dt>
538	579	<dt><a class="idx" href="debugging.html#chr_trace/0">chr_trace/0</a></dt>
539	580	<dd>
540		<a class="idx" href="debugging.html#idx:chrtrace0:1814">8.4.2</a></dd>
	581	<a class="idx" href="debugging.html#idx:chrtrace0:1818">8.4.2</a></dd>
541	582	<dt><a class="idx" href="practical.html#chr_type/1">chr_type/1</a></dt>
542	583	<dd>
543		<a class="idx" href="practical.html#idx:chrtype1:1812">8.3.2</a></dd>
	584	<a class="idx" href="practical.html#idx:chrtype1:1816">8.3.2</a></dd>
544	585	<dt><a class="idx" href="clpfd.html#circuit/1">circuit/1</a></dt>
545	586	<dt>clause</dt>
546	587	<dd>
547		<a class="idx" href="glossary.html#idx:clause:2279">D</a></dd>
	588	<a class="idx" href="glossary.html#idx:clause:2283">D</a></dd>
548	589	<dt><a class="idx" href="examineprog.html#clause/2">clause/2</a></dt>
549	590	<dd>
550		<a class="idx" href="flags.html#idx:clause2:128">2.11</a> <a class="idx" href="flags.html#idx:clause2:129">2.11</a> <a class="idx" href="listing.html#idx:clause2:595">4.5</a> <a class="idx" href="control.html#idx:clause2:648">4.8</a> <a class="idx" href="examineprog.html#idx:clause2:936">4.16</a> <a class="idx" href="runtime.html#idx:clause2:2105">12</a></dd>
	591	<a class="idx" href="flags.html#idx:clause2:128">2.11</a> <a class="idx" href="flags.html#idx:clause2:129">2.11</a> <a class="idx" href="listing.html#idx:clause2:595">4.5</a> <a class="idx" href="control.html#idx:clause2:648">4.8</a> <a class="idx" href="examineprog.html#idx:clause2:936">4.16</a> <a class="idx" href="runtime.html#idx:clause2:2109">12</a></dd>
551	592	<dt><a class="idx" href="examineprog.html#clause/3">clause/3</a></dt>
552	593	<dd>
553		<a class="idx" href="db.html#idx:clause3:838">4.14.1</a> <a class="idx" href="db.html#idx:clause3:848">4.14.2</a> <a class="idx" href="examineprog.html#idx:clause3:940">4.16</a> <a class="idx" href="examineprog.html#idx:clause3:946">4.16</a> <a class="idx" href="qsavelimits.html#idx:clause3:2114">12.1</a></dd>
	594	<a class="idx" href="db.html#idx:clause3:838">4.14.1</a> <a class="idx" href="db.html#idx:clause3:848">4.14.2</a> <a class="idx" href="examineprog.html#idx:clause3:940">4.16</a> <a class="idx" href="examineprog.html#idx:clause3:946">4.16</a> <a class="idx" href="qsavelimits.html#idx:clause3:2118">12.1</a></dd>
554	595	<dt>clause/[2,3]</dt>
555	596	<dd>
556	597	<a class="idx" href="flags.html#idx:clause23:117">2.11</a></dd>
557	598	<dt><a class="idx" href="examineprog.html#clause_property/2">clause_property/2</a></dt>
558	599	<dd>
559		<a class="idx" href="consulting.html#idx:clauseproperty2:450">4.3</a> <a class="idx" href="consulting.html#idx:clauseproperty2:474">4.3</a> <a class="idx" href="examineprog.html#idx:clauseproperty2:918">4.16</a> <a class="idx" href="examineprog.html#idx:clauseproperty2:921">4.16</a> <a class="idx" href="examineprog.html#idx:clauseproperty2:943">4.16</a> <a class="idx" href="manipstack.html#idx:clauseproperty2:2181">B.1</a></dd>
	600	<a class="idx" href="consulting.html#idx:clauseproperty2:450">4.3</a> <a class="idx" href="consulting.html#idx:clauseproperty2:474">4.3</a> <a class="idx" href="examineprog.html#idx:clauseproperty2:918">4.16</a> <a class="idx" href="examineprog.html#idx:clauseproperty2:921">4.16</a> <a class="idx" href="examineprog.html#idx:clauseproperty2:943">4.16</a> <a class="idx" href="manipstack.html#idx:clauseproperty2:2185">B.1</a></dd>
560	601	<dt><a class="idx" href="IO.html#close/1">close/1</a></dt>
561	602	<dd>
562	603	<a class="idx" href="IO.html#idx:close1:948">4.17</a> <a class="idx" href="IO.html#idx:close1:982">4.17.2</a> <a class="idx" href="IO.html#idx:close1:995">4.17.2</a></dd>

582	623	<a class="idx" href="chartype.html#idx:comparelanguagespecific:1308">4.24.3</a></dd>
583	624	<dt><a class="idx" href="compare.html#compare/3">compare/3</a></dt>
584	625	<dd>
585		<a class="idx" href="cyclic.html#idx:compare3:234">2.17</a> <a class="idx" href="builtinlist.html#idx:compare3:1358">4.29</a> <a class="idx" href="foreigninclude.html#idx:compare3:2051">11.4.14.1</a> <a class="idx" href="portabilitystrategies.html#idx:compare3:2259">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:compare3:2260">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:compare3:2261">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:compare3:2264">C.1</a></dd>
	626	<a class="idx" href="cyclic.html#idx:compare3:234">2.17</a> <a class="idx" href="builtinlist.html#idx:compare3:1358">4.29</a> <a class="idx" href="foreigninclude.html#idx:compare3:2055">11.4.14.1</a> <a class="idx" href="portabilitystrategies.html#idx:compare3:2263">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:compare3:2264">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:compare3:2265">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:compare3:2268">C.1</a></dd>
586	627	<dt><a class="idx" href="consulting.html#compile_aux_clauses/1">compile_aux_clauses/1</a></dt>
587	628	<dd>
588	629	<a class="idx" href="consulting.html#idx:compileauxclauses1:375">4.3</a> <a class="idx" href="examineprog.html#idx:compileauxclauses1:912">4.16</a></dd>

596	637	<dt><a class="idx" href="ugraphs.html#compose/3">compose/3</a></dt>
597	638	<dt>compound</dt>
598	639	<dd>
599		<a class="idx" href="glossary.html#idx:compound:2280">D</a></dd>
	640	<a class="idx" href="glossary.html#idx:compound:2284">D</a></dd>
600	641	<dt><a class="idx" href="typetest.html#compound/1">compound/1</a></dt>
601	642	<dt><a class="idx" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a></dt>
602	643	<dd>

609	650	<a class="idx" href="manipatom.html#idx:concatatom3:1276">4.22</a></dd>
610	651	<dt>constraint programming</dt>
611	652	<dd>
612		<a class="idx" href="clp.html#idx:constraintprogramming:1760">7</a></dd>
	653	<a class="idx" href="clp.html#idx:constraintprogramming:1764">7</a></dd>
613	654	<dt><a class="idx" href="simplex.html#constraint/3">constraint/3</a></dt>
614	655	<dt><a class="idx" href="simplex.html#constraint/4">constraint/4</a></dt>
615	656	<dt><a class="idx" href="simplex.html#constraint_add/4">constraint_add/4</a></dt>

618	659	<a class="idx" href="quickstart.html#idx:consult1:6">2.1.1.1</a> <a class="idx" href="initfile.html#idx:consult1:21">2.2</a> <a class="idx" href="hooks.html#idx:consult1:177">2.12</a> <a class="idx" href="pceemacs.html#idx:consult1:313">3.4.3.1</a> <a class="idx" href="consulting.html#idx:consult1:359">4.3</a> <a class="idx" href="consulting.html#idx:consult1:380">4.3</a> <a class="idx" href="consulting.html#idx:consult1:386">4.3</a> <a class="idx" href="consulting.html#idx:consult1:392">4.3</a> <a class="idx" href="consulting.html#idx:consult1:403">4.3</a> <a class="idx" href="consulting.html#idx:consult1:422">4.3</a> <a class="idx" href="consulting.html#idx:consult1:426">4.3</a> <a class="idx" href="consulting.html#idx:consult1:427">4.3</a> <a class="idx" href="consulting.html#idx:consult1:429">4.3</a> <a class="idx" href="consulting.html#idx:consult1:431">4.3</a> <a class="idx" href="consulting.html#idx:consult1:441">4.3</a> <a class="idx" href="consulting.html#idx:consult1:454">4.3</a> <a class="idx" href="consulting.html#idx:consult1:565">4.3.2.1</a> <a class="idx" href="consulting.html#idx:consult1:566">4.3.2.1</a> <a class="idx" href="consulting.html#idx:consult1:572">4.3.2.1</a> <a class="idx" href="consulting.html#idx:consult1:577">4.3.3</a> <a class="idx" href="consulting.html#idx:consult1:578">4.3.3</a> <a class="idx" href="consulting.html#idx:consult1:579">4.3.3</a> <a class="idx" href="dynamic.html#idx:consult1:888">4.15</a></dd>
619	660	<dt>context module</dt>
620	661	<dd>
621		<a class="idx" href="glossary.html#idx:contextmodule:2281">D</a></dd>
	662	<a class="idx" href="glossary.html#idx:contextmodule:2285">D</a></dd>
622	663	<dt><a class="idx" href="ctxmodule.html#context_module/1">context_module/1</a></dt>
623	664	<dd>
624		<a class="idx" href="metapred.html#idx:contextmodule1:1700">6.4</a> <a class="idx" href="ctxmodule.html#idx:contextmodule1:1745">6.13</a> <a class="idx" href="foreigninclude.html#idx:contextmodule1:2042">11.4.9.2</a></dd>
	665	<a class="idx" href="metapred.html#idx:contextmodule1:1704">6.4</a> <a class="idx" href="ctxmodule.html#idx:contextmodule1:1749">6.13</a> <a class="idx" href="foreigninclude.html#idx:contextmodule1:2046">11.4.9.2</a></dd>
625	666	<dt>convert_time/[2,8]</dt>
626	667	<dd>
627	668	<a class="idx" href="files.html#idx:converttime28:1502">4.36</a></dd>

638	679	<a class="idx" href="IO.html#idx:copystreamdata3:1008">4.17.2</a></dd>
639	680	<dt><a class="idx" href="manipterm.html#copy_term/2">copy_term/2</a></dt>
640	681	<dd>
641		<a class="idx" href="cyclic.html#idx:copyterm2:235">2.17</a> <a class="idx" href="compare.html#idx:copyterm2:634">4.7.2</a> <a class="idx" href="manipterm.html#idx:copyterm2:1215">4.21</a> <a class="idx" href="manipterm.html#idx:copyterm2:1222">4.21.1</a> <a class="idx" href="manipterm.html#idx:copyterm2:1233">4.21.1</a> <a class="idx" href="gvar.html#idx:copyterm2:1420">4.33</a> <a class="idx" href="dicts.html#idx:copyterm2:1639">5.4.2.1</a> <a class="idx" href="clp.html#idx:copyterm2:1769">7</a> <a class="idx" href="attvar.html#idx:copyterm2:1787">7.1.3</a></dd>
	682	<a class="idx" href="cyclic.html#idx:copyterm2:235">2.17</a> <a class="idx" href="compare.html#idx:copyterm2:634">4.7.2</a> <a class="idx" href="manipterm.html#idx:copyterm2:1215">4.21</a> <a class="idx" href="manipterm.html#idx:copyterm2:1222">4.21.1</a> <a class="idx" href="manipterm.html#idx:copyterm2:1233">4.21.1</a> <a class="idx" href="gvar.html#idx:copyterm2:1420">4.33</a> <a class="idx" href="dicts.html#idx:copyterm2:1643">5.4.2.1</a> <a class="idx" href="clp.html#idx:copyterm2:1773">7</a> <a class="idx" href="attvar.html#idx:copyterm2:1791">7.1.3</a></dd>
642	683	<dt><a class="idx" href="attvar.html#copy_term/3">copy_term/3</a></dt>
643	684	<dd>
644		<a class="idx" href="IO.html#idx:copyterm3:1064">4.17.6</a> <a class="idx" href="termrw.html#idx:copyterm3:1137">4.20</a> <a class="idx" href="clp.html#idx:copyterm3:1770">7</a> <a class="idx" href="attvar.html#idx:copyterm3:1781">7.1.2</a> <a class="idx" href="attvar.html#idx:copyterm3:1784">7.1.2</a></dd>
	685	<a class="idx" href="IO.html#idx:copyterm3:1064">4.17.6</a> <a class="idx" href="termrw.html#idx:copyterm3:1137">4.20</a> <a class="idx" href="clp.html#idx:copyterm3:1774">7</a> <a class="idx" href="attvar.html#idx:copyterm3:1785">7.1.2</a> <a class="idx" href="attvar.html#idx:copyterm3:1788">7.1.2</a></dd>
645	686	<dt><a class="idx" href="attvar.html#copy_term_nat/2">copy_term_nat/2</a></dt>
646	687	<dt>count_atom_results/3</dt>
647	688	<dd>
648		<a class="idx" href="ctxmodule.html#idx:countatomresults3:1740">6.13</a> <a class="idx" href="ctxmodule.html#idx:countatomresults3:1742">6.13</a></dd>
	689	<a class="idx" href="ctxmodule.html#idx:countatomresults3:1744">6.13</a> <a class="idx" href="ctxmodule.html#idx:countatomresults3:1746">6.13</a></dd>
649	690	<dt><a class="idx" href="threadpool.html#create_pool/1">create_pool/1</a></dt>
650	691	<dt><a class="idx" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a></dt>
651	692	<dd>
652		<a class="idx" href="flags.html#idx:createprologflag3:84">2.11</a> <a class="idx" href="flags.html#idx:createprologflag3:151">2.11</a> <a class="idx" href="flags.html#idx:createprologflag3:152">2.11</a> <a class="idx" href="flags.html#idx:createprologflag3:165">2.11</a> <a class="idx" href="foreigninclude.html#idx:createprologflag3:2059">11.4.14.4</a></dd>
	693	<a class="idx" href="flags.html#idx:createprologflag3:84">2.11</a> <a class="idx" href="flags.html#idx:createprologflag3:151">2.11</a> <a class="idx" href="flags.html#idx:createprologflag3:152">2.11</a> <a class="idx" href="flags.html#idx:createprologflag3:165">2.11</a> <a class="idx" href="foreigninclude.html#idx:createprologflag3:2063">11.4.14.4</a></dd>
653	694	<dt>crypto_n_random_bytes/2</dt>
654	695	<dd>
655	696	<a class="idx" href="arith.html#idx:cryptonrandombytes2:1335">4.27.2.3</a></dd>
656		<dt><a class="idx" href="csv.html#csv/1">csv/1</a></dt>
657		<dt><a class="idx" href="csv.html#csv/2">csv/2</a></dt>
	697	<dt><a class="idx" href="csv.html#csv//1">csv//1</a></dt>
	698	<dt><a class="idx" href="csv.html#csv//2">csv//2</a></dt>
658	699	<dt><a class="idx" href="csv.html#csv_options/2">csv_options/2</a></dt>
659	700	<dt><a class="idx" href="csv.html#csv_read_file/2">csv_read_file/2</a></dt>
660	701	<dd>

673	714	<a class="idx" href="examineprog.html#idx:currentatom1:895">4.16</a></dd>
674	715	<dt><a class="idx" href="examineprog.html#current_blob/2">current_blob/2</a></dt>
675	716	<dd>
676		<a class="idx" href="foreigninclude.html#idx:currentblob2:2038">11.4.7.1</a></dd>
	717	<a class="idx" href="foreigninclude.html#idx:currentblob2:2042">11.4.7.1</a></dd>
677	718	<dt><a class="idx" href="charconv.html#current_char_conversion/2">current_char_conversion/2</a></dt>
678	719	<dd>
679	720	<a class="idx" href="charconv.html#idx:currentcharconversion2:1319">4.26</a></dd>

681	722	<dt><a class="idx" href="examineprog.html#current_flag/1">current_flag/1</a></dt>
682	723	<dt><a class="idx" href="foreignlink.html#current_foreign_library/2">current_foreign_library/2</a></dt>
683	724	<dd>
684		<a class="idx" href="runtime.html#idx:currentforeignlibrary2:2101">12</a></dd>
	725	<a class="idx" href="runtime.html#idx:currentforeignlibrary2:2105">12</a></dd>
685	726	<dt><a class="idx" href="format.html#current_format_predicate/2">current_format_predicate/2</a></dt>
686	727	<dt><a class="idx" href="examineprog.html#current_functor/2">current_functor/2</a></dt>
687	728	<dd>

712	753	<dt><a class="idx" href="predicate_options.html#current_predicate_options/3">current_predicate_options/3</a></dt>
713	754	<dt><a class="idx" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a></dt>
714	755	<dd>
715		<a class="idx" href="cmdline.html#idx:currentprologflag2:27">2.4.2</a> <a class="idx" href="cmdline.html#idx:currentprologflag2:32">2.4.2</a> <a class="idx" href="cmdline.html#idx:currentprologflag2:40">2.4.2</a> <a class="idx" href="flags.html#idx:currentprologflag2:80">2.11</a> <a class="idx" href="flags.html#idx:currentprologflag2:82">2.11</a> <a class="idx" href="autoload.html#idx:currentprologflag2:192">2.13</a> <a class="idx" href="gc.html#idx:currentprologflag2:211">2.15</a> <a class="idx" href="syntax.html#idx:currentprologflag2:214">2.16.1.3</a> <a class="idx" href="consulting.html#idx:currentprologflag2:399">4.3</a> <a class="idx" href="termrw.html#idx:currentprologflag2:1168">4.20</a> <a class="idx" href="DDE.html#idx:currentprologflag2:1585">4.43.2</a> <a class="idx" href="foreignlink.html#idx:currentprologflag2:2008">11.2.1</a> <a class="idx" href="foreigninclude.html#idx:currentprologflag2:2060">11.4.14.4</a> <a class="idx" href="libpl.html#idx:currentprologflag2:2131">A</a> <a class="idx" href="glossary.html#idx:currentprologflag2:2303">D</a></dd>
	756	<a class="idx" href="cmdline.html#idx:currentprologflag2:27">2.4.2</a> <a class="idx" href="cmdline.html#idx:currentprologflag2:32">2.4.2</a> <a class="idx" href="cmdline.html#idx:currentprologflag2:40">2.4.2</a> <a class="idx" href="flags.html#idx:currentprologflag2:80">2.11</a> <a class="idx" href="flags.html#idx:currentprologflag2:82">2.11</a> <a class="idx" href="autoload.html#idx:currentprologflag2:192">2.13</a> <a class="idx" href="gc.html#idx:currentprologflag2:211">2.15</a> <a class="idx" href="syntax.html#idx:currentprologflag2:214">2.16.1.3</a> <a class="idx" href="consulting.html#idx:currentprologflag2:399">4.3</a> <a class="idx" href="termrw.html#idx:currentprologflag2:1168">4.20</a> <a class="idx" href="DDE.html#idx:currentprologflag2:1585">4.43.2</a> <a class="idx" href="foreignlink.html#idx:currentprologflag2:2012">11.2.1</a> <a class="idx" href="foreigninclude.html#idx:currentprologflag2:2064">11.4.14.4</a> <a class="idx" href="libpl.html#idx:currentprologflag2:2135">A</a> <a class="idx" href="glossary.html#idx:currentprologflag2:2307">D</a></dd>
716	757	<dt><a class="idx" href="signal.html#current_signal/3">current_signal/3</a></dt>
717	758	<dd>
718	759	<a class="idx" href="signal.html#idx:currentsignal3:774">4.12</a></dd>

732	773	<a class="idx" href="cyclic.html#idx:cyclicterm1:236">2.17</a> <a class="idx" href="typetest.html#idx:cyclicterm1:621">4.6</a> <a class="idx" href="typetest.html#idx:cyclicterm1:623">4.6</a></dd>
733	774	<dt>daemon</dt>
734	775	<dd>
735		<a class="idx" href="broadcast.html#idx:daemon:2136">A.4</a></dd>
	776	<a class="idx" href="broadcast.html#idx:daemon:2140">A.4</a></dd>
736	777	<dt><a class="idx" href="system.html#date_time_stamp/2">date_time_stamp/2</a></dt>
737	778	<dt><a class="idx" href="system.html#date_time_value/3">date_time_value/3</a></dt>
738	779	<dd>

745	786	<dt><a class="idx" href="persistency.html#db_sync_all/1">db_sync_all/1</a></dt>
746	787	<dt>dcg</dt>
747	788	<dd>
748		<a class="idx" href="glossary.html#idx:dcg:2284">D</a></dd>
	789	<a class="idx" href="glossary.html#idx:dcg:2288">D</a></dd>
749	790	<dt><a class="idx" href="consulting.html#dcg_translate_rule/2">dcg_translate_rule/2</a></dt>
750	791	<dd>
751	792	<a class="idx" href="consulting.html#idx:dcgtranslaterule2:530">4.3.1</a></dd>

759	800	<dt><a class="idx" href="DDE.html#dde_unregister_service/1">dde_unregister_service/1</a></dt>
760	801	<dt><a class="idx" href="debugger.html#debug/0">debug/0</a></dt>
761	802	<dd>
762		<a class="idx" href="debugoverview.html#idx:debug0:57">2.9</a> <a class="idx" href="debugoverview.html#idx:debug0:70">2.9</a> <a class="idx" href="flags.html#idx:debug0:144">2.11</a> <a class="idx" href="exception.html#idx:debug0:728">4.11.2</a> <a class="idx" href="debugger.html#idx:debug0:1548">4.39</a> <a class="idx" href="debugger.html#idx:debug0:1556">4.39</a> <a class="idx" href="memory.html#idx:debug0:1579">4.42</a> <a class="idx" href="thutil.html#idx:debug0:1942">9.5.1</a> <a class="idx" href="foreigninclude.html#idx:debug0:2062">11.4.16</a> <a class="idx" href="breakpoint.html#idx:debug0:2200">B.4</a> <a class="idx" href="excepthook.html#idx:debug0:2210">B.5</a></dd>
	803	<a class="idx" href="debugoverview.html#idx:debug0:57">2.9</a> <a class="idx" href="debugoverview.html#idx:debug0:70">2.9</a> <a class="idx" href="flags.html#idx:debug0:144">2.11</a> <a class="idx" href="exception.html#idx:debug0:728">4.11.2</a> <a class="idx" href="debugger.html#idx:debug0:1548">4.39</a> <a class="idx" href="debugger.html#idx:debug0:1556">4.39</a> <a class="idx" href="memory.html#idx:debug0:1579">4.42</a> <a class="idx" href="thutil.html#idx:debug0:1946">9.5.1</a> <a class="idx" href="foreigninclude.html#idx:debug0:2066">11.4.16</a> <a class="idx" href="breakpoint.html#idx:debug0:2204">B.4</a> <a class="idx" href="excepthook.html#idx:debug0:2214">B.5</a></dd>
763	804	<dt><a class="idx" href="debug.html#debug/1">debug/1</a></dt>
764	805	<dt><a class="idx" href="debug.html#debug/3">debug/3</a></dt>
765	806	<dd>

770	811	<a class="idx" href="exception.html#idx:debuggingexceptions:724">4.11.2</a></dd>
771	812	<dt><a class="idx" href="debugger.html#debugging/0">debugging/0</a></dt>
772	813	<dd>
773		<a class="idx" href="hooks.html#idx:debugging0:185">2.12</a> <a class="idx" href="debugger.html#idx:debugging0:1551">4.39</a> <a class="idx" href="intlibs.html#idx:debugging0:2228">B.7</a> <a class="idx" href="intlibs.html#idx:debugging0:2229">B.7</a></dd>
	814	<a class="idx" href="hooks.html#idx:debugging0:185">2.12</a> <a class="idx" href="debugger.html#idx:debugging0:1551">4.39</a> <a class="idx" href="intlibs.html#idx:debugging0:2232">B.7</a> <a class="idx" href="intlibs.html#idx:debugging0:2233">B.7</a></dd>
774	815	<dt><a class="idx" href="debug.html#debugging/1">debugging/1</a></dt>
775	816	<dt><a class="idx" href="debug.html#debugging/2">debugging/2</a></dt>
776	817	<dt>declarative</dt>
777	818	<dd>
778		<a class="idx" href="clp.html#idx:declarative:1764">7</a></dd>
	819	<a class="idx" href="clp.html#idx:declarative:1768">7</a></dd>
779	820	<dt><a class="idx" href="importmodule.html#default_module/2">default_module/2</a></dt>
780	821	<dd>
781		<a class="idx" href="consulting.html#idx:defaultmodule2:538">4.3.1</a> <a class="idx" href="examineprog.html#idx:defaultmodule2:909">4.16</a> <a class="idx" href="examineprog.html#idx:defaultmodule2:919">4.16</a> <a class="idx" href="examineprog.html#idx:defaultmodule2:932">4.16</a> <a class="idx" href="importmodule.html#idx:defaultmodule2:1721">6.9</a></dd>
	822	<a class="idx" href="consulting.html#idx:defaultmodule2:538">4.3.1</a> <a class="idx" href="examineprog.html#idx:defaultmodule2:909">4.16</a> <a class="idx" href="examineprog.html#idx:defaultmodule2:919">4.16</a> <a class="idx" href="examineprog.html#idx:defaultmodule2:932">4.16</a> <a class="idx" href="importmodule.html#idx:defaultmodule2:1725">6.9</a></dd>
782	823	<dt><a class="idx" href="assoc.html#del_assoc/4">del_assoc/4</a></dt>
783	824	<dt><a class="idx" href="attvar.html#del_attr/2">del_attr/2</a></dt>
784	825	<dd>
785		<a class="idx" href="attvar.html#idx:delattr2:1791">7.1.4</a></dd>
	826	<a class="idx" href="attvar.html#idx:delattr2:1795">7.1.4</a></dd>
786	827	<dt><a class="idx" href="attvar.html#del_attrs/1">del_attrs/1</a></dt>
787	828	<dt><a class="idx" href="dicts.html#del_dict/4">del_dict/4</a></dt>
788	829	<dt><a class="idx" href="ugraphs.html#del_edges/3">del_edges/3</a></dt>

796	837	<a class="idx" href="system.html#idx:deletefile1:1445">4.35</a> <a class="idx" href="files.html#idx:deletefile1:1518">4.36</a></dd>
797	838	<dt><a class="idx" href="importmodule.html#delete_import_module/2">delete_import_module/2</a></dt>
798	839	<dd>
799		<a class="idx" href="importmodule.html#idx:deleteimportmodule2:1720">6.9</a> <a class="idx" href="importmodule.html#idx:deleteimportmodule2:1724">6.9</a> <a class="idx" href="modulecompat.html#idx:deleteimportmodule2:1758">6.15</a></dd>
	840	<a class="idx" href="importmodule.html#idx:deleteimportmodule2:1724">6.9</a> <a class="idx" href="importmodule.html#idx:deleteimportmodule2:1728">6.9</a> <a class="idx" href="modulecompat.html#idx:deleteimportmodule2:1762">6.15</a></dd>
800	841	<dt><a class="idx" href="predicate_options.html#derive_predicate_options/0">derive_predicate_options/0</a></dt>
801	842	<dt><a class="idx" href="predicate_options.html#derived_predicate_options/1">derived_predicate_options/1</a></dt>
802	843	<dt><a class="idx" href="predicate_options.html#derived_predicate_options/3">derived_predicate_options/3</a></dt>

805	846	<a class="idx" href="DCG.html#idx:deserialize:779">4.13</a></dd>
806	847	<dt>det</dt>
807	848	<dd>
808		<a class="idx" href="glossary.html#idx:det:2285">D</a></dd>
	849	<a class="idx" href="glossary.html#idx:det:2289">D</a></dd>
809	850	<dt>determinism</dt>
810	851	<dd>
811		<a class="idx" href="glossary.html#idx:determinism:2286">D</a></dd>
	852	<a class="idx" href="glossary.html#idx:determinism:2290">D</a></dd>
812	853	<dt>deterministic</dt>
813	854	<dd>
814		<a class="idx" href="glossary.html#idx:deterministic:2287">D</a></dd>
	855	<a class="idx" href="glossary.html#idx:deterministic:2291">D</a></dd>
815	856	<dt><a class="idx" href="manipstack.html#deterministic/1">deterministic/1</a></dt>
816	857	<dd>
817	858	<a class="idx" href="metacall.html#idx:deterministic1:673">4.9</a></dd>
818	859	<dt><a class="idx" href="dicts.html#dict_create/3">dict_create/3</a></dt>
819	860	<dd>
820		<a class="idx" href="dicts.html#idx:dictcreate3:1636">5.4.2</a></dd>
	861	<a class="idx" href="dicts.html#idx:dictcreate3:1640">5.4.2</a></dd>
821	862	<dt><a class="idx" href="option.html#dict_options/2">dict_options/2</a></dt>
822	863	<dt><a class="idx" href="dicts.html#dict_pairs/3">dict_pairs/3</a></dt>
823	864	<dd>
824		<a class="idx" href="dicts.html#idx:dictpairs3:1653">5.4.3</a></dd>
	865	<a class="idx" href="dicts.html#idx:dictpairs3:1657">5.4.3</a></dd>
825	866	<dt><a class="idx" href="coroutining.html#dif/2">dif/2</a></dt>
826	867	<dd>
827		<a class="idx" href="cyclic.html#idx:dif2:237">2.17</a> <a class="idx" href="compare.html#idx:dif2:624">4.7</a> <a class="idx" href="compare.html#idx:dif2:640">4.7.2</a> <a class="idx" href="clp.html#idx:dif2:1762">7</a> <a class="idx" href="coroutining.html#idx:dif2:1793">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1799">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1800">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1801">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1802">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1807">7.2</a></dd>
	868	<a class="idx" href="cyclic.html#idx:dif2:237">2.17</a> <a class="idx" href="compare.html#idx:dif2:624">4.7</a> <a class="idx" href="compare.html#idx:dif2:640">4.7.2</a> <a class="idx" href="clp.html#idx:dif2:1766">7</a> <a class="idx" href="coroutining.html#idx:dif2:1797">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1803">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1804">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1805">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1806">7.2</a> <a class="idx" href="coroutining.html#idx:dif2:1811">7.2</a></dd>
828	869	<dt>directory_file_path/3</dt>
829	870	<dd>
830	871	<a class="idx" href="files.html#idx:directoryfilepath3:1495">4.36</a></dd>

835	876	<dt><a class="idx" href="clpfd.html#disjoint2/1">disjoint2/1</a></dt>
836	877	<dt>display/1</dt>
837	878	<dd>
838		<a class="idx" href="format.html#idx:display1:1395">4.32.1</a> <a class="idx" href="foreigninclude.html#idx:display1:2025">11.4.3.6</a> <a class="idx" href="foreigninclude.html#idx:display1:2026">11.4.3.6</a></dd>
	879	<a class="idx" href="format.html#idx:display1:1395">4.32.1</a> <a class="idx" href="foreigninclude.html#idx:display1:2029">11.4.3.6</a> <a class="idx" href="foreigninclude.html#idx:display1:2030">11.4.3.6</a></dd>
839	880	<dt><a class="idx" href="solutionsequences.html#distinct/1">distinct/1</a></dt>
840	881	<dt><a class="idx" href="solutionsequences.html#distinct/2">distinct/2</a></dt>
841	882	<dt><a class="idx" href="arith.html#divmod/4">divmod/4</a></dt>

843	884	<a class="idx" href="arith.html#idx:divmod4:1323">4.27.1</a></dd>
844	885	<dt>dld</dt>
845	886	<dd>
846		<a class="idx" href="foreignlink.html#idx:dld:2007">11.2</a></dd>
	887	<a class="idx" href="foreignlink.html#idx:dld:2011">11.2</a></dd>
847	888	<dt>do_not_use/1</dt>
848	889	<dd>
849		<a class="idx" href="reexport.html#idx:donotuse1:1711">6.7</a></dd>
	890	<a class="idx" href="reexport.html#idx:donotuse1:1715">6.7</a></dd>
850	891	<dt>domain/2</dt>
851	892	<dd>
852		<a class="idx" href="attvar.html#idx:domain2:1772">7.1</a></dd>
	893	<a class="idx" href="attvar.html#idx:domain2:1776">7.1</a></dd>
853	894	<dt><a class="idx" href="error.html#domain_error/2">domain_error/2</a></dt>
854	895	<dd>
855		<a class="idx" href="foreigninclude.html#idx:domainerror2:2032">11.4.6</a></dd>
	896	<a class="idx" href="foreigninclude.html#idx:domainerror2:2036">11.4.6</a></dd>
856	897	<dt><a class="idx" href="chartype.html#downcase_atom/2">downcase_atom/2</a></dt>
857	898	<dd>
858	899	<a class="idx" href="chartype.html#idx:downcaseatom2:1294">4.24</a> <a class="idx" href="chartype.html#idx:downcaseatom2:1296">4.24</a> <a class="idx" href="chartype.html#idx:downcaseatom2:1303">4.24.1</a></dd>
859	900	<dt><a class="idx" href="clpqr.html#dump/3">dump/3</a></dt>
860	901	<dd>
861		<a class="idx" href="clpqr.html#idx:dump3:2144">A.9.5</a></dd>
	902	<a class="idx" href="clpqr.html#idx:dump3:2148">A.9.5</a></dd>
862	903	<dt><a class="idx" href="manipterm.html#duplicate_term/2">duplicate_term/2</a></dt>
863	904	<dd>
864	905	<a class="idx" href="cyclic.html#idx:duplicateterm2:238">2.17</a> <a class="idx" href="manipterm.html#idx:duplicateterm2:1217">4.21</a> <a class="idx" href="manipterm.html#idx:duplicateterm2:1225">4.21.1</a> <a class="idx" href="gvar.html#idx:duplicateterm2:1422">4.33</a></dd>

869	910	<dt><a class="idx" href="examineprog.html#dwim_predicate/2">dwim_predicate/2</a></dt>
870	911	<dt>dynamic predicate</dt>
871	912	<dd>
872		<a class="idx" href="glossary.html#idx:dynamicpredicate:2288">D</a></dd>
	913	<a class="idx" href="glossary.html#idx:dynamicpredicate:2292">D</a></dd>
873	914	<dt><a class="idx" href="dynamic.html#dynamic/1">dynamic/1</a></dt>
874	915	<dd>
875		<a class="idx" href="flags.html#idx:dynamic1:123">2.11</a> <a class="idx" href="flags.html#idx:dynamic1:148">2.11</a> <a class="idx" href="preddesc.html#idx:dynamic1:339">4.1</a> <a class="idx" href="consulting.html#idx:dynamic1:434">4.3</a> <a class="idx" href="db.html#idx:dynamic1:798">4.14</a> <a class="idx" href="db.html#idx:dynamic1:827">4.14.1</a> <a class="idx" href="db.html#idx:dynamic1:828">4.14.1</a> <a class="idx" href="dynamic.html#idx:dynamic1:875">4.15</a> <a class="idx" href="dynamic.html#idx:dynamic1:884">4.15</a> <a class="idx" href="examineprog.html#idx:dynamic1:915">4.16</a> <a class="idx" href="ctxmodule.html#idx:dynamic1:1744">6.13</a> <a class="idx" href="threadcom.html#idx:dynamic1:1914">9.3.3</a> <a class="idx" href="threadcom.html#idx:dynamic1:1916">9.3.3</a> <a class="idx" href="runtime.html#idx:dynamic1:2110">12</a></dd>
	916	<a class="idx" href="flags.html#idx:dynamic1:123">2.11</a> <a class="idx" href="flags.html#idx:dynamic1:148">2.11</a> <a class="idx" href="preddesc.html#idx:dynamic1:339">4.1</a> <a class="idx" href="consulting.html#idx:dynamic1:434">4.3</a> <a class="idx" href="db.html#idx:dynamic1:798">4.14</a> <a class="idx" href="db.html#idx:dynamic1:827">4.14.1</a> <a class="idx" href="db.html#idx:dynamic1:828">4.14.1</a> <a class="idx" href="dynamic.html#idx:dynamic1:875">4.15</a> <a class="idx" href="dynamic.html#idx:dynamic1:884">4.15</a> <a class="idx" href="examineprog.html#idx:dynamic1:915">4.16</a> <a class="idx" href="ctxmodule.html#idx:dynamic1:1748">6.13</a> <a class="idx" href="threadcom.html#idx:dynamic1:1918">9.3.3</a> <a class="idx" href="threadcom.html#idx:dynamic1:1920">9.3.3</a> <a class="idx" href="runtime.html#idx:dynamic1:2114">12</a></dd>
876	917	<dt><a class="idx" href="ugraphs.html#edges/2">edges/2</a></dt>
877	918	<dt><a class="idx" href="edit.html#edit/0">edit/0</a></dt>
878	919	<dd>
879	920	<a class="idx" href="flags.html#idx:edit0:90">2.11</a></dd>
880	921	<dt><a class="idx" href="edit.html#edit/1">edit/1</a></dt>
881	922	<dd>
882		<a class="idx" href="quickstart.html#idx:edit1:10">2.1.4</a> <a class="idx" href="flags.html#idx:edit1:105">2.11</a> <a class="idx" href="hooks.html#idx:edit1:179">2.12</a> <a class="idx" href="hooks.html#idx:edit1:180">2.12</a> <a class="idx" href="hooks.html#idx:edit1:181">2.12</a> <a class="idx" href="editreload.html#idx:edit1:306">3.3.1</a> <a class="idx" href="pceemacs.html#idx:edit1:309">3.4.1</a> <a class="idx" href="pceemacs.html#idx:edit1:310">3.4.3.1</a> <a class="idx" href="idesummary.html#idx:edit1:327">3.9</a> <a class="idx" href="idesummary.html#idx:edit1:328">3.9</a> <a class="idx" href="consulting.html#idx:edit1:447">4.3</a> <a class="idx" href="consulting.html#idx:edit1:456">4.3</a> <a class="idx" href="edit.html#idx:edit1:585">4.4</a> <a class="idx" href="edit.html#idx:edit1:586">4.4</a> <a class="idx" href="edit.html#idx:edit1:587">4.4</a> <a class="idx" href="edit.html#idx:edit1:588">4.4</a> <a class="idx" href="edit.html#idx:edit1:589">4.4.1</a> <a class="idx" href="edit.html#idx:edit1:590">4.4.1</a> <a class="idx" href="edit.html#idx:edit1:591">4.4.1</a> <a class="idx" href="edit.html#idx:edit1:592">4.4.1</a> <a class="idx" href="mtoplevel.html#idx:edit1:1706">6.6</a> <a class="idx" href="predsummary.html#idx:edit1:2362">F.1</a> <a class="idx" href="predsummary.html#idx:edit1:2363">F.1</a> <a class="idx" href="predsummary.html#idx:edit1:2364">F.1</a> <a class="idx" href="predsummary.html#idx:edit1:2365">F.1</a></dd>
	923	<a class="idx" href="quickstart.html#idx:edit1:10">2.1.4</a> <a class="idx" href="flags.html#idx:edit1:105">2.11</a> <a class="idx" href="hooks.html#idx:edit1:179">2.12</a> <a class="idx" href="hooks.html#idx:edit1:180">2.12</a> <a class="idx" href="hooks.html#idx:edit1:181">2.12</a> <a class="idx" href="editreload.html#idx:edit1:306">3.3.1</a> <a class="idx" href="pceemacs.html#idx:edit1:309">3.4.1</a> <a class="idx" href="pceemacs.html#idx:edit1:310">3.4.3.1</a> <a class="idx" href="idesummary.html#idx:edit1:327">3.9</a> <a class="idx" href="idesummary.html#idx:edit1:328">3.9</a> <a class="idx" href="consulting.html#idx:edit1:447">4.3</a> <a class="idx" href="consulting.html#idx:edit1:456">4.3</a> <a class="idx" href="edit.html#idx:edit1:585">4.4</a> <a class="idx" href="edit.html#idx:edit1:586">4.4</a> <a class="idx" href="edit.html#idx:edit1:587">4.4</a> <a class="idx" href="edit.html#idx:edit1:588">4.4</a> <a class="idx" href="edit.html#idx:edit1:589">4.4.1</a> <a class="idx" href="edit.html#idx:edit1:590">4.4.1</a> <a class="idx" href="edit.html#idx:edit1:591">4.4.1</a> <a class="idx" href="edit.html#idx:edit1:592">4.4.1</a> <a class="idx" href="mtoplevel.html#idx:edit1:1710">6.6</a> <a class="idx" href="predsummary.html#idx:edit1:2366">F.1</a> <a class="idx" href="predsummary.html#idx:edit1:2367">F.1</a> <a class="idx" href="predsummary.html#idx:edit1:2368">F.1</a> <a class="idx" href="predsummary.html#idx:edit1:2369">F.1</a></dd>
883	924	<dt><a class="idx" href="clpfd.html#element/3">element/3</a></dt>
884	925	<dt><a class="idx" href="consulting.html#elif/1">elif/1</a></dt>
885	926	<dt><a class="idx" href="consulting.html#else/0">else/0</a></dt>

891	932	<dt><a class="idx" href="consulting.html#endif/0">endif/0</a></dt>
892	933	<dt><a class="idx" href="engine-predicates.html#engine_create/3">engine_create/3</a></dt>
893	934	<dd>
894		<a class="idx" href="engine-predicates.html#idx:enginecreate3:1993">10.3</a></dd>
	935	<a class="idx" href="engine-predicates.html#idx:enginecreate3:1997">10.3</a></dd>
895	936	<dt><a class="idx" href="engine-predicates.html#engine_create/4">engine_create/4</a></dt>
896	937	<dt><a class="idx" href="engine-predicates.html#engine_destroy/1">engine_destroy/1</a></dt>
897	938	<dd>
898		<a class="idx" href="engine-resources.html#idx:enginedestroy1:1984">10.2</a> <a class="idx" href="engine-resources.html#idx:enginedestroy1:1985">10.2</a> <a class="idx" href="engine-resources.html#idx:enginedestroy1:1986">10.2</a></dd>
	939	<a class="idx" href="engine-resources.html#idx:enginedestroy1:1988">10.2</a> <a class="idx" href="engine-resources.html#idx:enginedestroy1:1989">10.2</a> <a class="idx" href="engine-resources.html#idx:enginedestroy1:1990">10.2</a></dd>
899	940	<dt><a class="idx" href="engine-predicates.html#engine_fetch/1">engine_fetch/1</a></dt>
900	941	<dd>
901		<a class="idx" href="engine-examples.html#idx:enginefetch1:1976">10.1.2</a> <a class="idx" href="engine-predicates.html#idx:enginefetch1:1997">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginefetch1:1999">10.3</a></dd>
	942	<a class="idx" href="engine-examples.html#idx:enginefetch1:1980">10.1.2</a> <a class="idx" href="engine-predicates.html#idx:enginefetch1:2001">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginefetch1:2003">10.3</a></dd>
902	943	<dt>engine_next/1</dt>
903	944	<dd>
904		<a class="idx" href="engine-examples.html#idx:enginenext1:1965">10.1.1</a></dd>
	945	<a class="idx" href="engine-examples.html#idx:enginenext1:1969">10.1.1</a></dd>
905	946	<dt><a class="idx" href="engine-predicates.html#engine_next/2">engine_next/2</a></dt>
906	947	<dd>
907		<a class="idx" href="engines.html#idx:enginenext2:1963">10</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:1991">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:1996">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:1998">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:2001">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:2002">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:2003">10.3</a></dd>
	948	<a class="idx" href="engines.html#idx:enginenext2:1967">10</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:1995">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:2000">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:2002">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:2005">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:2006">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginenext2:2007">10.3</a></dd>
908	949	<dt><a class="idx" href="engine-predicates.html#engine_next_reified/2">engine_next_reified/2</a></dt>
909	950	<dt><a class="idx" href="engine-predicates.html#engine_post/2">engine_post/2</a></dt>
910	951	<dd>
911		<a class="idx" href="engine-predicates.html#idx:enginepost2:2000">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginepost2:2005">10.3</a></dd>
	952	<a class="idx" href="engine-predicates.html#idx:enginepost2:2004">10.3</a> <a class="idx" href="engine-predicates.html#idx:enginepost2:2009">10.3</a></dd>
912	953	<dt><a class="idx" href="engine-predicates.html#engine_post/3">engine_post/3</a></dt>
913	954	<dd>
914		<a class="idx" href="engine-predicates.html#idx:enginepost3:2006">10.3</a></dd>
	955	<a class="idx" href="engine-predicates.html#idx:enginepost3:2010">10.3</a></dd>
915	956	<dt><a class="idx" href="engine-predicates.html#engine_self/1">engine_self/1</a></dt>
916	957	<dt><a class="idx" href="engine-predicates.html#engine_yield/1">engine_yield/1</a></dt>
917	958	<dd>
918		<a class="idx" href="engines.html#idx:engineyield1:1964">10</a> <a class="idx" href="engine-examples.html#idx:engineyield1:1977">10.1.2</a> <a class="idx" href="engine-resources.html#idx:engineyield1:1989">10.2</a> <a class="idx" href="engine-predicates.html#idx:engineyield1:1994">10.3</a> <a class="idx" href="engine-predicates.html#idx:engineyield1:1995">10.3</a> <a class="idx" href="engine-predicates.html#idx:engineyield1:2004">10.3</a></dd>
	959	<a class="idx" href="engines.html#idx:engineyield1:1968">10</a> <a class="idx" href="engine-examples.html#idx:engineyield1:1981">10.1.2</a> <a class="idx" href="engine-resources.html#idx:engineyield1:1993">10.2</a> <a class="idx" href="engine-predicates.html#idx:engineyield1:1998">10.3</a> <a class="idx" href="engine-predicates.html#idx:engineyield1:1999">10.3</a> <a class="idx" href="engine-predicates.html#idx:engineyield1:2008">10.3</a></dd>
919	960	<dt><a class="idx" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a></dt>
920	961	<dd>
921		<a class="idx" href="compilation.html#idx:ensureloaded1:72">2.10.1</a> <a class="idx" href="consulting.html#idx:ensureloaded1:360">4.3</a> <a class="idx" href="consulting.html#idx:ensureloaded1:381">4.3</a> <a class="idx" href="consulting.html#idx:ensureloaded1:387">4.3</a> <a class="idx" href="consulting.html#idx:ensureloaded1:430">4.3</a> <a class="idx" href="import.html#idx:ensureloaded1:1668">6.3</a> <a class="idx" href="import.html#idx:ensureloaded1:1669">6.3</a></dd>
	962	<a class="idx" href="compilation.html#idx:ensureloaded1:72">2.10.1</a> <a class="idx" href="consulting.html#idx:ensureloaded1:360">4.3</a> <a class="idx" href="consulting.html#idx:ensureloaded1:381">4.3</a> <a class="idx" href="consulting.html#idx:ensureloaded1:387">4.3</a> <a class="idx" href="consulting.html#idx:ensureloaded1:430">4.3</a> <a class="idx" href="import.html#idx:ensureloaded1:1672">6.3</a> <a class="idx" href="import.html#idx:ensureloaded1:1673">6.3</a></dd>
922	963	<dt><a class="idx" href="clpqr.html#entailed/1">entailed/1</a></dt>
923	964	<dt><a class="idx" href="prologpack.html#environment/2">environment/2</a></dt>
924	965	<dt><a class="idx" href="db.html#erase/1">erase/1</a></dt>

926	967	<a class="idx" href="db.html#idx:erase1:805">4.14</a> <a class="idx" href="db.html#idx:erase1:839">4.14.1</a> <a class="idx" href="db.html#idx:erase1:840">4.14.2</a> <a class="idx" href="examineprog.html#idx:erase1:938">4.16</a></dd>
927	968	<dt><a class="idx" href="exception3.html#exception/3">exception/3</a></dt>
928	969	<dd>
929		<a class="idx" href="gvar.html#idx:exception3:1419">4.33</a> <a class="idx" href="exception3.html#idx:exception3:2211">B.6</a> <a class="idx" href="exception3.html#idx:exception3:2214">B.6</a></dd>
	970	<a class="idx" href="gvar.html#idx:exception3:1419">4.33</a> <a class="idx" href="exception3.html#idx:exception3:2215">B.6</a> <a class="idx" href="exception3.html#idx:exception3:2218">B.6</a></dd>
930	971	<dt>exceptions,debugging</dt>
931	972	<dd>
932	973	<a class="idx" href="exception.html#idx:exceptionsdebugging:723">4.11.2</a></dd>

938	979	<a class="idx" href="flags.html#idx:existsfile1:110">2.11</a></dd>
939	980	<dt><a class="idx" href="dialect.html#exists_source/1">exists_source/1</a></dt>
940	981	<dd>
941		<a class="idx" href="dialect.html#idx:existssource1:2246">C</a></dd>
	982	<a class="idx" href="dialect.html#idx:existssource1:2250">C</a></dd>
942	983	<dt><a class="idx" href="toplevel.html#expand_answer/2">expand_answer/2</a></dt>
943	984	<dd>
944	985	<a class="idx" href="toplevel.html#idx:expandanswer2:1536">4.37</a></dd>

953	994	<dt><a class="idx" href="toplevel.html#expand_query/4">expand_query/4</a></dt>
954	995	<dt><a class="idx" href="consulting.html#expand_term/2">expand_term/2</a></dt>
955	996	<dd>
956		<a class="idx" href="consulting.html#idx:expandterm2:492">4.3</a> <a class="idx" href="consulting.html#idx:expandterm2:517">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:522">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:524">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:526">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:534">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:549">4.3.1</a> <a class="idx" href="DCG.html#idx:expandterm2:780">4.13</a> <a class="idx" href="record.html#idx:expandterm2:2169">A.31</a></dd>
	997	<a class="idx" href="consulting.html#idx:expandterm2:492">4.3</a> <a class="idx" href="consulting.html#idx:expandterm2:517">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:522">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:524">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:526">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:534">4.3.1</a> <a class="idx" href="consulting.html#idx:expandterm2:549">4.3.1</a> <a class="idx" href="DCG.html#idx:expandterm2:780">4.13</a> <a class="idx" href="record.html#idx:expandterm2:2173">A.31</a></dd>
957	998	<dt><a class="idx" href="consulting.html#expand_term/4">expand_term/4</a></dt>
958	999	<dt><a class="idx" href="dialect.html#expects_dialect/1">expects_dialect/1</a></dt>
959	1000	<dd>
960		<a class="idx" href="consulting.html#idx:expectsdialect1:401">4.3</a> <a class="idx" href="consulting.html#idx:expectsdialect1:421">4.3</a> <a class="idx" href="consulting.html#idx:expectsdialect1:488">4.3</a> <a class="idx" href="dialect.html#idx:expectsdialect1:2245">C</a></dd>
	1001	<a class="idx" href="consulting.html#idx:expectsdialect1:401">4.3</a> <a class="idx" href="consulting.html#idx:expectsdialect1:421">4.3</a> <a class="idx" href="consulting.html#idx:expectsdialect1:488">4.3</a> <a class="idx" href="dialect.html#idx:expectsdialect1:2249">C</a></dd>
961	1002	<dt><a class="idx" href="help.html#explain/1">explain/1</a></dt>
962	1003	<dd>
963	1004	<a class="idx" href="help.html#idx:explain1:51">2.6</a></dd>
964	1005	<dt><a class="idx" href="help.html#explain/2">explain/2</a></dt>
965	1006	<dt><a class="idx" href="altmoduleapi.html#export/1">export/1</a></dt>
966	1007	<dd>
967		<a class="idx" href="consulting.html#idx:export1:558">4.3.2</a> <a class="idx" href="dynamic.html#idx:export1:894">4.15</a> <a class="idx" href="altmoduleapi.html#idx:export1:1729">6.11</a> <a class="idx" href="altmoduleapi.html#idx:export1:1732">6.11</a> <a class="idx" href="dynamic-modules.html#idx:export1:1735">6.12</a></dd>
	1008	<a class="idx" href="consulting.html#idx:export1:558">4.3.2</a> <a class="idx" href="dynamic.html#idx:export1:894">4.15</a> <a class="idx" href="altmoduleapi.html#idx:export1:1733">6.11</a> <a class="idx" href="altmoduleapi.html#idx:export1:1736">6.11</a> <a class="idx" href="dynamic-modules.html#idx:export1:1739">6.12</a></dd>
968	1009	<dt>export_list/2</dt>
969	1010	<dd>
970		<a class="idx" href="altmoduleapi.html#idx:exportlist2:1733">6.11</a></dd>
	1011	<a class="idx" href="altmoduleapi.html#idx:exportlist2:1737">6.11</a></dd>
971	1012	<dt>exported predicate</dt>
972	1013	<dd>
973		<a class="idx" href="glossary.html#idx:exportedpredicate:2290">D</a></dd>
	1014	<a class="idx" href="glossary.html#idx:exportedpredicate:2294">D</a></dd>
974	1015	<dt><a class="idx" href="arith.html#f-/2">f-/2</a></dt>
975	1016	<dt><a class="idx" href="arith.html#f-/2">f-/2</a></dt>
976	1017	<dt><a class="idx" href="arith.html#f-+/1">f-+/1</a></dt>

1045	1086	<dt><a class="idx" href="arith.html#f-xor/2">f-xor/2</a></dt>
1046	1087	<dt>fact</dt>
1047	1088	<dd>
1048		<a class="idx" href="glossary.html#idx:fact:2293">D</a></dd>
	1089	<a class="idx" href="glossary.html#idx:fact:2297">D</a></dd>
1049	1090	<dt><a class="idx" href="control.html#fail/0">fail/0</a></dt>
1050	1091	<dd>
1051	1092	<a class="idx" href="consulting.html#idx:fail0:545">4.3.1</a> <a class="idx" href="control.html#idx:fail0:644">4.8</a></dd>

1068	1109	<dt><a class="idx" href="url.html#file_name_to_url/2">file_name_to_url/2</a></dt>
1069	1110	<dt>file_of_label/2</dt>
1070	1111	<dd>
1071		<a class="idx" href="mtoplevel.html#idx:fileoflabel2:1709">6.6</a></dd>
	1112	<a class="idx" href="mtoplevel.html#idx:fileoflabel2:1713">6.6</a></dd>
1072	1113	<dt><a class="idx" href="consulting.html#file_search_path/2">file_search_path/2</a></dt>
1073	1114	<dd>
1074		<a class="idx" href="initfile.html#idx:filesearchpath2:22">2.2</a> <a class="idx" href="cmdline.html#idx:filesearchpath2:36">2.4.2</a> <a class="idx" href="cmdline.html#idx:filesearchpath2:38">2.4.2</a> <a class="idx" href="flags.html#idx:filesearchpath2:89">2.11</a> <a class="idx" href="flags.html#idx:filesearchpath2:156">2.11</a> <a class="idx" href="autoload.html#idx:filesearchpath2:190">2.13</a> <a class="idx" href="autoload.html#idx:filesearchpath2:196">2.13</a> <a class="idx" href="autoload.html#idx:filesearchpath2:202">2.13</a> <a class="idx" href="projectfiles.html#idx:filesearchpath2:299">3.1.1.3</a> <a class="idx" href="projectfiles.html#idx:filesearchpath2:300">3.1.1.3</a> <a class="idx" href="xref.html#idx:filesearchpath2:323">3.7</a> <a class="idx" href="consulting.html#idx:filesearchpath2:404">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:463">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:465">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:467">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:470">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:471">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:494">4.3</a> <a class="idx" href="foreigninclude.html#idx:filesearchpath2:2057">11.4.14.3</a> <a class="idx" href="findhome.html#idx:filesearchpath2:2089">11.6</a> <a class="idx" href="qsaveforeign.html#idx:filesearchpath2:2117">12.2</a> <a class="idx" href="qsaveforeign.html#idx:filesearchpath2:2118">12.2</a> <a class="idx" href="useresource.html#idx:filesearchpath2:2123">12.3.1</a> <a class="idx" href="useresource.html#idx:filesearchpath2:2125">12.3.1</a> <a class="idx" href="findappfile.html#idx:filesearchpath2:2129">12.4</a></dd>
	1115	<a class="idx" href="initfile.html#idx:filesearchpath2:22">2.2</a> <a class="idx" href="cmdline.html#idx:filesearchpath2:36">2.4.2</a> <a class="idx" href="cmdline.html#idx:filesearchpath2:38">2.4.2</a> <a class="idx" href="flags.html#idx:filesearchpath2:89">2.11</a> <a class="idx" href="flags.html#idx:filesearchpath2:156">2.11</a> <a class="idx" href="autoload.html#idx:filesearchpath2:190">2.13</a> <a class="idx" href="autoload.html#idx:filesearchpath2:196">2.13</a> <a class="idx" href="autoload.html#idx:filesearchpath2:202">2.13</a> <a class="idx" href="projectfiles.html#idx:filesearchpath2:299">3.1.1.3</a> <a class="idx" href="projectfiles.html#idx:filesearchpath2:300">3.1.1.3</a> <a class="idx" href="xref.html#idx:filesearchpath2:323">3.7</a> <a class="idx" href="consulting.html#idx:filesearchpath2:404">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:463">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:465">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:467">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:470">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:471">4.3</a> <a class="idx" href="consulting.html#idx:filesearchpath2:494">4.3</a> <a class="idx" href="foreigninclude.html#idx:filesearchpath2:2061">11.4.14.3</a> <a class="idx" href="findhome.html#idx:filesearchpath2:2093">11.6</a> <a class="idx" href="qsaveforeign.html#idx:filesearchpath2:2121">12.2</a> <a class="idx" href="qsaveforeign.html#idx:filesearchpath2:2122">12.2</a> <a class="idx" href="useresource.html#idx:filesearchpath2:2127">12.3.1</a> <a class="idx" href="useresource.html#idx:filesearchpath2:2129">12.3.1</a> <a class="idx" href="findappfile.html#idx:filesearchpath2:2133">12.4</a></dd>
1075	1116	<dt><a class="idx" href="chario.html#fill_buffer/1">fill_buffer/1</a></dt>
1076	1117	<dt><a class="idx" href="debugging.html#find_chr_constraint/1">find_chr_constraint/1</a></dt>
1077	1118	<dt><a class="idx" href="allsolutions.html#findall/3">findall/3</a></dt>
1078	1119	<dd>
1079		<a class="idx" href="cyclic.html#idx:findall3:239">2.17</a> <a class="idx" href="compare.html#idx:findall3:635">4.7.2</a> <a class="idx" href="control.html#idx:findall3:643">4.8</a> <a class="idx" href="db.html#idx:findall3:792">4.14</a> <a class="idx" href="allsolutions.html#idx:findall3:1361">4.30</a> <a class="idx" href="allsolutions.html#idx:findall3:1364">4.30</a> <a class="idx" href="allsolutions.html#idx:findall3:1365">4.30</a> <a class="idx" href="forall2.html#idx:findall3:1381">4.31</a> <a class="idx" href="dicts.html#idx:findall3:1649">5.4.3</a> <a class="idx" href="clp.html#idx:findall3:1768">7</a> <a class="idx" href="engine-examples.html#idx:findall3:1966">10.1.1</a> <a class="idx" href="engine-examples.html#idx:findall3:1968">10.1.1</a> <a class="idx" href="engine-examples.html#idx:findall3:1969">10.1.1</a> <a class="idx" href="engine-examples.html#idx:findall3:1970">10.1.1</a> <a class="idx" href="engine-predicates.html#idx:findall3:1990">10.3</a> <a class="idx" href="predsummary.html#idx:findall3:2355">F.1</a></dd>
	1120	<a class="idx" href="cyclic.html#idx:findall3:239">2.17</a> <a class="idx" href="compare.html#idx:findall3:635">4.7.2</a> <a class="idx" href="control.html#idx:findall3:643">4.8</a> <a class="idx" href="db.html#idx:findall3:792">4.14</a> <a class="idx" href="allsolutions.html#idx:findall3:1361">4.30</a> <a class="idx" href="allsolutions.html#idx:findall3:1364">4.30</a> <a class="idx" href="allsolutions.html#idx:findall3:1365">4.30</a> <a class="idx" href="forall2.html#idx:findall3:1381">4.31</a> <a class="idx" href="dicts.html#idx:findall3:1653">5.4.3</a> <a class="idx" href="clp.html#idx:findall3:1772">7</a> <a class="idx" href="engine-examples.html#idx:findall3:1970">10.1.1</a> <a class="idx" href="engine-examples.html#idx:findall3:1972">10.1.1</a> <a class="idx" href="engine-examples.html#idx:findall3:1973">10.1.1</a> <a class="idx" href="engine-examples.html#idx:findall3:1974">10.1.1</a> <a class="idx" href="engine-predicates.html#idx:findall3:1994">10.3</a> <a class="idx" href="predsummary.html#idx:findall3:2359">F.1</a></dd>
1080	1121	<dt><a class="idx" href="allsolutions.html#findall/4">findall/4</a></dt>
1081	1122	<dd>
1082	1123	<a class="idx" href="allsolutions.html#idx:findall4:1366">4.30</a></dd>
1083	1124	<dt><a class="idx" href="allsolutions.html#findnsols/4">findnsols/4</a></dt>
1084	1125	<dd>
1085		<a class="idx" href="predsummary.html#idx:findnsols4:2356">F.1</a></dd>
	1126	<a class="idx" href="predsummary.html#idx:findnsols4:2360">F.1</a></dd>
1086	1127	<dt><a class="idx" href="allsolutions.html#findnsols/5">findnsols/5</a></dt>
1087	1128	<dt><a class="idx" href="db.html#flag/3">flag/3</a></dt>
1088	1129	<dd>
1089	1130	<a class="idx" href="db.html#idx:flag3:807">4.14</a> <a class="idx" href="db.html#idx:flag3:808">4.14</a> <a class="idx" href="db.html#idx:flag3:852">4.14.3</a> <a class="idx" href="examineprog.html#idx:flag3:897">4.16</a> <a class="idx" href="manipterm.html#idx:flag3:1229">4.21.1</a></dd>
1090	1131	<dt><a class="idx" href="lists.html#flatten/2">flatten/2</a></dt>
1091	1132	<dd>
1092		<a class="idx" href="import.html#idx:flatten2:1670">6.3</a> <a class="idx" href="import.html#idx:flatten2:1673">6.3</a></dd>
	1133	<a class="idx" href="import.html#idx:flatten2:1674">6.3</a> <a class="idx" href="import.html#idx:flatten2:1677">6.3</a></dd>
1093	1134	<dt><a class="idx" href="typetest.html#float/1">float/1</a></dt>
1094	1135	<dd>
1095	1136	<a class="idx" href="typetest.html#idx:float1:607">4.6</a></dd>
1096	1137	<dt>flounder</dt>
1097	1138	<dd>
1098		<a class="idx" href="coroutining.html#idx:flounder:1797">7.2</a></dd>
	1139	<a class="idx" href="coroutining.html#idx:flounder:1801">7.2</a></dd>
1099	1140	<dt><a class="idx" href="chario.html#flush_output/0">flush_output/0</a></dt>
1100	1141	<dd>
1101	1142	<a class="idx" href="chario.html#idx:flushoutput0:1080">4.19</a></dd>

1126	1167	<a class="idx" href="exception.html#idx:format3:734">4.11.4</a> <a class="idx" href="exception.html#idx:format3:747">4.11.4</a> <a class="idx" href="exception.html#idx:format3:750">4.11.4</a> <a class="idx" href="exception.html#idx:format3:761">4.11.4</a> <a class="idx" href="exception.html#idx:format3:765">4.11.4.1</a> <a class="idx" href="IO.html#idx:format3:961">4.17.1</a> <a class="idx" href="IO.html#idx:format3:1054">4.17.5</a> <a class="idx" href="termrw.html#idx:format3:1117">4.20</a> <a class="idx" href="manipatom.html#idx:format3:1254">4.22</a> <a class="idx" href="manipatom.html#idx:format3:1267">4.22</a> <a class="idx" href="locale.html#idx:format3:1287">4.23</a> <a class="idx" href="chartype.html#idx:format3:1305">4.24.2</a> <a class="idx" href="arith.html#idx:format3:1331">4.27.2.1</a> <a class="idx" href="arith.html#idx:format3:1333">4.27.2.2</a> <a class="idx" href="format.html#idx:format3:1388">4.32</a> <a class="idx" href="format.html#idx:format3:1404">4.32.2</a> <a class="idx" href="format.html#idx:format3:1409">4.32.3</a> <a class="idx" href="strings.html#idx:format3:1611">5.2.2</a> <a class="idx" href="strings.html#idx:format3:1620">5.2.3</a></dd>
1127	1168	<dt>format/[1,2]</dt>
1128	1169	<dd>
1129		<a class="idx" href="termrw.html#idx:format12:1114">4.20</a> <a class="idx" href="predsummary.html#idx:format12:2357">F.1</a></dd>
	1170	<a class="idx" href="termrw.html#idx:format12:1114">4.20</a> <a class="idx" href="predsummary.html#idx:format12:2361">F.1</a></dd>
1130	1171	<dt>format/[2,3]</dt>
1131	1172	<dd>
1132	1173	<a class="idx" href="syntax.html#idx:format23:218">2.16.1.3</a></dd>

1142	1183	<dt><a class="idx" href="aggregate.html#free_variables/4">free_variables/4</a></dt>
1143	1184	<dt><a class="idx" href="coroutining.html#freeze/2">freeze/2</a></dt>
1144	1185	<dd>
1145		<a class="idx" href="coroutining.html#idx:freeze2:1794">7.2</a> <a class="idx" href="coroutining.html#idx:freeze2:1803">7.2</a> <a class="idx" href="coroutining.html#idx:freeze2:1805">7.2</a> <a class="idx" href="coroutining.html#idx:freeze2:1806">7.2</a></dd>
	1186	<a class="idx" href="coroutining.html#idx:freeze2:1798">7.2</a> <a class="idx" href="coroutining.html#idx:freeze2:1807">7.2</a> <a class="idx" href="coroutining.html#idx:freeze2:1809">7.2</a> <a class="idx" href="coroutining.html#idx:freeze2:1810">7.2</a></dd>
1146	1187	<dt><a class="idx" href="coroutining.html#frozen/2">frozen/2</a></dt>
1147	1188	<dt>functor</dt>
1148	1189	<dd>
1149		<a class="idx" href="glossary.html#idx:functor:2294">D</a></dd>
	1190	<a class="idx" href="glossary.html#idx:functor:2298">D</a></dd>
1150	1191	<dt><a class="idx" href="manipterm.html#functor/3">functor/3</a></dt>
1151	1192	<dd>
1152	1193	<a class="idx" href="typetest.html#idx:functor3:609">4.6</a> <a class="idx" href="examineprog.html#idx:functor3:906">4.16</a> <a class="idx" href="manipterm.html#idx:functor3:1191">4.21</a> <a class="idx" href="manipterm.html#idx:functor3:1194">4.21</a> <a class="idx" href="manipterm.html#idx:functor3:1195">4.21</a> <a class="idx" href="gvar.html#idx:functor3:1433">4.33.1</a> <a class="idx" href="ext-syntax.html#idx:functor3:1625">5.3.2</a> <a class="idx" href="dicts.html#idx:functor3:1631">5.4.1</a></dd>
1153	1194	<dt><a class="idx" href="memory.html#garbage_collect/0">garbage_collect/0</a></dt>
1154	1195	<dd>
1155		<a class="idx" href="engine-examples.html#idx:garbagecollect0:1981">10.1.3</a> <a class="idx" href="engine-resources.html#idx:garbagecollect0:1987">10.2</a></dd>
	1196	<a class="idx" href="engine-examples.html#idx:garbagecollect0:1985">10.1.3</a> <a class="idx" href="engine-resources.html#idx:garbagecollect0:1991">10.2</a></dd>
1156	1197	<dt><a class="idx" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a></dt>
1157	1198	<dd>
1158		<a class="idx" href="flags.html#idx:garbagecollectatoms0:85">2.11</a> <a class="idx" href="memory.html#idx:garbagecollectatoms0:1576">4.42</a> <a class="idx" href="engine-resources.html#idx:garbagecollectatoms0:1983">10.2</a> <a class="idx" href="foreigninclude.html#idx:garbagecollectatoms0:2073">11.4.19</a></dd>
	1199	<a class="idx" href="flags.html#idx:garbagecollectatoms0:85">2.11</a> <a class="idx" href="memory.html#idx:garbagecollectatoms0:1576">4.42</a> <a class="idx" href="engine-resources.html#idx:garbagecollectatoms0:1987">10.2</a> <a class="idx" href="foreigninclude.html#idx:garbagecollectatoms0:2077">11.4.19</a></dd>
1159	1200	<dt><a class="idx" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a></dt>
1160	1201	<dd>
1161	1202	<a class="idx" href="jitindex.html#idx:garbagecollectclauses0:257">2.18</a> <a class="idx" href="jitindex.html#idx:garbagecollectclauses0:258">2.18</a> <a class="idx" href="consulting.html#idx:garbagecollectclauses0:557">4.3.2</a> <a class="idx" href="consulting.html#idx:garbagecollectclauses0:559">4.3.2</a> <a class="idx" href="db.html#idx:garbagecollectclauses0:801">4.14</a></dd>

1176	1217	<a class="idx" href="chario.html#idx:get02:1098">4.19</a></dd>
1177	1218	<dt><a class="idx" href="assoc.html#get_assoc/3">get_assoc/3</a></dt>
1178	1219	<dd>
1179		<a class="idx" href="dicts.html#idx:getassoc3:1652">5.4.3</a></dd>
	1220	<a class="idx" href="dicts.html#idx:getassoc3:1656">5.4.3</a></dd>
1180	1221	<dt><a class="idx" href="assoc.html#get_assoc/5">get_assoc/5</a></dt>
1181	1222	<dt><a class="idx" href="attvar.html#get_attr/3">get_attr/3</a></dt>
1182	1223	<dd>
1183		<a class="idx" href="attvar.html#idx:getattr3:1790">7.1.4</a></dd>
	1224	<a class="idx" href="attvar.html#idx:getattr3:1794">7.1.4</a></dd>
1184	1225	<dt><a class="idx" href="attvar.html#get_attrs/2">get_attrs/2</a></dt>
1185	1226	<dd>
1186		<a class="idx" href="attvar.html#idx:getattrs2:1792">7.1.4</a></dd>
	1227	<a class="idx" href="attvar.html#idx:getattrs2:1796">7.1.4</a></dd>
1187	1228	<dt><a class="idx" href="chario.html#get_byte/1">get_byte/1</a></dt>
1188	1229	<dd>
1189	1230	<a class="idx" href="chario.html#idx:getbyte1:1090">4.19</a></dd>

1212	1253	<dd>
1213	1254	<a class="idx" href="chars.html#idx:getcode12:350">4.2</a></dd>
1214	1255	<dt><a class="idx" href="dicts.html#get_dict/3">get_dict/3</a></dt>
	1256	<dd>
	1257	<a class="idx" href="dicts.html#idx:getdict3:1636">5.4.1.2</a></dd>
1215	1258	<dt><a class="idx" href="dicts.html#get_dict/5">get_dict/5</a></dt>
1216	1259	<dt>get_dict_ex/3</dt>
1217	1260	<dd>
1218		<a class="idx" href="dicts.html#idx:getdictex3:1634">5.4.1</a></dd>
	1261	<a class="idx" href="dicts.html#idx:getdictex3:1634">5.4.1</a> <a class="idx" href="dicts.html#idx:getdictex3:1637">5.4.1.2</a></dd>
1219	1262	<dt><a class="idx" href="db.html#get_flag/2">get_flag/2</a></dt>
1220	1263	<dt><a class="idx" href="chario.html#get_single_char/1">get_single_char/1</a></dt>
1221	1264	<dd>

1223	1266	<dt><a class="idx" href="strings.html#get_string_code/3">get_string_code/3</a></dt>
1224	1267	<dt><a class="idx" href="system.html#get_time/1">get_time/1</a></dt>
1225	1268	<dd>
1226		<a class="idx" href="files.html#idx:gettime1:1503">4.36</a> <a class="idx" href="statistics.html#idx:gettime1:1563">4.40</a> <a class="idx" href="threadcom.html#idx:gettime1:1888">9.3.1</a> <a class="idx" href="threadcom.html#idx:gettime1:1902">9.3.1</a></dd>
	1269	<a class="idx" href="files.html#idx:gettime1:1503">4.36</a> <a class="idx" href="statistics.html#idx:gettime1:1563">4.40</a> <a class="idx" href="threadcom.html#idx:gettime1:1892">9.3.1</a> <a class="idx" href="threadcom.html#idx:gettime1:1906">9.3.1</a></dd>
1227	1270	<dt><a class="idx" href="system.html#getenv/2">getenv/2</a></dt>
1228	1271	<dd>
1229		<a class="idx" href="system.html#idx:getenv2:1450">4.35</a> <a class="idx" href="www_browser.html#idx:getenv2:2149">A.18</a></dd>
	1272	<a class="idx" href="system.html#idx:getenv2:1450">4.35</a> <a class="idx" href="www_browser.html#idx:getenv2:2153">A.18</a></dd>
1230	1273	<dt><a class="idx" href="random.html#getrand/1">getrand/1</a></dt>
1231	1274	<dt><a class="idx" href="clpfd.html#global_cardinality/2">global_cardinality/2</a></dt>
1232	1275	<dt><a class="idx" href="clpfd.html#global_cardinality/3">global_cardinality/3</a></dt>

1236	1279	<a class="idx" href="ext-syntax.html#idx:go0:1630">5.3.2</a></dd>
1237	1280	<dt>goal</dt>
1238	1281	<dd>
1239		<a class="idx" href="glossary.html#idx:goal:2295">D</a></dd>
	1282	<a class="idx" href="glossary.html#idx:goal:2299">D</a></dd>
1240	1283	<dt><a class="idx" href="consulting.html#goal_expansion/2">goal_expansion/2</a></dt>
1241	1284	<dd>
1242		<a class="idx" href="flags.html#idx:goalexpansion2:164">2.11</a> <a class="idx" href="consulting.html#idx:goalexpansion2:369">4.3</a> <a class="idx" href="consulting.html#idx:goalexpansion2:485">4.3</a> <a class="idx" href="consulting.html#idx:goalexpansion2:519">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:527">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:533">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:536">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:537">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:539">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:542">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:546">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:547">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:550">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:554">4.3.1.2</a> <a class="idx" href="consulting.html#idx:goalexpansion2:561">4.3.2</a> <a class="idx" href="dialect.html#idx:goalexpansion2:2254">C</a> <a class="idx" href="portabilitystrategies.html#idx:goalexpansion2:2258">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:goalexpansion2:2263">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:goalexpansion2:2265">C.1</a> <a class="idx" href="predsummary.html#idx:goalexpansion2:2353">F.1</a></dd>
	1285	<a class="idx" href="flags.html#idx:goalexpansion2:164">2.11</a> <a class="idx" href="consulting.html#idx:goalexpansion2:369">4.3</a> <a class="idx" href="consulting.html#idx:goalexpansion2:485">4.3</a> <a class="idx" href="consulting.html#idx:goalexpansion2:519">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:527">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:533">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:536">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:537">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:539">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:542">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:546">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:547">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:550">4.3.1</a> <a class="idx" href="consulting.html#idx:goalexpansion2:554">4.3.1.2</a> <a class="idx" href="consulting.html#idx:goalexpansion2:561">4.3.2</a> <a class="idx" href="dialect.html#idx:goalexpansion2:2258">C</a> <a class="idx" href="portabilitystrategies.html#idx:goalexpansion2:2262">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:goalexpansion2:2267">C.1</a> <a class="idx" href="portabilitystrategies.html#idx:goalexpansion2:2269">C.1</a> <a class="idx" href="predsummary.html#idx:goalexpansion2:2357">F.1</a></dd>
1243	1286	<dt><a class="idx" href="consulting.html#goal_expansion/4">goal_expansion/4</a></dt>
1244	1287	<dd>
1245	1288	<a class="idx" href="consulting.html#idx:goalexpansion4:370">4.3</a></dd>
1246	1289	<dt><a class="idx" href="typetest.html#ground/1">ground/1</a></dt>
1247	1290	<dd>
1248		<a class="idx" href="cyclic.html#idx:ground1:240">2.17</a> <a class="idx" href="db.html#idx:ground1:867">4.14.6</a> <a class="idx" href="manipterm.html#idx:ground1:1210">4.21</a> <a class="idx" href="foreigninclude.html#idx:ground1:2017">11.4.3.1</a></dd>
	1291	<a class="idx" href="cyclic.html#idx:ground1:240">2.17</a> <a class="idx" href="db.html#idx:ground1:867">4.14.6</a> <a class="idx" href="manipterm.html#idx:ground1:1210">4.21</a> <a class="idx" href="foreigninclude.html#idx:ground1:2021">11.4.3.1</a></dd>
1249	1292	<dt><a class="idx" href="solutionsequences.html#group_by/4">group_by/4</a></dt>
1250	1293	<dt><a class="idx" href="pairs.html#group_pairs_by_key/2">group_pairs_by_key/2</a></dt>
1251	1294	<dt><a class="idx" href="guitracer.html#gspy/1">gspy/1</a></dt>
1252	1295	<dt><a class="idx" href="guitracer.html#gtrace/0">gtrace/0</a></dt>
1253	1296	<dd>
1254		<a class="idx" href="thutil.html#idx:gtrace0:1941">9.5.1</a></dd>
	1297	<a class="idx" href="thutil.html#idx:gtrace0:1945">9.5.1</a></dd>
1255	1298	<dt><a class="idx" href="guitracer.html#guitracer/0">guitracer/0</a></dt>
1256	1299	<dd>
1257	1300	<a class="idx" href="guitracer.html#idx:guitracer0:315">3.5.1</a> <a class="idx" href="guitracer.html#idx:guitracer0:321">3.5.1</a> <a class="idx" href="idesummary.html#idx:guitracer0:330">3.9</a> <a class="idx" href="debugger.html#idx:guitracer0:1541">4.39</a></dd>
1258	1301	<dt><a class="idx" href="xref.html#gxref/0">gxref/0</a></dt>
1259	1302	<dd>
1260		<a class="idx" href="help.html#idx:gxref0:52">2.6</a> <a class="idx" href="import.html#idx:gxref0:1684">6.3</a> <a class="idx" href="runtime.html#idx:gxref0:2108">12</a> <a class="idx" href="prolog_xref.html#idx:gxref0:2151">A.27</a></dd>
	1303	<a class="idx" href="help.html#idx:gxref0:52">2.6</a> <a class="idx" href="import.html#idx:gxref0:1688">6.3</a> <a class="idx" href="runtime.html#idx:gxref0:2112">12</a> <a class="idx" href="prolog_xref.html#idx:gxref0:2155">A.27</a></dd>
1261	1304	<dt><a class="idx" href="toplevel.html#halt/0">halt/0</a></dt>
1262	1305	<dd>
1263		<a class="idx" href="quickstart.html#idx:halt0:17">2.1.5</a> <a class="idx" href="debugoverview.html#idx:halt0:68">2.9</a> <a class="idx" href="flags.html#idx:halt0:139">2.11</a> <a class="idx" href="consulting.html#idx:halt0:500">4.3</a> <a class="idx" href="consulting.html#idx:halt0:512">4.3</a> <a class="idx" href="predsummary.html#idx:halt0:2351">F.1</a></dd>
	1306	<a class="idx" href="quickstart.html#idx:halt0:17">2.1.5</a> <a class="idx" href="debugoverview.html#idx:halt0:68">2.9</a> <a class="idx" href="flags.html#idx:halt0:139">2.11</a> <a class="idx" href="consulting.html#idx:halt0:500">4.3</a> <a class="idx" href="consulting.html#idx:halt0:512">4.3</a> <a class="idx" href="predsummary.html#idx:halt0:2355">F.1</a></dd>
1264	1307	<dt><a class="idx" href="toplevel.html#halt/1">halt/1</a></dt>
1265	1308	<dd>
1266		<a class="idx" href="flags.html#idx:halt1:107">2.11</a> <a class="idx" href="toplevel.html#idx:halt1:1529">4.37</a> <a class="idx" href="foreigninclude.html#idx:halt1:2063">11.4.16</a> <a class="idx" href="predsummary.html#idx:halt1:2349">F.1</a></dd>
	1309	<a class="idx" href="flags.html#idx:halt1:107">2.11</a> <a class="idx" href="toplevel.html#idx:halt1:1529">4.37</a> <a class="idx" href="foreigninclude.html#idx:halt1:2067">11.4.16</a> <a class="idx" href="predsummary.html#idx:halt1:2353">F.1</a></dd>
1267	1310	<dt>halt/[0,1]</dt>
1268	1311	<dd>
1269	1312	<a class="idx" href="consulting.html#idx:halt01:498">4.3</a></dd>
1270	1313	<dt><a class="idx" href="error.html#has_type/2">has_type/2</a></dt>
1271	1314	<dt>hashing</dt>
1272	1315	<dd>
1273		<a class="idx" href="glossary.html#idx:hashing:2297">D</a></dd>
	1316	<a class="idx" href="glossary.html#idx:hashing:2301">D</a></dd>
1274	1317	<dt>head</dt>
1275	1318	<dd>
1276		<a class="idx" href="glossary.html#idx:head:2298">D</a></dd>
	1319	<a class="idx" href="glossary.html#idx:head:2302">D</a></dd>
1277	1320	<dt><a class="idx" href="help.html#help/0">help/0</a></dt>
1278	1321	<dd>
1279		<a class="idx" href="hooks.html#idx:help0:186">2.12</a> <a class="idx" href="useresource.html#idx:help0:2122">12.3</a> <a class="idx" href="intlibs.html#idx:help0:2230">B.7</a> <a class="idx" href="intlibs.html#idx:help0:2232">B.7</a></dd>
	1322	<a class="idx" href="hooks.html#idx:help0:186">2.12</a> <a class="idx" href="useresource.html#idx:help0:2126">12.3</a> <a class="idx" href="intlibs.html#idx:help0:2234">B.7</a> <a class="idx" href="intlibs.html#idx:help0:2236">B.7</a></dd>
1280	1323	<dt><a class="idx" href="help.html#help/1">help/1</a></dt>
1281	1324	<dd>
1282		<a class="idx" href="help.html#idx:help1:48">2.6</a> <a class="idx" href="flags.html#idx:help1:162">2.11</a> <a class="idx" href="hooks.html#idx:help1:187">2.12</a> <a class="idx" href="intlibs.html#idx:help1:2231">B.7</a> <a class="idx" href="intlibs.html#idx:help1:2233">B.7</a> <a class="idx" href="intlibs.html#idx:help1:2234">B.7</a></dd>
	1325	<a class="idx" href="help.html#idx:help1:48">2.6</a> <a class="idx" href="flags.html#idx:help1:162">2.11</a> <a class="idx" href="hooks.html#idx:help1:187">2.12</a> <a class="idx" href="intlibs.html#idx:help1:2235">B.7</a> <a class="idx" href="intlibs.html#idx:help1:2237">B.7</a> <a class="idx" href="intlibs.html#idx:help1:2238">B.7</a></dd>
1283	1326	<dt>hooks</dt>
1284	1327	<dd>
1285	1328	<a class="idx" href="hooks.html#idx:hooks:167">2.12</a></dd>

1298	1341	<a class="idx" href="consulting.html#idx:if1:487">4.3</a></dd>
1299	1342	<dt><a class="idx" href="metacall.html#ignore/1">ignore/1</a></dt>
1300	1343	<dd>
1301		<a class="idx" href="profile.html#idx:ignore1:1571">4.41.1</a> <a class="idx" href="threadcreate.html#idx:ignore1:1843">9.1</a></dd>
	1344	<a class="idx" href="profile.html#idx:ignore1:1571">4.41.1</a> <a class="idx" href="threadcreate.html#idx:ignore1:1847">9.1</a></dd>
1302	1345	<dt>immediate, update view</dt>
1303	1346	<dd>
1304	1347	<a class="idx" href="db.html#idx:immediateupdateview:860">4.14.5</a></dd>
1305	1348	<dt><a class="idx" href="altmoduleapi.html#import/1">import/1</a></dt>
1306	1349	<dd>
1307		<a class="idx" href="altmoduleapi.html#idx:import1:1731">6.11</a> <a class="idx" href="dynamic-modules.html#idx:import1:1734">6.12</a></dd>
	1350	<a class="idx" href="altmoduleapi.html#idx:import1:1735">6.11</a> <a class="idx" href="dynamic-modules.html#idx:import1:1738">6.12</a></dd>
1308	1351	<dt><a class="idx" href="importmodule.html#import_module/2">import_module/2</a></dt>
1309	1352	<dd>
1310		<a class="idx" href="examineprog.html#idx:importmodule2:903">4.16</a> <a class="idx" href="importmodule.html#idx:importmodule2:1722">6.9</a> <a class="idx" href="importmodule.html#idx:importmodule2:1723">6.9</a></dd>
	1353	<a class="idx" href="examineprog.html#idx:importmodule2:903">4.16</a> <a class="idx" href="importmodule.html#idx:importmodule2:1726">6.9</a> <a class="idx" href="importmodule.html#idx:importmodule2:1727">6.9</a></dd>
1311	1354	<dt>imported predicate</dt>
1312	1355	<dd>
1313		<a class="idx" href="glossary.html#idx:importedpredicate:2299">D</a></dd>
	1356	<a class="idx" href="glossary.html#idx:importedpredicate:2303">D</a></dd>
1314	1357	<dt><a class="idx" href="clpfd.html#in/2">in/2</a></dt>
1315	1358	<dt><a class="idx" href="mt-xpce.html#in_pce_thread/1">in_pce_thread/1</a></dt>
1316	1359	<dd>
1317		<a class="idx" href="mt-xpce.html#idx:inpcethread1:1956">9.7</a> <a class="idx" href="mt-xpce.html#idx:inpcethread1:1957">9.7</a> <a class="idx" href="mt-xpce.html#idx:inpcethread1:1958">9.7</a></dd>
	1360	<a class="idx" href="mt-xpce.html#idx:inpcethread1:1960">9.7</a> <a class="idx" href="mt-xpce.html#idx:inpcethread1:1961">9.7</a> <a class="idx" href="mt-xpce.html#idx:inpcethread1:1962">9.7</a></dd>
1318	1361	<dt><a class="idx" href="mt-xpce.html#in_pce_thread_sync/1">in_pce_thread_sync/1</a></dt>
1319	1362	<dd>
1320		<a class="idx" href="mt-xpce.html#idx:inpcethreadsync1:1959">9.7</a> <a class="idx" href="mt-xpce.html#idx:inpcethreadsync1:1961">9.7</a></dd>
	1363	<a class="idx" href="mt-xpce.html#idx:inpcethreadsync1:1963">9.7</a> <a class="idx" href="mt-xpce.html#idx:inpcethreadsync1:1965">9.7</a></dd>
1321	1364	<dt><a class="idx" href="consulting.html#include/1">include/1</a></dt>
1322	1365	<dd>
1323	1366	<a class="idx" href="consulting.html#idx:include1:362">4.3</a> <a class="idx" href="consulting.html#idx:include1:395">4.3</a> <a class="idx" href="consulting.html#idx:include1:437">4.3</a> <a class="idx" href="consulting.html#idx:include1:439">4.3</a> <a class="idx" href="consulting.html#idx:include1:440">4.3</a> <a class="idx" href="consulting.html#idx:include1:442">4.3</a> <a class="idx" href="consulting.html#idx:include1:443">4.3</a> <a class="idx" href="consulting.html#idx:include1:444">4.3</a> <a class="idx" href="consulting.html#idx:include1:475">4.3</a> <a class="idx" href="consulting.html#idx:include1:476">4.3</a> <a class="idx" href="consulting.html#idx:include1:479">4.3</a> <a class="idx" href="examineprog.html#idx:include1:945">4.16</a></dd>
1324	1367	<dt><a class="idx" href="apply.html#include/3">include/3</a></dt>
1325	1368	<dt>indexing</dt>
1326	1369	<dd>
1327		<a class="idx" href="glossary.html#idx:indexing:2301">D</a></dd>
	1370	<a class="idx" href="glossary.html#idx:indexing:2305">D</a></dd>
1328	1371	<dt>indexing,term-hashes</dt>
1329	1372	<dd>
1330	1373	<a class="idx" href="db.html#idx:indexingtermhashes:864">4.14.6</a></dd>

1336	1379	<dt><a class="idx" href="consulting.html#initialization/0">initialization/0</a></dt>
1337	1380	<dt><a class="idx" href="consulting.html#initialization/1">initialization/1</a></dt>
1338	1381	<dd>
1339		<a class="idx" href="consulting.html#idx:initialization1:377">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:503">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:504">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:506">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:509">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:510">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:563">4.3.2</a> <a class="idx" href="consulting.html#idx:initialization1:574">4.3.2.2</a> <a class="idx" href="gvar.html#idx:initialization1:1417">4.33</a> <a class="idx" href="threadcreate.html#idx:initialization1:1863">9.1</a> <a class="idx" href="threadcreate.html#idx:initialization1:1864">9.1</a> <a class="idx" href="foreignlink.html#idx:initialization1:2011">11.2.2</a> <a class="idx" href="foreigninclude.html#idx:initialization1:2075">11.4.21</a> <a class="idx" href="qsavelimits.html#idx:initialization1:2113">12.1</a></dd>
	1382	<a class="idx" href="consulting.html#idx:initialization1:377">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:503">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:504">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:506">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:509">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:510">4.3</a> <a class="idx" href="consulting.html#idx:initialization1:563">4.3.2</a> <a class="idx" href="consulting.html#idx:initialization1:574">4.3.2.2</a> <a class="idx" href="gvar.html#idx:initialization1:1417">4.33</a> <a class="idx" href="threadcreate.html#idx:initialization1:1867">9.1</a> <a class="idx" href="threadcreate.html#idx:initialization1:1868">9.1</a> <a class="idx" href="foreignlink.html#idx:initialization1:2015">11.2.2</a> <a class="idx" href="foreigninclude.html#idx:initialization1:2079">11.4.21</a> <a class="idx" href="qsavelimits.html#idx:initialization1:2117">12.1</a></dd>
1340	1383	<dt><a class="idx" href="consulting.html#initialization/2">initialization/2</a></dt>
1341	1384	<dd>
1342	1385	<a class="idx" href="cmdline.html#idx:initialization2:33">2.4.2</a> <a class="idx" href="compilation.html#idx:initialization2:73">2.10.2.1</a> <a class="idx" href="flags.html#idx:initialization2:138">2.11</a> <a class="idx" href="consulting.html#idx:initialization2:564">4.3.2</a></dd>

1347	1390	<dt><a class="idx" href="db.html#instance/2">instance/2</a></dt>
1348	1391	<dt>instantiation</dt>
1349	1392	<dd>
1350		<a class="idx" href="glossary.html#idx:instantiation:2305">D</a></dd>
	1393	<a class="idx" href="glossary.html#idx:instantiation:2309">D</a></dd>
1351	1394	<dt><a class="idx" href="error.html#instantiation_error/1">instantiation_error/1</a></dt>
1352	1395	<dd>
1353		<a class="idx" href="foreigninclude.html#idx:instantiationerror1:2028">11.4.6</a></dd>
	1396	<a class="idx" href="foreigninclude.html#idx:instantiationerror1:2032">11.4.6</a></dd>
1354	1397	<dt>integer</dt>
1355	1398	<dd>
1356		<a class="idx" href="glossary.html#idx:integer:2302">D</a></dd>
	1399	<a class="idx" href="glossary.html#idx:integer:2306">D</a></dd>
1357	1400	<dt>integer,unbounded</dt>
1358	1401	<dd>
1359	1402	<a class="idx" href="arith.html#idx:integerunbounded:1326">4.27.2.1</a></dd>

1371	1414	<a class="idx" href="widechars.html#idx:internationalization:265">2.19</a></dd>
1372	1415	<dt>interpreted</dt>
1373	1416	<dd>
1374		<a class="idx" href="glossary.html#idx:interpreted:2304">D</a></dd>
	1417	<a class="idx" href="glossary.html#idx:interpreted:2308">D</a></dd>
1375	1418	<dt><a class="idx" href="lists.html#intersection/3">intersection/3</a></dt>
1376	1419	<dt><a class="idx" href="arith.html#is/2">is/2</a></dt>
1377	1420	<dd>
1378		<a class="idx" href="arith.html#idx:is2:1325">4.27.2</a> <a class="idx" href="arith.html#idx:is2:1330">4.27.2.1</a> <a class="idx" href="arith.html#idx:is2:1336">4.27.2.3</a> <a class="idx" href="sicstus-chr.html#idx:is2:1825">8.6.1</a></dd>
	1421	<a class="idx" href="arith.html#idx:is2:1325">4.27.2</a> <a class="idx" href="arith.html#idx:is2:1330">4.27.2.1</a> <a class="idx" href="arith.html#idx:is2:1336">4.27.2.3</a> <a class="idx" href="sicstus-chr.html#idx:is2:1829">8.6.1</a></dd>
1379	1422	<dt><a class="idx" href="files.html#is_absolute_file_name/1">is_absolute_file_name/1</a></dt>
1380	1423	<dt><a class="idx" href="url.html#is_absolute_url/1">is_absolute_url/1</a></dt>
1381	1424	<dt><a class="idx" href="assoc.html#is_assoc/1">is_assoc/1</a></dt>

1402	1445	<a class="idx" href="jitindex.html#idx:jitindex:255">2.18</a></dd>
1403	1446	<dt><a class="idx" href="thutil.html#join_threads/0">join_threads/0</a></dt>
1404	1447	<dd>
1405		<a class="idx" href="thutil.html#idx:jointhreads0:1937">9.5</a></dd>
	1448	<a class="idx" href="thutil.html#idx:jointhreads0:1941">9.5</a></dd>
1406	1449	<dt><a class="idx" href="builtinlist.html#keysort/2">keysort/2</a></dt>
1407	1450	<dd>
1408	1451	<a class="idx" href="builtinlist.html#idx:keysort2:1352">4.29</a> <a class="idx" href="builtinlist.html#idx:keysort2:1356">4.29</a> <a class="idx" href="builtinlist.html#idx:keysort2:1360">4.29</a></dd>
1409	1452	<dt><a class="idx" href="softlicense.html#known_licenses/0">known_licenses/0</a></dt>
1410	1453	<dd>
1411		<a class="idx" href="softlicense.html#idx:knownlicenses0:2341">E.2</a></dd>
	1454	<a class="idx" href="softlicense.html#idx:knownlicenses0:2345">E.2</a></dd>
1412	1455	<dt><a class="idx" href="clpfd.html#label/1">label/1</a></dt>
1413	1456	<dt><a class="idx" href="clpb.html#labeling/1">labeling/1</a></dt>
1414	1457	<dt><a class="idx" href="clpfd.html#labeling/2">labeling/2</a></dt>
1415	1458	<dt><a class="idx" href="yall.html#lambda_calls/2">lambda_calls/2</a></dt>
1416	1459	<dt><a class="idx" href="yall.html#lambda_calls/3">lambda_calls/3</a></dt>
1417	1460	<dt><a class="idx" href="lists.html#last/2">last/2</a></dt>
1418		<dt><a class="idx" href="pio.html#lazy_list_character_count/1">lazy_list_character_count/1</a></dt>
1419		<dt><a class="idx" href="pio.html#lazy_list_location/1">lazy_list_location/1</a></dt>
	1461	<dt><a class="idx" href="pio.html#lazy_list_character_count//1">lazy_list_character_count//1</a></dt>
	1462	<dt><a class="idx" href="pio.html#lazy_list_location//1">lazy_list_location//1</a></dt>
1420	1463	<dt><a class="idx" href="debugger.html#leash/1">leash/1</a></dt>
1421	1464	<dd>
1422		<a class="idx" href="debugoverview.html#idx:leash1:60">2.9</a> <a class="idx" href="debugger.html#idx:leash1:1557">4.39</a> <a class="idx" href="debugging.html#idx:leash1:1822">8.4.3</a> <a class="idx" href="tracehook.html#idx:leash1:2189">B.3</a></dd>
	1465	<a class="idx" href="debugoverview.html#idx:leash1:60">2.9</a> <a class="idx" href="debugger.html#idx:leash1:1557">4.39</a> <a class="idx" href="debugging.html#idx:leash1:1826">8.4.3</a> <a class="idx" href="tracehook.html#idx:leash1:2193">B.3</a></dd>
1423	1466	<dt><a class="idx" href="builtinlist.html#length/2">length/2</a></dt>
1424	1467	<dd>
1425	1468	<a class="idx" href="dicts.html#idx:length2:1635">5.4.1.1</a></dd>

1429	1472	<a class="idx" href="autoload.html#idx:librarydirectory1:189">2.13</a> <a class="idx" href="autoload.html#idx:librarydirectory1:195">2.13</a> <a class="idx" href="autoload.html#idx:librarydirectory1:199">2.13</a> <a class="idx" href="autoload.html#idx:librarydirectory1:201">2.13</a></dd>
1430	1473	<dt><a class="idx" href="softlicense.html#license/0">license/0</a></dt>
1431	1474	<dd>
1432		<a class="idx" href="softlicense.html#idx:license0:2340">E.2</a></dd>
	1475	<a class="idx" href="softlicense.html#idx:license0:2344">E.2</a></dd>
1433	1476	<dt><a class="idx" href="softlicense.html#license/1">license/1</a></dt>
1434	1477	<dd>
1435		<a class="idx" href="contrib.html#idx:license1:2339">E.1</a></dd>
	1478	<a class="idx" href="contrib.html#idx:license1:2343">E.1</a></dd>
1436	1479	<dt><a class="idx" href="softlicense.html#license/2">license/2</a></dt>
1437	1480	<dd>
1438		<a class="idx" href="softlicense.html#idx:license2:2342">E.2</a> <a class="idx" href="softlicense.html#idx:license2:2343">E.2</a></dd>
	1481	<a class="idx" href="softlicense.html#idx:license2:2346">E.2</a> <a class="idx" href="softlicense.html#idx:license2:2347">E.2</a></dd>
1439	1482	<dt><a class="idx" href="solutionsequences.html#limit/2">limit/2</a></dt>
1440	1483	<dt><a class="idx" href="streamstat.html#line_count/2">line_count/2</a></dt>
1441	1484	<dd>

1452	1495	<dt><a class="idx" href="check.html#list_strings/1">list_strings/1</a></dt>
1453	1496	<dt><a class="idx" href="assoc.html#list_to_assoc/2">list_to_assoc/2</a></dt>
1454	1497	<dd>
1455		<a class="idx" href="dicts.html#idx:listtoassoc2:1651">5.4.3</a></dd>
	1498	<a class="idx" href="dicts.html#idx:listtoassoc2:1655">5.4.3</a></dd>
1456	1499	<dt><a class="idx" href="ordsets.html#list_to_ord_set/2">list_to_ord_set/2</a></dt>
1457	1500	<dt><a class="idx" href="lists.html#list_to_set/2">list_to_set/2</a></dt>
1458	1501	<dt><a class="idx" href="check.html#list_trivial_fails/0">list_trivial_fails/0</a></dt>

1464	1507	<dt><a class="idx" href="check.html#list_void_declarations/0">list_void_declarations/0</a></dt>
1465	1508	<dt><a class="idx" href="broadcast.html#listen/2">listen/2</a></dt>
1466	1509	<dd>
1467		<a class="idx" href="broadcast.html#idx:listen2:2139">A.4</a></dd>
	1510	<a class="idx" href="broadcast.html#idx:listen2:2143">A.4</a></dd>
1468	1511	<dt><a class="idx" href="broadcast.html#listen/3">listen/3</a></dt>
1469	1512	<dd>
1470		<a class="idx" href="broadcast.html#idx:listen3:2141">A.4</a> <a class="idx" href="broadcast.html#idx:listen3:2142">A.4</a> <a class="idx" href="broadcast.html#idx:listen3:2143">A.4</a></dd>
	1513	<a class="idx" href="broadcast.html#idx:listen3:2145">A.4</a> <a class="idx" href="broadcast.html#idx:listen3:2146">A.4</a> <a class="idx" href="broadcast.html#idx:listen3:2147">A.4</a></dd>
1471	1514	<dt><a class="idx" href="broadcast.html#listening/3">listening/3</a></dt>
1472	1515	<dt><a class="idx" href="listing.html#listing/0">listing/0</a></dt>
1473	1516	<dd>

1478	1521	<dt><a class="idx" href="consulting.html#load_files/1">load_files/1</a></dt>
1479	1522	<dt><a class="idx" href="consulting.html#load_files/2">load_files/2</a></dt>
1480	1523	<dd>
1481		<a class="idx" href="flags.html#idx:loadfiles2:130">2.11</a> <a class="idx" href="flags.html#idx:loadfiles2:132">2.11</a> <a class="idx" href="flags.html#idx:loadfiles2:154">2.11</a> <a class="idx" href="hooks.html#idx:loadfiles2:173">2.12</a> <a class="idx" href="hooks.html#idx:loadfiles2:175">2.12</a> <a class="idx" href="hooks.html#idx:loadfiles2:176">2.12</a> <a class="idx" href="widechars.html#idx:loadfiles2:268">2.19.1</a> <a class="idx" href="consulting.html#idx:loadfiles2:379">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:385">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:393">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:394">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:396">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:413">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:423">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:425">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:428">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:477">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:478">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:480">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:481">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:483">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:567">4.3.2.1</a> <a class="idx" href="consulting.html#idx:loadfiles2:570">4.3.2.1</a> <a class="idx" href="consulting.html#idx:loadfiles2:573">4.3.2.2</a> <a class="idx" href="consulting.html#idx:loadfiles2:575">4.3.2.2</a> <a class="idx" href="consulting.html#idx:loadfiles2:584">4.3.3</a> <a class="idx" href="debugger.html#idx:loadfiles2:1559">4.39</a> <a class="idx" href="import.html#idx:loadfiles2:1676">6.3</a> <a class="idx" href="prolog_xref.html#idx:loadfiles2:2152">A.27</a> <a class="idx" href="loadfilehook.html#idx:loadfiles2:2236">B.8</a> <a class="idx" href="loadfilehook.html#idx:loadfiles2:2238">B.8</a> <a class="idx" href="dialect.html#idx:loadfiles2:2255">C</a> <a class="idx" href="predsummary.html#idx:loadfiles2:2366">F.1</a></dd>
	1524	<a class="idx" href="flags.html#idx:loadfiles2:130">2.11</a> <a class="idx" href="flags.html#idx:loadfiles2:132">2.11</a> <a class="idx" href="flags.html#idx:loadfiles2:154">2.11</a> <a class="idx" href="hooks.html#idx:loadfiles2:173">2.12</a> <a class="idx" href="hooks.html#idx:loadfiles2:175">2.12</a> <a class="idx" href="hooks.html#idx:loadfiles2:176">2.12</a> <a class="idx" href="widechars.html#idx:loadfiles2:268">2.19.1</a> <a class="idx" href="consulting.html#idx:loadfiles2:379">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:385">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:393">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:394">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:396">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:413">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:423">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:425">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:428">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:477">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:478">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:480">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:481">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:483">4.3</a> <a class="idx" href="consulting.html#idx:loadfiles2:567">4.3.2.1</a> <a class="idx" href="consulting.html#idx:loadfiles2:570">4.3.2.1</a> <a class="idx" href="consulting.html#idx:loadfiles2:573">4.3.2.2</a> <a class="idx" href="consulting.html#idx:loadfiles2:575">4.3.2.2</a> <a class="idx" href="consulting.html#idx:loadfiles2:584">4.3.3</a> <a class="idx" href="debugger.html#idx:loadfiles2:1559">4.39</a> <a class="idx" href="import.html#idx:loadfiles2:1680">6.3</a> <a class="idx" href="prolog_xref.html#idx:loadfiles2:2156">A.27</a> <a class="idx" href="loadfilehook.html#idx:loadfiles2:2240">B.8</a> <a class="idx" href="loadfilehook.html#idx:loadfiles2:2242">B.8</a> <a class="idx" href="dialect.html#idx:loadfiles2:2259">C</a> <a class="idx" href="predsummary.html#idx:loadfiles2:2370">F.1</a></dd>
1482	1525	<dt><a class="idx" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a></dt>
1483	1526	<dd>
1484		<a class="idx" href="consulting.html#idx:loadforeignlibrary1:507">4.3</a> <a class="idx" href="foreignlink.html#idx:loadforeignlibrary1:2013">11.2.4</a> <a class="idx" href="plld.html#idx:loadforeignlibrary1:2087">11.5</a> <a class="idx" href="qsaveforeign.html#idx:loadforeignlibrary1:2116">12.2</a></dd>
	1527	<a class="idx" href="consulting.html#idx:loadforeignlibrary1:507">4.3</a> <a class="idx" href="foreignlink.html#idx:loadforeignlibrary1:2017">11.2.4</a> <a class="idx" href="plld.html#idx:loadforeignlibrary1:2091">11.5</a> <a class="idx" href="qsaveforeign.html#idx:loadforeignlibrary1:2120">12.2</a></dd>
1485	1528	<dt><a class="idx" href="foreignlink.html#load_foreign_library/2">load_foreign_library/2</a></dt>
1486	1529	<dt>locale</dt>
1487	1530	<dd>

1499	1542	<dt>logical,update view</dt>
1500	1543	<dd>
1501	1544	<a class="idx" href="db.html#idx:logicalupdateview:859">4.14.5</a></dd>
	1545	<dt><a class="idx" href="dicts.html#m-get-1">m-get-1</a></dt>
	1546	<dt><a class="idx" href="dicts.html#m-put-1">m-put-1</a></dt>
	1547	<dt><a class="idx" href="dicts.html#m-put-2">m-put-2</a></dt>
1502	1548	<dt><a class="idx" href="main.html#main/0">main/0</a></dt>
1503	1549	<dd>
1504	1550	<a class="idx" href="compilation.html#idx:main0:74">2.10.2.1</a></dd>

1525	1571	<dt><a class="idx" href="pairs.html#map_list_to_pairs/3">map_list_to_pairs/3</a></dt>
1526	1572	<dt><a class="idx" href="apply.html#maplist/2">maplist/2</a></dt>
1527	1573	<dd>
1528		<a class="idx" href="forall2.html#idx:maplist2:1380">4.31</a> <a class="idx" href="ext-issues.html#idx:maplist2:1657">5.6</a></dd>
	1574	<a class="idx" href="forall2.html#idx:maplist2:1380">4.31</a> <a class="idx" href="ext-issues.html#idx:maplist2:1661">5.6</a></dd>
1529	1575	<dt><a class="idx" href="apply.html#maplist/3">maplist/3</a></dt>
1530	1576	<dd>
1531		<a class="idx" href="dicts.html#idx:maplist3:1650">5.4.3</a> <a class="idx" href="metapred.html#idx:maplist3:1688">6.4</a> <a class="idx" href="metapred.html#idx:maplist3:1690">6.4</a> <a class="idx" href="ctxmodule.html#idx:maplist3:1737">6.13</a> <a class="idx" href="ctxmodule.html#idx:maplist3:1738">6.13</a></dd>
	1577	<a class="idx" href="dicts.html#idx:maplist3:1654">5.4.3</a> <a class="idx" href="metapred.html#idx:maplist3:1692">6.4</a> <a class="idx" href="metapred.html#idx:maplist3:1694">6.4</a> <a class="idx" href="ctxmodule.html#idx:maplist3:1741">6.13</a> <a class="idx" href="ctxmodule.html#idx:maplist3:1742">6.13</a></dd>
1532	1578	<dt><a class="idx" href="apply.html#maplist/4">maplist/4</a></dt>
1533	1579	<dt><a class="idx" href="apply.html#maplist/5">maplist/5</a></dt>
1534	1580	<dt>maplist_/3</dt>
1535	1581	<dd>
1536		<a class="idx" href="metapred.html#idx:maplist3:1689">6.4</a> <a class="idx" href="ctxmodule.html#idx:maplist3:1739">6.13</a></dd>
	1582	<a class="idx" href="metapred.html#idx:maplist3:1693">6.4</a> <a class="idx" href="ctxmodule.html#idx:maplist3:1743">6.13</a></dd>
1537	1583	<dt><a class="idx" href="assoc.html#max_assoc/3">max_assoc/3</a></dt>
1538	1584	<dt><a class="idx" href="lists.html#max_list/2">max_list/2</a></dt>
1539	1585	<dt><a class="idx" href="lists.html#max_member/2">max_member/2</a></dt>

1545	1591	<dt><a class="idx" href="random.html#maybe/2">maybe/2</a></dt>
1546	1592	<dt><a class="idx" href="lists.html#member/2">member/2</a></dt>
1547	1593	<dd>
1548		<a class="idx" href="debugoverview.html#idx:member2:63">2.9</a> <a class="idx" href="debugoverview.html#idx:member2:64">2.9</a> <a class="idx" href="metacall.html#idx:member2:669">4.9</a> <a class="idx" href="builtinlist.html#idx:member2:1345">4.29</a> <a class="idx" href="files.html#idx:member2:1512">4.36</a> <a class="idx" href="import.html#idx:member2:1677">6.3</a> <a class="idx" href="predsummary.html#idx:member2:2358">F.1</a></dd>
	1594	<a class="idx" href="debugoverview.html#idx:member2:63">2.9</a> <a class="idx" href="debugoverview.html#idx:member2:64">2.9</a> <a class="idx" href="metacall.html#idx:member2:669">4.9</a> <a class="idx" href="builtinlist.html#idx:member2:1345">4.29</a> <a class="idx" href="files.html#idx:member2:1512">4.36</a> <a class="idx" href="import.html#idx:member2:1681">6.3</a> <a class="idx" href="predsummary.html#idx:member2:2362">F.1</a></dd>
1549	1595	<dt><a class="idx" href="builtinlist.html#memberchk/2">memberchk/2</a></dt>
1550	1596	<dd>
1551	1597	<a class="idx" href="compare.html#idx:memberchk2:639">4.7.2</a> <a class="idx" href="builtinlist.html#idx:memberchk2:1346">4.29</a> <a class="idx" href="builtinlist.html#idx:memberchk2:1347">4.29</a> <a class="idx" href="strings.html#idx:memberchk2:1623">5.2.4</a></dd>

1555	1601	<dt><a class="idx" href="option.html#merge_options/3">merge_options/3</a></dt>
1556	1602	<dt>message,service</dt>
1557	1603	<dd>
1558		<a class="idx" href="broadcast.html#idx:messageservice:2133">A.4</a></dd>
	1604	<a class="idx" href="broadcast.html#idx:messageservice:2137">A.4</a></dd>
1559	1605	<dt><a class="idx" href="exception.html#message_hook/3">message_hook/3</a></dt>
1560	1606	<dd>
1561		<a class="idx" href="exception.html#idx:messagehook3:732">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:735">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:738">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:742">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:743">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:752">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:757">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:759">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:772">4.11.4.1</a> <a class="idx" href="memory.html#idx:messagehook3:1581">4.42</a> <a class="idx" href="predsummary.html#idx:messagehook3:2369">F.1</a></dd>
	1607	<a class="idx" href="exception.html#idx:messagehook3:732">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:735">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:738">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:742">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:743">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:752">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:757">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:759">4.11.4</a> <a class="idx" href="exception.html#idx:messagehook3:772">4.11.4.1</a> <a class="idx" href="memory.html#idx:messagehook3:1581">4.42</a> <a class="idx" href="predsummary.html#idx:messagehook3:2373">F.1</a></dd>
1562	1608	<dt><a class="idx" href="exception.html#message_property/2">message_property/2</a></dt>
1563	1609	<dd>
1564	1610	<a class="idx" href="flags.html#idx:messageproperty2:94">2.11</a></dd>
1565	1611	<dt><a class="idx" href="threadcom.html#message_queue_create/1">message_queue_create/1</a></dt>
1566	1612	<dd>
1567		<a class="idx" href="threadcom.html#idx:messagequeuecreate1:1882">9.3.1</a> <a class="idx" href="threadcom.html#idx:messagequeuecreate1:1897">9.3.1</a></dd>
	1613	<a class="idx" href="threadcom.html#idx:messagequeuecreate1:1886">9.3.1</a> <a class="idx" href="threadcom.html#idx:messagequeuecreate1:1901">9.3.1</a></dd>
1568	1614	<dt><a class="idx" href="threadcom.html#message_queue_create/2">message_queue_create/2</a></dt>
1569	1615	<dd>
1570		<a class="idx" href="threadcom.html#idx:messagequeuecreate2:1895">9.3.1</a> <a class="idx" href="threadcom.html#idx:messagequeuecreate2:1908">9.3.1</a></dd>
	1616	<a class="idx" href="threadcom.html#idx:messagequeuecreate2:1899">9.3.1</a> <a class="idx" href="threadcom.html#idx:messagequeuecreate2:1912">9.3.1</a></dd>
1571	1617	<dt>message_queue_create/3</dt>
1572	1618	<dd>
1573		<a class="idx" href="threadsync.html#idx:messagequeuecreate3:1924">9.4</a></dd>
	1619	<a class="idx" href="threadsync.html#idx:messagequeuecreate3:1928">9.4</a></dd>
1574	1620	<dt><a class="idx" href="threadcom.html#message_queue_destroy/1">message_queue_destroy/1</a></dt>
1575	1621	<dd>
1576		<a class="idx" href="threadcom.html#idx:messagequeuedestroy1:1900">9.3.1</a></dd>
	1622	<a class="idx" href="threadcom.html#idx:messagequeuedestroy1:1904">9.3.1</a></dd>
1577	1623	<dt><a class="idx" href="threadcom.html#message_queue_property/2">message_queue_property/2</a></dt>
1578	1624	<dd>
1579		<a class="idx" href="thmonitor.html#idx:messagequeueproperty2:1879">9.2</a></dd>
	1625	<a class="idx" href="thmonitor.html#idx:messagequeueproperty2:1883">9.2</a></dd>
1580	1626	<dt><a class="idx" href="exception.html#message_to_string/2">message_to_string/2</a></dt>
1581	1627	<dd>
1582	1628	<a class="idx" href="exception.html#idx:messagetostring2:745">4.11.4</a> <a class="idx" href="exception.html#idx:messagetostring2:756">4.11.4</a></dd>
1583	1629	<dt>meta-predicate</dt>
1584	1630	<dd>
1585		<a class="idx" href="glossary.html#idx:metapredicate:2306">D</a></dd>
	1631	<a class="idx" href="glossary.html#idx:metapredicate:2310">D</a></dd>
1586	1632	<dt><a class="idx" href="option.html#meta_options/3">meta_options/3</a></dt>
1587	1633	<dd>
1588		<a class="idx" href="import.html#idx:metaoptions3:1679">6.3</a></dd>
	1634	<a class="idx" href="import.html#idx:metaoptions3:1683">6.3</a></dd>
1589	1635	<dt><a class="idx" href="metapred.html#meta_predicate/1">meta_predicate/1</a></dt>
1590	1636	<dd>
1591		<a class="idx" href="flags.html#idx:metapredicate1:96">2.11</a> <a class="idx" href="consulting.html#idx:metapredicate1:540">4.3.1</a> <a class="idx" href="typetest.html#idx:metapredicate1:615">4.6</a> <a class="idx" href="examineprog.html#idx:metapredicate1:923">4.16</a> <a class="idx" href="examineprog.html#idx:metapredicate1:924">4.16</a> <a class="idx" href="examineprog.html#idx:metapredicate1:930">4.16</a> <a class="idx" href="metapred.html#idx:metapredicate1:1687">6.4</a> <a class="idx" href="metapred.html#idx:metapredicate1:1691">6.4</a> <a class="idx" href="metapred.html#idx:metapredicate1:1698">6.4</a> <a class="idx" href="ctxmodule.html#idx:metapredicate1:1736">6.13</a> <a class="idx" href="modulecompat.html#idx:metapredicate1:1754">6.15</a> <a class="idx" href="modulecompat.html#idx:metapredicate1:1755">6.15</a> <a class="idx" href="foreigninclude.html#idx:metapredicate1:2041">11.4.9.2</a> <a class="idx" href="foreigninclude.html#idx:metapredicate1:2067">11.4.18</a> <a class="idx" href="runtime.html#idx:metapredicate1:2106">12</a> <a class="idx" href="runtime.html#idx:metapredicate1:2109">12</a></dd>
	1637	<a class="idx" href="flags.html#idx:metapredicate1:96">2.11</a> <a class="idx" href="consulting.html#idx:metapredicate1:540">4.3.1</a> <a class="idx" href="typetest.html#idx:metapredicate1:615">4.6</a> <a class="idx" href="examineprog.html#idx:metapredicate1:923">4.16</a> <a class="idx" href="examineprog.html#idx:metapredicate1:924">4.16</a> <a class="idx" href="examineprog.html#idx:metapredicate1:930">4.16</a> <a class="idx" href="metapred.html#idx:metapredicate1:1691">6.4</a> <a class="idx" href="metapred.html#idx:metapredicate1:1695">6.4</a> <a class="idx" href="metapred.html#idx:metapredicate1:1702">6.4</a> <a class="idx" href="ctxmodule.html#idx:metapredicate1:1740">6.13</a> <a class="idx" href="modulecompat.html#idx:metapredicate1:1758">6.15</a> <a class="idx" href="modulecompat.html#idx:metapredicate1:1759">6.15</a> <a class="idx" href="foreigninclude.html#idx:metapredicate1:2045">11.4.9.2</a> <a class="idx" href="foreigninclude.html#idx:metapredicate1:2071">11.4.18</a> <a class="idx" href="runtime.html#idx:metapredicate1:2110">12</a> <a class="idx" href="runtime.html#idx:metapredicate1:2113">12</a></dd>
1592	1638	<dt>mild/1</dt>
1593	1639	<dd>
1594	1640	<a class="idx" href="quickstart.html#idx:mild1:15">2.1.4</a></dd>

1599	1645	<dt><a class="idx" href="simplex.html#minimize/3">minimize/3</a></dt>
1600	1646	<dt>mode</dt>
1601	1647	<dd>
1602		<a class="idx" href="glossary.html#idx:mode:2307">D</a></dd>
	1648	<a class="idx" href="glossary.html#idx:mode:2311">D</a></dd>
1603	1649	<dt>module</dt>
1604	1650	<dd>
1605		<a class="idx" href="glossary.html#idx:module:2308">D</a></dd>
	1651	<a class="idx" href="glossary.html#idx:module:2312">D</a></dd>
1606	1652	<dt>module transparent</dt>
1607	1653	<dd>
1608		<a class="idx" href="glossary.html#idx:moduletransparent:2309">D</a></dd>
	1654	<a class="idx" href="glossary.html#idx:moduletransparent:2313">D</a></dd>
1609	1655	<dt>module,contex</dt>
1610	1656	<dd>
1611		<a class="idx" href="glossary.html#idx:modulecontex:2282">D</a></dd>
	1657	<a class="idx" href="glossary.html#idx:modulecontex:2286">D</a></dd>
1612	1658	<dt><a class="idx" href="mtoplevel.html#module/1">module/1</a></dt>
1613	1659	<dd>
1614		<a class="idx" href="flags.html#idx:module1:142">2.11</a> <a class="idx" href="consulting.html#idx:module1:358">4.3</a> <a class="idx" href="dynamic.html#idx:module1:893">4.15</a> <a class="idx" href="mtoplevel.html#idx:module1:1707">6.6</a> <a class="idx" href="threadcreate.html#idx:module1:1847">9.1</a></dd>
	1660	<a class="idx" href="flags.html#idx:module1:142">2.11</a> <a class="idx" href="consulting.html#idx:module1:358">4.3</a> <a class="idx" href="dynamic.html#idx:module1:893">4.15</a> <a class="idx" href="mtoplevel.html#idx:module1:1711">6.6</a> <a class="idx" href="threadcreate.html#idx:module1:1851">9.1</a></dd>
1615	1661	<dt><a class="idx" href="defmodule.html#module/2">module/2</a></dt>
1616	1662	<dd>
1617		<a class="idx" href="consulting.html#idx:module2:521">4.3.1</a> <a class="idx" href="operators.html#idx:module2:1315">4.25</a> <a class="idx" href="operators.html#idx:module2:1316">4.25</a> <a class="idx" href="defmodule.html#idx:module2:1660">6.2</a> <a class="idx" href="defmodule.html#idx:module2:1661">6.2</a> <a class="idx" href="defmodule.html#idx:module2:1664">6.2</a> <a class="idx" href="import.html#idx:module2:1681">6.3</a> <a class="idx" href="moduleop.html#idx:module2:1717">6.8</a> <a class="idx" href="altmoduleapi.html#idx:module2:1728">6.11</a> <a class="idx" href="modulecompat.html#idx:module2:1756">6.15</a></dd>
	1663	<a class="idx" href="consulting.html#idx:module2:521">4.3.1</a> <a class="idx" href="operators.html#idx:module2:1315">4.25</a> <a class="idx" href="operators.html#idx:module2:1316">4.25</a> <a class="idx" href="defmodule.html#idx:module2:1664">6.2</a> <a class="idx" href="defmodule.html#idx:module2:1665">6.2</a> <a class="idx" href="defmodule.html#idx:module2:1668">6.2</a> <a class="idx" href="import.html#idx:module2:1685">6.3</a> <a class="idx" href="moduleop.html#idx:module2:1721">6.8</a> <a class="idx" href="altmoduleapi.html#idx:module2:1732">6.11</a> <a class="idx" href="modulecompat.html#idx:module2:1760">6.15</a></dd>
1618	1664	<dt><a class="idx" href="defmodule.html#module/3">module/3</a></dt>
1619	1665	<dt><a class="idx" href="manipmodule.html#module_property/2">module_property/2</a></dt>
1620	1666	<dd>
1621		<a class="idx" href="manipmodule.html#idx:moduleproperty2:1749">6.14</a> <a class="idx" href="manipmodule.html#idx:moduleproperty2:1751">6.14</a></dd>
	1667	<a class="idx" href="manipmodule.html#idx:moduleproperty2:1753">6.14</a> <a class="idx" href="manipmodule.html#idx:moduleproperty2:1755">6.14</a></dd>
1622	1668	<dt><a class="idx" href="ctxmodule.html#module_transparent/1">module_transparent/1</a></dt>
1623	1669	<dd>
1624		<a class="idx" href="examineprog.html#idx:moduletransparent1:929">4.16</a> <a class="idx" href="metapred.html#idx:moduletransparent1:1699">6.4</a> <a class="idx" href="overrule.html#idx:moduletransparent1:1703">6.5.1</a> <a class="idx" href="modulecompat.html#idx:moduletransparent1:1752">6.15</a> <a class="idx" href="foreigninclude.html#idx:moduletransparent1:2043">11.4.9.2</a> <a class="idx" href="glossary.html#idx:moduletransparent1:2283">D</a></dd>
	1670	<a class="idx" href="examineprog.html#idx:moduletransparent1:929">4.16</a> <a class="idx" href="metapred.html#idx:moduletransparent1:1703">6.4</a> <a class="idx" href="overrule.html#idx:moduletransparent1:1707">6.5.1</a> <a class="idx" href="modulecompat.html#idx:moduletransparent1:1756">6.15</a> <a class="idx" href="foreigninclude.html#idx:moduletransparent1:2047">11.4.9.2</a> <a class="idx" href="glossary.html#idx:moduletransparent1:2287">D</a></dd>
1625	1671	<dt><a class="idx" href="builtinlist.html#msort/2">msort/2</a></dt>
1626	1672	<dd>
1627	1673	<a class="idx" href="builtinlist.html#idx:msort2:1351">4.29</a></dd>
1628	1674	<dt>multi</dt>
1629	1675	<dd>
1630		<a class="idx" href="glossary.html#idx:multi:2311">D</a></dd>
	1676	<a class="idx" href="glossary.html#idx:multi:2315">D</a></dd>
1631	1677	<dt><a class="idx" href="dynamic.html#multifile/1">multifile/1</a></dt>
1632	1678	<dd>
1633		<a class="idx" href="flags.html#idx:multifile1:149">2.11</a> <a class="idx" href="consulting.html#idx:multifile1:435">4.3</a> <a class="idx" href="consulting.html#idx:multifile1:446">4.3</a> <a class="idx" href="dynamic.html#idx:multifile1:876">4.15</a> <a class="idx" href="examineprog.html#idx:multifile1:922">4.16</a> <a class="idx" href="intlibs.html#idx:multifile1:2220">B.7</a> <a class="idx" href="glossary.html#idx:multifile1:2312">D</a></dd>
	1679	<a class="idx" href="flags.html#idx:multifile1:149">2.11</a> <a class="idx" href="consulting.html#idx:multifile1:435">4.3</a> <a class="idx" href="consulting.html#idx:multifile1:446">4.3</a> <a class="idx" href="dynamic.html#idx:multifile1:876">4.15</a> <a class="idx" href="examineprog.html#idx:multifile1:922">4.16</a> <a class="idx" href="intlibs.html#idx:multifile1:2224">B.7</a> <a class="idx" href="glossary.html#idx:multifile1:2316">D</a></dd>
1634	1680	<dt><a class="idx" href="error.html#must_be/2">must_be/2</a></dt>
1635	1681	<dd>
1636		<a class="idx" href="record.html#idx:mustbe2:2166">A.31</a></dd>
	1682	<a class="idx" href="record.html#idx:mustbe2:2170">A.31</a></dd>
1637	1683	<dt><a class="idx" href="threadsync.html#mutex_create/1">mutex_create/1</a></dt>
1638	1684	<dd>
1639		<a class="idx" href="threadsync.html#idx:mutexcreate1:1926">9.4</a> <a class="idx" href="threadsync.html#idx:mutexcreate1:1929">9.4</a></dd>
	1685	<a class="idx" href="threadsync.html#idx:mutexcreate1:1930">9.4</a> <a class="idx" href="threadsync.html#idx:mutexcreate1:1933">9.4</a></dd>
1640	1686	<dt><a class="idx" href="threadsync.html#mutex_create/2">mutex_create/2</a></dt>
1641	1687	<dd>
1642		<a class="idx" href="threadsync.html#idx:mutexcreate2:1936">9.4</a></dd>
	1688	<a class="idx" href="threadsync.html#idx:mutexcreate2:1940">9.4</a></dd>
1643	1689	<dt><a class="idx" href="threadsync.html#mutex_destroy/1">mutex_destroy/1</a></dt>
1644	1690	<dt><a class="idx" href="threadsync.html#mutex_lock/1">mutex_lock/1</a></dt>
1645	1691	<dd>
1646		<a class="idx" href="threadsync.html#idx:mutexlock1:1932">9.4</a></dd>
	1692	<a class="idx" href="threadsync.html#idx:mutexlock1:1936">9.4</a></dd>
1647	1693	<dt><a class="idx" href="threadsync.html#mutex_property/2">mutex_property/2</a></dt>
1648	1694	<dt><a class="idx" href="thmonitor.html#mutex_statistics/0">mutex_statistics/0</a></dt>
1649	1695	<dt><a class="idx" href="threadsync.html#mutex_trylock/1">mutex_trylock/1</a></dt>

1651	1697	<dt><a class="idx" href="threadsync.html#mutex_unlock_all/0">mutex_unlock_all/0</a></dt>
1652	1698	<dt>my_compare/3</dt>
1653	1699	<dd>
1654		<a class="idx" href="portabilitystrategies.html#idx:mycompare3:2262">C.1</a></dd>
	1700	<a class="idx" href="portabilitystrategies.html#idx:mycompare3:2266">C.1</a></dd>
1655	1701	<dt>mypred/1</dt>
1656	1702	<dd>
1657		<a class="idx" href="reexport.html#idx:mypred1:1713">6.7</a></dd>
	1703	<a class="idx" href="reexport.html#idx:mypred1:1717">6.7</a></dd>
1658	1704	<dt>name/1</dt>
1659	1705	<dd>
1660		<a class="idx" href="metapred.html#idx:name1:1685">6.4</a></dd>
	1706	<a class="idx" href="metapred.html#idx:name1:1689">6.4</a></dd>
1661	1707	<dt><a class="idx" href="manipatom.html#name/2">name/2</a></dt>
1662	1708	<dd>
1663	1709	<a class="idx" href="manipatom.html#idx:name2:1242">4.22</a> <a class="idx" href="manipatom.html#idx:name2:1245">4.22</a></dd>
1664	1710	<dt>name_of/2</dt>
1665	1711	<dd>
1666		<a class="idx" href="broadcast.html#idx:nameof2:2140">A.4</a></dd>
	1712	<a class="idx" href="broadcast.html#idx:nameof2:2144">A.4</a></dd>
1667	1713	<dt><a class="idx" href="gvar.html#nb_current/2">nb_current/2</a></dt>
1668	1714	<dd>
1669	1715	<a class="idx" href="gvar.html#idx:nbcurrent2:1426">4.33</a> <a class="idx" href="gvar.html#idx:nbcurrent2:1428">4.33</a></dd>

1674	1720	<dt><a class="idx" href="dicts.html#nb_link_dict/3">nb_link_dict/3</a></dt>
1675	1721	<dt><a class="idx" href="manipterm.html#nb_linkarg/3">nb_linkarg/3</a></dt>
1676	1722	<dd>
1677		<a class="idx" href="manipterm.html#idx:nblinkarg3:1228">4.21.1</a> <a class="idx" href="manipterm.html#idx:nblinkarg3:1238">4.21.1</a> <a class="idx" href="dicts.html#idx:nblinkarg3:1644">5.4.2.1</a></dd>
	1723	<a class="idx" href="manipterm.html#idx:nblinkarg3:1228">4.21.1</a> <a class="idx" href="manipterm.html#idx:nblinkarg3:1238">4.21.1</a> <a class="idx" href="dicts.html#idx:nblinkarg3:1648">5.4.2.1</a></dd>
1678	1724	<dt><a class="idx" href="gvar.html#nb_linkval/2">nb_linkval/2</a></dt>
1679	1725	<dd>
1680		<a class="idx" href="manipterm.html#idx:nblinkval2:1231">4.21.1</a> <a class="idx" href="manipterm.html#idx:nblinkval2:1232">4.21.1</a> <a class="idx" href="manipterm.html#idx:nblinkval2:1236">4.21.1</a> <a class="idx" href="gvar.html#idx:nblinkval2:1431">4.33.1</a> <a class="idx" href="dicts.html#idx:nblinkval2:1645">5.4.2.1</a> <a class="idx" href="dicts.html#idx:nblinkval2:1646">5.4.2.1</a></dd>
	1726	<a class="idx" href="manipterm.html#idx:nblinkval2:1231">4.21.1</a> <a class="idx" href="manipterm.html#idx:nblinkval2:1232">4.21.1</a> <a class="idx" href="manipterm.html#idx:nblinkval2:1236">4.21.1</a> <a class="idx" href="gvar.html#idx:nblinkval2:1431">4.33.1</a> <a class="idx" href="dicts.html#idx:nblinkval2:1649">5.4.2.1</a> <a class="idx" href="dicts.html#idx:nblinkval2:1650">5.4.2.1</a></dd>
1681	1727	<dt><a class="idx" href="dicts.html#nb_set_dict/3">nb_set_dict/3</a></dt>
1682	1728	<dt><a class="idx" href="nb_set.html#nb_set_to_list/2">nb_set_to_list/2</a></dt>
1683	1729	<dt><a class="idx" href="manipterm.html#nb_setarg/3">nb_setarg/3</a></dt>
1684	1730	<dd>
1685		<a class="idx" href="preddesc.html#idx:nbsetarg3:336">4.1</a> <a class="idx" href="db.html#idx:nbsetarg3:812">4.14</a> <a class="idx" href="manipterm.html#idx:nbsetarg3:1219">4.21.1</a> <a class="idx" href="manipterm.html#idx:nbsetarg3:1230">4.21.1</a> <a class="idx" href="manipterm.html#idx:nbsetarg3:1237">4.21.1</a> <a class="idx" href="allsolutions.html#idx:nbsetarg3:1367">4.30</a> <a class="idx" href="dicts.html#idx:nbsetarg3:1642">5.4.2.1</a> <a class="idx" href="nb_set.html#idx:nbsetarg3:2145">A.17</a> <a class="idx" href="record.html#idx:nbsetarg3:2168">A.31</a></dd>
	1731	<a class="idx" href="preddesc.html#idx:nbsetarg3:336">4.1</a> <a class="idx" href="db.html#idx:nbsetarg3:812">4.14</a> <a class="idx" href="manipterm.html#idx:nbsetarg3:1219">4.21.1</a> <a class="idx" href="manipterm.html#idx:nbsetarg3:1230">4.21.1</a> <a class="idx" href="manipterm.html#idx:nbsetarg3:1237">4.21.1</a> <a class="idx" href="allsolutions.html#idx:nbsetarg3:1367">4.30</a> <a class="idx" href="dicts.html#idx:nbsetarg3:1646">5.4.2.1</a> <a class="idx" href="nb_set.html#idx:nbsetarg3:2149">A.17</a> <a class="idx" href="record.html#idx:nbsetarg3:2172">A.31</a></dd>
1686	1732	<dt><a class="idx" href="gvar.html#nb_setval/2">nb_setval/2</a></dt>
1687	1733	<dd>
1688		<a class="idx" href="db.html#idx:nbsetval2:810">4.14</a> <a class="idx" href="manipterm.html#idx:nbsetval2:1226">4.21.1</a> <a class="idx" href="manipterm.html#idx:nbsetval2:1227">4.21.1</a> <a class="idx" href="manipterm.html#idx:nbsetval2:1235">4.21.1</a> <a class="idx" href="gvar.html#idx:nbsetval2:1413">4.33</a> <a class="idx" href="gvar.html#idx:nbsetval2:1416">4.33</a> <a class="idx" href="gvar.html#idx:nbsetval2:1427">4.33</a> <a class="idx" href="gvar.html#idx:nbsetval2:1430">4.33.1</a> <a class="idx" href="dicts.html#idx:nbsetval2:1643">5.4.2.1</a> <a class="idx" href="engine-examples.html#idx:nbsetval2:1974">10.1.2</a> <a class="idx" href="exception3.html#idx:nbsetval2:2217">B.6</a></dd>
	1734	<a class="idx" href="db.html#idx:nbsetval2:810">4.14</a> <a class="idx" href="manipterm.html#idx:nbsetval2:1226">4.21.1</a> <a class="idx" href="manipterm.html#idx:nbsetval2:1227">4.21.1</a> <a class="idx" href="manipterm.html#idx:nbsetval2:1235">4.21.1</a> <a class="idx" href="gvar.html#idx:nbsetval2:1413">4.33</a> <a class="idx" href="gvar.html#idx:nbsetval2:1416">4.33</a> <a class="idx" href="gvar.html#idx:nbsetval2:1427">4.33</a> <a class="idx" href="gvar.html#idx:nbsetval2:1430">4.33.1</a> <a class="idx" href="dicts.html#idx:nbsetval2:1647">5.4.2.1</a> <a class="idx" href="engine-examples.html#idx:nbsetval2:1978">10.1.2</a> <a class="idx" href="exception3.html#idx:nbsetval2:2221">B.6</a></dd>
1689	1735	<dt>neck</dt>
1690	1736	<dd>
1691		<a class="idx" href="glossary.html#idx:neck:2313">D</a></dd>
	1737	<a class="idx" href="glossary.html#idx:neck:2317">D</a></dd>
1692	1738	<dt><a class="idx" href="ugraphs.html#neighbors/3">neighbors/3</a></dt>
1693	1739	<dt><a class="idx" href="ugraphs.html#neighbours/3">neighbours/3</a></dt>
1694	1740	<dd>
1695		<a class="idx" href="ugraphs.html#idx:neighbours3:2176">A.37</a></dd>
	1741	<a class="idx" href="ugraphs.html#idx:neighbours3:2180">A.37</a></dd>
1696	1742	<dt><a class="idx" href="lists.html#nextto/3">nextto/3</a></dt>
1697	1743	<dt><a class="idx" href="chario.html#nl/0">nl/0</a></dt>
1698	1744	<dd>

1703	1749	<a class="idx" href="format.html#idx:nl01:1390">4.32.1</a></dd>
1704	1750	<dt><a class="idx" href="debugger.html#nodebug/0">nodebug/0</a></dt>
1705	1751	<dd>
1706		<a class="idx" href="debugger.html#idx:nodebug0:1554">4.39</a> <a class="idx" href="tracehook.html#idx:nodebug0:2195">B.3</a></dd>
	1752	<a class="idx" href="debugger.html#idx:nodebug0:1554">4.39</a> <a class="idx" href="tracehook.html#idx:nodebug0:2199">B.3</a></dd>
1707	1753	<dt><a class="idx" href="debug.html#nodebug/1">nodebug/1</a></dt>
1708	1754	<dt><a class="idx" href="guitracer.html#noguitracer/0">noguitracer/0</a></dt>
1709	1755	<dd>
1710	1756	<a class="idx" href="guitracer.html#idx:noguitracer0:316">3.5.1</a> <a class="idx" href="idesummary.html#idx:noguitracer0:331">3.9</a></dd>
1711	1757	<dt>non deterministic</dt>
1712	1758	<dd>
1713		<a class="idx" href="glossary.html#idx:nondeterministic:2315">D</a></dd>
	1759	<a class="idx" href="glossary.html#idx:nondeterministic:2319">D</a></dd>
1714	1760	<dt>nondet</dt>
1715	1761	<dd>
1716		<a class="idx" href="glossary.html#idx:nondet:2314">D</a></dd>
	1762	<a class="idx" href="glossary.html#idx:nondet:2318">D</a></dd>
1717	1763	<dt><a class="idx" href="manipterm.html#nonground/2">nonground/2</a></dt>
1718	1764	<dd>
1719	1765	<a class="idx" href="typetest.html#idx:nonground2:618">4.6</a> <a class="idx" href="manipterm.html#idx:nonground2:1209">4.21</a></dd>

1723	1769	<dt><a class="idx" href="chartype.html#normalize_space/2">normalize_space/2</a></dt>
1724	1770	<dt><a class="idx" href="debugger.html#nospy/1">nospy/1</a></dt>
1725	1771	<dd>
1726		<a class="idx" href="debugoverview.html#idx:nospy1:62">2.9</a> <a class="idx" href="hooks.html#idx:nospy1:183">2.12</a> <a class="idx" href="thutil.html#idx:nospy1:1949">9.5.1</a> <a class="idx" href="intlibs.html#idx:nospy1:2223">B.7</a> <a class="idx" href="intlibs.html#idx:nospy1:2224">B.7</a> <a class="idx" href="intlibs.html#idx:nospy1:2226">B.7</a></dd>
	1772	<a class="idx" href="debugoverview.html#idx:nospy1:62">2.9</a> <a class="idx" href="hooks.html#idx:nospy1:183">2.12</a> <a class="idx" href="thutil.html#idx:nospy1:1953">9.5.1</a> <a class="idx" href="intlibs.html#idx:nospy1:2227">B.7</a> <a class="idx" href="intlibs.html#idx:nospy1:2228">B.7</a> <a class="idx" href="intlibs.html#idx:nospy1:2230">B.7</a></dd>
1727	1773	<dt><a class="idx" href="debugger.html#nospyall/0">nospyall/0</a></dt>
1728	1774	<dd>
1729		<a class="idx" href="hooks.html#idx:nospyall0:184">2.12</a> <a class="idx" href="intlibs.html#idx:nospyall0:2227">B.7</a></dd>
	1775	<a class="idx" href="hooks.html#idx:nospyall0:184">2.12</a> <a class="idx" href="intlibs.html#idx:nospyall0:2231">B.7</a></dd>
1730	1776	<dt><a class="idx" href="metacall.html#not/1">not/1</a></dt>
1731	1777	<dd>
1732		<a class="idx" href="predsummary.html#idx:not1:2346">F.1</a></dd>
	1778	<a class="idx" href="predsummary.html#idx:not1:2350">F.1</a></dd>
1733	1779	<dt><a class="idx" href="debugger.html#notrace/0">notrace/0</a></dt>
1734	1780	<dd>
1735		<a class="idx" href="debugger.html#idx:notrace0:1545">4.39</a> <a class="idx" href="debugging.html#idx:notrace0:1819">8.4.3</a> <a class="idx" href="debugging.html#idx:notrace0:1821">8.4.3</a></dd>
	1781	<a class="idx" href="debugger.html#idx:notrace0:1545">4.39</a> <a class="idx" href="debugging.html#idx:notrace0:1823">8.4.3</a> <a class="idx" href="debugging.html#idx:notrace0:1825">8.4.3</a></dd>
1736	1782	<dt><a class="idx" href="debugger.html#notrace/1">notrace/1</a></dt>
1737	1783	<dt><a class="idx" href="lists.html#nth0/3">nth0/3</a></dt>
1738	1784	<dt><a class="idx" href="lists.html#nth0/4">nth0/4</a></dt>

1740	1786	<dt><a class="idx" href="lists.html#nth1/4">nth1/4</a></dt>
1741	1787	<dt><a class="idx" href="examineprog.html#nth_clause/3">nth_clause/3</a></dt>
1742	1788	<dd>
1743		<a class="idx" href="examineprog.html#idx:nthclause3:917">4.16</a> <a class="idx" href="examineprog.html#idx:nthclause3:941">4.16</a> <a class="idx" href="manipstack.html#idx:nthclause3:2180">B.1</a></dd>
	1789	<a class="idx" href="examineprog.html#idx:nthclause3:917">4.16</a> <a class="idx" href="examineprog.html#idx:nthclause3:941">4.16</a> <a class="idx" href="manipstack.html#idx:nthclause3:2184">B.1</a></dd>
1744	1790	<dt><a class="idx" href="arith.html#nth_integer_root_and_remainder/4">nth_integer_root_and_remainder/4</a></dt>
1745	1791	<dt>number,rational</dt>
1746	1792	<dd>

1775	1821	<a class="idx" href="signal.html#idx:onsignal3:773">4.12</a> <a class="idx" href="signal.html#idx:onsignal3:775">4.12</a></dd>
1776	1822	<dt><a class="idx" href="metacall.html#once/1">once/1</a></dt>
1777	1823	<dd>
1778		<a class="idx" href="control.html#idx:once1:647">4.8</a> <a class="idx" href="metacall.html#idx:once1:653">4.9</a> <a class="idx" href="metacall.html#idx:once1:654">4.9</a> <a class="idx" href="metacall.html#idx:once1:655">4.9</a> <a class="idx" href="metacall.html#idx:once1:668">4.9</a> <a class="idx" href="IO.html#idx:once1:1050">4.17.5</a> <a class="idx" href="allsolutions.html#idx:once1:1368">4.30</a> <a class="idx" href="toplevel.html#idx:once1:1528">4.37</a> <a class="idx" href="debugger.html#idx:once1:1552">4.39</a> <a class="idx" href="profile.html#idx:once1:1566">4.41.1</a> <a class="idx" href="profile.html#idx:once1:1567">4.41.1</a> <a class="idx" href="threadsync.html#idx:once1:1922">9.4</a> <a class="idx" href="threadsync.html#idx:once1:1925">9.4</a> <a class="idx" href="threadsync.html#idx:once1:1928">9.4</a> <a class="idx" href="foreigninclude.html#idx:once1:2046">11.4.9.2</a></dd>
	1824	<a class="idx" href="control.html#idx:once1:647">4.8</a> <a class="idx" href="metacall.html#idx:once1:653">4.9</a> <a class="idx" href="metacall.html#idx:once1:654">4.9</a> <a class="idx" href="metacall.html#idx:once1:655">4.9</a> <a class="idx" href="metacall.html#idx:once1:668">4.9</a> <a class="idx" href="IO.html#idx:once1:1050">4.17.5</a> <a class="idx" href="allsolutions.html#idx:once1:1368">4.30</a> <a class="idx" href="toplevel.html#idx:once1:1528">4.37</a> <a class="idx" href="debugger.html#idx:once1:1552">4.39</a> <a class="idx" href="profile.html#idx:once1:1566">4.41.1</a> <a class="idx" href="profile.html#idx:once1:1567">4.41.1</a> <a class="idx" href="threadsync.html#idx:once1:1926">9.4</a> <a class="idx" href="threadsync.html#idx:once1:1929">9.4</a> <a class="idx" href="threadsync.html#idx:once1:1932">9.4</a> <a class="idx" href="foreigninclude.html#idx:once1:2050">11.4.9.2</a></dd>
1779	1825	<dt><a class="idx" href="operators.html#op/3">op/3</a></dt>
1780	1826	<dd>
1781		<a class="idx" href="dynamic.html#idx:op3:879">4.15</a> <a class="idx" href="termrw.html#idx:op3:1125">4.20</a> <a class="idx" href="operators.html#idx:op3:1317">4.25</a> <a class="idx" href="moduleop.html#idx:op3:1716">6.8</a></dd>
	1827	<a class="idx" href="dynamic.html#idx:op3:879">4.15</a> <a class="idx" href="termrw.html#idx:op3:1125">4.20</a> <a class="idx" href="operators.html#idx:op3:1317">4.25</a> <a class="idx" href="moduleop.html#idx:op3:1720">6.8</a></dd>
1782	1828	<dt><a class="idx" href="IO.html#open/3">open/3</a></dt>
1783	1829	<dd>
1784		<a class="idx" href="flags.html#idx:open3:109">2.11</a> <a class="idx" href="preddesc.html#idx:open3:334">4.1</a> <a class="idx" href="IO.html#idx:open3:947">4.17</a> <a class="idx" href="IO.html#idx:open3:966">4.17.2</a> <a class="idx" href="foreigninclude.html#idx:open3:2029">11.4.6</a></dd>
	1830	<a class="idx" href="flags.html#idx:open3:109">2.11</a> <a class="idx" href="preddesc.html#idx:open3:334">4.1</a> <a class="idx" href="IO.html#idx:open3:947">4.17</a> <a class="idx" href="IO.html#idx:open3:966">4.17.2</a> <a class="idx" href="foreigninclude.html#idx:open3:2033">11.4.6</a></dd>
1785	1831	<dt><a class="idx" href="IO.html#open/4">open/4</a></dt>
1786	1832	<dd>
1787		<a class="idx" href="widechars.html#idx:open4:269">2.19.1</a> <a class="idx" href="widechars.html#idx:open4:275">2.19.1.1</a> <a class="idx" href="widechars.html#idx:open4:277">2.19.1.1</a> <a class="idx" href="chars.html#idx:open4:340">4.2</a> <a class="idx" href="IO.html#idx:open4:972">4.17.2</a> <a class="idx" href="IO.html#idx:open4:980">4.17.2</a> <a class="idx" href="IO.html#idx:open4:983">4.17.2</a> <a class="idx" href="IO.html#idx:open4:986">4.17.2</a> <a class="idx" href="IO.html#idx:open4:987">4.17.2</a> <a class="idx" href="IO.html#idx:open4:1004">4.17.2</a> <a class="idx" href="IO.html#idx:open4:1015">4.17.2</a> <a class="idx" href="IO.html#idx:open4:1025">4.17.2</a> <a class="idx" href="chario.html#idx:open4:1103">4.19</a> <a class="idx" href="locale.html#idx:open4:1290">4.23</a> <a class="idx" href="files.html#idx:open4:1493">4.36</a> <a class="idx" href="dicts.html#idx:open4:1648">5.4.3</a> <a class="idx" href="dicts.html#idx:open4:1654">5.4.4</a> <a class="idx" href="readutil.html#idx:open4:2160">A.30</a> <a class="idx" href="readutil.html#idx:open4:2164">A.30</a></dd>
	1833	<a class="idx" href="widechars.html#idx:open4:269">2.19.1</a> <a class="idx" href="widechars.html#idx:open4:275">2.19.1.1</a> <a class="idx" href="widechars.html#idx:open4:277">2.19.1.1</a> <a class="idx" href="chars.html#idx:open4:340">4.2</a> <a class="idx" href="IO.html#idx:open4:972">4.17.2</a> <a class="idx" href="IO.html#idx:open4:980">4.17.2</a> <a class="idx" href="IO.html#idx:open4:983">4.17.2</a> <a class="idx" href="IO.html#idx:open4:986">4.17.2</a> <a class="idx" href="IO.html#idx:open4:987">4.17.2</a> <a class="idx" href="IO.html#idx:open4:1004">4.17.2</a> <a class="idx" href="IO.html#idx:open4:1015">4.17.2</a> <a class="idx" href="IO.html#idx:open4:1025">4.17.2</a> <a class="idx" href="chario.html#idx:open4:1103">4.19</a> <a class="idx" href="locale.html#idx:open4:1290">4.23</a> <a class="idx" href="files.html#idx:open4:1493">4.36</a> <a class="idx" href="dicts.html#idx:open4:1652">5.4.3</a> <a class="idx" href="dicts.html#idx:open4:1658">5.4.4</a> <a class="idx" href="readutil.html#idx:open4:2164">A.30</a> <a class="idx" href="readutil.html#idx:open4:2168">A.30</a></dd>
1788	1834	<dt><a class="idx" href="iostream.html#open_any/5">open_any/5</a></dt>
1789	1835	<dt><a class="idx" href="charsio.html#open_chars_stream/2">open_chars_stream/2</a></dt>
1790	1836	<dt><a class="idx" href="DDE.html#open_dde_conversation/3">open_dde_conversation/3</a></dt>

1794	1840	<a class="idx" href="IO.html#idx:opennullstream1:1009">4.17.2</a></dd>
1795	1841	<dt><a class="idx" href="useresource.html#open_resource/3">open_resource/3</a></dt>
1796	1842	<dd>
1797		<a class="idx" href="foreigninclude.html#idx:openresource3:2078">11.4.21</a> <a class="idx" href="foreigninclude.html#idx:openresource3:2079">11.4.21</a> <a class="idx" href="foreigninclude.html#idx:openresource3:2080">11.4.21</a> <a class="idx" href="runtime.html#idx:openresource3:2097">12</a> <a class="idx" href="useresource.html#idx:openresource3:2121">12.3</a> <a class="idx" href="useresource.html#idx:openresource3:2126">12.3.1</a></dd>
	1843	<a class="idx" href="foreigninclude.html#idx:openresource3:2082">11.4.21</a> <a class="idx" href="foreigninclude.html#idx:openresource3:2083">11.4.21</a> <a class="idx" href="foreigninclude.html#idx:openresource3:2084">11.4.21</a> <a class="idx" href="runtime.html#idx:openresource3:2101">12</a> <a class="idx" href="useresource.html#idx:openresource3:2125">12.3</a> <a class="idx" href="useresource.html#idx:openresource3:2130">12.3.1</a></dd>
1798	1844	<dt><a class="idx" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a></dt>
1799	1845	<dd>
1800		<a class="idx" href="flags.html#idx:opensharedobject2:120">2.11</a> <a class="idx" href="system.html#idx:opensharedobject2:1476">4.35.1</a> <a class="idx" href="foreignlink.html#idx:opensharedobject2:2009">11.2.1</a> <a class="idx" href="foreignlink.html#idx:opensharedobject2:2014">11.2.4</a></dd>
	1846	<a class="idx" href="flags.html#idx:opensharedobject2:120">2.11</a> <a class="idx" href="system.html#idx:opensharedobject2:1476">4.35.1</a> <a class="idx" href="foreignlink.html#idx:opensharedobject2:2013">11.2.1</a> <a class="idx" href="foreignlink.html#idx:opensharedobject2:2018">11.2.4</a></dd>
1801	1847	<dt><a class="idx" href="foreignlink.html#open_shared_object/3">open_shared_object/3</a></dt>
1802	1848	<dd>
1803		<a class="idx" href="foreignlink.html#idx:opensharedobject3:2012">11.2.4</a></dd>
	1849	<a class="idx" href="foreignlink.html#idx:opensharedobject3:2016">11.2.4</a></dd>
1804	1850	<dt><a class="idx" href="strings.html#open_string/2">open_string/2</a></dt>
1805	1851	<dt>operand</dt>
1806	1852	<dd>
1807		<a class="idx" href="glossary.html#idx:operand:2317">D</a></dd>
	1853	<a class="idx" href="glossary.html#idx:operand:2321">D</a></dd>
1808	1854	<dt>operator</dt>
1809	1855	<dd>
1810		<a class="idx" href="glossary.html#idx:operator:2316">D</a></dd>
	1856	<a class="idx" href="glossary.html#idx:operator:2320">D</a></dd>
1811	1857	<dt>operator,and modules</dt>
1812	1858	<dd>
1813	1859	<a class="idx" href="operators.html#idx:operatorandmodules:1314">4.25</a></dd>

1866	1912	<dt><a class="idx" href="apply.html#partition/5">partition/5</a></dt>
1867	1913	<dt><a class="idx" href="mt-xpce.html#pce_dispatch/1">pce_dispatch/1</a></dt>
1868	1914	<dd>
1869		<a class="idx" href="mt-xpce.html#idx:pcedispatch1:1955">9.7</a></dd>
	1915	<a class="idx" href="mt-xpce.html#idx:pcedispatch1:1959">9.7</a></dd>
1870	1916	<dt>pce_thread/1</dt>
1871	1917	<dd>
1872		<a class="idx" href="mt-xpce.html#idx:pcethread1:1960">9.7</a></dd>
	1918	<a class="idx" href="mt-xpce.html#idx:pcethread1:1964">9.7</a></dd>
1873	1919	<dt><a class="idx" href="chario.html#peek_byte/1">peek_byte/1</a></dt>
1874	1920	<dt><a class="idx" href="chario.html#peek_byte/2">peek_byte/2</a></dt>
1875	1921	<dt>peek_byte/[1,2]</dt>

1888	1934	<dt><a class="idx" href="chario.html#peek_string/3">peek_string/3</a></dt>
1889	1935	<dt><a class="idx" href="error.html#permission_error/3">permission_error/3</a></dt>
1890	1936	<dd>
1891		<a class="idx" href="foreigninclude.html#idx:permissionerror3:2034">11.4.6</a></dd>
	1937	<a class="idx" href="foreigninclude.html#idx:permissionerror3:2038">11.4.6</a></dd>
1892	1938	<dt><a class="idx" href="lists.html#permutation/2">permutation/2</a></dt>
1893	1939	<dt><a class="idx" href="persistency.html#persistent/1">persistent/1</a></dt>
1894	1940	<dt><a class="idx" href="DCG.html#phrase/2">phrase/2</a></dt>

1896	1942	<a class="idx" href="DCG.html#idx:phrase2:781">4.13</a></dd>
1897	1943	<dt><a class="idx" href="DCG.html#phrase/3">phrase/3</a></dt>
1898	1944	<dd>
1899		<a class="idx" href="DCG.html#idx:phrase3:782">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:784">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:786">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:788">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:789">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:790">4.13</a> <a class="idx" href="strings.html#idx:phrase3:1609">5.2.2</a> <a class="idx" href="metapred.html#idx:phrase3:1697">6.4</a> <a class="idx" href="predsummary.html#idx:phrase3:2350">F.1</a></dd>
	1945	<a class="idx" href="DCG.html#idx:phrase3:782">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:784">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:786">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:788">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:789">4.13</a> <a class="idx" href="DCG.html#idx:phrase3:790">4.13</a> <a class="idx" href="strings.html#idx:phrase3:1609">5.2.2</a> <a class="idx" href="metapred.html#idx:phrase3:1701">6.4</a> <a class="idx" href="predsummary.html#idx:phrase3:2354">F.1</a></dd>
1900	1946	<dt><a class="idx" href="pio.html#phrase_from_file/2">phrase_from_file/2</a></dt>
1901	1947	<dt><a class="idx" href="pio.html#phrase_from_file/3">phrase_from_file/3</a></dt>
1902	1948	<dt><a class="idx" href="quasiquotations.html#phrase_from_quasi_quotation/2">phrase_from_quasi_quotation/2</a></dt>

1907	1953	<a class="idx" href="streamstat.html#idx:poll:1069">4.18</a></dd>
1908	1954	<dt>portable,prolog code</dt>
1909	1955	<dd>
1910		<a class="idx" href="dialect.html#idx:portableprologcode:2244">C</a></dd>
	1956	<a class="idx" href="dialect.html#idx:portableprologcode:2248">C</a></dd>
1911	1957	<dt><a class="idx" href="termrw.html#portray/1">portray/1</a></dt>
1912	1958	<dd>
1913		<a class="idx" href="debugoverview.html#idx:portray1:69">2.9</a> <a class="idx" href="projectfiles.html#idx:portray1:303">3.1.2</a> <a class="idx" href="termrw.html#idx:portray1:1121">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1128">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1130">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1131">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1150">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1151">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1154">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1155">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1156">4.20</a> <a class="idx" href="foreigninclude.html#idx:portray1:2045">11.4.9.2</a> <a class="idx" href="foreigninclude.html#idx:portray1:2074">11.4.20</a> <a class="idx" href="intlibs.html#idx:portray1:2219">B.7</a></dd>
	1959	<a class="idx" href="debugoverview.html#idx:portray1:69">2.9</a> <a class="idx" href="projectfiles.html#idx:portray1:303">3.1.2</a> <a class="idx" href="termrw.html#idx:portray1:1121">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1128">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1130">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1131">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1150">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1151">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1154">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1155">4.20</a> <a class="idx" href="termrw.html#idx:portray1:1156">4.20</a> <a class="idx" href="foreigninclude.html#idx:portray1:2049">11.4.9.2</a> <a class="idx" href="foreigninclude.html#idx:portray1:2078">11.4.20</a> <a class="idx" href="intlibs.html#idx:portray1:2223">B.7</a></dd>
1914	1960	<dt><a class="idx" href="listing.html#portray_clause/1">portray_clause/1</a></dt>
1915	1961	<dd>
1916	1962	<a class="idx" href="listing.html#idx:portrayclause1:596">4.5</a> <a class="idx" href="listing.html#idx:portrayclause1:597">4.5</a> <a class="idx" href="listing.html#idx:portrayclause1:600">4.5</a></dd>

1922	1968	<a class="idx" href="DCG.html#idx:portraytext1:787">4.13</a> <a class="idx" href="strings.html#idx:portraytext1:1621">5.2.4</a></dd>
1923	1969	<dt>precedence</dt>
1924	1970	<dd>
1925		<a class="idx" href="glossary.html#idx:precedence:2318">D</a></dd>
	1971	<a class="idx" href="glossary.html#idx:precedence:2322">D</a></dd>
1926	1972	<dt>pred/1</dt>
1927	1973	<dd>
1928		<a class="idx" href="reexport.html#idx:pred1:1710">6.7</a> <a class="idx" href="reexport.html#idx:pred1:1712">6.7</a></dd>
	1974	<a class="idx" href="reexport.html#idx:pred1:1714">6.7</a> <a class="idx" href="reexport.html#idx:pred1:1716">6.7</a></dd>
1929	1975	<dt>predicate</dt>
1930	1976	<dd>
1931		<a class="idx" href="glossary.html#idx:predicate:2319">D</a></dd>
	1977	<a class="idx" href="glossary.html#idx:predicate:2323">D</a></dd>
1932	1978	<dt>predicate indicator</dt>
1933	1979	<dd>
1934		<a class="idx" href="preddesc.html#idx:predicateindicator:337">4.1</a> <a class="idx" href="glossary.html#idx:predicateindicator:2320">D</a></dd>
	1980	<a class="idx" href="preddesc.html#idx:predicateindicator:337">4.1</a> <a class="idx" href="glossary.html#idx:predicateindicator:2324">D</a></dd>
1935	1981	<dt>predicate,dynamic</dt>
1936	1982	<dd>
1937		<a class="idx" href="glossary.html#idx:predicatedynamic:2289">D</a></dd>
	1983	<a class="idx" href="glossary.html#idx:predicatedynamic:2293">D</a></dd>
1938	1984	<dt>predicate,exported</dt>
1939	1985	<dd>
1940		<a class="idx" href="glossary.html#idx:predicateexported:2291">D</a></dd>
	1986	<a class="idx" href="glossary.html#idx:predicateexported:2295">D</a></dd>
1941	1987	<dt>predicate,imported</dt>
1942	1988	<dd>
1943		<a class="idx" href="glossary.html#idx:predicateimported:2300">D</a></dd>
	1989	<a class="idx" href="glossary.html#idx:predicateimported:2304">D</a></dd>
1944	1990	<dt><a class="idx" href="predicate_options.html#predicate_options/3">predicate_options/3</a></dt>
1945	1991	<dt><a class="idx" href="examineprog.html#predicate_property/2">predicate_property/2</a></dt>
1946	1992	<dd>
1947		<a class="idx" href="consulting.html#idx:predicateproperty2:410">4.3</a> <a class="idx" href="consulting.html#idx:predicateproperty2:449">4.3</a> <a class="idx" href="consulting.html#idx:predicateproperty2:548">4.3.1</a> <a class="idx" href="metacall.html#idx:predicateproperty2:652">4.9</a> <a class="idx" href="dynamic.html#idx:predicateproperty2:891">4.15</a> <a class="idx" href="examineprog.html#idx:predicateproperty2:901">4.16</a> <a class="idx" href="examineprog.html#idx:predicateproperty2:904">4.16</a> <a class="idx" href="examineprog.html#idx:predicateproperty2:908">4.16</a> <a class="idx" href="examineprog.html#idx:predicateproperty2:910">4.16</a> <a class="idx" href="metapred.html#idx:predicateproperty2:1692">6.4</a> <a class="idx" href="manipmodule.html#idx:predicateproperty2:1746">6.14</a> <a class="idx" href="manipmodule.html#idx:predicateproperty2:1748">6.14</a></dd>
	1993	<a class="idx" href="consulting.html#idx:predicateproperty2:410">4.3</a> <a class="idx" href="consulting.html#idx:predicateproperty2:449">4.3</a> <a class="idx" href="consulting.html#idx:predicateproperty2:548">4.3.1</a> <a class="idx" href="metacall.html#idx:predicateproperty2:652">4.9</a> <a class="idx" href="dynamic.html#idx:predicateproperty2:891">4.15</a> <a class="idx" href="examineprog.html#idx:predicateproperty2:901">4.16</a> <a class="idx" href="examineprog.html#idx:predicateproperty2:904">4.16</a> <a class="idx" href="examineprog.html#idx:predicateproperty2:908">4.16</a> <a class="idx" href="examineprog.html#idx:predicateproperty2:910">4.16</a> <a class="idx" href="metapred.html#idx:predicateproperty2:1696">6.4</a> <a class="idx" href="manipmodule.html#idx:predicateproperty2:1750">6.14</a> <a class="idx" href="manipmodule.html#idx:predicateproperty2:1752">6.14</a></dd>
1948	1994	<dt><a class="idx" href="builtinlist.html#predsort/3">predsort/3</a></dt>
1949	1995	<dd>
1950	1996	<a class="idx" href="builtinlist.html#idx:predsort3:1353">4.29</a></dd>
1951	1997	<dt><a class="idx" href="lists.html#prefix/2">prefix/2</a></dt>
1952	1998	<dt><a class="idx" href="termrw.html#print/1">print/1</a></dt>
1953	1999	<dd>
1954		<a class="idx" href="flags.html#idx:print1:125">2.11</a> <a class="idx" href="termrw.html#idx:print1:1132">4.20</a> <a class="idx" href="termrw.html#idx:print1:1145">4.20</a> <a class="idx" href="termrw.html#idx:print1:1146">4.20</a> <a class="idx" href="termrw.html#idx:print1:1152">4.20</a> <a class="idx" href="termrw.html#idx:print1:1153">4.20</a> <a class="idx" href="termrw.html#idx:print1:1157">4.20</a> <a class="idx" href="format.html#idx:print1:1391">4.32.1</a> <a class="idx" href="format.html#idx:print1:1396">4.32.1</a> <a class="idx" href="format.html#idx:print1:1401">4.32.2</a> <a class="idx" href="foreigninclude.html#idx:print1:2044">11.4.9.2</a> <a class="idx" href="predsummary.html#idx:print1:2361">F.1</a></dd>
	2000	<a class="idx" href="flags.html#idx:print1:125">2.11</a> <a class="idx" href="termrw.html#idx:print1:1132">4.20</a> <a class="idx" href="termrw.html#idx:print1:1145">4.20</a> <a class="idx" href="termrw.html#idx:print1:1146">4.20</a> <a class="idx" href="termrw.html#idx:print1:1152">4.20</a> <a class="idx" href="termrw.html#idx:print1:1153">4.20</a> <a class="idx" href="termrw.html#idx:print1:1157">4.20</a> <a class="idx" href="format.html#idx:print1:1391">4.32.1</a> <a class="idx" href="format.html#idx:print1:1396">4.32.1</a> <a class="idx" href="format.html#idx:print1:1401">4.32.2</a> <a class="idx" href="foreigninclude.html#idx:print1:2048">11.4.9.2</a> <a class="idx" href="predsummary.html#idx:print1:2365">F.1</a></dd>
1955	2001	<dt><a class="idx" href="termrw.html#print/2">print/2</a></dt>
1956	2002	<dd>
1957	2003	<a class="idx" href="flags.html#idx:print2:126">2.11</a></dd>
1958	2004	<dt><a class="idx" href="exception.html#print_message/2">print_message/2</a></dt>
1959	2005	<dd>
1960		<a class="idx" href="flags.html#idx:printmessage2:95">2.11</a> <a class="idx" href="flags.html#idx:printmessage2:153">2.11</a> <a class="idx" href="hooks.html#idx:printmessage2:169">2.12</a> <a class="idx" href="hooks.html#idx:printmessage2:170">2.12</a> <a class="idx" href="consulting.html#idx:printmessage2:398">4.3</a> <a class="idx" href="consulting.html#idx:printmessage2:497">4.3</a> <a class="idx" href="exception.html#idx:printmessage2:715">4.11.1</a> <a class="idx" href="exception.html#idx:printmessage2:730">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:731">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:733">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:740">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:744">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:746">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:751">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:753">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:754">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:766">4.11.4.1</a> <a class="idx" href="exception.html#idx:printmessage2:767">4.11.4.1</a> <a class="idx" href="termrw.html#idx:printmessage2:1148">4.20</a> <a class="idx" href="termrw.html#idx:printmessage2:1175">4.20</a> <a class="idx" href="termrw.html#idx:printmessage2:1176">4.20</a> <a class="idx" href="memory.html#idx:printmessage2:1580">4.42</a> <a class="idx" href="threadcreate.html#idx:printmessage2:1842">9.1</a> <a class="idx" href="threadcreate.html#idx:printmessage2:1854">9.1</a> <a class="idx" href="predsummary.html#idx:printmessage2:2359">F.1</a></dd>
	2006	<a class="idx" href="flags.html#idx:printmessage2:95">2.11</a> <a class="idx" href="flags.html#idx:printmessage2:153">2.11</a> <a class="idx" href="hooks.html#idx:printmessage2:169">2.12</a> <a class="idx" href="hooks.html#idx:printmessage2:170">2.12</a> <a class="idx" href="consulting.html#idx:printmessage2:398">4.3</a> <a class="idx" href="consulting.html#idx:printmessage2:497">4.3</a> <a class="idx" href="exception.html#idx:printmessage2:715">4.11.1</a> <a class="idx" href="exception.html#idx:printmessage2:730">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:731">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:733">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:740">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:744">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:746">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:751">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:753">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:754">4.11.4</a> <a class="idx" href="exception.html#idx:printmessage2:766">4.11.4.1</a> <a class="idx" href="exception.html#idx:printmessage2:767">4.11.4.1</a> <a class="idx" href="termrw.html#idx:printmessage2:1148">4.20</a> <a class="idx" href="termrw.html#idx:printmessage2:1175">4.20</a> <a class="idx" href="termrw.html#idx:printmessage2:1176">4.20</a> <a class="idx" href="memory.html#idx:printmessage2:1580">4.42</a> <a class="idx" href="threadcreate.html#idx:printmessage2:1846">9.1</a> <a class="idx" href="threadcreate.html#idx:printmessage2:1858">9.1</a> <a class="idx" href="predsummary.html#idx:printmessage2:2363">F.1</a></dd>
1961	2007	<dt><a class="idx" href="exception.html#print_message_lines/3">print_message_lines/3</a></dt>
1962	2008	<dd>
1963		<a class="idx" href="exception.html#idx:printmessagelines3:741">4.11.4</a> <a class="idx" href="exception.html#idx:printmessagelines3:755">4.11.4</a> <a class="idx" href="exception.html#idx:printmessagelines3:762">4.11.4</a> <a class="idx" href="exception.html#idx:printmessagelines3:771">4.11.4.1</a> <a class="idx" href="predsummary.html#idx:printmessagelines3:2360">F.1</a></dd>
	2009	<a class="idx" href="exception.html#idx:printmessagelines3:741">4.11.4</a> <a class="idx" href="exception.html#idx:printmessagelines3:755">4.11.4</a> <a class="idx" href="exception.html#idx:printmessagelines3:762">4.11.4</a> <a class="idx" href="exception.html#idx:printmessagelines3:771">4.11.4.1</a> <a class="idx" href="predsummary.html#idx:printmessagelines3:2364">F.1</a></dd>
1964	2010	<dt>priority</dt>
1965	2011	<dd>
1966		<a class="idx" href="glossary.html#idx:priority:2321">D</a></dd>
	2012	<a class="idx" href="glossary.html#idx:priority:2325">D</a></dd>
1967	2013	<dt>process_create/3</dt>
1968	2014	<dd>
1969	2015	<a class="idx" href="IO.html#idx:processcreate3:971">4.17.2</a> <a class="idx" href="system.html#idx:processcreate3:1448">4.35</a> <a class="idx" href="system.html#idx:processcreate3:1468">4.35.1</a></dd>

1972	2018	<a class="idx" href="initfile.html#idx:profilefile:20">2.2</a></dd>
1973	2019	<dt><a class="idx" href="profile.html#profile/1">profile/1</a></dt>
1974	2020	<dd>
1975		<a class="idx" href="thutil.html#idx:profile1:1951">9.5.2</a> <a class="idx" href="foreigninclude.html#idx:profile1:2085">11.4.21</a></dd>
	2021	<a class="idx" href="thutil.html#idx:profile1:1955">9.5.2</a> <a class="idx" href="foreigninclude.html#idx:profile1:2089">11.4.21</a></dd>
1976	2022	<dt><a class="idx" href="profile.html#profile/3">profile/3</a></dt>
1977	2023	<dt><a class="idx" href="profile.html#profiler/2">profiler/2</a></dt>
1978	2024	<dt>profiling,foreign code</dt>
1979	2025	<dd>
1980		<a class="idx" href="foreignnotes.html#idx:profilingforeigncode:2095">11.8.4</a></dd>
	2026	<a class="idx" href="foreignnotes.html#idx:profilingforeigncode:2099">11.8.4</a></dd>
1981	2027	<dt>program</dt>
1982	2028	<dd>
1983		<a class="idx" href="glossary.html#idx:program:2322">D</a></dd>
	2029	<a class="idx" href="glossary.html#idx:program:2326">D</a></dd>
1984	2030	<dt><a class="idx" href="attvar.html#project_attributes/2">project_attributes/2</a></dt>
1985	2031	<dd>
1986		<a class="idx" href="attvar.html#idx:projectattributes2:1782">7.1.2</a></dd>
	2032	<a class="idx" href="attvar.html#idx:projectattributes2:1786">7.1.2</a></dd>
1987	2033	<dt><a class="idx" href="toplevel.html#prolog/0">prolog/0</a></dt>
1988	2034	<dd>
1989		<a class="idx" href="cmdline.html#idx:prolog0:43">2.4.4</a> <a class="idx" href="IO.html#idx:prolog0:1030">4.17.2</a> <a class="idx" href="toplevel.html#idx:prolog0:1525">4.37</a> <a class="idx" href="toplevel.html#idx:prolog0:1533">4.37</a> <a class="idx" href="toplevel.html#idx:prolog0:1535">4.37</a> <a class="idx" href="mtoplevel.html#idx:prolog0:1708">6.6</a> <a class="idx" href="foreigninclude.html#idx:prolog0:2082">11.4.21</a> <a class="idx" href="manipstack.html#idx:prolog0:2185">B.1</a></dd>
	2035	<a class="idx" href="cmdline.html#idx:prolog0:43">2.4.4</a> <a class="idx" href="IO.html#idx:prolog0:1030">4.17.2</a> <a class="idx" href="toplevel.html#idx:prolog0:1525">4.37</a> <a class="idx" href="toplevel.html#idx:prolog0:1533">4.37</a> <a class="idx" href="toplevel.html#idx:prolog0:1535">4.37</a> <a class="idx" href="mtoplevel.html#idx:prolog0:1712">6.6</a> <a class="idx" href="foreigninclude.html#idx:prolog0:2086">11.4.21</a> <a class="idx" href="manipstack.html#idx:prolog0:2189">B.1</a></dd>
1990	2036	<dt><a class="idx" href="debug.html#prolog:assertion_failed/2">prolog:assertion_failed/2</a></dt>
1991	2037	<dt><a class="idx" href="breakpoint.html#prolog:break_hook/6">prolog:break_hook/6</a></dt>
1992	2038	<dt><a class="idx" href="prolog_xref.html#prolog:called_by/2">prolog:called_by/2</a></dt>

1997	2043	<dt><a class="idx" href="exception.html#prolog:message_line_element/2">prolog:message_line_element/2</a></dt>
1998	2044	<dt><a class="idx" href="manipstack.html#prolog_choice_attribute/3">prolog_choice_attribute/3</a></dt>
1999	2045	<dd>
2000		<a class="idx" href="manipstack.html#idx:prologchoiceattribute3:2177">B.1</a> <a class="idx" href="tracehook.html#idx:prologchoiceattribute3:2193">B.3</a></dd>
	2046	<a class="idx" href="manipstack.html#idx:prologchoiceattribute3:2181">B.1</a> <a class="idx" href="tracehook.html#idx:prologchoiceattribute3:2197">B.3</a></dd>
2001	2047	<dt><a class="idx" href="manipstack.html#prolog_current_choice/1">prolog_current_choice/1</a></dt>
2002	2048	<dd>
2003		<a class="idx" href="manipstack.html#idx:prologcurrentchoice1:2183">B.1</a> <a class="idx" href="ancestral-cut.html#idx:prologcurrentchoice1:2187">B.2</a></dd>
	2049	<a class="idx" href="manipstack.html#idx:prologcurrentchoice1:2187">B.1</a> <a class="idx" href="ancestral-cut.html#idx:prologcurrentchoice1:2191">B.2</a></dd>
2004	2050	<dt><a class="idx" href="manipstack.html#prolog_current_frame/1">prolog_current_frame/1</a></dt>
2005	2051	<dd>
2006		<a class="idx" href="manipstack.html#idx:prologcurrentframe1:2178">B.1</a></dd>
	2052	<a class="idx" href="manipstack.html#idx:prologcurrentframe1:2182">B.1</a></dd>
2007	2053	<dt><a class="idx" href="ancestral-cut.html#prolog_cut_to/1">prolog_cut_to/1</a></dt>
2008	2054	<dd>
2009		<a class="idx" href="ancestral-cut.html#idx:prologcutto1:2188">B.2</a></dd>
	2055	<a class="idx" href="ancestral-cut.html#idx:prologcutto1:2192">B.2</a></dd>
2010	2056	<dt><a class="idx" href="foreignnotes.html#prolog_debug/1">prolog_debug/1</a></dt>
2011	2057	<dd>
2012		<a class="idx" href="foreignnotes.html#idx:prologdebug1:2090">11.8.1</a></dd>
	2058	<a class="idx" href="foreignnotes.html#idx:prologdebug1:2094">11.8.1</a></dd>
2013	2059	<dt><a class="idx" href="edit.html#prolog_edit:edit_command/2">prolog_edit:edit_command/2</a></dt>
2014	2060	<dt><a class="idx" href="edit.html#prolog_edit:edit_source/1">prolog_edit:edit_source/1</a></dt>
2015	2061	<dt><a class="idx" href="edit.html#prolog_edit:load/0">prolog_edit:load/0</a></dt>

2020	2066	<a class="idx" href="exception.html#idx:prologeventhook1:713">4.11.1</a></dd>
2021	2067	<dt><a class="idx" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a></dt>
2022	2068	<dd>
2023		<a class="idx" href="exception.html#idx:prologexceptionhook4:700">4.11</a> <a class="idx" href="exception.html#idx:prologexceptionhook4:714">4.11.1</a> <a class="idx" href="exception.html#idx:prologexceptionhook4:729">4.11.2</a> <a class="idx" href="memory.html#idx:prologexceptionhook4:1583">4.42</a> <a class="idx" href="excepthook.html#idx:prologexceptionhook4:2204">B.5</a> <a class="idx" href="excepthook.html#idx:prologexceptionhook4:2208">B.5</a></dd>
	2069	<a class="idx" href="exception.html#idx:prologexceptionhook4:700">4.11</a> <a class="idx" href="exception.html#idx:prologexceptionhook4:714">4.11.1</a> <a class="idx" href="exception.html#idx:prologexceptionhook4:729">4.11.2</a> <a class="idx" href="memory.html#idx:prologexceptionhook4:1583">4.42</a> <a class="idx" href="excepthook.html#idx:prologexceptionhook4:2208">B.5</a> <a class="idx" href="excepthook.html#idx:prologexceptionhook4:2212">B.5</a></dd>
2024	2070	<dt><a class="idx" href="consulting.html#prolog_file_type/2">prolog_file_type/2</a></dt>
2025	2071	<dd>
2026	2072	<a class="idx" href="consulting.html#idx:prologfiletype2:364">4.3</a> <a class="idx" href="consulting.html#idx:prologfiletype2:472">4.3</a> <a class="idx" href="files.html#idx:prologfiletype2:1510">4.36</a></dd>
2027	2073	<dt><a class="idx" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a></dt>
2028	2074	<dd>
2029		<a class="idx" href="examineprog.html#idx:prologframeattribute3:942">4.16</a> <a class="idx" href="tracehook.html#idx:prologframeattribute3:2191">B.3</a> <a class="idx" href="tracehook.html#idx:prologframeattribute3:2192">B.3</a> <a class="idx" href="excepthook.html#idx:prologframeattribute3:2206">B.5</a></dd>
	2075	<a class="idx" href="examineprog.html#idx:prologframeattribute3:942">4.16</a> <a class="idx" href="tracehook.html#idx:prologframeattribute3:2195">B.3</a> <a class="idx" href="tracehook.html#idx:prologframeattribute3:2196">B.3</a> <a class="idx" href="excepthook.html#idx:prologframeattribute3:2210">B.5</a></dd>
2030	2076	<dt><a class="idx" href="idepreds.html#prolog_ide/1">prolog_ide/1</a></dt>
2031	2077	<dd>
2032	2078	<a class="idx" href="idepreds.html#idx:prologide1:326">3.8</a></dd>
2033	2079	<dt><a class="idx" href="intlibs.html#prolog_list_goal/1">prolog_list_goal/1</a></dt>
2034	2080	<dt><a class="idx" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a></dt>
2035	2081	<dd>
2036		<a class="idx" href="consulting.html#idx:prologloadcontext2:496">4.3</a> <a class="idx" href="consulting.html#idx:prologloadcontext2:541">4.3.1</a> <a class="idx" href="termrw.html#idx:prologloadcontext2:1165">4.20</a> <a class="idx" href="dialect.html#idx:prologloadcontext2:2253">C</a></dd>
	2082	<a class="idx" href="consulting.html#idx:prologloadcontext2:496">4.3</a> <a class="idx" href="consulting.html#idx:prologloadcontext2:541">4.3.1</a> <a class="idx" href="termrw.html#idx:prologloadcontext2:1165">4.20</a> <a class="idx" href="dialect.html#idx:prologloadcontext2:2257">C</a></dd>
2037	2083	<dt><a class="idx" href="loadfilehook.html#prolog_load_file/2">prolog_load_file/2</a></dt>
2038	2084	<dd>
2039		<a class="idx" href="consulting.html#idx:prologloadfile2:424">4.3</a> <a class="idx" href="loadfilehook.html#idx:prologloadfile2:2237">B.8</a></dd>
	2085	<a class="idx" href="consulting.html#idx:prologloadfile2:424">4.3</a> <a class="idx" href="loadfilehook.html#idx:prologloadfile2:2241">B.8</a></dd>
2040	2086	<dt><a class="idx" href="foreignnotes.html#prolog_nodebug/1">prolog_nodebug/1</a></dt>
2041	2087	<dd>
2042		<a class="idx" href="foreignnotes.html#idx:prolognodebug1:2091">11.8.1</a></dd>
	2088	<a class="idx" href="foreignnotes.html#idx:prolognodebug1:2095">11.8.1</a></dd>
2043	2089	<dt><a class="idx" href="tracehook.html#prolog_skip_frame/1">prolog_skip_frame/1</a></dt>
2044	2090	<dd>
2045		<a class="idx" href="tracehook.html#idx:prologskipframe1:2197">B.3</a> <a class="idx" href="tracehook.html#idx:prologskipframe1:2198">B.3</a></dd>
	2091	<a class="idx" href="tracehook.html#idx:prologskipframe1:2201">B.3</a> <a class="idx" href="tracehook.html#idx:prologskipframe1:2202">B.3</a></dd>
2046	2092	<dt><a class="idx" href="tracehook.html#prolog_skip_level/2">prolog_skip_level/2</a></dt>
2047	2093	<dd>
2048		<a class="idx" href="tracehook.html#idx:prologskiplevel2:2196">B.3</a></dd>
	2094	<a class="idx" href="tracehook.html#idx:prologskiplevel2:2200">B.3</a></dd>
2049	2095	<dt><a class="idx" href="memory.html#prolog_stack_property/2">prolog_stack_property/2</a></dt>
2050	2096	<dd>
2051	2097	<a class="idx" href="memory.html#idx:prologstackproperty2:1577">4.42</a></dd>

2054	2100	<a class="idx" href="projectfiles.html#idx:prologtoosfilename2:296">3.1.1.2</a> <a class="idx" href="projectfiles.html#idx:prologtoosfilename2:297">3.1.1.2</a> <a class="idx" href="system.html#idx:prologtoosfilename2:1472">4.35.1</a> <a class="idx" href="files.html#idx:prologtoosfilename2:1498">4.36</a> <a class="idx" href="files.html#idx:prologtoosfilename2:1514">4.36</a></dd>
2055	2101	<dt><a class="idx" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a></dt>
2056	2102	<dd>
2057		<a class="idx" href="guitracer.html#idx:prologtraceinterception4:314">3.5</a> <a class="idx" href="debugger.html#idx:prologtraceinterception4:1546">4.39</a> <a class="idx" href="memory.html#idx:prologtraceinterception4:1582">4.42</a> <a class="idx" href="manipstack.html#idx:prologtraceinterception4:2179">B.1</a> <a class="idx" href="manipstack.html#idx:prologtraceinterception4:2182">B.1</a></dd>
	2103	<a class="idx" href="guitracer.html#idx:prologtraceinterception4:314">3.5</a> <a class="idx" href="debugger.html#idx:prologtraceinterception4:1546">4.39</a> <a class="idx" href="memory.html#idx:prologtraceinterception4:1582">4.42</a> <a class="idx" href="manipstack.html#idx:prologtraceinterception4:2183">B.1</a> <a class="idx" href="manipstack.html#idx:prologtraceinterception4:2186">B.1</a></dd>
2058	2104	<dt>prompt, alternatives</dt>
2059	2105	<dd>
2060	2106	<a class="idx" href="flags.html#idx:promptalternatives:127">2.11</a></dd>
2061	2107	<dt><a class="idx" href="termrw.html#prompt/2">prompt/2</a></dt>
2062	2108	<dd>
2063		<a class="idx" href="termrw.html#idx:prompt2:1186">4.20</a> <a class="idx" href="termrw.html#idx:prompt2:1189">4.20</a> <a class="idx" href="threadcreate.html#idx:prompt2:1846">9.1</a></dd>
	2109	<a class="idx" href="termrw.html#idx:prompt2:1186">4.20</a> <a class="idx" href="termrw.html#idx:prompt2:1189">4.20</a> <a class="idx" href="threadcreate.html#idx:prompt2:1850">9.1</a></dd>
2064	2110	<dt><a class="idx" href="termrw.html#prompt1/1">prompt1/1</a></dt>
2065	2111	<dt>propagation</dt>
2066	2112	<dd>
2067		<a class="idx" href="clp.html#idx:propagation:1763">7</a></dd>
	2113	<a class="idx" href="clp.html#idx:propagation:1767">7</a></dd>
2068	2114	<dt><a class="idx" href="lists.html#proper_length/2">proper_length/2</a></dt>
2069	2115	<dt>property</dt>
2070	2116	<dd>
2071		<a class="idx" href="glossary.html#idx:property:2323">D</a></dd>
	2117	<a class="idx" href="glossary.html#idx:property:2327">D</a></dd>
2072	2118	<dt><a class="idx" href="protocol.html#protocol/1">protocol/1</a></dt>
2073	2119	<dd>
2074	2120	<a class="idx" href="protocol.html#idx:protocol1:1538">4.38</a> <a class="idx" href="protocol.html#idx:protocol1:1539">4.38</a></dd>

2078	2124	<dt><a class="idx" href="protocol.html#protocolling/1">protocolling/1</a></dt>
2079	2125	<dt>prove</dt>
2080	2126	<dd>
2081		<a class="idx" href="glossary.html#idx:prove:2324">D</a></dd>
	2127	<a class="idx" href="glossary.html#idx:prove:2328">D</a></dd>
2082	2128	<dt>public list</dt>
2083	2129	<dd>
2084		<a class="idx" href="glossary.html#idx:publiclist:2325">D</a></dd>
	2130	<a class="idx" href="glossary.html#idx:publiclist:2329">D</a></dd>
2085	2131	<dt><a class="idx" href="dynamic.html#public/1">public/1</a></dt>
2086	2132	<dd>
2087		<a class="idx" href="dynamic.html#idx:public1:878">4.15</a> <a class="idx" href="dynamic.html#idx:public1:890">4.15</a> <a class="idx" href="dynamic.html#idx:public1:892">4.15</a> <a class="idx" href="examineprog.html#idx:public1:925">4.16</a> <a class="idx" href="runtime.html#idx:public1:2111">12</a></dd>
	2133	<a class="idx" href="dynamic.html#idx:public1:878">4.15</a> <a class="idx" href="dynamic.html#idx:public1:890">4.15</a> <a class="idx" href="dynamic.html#idx:public1:892">4.15</a> <a class="idx" href="examineprog.html#idx:public1:925">4.16</a> <a class="idx" href="runtime.html#idx:public1:2115">12</a></dd>
2088	2134	<dt><a class="idx" href="chario.html#put/1">put/1</a></dt>
2089	2135	<dd>
2090	2136	<a class="idx" href="chario.html#idx:put1:1077">4.19</a></dd>

2092	2138	<dt><a class="idx" href="assoc.html#put_assoc/4">put_assoc/4</a></dt>
2093	2139	<dt><a class="idx" href="attvar.html#put_attr/3">put_attr/3</a></dt>
2094	2140	<dd>
2095		<a class="idx" href="manipterm.html#idx:putattr3:1223">4.21.1</a> <a class="idx" href="attvar.html#idx:putattr3:1777">7.1.1</a> <a class="idx" href="attvar.html#idx:putattr3:1779">7.1.2</a> <a class="idx" href="attvar.html#idx:putattr3:1789">7.1.4</a></dd>
	2141	<a class="idx" href="manipterm.html#idx:putattr3:1223">4.21.1</a> <a class="idx" href="attvar.html#idx:putattr3:1781">7.1.1</a> <a class="idx" href="attvar.html#idx:putattr3:1783">7.1.2</a> <a class="idx" href="attvar.html#idx:putattr3:1793">7.1.4</a></dd>
2096	2142	<dt><a class="idx" href="attvar.html#put_attrs/2">put_attrs/2</a></dt>
2097	2143	<dt><a class="idx" href="chario.html#put_byte/1">put_byte/1</a></dt>
2098	2144	<dt><a class="idx" href="chario.html#put_byte/2">put_byte/2</a></dt>

2116	2162	<dd>
2117	2163	<a class="idx" href="chars.html#idx:putcode12:355">4.2</a></dd>
2118	2164	<dt><a class="idx" href="dicts.html#put_dict/3">put_dict/3</a></dt>
	2165	<dd>
	2166	<a class="idx" href="dicts.html#idx:putdict3:1638">5.4.1.2</a></dd>
2119	2167	<dt><a class="idx" href="dicts.html#put_dict/4">put_dict/4</a></dt>
	2168	<dd>
	2169	<a class="idx" href="dicts.html#idx:putdict4:1639">5.4.1.2</a></dd>
2120	2170	<dt><a class="idx" href="consulting.html#qcompile/1">qcompile/1</a></dt>
2121	2171	<dd>
2122		<a class="idx" href="swiorother.html#idx:qcompile1:2">1.3</a> <a class="idx" href="consulting.html#idx:qcompile1:374">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:405">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:412">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:414">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:513">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:576">4.3.3</a> <a class="idx" href="consulting.html#idx:qcompile1:583">4.3.3</a> <a class="idx" href="guidelines.html#idx:qcompile1:1826">8.7</a></dd>
	2172	<a class="idx" href="swiorother.html#idx:qcompile1:2">1.3</a> <a class="idx" href="consulting.html#idx:qcompile1:374">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:405">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:412">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:414">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:513">4.3</a> <a class="idx" href="consulting.html#idx:qcompile1:576">4.3.3</a> <a class="idx" href="consulting.html#idx:qcompile1:583">4.3.3</a> <a class="idx" href="guidelines.html#idx:qcompile1:1830">8.7</a></dd>
2123	2173	<dt><a class="idx" href="consulting.html#qcompile/2">qcompile/2</a></dt>
2124	2174	<dt><a class="idx" href="runtime.html#qsave_program/1">qsave_program/1</a></dt>
2125	2175	<dd>
2126	2176	<a class="idx" href="flags.html#idx:qsaveprogram1:101">2.11</a> <a class="idx" href="consulting.html#idx:qsaveprogram1:502">4.3</a> <a class="idx" href="consulting.html#idx:qsaveprogram1:505">4.3</a></dd>
2127	2177	<dt><a class="idx" href="runtime.html#qsave_program/2">qsave_program/2</a></dt>
2128	2178	<dd>
2129		<a class="idx" href="swiorother.html#idx:qsaveprogram2:3">1.3</a> <a class="idx" href="compilation.html#idx:qsaveprogram2:77">2.10.2.4</a> <a class="idx" href="compilation.html#idx:qsaveprogram2:78">2.10.2.4</a> <a class="idx" href="compilation.html#idx:qsaveprogram2:79">2.10.2.4</a> <a class="idx" href="flags.html#idx:qsaveprogram2:106">2.11</a> <a class="idx" href="autoload.html#idx:qsaveprogram2:206">2.13</a> <a class="idx" href="projectfiles.html#idx:qsaveprogram2:302">3.1.2</a> <a class="idx" href="idepreds.html#idx:qsaveprogram2:325">3.8</a> <a class="idx" href="foreigninclude.html#idx:qsaveprogram2:2077">11.4.21</a> <a class="idx" href="foreigninclude.html#idx:qsaveprogram2:2081">11.4.21</a> <a class="idx" href="runtime.html#idx:qsaveprogram2:2098">12</a> <a class="idx" href="useresource.html#idx:qsaveprogram2:2119">12.3</a></dd>
	2179	<a class="idx" href="swiorother.html#idx:qsaveprogram2:3">1.3</a> <a class="idx" href="compilation.html#idx:qsaveprogram2:77">2.10.2.4</a> <a class="idx" href="compilation.html#idx:qsaveprogram2:78">2.10.2.4</a> <a class="idx" href="compilation.html#idx:qsaveprogram2:79">2.10.2.4</a> <a class="idx" href="flags.html#idx:qsaveprogram2:106">2.11</a> <a class="idx" href="autoload.html#idx:qsaveprogram2:206">2.13</a> <a class="idx" href="projectfiles.html#idx:qsaveprogram2:302">3.1.2</a> <a class="idx" href="idepreds.html#idx:qsaveprogram2:325">3.8</a> <a class="idx" href="foreigninclude.html#idx:qsaveprogram2:2081">11.4.21</a> <a class="idx" href="foreigninclude.html#idx:qsaveprogram2:2085">11.4.21</a> <a class="idx" href="runtime.html#idx:qsaveprogram2:2102">12</a> <a class="idx" href="useresource.html#idx:qsaveprogram2:2123">12.3</a></dd>
2130	2180	<dt>qsave_program/[1,2]</dt>
2131	2181	<dd>
2132		<a class="idx" href="cmdline.html#idx:qsaveprogram12:35">2.4.2</a> <a class="idx" href="compilation.html#idx:qsaveprogram12:76">2.10.2.3</a> <a class="idx" href="flags.html#idx:qsaveprogram12:133">2.11</a> <a class="idx" href="examineprog.html#idx:qsaveprogram12:933">4.16</a> <a class="idx" href="foreignlink.html#idx:qsaveprogram12:2010">11.2.2</a> <a class="idx" href="foreigninclude.html#idx:qsaveprogram12:2076">11.4.21</a> <a class="idx" href="findhome.html#idx:qsaveprogram12:2088">11.6</a> <a class="idx" href="runtime.html#idx:qsaveprogram12:2103">12</a> <a class="idx" href="qsavelimits.html#idx:qsaveprogram12:2112">12.1</a></dd>
	2182	<a class="idx" href="cmdline.html#idx:qsaveprogram12:35">2.4.2</a> <a class="idx" href="compilation.html#idx:qsaveprogram12:76">2.10.2.3</a> <a class="idx" href="flags.html#idx:qsaveprogram12:133">2.11</a> <a class="idx" href="examineprog.html#idx:qsaveprogram12:933">4.16</a> <a class="idx" href="foreignlink.html#idx:qsaveprogram12:2014">11.2.2</a> <a class="idx" href="foreigninclude.html#idx:qsaveprogram12:2080">11.4.21</a> <a class="idx" href="findhome.html#idx:qsaveprogram12:2092">11.6</a> <a class="idx" href="runtime.html#idx:qsaveprogram12:2107">12</a> <a class="idx" href="qsavelimits.html#idx:qsaveprogram12:2116">12.1</a></dd>
2133	2183	<dt><a class="idx" href="quasiquotations.html#quasi_quotation_syntax/1">quasi_quotation_syntax/1</a></dt>
2134	2184	<dd>
2135	2185	<a class="idx" href="examineprog.html#idx:quasiquotationsyntax1:926">4.16</a></dd>
2136	2186	<dt><a class="idx" href="quasiquotations.html#quasi_quotation_syntax_error/1">quasi_quotation_syntax_error/1</a></dt>
2137	2187	<dt>query</dt>
2138	2188	<dd>
2139		<a class="idx" href="glossary.html#idx:query:2296">D</a></dd>
	2189	<a class="idx" href="glossary.html#idx:query:2300">D</a></dd>
2140	2190	<dt>quiet</dt>
2141	2191	<dd>
2142	2192	<a class="idx" href="cmdline.html#idx:quiet:26">2.4.2</a></dd>

2166	2216	<dt><a class="idx" href="ugraphs.html#reachable/3">reachable/3</a></dt>
2167	2217	<dt><a class="idx" href="termrw.html#read/1">read/1</a></dt>
2168	2218	<dd>
2169		<a class="idx" href="flags.html#idx:read1:87">2.11</a> <a class="idx" href="flags.html#idx:read1:93">2.11</a> <a class="idx" href="limits.html#idx:read1:283">2.20.2</a> <a class="idx" href="IO.html#idx:read1:953">4.17.1</a> <a class="idx" href="IO.html#idx:read1:969">4.17.2</a> <a class="idx" href="IO.html#idx:read1:978">4.17.2</a> <a class="idx" href="chario.html#idx:read1:1081">4.19</a> <a class="idx" href="termrw.html#idx:read1:1144">4.20</a> <a class="idx" href="termrw.html#idx:read1:1158">4.20</a> <a class="idx" href="termrw.html#idx:read1:1166">4.20</a> <a class="idx" href="termrw.html#idx:read1:1188">4.20</a> <a class="idx" href="gvar.html#idx:read1:1432">4.33.1</a> <a class="idx" href="readutil.html#idx:read1:2161">A.30</a> <a class="idx" href="predsummary.html#idx:read1:2367">F.1</a></dd>
	2219	<a class="idx" href="flags.html#idx:read1:87">2.11</a> <a class="idx" href="flags.html#idx:read1:93">2.11</a> <a class="idx" href="limits.html#idx:read1:283">2.20.2</a> <a class="idx" href="IO.html#idx:read1:953">4.17.1</a> <a class="idx" href="IO.html#idx:read1:969">4.17.2</a> <a class="idx" href="IO.html#idx:read1:978">4.17.2</a> <a class="idx" href="chario.html#idx:read1:1081">4.19</a> <a class="idx" href="termrw.html#idx:read1:1144">4.20</a> <a class="idx" href="termrw.html#idx:read1:1158">4.20</a> <a class="idx" href="termrw.html#idx:read1:1166">4.20</a> <a class="idx" href="termrw.html#idx:read1:1188">4.20</a> <a class="idx" href="gvar.html#idx:read1:1432">4.33.1</a> <a class="idx" href="readutil.html#idx:read1:2165">A.30</a> <a class="idx" href="predsummary.html#idx:read1:2371">F.1</a></dd>
2170	2220	<dt><a class="idx" href="termrw.html#read/2">read/2</a></dt>
2171	2221	<dd>
2172	2222	<a class="idx" href="streamstat.html#idx:read2:1071">4.18</a></dd>

2183	2233	<a class="idx" href="termrw.html#idx:readhistory6:1185">4.20</a> <a class="idx" href="termrw.html#idx:readhistory6:1187">4.20</a></dd>
2184	2234	<dt><a class="idx" href="readutil.html#read_line_to_codes/2">read_line_to_codes/2</a></dt>
2185	2235	<dd>
2186		<a class="idx" href="strings.html#idx:readlinetocodes2:1610">5.2.2</a> <a class="idx" href="readutil.html#idx:readlinetocodes2:2156">A.30</a></dd>
	2236	<a class="idx" href="strings.html#idx:readlinetocodes2:1610">5.2.2</a> <a class="idx" href="readutil.html#idx:readlinetocodes2:2160">A.30</a></dd>
2187	2237	<dt><a class="idx" href="readutil.html#read_line_to_codes/3">read_line_to_codes/3</a></dt>
2188	2238	<dd>
2189		<a class="idx" href="readutil.html#idx:readlinetocodes3:2154">A.30</a></dd>
	2239	<a class="idx" href="readutil.html#idx:readlinetocodes3:2158">A.30</a></dd>
2190	2240	<dt><a class="idx" href="files.html#read_link/3">read_link/3</a></dt>
2191	2241	<dt><a class="idx" href="chario.html#read_pending_chars/3">read_pending_chars/3</a></dt>
2192	2242	<dt><a class="idx" href="chario.html#read_pending_codes/3">read_pending_codes/3</a></dt>

2194	2244	<a class="idx" href="chario.html#idx:readpendingcodes3:1106">4.19</a> <a class="idx" href="chario.html#idx:readpendingcodes3:1113">4.19</a></dd>
2195	2245	<dt><a class="idx" href="readutil.html#read_stream_to_codes/2">read_stream_to_codes/2</a></dt>
2196	2246	<dd>
2197		<a class="idx" href="readutil.html#idx:readstreamtocodes2:2157">A.30</a></dd>
	2247	<a class="idx" href="readutil.html#idx:readstreamtocodes2:2161">A.30</a></dd>
2198	2248	<dt><a class="idx" href="readutil.html#read_stream_to_codes/3">read_stream_to_codes/3</a></dt>
2199	2249	<dt><a class="idx" href="strings.html#read_string/3">read_string/3</a></dt>
2200	2250	<dt><a class="idx" href="strings.html#read_string/5">read_string/5</a></dt>

2202	2252	<a class="idx" href="strings.html#idx:readstring5:1603">5.2.1</a> <a class="idx" href="strings.html#idx:readstring5:1607">5.2.1</a></dd>
2203	2253	<dt><a class="idx" href="termrw.html#read_term/2">read_term/2</a></dt>
2204	2254	<dd>
2205		<a class="idx" href="flags.html#idx:readterm2:88">2.11</a> <a class="idx" href="consulting.html#idx:readterm2:493">4.3</a> <a class="idx" href="consulting.html#idx:readterm2:551">4.3.1.1</a> <a class="idx" href="termrw.html#idx:readterm2:1123">4.20</a> <a class="idx" href="termrw.html#idx:readterm2:1136">4.20</a> <a class="idx" href="termrw.html#idx:readterm2:1170">4.20</a> <a class="idx" href="termrw.html#idx:readterm2:1181">4.20</a> <a class="idx" href="termrw.html#idx:readterm2:1184">4.20</a> <a class="idx" href="manipatom.html#idx:readterm2:1270">4.22</a> <a class="idx" href="manipatom.html#idx:readterm2:1271">4.22</a> <a class="idx" href="ext-lists.html#idx:readterm2:1590">5.1</a> <a class="idx" href="ext-lists.html#idx:readterm2:1592">5.1</a> <a class="idx" href="strings.html#idx:readterm2:1597">5.2.1</a> <a class="idx" href="loadfilehook.html#idx:readterm2:2239">B.8</a> <a class="idx" href="loadfilehook.html#idx:readterm2:2240">B.8</a></dd>
	2255	<a class="idx" href="flags.html#idx:readterm2:88">2.11</a> <a class="idx" href="consulting.html#idx:readterm2:493">4.3</a> <a class="idx" href="consulting.html#idx:readterm2:551">4.3.1.1</a> <a class="idx" href="termrw.html#idx:readterm2:1123">4.20</a> <a class="idx" href="termrw.html#idx:readterm2:1136">4.20</a> <a class="idx" href="termrw.html#idx:readterm2:1170">4.20</a> <a class="idx" href="termrw.html#idx:readterm2:1181">4.20</a> <a class="idx" href="termrw.html#idx:readterm2:1184">4.20</a> <a class="idx" href="manipatom.html#idx:readterm2:1270">4.22</a> <a class="idx" href="manipatom.html#idx:readterm2:1271">4.22</a> <a class="idx" href="ext-lists.html#idx:readterm2:1590">5.1</a> <a class="idx" href="ext-lists.html#idx:readterm2:1592">5.1</a> <a class="idx" href="strings.html#idx:readterm2:1597">5.2.1</a> <a class="idx" href="loadfilehook.html#idx:readterm2:2243">B.8</a> <a class="idx" href="loadfilehook.html#idx:readterm2:2244">B.8</a></dd>
2206	2256	<dt><a class="idx" href="termrw.html#read_term/3">read_term/3</a></dt>
2207	2257	<dd>
2208		<a class="idx" href="syntax.html#idx:readterm3:227">2.16.1.9</a> <a class="idx" href="termrw.html#idx:readterm3:1133">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1159">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1160">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1161">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1162">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1163">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1164">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1174">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1182">4.20</a> <a class="idx" href="charconv.html#idx:readterm3:1318">4.26</a> <a class="idx" href="toplevel.html#idx:readterm3:1534">4.37</a> <a class="idx" href="dicts.html#idx:readterm3:1647">5.4.3</a> <a class="idx" href="loadfilehook.html#idx:readterm3:2242">B.8</a></dd>
	2258	<a class="idx" href="syntax.html#idx:readterm3:227">2.16.1.9</a> <a class="idx" href="termrw.html#idx:readterm3:1133">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1159">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1160">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1161">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1162">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1163">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1164">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1174">4.20</a> <a class="idx" href="termrw.html#idx:readterm3:1182">4.20</a> <a class="idx" href="charconv.html#idx:readterm3:1318">4.26</a> <a class="idx" href="toplevel.html#idx:readterm3:1534">4.37</a> <a class="idx" href="dicts.html#idx:readterm3:1651">5.4.3</a> <a class="idx" href="loadfilehook.html#idx:readterm3:2246">B.8</a></dd>
2209	2259	<dt>read_term/[2,3]</dt>
2210	2260	<dd>
2211	2261	<a class="idx" href="termrw.html#idx:readterm23:1177">4.20</a> <a class="idx" href="termrw.html#idx:readterm23:1178">4.20</a></dd>

2218	2268	<a class="idx" href="consulting.html#idx:reconsult:378">4.3</a></dd>
2219	2269	<dt><a class="idx" href="record.html#record/1">record/1</a></dt>
2220	2270	<dd>
2221		<a class="idx" href="record.html#idx:record1:2165">A.31</a></dd>
	2271	<a class="idx" href="record.html#idx:record1:2169">A.31</a></dd>
2222	2272	<dt><a class="idx" href="db.html#recorda/2">recorda/2</a></dt>
2223	2273	<dd>
2224	2274	<a class="idx" href="db.html#idx:recorda2:842">4.14.2</a></dd>
2225	2275	<dt><a class="idx" href="db.html#recorda/3">recorda/3</a></dt>
2226	2276	<dd>
2227		<a class="idx" href="cyclic.html#idx:recorda3:244">2.17</a> <a class="idx" href="db.html#idx:recorda3:803">4.14</a> <a class="idx" href="db.html#idx:recorda3:841">4.14.2</a> <a class="idx" href="db.html#idx:recorda3:845">4.14.2</a> <a class="idx" href="examineprog.html#idx:recorda3:898">4.16</a> <a class="idx" href="gvar.html#idx:recorda3:1412">4.33</a> <a class="idx" href="foreigninclude.html#idx:recorda3:2052">11.4.14.2</a> <a class="idx" href="foreigninclude.html#idx:recorda3:2053">11.4.14.2</a> <a class="idx" href="foreigninclude.html#idx:recorda3:2054">11.4.14.2</a></dd>
	2277	<a class="idx" href="cyclic.html#idx:recorda3:244">2.17</a> <a class="idx" href="db.html#idx:recorda3:803">4.14</a> <a class="idx" href="db.html#idx:recorda3:841">4.14.2</a> <a class="idx" href="db.html#idx:recorda3:845">4.14.2</a> <a class="idx" href="examineprog.html#idx:recorda3:898">4.16</a> <a class="idx" href="gvar.html#idx:recorda3:1412">4.33</a> <a class="idx" href="foreigninclude.html#idx:recorda3:2056">11.4.14.2</a> <a class="idx" href="foreigninclude.html#idx:recorda3:2057">11.4.14.2</a> <a class="idx" href="foreigninclude.html#idx:recorda3:2058">11.4.14.2</a></dd>
2228	2278	<dt><a class="idx" href="db.html#recorded/2">recorded/2</a></dt>
2229	2279	<dt><a class="idx" href="db.html#recorded/3">recorded/3</a></dt>
2230	2280	<dd>
2231		<a class="idx" href="db.html#idx:recorded3:806">4.14</a> <a class="idx" href="db.html#idx:recorded3:847">4.14.2</a> <a class="idx" href="qsavelimits.html#idx:recorded3:2115">12.1</a></dd>
	2281	<a class="idx" href="db.html#idx:recorded3:806">4.14</a> <a class="idx" href="db.html#idx:recorded3:847">4.14.2</a> <a class="idx" href="qsavelimits.html#idx:recorded3:2119">12.1</a></dd>
2232	2282	<dt><a class="idx" href="db.html#recordz/2">recordz/2</a></dt>
2233	2283	<dd>
2234	2284	<a class="idx" href="db.html#idx:recordz2:843">4.14.2</a></dd>

2237	2287	<a class="idx" href="cyclic.html#idx:recordz3:245">2.17</a> <a class="idx" href="db.html#idx:recordz3:804">4.14</a> <a class="idx" href="db.html#idx:recordz3:846">4.14.2</a></dd>
2238	2288	<dt><a class="idx" href="db.html#redefine_system_predicate/1">redefine_system_predicate/1</a></dt>
2239	2289	<dd>
2240		<a class="idx" href="glossary.html#idx:redefinesystempredicate1:2276">D</a></dd>
	2290	<a class="idx" href="glossary.html#idx:redefinesystempredicate1:2280">D</a></dd>
2241	2291	<dt><a class="idx" href="solutionsequences.html#reduced/1">reduced/1</a></dt>
2242	2292	<dt><a class="idx" href="solutionsequences.html#reduced/3">reduced/3</a></dt>
2243	2293	<dt><a class="idx" href="reexport.html#reexport/1">reexport/1</a></dt>
2244	2294	<dd>
2245		<a class="idx" href="consulting.html#idx:reexport1:384">4.3</a> <a class="idx" href="consulting.html#idx:reexport1:390">4.3</a> <a class="idx" href="consulting.html#idx:reexport1:416">4.3</a> <a class="idx" href="dialect.html#idx:reexport1:2251">C</a></dd>
	2295	<a class="idx" href="consulting.html#idx:reexport1:384">4.3</a> <a class="idx" href="consulting.html#idx:reexport1:390">4.3</a> <a class="idx" href="consulting.html#idx:reexport1:416">4.3</a> <a class="idx" href="dialect.html#idx:reexport1:2255">C</a></dd>
2246	2296	<dt><a class="idx" href="reexport.html#reexport/2">reexport/2</a></dt>
2247	2297	<dd>
2248		<a class="idx" href="consulting.html#idx:reexport2:391">4.3</a> <a class="idx" href="consulting.html#idx:reexport2:408">4.3</a> <a class="idx" href="consulting.html#idx:reexport2:417">4.3</a> <a class="idx" href="dialect.html#idx:reexport2:2252">C</a></dd>
	2298	<a class="idx" href="consulting.html#idx:reexport2:391">4.3</a> <a class="idx" href="consulting.html#idx:reexport2:408">4.3</a> <a class="idx" href="consulting.html#idx:reexport2:417">4.3</a> <a class="idx" href="dialect.html#idx:reexport2:2256">C</a></dd>
2249	2299	<dt>registry</dt>
2250	2300	<dd>
2251	2301	<a class="idx" href="limits.html#idx:registry:279">2.20.1</a></dd>

2267	2317	<a class="idx" href="control.html#idx:repeat0:642">4.8</a> <a class="idx" href="metacall.html#idx:repeat0:658">4.9</a> <a class="idx" href="metacall.html#idx:repeat0:671">4.9</a></dd>
2268	2318	<dt><a class="idx" href="error.html#representation_error/1">representation_error/1</a></dt>
2269	2319	<dd>
2270		<a class="idx" href="foreigninclude.html#idx:representationerror1:2030">11.4.6</a></dd>
	2320	<a class="idx" href="foreigninclude.html#idx:representationerror1:2034">11.4.6</a></dd>
2271	2321	<dt><a class="idx" href="consulting.html#require/1">require/1</a></dt>
2272	2322	<dd>
2273		<a class="idx" href="dialect.html#idx:require1:2248">C</a></dd>
	2323	<a class="idx" href="dialect.html#idx:require1:2252">C</a></dd>
2274	2324	<dt><a class="idx" href="delcont.html#reset/3">reset/3</a></dt>
2275	2325	<dd>
2276		<a class="idx" href="delcont.html#idx:reset3:678">4.10</a> <a class="idx" href="delcont.html#idx:reset3:684">4.10</a> <a class="idx" href="delcont.html#idx:reset3:687">4.10</a> <a class="idx" href="delcont.html#idx:reset3:689">4.10</a> <a class="idx" href="delcont.html#idx:reset3:690">4.10</a> <a class="idx" href="predsummary.html#idx:reset3:2368">F.1</a></dd>
	2326	<a class="idx" href="delcont.html#idx:reset3:678">4.10</a> <a class="idx" href="delcont.html#idx:reset3:684">4.10</a> <a class="idx" href="delcont.html#idx:reset3:687">4.10</a> <a class="idx" href="delcont.html#idx:reset3:689">4.10</a> <a class="idx" href="delcont.html#idx:reset3:690">4.10</a> <a class="idx" href="predsummary.html#idx:reset3:2372">F.1</a></dd>
2277	2327	<dt><a class="idx" href="gensym.html#reset_gensym/0">reset_gensym/0</a></dt>
2278	2328	<dt><a class="idx" href="gensym.html#reset_gensym/1">reset_gensym/1</a></dt>
2279	2329	<dt><a class="idx" href="profile.html#reset_profiler/0">reset_profiler/0</a></dt>
2280	2330	<dt>residual</dt>
2281	2331	<dd>
2282		<a class="idx" href="coroutining.html#idx:residual:1796">7.2</a></dd>
	2332	<a class="idx" href="coroutining.html#idx:residual:1800">7.2</a></dd>
2283	2333	<dt><a class="idx" href="useresource.html#resource/3">resource/3</a></dt>
2284	2334	<dd>
2285		<a class="idx" href="flags.html#idx:resource3:131">2.11</a> <a class="idx" href="runtime.html#idx:resource3:2096">12</a> <a class="idx" href="runtime.html#idx:resource3:2099">12</a> <a class="idx" href="useresource.html#idx:resource3:2120">12.3</a> <a class="idx" href="useresource.html#idx:resource3:2127">12.3.1</a> <a class="idx" href="useresource.html#idx:resource3:2128">12.3.1</a></dd>
	2335	<a class="idx" href="flags.html#idx:resource3:131">2.11</a> <a class="idx" href="runtime.html#idx:resource3:2100">12</a> <a class="idx" href="runtime.html#idx:resource3:2103">12</a> <a class="idx" href="useresource.html#idx:resource3:2124">12.3</a> <a class="idx" href="useresource.html#idx:resource3:2131">12.3.1</a> <a class="idx" href="useresource.html#idx:resource3:2132">12.3.1</a></dd>
2286	2336	<dt><a class="idx" href="error.html#resource_error/1">resource_error/1</a></dt>
2287	2337	<dd>
2288		<a class="idx" href="foreigninclude.html#idx:resourceerror1:2035">11.4.6</a></dd>
	2338	<a class="idx" href="foreigninclude.html#idx:resourceerror1:2039">11.4.6</a></dd>
2289	2339	<dt>retract</dt>
2290	2340	<dd>
2291		<a class="idx" href="glossary.html#idx:retract:2326">D</a></dd>
	2341	<a class="idx" href="glossary.html#idx:retract:2330">D</a></dd>
2292	2342	<dt><a class="idx" href="db.html#retract/1">retract/1</a></dt>
2293	2343	<dd>
2294		<a class="idx" href="quickstart.html#idx:retract1:9">2.1.2</a> <a class="idx" href="consulting.html#idx:retract1:372">4.3</a> <a class="idx" href="consulting.html#idx:retract1:462">4.3</a> <a class="idx" href="db.html#idx:retract1:796">4.14</a> <a class="idx" href="db.html#idx:retract1:799">4.14</a> <a class="idx" href="db.html#idx:retract1:815">4.14.1</a> <a class="idx" href="db.html#idx:retract1:823">4.14.1</a> <a class="idx" href="db.html#idx:retract1:824">4.14.1</a> <a class="idx" href="db.html#idx:retract1:825">4.14.1</a> <a class="idx" href="db.html#idx:retract1:826">4.14.1</a> <a class="idx" href="db.html#idx:retract1:863">4.14.5</a> <a class="idx" href="dynamic.html#idx:retract1:881">4.15</a> <a class="idx" href="dynamic.html#idx:retract1:887">4.15</a> <a class="idx" href="examineprog.html#idx:retract1:914">4.16</a> <a class="idx" href="clp.html#idx:retract1:1767">7</a> <a class="idx" href="threadcom.html#idx:retract1:1918">9.3.3</a> <a class="idx" href="engine-examples.html#idx:retract1:1972">10.1.2</a></dd>
	2344	<a class="idx" href="quickstart.html#idx:retract1:9">2.1.2</a> <a class="idx" href="consulting.html#idx:retract1:372">4.3</a> <a class="idx" href="consulting.html#idx:retract1:462">4.3</a> <a class="idx" href="db.html#idx:retract1:796">4.14</a> <a class="idx" href="db.html#idx:retract1:799">4.14</a> <a class="idx" href="db.html#idx:retract1:815">4.14.1</a> <a class="idx" href="db.html#idx:retract1:823">4.14.1</a> <a class="idx" href="db.html#idx:retract1:824">4.14.1</a> <a class="idx" href="db.html#idx:retract1:825">4.14.1</a> <a class="idx" href="db.html#idx:retract1:826">4.14.1</a> <a class="idx" href="db.html#idx:retract1:863">4.14.5</a> <a class="idx" href="dynamic.html#idx:retract1:881">4.15</a> <a class="idx" href="dynamic.html#idx:retract1:887">4.15</a> <a class="idx" href="examineprog.html#idx:retract1:914">4.16</a> <a class="idx" href="clp.html#idx:retract1:1771">7</a> <a class="idx" href="threadcom.html#idx:retract1:1922">9.3.3</a> <a class="idx" href="engine-examples.html#idx:retract1:1976">10.1.2</a></dd>
2295	2345	<dt><a class="idx" href="db.html#retractall/1">retractall/1</a></dt>
2296	2346	<dd>
2297	2347	<a class="idx" href="db.html#idx:retractall1:797">4.14</a> <a class="idx" href="db.html#idx:retractall1:800">4.14</a> <a class="idx" href="db.html#idx:retractall1:816">4.14.1</a> <a class="idx" href="db.html#idx:retractall1:819">4.14.1</a></dd>
2298	2348	<dt><a class="idx" href="predicate_options.html#retractall_predicate_options/0">retractall_predicate_options/0</a></dt>
2299	2349	<dt>rev/3</dt>
2300	2350	<dd>
2301		<a class="idx" href="defmodule.html#idx:rev3:1663">6.2</a></dd>
	2351	<a class="idx" href="defmodule.html#idx:rev3:1667">6.2</a></dd>
2302	2352	<dt><a class="idx" href="lists.html#reverse/2">reverse/2</a></dt>
2303	2353	<dd>
2304		<a class="idx" href="DCG.html#idx:reverse2:791">4.13</a> <a class="idx" href="defmodule.html#idx:reverse2:1662">6.2</a></dd>
	2354	<a class="idx" href="DCG.html#idx:reverse2:791">4.13</a> <a class="idx" href="defmodule.html#idx:reverse2:1666">6.2</a></dd>
2305	2355	<dt><a class="idx" href="files.html#same_file/2">same_file/2</a></dt>
2306	2356	<dd>
2307	2357	<a class="idx" href="files.html#idx:samefile2:1496">4.36</a> <a class="idx" href="files.html#idx:samefile2:1497">4.36</a> <a class="idx" href="files.html#idx:samefile2:1500">4.36</a> <a class="idx" href="files.html#idx:samefile2:1501">4.36</a></dd>

2332	2382	<dt><a class="idx" href="lists.html#select/4">select/4</a></dt>
2333	2383	<dt>select_dict/2</dt>
2334	2384	<dd>
2335		<a class="idx" href="dicts.html#idx:selectdict2:1637">5.4.2</a></dd>
	2385	<a class="idx" href="dicts.html#idx:selectdict2:1641">5.4.2</a></dd>
2336	2386	<dt><a class="idx" href="dicts.html#select_dict/3">select_dict/3</a></dt>
2337	2387	<dd>
2338		<a class="idx" href="dicts.html#idx:selectdict3:1638">5.4.2</a></dd>
	2388	<a class="idx" href="dicts.html#idx:selectdict3:1642">5.4.2</a></dd>
2339	2389	<dt><a class="idx" href="option.html#select_option/3">select_option/3</a></dt>
2340	2390	<dt><a class="idx" href="option.html#select_option/4">select_option/4</a></dt>
2341	2391	<dt><a class="idx" href="lists.html#selectchk/3">selectchk/3</a></dt>
2342	2392	<dt><a class="idx" href="lists.html#selectchk/4">selectchk/4</a></dt>
2343	2393	<dt>semi deterministic</dt>
2344	2394	<dd>
2345		<a class="idx" href="glossary.html#idx:semideterministic:2328">D</a></dd>
	2395	<a class="idx" href="glossary.html#idx:semideterministic:2332">D</a></dd>
2346	2396	<dt>semidet</dt>
2347	2397	<dd>
2348		<a class="idx" href="glossary.html#idx:semidet:2327">D</a></dd>
2349		<dt><a class="idx" href="control.html#send_arrow/2">send_arrow/2</a></dt>
	2398	<a class="idx" href="glossary.html#idx:semidet:2331">D</a></dd>
2350	2399	<dt>serialize</dt>
2351	2400	<dd>
2352	2401	<a class="idx" href="DCG.html#idx:serialize:778">4.13</a></dd>
2353	2402	<dt><a class="idx" href="clpfd.html#serialized/2">serialized/2</a></dt>
2354	2403	<dt>set_breakpoint/4</dt>
2355	2404	<dd>
2356		<a class="idx" href="breakpoint.html#idx:setbreakpoint4:2199">B.4</a></dd>
	2405	<a class="idx" href="breakpoint.html#idx:setbreakpoint4:2203">B.4</a></dd>
2357	2406	<dt><a class="idx" href="chario.html#set_end_of_stream/1">set_end_of_stream/1</a></dt>
2358	2407	<dt><a class="idx" href="db.html#set_flag/2">set_flag/2</a></dt>
2359	2408	<dt><a class="idx" href="IO.html#set_input/1">set_input/1</a></dt>

2362	2411	<dt><a class="idx" href="locale.html#set_locale/1">set_locale/1</a></dt>
2363	2412	<dt><a class="idx" href="manipmodule.html#set_module/1">set_module/1</a></dt>
2364	2413	<dd>
2365		<a class="idx" href="db.html#idx:setmodule1:833">4.14.1</a> <a class="idx" href="importmodule.html#idx:setmodule1:1718">6.9</a> <a class="idx" href="manipmodule.html#idx:setmodule1:1747">6.14</a></dd>
	2414	<a class="idx" href="db.html#idx:setmodule1:833">4.14.1</a> <a class="idx" href="importmodule.html#idx:setmodule1:1722">6.9</a> <a class="idx" href="manipmodule.html#idx:setmodule1:1751">6.14</a></dd>
2366	2415	<dt><a class="idx" href="IO.html#set_output/1">set_output/1</a></dt>
2367	2416	<dd>
2368	2417	<a class="idx" href="IO.html#idx:setoutput1:959">4.17.1</a> <a class="idx" href="IO.html#idx:setoutput1:1045">4.17.3</a></dd>
2369	2418	<dt><a class="idx" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a></dt>
2370	2419	<dd>
2371		<a class="idx" href="history.html#idx:setprologflag2:53">2.7</a> <a class="idx" href="flags.html#idx:setprologflag2:81">2.11</a> <a class="idx" href="flags.html#idx:setprologflag2:83">2.11</a> <a class="idx" href="flags.html#idx:setprologflag2:150">2.11</a> <a class="idx" href="flags.html#idx:setprologflag2:166">2.11</a> <a class="idx" href="consulting.html#idx:setprologflag2:376">4.3</a> <a class="idx" href="arith.html#idx:setprologflag2:1324">4.27.2</a> <a class="idx" href="foreigninclude.html#idx:setprologflag2:2058">11.4.14.4</a></dd>
	2420	<a class="idx" href="history.html#idx:setprologflag2:53">2.7</a> <a class="idx" href="flags.html#idx:setprologflag2:81">2.11</a> <a class="idx" href="flags.html#idx:setprologflag2:83">2.11</a> <a class="idx" href="flags.html#idx:setprologflag2:150">2.11</a> <a class="idx" href="flags.html#idx:setprologflag2:166">2.11</a> <a class="idx" href="consulting.html#idx:setprologflag2:376">4.3</a> <a class="idx" href="arith.html#idx:setprologflag2:1324">4.27.2</a> <a class="idx" href="foreigninclude.html#idx:setprologflag2:2062">11.4.14.4</a></dd>
2372	2421	<dt><a class="idx" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a></dt>
2373	2422	<dd>
2374		<a class="idx" href="cmdline.html#idx:setprologstack2:41">2.4.3</a> <a class="idx" href="limits.html#idx:setprologstack2:278">2.20.1</a> <a class="idx" href="limits.html#idx:setprologstack2:280">2.20.1</a> <a class="idx" href="debugger.html#idx:setprologstack2:1555">4.39</a> <a class="idx" href="memory.html#idx:setprologstack2:1584">4.42</a> <a class="idx" href="strings.html#idx:setprologstack2:1594">5.2</a> <a class="idx" href="threadcreate.html#idx:setprologstack2:1849">9.1</a></dd>
	2423	<a class="idx" href="cmdline.html#idx:setprologstack2:41">2.4.3</a> <a class="idx" href="limits.html#idx:setprologstack2:278">2.20.1</a> <a class="idx" href="limits.html#idx:setprologstack2:280">2.20.1</a> <a class="idx" href="debugger.html#idx:setprologstack2:1555">4.39</a> <a class="idx" href="memory.html#idx:setprologstack2:1584">4.42</a> <a class="idx" href="strings.html#idx:setprologstack2:1594">5.2</a> <a class="idx" href="threadcreate.html#idx:setprologstack2:1853">9.1</a></dd>
2375	2424	<dt><a class="idx" href="miscarith.html#set_random/1">set_random/1</a></dt>
2376	2425	<dd>
2377	2426	<a class="idx" href="arith.html#idx:setrandom1:1334">4.27.2.3</a> <a class="idx" href="miscarith.html#idx:setrandom1:1341">4.28</a></dd>

2384	2433	<dt><a class="idx" href="url.html#set_url_encoding/2">set_url_encoding/2</a></dt>
2385	2434	<dt><a class="idx" href="manipterm.html#setarg/3">setarg/3</a></dt>
2386	2435	<dd>
2387		<a class="idx" href="preddesc.html#idx:setarg3:335">4.1</a> <a class="idx" href="db.html#idx:setarg3:811">4.14</a> <a class="idx" href="manipterm.html#idx:setarg3:1216">4.21</a> <a class="idx" href="manipterm.html#idx:setarg3:1218">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1220">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1221">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1224">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1234">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1239">4.21.1</a> <a class="idx" href="gvar.html#idx:setarg3:1434">4.33.1</a> <a class="idx" href="dicts.html#idx:setarg3:1640">5.4.2.1</a> <a class="idx" href="attvar.html#idx:setarg3:1775">7.1</a> <a class="idx" href="attvar.html#idx:setarg3:1778">7.1.1</a> <a class="idx" href="record.html#idx:setarg3:2167">A.31</a></dd>
	2436	<a class="idx" href="preddesc.html#idx:setarg3:335">4.1</a> <a class="idx" href="db.html#idx:setarg3:811">4.14</a> <a class="idx" href="manipterm.html#idx:setarg3:1216">4.21</a> <a class="idx" href="manipterm.html#idx:setarg3:1218">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1220">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1221">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1224">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1234">4.21.1</a> <a class="idx" href="manipterm.html#idx:setarg3:1239">4.21.1</a> <a class="idx" href="gvar.html#idx:setarg3:1434">4.33.1</a> <a class="idx" href="dicts.html#idx:setarg3:1644">5.4.2.1</a> <a class="idx" href="attvar.html#idx:setarg3:1779">7.1</a> <a class="idx" href="attvar.html#idx:setarg3:1782">7.1.1</a> <a class="idx" href="record.html#idx:setarg3:2171">A.31</a></dd>
2388	2437	<dt><a class="idx" href="system.html#setenv/2">setenv/2</a></dt>
2389	2438	<dd>
2390	2439	<a class="idx" href="system.html#idx:setenv2:1452">4.35</a></dd>
2391	2440	<dt>setlocale/1</dt>
2392	2441	<dd>
2393		<a class="idx" href="threadcreate.html#idx:setlocale1:1848">9.1</a></dd>
	2442	<a class="idx" href="threadcreate.html#idx:setlocale1:1852">9.1</a></dd>
2394	2443	<dt><a class="idx" href="system.html#setlocale/3">setlocale/3</a></dt>
2395	2444	<dd>
2396	2445	<a class="idx" href="chartype.html#idx:setlocale3:1313">4.24.3</a> <a class="idx" href="system.html#idx:setlocale3:1455">4.35</a></dd>
2397	2446	<dt><a class="idx" href="allsolutions.html#setof/3">setof/3</a></dt>
2398	2447	<dd>
2399		<a class="idx" href="cyclic.html#idx:setof3:246">2.17</a> <a class="idx" href="metapred.html#idx:setof3:1693">6.4</a> <a class="idx" href="predsummary.html#idx:setof3:2348">F.1</a></dd>
	2448	<a class="idx" href="cyclic.html#idx:setof3:246">2.17</a> <a class="idx" href="metapred.html#idx:setof3:1697">6.4</a> <a class="idx" href="predsummary.html#idx:setof3:2352">F.1</a></dd>
2400	2449	<dt><a class="idx" href="random.html#setrand/1">setrand/1</a></dt>
2401	2450	<dt><a class="idx" href="metacall.html#setup_call_catcher_cleanup/4">setup_call_catcher_cleanup/4</a></dt>
2402	2451	<dt>setup_call_cleanup/2</dt>
2403	2452	<dd>
2404		<a class="idx" href="threadsync.html#idx:setupcallcleanup2:1923">9.4</a></dd>
	2453	<a class="idx" href="threadsync.html#idx:setupcallcleanup2:1927">9.4</a></dd>
2405	2454	<dt><a class="idx" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a></dt>
2406	2455	<dd>
2407		<a class="idx" href="metacall.html#idx:setupcallcleanup3:670">4.9</a> <a class="idx" href="metacall.html#idx:setupcallcleanup3:672">4.9</a> <a class="idx" href="metacall.html#idx:setupcallcleanup3:676">4.9</a> <a class="idx" href="exception.html#idx:setupcallcleanup3:711">4.11.1</a> <a class="idx" href="exception.html#idx:setupcallcleanup3:716">4.11.1</a> <a class="idx" href="exception.html#idx:setupcallcleanup3:719">4.11.1</a> <a class="idx" href="threadcreate.html#idx:setupcallcleanup3:1861">9.1</a> <a class="idx" href="threadsync.html#idx:setupcallcleanup3:1927">9.4</a> <a class="idx" href="threadsync.html#idx:setupcallcleanup3:1931">9.4</a> <a class="idx" href="threadsync.html#idx:setupcallcleanup3:1934">9.4</a></dd>
	2456	<a class="idx" href="metacall.html#idx:setupcallcleanup3:670">4.9</a> <a class="idx" href="metacall.html#idx:setupcallcleanup3:672">4.9</a> <a class="idx" href="metacall.html#idx:setupcallcleanup3:676">4.9</a> <a class="idx" href="exception.html#idx:setupcallcleanup3:711">4.11.1</a> <a class="idx" href="exception.html#idx:setupcallcleanup3:716">4.11.1</a> <a class="idx" href="exception.html#idx:setupcallcleanup3:719">4.11.1</a> <a class="idx" href="threadcreate.html#idx:setupcallcleanup3:1865">9.1</a> <a class="idx" href="threadsync.html#idx:setupcallcleanup3:1931">9.4</a> <a class="idx" href="threadsync.html#idx:setupcallcleanup3:1935">9.4</a> <a class="idx" href="threadsync.html#idx:setupcallcleanup3:1938">9.4</a></dd>
2408	2457	<dt><a class="idx" href="simplex.html#shadow_price/3">shadow_price/3</a></dt>
2409	2458	<dt>shared</dt>
2410	2459	<dd>
2411		<a class="idx" href="glossary.html#idx:shared:2329">D</a></dd>
	2460	<a class="idx" href="glossary.html#idx:shared:2333">D</a></dd>
2412	2461	<dt>shell/0</dt>
2413	2462	<dd>
2414	2463	<a class="idx" href="system.html#idx:shell0:1461">4.35</a></dd>

2427	2476	<dt><a class="idx" href="registry.html#shell_register_dde/6">shell_register_dde/6</a></dt>
2428	2477	<dt><a class="idx" href="registry.html#shell_register_file_type/4">shell_register_file_type/4</a></dt>
2429	2478	<dd>
2430		<a class="idx" href="registry.html#idx:shellregisterfiletype4:2170">A.32</a></dd>
	2479	<a class="idx" href="registry.html#idx:shellregisterfiletype4:2174">A.32</a></dd>
2431	2480	<dt><a class="idx" href="registry.html#shell_register_prolog/1">shell_register_prolog/1</a></dt>
2432	2481	<dt><a class="idx" href="delcont.html#shift/1">shift/1</a></dt>
2433	2482	<dd>

2437	2486	<a class="idx" href="profile.html#idx:showprofile1:1568">4.41.1</a> <a class="idx" href="profile.html#idx:showprofile1:1569">4.41.1</a></dd>
2438	2487	<dt>singleton</dt>
2439	2488	<dd>
2440		<a class="idx" href="glossary.html#idx:singleton:2330">D</a></dd>
	2489	<a class="idx" href="glossary.html#idx:singleton:2334">D</a></dd>
2441	2490	<dt>singleton,variable</dt>
2442	2491	<dd>
2443	2492	<a class="idx" href="syntax.html#idx:singletonvariable:222">2.16.1.9</a></dd>

2452	2501	<a class="idx" href="cmdline.html#idx:sleep1:29">2.4.2</a> <a class="idx" href="miscpreds.html#idx:sleep1:1587">4.44</a></dd>
2453	2502	<dt>solution</dt>
2454	2503	<dd>
2455		<a class="idx" href="glossary.html#idx:solution:2331">D</a></dd>
	2504	<a class="idx" href="glossary.html#idx:solution:2335">D</a></dd>
2456	2505	<dt><a class="idx" href="builtinlist.html#sort/2">sort/2</a></dt>
2457	2506	<dd>
2458	2507	<a class="idx" href="compare.html#idx:sort2:625">4.7.1</a> <a class="idx" href="metacall.html#idx:sort2:663">4.9</a> <a class="idx" href="builtinlist.html#idx:sort2:1348">4.29</a> <a class="idx" href="builtinlist.html#idx:sort2:1350">4.29</a> <a class="idx" href="builtinlist.html#idx:sort2:1355">4.29</a> <a class="idx" href="builtinlist.html#idx:sort2:1357">4.29</a> <a class="idx" href="builtinlist.html#idx:sort2:1359">4.29</a> <a class="idx" href="allsolutions.html#idx:sort2:1374">4.30</a></dd>
2459	2508	<dt><a class="idx" href="builtinlist.html#sort/4">sort/4</a></dt>
2460	2509	<dt><a class="idx" href="dialect.html#source_exports/2">source_exports/2</a></dt>
2461	2510	<dd>
2462		<a class="idx" href="dialect.html#idx:sourceexports2:2247">C</a></dd>
	2511	<a class="idx" href="dialect.html#idx:sourceexports2:2251">C</a></dd>
2463	2512	<dt><a class="idx" href="consulting.html#source_file/1">source_file/1</a></dt>
2464	2513	<dt><a class="idx" href="consulting.html#source_file/2">source_file/2</a></dt>
2465	2514	<dd>

2475	2524	<a class="idx" href="manipatom.html#idx:splitstring4:1277">4.22</a> <a class="idx" href="strings.html#idx:splitstring4:1606">5.2.1</a> <a class="idx" href="strings.html#idx:splitstring4:1608">5.2.1</a></dd>
2476	2525	<dt><a class="idx" href="debugger.html#spy/1">spy/1</a></dt>
2477	2526	<dd>
2478		<a class="idx" href="debugoverview.html#idx:spy1:56">2.9</a> <a class="idx" href="debugoverview.html#idx:spy1:61">2.9</a> <a class="idx" href="flags.html#idx:spy1:102">2.11</a> <a class="idx" href="flags.html#idx:spy1:115">2.11</a> <a class="idx" href="hooks.html#idx:spy1:182">2.12</a> <a class="idx" href="guitracer.html#idx:spy1:318">3.5.1</a> <a class="idx" href="guitracer.html#idx:spy1:320">3.5.1</a> <a class="idx" href="idesummary.html#idx:spy1:333">3.9</a> <a class="idx" href="preddesc.html#idx:spy1:338">4.1</a> <a class="idx" href="mtoplevel.html#idx:spy1:1705">6.6</a> <a class="idx" href="thutil.html#idx:spy1:1945">9.5.1</a> <a class="idx" href="thutil.html#idx:spy1:1947">9.5.1</a> <a class="idx" href="intlibs.html#idx:spy1:2221">B.7</a> <a class="idx" href="intlibs.html#idx:spy1:2222">B.7</a> <a class="idx" href="intlibs.html#idx:spy1:2225">B.7</a> <a class="idx" href="predsummary.html#idx:spy1:2354">F.1</a></dd>
	2527	<a class="idx" href="debugoverview.html#idx:spy1:56">2.9</a> <a class="idx" href="debugoverview.html#idx:spy1:61">2.9</a> <a class="idx" href="flags.html#idx:spy1:102">2.11</a> <a class="idx" href="flags.html#idx:spy1:115">2.11</a> <a class="idx" href="hooks.html#idx:spy1:182">2.12</a> <a class="idx" href="guitracer.html#idx:spy1:318">3.5.1</a> <a class="idx" href="guitracer.html#idx:spy1:320">3.5.1</a> <a class="idx" href="idesummary.html#idx:spy1:333">3.9</a> <a class="idx" href="preddesc.html#idx:spy1:338">4.1</a> <a class="idx" href="mtoplevel.html#idx:spy1:1709">6.6</a> <a class="idx" href="thutil.html#idx:spy1:1949">9.5.1</a> <a class="idx" href="thutil.html#idx:spy1:1951">9.5.1</a> <a class="idx" href="intlibs.html#idx:spy1:2225">B.7</a> <a class="idx" href="intlibs.html#idx:spy1:2226">B.7</a> <a class="idx" href="intlibs.html#idx:spy1:2229">B.7</a> <a class="idx" href="predsummary.html#idx:spy1:2358">F.1</a></dd>
2479	2528	<dt>stack,memory management</dt>
2480	2529	<dd>
2481	2530	<a class="idx" href="limits.html#idx:stackmemorymanagement:281">2.20.1.1</a></dd>

2490	2539	<a class="idx" href="exception.html#idx:statistics0:737">4.11.4</a></dd>
2491	2540	<dt><a class="idx" href="statistics.html#statistics/2">statistics/2</a></dt>
2492	2541	<dd>
2493		<a class="idx" href="arith.html#idx:statistics2:1338">4.27.2.3</a> <a class="idx" href="statistics.html#idx:statistics2:1562">4.40</a> <a class="idx" href="statistics.html#idx:statistics2:1564">4.40</a> <a class="idx" href="thmonitor.html#idx:statistics2:1880">9.2</a> <a class="idx" href="thmonitor.html#idx:statistics2:1881">9.2</a></dd>
	2542	<a class="idx" href="arith.html#idx:statistics2:1338">4.27.2.3</a> <a class="idx" href="statistics.html#idx:statistics2:1562">4.40</a> <a class="idx" href="statistics.html#idx:statistics2:1564">4.40</a> <a class="idx" href="thmonitor.html#idx:statistics2:1884">9.2</a> <a class="idx" href="thmonitor.html#idx:statistics2:1885">9.2</a></dd>
2494	2543	<dt><a class="idx" href="IO.html#stream_pair/3">stream_pair/3</a></dt>
2495	2544	<dd>
2496	2545	<a class="idx" href="IO.html#idx:streampair3:968">4.17.2</a> <a class="idx" href="IO.html#idx:streampair3:981">4.17.2</a> <a class="idx" href="IO.html#idx:streampair3:1013">4.17.2</a></dd>
2497	2546	<dt><a class="idx" href="IO.html#stream_position_data/3">stream_position_data/3</a></dt>
2498	2547	<dd>
2499		<a class="idx" href="consulting.html#idx:streampositiondata3:491">4.3</a> <a class="idx" href="IO.html#idx:streampositiondata3:988">4.17.2</a> <a class="idx" href="termrw.html#idx:streampositiondata3:1169">4.20</a> <a class="idx" href="loadfilehook.html#idx:streampositiondata3:2241">B.8</a></dd>
	2548	<a class="idx" href="consulting.html#idx:streampositiondata3:491">4.3</a> <a class="idx" href="IO.html#idx:streampositiondata3:988">4.17.2</a> <a class="idx" href="termrw.html#idx:streampositiondata3:1169">4.20</a> <a class="idx" href="loadfilehook.html#idx:streampositiondata3:2245">B.8</a></dd>
2500	2549	<dt><a class="idx" href="IO.html#stream_property/2">stream_property/2</a></dt>
2501	2550	<dd>
2502	2551	<a class="idx" href="widechars.html#idx:streamproperty2:276">2.19.1.1</a> <a class="idx" href="consulting.html#idx:streamproperty2:490">4.3</a> <a class="idx" href="IO.html#idx:streamproperty2:974">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:996">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:998">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:1005">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:1011">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:1014">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:1019">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:1021">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:1022">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:1028">4.17.2</a> <a class="idx" href="IO.html#idx:streamproperty2:1029">4.17.2</a> <a class="idx" href="termrw.html#idx:streamproperty2:1179">4.20</a></dd>

2520	2569	<dt><a class="idx" href="strings.html#string_upper/2">string_upper/2</a></dt>
2521	2570	<dt><a class="idx" href="ctxmodule.html#strip_module/3">strip_module/3</a></dt>
2522	2571	<dd>
2523		<a class="idx" href="metapred.html#idx:stripmodule3:1701">6.4</a> <a class="idx" href="ctxmodule.html#idx:stripmodule3:1743">6.13</a> <a class="idx" href="modulecompat.html#idx:stripmodule3:1753">6.15</a></dd>
	2572	<a class="idx" href="metapred.html#idx:stripmodule3:1705">6.4</a> <a class="idx" href="ctxmodule.html#idx:stripmodule3:1747">6.13</a> <a class="idx" href="modulecompat.html#idx:stripmodule3:1757">6.15</a></dd>
2524	2573	<dt>structure</dt>
2525	2574	<dd>
2526		<a class="idx" href="glossary.html#idx:structure:2332">D</a></dd>
	2575	<a class="idx" href="glossary.html#idx:structure:2336">D</a></dd>
2527	2576	<dt><a class="idx" href="debugger.html#style_check/1">style_check/1</a></dt>
2528	2577	<dd>
2529	2578	<a class="idx" href="syntax.html#idx:stylecheck1:224">2.16.1.9</a> <a class="idx" href="syntax.html#idx:stylecheck1:225">2.16.1.9</a> <a class="idx" href="consulting.html#idx:stylecheck1:420">4.3</a> <a class="idx" href="dynamic.html#idx:stylecheck1:889">4.15</a></dd>

2547	2596	<a class="idx" href="arith.html#idx:succ2:1322">4.27.1</a></dd>
2548	2597	<dt>succeed</dt>
2549	2598	<dd>
2550		<a class="idx" href="glossary.html#idx:succeed:2333">D</a></dd>
	2599	<a class="idx" href="glossary.html#idx:succeed:2337">D</a></dd>
2551	2600	<dt><a class="idx" href="clpfd.html#sum/3">sum/3</a></dt>
2552	2601	<dt><a class="idx" href="lists.html#sum_list/2">sum_list/2</a></dt>
2553	2602	<dt><a class="idx" href="clpqr.html#sup/2">sup/2</a></dt>

2555	2604	<dt><a class="idx" href="format.html#swritef/3">swritef/3</a></dt>
2556	2605	<dd>
2557	2606	<a class="idx" href="IO.html#idx:swritef3:1051">4.17.5</a> <a class="idx" href="format.html#idx:swritef3:1385">4.32</a></dd>
	2607	<dt><a class="idx" href="pio.html#syntax_error//1">syntax_error//1</a></dt>
2558	2608	<dt><a class="idx" href="error.html#syntax_error/1">syntax_error/1</a></dt>
2559	2609	<dt><a class="idx" href="chario.html#tab/1">tab/1</a></dt>
2560	2610	<dt><a class="idx" href="chario.html#tab/2">tab/2</a></dt>
2561	2611	<dt><a class="idx" href="tabling.html#table/1">table/1</a></dt>
2562	2612	<dd>
2563		<a class="idx" href="flags.html#idx:table1:136">2.11</a> <a class="idx" href="tabling.html#idx:table1:2172">A.35</a> <a class="idx" href="tabling.html#idx:table1:2173">A.35.2</a> <a class="idx" href="tabling.html#idx:table1:2175">A.35.1.1</a></dd>
	2613	<a class="idx" href="flags.html#idx:table1:136">2.11</a> <a class="idx" href="tabling.html#idx:table1:2176">A.35</a> <a class="idx" href="tabling.html#idx:table1:2177">A.35.2</a> <a class="idx" href="tabling.html#idx:table1:2179">A.35.1.1</a></dd>
2564	2614	<dt><a class="idx" href="clpb.html#taut/2">taut/2</a></dt>
2565	2615	<dt><a class="idx" href="thutil.html#tdebug/0">tdebug/0</a></dt>
2566	2616	<dd>
2567		<a class="idx" href="threadcreate.html#idx:tdebug0:1837">9.1</a> <a class="idx" href="thutil.html#idx:tdebug0:1948">9.5.1</a></dd>
	2617	<a class="idx" href="threadcreate.html#idx:tdebug0:1841">9.1</a> <a class="idx" href="thutil.html#idx:tdebug0:1952">9.5.1</a></dd>
2568	2618	<dt><a class="idx" href="thutil.html#tdebug/1">tdebug/1</a></dt>
2569	2619	<dd>
2570		<a class="idx" href="thutil.html#idx:tdebug1:1944">9.5.1</a> <a class="idx" href="thutil.html#idx:tdebug1:1946">9.5.1</a></dd>
	2620	<a class="idx" href="thutil.html#idx:tdebug1:1948">9.5.1</a> <a class="idx" href="thutil.html#idx:tdebug1:1950">9.5.1</a></dd>
2571	2621	<dt><a class="idx" href="IO.html#tell/1">tell/1</a></dt>
2572	2622	<dd>
2573	2623	<a class="idx" href="IO.html#idx:tell1:949">4.17</a> <a class="idx" href="IO.html#idx:tell1:957">4.17.1</a> <a class="idx" href="IO.html#idx:tell1:1032">4.17.3</a> <a class="idx" href="IO.html#idx:tell1:1037">4.17.3</a> <a class="idx" href="IO.html#idx:tell1:1040">4.17.3</a> <a class="idx" href="IO.html#idx:tell1:1042">4.17.3</a> <a class="idx" href="IO.html#idx:tell1:1046">4.17.3</a></dd>

2576	2626	<a class="idx" href="IO.html#idx:telling1:1035">4.17.3</a> <a class="idx" href="IO.html#idx:telling1:1038">4.17.3</a> <a class="idx" href="files.html#idx:telling1:1521">4.36</a></dd>
2577	2627	<dt>term</dt>
2578	2628	<dd>
2579		<a class="idx" href="glossary.html#idx:term:2334">D</a></dd>
	2629	<a class="idx" href="glossary.html#idx:term:2338">D</a></dd>
2580	2630	<dt>term//1</dt>
2581	2631	<dd>
2582	2632	<a class="idx" href="IO.html#idx:term1:1055">4.17.5</a></dd>
2583	2633	<dt><a class="idx" href="attvar.html#term_attvars/2">term_attvars/2</a></dt>
2584	2634	<dd>
2585		<a class="idx" href="attvar.html#idx:termattvars2:1788">7.1.3</a></dd>
	2635	<a class="idx" href="attvar.html#idx:termattvars2:1792">7.1.3</a></dd>
2586	2636	<dt><a class="idx" href="consulting.html#term_expansion/2">term_expansion/2</a></dt>
2587	2637	<dd>
2588		<a class="idx" href="flags.html#idx:termexpansion2:163">2.11</a> <a class="idx" href="hooks.html#idx:termexpansion2:174">2.12</a> <a class="idx" href="consulting.html#idx:termexpansion2:367">4.3</a> <a class="idx" href="consulting.html#idx:termexpansion2:373">4.3</a> <a class="idx" href="consulting.html#idx:termexpansion2:484">4.3</a> <a class="idx" href="consulting.html#idx:termexpansion2:514">4.3</a> <a class="idx" href="consulting.html#idx:termexpansion2:516">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:518">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:523">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:525">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:529">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:532">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:553">4.3.1.2</a> <a class="idx" href="consulting.html#idx:termexpansion2:562">4.3.2</a> <a class="idx" href="consulting.html#idx:termexpansion2:580">4.3.3</a> <a class="idx" href="toplevel.html#idx:termexpansion2:1537">4.37</a> <a class="idx" href="practical.html#idx:termexpansion2:1813">8.3.3</a> <a class="idx" href="portabilitystrategies.html#idx:termexpansion2:2257">C.1</a></dd>
	2638	<a class="idx" href="flags.html#idx:termexpansion2:163">2.11</a> <a class="idx" href="hooks.html#idx:termexpansion2:174">2.12</a> <a class="idx" href="consulting.html#idx:termexpansion2:367">4.3</a> <a class="idx" href="consulting.html#idx:termexpansion2:373">4.3</a> <a class="idx" href="consulting.html#idx:termexpansion2:484">4.3</a> <a class="idx" href="consulting.html#idx:termexpansion2:514">4.3</a> <a class="idx" href="consulting.html#idx:termexpansion2:516">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:518">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:523">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:525">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:529">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:532">4.3.1</a> <a class="idx" href="consulting.html#idx:termexpansion2:553">4.3.1.2</a> <a class="idx" href="consulting.html#idx:termexpansion2:562">4.3.2</a> <a class="idx" href="consulting.html#idx:termexpansion2:580">4.3.3</a> <a class="idx" href="toplevel.html#idx:termexpansion2:1537">4.37</a> <a class="idx" href="practical.html#idx:termexpansion2:1817">8.3.3</a> <a class="idx" href="portabilitystrategies.html#idx:termexpansion2:2261">C.1</a></dd>
2589	2639	<dt><a class="idx" href="consulting.html#term_expansion/4">term_expansion/4</a></dt>
2590	2640	<dd>
2591	2641	<a class="idx" href="consulting.html#idx:termexpansion4:368">4.3</a></dd>

2606	2656	<dt><a class="idx" href="compare.html#term_subsumer/3">term_subsumer/3</a></dt>
2607	2657	<dt><a class="idx" href="manipatom.html#term_to_atom/2">term_to_atom/2</a></dt>
2608	2658	<dd>
2609		<a class="idx" href="IO.html#idx:termtoatom2:1052">4.17.5</a> <a class="idx" href="foreigninclude.html#idx:termtoatom2:2027">11.4.5</a></dd>
	2659	<a class="idx" href="IO.html#idx:termtoatom2:1052">4.17.5</a> <a class="idx" href="foreigninclude.html#idx:termtoatom2:2031">11.4.5</a></dd>
2610	2660	<dt><a class="idx" href="manipterm.html#term_variables/2">term_variables/2</a></dt>
2611	2661	<dd>
2612	2662	<a class="idx" href="cyclic.html#idx:termvariables2:248">2.17</a> <a class="idx" href="typetest.html#idx:termvariables2:619">4.6</a> <a class="idx" href="termrw.html#idx:termvariables2:1180">4.20</a> <a class="idx" href="manipterm.html#idx:termvariables2:1207">4.21</a> <a class="idx" href="manipterm.html#idx:termvariables2:1212">4.21</a> <a class="idx" href="manipterm.html#idx:termvariables2:1213">4.21</a></dd>

2619	2669	<dt><a class="idx" href="strings.html#text_to_string/2">text_to_string/2</a></dt>
2620	2670	<dt><a class="idx" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a></dt>
2621	2671	<dd>
2622		<a class="idx" href="toplevel.html#idx:threadatexit1:1532">4.37</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1832">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1833">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1834">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1835">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1868">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1869">9.1</a> <a class="idx" href="foreignthread.html#idx:threadatexit1:1954">9.6.1</a></dd>
	2672	<a class="idx" href="toplevel.html#idx:threadatexit1:1532">4.37</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1836">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1837">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1838">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1839">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1872">9.1</a> <a class="idx" href="threadcreate.html#idx:threadatexit1:1873">9.1</a> <a class="idx" href="foreignthread.html#idx:threadatexit1:1958">9.6.1</a></dd>
2623	2673	<dt><a class="idx" href="threadcreate.html#thread_create/2">thread_create/2</a></dt>
2624	2674	<dt><a class="idx" href="threadcreate.html#thread_create/3">thread_create/3</a></dt>
2625	2675	<dd>
2626		<a class="idx" href="threadcreate.html#idx:threadcreate3:1827">9.1</a> <a class="idx" href="threadcreate.html#idx:threadcreate3:1856">9.1</a> <a class="idx" href="threadcreate.html#idx:threadcreate3:1870">9.1</a> <a class="idx" href="mt-xpce.html#idx:threadcreate3:1962">9.7</a> <a class="idx" href="engine-predicates.html#idx:threadcreate3:1992">10.3</a></dd>
	2676	<a class="idx" href="threadcreate.html#idx:threadcreate3:1831">9.1</a> <a class="idx" href="threadcreate.html#idx:threadcreate3:1860">9.1</a> <a class="idx" href="threadcreate.html#idx:threadcreate3:1874">9.1</a> <a class="idx" href="mt-xpce.html#idx:threadcreate3:1966">9.7</a> <a class="idx" href="engine-predicates.html#idx:threadcreate3:1996">10.3</a></dd>
2627	2677	<dt><a class="idx" href="threadpool.html#thread_create_in_pool/4">thread_create_in_pool/4</a></dt>
2628	2678	<dd>
2629		<a class="idx" href="threadcreate.html#idx:threadcreateinpool4:1845">9.1</a></dd>
	2679	<a class="idx" href="threadcreate.html#idx:threadcreateinpool4:1849">9.1</a></dd>
2630	2680	<dt><a class="idx" href="threadcreate.html#thread_detach/1">thread_detach/1</a></dt>
2631	2681	<dd>
2632		<a class="idx" href="threadcreate.html#idx:threaddetach1:1829">9.1</a> <a class="idx" href="threadcreate.html#idx:threaddetach1:1841">9.1</a></dd>
	2682	<a class="idx" href="threadcreate.html#idx:threaddetach1:1833">9.1</a> <a class="idx" href="threadcreate.html#idx:threaddetach1:1845">9.1</a></dd>
2633	2683	<dt><a class="idx" href="threadcreate.html#thread_exit/1">thread_exit/1</a></dt>
2634	2684	<dd>
2635		<a class="idx" href="threadcreate.html#idx:threadexit1:1855">9.1</a> <a class="idx" href="thmonitor.html#idx:threadexit1:1875">9.2</a> <a class="idx" href="threadsync.html#idx:threadexit1:1935">9.4</a></dd>
	2685	<a class="idx" href="threadcreate.html#idx:threadexit1:1859">9.1</a> <a class="idx" href="thmonitor.html#idx:threadexit1:1879">9.2</a> <a class="idx" href="threadsync.html#idx:threadexit1:1939">9.4</a></dd>
2636	2686	<dt><a class="idx" href="threadcom.html#thread_get_message/1">thread_get_message/1</a></dt>
2637	2687	<dd>
2638		<a class="idx" href="threadcom.html#idx:threadgetmessage1:1899">9.3.1</a> <a class="idx" href="engine-examples.html#idx:threadgetmessage1:1980">10.1.3</a></dd>
	2688	<a class="idx" href="threadcom.html#idx:threadgetmessage1:1903">9.3.1</a> <a class="idx" href="engine-examples.html#idx:threadgetmessage1:1984">10.1.3</a></dd>
2639	2689	<dt><a class="idx" href="threadcom.html#thread_get_message/2">thread_get_message/2</a></dt>
2640	2690	<dd>
2641		<a class="idx" href="threadcom.html#idx:threadgetmessage2:1898">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage2:1901">9.3.1</a></dd>
	2691	<a class="idx" href="threadcom.html#idx:threadgetmessage2:1902">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage2:1905">9.3.1</a></dd>
2642	2692	<dt><a class="idx" href="threadcom.html#thread_get_message/3">thread_get_message/3</a></dt>
2643	2693	<dd>
2644		<a class="idx" href="threadcom.html#idx:threadgetmessage3:1887">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage3:1894">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage3:1903">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage3:1904">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage3:1906">9.3.1</a></dd>
	2694	<a class="idx" href="threadcom.html#idx:threadgetmessage3:1891">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage3:1898">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage3:1907">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage3:1908">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadgetmessage3:1910">9.3.1</a></dd>
2645	2695	<dt><a class="idx" href="threadcreate.html#thread_initialization/1">thread_initialization/1</a></dt>
2646	2696	<dd>
2647	2697	<a class="idx" href="gvar.html#idx:threadinitialization1:1418">4.33</a></dd>
2648	2698	<dt><a class="idx" href="threadcreate.html#thread_join/2">thread_join/2</a></dt>
2649	2699	<dd>
2650		<a class="idx" href="threadcreate.html#idx:threadjoin2:1828">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1831">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1838">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1839">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1840">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1850">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1852">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1853">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1859">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1860">9.1</a> <a class="idx" href="thmonitor.html#idx:threadjoin2:1874">9.2</a></dd>
	2700	<a class="idx" href="threadcreate.html#idx:threadjoin2:1832">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1835">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1842">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1843">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1844">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1854">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1856">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1857">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1863">9.1</a> <a class="idx" href="threadcreate.html#idx:threadjoin2:1864">9.1</a> <a class="idx" href="thmonitor.html#idx:threadjoin2:1878">9.2</a></dd>
2651	2701	<dt><a class="idx" href="threadcom.html#thread_local/1">thread_local/1</a></dt>
2652	2702	<dd>
2653		<a class="idx" href="exception.html#idx:threadlocal1:758">4.11.4</a> <a class="idx" href="db.html#idx:threadlocal1:802">4.14</a> <a class="idx" href="dynamic.html#idx:threadlocal1:882">4.15</a> <a class="idx" href="examineprog.html#idx:threadlocal1:928">4.16</a> <a class="idx" href="toplevel.html#idx:threadlocal1:1526">4.37</a> <a class="idx" href="threadcom.html#idx:threadlocal1:1915">9.3.3</a> <a class="idx" href="engine-examples.html#idx:threadlocal1:1975">10.1.2</a></dd>
	2703	<a class="idx" href="exception.html#idx:threadlocal1:758">4.11.4</a> <a class="idx" href="db.html#idx:threadlocal1:802">4.14</a> <a class="idx" href="dynamic.html#idx:threadlocal1:882">4.15</a> <a class="idx" href="examineprog.html#idx:threadlocal1:928">4.16</a> <a class="idx" href="toplevel.html#idx:threadlocal1:1526">4.37</a> <a class="idx" href="threadcom.html#idx:threadlocal1:1919">9.3.3</a> <a class="idx" href="engine-examples.html#idx:threadlocal1:1979">10.1.2</a></dd>
2654	2704	<dt><a class="idx" href="exception.html#thread_message_hook/3">thread_message_hook/3</a></dt>
2655	2705	<dt><a class="idx" href="threadcom.html#thread_peek_message/1">thread_peek_message/1</a></dt>
2656	2706	<dd>
2657		<a class="idx" href="threadcom.html#idx:threadpeekmessage1:1892">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadpeekmessage1:1893">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadpeekmessage1:1907">9.3.1</a></dd>
	2707	<a class="idx" href="threadcom.html#idx:threadpeekmessage1:1896">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadpeekmessage1:1897">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadpeekmessage1:1911">9.3.1</a></dd>
2658	2708	<dt><a class="idx" href="threadcom.html#thread_peek_message/2">thread_peek_message/2</a></dt>
2659	2709	<dd>
2660		<a class="idx" href="threadcom.html#idx:threadpeekmessage2:1905">9.3.1</a></dd>
	2710	<a class="idx" href="threadcom.html#idx:threadpeekmessage2:1909">9.3.1</a></dd>
2661	2711	<dt><a class="idx" href="threadpool.html#thread_pool_create/3">thread_pool_create/3</a></dt>
2662	2712	<dt><a class="idx" href="threadpool.html#thread_pool_destroy/1">thread_pool_destroy/1</a></dt>
2663	2713	<dt><a class="idx" href="threadpool.html#thread_pool_property/2">thread_pool_property/2</a></dt>
2664	2714	<dt><a class="idx" href="thmonitor.html#thread_property/2">thread_property/2</a></dt>
2665	2715	<dd>
2666		<a class="idx" href="threadcreate.html#idx:threadproperty2:1830">9.1</a> <a class="idx" href="threadcreate.html#idx:threadproperty2:1851">9.1</a> <a class="idx" href="threadcreate.html#idx:threadproperty2:1858">9.1</a> <a class="idx" href="threadcreate.html#idx:threadproperty2:1866">9.1</a> <a class="idx" href="thmonitor.html#idx:threadproperty2:1873">9.2</a></dd>
	2716	<a class="idx" href="threadcreate.html#idx:threadproperty2:1834">9.1</a> <a class="idx" href="threadcreate.html#idx:threadproperty2:1855">9.1</a> <a class="idx" href="threadcreate.html#idx:threadproperty2:1862">9.1</a> <a class="idx" href="threadcreate.html#idx:threadproperty2:1870">9.1</a> <a class="idx" href="thmonitor.html#idx:threadproperty2:1877">9.2</a></dd>
2667	2717	<dt><a class="idx" href="threadcreate.html#thread_self/1">thread_self/1</a></dt>
2668	2718	<dd>
2669		<a class="idx" href="flags.html#idx:threadself1:135">2.11</a> <a class="idx" href="threadcreate.html#idx:threadself1:1857">9.1</a> <a class="idx" href="threadcreate.html#idx:threadself1:1867">9.1</a> <a class="idx" href="threadcom.html#idx:threadself1:1883">9.3.1</a></dd>
	2719	<a class="idx" href="flags.html#idx:threadself1:135">2.11</a> <a class="idx" href="threadcreate.html#idx:threadself1:1861">9.1</a> <a class="idx" href="threadcreate.html#idx:threadself1:1871">9.1</a> <a class="idx" href="threadcom.html#idx:threadself1:1887">9.3.1</a></dd>
2670	2720	<dt><a class="idx" href="threadcom.html#thread_send_message/2">thread_send_message/2</a></dt>
2671	2721	<dd>
2672		<a class="idx" href="threadcom.html#idx:threadsendmessage2:1884">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage2:1885">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage2:1896">9.3.1</a> <a class="idx" href="engine-examples.html#idx:threadsendmessage2:1979">10.1.3</a></dd>
	2722	<a class="idx" href="threadcom.html#idx:threadsendmessage2:1888">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage2:1889">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage2:1900">9.3.1</a> <a class="idx" href="engine-examples.html#idx:threadsendmessage2:1983">10.1.3</a></dd>
2673	2723	<dt><a class="idx" href="threadcom.html#thread_send_message/3">thread_send_message/3</a></dt>
2674	2724	<dd>
2675		<a class="idx" href="threadcom.html#idx:threadsendmessage3:1886">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage3:1889">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage3:1890">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage3:1891">9.3.1</a></dd>
	2725	<a class="idx" href="threadcom.html#idx:threadsendmessage3:1890">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage3:1893">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage3:1894">9.3.1</a> <a class="idx" href="threadcom.html#idx:threadsendmessage3:1895">9.3.1</a></dd>
2676	2726	<dt><a class="idx" href="threadcreate.html#thread_setconcurrency/2">thread_setconcurrency/2</a></dt>
2677	2727	<dd>
2678	2728	<a class="idx" href="flags.html#idx:threadsetconcurrency2:100">2.11</a></dd>
2679	2729	<dt><a class="idx" href="threadcom.html#thread_signal/2">thread_signal/2</a></dt>
2680	2730	<dd>
2681		<a class="idx" href="cmdline.html#idx:threadsignal2:28">2.4.2</a> <a class="idx" href="metacall.html#idx:threadsignal2:667">4.9</a> <a class="idx" href="threadcom.html#idx:threadsignal2:1911">9.3.2</a> <a class="idx" href="thutil.html#idx:threadsignal2:1943">9.5.1</a> <a class="idx" href="foreigninclude.html#idx:threadsignal2:2050">11.4.13</a> <a class="idx" href="foreigninclude.html#idx:threadsignal2:2086">11.4.21.1</a></dd>
	2731	<a class="idx" href="cmdline.html#idx:threadsignal2:28">2.4.2</a> <a class="idx" href="metacall.html#idx:threadsignal2:667">4.9</a> <a class="idx" href="threadcom.html#idx:threadsignal2:1915">9.3.2</a> <a class="idx" href="thutil.html#idx:threadsignal2:1947">9.5.1</a> <a class="idx" href="foreigninclude.html#idx:threadsignal2:2054">11.4.13</a> <a class="idx" href="foreigninclude.html#idx:threadsignal2:2090">11.4.21.1</a></dd>
2682	2732	<dt><a class="idx" href="thmonitor.html#thread_statistics/3">thread_statistics/3</a></dt>
2683	2733	<dd>
2684		<a class="idx" href="thmonitor.html#idx:threadstatistics3:1878">9.2</a></dd>
	2734	<a class="idx" href="thmonitor.html#idx:threadstatistics3:1882">9.2</a></dd>
2685	2735	<dt><a class="idx" href="thutil.html#threads/0">threads/0</a></dt>
2686	2736	<dt><a class="idx" href="exception.html#throw/1">throw/1</a></dt>
2687	2737	<dd>
2688		<a class="idx" href="debugoverview.html#idx:throw1:54">2.9</a> <a class="idx" href="cyclic.html#idx:throw1:249">2.17</a> <a class="idx" href="delcont.html#idx:throw1:688">4.10</a> <a class="idx" href="exception.html#idx:throw1:692">4.11</a> <a class="idx" href="exception.html#idx:throw1:694">4.11</a> <a class="idx" href="exception.html#idx:throw1:695">4.11</a> <a class="idx" href="exception.html#idx:throw1:704">4.11</a> <a class="idx" href="exception.html#idx:throw1:709">4.11</a> <a class="idx" href="exception.html#idx:throw1:768">4.11.4.1</a> <a class="idx" href="signal.html#idx:throw1:776">4.12.1</a> <a class="idx" href="threadcreate.html#idx:throw1:1862">9.1</a> <a class="idx" href="thmonitor.html#idx:throw1:1876">9.2</a> <a class="idx" href="threadcom.html#idx:throw1:1910">9.3.2</a> <a class="idx" href="threadcom.html#idx:throw1:1912">9.3.2</a> <a class="idx" href="foreigninclude.html#idx:throw1:2048">11.4.12</a> <a class="idx" href="foreigninclude.html#idx:throw1:2049">11.4.12</a> <a class="idx" href="excepthook.html#idx:throw1:2205">B.5</a> <a class="idx" href="exception3.html#idx:throw1:2213">B.6</a> <a class="idx" href="exception3.html#idx:throw1:2216">B.6</a></dd>
	2738	<a class="idx" href="debugoverview.html#idx:throw1:54">2.9</a> <a class="idx" href="cyclic.html#idx:throw1:249">2.17</a> <a class="idx" href="delcont.html#idx:throw1:688">4.10</a> <a class="idx" href="exception.html#idx:throw1:692">4.11</a> <a class="idx" href="exception.html#idx:throw1:694">4.11</a> <a class="idx" href="exception.html#idx:throw1:695">4.11</a> <a class="idx" href="exception.html#idx:throw1:704">4.11</a> <a class="idx" href="exception.html#idx:throw1:709">4.11</a> <a class="idx" href="exception.html#idx:throw1:768">4.11.4.1</a> <a class="idx" href="signal.html#idx:throw1:776">4.12.1</a> <a class="idx" href="threadcreate.html#idx:throw1:1866">9.1</a> <a class="idx" href="thmonitor.html#idx:throw1:1880">9.2</a> <a class="idx" href="threadcom.html#idx:throw1:1914">9.3.2</a> <a class="idx" href="threadcom.html#idx:throw1:1916">9.3.2</a> <a class="idx" href="foreigninclude.html#idx:throw1:2052">11.4.12</a> <a class="idx" href="foreigninclude.html#idx:throw1:2053">11.4.12</a> <a class="idx" href="excepthook.html#idx:throw1:2209">B.5</a> <a class="idx" href="exception3.html#idx:throw1:2217">B.6</a> <a class="idx" href="exception3.html#idx:throw1:2220">B.6</a></dd>
2689	2739	<dt><a class="idx" href="statistics.html#time/1">time/1</a></dt>
2690	2740	<dd>
2691	2741	<a class="idx" href="arith.html#idx:time1:1339">4.27.2.3</a></dd>

2699	2749	<dt><a class="idx" href="thutil.html#tnodebug/0">tnodebug/0</a></dt>
2700	2750	<dt><a class="idx" href="thutil.html#tnodebug/1">tnodebug/1</a></dt>
2701	2751	<dd>
2702		<a class="idx" href="thutil.html#idx:tnodebug1:1950">9.5.1</a></dd>
	2752	<a class="idx" href="thutil.html#idx:tnodebug1:1954">9.5.1</a></dd>
2703	2753	<dt><a class="idx" href="IO.html#told/0">told/0</a></dt>
2704	2754	<dt><a class="idx" href="ugraphs.html#top_sort/2">top_sort/2</a></dt>
2705	2755	<dt><a class="idx" href="ugraphs.html#top_sort/3">top_sort/3</a></dt>
2706	2756	<dt><a class="idx" href="thutil.html#tprofile/1">tprofile/1</a></dt>
2707	2757	<dd>
2708		<a class="idx" href="thutil.html#idx:tprofile1:1952">9.5.2</a></dd>
	2758	<a class="idx" href="thutil.html#idx:tprofile1:1956">9.5.2</a></dd>
2709	2759	<dt><a class="idx" href="debugger.html#trace/0">trace/0</a></dt>
2710	2760	<dd>
2711		<a class="idx" href="debugoverview.html#idx:trace0:55">2.9</a> <a class="idx" href="debugoverview.html#idx:trace0:58">2.9</a> <a class="idx" href="flags.html#idx:trace0:114">2.11</a> <a class="idx" href="flags.html#idx:trace0:145">2.11</a> <a class="idx" href="guitracer.html#idx:trace0:317">3.5.1</a> <a class="idx" href="guitracer.html#idx:trace0:319">3.5.1</a> <a class="idx" href="idesummary.html#idx:trace0:332">3.9</a> <a class="idx" href="debugger.html#idx:trace0:1542">4.39</a> <a class="idx" href="debugger.html#idx:trace0:1543">4.39</a> <a class="idx" href="debugger.html#idx:trace0:1549">4.39</a> <a class="idx" href="debugger.html#idx:trace0:1550">4.39</a> <a class="idx" href="debugging.html#idx:trace0:1818">8.4.3</a> <a class="idx" href="debugging.html#idx:trace0:1820">8.4.3</a> <a class="idx" href="threadcom.html#idx:trace0:1913">9.3.2</a> <a class="idx" href="foreigninclude.html#idx:trace0:2061">11.4.16</a> <a class="idx" href="breakpoint.html#idx:trace0:2201">B.4</a> <a class="idx" href="excepthook.html#idx:trace0:2209">B.5</a></dd>
	2761	<a class="idx" href="debugoverview.html#idx:trace0:55">2.9</a> <a class="idx" href="debugoverview.html#idx:trace0:58">2.9</a> <a class="idx" href="flags.html#idx:trace0:114">2.11</a> <a class="idx" href="flags.html#idx:trace0:145">2.11</a> <a class="idx" href="guitracer.html#idx:trace0:317">3.5.1</a> <a class="idx" href="guitracer.html#idx:trace0:319">3.5.1</a> <a class="idx" href="idesummary.html#idx:trace0:332">3.9</a> <a class="idx" href="debugger.html#idx:trace0:1542">4.39</a> <a class="idx" href="debugger.html#idx:trace0:1543">4.39</a> <a class="idx" href="debugger.html#idx:trace0:1549">4.39</a> <a class="idx" href="debugger.html#idx:trace0:1550">4.39</a> <a class="idx" href="debugging.html#idx:trace0:1822">8.4.3</a> <a class="idx" href="debugging.html#idx:trace0:1824">8.4.3</a> <a class="idx" href="threadcom.html#idx:trace0:1917">9.3.2</a> <a class="idx" href="foreigninclude.html#idx:trace0:2065">11.4.16</a> <a class="idx" href="breakpoint.html#idx:trace0:2205">B.4</a> <a class="idx" href="excepthook.html#idx:trace0:2213">B.5</a></dd>
2712	2762	<dt><a class="idx" href="debugger.html#trace/1">trace/1</a></dt>
2713	2763	<dd>
2714	2764	<a class="idx" href="flags.html#idx:trace1:103">2.11</a></dd>

2724	2774	<dt><a class="idx" href="ugraphs.html#transitive_closure/2">transitive_closure/2</a></dt>
2725	2775	<dt>transparent</dt>
2726	2776	<dd>
2727		<a class="idx" href="glossary.html#idx:transparent:2310">D</a></dd>
	2777	<a class="idx" href="glossary.html#idx:transparent:2314">D</a></dd>
2728	2778	<dt><a class="idx" href="simplex.html#transportation/4">transportation/4</a></dt>
2729	2779	<dt><a class="idx" href="pairs.html#transpose_pairs/2">transpose_pairs/2</a></dt>
2730	2780	<dt><a class="idx" href="ugraphs.html#transpose_ugraph/2">transpose_ugraph/2</a></dt>

2747	2797	<dt><a class="idx" href="db.html#trie_update/3">trie_update/3</a></dt>
2748	2798	<dt><a class="idx" href="memory.html#trim_stacks/0">trim_stacks/0</a></dt>
2749	2799	<dd>
2750		<a class="idx" href="memory.html#idx:trimstacks0:1575">4.42</a> <a class="idx" href="memory.html#idx:trimstacks0:1578">4.42</a> <a class="idx" href="engine-examples.html#idx:trimstacks0:1982">10.1.3</a></dd>
	2800	<a class="idx" href="memory.html#idx:trimstacks0:1575">4.42</a> <a class="idx" href="memory.html#idx:trimstacks0:1578">4.42</a> <a class="idx" href="engine-examples.html#idx:trimstacks0:1986">10.1.3</a></dd>
2751	2801	<dt>trimm_stacks/0</dt>
2752	2802	<dd>
2753		<a class="idx" href="engine-resources.html#idx:trimmstacks0:1988">10.2</a></dd>
	2803	<a class="idx" href="engine-resources.html#idx:trimmstacks0:1992">10.2</a></dd>
2754	2804	<dt><a class="idx" href="check.html#trivial_fail_goal/1">trivial_fail_goal/1</a></dt>
2755	2805	<dt><a class="idx" href="control.html#true/0">true/0</a></dt>
2756	2806	<dd>

2760	2810	<a class="idx" href="arith.html#idx:truncate1:1337">4.27.2.3</a></dd>
2761	2811	<dt><a class="idx" href="thutil.html#tspy/1">tspy/1</a></dt>
2762	2812	<dd>
2763		<a class="idx" href="threadcreate.html#idx:tspy1:1836">9.1</a> <a class="idx" href="thutil.html#idx:tspy1:1939">9.5.1</a></dd>
	2813	<a class="idx" href="threadcreate.html#idx:tspy1:1840">9.1</a> <a class="idx" href="thutil.html#idx:tspy1:1943">9.5.1</a></dd>
2764	2814	<dt><a class="idx" href="thutil.html#tspy/2">tspy/2</a></dt>
2765	2815	<dt><a class="idx" href="tty.html#tty_get_capability/3">tty_get_capability/3</a></dt>
2766	2816	<dd>

2776	2826	<dt><a class="idx" href="clpfd.html#tuples_in/2">tuples_in/2</a></dt>
2777	2827	<dt><a class="idx" href="error.html#type_error/2">type_error/2</a></dt>
2778	2828	<dd>
2779		<a class="idx" href="exception.html#idx:typeerror2:769">4.11.4.1</a> <a class="idx" href="foreigninclude.html#idx:typeerror2:2031">11.4.6</a> <a class="idx" href="foreigninclude.html#idx:typeerror2:2033">11.4.6</a></dd>
	2829	<a class="idx" href="exception.html#idx:typeerror2:769">4.11.4.1</a> <a class="idx" href="foreigninclude.html#idx:typeerror2:2035">11.4.6</a> <a class="idx" href="foreigninclude.html#idx:typeerror2:2037">11.4.6</a></dd>
2780	2830	<dt><a class="idx" href="ugraphs.html#ugraph_union/3">ugraph_union/3</a></dt>
2781	2831	<dt><a class="idx" href="compare.html#unifiable/3">unifiable/3</a></dt>
2782	2832	<dd>
2783	2833	<a class="idx" href="cyclic.html#idx:unifiable3:251">2.17</a> <a class="idx" href="compare.html#idx:unifiable3:628">4.7.2</a></dd>
2784	2834	<dt>unify</dt>
2785	2835	<dd>
2786		<a class="idx" href="glossary.html#idx:unify:2335">D</a></dd>
	2836	<a class="idx" href="glossary.html#idx:unify:2339">D</a></dd>
2787	2837	<dt><a class="idx" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a></dt>
2788	2838	<dd>
2789	2839	<a class="idx" href="flags.html#idx:unifywithoccurscheck2:119">2.11</a> <a class="idx" href="cyclic.html#idx:unifywithoccurscheck2:250">2.17</a> <a class="idx" href="compare.html#idx:unifywithoccurscheck2:626">4.7.2</a> <a class="idx" href="compare.html#idx:unifywithoccurscheck2:630">4.7.2</a> <a class="idx" href="compare.html#idx:unifywithoccurscheck2:631">4.7.2</a></dd>

2795	2845	<dt><a class="idx" href="system.html#unix/1">unix/1</a></dt>
2796	2846	<dt><a class="idx" href="debugger.html#unknown/2">unknown/2</a></dt>
2797	2847	<dd>
2798		<a class="idx" href="debugger.html#idx:unknown2:1558">4.39</a> <a class="idx" href="libpl.html#idx:unknown2:2130">A</a></dd>
	2848	<a class="idx" href="debugger.html#idx:unknown2:1558">4.39</a> <a class="idx" href="libpl.html#idx:unknown2:2134">A</a></dd>
2799	2849	<dt><a class="idx" href="broadcast.html#unlisten/1">unlisten/1</a></dt>
2800	2850	<dt><a class="idx" href="broadcast.html#unlisten/2">unlisten/2</a></dt>
2801	2851	<dt><a class="idx" href="broadcast.html#unlisten/3">unlisten/3</a></dt>

2812	2862	<a class="idx" href="chartype.html#idx:upcaseatom2:1293">4.24</a> <a class="idx" href="chartype.html#idx:upcaseatom2:1295">4.24</a></dd>
2813	2863	<dt>update view</dt>
2814	2864	<dd>
2815		<a class="idx" href="db.html#idx:updateview:861">4.14.5</a> <a class="idx" href="glossary.html#idx:updateview:2336">D</a></dd>
	2865	<a class="idx" href="db.html#idx:updateview:861">4.14.5</a> <a class="idx" href="glossary.html#idx:updateview:2340">D</a></dd>
2816	2866	<dt><a class="idx" href="url.html#url_iri/2">url_iri/2</a></dt>
2817	2867	<dt><a class="idx" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a></dt>
2818	2868	<dd>
2819		<a class="idx" href="consulting.html#idx:useforeignlibrary1:466">4.3</a> <a class="idx" href="consulting.html#idx:useforeignlibrary1:508">4.3</a> <a class="idx" href="system.html#idx:useforeignlibrary1:1473">4.35.1</a> <a class="idx" href="runtime.html#idx:useforeignlibrary1:2102">12</a></dd>
	2869	<a class="idx" href="consulting.html#idx:useforeignlibrary1:466">4.3</a> <a class="idx" href="consulting.html#idx:useforeignlibrary1:508">4.3</a> <a class="idx" href="system.html#idx:useforeignlibrary1:1473">4.35.1</a> <a class="idx" href="runtime.html#idx:useforeignlibrary1:2106">12</a></dd>
2820	2870	<dt><a class="idx" href="foreignlink.html#use_foreign_library/2">use_foreign_library/2</a></dt>
2821	2871	<dt><a class="idx" href="import.html#use_module/1">use_module/1</a></dt>
2822	2872	<dd>
2823		<a class="idx" href="flags.html#idx:usemodule1:157">2.11</a> <a class="idx" href="hooks.html#idx:usemodule1:178">2.12</a> <a class="idx" href="projectfiles.html#idx:usemodule1:301">3.1.1.3</a> <a class="idx" href="consulting.html#idx:usemodule1:382">4.3</a> <a class="idx" href="consulting.html#idx:usemodule1:388">4.3</a> <a class="idx" href="consulting.html#idx:usemodule1:406">4.3</a> <a class="idx" href="consulting.html#idx:usemodule1:438">4.3</a> <a class="idx" href="consulting.html#idx:usemodule1:568">4.3.2.1</a> <a class="idx" href="consulting.html#idx:usemodule1:569">4.3.2.1</a> <a class="idx" href="consulting.html#idx:usemodule1:571">4.3.2.1</a> <a class="idx" href="defmodule.html#idx:usemodule1:1665">6.2</a> <a class="idx" href="import.html#idx:usemodule1:1666">6.3</a> <a class="idx" href="import.html#idx:usemodule1:1674">6.3</a> <a class="idx" href="import.html#idx:usemodule1:1682">6.3</a> <a class="idx" href="reexport.html#idx:usemodule1:1714">6.7</a> <a class="idx" href="resmodules.html#idx:usemodule1:1725">6.10</a> <a class="idx" href="altmoduleapi.html#idx:usemodule1:1726">6.11</a> <a class="idx" href="runtime.html#idx:usemodule1:2107">12</a> <a class="idx" href="dialect.html#idx:usemodule1:2249">C</a></dd>
	2873	<a class="idx" href="flags.html#idx:usemodule1:157">2.11</a> <a class="idx" href="hooks.html#idx:usemodule1:178">2.12</a> <a class="idx" href="projectfiles.html#idx:usemodule1:301">3.1.1.3</a> <a class="idx" href="consulting.html#idx:usemodule1:382">4.3</a> <a class="idx" href="consulting.html#idx:usemodule1:388">4.3</a> <a class="idx" href="consulting.html#idx:usemodule1:406">4.3</a> <a class="idx" href="consulting.html#idx:usemodule1:438">4.3</a> <a class="idx" href="consulting.html#idx:usemodule1:568">4.3.2.1</a> <a class="idx" href="consulting.html#idx:usemodule1:569">4.3.2.1</a> <a class="idx" href="consulting.html#idx:usemodule1:571">4.3.2.1</a> <a class="idx" href="defmodule.html#idx:usemodule1:1669">6.2</a> <a class="idx" href="import.html#idx:usemodule1:1670">6.3</a> <a class="idx" href="import.html#idx:usemodule1:1678">6.3</a> <a class="idx" href="import.html#idx:usemodule1:1686">6.3</a> <a class="idx" href="reexport.html#idx:usemodule1:1718">6.7</a> <a class="idx" href="resmodules.html#idx:usemodule1:1729">6.10</a> <a class="idx" href="altmoduleapi.html#idx:usemodule1:1730">6.11</a> <a class="idx" href="runtime.html#idx:usemodule1:2111">12</a> <a class="idx" href="dialect.html#idx:usemodule1:2253">C</a></dd>
2824	2874	<dt><a class="idx" href="import.html#use_module/2">use_module/2</a></dt>
2825	2875	<dd>
2826		<a class="idx" href="autoload.html#idx:usemodule2:193">2.13</a> <a class="idx" href="consulting.html#idx:usemodule2:383">4.3</a> <a class="idx" href="consulting.html#idx:usemodule2:389">4.3</a> <a class="idx" href="consulting.html#idx:usemodule2:407">4.3</a> <a class="idx" href="consulting.html#idx:usemodule2:409">4.3</a> <a class="idx" href="import.html#idx:usemodule2:1667">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1671">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1672">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1675">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1680">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1683">6.3</a> <a class="idx" href="reexport.html#idx:usemodule2:1715">6.7</a> <a class="idx" href="dialect.html#idx:usemodule2:2250">C</a></dd>
	2876	<a class="idx" href="autoload.html#idx:usemodule2:193">2.13</a> <a class="idx" href="consulting.html#idx:usemodule2:383">4.3</a> <a class="idx" href="consulting.html#idx:usemodule2:389">4.3</a> <a class="idx" href="consulting.html#idx:usemodule2:407">4.3</a> <a class="idx" href="consulting.html#idx:usemodule2:409">4.3</a> <a class="idx" href="import.html#idx:usemodule2:1671">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1675">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1676">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1679">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1684">6.3</a> <a class="idx" href="import.html#idx:usemodule2:1687">6.3</a> <a class="idx" href="reexport.html#idx:usemodule2:1719">6.7</a> <a class="idx" href="dialect.html#idx:usemodule2:2254">C</a></dd>
2827	2877	<dt>use_module/[1,2]</dt>
2828	2878	<dd>
2829		<a class="idx" href="compilation.html#idx:usemodule12:71">2.10.1</a> <a class="idx" href="pceemacs.html#idx:usemodule12:312">3.4.3.1</a> <a class="idx" href="consulting.html#idx:usemodule12:361">4.3</a> <a class="idx" href="consulting.html#idx:usemodule12:411">4.3</a> <a class="idx" href="consulting.html#idx:usemodule12:432">4.3</a> <a class="idx" href="altmoduleapi.html#idx:usemodule12:1727">6.11</a> <a class="idx" href="altmoduleapi.html#idx:usemodule12:1730">6.11</a> <a class="idx" href="glossary.html#idx:usemodule12:2292">D</a></dd>
	2879	<a class="idx" href="compilation.html#idx:usemodule12:71">2.10.1</a> <a class="idx" href="pceemacs.html#idx:usemodule12:312">3.4.3.1</a> <a class="idx" href="consulting.html#idx:usemodule12:361">4.3</a> <a class="idx" href="consulting.html#idx:usemodule12:411">4.3</a> <a class="idx" href="consulting.html#idx:usemodule12:432">4.3</a> <a class="idx" href="altmoduleapi.html#idx:usemodule12:1731">6.11</a> <a class="idx" href="altmoduleapi.html#idx:usemodule12:1734">6.11</a> <a class="idx" href="glossary.html#idx:usemodule12:2296">D</a></dd>
2830	2880	<dt>user profile file</dt>
2831	2881	<dd>
2832	2882	<a class="idx" href="initfile.html#idx:userprofilefile:19">2.2</a></dd>

2835	2885	<a class="idx" href="chars.html#idx:utf8:341">4.2</a></dd>
2836	2886	<dt>valgrind</dt>
2837	2887	<dd>
2838		<a class="idx" href="foreignnotes.html#idx:valgrind:2094">11.8.4</a></dd>
	2888	<a class="idx" href="foreignnotes.html#idx:valgrind:2098">11.8.4</a></dd>
2839	2889	<dt><a class="idx" href="check.html#valid_string_goal/1">valid_string_goal/1</a></dt>
2840	2890	<dt><a class="idx" href="typetest.html#var/1">var/1</a></dt>
2841	2891	<dd>
2842		<a class="idx" href="attvar.html#idx:var1:1776">7.1.1</a> <a class="idx" href="foreigninclude.html#idx:var1:2015">11.4.3</a></dd>
	2892	<a class="idx" href="attvar.html#idx:var1:1780">7.1.1</a> <a class="idx" href="foreigninclude.html#idx:var1:2019">11.4.3</a></dd>
2843	2893	<dt><a class="idx" href="manipterm.html#var_number/2">var_number/2</a></dt>
2844	2894	<dt><a class="idx" href="consulting.html#var_property/2">var_property/2</a></dt>
2845	2895	<dt>variable</dt>
2846	2896	<dd>
2847		<a class="idx" href="glossary.html#idx:variable:2338">D</a></dd>
	2897	<a class="idx" href="glossary.html#idx:variable:2342">D</a></dd>
2848	2898	<dt>variable,anonymous</dt>
2849	2899	<dd>
2850		<a class="idx" href="glossary.html#idx:variableanonymous:2267">D</a></dd>
	2900	<a class="idx" href="glossary.html#idx:variableanonymous:2271">D</a></dd>
2851	2901	<dt><a class="idx" href="simplex.html#variable_value/3">variable_value/3</a></dt>
2852	2902	<dt>variant</dt>
2853	2903	<dd>

2855	2905	<dt><a class="idx" href="db.html#variant_hash/2">variant_hash/2</a></dt>
2856	2906	<dt><a class="idx" href="db.html#variant_sha1/2">variant_sha1/2</a></dt>
2857	2907	<dd>
2858		<a class="idx" href="db.html#idx:variantsha12:872">4.14.6</a> <a class="idx" href="db.html#idx:variantsha12:874">4.14.6</a> <a class="idx" href="otherlicenses.html#idx:variantsha12:2344">E.3.1</a></dd>
	2908	<a class="idx" href="db.html#idx:variantsha12:872">4.14.6</a> <a class="idx" href="db.html#idx:variantsha12:874">4.14.6</a> <a class="idx" href="otherlicenses.html#idx:variantsha12:2348">E.3.1</a></dd>
2859	2909	<dt><a class="idx" href="varnumbers.html#varnumbers/2">varnumbers/2</a></dt>
2860	2910	<dt><a class="idx" href="varnumbers.html#varnumbers/3">varnumbers/3</a></dt>
2861	2911	<dt><a class="idx" href="varnumbers.html#varnumbers_names/3">varnumbers_names/3</a></dt>

2872	2922	<dt><a class="idx" href="ugraphs.html#vertices_edges_to_ugraph/3">vertices_edges_to_ugraph/3</a></dt>
2873	2923	<dt>view,update</dt>
2874	2924	<dd>
2875		<a class="idx" href="glossary.html#idx:viewupdate:2337">D</a></dd>
	2925	<a class="idx" href="glossary.html#idx:viewupdate:2341">D</a></dd>
2876	2926	<dt><a class="idx" href="debugger.html#visible/1">visible/1</a></dt>
2877	2927	<dd>
2878		<a class="idx" href="tracehook.html#idx:visible1:2190">B.3</a></dd>
	2928	<a class="idx" href="tracehook.html#idx:visible1:2194">B.3</a></dd>
2879	2929	<dt><a class="idx" href="runtime.html#volatile/1">volatile/1</a></dt>
2880	2930	<dd>
2881		<a class="idx" href="examineprog.html#idx:volatile1:934">4.16</a> <a class="idx" href="threadcom.html#idx:volatile1:1919">9.3.3</a></dd>
	2931	<a class="idx" href="examineprog.html#idx:volatile1:934">4.16</a> <a class="idx" href="threadcom.html#idx:volatile1:1923">9.3.3</a></dd>
2882	2932	<dt><a class="idx" href="streamstat.html#wait_for_input/3">wait_for_input/3</a></dt>
2883	2933	<dd>
2884	2934	<a class="idx" href="IO.html#idx:waitforinput3:1023">4.17.2</a> <a class="idx" href="IO.html#idx:waitforinput3:1024">4.17.2</a> <a class="idx" href="streamstat.html#idx:waitforinput3:1066">4.18</a> <a class="idx" href="streamstat.html#idx:waitforinput3:1067">4.18</a> <a class="idx" href="streamstat.html#idx:waitforinput3:1070">4.18</a></dd>
2885	2935	<dt><a class="idx" href="clpb.html#weighted_maximum/3">weighted_maximum/3</a></dt>
2886	2936	<dt><a class="idx" href="coroutining.html#when/2">when/2</a></dt>
2887	2937	<dd>
2888		<a class="idx" href="cyclic.html#idx:when2:252">2.17</a> <a class="idx" href="compare.html#idx:when2:641">4.7.2</a> <a class="idx" href="manipterm.html#idx:when2:1211">4.21</a> <a class="idx" href="coroutining.html#idx:when2:1808">7.2</a></dd>
	2938	<a class="idx" href="cyclic.html#idx:when2:252">2.17</a> <a class="idx" href="compare.html#idx:when2:641">4.7.2</a> <a class="idx" href="manipterm.html#idx:when2:1211">4.21</a> <a class="idx" href="coroutining.html#idx:when2:1812">7.2</a></dd>
2889	2939	<dt><a class="idx" href="miscpreds.html#wildcard_match/2">wildcard_match/2</a></dt>
2890	2940	<dt><a class="idx" href="system.html#win_add_dll_directory/1">win_add_dll_directory/1</a></dt>
2891	2941	<dt><a class="idx" href="system.html#win_add_dll_directory/2">win_add_dll_directory/2</a></dt>

2910	2960	<a class="idx" href="system.html#idx:winremovedlldirectory1:1475">4.35.1</a></dd>
2911	2961	<dt><a class="idx" href="system.html#win_shell/2">win_shell/2</a></dt>
2912	2962	<dd>
2913		<a class="idx" href="system.html#idx:winshell2:1443">4.35</a> <a class="idx" href="system.html#idx:winshell2:1466">4.35.1</a> <a class="idx" href="www_browser.html#idx:winshell2:2148">A.18</a></dd>
	2963	<a class="idx" href="system.html#idx:winshell2:1443">4.35</a> <a class="idx" href="system.html#idx:winshell2:1466">4.35.1</a> <a class="idx" href="www_browser.html#idx:winshell2:2152">A.18</a></dd>
2914	2964	<dt><a class="idx" href="system.html#win_shell/3">win_shell/3</a></dt>
2915	2965	<dt><a class="idx" href="system.html#win_window_pos/1">win_window_pos/1</a></dt>
2916	2966	<dt><a class="idx" href="system.html#window_title/2">window_title/2</a></dt>

2919	2969	<a class="idx" href="flags.html#idx:windows:159">2.11</a></dd>
2920	2970	<dt><a class="idx" href="threadsync.html#with_mutex/2">with_mutex/2</a></dt>
2921	2971	<dd>
2922		<a class="idx" href="threadcom.html#idx:withmutex2:1909">9.3.2</a> <a class="idx" href="threadsync.html#idx:withmutex2:1920">9.4</a> <a class="idx" href="threadsync.html#idx:withmutex2:1921">9.4</a> <a class="idx" href="threadsync.html#idx:withmutex2:1930">9.4</a> <a class="idx" href="threadsync.html#idx:withmutex2:1933">9.4</a> <a class="idx" href="foreignthread.html#idx:withmutex2:1953">9.6</a></dd>
	2972	<a class="idx" href="threadcom.html#idx:withmutex2:1913">9.3.2</a> <a class="idx" href="threadsync.html#idx:withmutex2:1924">9.4</a> <a class="idx" href="threadsync.html#idx:withmutex2:1925">9.4</a> <a class="idx" href="threadsync.html#idx:withmutex2:1934">9.4</a> <a class="idx" href="threadsync.html#idx:withmutex2:1937">9.4</a> <a class="idx" href="foreignthread.html#idx:withmutex2:1957">9.6</a></dd>
2923	2973	<dt><a class="idx" href="IO.html#with_output_to/2">with_output_to/2</a></dt>
2924	2974	<dd>
2925	2975	<a class="idx" href="IO.html#idx:withoutputto2:960">4.17.1</a> <a class="idx" href="IO.html#idx:withoutputto2:962">4.17.1</a> <a class="idx" href="IO.html#idx:withoutputto2:967">4.17.2</a> <a class="idx" href="IO.html#idx:withoutputto2:1049">4.17.4</a> <a class="idx" href="IO.html#idx:withoutputto2:1056">4.17.5</a> <a class="idx" href="termrw.html#idx:withoutputto2:1116">4.20</a> <a class="idx" href="manipatom.html#idx:withoutputto2:1268">4.22</a> <a class="idx" href="chartype.html#idx:withoutputto2:1304">4.24.2</a> <a class="idx" href="format.html#idx:withoutputto2:1408">4.32.2</a> <a class="idx" href="system.html#idx:withoutputto2:1483">4.35.2.2</a></dd>

2933	2983	<dt><a class="idx" href="foreigninclude.html#write()">write()</a></dt>
2934	2984	<dt><a class="idx" href="termrw.html#write/1">write/1</a></dt>
2935	2985	<dd>
2936		<a class="idx" href="flags.html#idx:write1:160">2.11</a> <a class="idx" href="cyclic.html#idx:write1:253">2.17</a> <a class="idx" href="limits.html#idx:write1:284">2.20.2</a> <a class="idx" href="IO.html#idx:write1:954">4.17.1</a> <a class="idx" href="IO.html#idx:write1:965">4.17.1</a> <a class="idx" href="format.html#idx:write1:1392">4.32.1</a> <a class="idx" href="format.html#idx:write1:1405">4.32.2</a> <a class="idx" href="foreigninclude.html#idx:write1:2019">11.4.3.2</a> <a class="idx" href="foreigninclude.html#idx:write1:2020">11.4.3.2</a> <b>11.4.3.5</b> <a class="idx" href="foreigninclude.html#idx:write1:2024">11.4.3.6</a> <a class="idx" href="foreigninclude.html#idx:write1:2039">11.4.7.1</a></dd>
	2986	<a class="idx" href="flags.html#idx:write1:160">2.11</a> <a class="idx" href="cyclic.html#idx:write1:253">2.17</a> <a class="idx" href="limits.html#idx:write1:284">2.20.2</a> <a class="idx" href="IO.html#idx:write1:954">4.17.1</a> <a class="idx" href="IO.html#idx:write1:965">4.17.1</a> <a class="idx" href="format.html#idx:write1:1392">4.32.1</a> <a class="idx" href="format.html#idx:write1:1405">4.32.2</a> <a class="idx" href="foreigninclude.html#idx:write1:2023">11.4.3.2</a> <a class="idx" href="foreigninclude.html#idx:write1:2024">11.4.3.2</a> <b>11.4.3.5</b> <a class="idx" href="foreigninclude.html#idx:write1:2028">11.4.3.6</a> <a class="idx" href="foreigninclude.html#idx:write1:2043">11.4.7.1</a></dd>
2937	2987	<dt><a class="idx" href="termrw.html#write/2">write/2</a></dt>
2938	2988	<dt><a class="idx" href="termrw.html#write_canonical/1">write_canonical/1</a></dt>
2939	2989	<dd>
2940	2990	<a class="idx" href="termrw.html#idx:writecanonical1:1134">4.20</a> <a class="idx" href="termrw.html#idx:writecanonical1:1143">4.20</a> <a class="idx" href="termrw.html#idx:writecanonical1:1173">4.20</a> <a class="idx" href="format.html#idx:writecanonical1:1400">4.32.2</a> <a class="idx" href="ext-lists.html#idx:writecanonical1:1589">5.1</a></dd>
2941	2991	<dt><a class="idx" href="termrw.html#write_canonical/2">write_canonical/2</a></dt>
2942	2992	<dd>
2943		<a class="idx" href="IO.html#idx:writecanonical2:1060">4.17.6</a> <a class="idx" href="IO.html#idx:writecanonical2:1061">4.17.6</a> <a class="idx" href="IO.html#idx:writecanonical2:1062">4.17.6</a> <a class="idx" href="manipterm.html#idx:writecanonical2:1205">4.21</a> <a class="idx" href="foreigninclude.html#idx:writecanonical2:2021">11.4.3.2</a></dd>
	2993	<a class="idx" href="IO.html#idx:writecanonical2:1060">4.17.6</a> <a class="idx" href="IO.html#idx:writecanonical2:1061">4.17.6</a> <a class="idx" href="IO.html#idx:writecanonical2:1062">4.17.6</a> <a class="idx" href="manipterm.html#idx:writecanonical2:1205">4.21</a> <a class="idx" href="foreigninclude.html#idx:writecanonical2:2025">11.4.3.2</a></dd>
2944	2994	<dt><a class="idx" href="termrw.html#write_length/3">write_length/3</a></dt>
2945	2995	<dd>
2946	2996	<a class="idx" href="manipatom.html#idx:writelength3:1278">4.22</a></dd>
2947	2997	<dt><a class="idx" href="termrw.html#write_term/2">write_term/2</a></dt>
2948	2998	<dd>
2949		<a class="idx" href="debugoverview.html#idx:writeterm2:59">2.9</a> <a class="idx" href="flags.html#idx:writeterm2:104">2.11</a> <a class="idx" href="flags.html#idx:writeterm2:124">2.11</a> <a class="idx" href="flags.html#idx:writeterm2:141">2.11</a> <a class="idx" href="termrw.html#idx:writeterm2:1118">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1119">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1122">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1124">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1135">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1138">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1139">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1140">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1149">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1171">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1172">4.20</a> <a class="idx" href="manipterm.html#idx:writeterm2:1203">4.21</a> <a class="idx" href="manipatom.html#idx:writeterm2:1266">4.22</a> <a class="idx" href="format.html#idx:writeterm2:1394">4.32.1</a> <a class="idx" href="format.html#idx:writeterm2:1406">4.32.2</a> <a class="idx" href="ext-lists.html#idx:writeterm2:1591">5.1</a> <a class="idx" href="ext-lists.html#idx:writeterm2:1593">5.1</a> <a class="idx" href="strings.html#idx:writeterm2:1598">5.2.1</a> <a class="idx" href="attvar.html#idx:writeterm2:1783">7.1.2</a></dd>
	2999	<a class="idx" href="debugoverview.html#idx:writeterm2:59">2.9</a> <a class="idx" href="flags.html#idx:writeterm2:104">2.11</a> <a class="idx" href="flags.html#idx:writeterm2:124">2.11</a> <a class="idx" href="flags.html#idx:writeterm2:141">2.11</a> <a class="idx" href="termrw.html#idx:writeterm2:1118">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1119">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1122">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1124">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1135">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1138">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1139">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1140">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1149">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1171">4.20</a> <a class="idx" href="termrw.html#idx:writeterm2:1172">4.20</a> <a class="idx" href="manipterm.html#idx:writeterm2:1203">4.21</a> <a class="idx" href="manipatom.html#idx:writeterm2:1266">4.22</a> <a class="idx" href="format.html#idx:writeterm2:1394">4.32.1</a> <a class="idx" href="format.html#idx:writeterm2:1406">4.32.2</a> <a class="idx" href="ext-lists.html#idx:writeterm2:1591">5.1</a> <a class="idx" href="ext-lists.html#idx:writeterm2:1593">5.1</a> <a class="idx" href="strings.html#idx:writeterm2:1598">5.2.1</a> <a class="idx" href="attvar.html#idx:writeterm2:1787">7.1.2</a></dd>
2950	3000	<dt><a class="idx" href="termrw.html#write_term/3">write_term/3</a></dt>
2951	3001	<dd>
2952	3002	<a class="idx" href="flags.html#idx:writeterm3:161">2.11</a> <a class="idx" href="hooks.html#idx:writeterm3:168">2.12</a> <a class="idx" href="termrw.html#idx:writeterm3:1127">4.20</a> <a class="idx" href="manipterm.html#idx:writeterm3:1198">4.21</a> <a class="idx" href="manipatom.html#idx:writeterm3:1279">4.22</a></dd>

2965	3015	<a class="idx" href="format.html#idx:writeq1:1393">4.32.1</a> <a class="idx" href="format.html#idx:writeq1:1402">4.32.2</a></dd>
2966	3016	<dt><a class="idx" href="termrw.html#writeq/2">writeq/2</a></dt>
2967	3017	<dd>
2968		<a class="idx" href="foreigninclude.html#idx:writeq2:2022">11.4.3.2</a></dd>
	3018	<a class="idx" href="foreigninclude.html#idx:writeq2:2026">11.4.3.2</a></dd>
2969	3019	<dt><a class="idx" href="url.html#www_form_encode/2">www_form_encode/2</a></dt>
2970	3020	<dt><a class="idx" href="www_browser.html#www_open_url/1">www_open_url/1</a></dt>
2971	3021	<dd>
2972		<a class="idx" href="www_browser.html#idx:wwwopenurl1:2150">A.18</a></dd>
	3022	<a class="idx" href="www_browser.html#idx:wwwopenurl1:2154">A.18</a></dd>
2973	3023	<dt><a class="idx" href="prolog_xref.html#xref_built_in/1">xref_built_in/1</a></dt>
2974	3024	<dt><a class="idx" href="prolog_xref.html#xref_called/3">xref_called/3</a></dt>
2975	3025	<dt><a class="idx" href="prolog_xref.html#xref_clean/1">xref_clean/1</a></dt>

2980	3030	<dt><a class="idx" href="prolog_xref.html#xref_source/1">xref_source/1</a></dt>
2981	3031	<dt><a class="idx" href="clpfd.html#zcompare/3">zcompare/3</a></dt>
2982	3032	<dd>
2983		<a class="idx" href="clp.html#idx:zcompare3:1765">7</a></dd>
	3033	<a class="idx" href="clp.html#idx:zcompare3:1769">7</a></dd>
2984	3034	<dt><a class="idx" href="control.html#!/0">!/0</a></dt>
2985	3035	<dt class="index-sep">#</dt>
2986	3036	<dt><a class="idx" href="clpfd.html##/\/2">#/ 2</a></dt>

3000	3050	<dt><a class="idx" href="control.html#->/2">->/2</a></dt>
3001	3051	<dt class="index-sep">,</dt>
3002	3052	<dt><a class="idx" href="control.html#,/2">,/2</a></dt>
	3053	<dt class="index-sep">-</dt>
	3054	<dt><a class="idx" href="control.html#->/2">->/2</a></dt>
3003	3055	<dt class="index-sep">.</dt>
3004	3056	<dt><a class="idx" href="dicts.html#./3">./3</a></dt>
3005	3057	<dt class="index-sep">/</dt>

3059	3111	<dt class="index-sep">B</dt>
3060	3112	<dt>Boehm GC</dt>
3061	3113	<dd>
3062		<a class="idx" href="foreignnotes.html#idx:BoehmGC:2092">11.8.2.1</a></dd>
	3114	<a class="idx" href="foreignnotes.html#idx:BoehmGC:2096">11.8.2.1</a></dd>
3063	3115	<dt>BOM</dt>
3064	3116	<dd>
3065	3117	<a class="idx" href="widechars.html#idx:BOM:273">2.19.1.1</a></dd>

3069	3121	<dt class="index-sep">C</dt>
3070	3122	<dt>CLP</dt>
3071	3123	<dd>
3072		<a class="idx" href="clp.html#idx:CLP:1759">7</a></dd>
	3124	<a class="idx" href="clp.html#idx:CLP:1763">7</a></dd>
3073	3125	<dt>COM</dt>
3074	3126	<dd>
3075		<a class="idx" href="foreigninclude.html#idx:COM:2037">11.4.7</a></dd>
	3127	<a class="idx" href="foreigninclude.html#idx:COM:2041">11.4.7</a></dd>
3076	3128	<dt class="index-sep">D</dt>
3077	3129	<dt>Development environment</dt>
3078	3130	<dd>

3094	3146	<dt class="index-sep">H</dt>
3095	3147	<dt>Herbrand term</dt>
3096	3148	<dd>
3097		<a class="idx" href="clp.html#idx:Herbrandterm:1761">7</a></dd>
	3149	<a class="idx" href="clp.html#idx:Herbrandterm:1765">7</a></dd>
3098	3150	<dt class="index-sep">I</dt>
3099	3151	<dt>IA32</dt>
3100	3152	<dd>

3111	3163	<dt class="index-sep">J</dt>
3112	3164	<dt>Java</dt>
3113	3165	<dd>
3114		<a class="idx" href="foreigninclude.html#idx:Java:2036">11.4.7</a></dd>
	3166	<a class="idx" href="foreigninclude.html#idx:Java:2040">11.4.7</a></dd>
3115	3167	<dt class="index-sep">M</dt>
3116	3168	<dt>MacOS</dt>
3117	3169	<dd>

3354	3406	<dt><a class="idx" href="foreigninclude.html#PL_PARTIAL_LIST">PL_PARTIAL_LIST</a></dt>
3355	3407	<dt>PLVERSION</dt>
3356	3408	<dd>
3357		<a class="idx" href="foreignnotes.html#idx:PLVERSION:2093">11.8.3</a></dd>
	3409	<a class="idx" href="foreignnotes.html#idx:PLVERSION:2097">11.8.3</a></dd>
3358	3410	<dt><a class="idx" href="foreigninclude.html#PL_get_file_nameW()">PL_get_file_nameW()</a></dt>
3359	3411	<dt class="index-sep">R</dt>
3360	3412	<dt>RDF,memory usage</dt>

3363	3415	<dt class="index-sep">S</dt>
3364	3416	<dt>Solaris</dt>
3365	3417	<dd>
3366		<a class="idx" href="threadcreate.html#idx:Solaris:1871">9.1</a></dd>
	3418	<a class="idx" href="threadcreate.html#idx:Solaris:1875">9.1</a></dd>
3367	3419	<dt><code>/</code></dt>
3368	3420	<dd>
3369	3421	<a class="idx" href="projectfiles.html#idx:Sdiv:294">3.1.1.2</a></dd>

3372	3424	<a class="idx" href="projectfiles.html#idx:chrSneg:295">3.1.1.2</a></dd>
3373	3425	<dt>SLG,resolution</dt>
3374	3426	<dd>
3375		<a class="idx" href="tabling.html#idx:SLGresolution:2171">A.35</a></dd>
	3427	<a class="idx" href="tabling.html#idx:SLGresolution:2175">A.35</a></dd>
3376	3428	<dt class="index-sep">T</dt>
3377	3429	<dt>TAB,completion</dt>
3378	3430	<dd>

3396	3448	<dt class="index-sep">Y</dt>
3397	3449	<dt>YAP,prolog</dt>
3398	3450	<dd>
3399		<a class="idx" href="dialect.html#idx:YAPprolog:2243">C</a></dd>
	3451	<a class="idx" href="dialect.html#idx:YAPprolog:2247">C</a></dd>
3400	3452	<dt class="index-sep">{</dt>
3401	3453	<dt><a class="idx" href="clpqr.html#{}/1">/1</a></dt>
3402	3454	<dt class="index-sep">\|</dt>

+67

-26

man/Manual/IDE.html less more

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2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="64bits.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="projectfiles.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h1 id="sec:IDE"><a name="sec:3"><span class="sec-nr">3</span> <span class="sec-title">Initialising
	235	<h1 id="sec:IDE"><a id="sec:3"><span class="sec-nr">3</span> <span class="sec-title">Initialising
195	236	and Managing a Prolog Project</span></a></h1>
196	237
197		<a name="sec:IDE"></a>
198
199		<p><a name="idx:IDE:290"></a><a name="idx:Developmentenvironment:291"></a>Prolog
	238	<a id="sec:IDE"></a>
	239
	240	<p><a id="idx:IDE:290"></a><a id="idx:Developmentenvironment:291"></a>Prolog
200	241	text-books give you an overview of the Prolog language. The manual tells
201	242	you what predicates are provided in the system and what they do. This
202	243	chapter explains how to run a project. There is no ultimate `right' way

204	245	SWI-Prolog's commands are there to support this practice. This chapter
205	246	describes the conventions and supporting commands.
206	247
207		<p>The first two sections (<a class="sec" href="projectfiles.html">section
208		3.1</a> and <a class="sec" href="usingmodules.html">section 3.2</a>)
	248	<p>The first two sections (<a class="sec" href="projectfiles.html#sec:3.1">section
	249	3.1</a> and <a class="sec" href="usingmodules.html#sec:3.2">section 3.2</a>)
209	250	only require plain Prolog. The remainder discusses the use of the
210	251	built-in graphical tools that require the XPCE graphical library
211	252	installed on your system.

+248

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 4.17</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.17</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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193	234	</div>
194		<h2 id="sec:IO"><a name="sec:4.17"><span class="sec-nr">4.17</span> <span class="sec-title">Input
	235	<h2 id="sec:IO"><a id="sec:4.17"><span class="sec-nr">4.17</span> <span class="sec-title">Input
195	236	and output</span></a></h2>
196	237
197		<a name="sec:IO"></a>
	238	<a id="sec:IO"></a>
198	239
199	240	<p>SWI-Prolog provides two different packages for input and output. The
200		native I/O system is based on the ISO standard predicates <a name="idx:open3:947"></a><a class="pred" href="IO.html#open/3">open/3</a>,
201		<a name="idx:close1:948"></a><a class="pred" href="IO.html#close/1">close/1</a>
	241	native I/O system is based on the ISO standard predicates <a id="idx:open3:947"></a><a class="pred" href="IO.html#open/3">open/3</a>,
	242	<a id="idx:close1:948"></a><a class="pred" href="IO.html#close/1">close/1</a>
202	243	and friends.<sup class="fn">82<span class="fn-text">Actually based on
203	244	Quintus Prolog, providing this interface before the ISO standard
204	245	existed.</span></sup> Being more widely portable and equipped with a
205	246	clearer and more robust specification, new code is encouraged to use
206	247	these predicates for manipulation of I/O streams.
207	248
208		<p><a class="sec" href="IO.html">Section 4.17.3</a> describes <a name="idx:tell1:949"></a><a class="pred" href="IO.html#tell/1">tell/1</a>, <a name="idx:see1:950"></a><a class="pred" href="IO.html#see/1">see/1</a>
	249	<p><a class="sec" href="IO.html#sec:4.17.3">Section 4.17.3</a> describes <a id="idx:tell1:949"></a><a class="pred" href="IO.html#tell/1">tell/1</a>, <a id="idx:see1:950"></a><a class="pred" href="IO.html#see/1">see/1</a>
209	250	and friends, providing I/O in the spirit of the traditional Edinburgh
210	251	standard. These predicates are layered on top of the ISO predicates.
211	252	Both packages are fully integrated; the user may switch freely between
212	253	them.
213	254
214		<p><h3 id="sec:streamalias"><a name="sec:4.17.1"><span class="sec-nr">4.17.1</span> <span class="sec-title">Predefined
	255	<p><h3 id="sec:streamalias"><a id="sec:4.17.1"><span class="sec-nr">4.17.1</span> <span class="sec-title">Predefined
215	256	stream aliases</span></a></h3>
216	257
217		<a name="sec:streamalias"></a>
	258	<a id="sec:streamalias"></a>
218	259
219	260	<p>Each thread has five stream aliases: <code>user_input</code>,
220	261	<code>user_output</code>, <code>user_error</code>, <code>current_input</code>,

227	268	handles 0, 1 and 2). These aliases may be re-bound, for
228	269	example if standard I/O refers to a window such as in the <b>swipl-win.exe</b>
229	270	GUI executable for Windows. They can be re-bound by the user using
230		<a name="idx:setprologIO3:951"></a><a class="pred" href="IO.html#set_prolog_IO/3">set_prolog_IO/3</a>
231		and <a name="idx:setstream2:952"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>
	271	<a id="idx:setprologIO3:951"></a><a class="pred" href="IO.html#set_prolog_IO/3">set_prolog_IO/3</a>
	272	and <a id="idx:setstream2:952"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>
232	273	by setting the alias of a stream (e.g,
233	274	<code>set_stream(S, alias(user_output))</code>). An example of rebinding
234	275	can be found in library <code>library(prolog_server)</code>, providing a <b>telnet</b>
235	276	service. The aliases <code>current_input</code> and <code>current_output</code>
236	277	define the source and destination for predicates that do not take a
237		stream argument (e.g., <a name="idx:read1:953"></a><a class="pred" href="termrw.html#read/1">read/1</a>, <a name="idx:write1:954"></a><a class="pred" href="termrw.html#write/1">write/1</a>, <a name="idx:getcode1:955"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>,
	278	stream argument (e.g., <a id="idx:read1:953"></a><a class="pred" href="termrw.html#read/1">read/1</a>, <a id="idx:write1:954"></a><a class="pred" href="termrw.html#write/1">write/1</a>, <a id="idx:getcode1:955"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>,
238	279	... ). Initially, these are bound to the same stream as <code>user_input</code>
239	280	and
240		<code>user_error</code>. They are re-bound by <a name="idx:see1:956"></a><a class="pred" href="IO.html#see/1">see/1</a>, <a name="idx:tell1:957"></a><a class="pred" href="IO.html#tell/1">tell/1</a>, <a name="idx:setinput1:958"></a><a class="pred" href="IO.html#set_input/1">set_input/1</a>
	281	<code>user_error</code>. They are re-bound by <a id="idx:see1:956"></a><a class="pred" href="IO.html#see/1">see/1</a>, <a id="idx:tell1:957"></a><a class="pred" href="IO.html#tell/1">tell/1</a>, <a id="idx:setinput1:958"></a><a class="pred" href="IO.html#set_input/1">set_input/1</a>
241	282	and
242		<a name="idx:setoutput1:959"></a><a class="pred" href="IO.html#set_output/1">set_output/1</a>.
243		The <code>current_output</code> stream is also temporary re-bound by <a name="idx:withoutputto2:960"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
244		or <a name="idx:format3:961"></a><a class="pred" href="format.html#format/3">format/3</a>
	283	<a id="idx:setoutput1:959"></a><a class="pred" href="IO.html#set_output/1">set_output/1</a>.
	284	The <code>current_output</code> stream is also temporary re-bound by <a id="idx:withoutputto2:960"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
	285	or <a id="idx:format3:961"></a><a class="pred" href="format.html#format/3">format/3</a>
245	286	using e.g.,
246	287	<code>format(atom(A), ...</code>. Note that code which explicitly writes
247	288	to the streams <code>user_output</code> and <code>user_error</code> will
248		not be redirected by <a name="idx:withoutputto2:962"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>.
	289	not be redirected by <a id="idx:withoutputto2:962"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>.
249	290
250	291	<p><b>Compatibility</b>
251	292
252	293	<p>Note that the ISO standard only defines the <code>user_*</code>
253		streams. The `current' streams can be accessed using <a name="idx:currentinput1:963"></a><a class="pred" href="IO.html#current_input/1">current_input/1</a>
	294	streams. The `current' streams can be accessed using <a id="idx:currentinput1:963"></a><a class="pred" href="IO.html#current_input/1">current_input/1</a>
254	295	and
255		<a name="idx:currentoutput1:964"></a><a class="pred" href="IO.html#current_output/1">current_output/1</a>.
	296	<a id="idx:currentoutput1:964"></a><a class="pred" href="IO.html#current_output/1">current_output/1</a>.
256	297	For example, an ISO compatible implementation of
257		<a name="idx:write1:965"></a><a class="pred" href="termrw.html#write/1">write/1</a>
	298	<a id="idx:write1:965"></a><a class="pred" href="termrw.html#write/1">write/1</a>
258	299	is
259	300
260	301	<pre class="code">

267	308	write(Term) :- write(current_output, Term).
268	309	</pre>
269	310
270		<p><h3 id="sec:isoIO"><a name="sec:4.17.2"><span class="sec-nr">4.17.2</span> <span class="sec-title">ISO
	311	<p><h3 id="sec:isoIO"><a id="sec:4.17.2"><span class="sec-nr">4.17.2</span> <span class="sec-title">ISO
271	312	Input and Output Streams</span></a></h3>
272	313
273		<a name="sec:isoIO"></a>
	314	<a id="sec:isoIO"></a>
274	315
275	316	<p>The predicates described in this section provide ISO compliant I/O,
276		where streams are explicitly created using the predicate <a name="idx:open3:966"></a><a class="pred" href="IO.html#open/3">open/3</a>.
	317	where streams are explicitly created using the predicate <a id="idx:open3:966"></a><a class="pred" href="IO.html#open/3">open/3</a>.
277	318	The resulting stream identifier is then passed as a parameter to the
278	319	reading and writing predicates to specify the source or destination of
279	320	the data.

281	322	<p>This schema is not vulnerable to filename and stream ambiguities as
282	323	well as changes to the working directory. On the other hand, using the
283	324	notion of current-I/O simplifies reusability of code without the need to
284		pass arguments around. E.g., see <a name="idx:withoutputto2:967"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>.
	325	pass arguments around. E.g., see <a id="idx:withoutputto2:967"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>.
285	326
286	327	<p>SWI-Prolog streams are, compatible with the ISO standard, either
287	328	input or output streams. To accommodate portability to other systems, a
288	329	pair of streams can be packed into a <em>stream-pair</em>. See
289		<a name="idx:streampair3:968"></a><a class="pred" href="IO.html#stream_pair/3">stream_pair/3</a>
	330	<a id="idx:streampair3:968"></a><a class="pred" href="IO.html#stream_pair/3">stream_pair/3</a>
290	331	for details.
291	332
292	333	<p>SWI-Prolog stream handles are unique symbols that have no syntactical
293	334	representation. They are written as <code><stream>(hex-number)</code>,
294		which is not valid input for <a name="idx:read1:969"></a><a class="pred" href="termrw.html#read/1">read/1</a>.
295		They are realised using a <em>blob</em> of type <code>stream</code> (see <a name="idx:blob2:970"></a><a class="pred" href="typetest.html#blob/2">blob/2</a>
296		and <a class="sec" href="foreigninclude.html">section 11.4.7</a>).
	335	which is not valid input for <a id="idx:read1:969"></a><a class="pred" href="termrw.html#read/1">read/1</a>.
	336	They are realised using a <em>blob</em> of type <code>stream</code> (see <a id="idx:blob2:970"></a><a class="pred" href="typetest.html#blob/2">blob/2</a>
	337	and <a class="sec" href="foreigninclude.html#sec:11.4.7">section 11.4.7</a>).
297	338
298	339	<dl class="latex">
299		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="open/4"><strong>open</strong>(<var>+SrcDest,
	340	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="open/4"><strong>open</strong>(<var>+SrcDest,
300	341	+Mode, --Stream, +Options</var>)</a></dt>
301	342	<dd class="defbody">
302	343	True when <var>SrcDest</var> can be opened in <var>Mode</var> and <var>Stream</var>

322	363	<code>read</code>, data written by <var>Command</var> to the standard
323	364	output may be read from <var>Stream</var>. On Unix systems, <var>Command</var>
324	365	is handed to popen() which hands it to the Unix shell. On Windows, <var>Command</var>
325		is executed directly. See also <a name="idx:processcreate3:971"></a><span class="pred-ext">process_create/3</span>
	366	is executed directly. See also <a id="idx:processcreate3:971"></a><span class="pred-ext">process_create/3</span>
326	367	from <code>library(process)</code>.
327	368
328		<p>The following <var>Options</var> are recognised by <a name="idx:open4:972"></a><a class="pred" href="IO.html#open/4">open/4</a>:
	369	<p>The following <var>Options</var> are recognised by <a id="idx:open4:972"></a><a class="pred" href="IO.html#open/4">open/4</a>:
329	370
330	371	<dl class="latex">
331	372	<dt><strong>alias</strong>(<var>Atom</var>)</dt>
332	373	<dd class="defbody">
333	374	Gives the stream a name. Below is an example. Be careful with this
334		option as stream names are global. See also <a name="idx:setstream2:973"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.
	375	option as stream names are global. See also <a id="idx:setstream2:973"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.
335	376
336	377	<pre class="code">
337	378	?- open(data, read, Fd, [alias(input)]).

346	387	<dd class="defbody">
347	388	Check for a BOM (<em>Byte Order Marker</em>) or write one. If omitted,
348	389	the default is <code>true</code> for mode <code>read</code> and
349		<code>false</code> for mode <code>write</code>. See also <a name="idx:streamproperty2:974"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
350		and especially <a class="sec" href="widechars.html">section 2.19.1.1</a>
351		for a discussion of this feature.</dd>
	390	<code>false</code> for mode <code>write</code>. See also <a id="idx:streamproperty2:974"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	391	and especially <a class="sec" href="widechars.html#sec:2.19.1.1">section
	392	2.19.1.1</a> for a discussion of this feature.</dd>
352	393	<dt><strong>buffer</strong>(<var>Buffering</var>)</dt>
353	394	<dd class="defbody">
354	395	Defines output buffering. The atom <code>full</code> (default) defines
355	396	full buffering, <code>line</code> buffering by line, and <code>false</code>
356	397	implies the stream is fully unbuffered. Smaller buffering is useful if
357	398	another process or the user is waiting for the output as it is being
358		produced. See also <a name="idx:flushoutput01:975"></a><a class="pred" href="chario.html#flush_output/0">flush_output/[0,1]</a>.
	399	produced. See also <a id="idx:flushoutput01:975"></a><a class="pred" href="chario.html#flush_output/0">flush_output/[0,1]</a>.
359	400	This option is not an ISO option.</dd>
360	401	<dt><strong>close_on_abort</strong>(<var>Bool</var>)</dt>
361	402	<dd class="defbody">
362	403	If <code>true</code> (default), the stream is closed on an abort (see
363		<a name="idx:abort0:976"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>).
	404	<a id="idx:abort0:976"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>).
364	405	If <code>false</code>, the stream is not closed. If it is an output
365	406	stream, however, it will be flushed. Useful for logfiles and if the
366	407	stream is associated to a process (using the <code>pipe/1</code>

408	449	The default encoding for type <code>text</code> is derived from the
409	450	Prolog flag <a class="flag" href="flags.html#flag:encoding">encoding</a>.
410	451	For <code>binary</code> streams the default encoding is <code>octet</code>.
411		For details on encoding issues, see <a class="sec" href="widechars.html">section
	452	For details on encoding issues, see <a class="sec" href="widechars.html#sec:2.19.1">section
412	453	2.19.1</a>.</dd>
413	454	<dt><strong>eof_action</strong>(<var>Action</var>)</dt>
414	455	<dd class="defbody">
415	456	Defines what happens if the end of the input stream is reached. The
416		default value for Action is <code>eof_code</code>, which makes <a name="idx:get01:977"></a><a class="pred" href="chario.html#get0/1">get0/1</a>
417		and friends return -1, and <a name="idx:read1:978"></a><a class="pred" href="termrw.html#read/1">read/1</a>
	457	default value for Action is <code>eof_code</code>, which makes <a id="idx:get01:977"></a><a class="pred" href="chario.html#get0/1">get0/1</a>
	458	and friends return -1, and <a id="idx:read1:978"></a><a class="pred" href="termrw.html#read/1">read/1</a>
418	459	and friends return the atom
419	460	<code>end_of_file</code>. Repetitive reading keeps yielding the same
420	461	result. Action <code>error</code> is like <code>eof_code</code>, but

423	464	grown.</dd>
424	465	<dt><strong>locale</strong>(<var>+Locale</var>)</dt>
425	466	<dd class="defbody">
426		Set the locale that is used by notably <a name="idx:format2:979"></a><a class="pred" href="format.html#format/2">format/2</a>
427		for output on this stream. See <a class="sec" href="locale.html">section
	467	Set the locale that is used by notably <a id="idx:format2:979"></a><a class="pred" href="format.html#format/2">format/2</a>
	468	for output on this stream. See <a class="sec" href="locale.html#sec:4.23">section
428	469	4.23</a>.</dd>
429	470	<dt><strong>lock</strong>(<var>LockingMode</var>)</dt>
430	471	<dd class="defbody">

462	503
463	504	<p>The option <code>reposition</code> is not supported in SWI-Prolog.
464	505	All streams connected to a file may be repositioned.</dd>
465		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="open/3"><strong>open</strong>(<var>+SrcDest,
	506	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="open/3"><strong>open</strong>(<var>+SrcDest,
466	507	+Mode, --Stream</var>)</a></dt>
467	508	<dd class="defbody">
468		Equivalent to <a name="idx:open4:980"></a><a class="pred" href="IO.html#open/4">open/4</a>
	509	Equivalent to <a id="idx:open4:980"></a><a class="pred" href="IO.html#open/4">open/4</a>
469	510	with an empty option list.</dd>
470		<dt class="pubdef"><a name="open_null_stream/1"><strong>open_null_stream</strong>(<var>--Stream</var>)</a></dt>
	511	<dt class="pubdef"><a id="open_null_stream/1"><strong>open_null_stream</strong>(<var>--Stream</var>)</a></dt>
471	512	<dd class="defbody">
472	513	Open an output stream that produces no output. All counting functions
473	514	are enabled on such a stream. It can be used to discard output (like

488	529	</pre>
489	530
490	531	</dd>
491		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="close/1"><strong>close</strong>(<var>+Stream</var>)</a></dt>
	532	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="close/1"><strong>close</strong>(<var>+Stream</var>)</a></dt>
492	533	<dd class="defbody">
493	534	Close the specified stream. If <var>Stream</var> is not open, an
494		existence error is raised. See <a name="idx:streampair3:981"></a><a class="pred" href="IO.html#stream_pair/3">stream_pair/3</a>
	535	existence error is raised. See <a id="idx:streampair3:981"></a><a class="pred" href="IO.html#stream_pair/3">stream_pair/3</a>
495	536	for the implications of closing a
496	537	<em>stream pair</em>.
497	538
498	539	<p>If the closed stream is the current input, output or error stream,
499	540	the stream alias is bound to the initial standard I/O streams of the
500		process. Calling <a name="idx:close1:982"></a><a class="pred" href="IO.html#close/1">close/1</a>
	541	process. Calling <a id="idx:close1:982"></a><a class="pred" href="IO.html#close/1">close/1</a>
501	542	on the initial standard I/O streams of the process is a no-op for an
502	543	input stream and flushes an output stream without closing it.<sup class="fn">85<span class="fn-text">This
503	544	behaviour was defined with purely interactive usage of Prolog in mind.
504	545	Applications should not count on this behaviour. Future versions may
505	546	allow for closing the initial standard I/O streams.</span></sup></dd>
506		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="close/2"><strong>close</strong>(<var>+Stream,
	547	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="close/2"><strong>close</strong>(<var>+Stream,
507	548	+Options</var>)</a></dt>
508	549	<dd class="defbody">
509	550	Provides <code>close(Stream, [force(true)])</code> as the only option.
510	551	Called this way, any resource errors (such as write errors while
511	552	flushing the output buffer) are ignored.</dd>
512		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="stream_property/2"><strong>stream_property</strong>(<var>?Stream,
	553	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="stream_property/2"><strong>stream_property</strong>(<var>?Stream,
513	554	?StreamProperty</var>)</a></dt>
514	555	<dd class="defbody">
515	556	True when <var>StreamProperty</var> is a property of <var>Stream</var>.

530	571	<dd class="defbody">
531	572	SWI-Prolog extension to query the buffering mode of this stream.
532	573	<var>Buffering</var> is one of <code>full</code>, <code>line</code> or <code>false</code>.
533		See also <a name="idx:open4:983"></a><a class="pred" href="IO.html#open/4">open/4</a>.</dd>
	574	See also <a id="idx:open4:983"></a><a class="pred" href="IO.html#open/4">open/4</a>.</dd>
534	575	<dt><strong>buffer_size</strong>(<var>Integer</var>)</dt>
535	576	<dd class="defbody">
536	577	SWI-Prolog extension to query the size of the I/O buffer associated to a

539	580	<dd class="defbody">
540	581	If present and <code>true</code>, a BOM (<em>Byte Order Mark</em>) was
541	582	detected while opening the file for reading, or a BOM was written while
542		opening the stream. See <a class="sec" href="widechars.html">section
	583	opening the stream. See <a class="sec" href="widechars.html#sec:2.19.1.1">section
543	584	2.19.1.1</a> for details.</dd>
544	585	<dt><strong>close_on_abort</strong>(<var>Bool</var>)</dt>
545	586	<dd class="defbody">
546		Determine whether or not <a name="idx:abort0:984"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
	587	Determine whether or not <a id="idx:abort0:984"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
547	588	closes the stream. By default streams are closed.</dd>
548	589	<dt><strong>close_on_exec</strong>(<var>Bool</var>)</dt>
549	590	<dd class="defbody">

554	595	on Windows.</dd>
555	596	<dt><strong>encoding</strong>(<var>Encoding</var>)</dt>
556	597	<dd class="defbody">
557		Query the encoding used for text. See <a class="sec" href="widechars.html">section
	598	Query the encoding used for text. See <a class="sec" href="widechars.html#sec:2.19.1">section
558	599	2.19.1</a> for an overview of wide character and encoding issues in
559	600	SWI-Prolog.</dd>
560	601	<dt><strong>end_of_stream</strong>(<var>E</var>)</dt>

562	603	If <var>Stream</var> is an input stream, unify <var>E</var> with one of
563	604	the atoms <code>not</code>, <code>at</code> or <code>past</code>. See
564	605	also
565		<a name="idx:atendofstream01:985"></a><a class="pred" href="chario.html#at_end_of_stream/0">at_end_of_stream/[0,1]</a>.</dd>
	606	<a id="idx:atendofstream01:985"></a><a class="pred" href="chario.html#at_end_of_stream/0">at_end_of_stream/[0,1]</a>.</dd>
566	607	<dt><strong>eof_action</strong>(<var>A</var>)</dt>
567	608	<dd class="defbody">
568	609	Unify <var>A</var> with one of <code>eof_code</code>, <code>reset</code>
569	610	or
570		<code>error</code>. See <a name="idx:open4:986"></a><a class="pred" href="IO.html#open/4">open/4</a>
	611	<code>error</code>. See <a id="idx:open4:986"></a><a class="pred" href="IO.html#open/4">open/4</a>
571	612	for details.</dd>
572	613	<dt><strong>file_name</strong>(<var>Atom</var>)</dt>
573	614	<dd class="defbody">

585	626	<dt><strong>locale</strong>(<var>Locale</var>)</dt>
586	627	<dd class="defbody">
587	628	True when <var>Locale</var> is the current locale associated with the
588		stream. See <a class="sec" href="locale.html">section 4.23</a>.</dd>
	629	stream. See <a class="sec" href="locale.html#sec:4.23">section 4.23</a>.</dd>
589	630	<dt><strong>mode</strong>(<var>IOMode</var>)</dt>
590	631	<dd class="defbody">
591		Unify <var>IOMode</var> to the mode given to <a name="idx:open4:987"></a><a class="pred" href="IO.html#open/4">open/4</a>
	632	Unify <var>IOMode</var> to the mode given to <a id="idx:open4:987"></a><a class="pred" href="IO.html#open/4">open/4</a>
592	633	for opening the stream. Values are: <code>read</code>, <code>write</code>, <code>append</code>
593	634	and the SWI-Prolog extension <code>update</code>.</dd>
594	635	<dt><strong>newline</strong>(<var>NewlineMode</var>)</dt>

611	652	<dd class="defbody">
612	653	Unify <var>Pos</var> with the current stream position. A stream position
613	654	is an opaque term whose fields can be extracted using
614		<a name="idx:streampositiondata3:988"></a><a class="pred" href="IO.html#stream_position_data/3">stream_position_data/3</a>.
615		See also <a name="idx:setstreamposition2:989"></a><a class="pred" href="IO.html#set_stream_position/2">set_stream_position/2</a>.</dd>
	655	<a id="idx:streampositiondata3:988"></a><a class="pred" href="IO.html#stream_position_data/3">stream_position_data/3</a>.
	656	See also <a id="idx:setstreamposition2:989"></a><a class="pred" href="IO.html#set_stream_position/2">set_stream_position/2</a>.</dd>
616	657	<dt><strong>reposition</strong>(<var>Bool</var>)</dt>
617	658	<dd class="defbody">
618	659	Unify <var>Bool</var> with <var>true</var> if the position of the stream
619		can be set (see <a name="idx:seek4:990"></a><a class="pred" href="IO.html#seek/4">seek/4</a>).
	660	can be set (see <a id="idx:seek4:990"></a><a class="pred" href="IO.html#seek/4">seek/4</a>).
620	661	It is assumed the position can be set if the stream has a <em>seek-function</em>
621	662	and is not based on a POSIX file descriptor that is not associated to a
622	663	regular file.</dd>

629	670	escape code) or <code>xml</code> (write <code>&#...;</code> XML
630	671	character entity). The initial mode is <code>prolog</code> for the user
631	672	streams and
632		<code>error</code> for all other streams. See also <a class="sec" href="widechars.html">section
633		2.19.1</a> and <a name="idx:setstream2:991"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.</dd>
	673	<code>error</code> for all other streams. See also <a class="sec" href="widechars.html#sec:2.19.1">section
	674	2.19.1</a> and <a id="idx:setstream2:991"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.</dd>
634	675	<dt><strong>timeout</strong>(<var>-Time</var>)</dt>
635	676	<dd class="defbody">
636	677	<var>Time</var> is the timeout currently associated with the stream. See
637		<a name="idx:setstream2:992"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>
	678	<a id="idx:setstream2:992"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>
638	679	with the same option. If no timeout is specified,
639	680	<var>Time</var> is unified to the atom <code>infinite</code>.</dd>
640	681	<dt><strong>type</strong>(<var>Type</var>)</dt>

643	684	<dt><strong>tty</strong>(<var>Bool</var>)</dt>
644	685	<dd class="defbody">
645	686	This property is reported with <var>Bool</var> equal to <code>true</code>
646		if the stream is associated with a terminal. See also <a name="idx:setstream2:993"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.</dd>
	687	if the stream is associated with a terminal. See also <a id="idx:setstream2:993"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.</dd>
647	688	<dt><strong>write_errors</strong>(<var>Atom</var>)</dt>
648	689	<dd class="defbody">
649	690	<var>Atom</var> is one of <code>error</code> (default) or <code>ignore</code>.

654	695	</dl>
655	696
656	697	</dd>
657		<dt class="pubdef"><a name="current_stream/3"><strong>current_stream</strong>(<var>?Object,
	698	<dt class="pubdef"><a id="current_stream/3"><strong>current_stream</strong>(<var>?Object,
658	699	?Mode, ?Stream</var>)</a></dt>
659	700	<dd class="defbody">
660		The predicate <a name="idx:currentstream3:994"></a><a class="pred" href="IO.html#current_stream/3">current_stream/3</a>
	701	The predicate <a id="idx:currentstream3:994"></a><a class="pred" href="IO.html#current_stream/3">current_stream/3</a>
661	702	is used to access the status of a stream as well as to generate all open
662	703	streams. <var>Object</var> is the name of the file opened if the stream
663	704	refers to an open file, an integer file descriptor if the stream
664	705	encapsulates an operating system stream, or the atom <code>[]</code> if
665	706	the stream refers to some other object.
666	707	<var>Mode</var> is one of <code>read</code> or <code>write</code>.</dd>
667		<dt class="pubdef"><a name="is_stream/1"><strong>is_stream</strong>(<var>+Term</var>)</a></dt>
	708	<dt class="pubdef"><a id="is_stream/1"><strong>is_stream</strong>(<var>+Term</var>)</a></dt>
668	709	<dd class="defbody">
669	710	True if <var>Term</var> is a stream name or valid stream handle. This
670	711	predicate realises a safe test for the existence of a stream alias or
671	712	handle.</dd>
672		<dt class="pubdef"><a name="stream_pair/3"><strong>stream_pair</strong>(<var>?StreamPair,
	713	<dt class="pubdef"><a id="stream_pair/3"><strong>stream_pair</strong>(<var>?StreamPair,
673	714	?Read, ?Write</var>)</a></dt>
674	715	<dd class="defbody">
675	716	This predicate can be used in mode (-,+,+) to create a

683	724
684	725	<p>Stream-pairs can be used by all I/O operations on streams, where the
685	726	operation selects the appropriate member of the pair. The predicate
686		<a name="idx:close1:995"></a><a class="pred" href="IO.html#close/1">close/1</a>
	727	<a id="idx:close1:995"></a><a class="pred" href="IO.html#close/1">close/1</a>
687	728	closes the still open streams of the pair.<sup class="fn">86<span class="fn-text">As
688	729	of version 7.1.19, it is allowed to close one of the members of the
689	730	stream directly and close the pair later.</span></sup> The output stream
690	731	is closed before the input stream. If closing the output stream results
691	732	in an error, the input stream is still closed. Success is only returned
692	733	if both streams were closed successfully.</dd>
693		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="set_stream_position/2"><strong>set_stream_position</strong>(<var>+Stream,
	734	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="set_stream_position/2"><strong>set_stream_position</strong>(<var>+Stream,
694	735	+Pos</var>)</a></dt>
695	736	<dd class="defbody">
696	737	Set the current position of <var>Stream</var> to <var>Pos</var>. <var>Pos</var>
697		is a term as returned by <a name="idx:streamproperty2:996"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
698		using the <code>position(Pos)</code> property. See also <a name="idx:seek4:997"></a><a class="pred" href="IO.html#seek/4">seek/4</a>.</dd>
699		<dt class="pubdef"><a name="stream_position_data/3"><strong>stream_position_data</strong>(<var>?Field,
	738	is a term as returned by <a id="idx:streamproperty2:996"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	739	using the <code>position(Pos)</code> property. See also <a id="idx:seek4:997"></a><a class="pred" href="IO.html#seek/4">seek/4</a>.</dd>
	740	<dt class="pubdef"><a id="stream_position_data/3"><strong>stream_position_data</strong>(<var>?Field,
700	741	+Pos, -Data</var>)</a></dt>
701	742	<dd class="defbody">
702		Extracts information from the opaque stream position term as returned by <a name="idx:streamproperty2:998"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	743	Extracts information from the opaque stream position term as returned by <a id="idx:streamproperty2:998"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
703	744	requesting the <code>position(Pos)</code> property.
704	745	<var>Field</var> is one of <code>line_count</code>, <code>line_position</code>,
705		<code>char_count</code> or <code>byte_count</code>. See also <a name="idx:linecount2:999"></a><a class="pred" href="streamstat.html#line_count/2">line_count/2</a>,
706		<a name="idx:lineposition2:1000"></a><a class="pred" href="streamstat.html#line_position/2">line_position/2</a>, <a name="idx:charactercount2:1001"></a><a class="pred" href="streamstat.html#character_count/2">character_count/2</a>
707		and <a name="idx:bytecount2:1002"></a><a class="pred" href="streamstat.html#byte_count/2">byte_count/2</a>.<sup class="fn">87<span class="fn-text">Introduced
	746	<code>char_count</code> or <code>byte_count</code>. See also <a id="idx:linecount2:999"></a><a class="pred" href="streamstat.html#line_count/2">line_count/2</a>,
	747	<a id="idx:lineposition2:1000"></a><a class="pred" href="streamstat.html#line_position/2">line_position/2</a>, <a id="idx:charactercount2:1001"></a><a class="pred" href="streamstat.html#character_count/2">character_count/2</a>
	748	and <a id="idx:bytecount2:1002"></a><a class="pred" href="streamstat.html#byte_count/2">byte_count/2</a>.<sup class="fn">87<span class="fn-text">Introduced
708	749	in version 5.6.4 after extending the position term with a byte count.
709	750	Compatible with SICStus Prolog.</span></sup></dd>
710		<dt class="pubdef"><a name="seek/4"><strong>seek</strong>(<var>+Stream,
	751	<dt class="pubdef"><a id="seek/4"><strong>seek</strong>(<var>+Stream,
711	752	+Offset, +Method, -NewLocation</var>)</a></dt>
712	753	<dd class="defbody">
713	754	Reposition the current point of the given <var>Stream</var>. <var>Method</var>

720	761	files using 2-byte Unicode encoding (2 bytes) or <em>wchar</em> encoding
721	762	(sizeof(wchar_t)). The latter guarantees comfortable interaction with
722	763	wide-character text objects. Otherwise, the use of
723		<a name="idx:seek4:1003"></a><a class="pred" href="IO.html#seek/4">seek/4</a>
724		on non-binary files (see <a name="idx:open4:1004"></a><a class="pred" href="IO.html#open/4">open/4</a>)
	764	<a id="idx:seek4:1003"></a><a class="pred" href="IO.html#seek/4">seek/4</a>
	765	on non-binary files (see <a id="idx:open4:1004"></a><a class="pred" href="IO.html#open/4">open/4</a>)
725	766	is of limited use, especially when using multi-byte text encodings (e.g. UTF-8)
726	767	or multi-byte newline files (e.g. DOS/Windows). On text files,
727		SWI-Prolog offers reliable backup to an old position using <a name="idx:streamproperty2:1005"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	768	SWI-Prolog offers reliable backup to an old position using <a id="idx:streamproperty2:1005"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
728	769	and
729		<a name="idx:setstreamposition2:1006"></a><a class="pred" href="IO.html#set_stream_position/2">set_stream_position/2</a>.
	770	<a id="idx:setstreamposition2:1006"></a><a class="pred" href="IO.html#set_stream_position/2">set_stream_position/2</a>.
730	771	Skipping <var>N</var> character codes is achieved calling
731		<a name="idx:getcode2:1007"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a> <var>N</var>
732		times or using <a name="idx:copystreamdata3:1008"></a><a class="pred" href="chario.html#copy_stream_data/3">copy_stream_data/3</a>,
733		directing the output to a null stream (see <a name="idx:opennullstream1:1009"></a><a class="pred" href="IO.html#open_null_stream/1">open_null_stream/1</a>).
	772	<a id="idx:getcode2:1007"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a> <var>N</var>
	773	times or using <a id="idx:copystreamdata3:1008"></a><a class="pred" href="chario.html#copy_stream_data/3">copy_stream_data/3</a>,
	774	directing the output to a null stream (see <a id="idx:opennullstream1:1009"></a><a class="pred" href="IO.html#open_null_stream/1">open_null_stream/1</a>).
734	775	If the seek modifies the current location, the line number and character
735	776	position in the line are set to 0.
736	777

738	779	is raised. If applying the offset would result in a file position less
739	780	than zero, a <code>domain_error</code> is raised. Behaviour when seeking
740	781	to positions beyond the size of the underlying object depend on the
741		object and possibly the operating system. The predicate <a name="idx:seek4:1010"></a><a class="pred" href="IO.html#seek/4">seek/4</a>
	782	object and possibly the operating system. The predicate <a id="idx:seek4:1010"></a><a class="pred" href="IO.html#seek/4">seek/4</a>
742	783	is compatible with Quintus Prolog, though the error conditions and
743		signalling is ISO compliant. See also <a name="idx:streamproperty2:1011"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
744		and <a name="idx:setstreamposition2:1012"></a><a class="pred" href="IO.html#set_stream_position/2">set_stream_position/2</a>.</dd>
745		<dt class="pubdef"><a name="set_stream/2"><strong>set_stream</strong>(<var>+Stream,
	784	signalling is ISO compliant. See also <a id="idx:streamproperty2:1011"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	785	and <a id="idx:setstreamposition2:1012"></a><a class="pred" href="IO.html#set_stream_position/2">set_stream_position/2</a>.</dd>
	786	<dt class="pubdef"><a id="set_stream/2"><strong>set_stream</strong>(<var>+Stream,
746	787	+Attribute</var>)</a></dt>
747	788	<dd class="defbody">
748	789	Modify an attribute of an existing stream. <var>Attribute</var>
749		specifies the stream property to set. If stream is a <em>pair</em> (see <a name="idx:streampair3:1013"></a><a class="pred" href="IO.html#stream_pair/3">stream_pair/3</a>)
	790	specifies the stream property to set. If stream is a <em>pair</em> (see <a id="idx:streampair3:1013"></a><a class="pred" href="IO.html#stream_pair/3">stream_pair/3</a>)
750	791	both streams are modified, unless the property is only meaningful on one
751	792	of the streams or setting both is not meaningful. In particular,
752	793	<code>eof_action</code> only applies to the <em>read</em> stream,
753	794	<code>representation_errors</code> only applies to the <em>write</em>
754	795	stream and trying to set <code>alias</code> or <code>line_position</code>
755	796	on a pair results in a <code>permission_error</code> exception. See also
756		<a name="idx:streamproperty2:1014"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
757		and <a name="idx:open4:1015"></a><a class="pred" href="IO.html#open/4">open/4</a>.
	797	<a id="idx:streamproperty2:1014"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	798	and <a id="idx:open4:1015"></a><a class="pred" href="IO.html#open/4">open/4</a>.
758	799
759	800	<dl class="latex">
760	801	<dt><strong>alias</strong>(<var>AliasName</var>)</dt>
761	802	<dd class="defbody">
762	803	Set the alias of an already created stream. If <var>AliasName</var> is
763	804	the name of one of the standard streams, this stream is rebound. Thus, <code>set_stream(S,
764		current_input)</code> is the same as <a name="idx:setinput1:1016"></a><a class="pred" href="IO.html#set_input/1">set_input/1</a>,
	805	current_input)</code> is the same as <a id="idx:setinput1:1016"></a><a class="pred" href="IO.html#set_input/1">set_input/1</a>,
765	806	and by setting the alias of a stream to <code>user_input</code>, etc.,
766		all user terminal input is read from this stream. See also <a name="idx:interactor0:1017"></a><a class="pred" href="thutil.html#interactor/0">interactor/0</a>.</dd>
	807	all user terminal input is read from this stream. See also <a id="idx:interactor0:1017"></a><a class="pred" href="thutil.html#interactor/0">interactor/0</a>.</dd>
767	808	<dt><strong>buffer</strong>(<var>Buffering</var>)</dt>
768	809	<dd class="defbody">
769	810	Set the buffering mode of an already created stream. Buffering is one of <code>full</code>, <code>line</code>

774	815	bytes.</dd>
775	816	<dt><strong>close_on_abort</strong>(<var>Bool</var>)</dt>
776	817	<dd class="defbody">
777		Determine whether or not the stream is closed by <a name="idx:abort0:1018"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
	818	Determine whether or not the stream is closed by <a id="idx:abort0:1018"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
778	819	By default, streams are closed.</dd>
779	820	<dt><strong>close_on_exec</strong>(<var>Bool</var>)</dt>
780	821	<dd class="defbody">
781		Set the <code>close_on_exec</code> property. See <a name="idx:streamproperty2:1019"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>.</dd>
	822	Set the <code>close_on_exec</code> property. See <a id="idx:streamproperty2:1019"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>.</dd>
782	823	<dt><strong>encoding</strong>(<var>Atom</var>)</dt>
783	824	<dd class="defbody">
784	825	Defines the mapping between bytes and character codes used for the
785		stream. See <a class="sec" href="widechars.html">section 2.19.1</a> for
786		supported encodings. The value
	826	stream. See <a class="sec" href="widechars.html#sec:2.19.1">section
	827	2.19.1</a> for supported encodings. The value
787	828	<code>bom</code> causes the stream to check whether the current
788	829	character is a Unicode BOM marker. If a BOM marker is found, the
789	830	encoding is set accordingly and the call succeeds. Otherwise the call

805	846	to correct position management of the stream after sending a terminal
806	847	escape sequence (e.g., setting ANSI character attributes). Setting this
807	848	attribute raises a permission error if the stream does not record
808		positions. See <a name="idx:lineposition2:1020"></a><a class="pred" href="streamstat.html#line_position/2">line_position/2</a>
809		and <a name="idx:streamproperty2:1021"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	849	positions. See <a id="idx:lineposition2:1020"></a><a class="pred" href="streamstat.html#line_position/2">line_position/2</a>
	850	and <a id="idx:streamproperty2:1021"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
810	851	(property <code>position</code>).</dd>
811	852	<dt><strong>locale</strong>(<var>+Locale</var>)</dt>
812	853	<dd class="defbody">
813		Change the locale of the stream. See <a class="sec" href="locale.html">section
	854	Change the locale of the stream. See <a class="sec" href="locale.html#sec:4.23">section
814	855	4.23</a>.</dd>
815	856	<dt><strong>newline</strong>(<var>NewlineMode</var>)</dt>
816	857	<dd class="defbody">
817	858	Set input or output translation for newlines. See corresponding
818		<a name="idx:streamproperty2:1022"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	859	<a id="idx:streamproperty2:1022"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
819	860	for details. In addition to the detected modes, an input stream can be
820	861	set in mode <code>detect</code>. It will be set to <code>dos</code> if a <code>\r</code>
821	862	character was removed.</dd>

824	865	This option can be used to make streams generate an exception if it
825	866	takes longer than <var>Seconds</var> before any new data arrives at the
826	867	stream. The value <var>infinite</var> (default) makes the stream block
827		indefinitely. Like <a name="idx:waitforinput3:1023"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>,
	868	indefinitely. Like <a id="idx:waitforinput3:1023"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>,
828	869	this call only applies to streams that support the select() system call.
829		For further information about timeout handling, see <a name="idx:waitforinput3:1024"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>.
	870	For further information about timeout handling, see <a id="idx:waitforinput3:1024"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>.
830	871	The exception is of the form
831	872	<blockquote>
832	873	<code>error(<code>timeout_error(read, Stream)</code>, _)</code>

835	876	<dt><strong>type</strong>(<var>Type</var>)</dt>
836	877	<dd class="defbody">
837	878	Set the type of the stream to one of <code>text</code> or <code>binary</code>.
838		See also <a name="idx:open4:1025"></a><a class="pred" href="IO.html#open/4">open/4</a>
	879	See also <a id="idx:open4:1025"></a><a class="pred" href="IO.html#open/4">open/4</a>
839	880	and the <code>encoding</code> property of streams. Switching to <code>binary</code>
840	881	sets the encoding to <code>octet</code>. Switching to
841	882	<code>text</code> sets the encoding to the default text encoding.</dd>
842	883	<dt><strong>record_position</strong>(<var>Bool</var>)</dt>
843	884	<dd class="defbody">
844		Do/do not record the line count and line position (see <a name="idx:linecount2:1026"></a><a class="pred" href="streamstat.html#line_count/2">line_count/2</a>
845		and <a name="idx:lineposition2:1027"></a><a class="pred" href="streamstat.html#line_position/2">line_position/2</a>).
	885	Do/do not record the line count and line position (see <a id="idx:linecount2:1026"></a><a class="pred" href="streamstat.html#line_count/2">line_count/2</a>
	886	and <a id="idx:lineposition2:1027"></a><a class="pred" href="streamstat.html#line_position/2">line_position/2</a>).
846	887	Calling <code>set_stream(S, record_position(true))</code> resets the
847	888	position the start of line 1.</dd>
848	889	<dt><strong>representation_errors</strong>(<var>Mode</var>)</dt>
849	890	<dd class="defbody">
850	891	Change the behaviour when writing characters to the stream that cannot
851		be represented by the encoding. See also <a name="idx:streamproperty2:1028"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	892	be represented by the encoding. See also <a id="idx:streamproperty2:1028"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
852	893	and
853		<a class="sec" href="widechars.html">section 2.19.1</a>.</dd>
	894	<a class="sec" href="widechars.html#sec:2.19.1">section 2.19.1</a>.</dd>
854	895	<dt><strong>tty</strong>(<var>Bool</var>)</dt>
855	896	<dd class="defbody">
856	897	Modify whether Prolog thinks there is a terminal (i.e. human
857	898	interaction) connected to this stream. On Unix systems the initial value
858	899	comes from isatty(). On Windows, the initial user streams are supposed
859		to be associated to a terminal. See also <a name="idx:streamproperty2:1029"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>.
	900	to be associated to a terminal. See also <a id="idx:streamproperty2:1029"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>.
860	901	</dd>
861	902	</dl>
862	903
863	904	</dd>
864		<dt class="pubdef"><a name="set_prolog_IO/3"><strong>set_prolog_IO</strong>(<var>+In,
	905	<dt class="pubdef"><a id="set_prolog_IO/3"><strong>set_prolog_IO</strong>(<var>+In,
865	906	+Out, +Error</var>)</a></dt>
866	907	<dd class="defbody">
867	908	Prepare the given streams for interactive behaviour normally associated

874	915	is used for
875	916	<code>user_error</code>. Output buffering for <var>Out</var> is set to
876	917	<code>line</code> and buffering on <var>Error</var> is disabled. See
877		also <a name="idx:prolog0:1030"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>
878		and <a name="idx:setstream2:1031"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.
	918	also <a id="idx:prolog0:1030"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>
	919	and <a id="idx:setstream2:1031"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.
879	920	The <em>clib</em> package provides the library <code>library(prolog_server)</code>,
880	921	creating a TCP/IP server for creating an interactive session to Prolog.
881	922	</dd>
882	923	</dl>
883	924
884		<p><h3 id="sec:edinburghIO"><a name="sec:4.17.3"><span class="sec-nr">4.17.3</span> <span class="sec-title">Edinburgh-style
	925	<p><h3 id="sec:edinburghIO"><a id="sec:4.17.3"><span class="sec-nr">4.17.3</span> <span class="sec-title">Edinburgh-style
885	926	I/O</span></a></h3>
886	927
887		<a name="sec:edinburghIO"></a>
	928	<a id="sec:edinburghIO"></a>
888	929
889	930	<p>The package for implicit input and output destinations is (almost)
890	931	compatible with Edinburgh DEC-10 and C-Prolog. The reading and writing
891	932	predicates refer to, resp., the <em>current</em> input and output
892	933	streams. Initially these streams are connected to the terminal. The
893		current output stream is changed using <a name="idx:tell1:1032"></a><a class="pred" href="IO.html#tell/1">tell/1</a>
894		or <a name="idx:append1:1033"></a><a class="pred" href="IO.html#append/1">append/1</a>.
895		The current input stream is changed using <a name="idx:see1:1034"></a><a class="pred" href="IO.html#see/1">see/1</a>.
896		The stream's current value can be obtained using <a name="idx:telling1:1035"></a><a class="pred" href="IO.html#telling/1">telling/1</a>
897		for output and <a name="idx:seeing1:1036"></a><a class="pred" href="IO.html#seeing/1">seeing/1</a>
	934	current output stream is changed using <a id="idx:tell1:1032"></a><a class="pred" href="IO.html#tell/1">tell/1</a>
	935	or <a id="idx:append1:1033"></a><a class="pred" href="IO.html#append/1">append/1</a>.
	936	The current input stream is changed using <a id="idx:see1:1034"></a><a class="pred" href="IO.html#see/1">see/1</a>.
	937	The stream's current value can be obtained using <a id="idx:telling1:1035"></a><a class="pred" href="IO.html#telling/1">telling/1</a>
	938	for output and <a id="idx:seeing1:1036"></a><a class="pred" href="IO.html#seeing/1">seeing/1</a>
898	939	for input.
899	940
900	941	<p>Source and destination are either a file, <code>user</code>, or a

904	945	In the predicate descriptions below we will call the source/destination
905	946	argument `<var>SrcDest</var>'. Below are some examples of
906	947	source/destination specifications.
907		<div style="text-align:center"><table border="0" frame="void" rules="groups">
908		<tr valign="top"><td><code>?- see(data).</code> </td><td>% Start reading
909		from file `data'. </td></tr>
910		<tr valign="top"><td><code>?- tell(user).</code> </td><td>% Start
911		writing to the terminal. </td></tr>
912		<tr valign="top"><td><code>?- tell(pipe(lpr)).</code> </td><td>% Start
913		writing to the printer.</td></tr>
	948
	949	<p><table class="latex frame-void center">
	950	<tr><td><code>?- see(data).</code> </td><td>% Start reading from file
	951	`data'. </td></tr>
	952	<tr><td><code>?- tell(user).</code> </td><td>% Start writing to the
	953	terminal. </td></tr>
	954	<tr><td><code>?- tell(pipe(lpr)).</code> </td><td>% Start writing to the
	955	printer.</td></tr>
914	956	</table>
915		</div>
916	957
917	958	<p>Another example of using the <code>pipe/1</code> construct is shown
918	959	below.<sup class="fn">89<span class="fn-text">As of version 5.3.15, the

935	976	collect_wd([]).
936	977	</pre>
937	978
938		<p>The effect of <a name="idx:tell1:1037"></a><a class="pred" href="IO.html#tell/1">tell/1</a>
	979	<p>The effect of <a id="idx:tell1:1037"></a><a class="pred" href="IO.html#tell/1">tell/1</a>
939	980	is not undone on backtracking, and since the stream handle is not
940	981	specified explicitly in further I/O operations when using
941	982	Edinburgh-style I/O, you may write to unintended streams more easily

948	989
949	990	<h4>Compatibility notes</h4>
950	991
951		<p>Unlike Edinburgh Prolog systems, <a name="idx:telling1:1038"></a><a class="pred" href="IO.html#telling/1">telling/1</a>
952		and <a name="idx:seeing1:1039"></a><a class="pred" href="IO.html#seeing/1">seeing/1</a>
	992	<p>Unlike Edinburgh Prolog systems, <a id="idx:telling1:1038"></a><a class="pred" href="IO.html#telling/1">telling/1</a>
	993	and <a id="idx:seeing1:1039"></a><a class="pred" href="IO.html#seeing/1">seeing/1</a>
953	994	do not return the filename of the current input/output but rather the
954	995	stream identifier, to ensure the design pattern below works under all
955	996	circumstances:<sup class="fn">90<span class="fn-text">Filenames can be

963	1004	...,
964	1005	</pre>
965	1006
966		<p>The predicates <a name="idx:tell1:1040"></a><a class="pred" href="IO.html#tell/1">tell/1</a>
967		and <a name="idx:see1:1041"></a><a class="pred" href="IO.html#see/1">see/1</a>
	1007	<p>The predicates <a id="idx:tell1:1040"></a><a class="pred" href="IO.html#tell/1">tell/1</a>
	1008	and <a id="idx:see1:1041"></a><a class="pred" href="IO.html#see/1">see/1</a>
968	1009	first check for <code>user</code>, the
969	1010	<code>pipe(command)</code> and a stream handle. Otherwise, if the
970	1011	argument is an atom it is first compared to open streams associated to a
971	1012	file with <em>exactly</em> the same name. If such a stream exists,
972	1013	created using
973		<a name="idx:tell1:1042"></a><a class="pred" href="IO.html#tell/1">tell/1</a>
974		or <a name="idx:see1:1043"></a><a class="pred" href="IO.html#see/1">see/1</a>,
	1014	<a id="idx:tell1:1042"></a><a class="pred" href="IO.html#tell/1">tell/1</a>
	1015	or <a id="idx:see1:1043"></a><a class="pred" href="IO.html#see/1">see/1</a>,
975	1016	output (input) is switched to the open stream. Otherwise a file with the
976	1017	specified name is opened.
977	1018

979	1020	without problems. Changing directory, non-file streams, and multiple
980	1021	names referring to the same file easily lead to unexpected behaviour.
981	1022	New code, especially when managing multiple I/O channels, should
982		consider using the ISO I/O predicates defined in <a class="sec" href="IO.html">section
	1023	consider using the ISO I/O predicates defined in <a class="sec" href="IO.html#sec:4.17.2">section
983	1024	4.17.2</a>.
984	1025
985	1026	<dl class="latex">
986		<dt class="pubdef"><a name="see/1"><strong>see</strong>(<var>+SrcDest</var>)</a></dt>
	1027	<dt class="pubdef"><a id="see/1"><strong>see</strong>(<var>+SrcDest</var>)</a></dt>
987	1028	<dd class="defbody">
988	1029	Open <var>SrcDest</var> for reading and make it the current input (see
989		<a name="idx:setinput1:1044"></a><a class="pred" href="IO.html#set_input/1">set_input/1</a>).
	1030	<a id="idx:setinput1:1044"></a><a class="pred" href="IO.html#set_input/1">set_input/1</a>).
990	1031	If <var>SrcDest</var> is a stream handle, just make this stream the
991		current input. See the introduction of <a class="sec" href="IO.html">section
	1032	current input. See the introduction of <a class="sec" href="IO.html#sec:4.17.3">section
992	1033	4.17.3</a> for details.</dd>
993		<dt class="pubdef"><a name="tell/1"><strong>tell</strong>(<var>+SrcDest</var>)</a></dt>
	1034	<dt class="pubdef"><a id="tell/1"><strong>tell</strong>(<var>+SrcDest</var>)</a></dt>
994	1035	<dd class="defbody">
995	1036	Open <var>SrcDest</var> for writing and make it the current output (see
996		<a name="idx:setoutput1:1045"></a><a class="pred" href="IO.html#set_output/1">set_output/1</a>).
	1037	<a id="idx:setoutput1:1045"></a><a class="pred" href="IO.html#set_output/1">set_output/1</a>).
997	1038	If <var>SrcDest</var> is a stream handle, just make this stream the
998		current output. See the introduction of <a class="sec" href="IO.html">section
	1039	current output. See the introduction of <a class="sec" href="IO.html#sec:4.17.3">section
999	1040	4.17.3</a> for details.</dd>
1000		<dt class="pubdef"><a name="append/1"><strong>append</strong>(<var>+File</var>)</a></dt>
1001		<dd class="defbody">
1002		Similar to <a name="idx:tell1:1046"></a><a class="pred" href="IO.html#tell/1">tell/1</a>,
	1041	<dt class="pubdef"><a id="append/1"><strong>append</strong>(<var>+File</var>)</a></dt>
	1042	<dd class="defbody">
	1043	Similar to <a id="idx:tell1:1046"></a><a class="pred" href="IO.html#tell/1">tell/1</a>,
1003	1044	but positions the file pointer at the end of <var>File</var> rather than
1004	1045	truncating an existing file. The pipe construct is not accepted by this
1005	1046	predicate.</dd>
1006		<dt class="pubdef"><a name="seeing/1"><strong>seeing</strong>(<var>?SrcDest</var>)</a></dt>
1007		<dd class="defbody">
1008		Same as <a name="idx:currentinput1:1047"></a><a class="pred" href="IO.html#current_input/1">current_input/1</a>,
	1047	<dt class="pubdef"><a id="seeing/1"><strong>seeing</strong>(<var>?SrcDest</var>)</a></dt>
	1048	<dd class="defbody">
	1049	Same as <a id="idx:currentinput1:1047"></a><a class="pred" href="IO.html#current_input/1">current_input/1</a>,
1009	1050	except that <code>user</code> is returned if the current input is the
1010	1051	stream <code>user_input</code> to improve compatibility with traditional
1011	1052	Edinburgh I/O. See the introduction of
1012		<a class="sec" href="IO.html">section 4.17.3</a> for details.</dd>
1013		<dt class="pubdef"><a name="telling/1"><strong>telling</strong>(<var>?SrcDest</var>)</a></dt>
1014		<dd class="defbody">
1015		Same as <a name="idx:currentoutput1:1048"></a><a class="pred" href="IO.html#current_output/1">current_output/1</a>,
	1053	<a class="sec" href="IO.html#sec:4.17.3">section 4.17.3</a> for details.</dd>
	1054	<dt class="pubdef"><a id="telling/1"><strong>telling</strong>(<var>?SrcDest</var>)</a></dt>
	1055	<dd class="defbody">
	1056	Same as <a id="idx:currentoutput1:1048"></a><a class="pred" href="IO.html#current_output/1">current_output/1</a>,
1016	1057	except that <code>user</code> is returned if the current output is the
1017	1058	stream <code>user_output</code> to improve compatibility with
1018	1059	traditional Edinburgh I/O. See the introduction of
1019		<a class="sec" href="IO.html">section 4.17.3</a> for details.</dd>
1020		<dt class="pubdef"><a name="seen/0"><strong>seen</strong></a></dt>
	1060	<a class="sec" href="IO.html#sec:4.17.3">section 4.17.3</a> for details.</dd>
	1061	<dt class="pubdef"><a id="seen/0"><strong>seen</strong></a></dt>
1021	1062	<dd class="defbody">
1022	1063	Close the current input stream. The new input stream becomes
1023	1064	<code>user_input</code>.</dd>
1024		<dt class="pubdef"><a name="told/0"><strong>told</strong></a></dt>
	1065	<dt class="pubdef"><a id="told/0"><strong>told</strong></a></dt>
1025	1066	<dd class="defbody">
1026	1067	Close the current output stream. The new output stream becomes
1027	1068	<code>user_output</code>.
1028	1069	</dd>
1029	1070	</dl>
1030	1071
1031		<p><h3 id="sec:edinburgh-iso-io"><a name="sec:4.17.4"><span class="sec-nr">4.17.4</span> <span class="sec-title">Switching
	1072	<p><h3 id="sec:edinburgh-iso-io"><a id="sec:4.17.4"><span class="sec-nr">4.17.4</span> <span class="sec-title">Switching
1032	1073	between Edinburgh and ISO I/O</span></a></h3>
1033	1074
1034		<a name="sec:edinburgh-iso-io"></a>
	1075	<a id="sec:edinburgh-iso-io"></a>
1035	1076
1036	1077	<p>The predicates below can be used for switching between the implicit
1037	1078	and the explicit stream-based I/O predicates.
1038	1079
1039	1080	<dl class="latex">
1040		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="set_input/1"><strong>set_input</strong>(<var>+Stream</var>)</a></dt>
	1081	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="set_input/1"><strong>set_input</strong>(<var>+Stream</var>)</a></dt>
1041	1082	<dd class="defbody">
1042	1083	Set the current input stream to become <var>Stream</var>. Thus, <code>open(file,
1043	1084	read, Stream), set_input(Stream)</code> is equivalent to <code>see(file)</code>.
1044	1085	</dd>
1045		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="set_output/1"><strong>set_output</strong>(<var>+Stream</var>)</a></dt>
	1086	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="set_output/1"><strong>set_output</strong>(<var>+Stream</var>)</a></dt>
1046	1087	<dd class="defbody">
1047	1088	Set the current output stream to become <var>Stream</var>. See also
1048		<a name="idx:withoutputto2:1049"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>.
1049		</dd>
1050		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="current_input/1"><strong>current_input</strong>(<var>-Stream</var>)</a></dt>
	1089	<a id="idx:withoutputto2:1049"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>.
	1090	</dd>
	1091	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="current_input/1"><strong>current_input</strong>(<var>-Stream</var>)</a></dt>
1051	1092	<dd class="defbody">
1052	1093	Get the current input stream. Useful for getting access to the status
1053	1094	predicates associated with streams.
1054	1095	</dd>
1055		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="current_output/1"><strong>current_output</strong>(<var>-Stream</var>)</a></dt>
	1096	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="current_output/1"><strong>current_output</strong>(<var>-Stream</var>)</a></dt>
1056	1097	<dd class="defbody">
1057	1098	Get the current output stream.
1058	1099	</dd>
1059	1100	</dl>
1060	1101
1061		<p><h3 id="sec:write-on-atom"><a name="sec:4.17.5"><span class="sec-nr">4.17.5</span> <span class="sec-title">Write
	1102	<p><h3 id="sec:write-on-atom"><a id="sec:4.17.5"><span class="sec-nr">4.17.5</span> <span class="sec-title">Write
1062	1103	onto atoms, code-lists, etc.</span></a></h3>
1063	1104
1064		<a name="sec:write-on-atom"></a>
	1105	<a id="sec:write-on-atom"></a>
1065	1106
1066	1107	<dl class="latex">
1067		<dt class="pubdef"><a name="with_output_to/2"><strong>with_output_to</strong>(<var>+Output,
	1108	<dt class="pubdef"><a id="with_output_to/2"><strong>with_output_to</strong>(<var>+Output,
1068	1109	:Goal</var>)</a></dt>
1069	1110	<dd class="defbody">
1070		Run <var>Goal</var> as <a name="idx:once1:1050"></a><a class="pred" href="metacall.html#once/1">once/1</a>,
	1111	Run <var>Goal</var> as <a id="idx:once1:1050"></a><a class="pred" href="metacall.html#once/1">once/1</a>,
1071	1112	while characters written to the current output are sent to <var>Output</var>.
1072	1113	The predicate is SWI-Prolog-specific, inspired by various posts to the
1073	1114	mailinglist. It provides a flexible replacement for predicates such as
1074		sformat/3 , <a name="idx:swritef3:1051"></a><a class="pred" href="format.html#swritef/3">swritef/3</a>,
1075		<a name="idx:termtoatom2:1052"></a><a class="pred" href="manipatom.html#term_to_atom/2">term_to_atom/2</a>, <a name="idx:atomnumber2:1053"></a><a class="pred" href="manipatom.html#atom_number/2">atom_number/2</a>
1076		converting numbers to atoms, etc. The predicate <a name="idx:format3:1054"></a><a class="pred" href="format.html#format/3">format/3</a>
	1115	sformat/3 , <a id="idx:swritef3:1051"></a><a class="pred" href="format.html#swritef/3">swritef/3</a>,
	1116	<a id="idx:termtoatom2:1052"></a><a class="pred" href="manipatom.html#term_to_atom/2">term_to_atom/2</a>, <a id="idx:atomnumber2:1053"></a><a class="pred" href="manipatom.html#atom_number/2">atom_number/2</a>
	1117	converting numbers to atoms, etc. The predicate <a id="idx:format3:1054"></a><a class="pred" href="format.html#format/3">format/3</a>
1077	1118	accepts the same terms as output argument.
1078	1119
1079	1120	<p>Applications should generally avoid creating atoms by breaking and

1081	1122	intermediate atoms generally leads to poor performance, even more so in
1082	1123	multithreaded applications. This predicate supports creating difference
1083	1124	lists from character data efficiently. The example below defines the DCG
1084		rule <a name="idx:term1:1055"></a><span class="pred-ext">term/3</span>
1085		to insert a term in the output:
	1125	rule <a id="idx:term1:1055"></a><span class="pred-ext">term//1</span> to
	1126	insert a term in the output:
1086	1127
1087	1128	<pre class="code">
1088	1129	term(Term, In, Tail) :-

1097	1138	<dt><b>A Stream handle or alias</b></dt>
1098	1139	<dd class="defbody">
1099	1140	Temporarily switch current output to the given stream. Redirection using
1100		<a name="idx:withoutputto2:1056"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
	1141	<a id="idx:withoutputto2:1056"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
1101	1142	guarantees the original output is restored, also if
1102		<var>Goal</var> fails or raises an exception. See also <a name="idx:callcleanup2:1057"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>.</dd>
	1143	<var>Goal</var> fails or raises an exception. See also <a id="idx:callcleanup2:1057"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>.</dd>
1103	1144	<dt><strong>atom</strong>(<var>-Atom</var>)</dt>
1104	1145	<dd class="defbody">
1105	1146	Create an atom from the emitted characters. Please note the remark
1106	1147	above.</dd>
1107	1148	<dt><strong>string</strong>(<var>-String</var>)</dt>
1108	1149	<dd class="defbody">
1109		Create a string object as defined in <a class="sec" href="strings.html">section
	1150	Create a string object as defined in <a class="sec" href="strings.html#sec:5.2">section
1110	1151	5.2</a>.</dd>
1111	1152	<dt><strong>codes</strong>(<var>-Codes</var>)</dt>
1112	1153	<dd class="defbody">
1113	1154	Create a list of character codes from the emitted characters, similar to
1114		<a name="idx:atomcodes2:1058"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>.</dd>
	1155	<a id="idx:atomcodes2:1058"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>.</dd>
1115	1156	<dt><strong>codes</strong>(<var>-Codes, -Tail</var>)</dt>
1116	1157	<dd class="defbody">
1117	1158	Create a list of character codes as a difference list.</dd>
1118	1159	<dt><strong>chars</strong>(<var>-Chars</var>)</dt>
1119	1160	<dd class="defbody">
1120	1161	Create a list of one-character atoms from the emitted characters,
1121		similar to <a name="idx:atomchars2:1059"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>.</dd>
	1162	similar to <a id="idx:atomchars2:1059"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>.</dd>
1122	1163	<dt><strong>chars</strong>(<var>-Chars, -Tail</var>)</dt>
1123	1164	<dd class="defbody">
1124	1165	Create a list of one-character atoms as a difference list.

1128	1169	</dd>
1129	1170	</dl>
1130	1171
1131		<p><h3 id="sec:fast-term-io"><a name="sec:4.17.6"><span class="sec-nr">4.17.6</span> <span class="sec-title">Fast
	1172	<p><h3 id="sec:fast-term-io"><a id="sec:4.17.6"><span class="sec-nr">4.17.6</span> <span class="sec-title">Fast
1132	1173	binary term I/O</span></a></h3>
1133	1174
1134		<a name="sec:fast-term-io"></a>
	1175	<a id="sec:fast-term-io"></a>
1135	1176
1136	1177	<p>The predicates in this section provide fast binary I/O of arbitrary
1137	1178	Prolog terms, including cyclic terms and terms holding attributed

1139	1180	compatible library that extends the core primitives described below.
1140	1181
1141	1182	<p>The binary representation the same as used by <a class="func" href="foreigninclude.html#PL_record_external()">PL_record_external()</a>.
1142		The use of these primitives instead of using <a name="idx:writecanonical2:1060"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>
	1183	The use of these primitives instead of using <a id="idx:writecanonical2:1060"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>
1143	1184	has advantages and disadvantages. Below are the main considerations:
1144	1185
1145	1186	<p>
1146	1187	<ul class="latex">
1147		<li>Using <a name="idx:writecanonical2:1061"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>
	1188	<li>Using <a id="idx:writecanonical2:1061"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>
1148	1189	allows or exchange of terms with other Prolog systems. The format is
1149	1190	stable and, as it is text based, it can be inspected and corrected.
1150	1191	<li>Using the binary format improves the performance roughly 3 times.
1151	1192	<li>The size of both representations is comparable.
1152	1193	<li>The binary format can deal with cycles, sharing and attributes.
1153		Special precautions are needed to transfer such terms using <a name="idx:writecanonical2:1062"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>.
1154		See <a name="idx:termfactorized3:1063"></a><span class="pred-ext">term_factorized/3</span>
1155		and <a name="idx:copyterm3:1064"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>.
	1194	Special precautions are needed to transfer such terms using <a id="idx:writecanonical2:1062"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>.
	1195	See <a id="idx:termfactorized3:1063"></a><span class="pred-ext">term_factorized/3</span>
	1196	and <a id="idx:copyterm3:1064"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>.
1156	1197	<li>In the current version, reading the binary format has only
1157	1198	incomplete consistency checks. This implies a user must be able to <b>trust
1158	1199	the source</b> as crafted messages may compromise the reading Prolog

1160	1201	</ul>
1161	1202
1162	1203	<dl class="latex">
1163		<dt class="pubdef"><a name="fast_term_serialized/2"><strong>fast_term_serialized</strong>(<var>?Term,
	1204	<dt class="pubdef"><a id="fast_term_serialized/2"><strong>fast_term_serialized</strong>(<var>?Term,
1164	1205	?String</var>)</a></dt>
1165	1206	<dd class="defbody">
1166	1207	(De-)serialize <var>Term</var> to/from <var>String</var>.</dd>
1167		<dt class="pubdef"><a name="fast_write/2"><strong>fast_write</strong>(<var>+Output,
	1208	<dt class="pubdef"><a id="fast_write/2"><strong>fast_write</strong>(<var>+Output,
1168	1209	+Term</var>)</a></dt>
1169	1210	<dd class="defbody">
1170	1211	Write <var>Term</var> using the fast serialization format to the
1171	1212	<var>Output</var> stream. <var>Output</var> <em>must</em> be a binary
1172	1213	stream.</dd>
1173		<dt class="pubdef"><a name="fast_read/2"><strong>fast_read</strong>(<var>+Input,
	1214	<dt class="pubdef"><a id="fast_read/2"><strong>fast_read</strong>(<var>+Input,
1174	1215	-Term</var>)</a></dt>
1175	1216	<dd class="defbody">
1176	1217	Read <var>Term</var> using the fast serialization format from the
1177	1218	<var>Input</var> stream. <var>Input</var> <em>must</em> be a binary
1178		stream.<sup class="fn">bug<span class="fn-text">The predicate <a name="idx:fastread2:1065"></a><a class="pred" href="IO.html#fast_read/2">fast_read/2</a>
	1219	stream.<sup class="fn">bug<span class="fn-text">The predicate <a id="idx:fastread2:1065"></a><a class="pred" href="IO.html#fast_read/2">fast_read/2</a>
1179	1220	may crash on arbitrary input.</span></sup>
1180	1221	</dd>
1181	1222	</dl>

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 8.2</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 8.2</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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191	232	<a class="nav" href="chrintro.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:SyntaxAndSemantics"><a name="sec:8.2"><span class="sec-nr">8.2</span> <span class="sec-title">Syntax
	235	<h2 id="sec:SyntaxAndSemantics"><a id="sec:8.2"><span class="sec-nr">8.2</span> <span class="sec-title">Syntax
195	236	and Semantics</span></a></h2>
196	237
197		<a name="sec:SyntaxAndSemantics"></a>
198		<h3 id="sec:chr-syntax"><a name="sec:8.2.1"><span class="sec-nr">8.2.1</span> <span class="sec-title">Syntax
	238	<a id="sec:SyntaxAndSemantics"></a>
	239	<h3 id="sec:chr-syntax"><a id="sec:8.2.1"><span class="sec-nr">8.2.1</span> <span class="sec-title">Syntax
199	240	of CHR rules</span></a></h3>
200	241
201		<a name="sec:chr-syntax"></a>
	242	<a id="sec:chr-syntax"></a>
202	243
203	244	<pre class="code">
204	245	rules --> rule, rules ; [].

247	288	do not appear in the head of the rule, e.g. an auxiliary variable
248	289	introduced in the guard.
249	290
250		<p><h3 id="sec:chr-semantics"><a name="sec:8.2.2"><span class="sec-nr">8.2.2</span> <span class="sec-title">Semantics</span></a></h3>
251
252		<a name="sec:chr-semantics"></a> In this subsection the operational
	291	<p><h3 id="sec:chr-semantics"><a id="sec:8.2.2"><span class="sec-nr">8.2.2</span> <span class="sec-title">Semantics</span></a></h3>
	292
	293	<a id="sec:chr-semantics"></a> In this subsection the operational
253	294	semantics of CHR in Prolog are presented informally. They do not differ
254	295	essentially from other CHR systems.
255	296

334	375	<p>Additional pragmas may be released in the future.
335	376
336	377	<dl class="latex">
337		<dt class="pubdef"><a name="chr_option/2">:- <strong>chr_option</strong>(<var>+Option,
	378	<dt class="pubdef"><a id="chr_option/2">:- <strong>chr_option</strong>(<var>+Option,
338	379	+Value</var>)</a></dt>
339	380	<dd class="defbody">
340	381	It is possible to specify options that apply to all the CHR rules in the

372	413	<dd class="defbody">
373	414	This option enables or disables the possibility to debug the CHR code.
374	415	Possible values are <code>on</code> (default) and <code>off</code>. See
375		<a class="sec" href="debugging.html">section 8.4</a> for more details on
376		debugging. The default is derived from the Prolog flag <a class="flag" href="flags.html#flag:generate_debug_info">generate_debug_info</a>,
	416	<a class="sec" href="debugging.html#sec:8.4">section 8.4</a> for more
	417	details on debugging. The default is derived from the Prolog flag <a class="flag" href="flags.html#flag:generate_debug_info">generate_debug_info</a>,
377	418	which is <code>true</code> by default. See <strong>-nodebug</strong>. If
378	419	debugging is enabled, optimization must be disabled.
379	420	</dd>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 1.6</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:acknowledge"><a name="sec:1.6"><span class="sec-nr">1.6</span> <span class="sec-title">Acknowledgements</span></a></h2>
195
196		<a name="sec:acknowledge"></a>
	235	<h2 id="sec:acknowledge"><a id="sec:1.6"><span class="sec-nr">1.6</span> <span class="sec-title">Acknowledgements</span></a></h2>
	236
	237	<a id="sec:acknowledge"></a>
197	238
198	239	<p>Some small parts of the Prolog code of SWI-Prolog are modified
199	240	versions of the corresponding Edinburgh C-Prolog code: grammar rule
200		compilation and <a name="idx:writef2:4"></a><a class="pred" href="format.html#writef/2">writef/2</a>.
	241	compilation and <a id="idx:writef2:4"></a><a class="pred" href="format.html#writef/2">writef/2</a>.
201	242	Also some of the C-code originates from C-Prolog: finding the path of
202		the currently running executable and some of the code underlying <a name="idx:absolutefilename2:5"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>.
	243	the currently running executable and some of the code underlying <a id="idx:absolutefilename2:5"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>.
203	244	Ideas on programming style and techniques originate from C-Prolog and
204	245	Richard O'Keefe's <em>thief</em> editor. An important source of
205	246	inspiration are the programming techniques introduced by Anjo

224	265	implementation.
225	266
226	267	<p>Tom Schrijvers and Bart Demoen initiated the implementation of
227		<em>delimited continuations</em> (<a class="sec" href="delcont.html">section
	268	<em>delimited continuations</em> (<a class="sec" href="delcont.html#sec:4.10">section
228	269	4.10</a>), which was used by Benoit Desouter and Tom Schrijvers to
229		implement <em>tabling</em> (<a class="sec" href="tabling.html">section
	270	implement <em>tabling</em> (<a class="sec" href="tabling.html#sec:A.35">section
230	271	A.35</a>) as a library. Fabrizio Riguzzi added a first implementation
231		for <em>mode directed tabling</em> (<a class="sec" href="tabling.html">section
	272	for <em>mode directed tabling</em> (<a class="sec" href="tabling.html#sec:A.35.3">section
232	273	A.35.3</a>).
233	274
234		<p>The SWI-Prolog 7 extensions (<a class="sec" href="extensions.html">section
	275	<p>The SWI-Prolog 7 extensions (<a class="sec" href="extensions.html#sec:5">section
235	276	5</a>) are the result of a long heated discussion on the mailinglist.
236	277	Nicos Angelopoulos' wish for a smooth integration with the R language
237	278	triggered the overall intend of these extensions to enable a smoother

263	304
264	305	<p>Kyndi (<a class="url" href="https://kyndi.com/">https://kyndi.com/</a>)
265	306	sponsored the development of the
266		<em>engines</em> interface (<a class="sec" href="engines.html">chapter
	307	<em>engines</em> interface (<a class="sec" href="engines.html#sec:10">chapter
267	308	10</a>). The final API was established after discussion with the
268	309	founding father of engines, Paul Tarau and Paulo Moura. Kyndi also
269	310	sponsored JIT indexing on multiple arguments.

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193	234	</div>
194		<h2 id="sec:aggregate"><a name="sec:A.1"><span class="sec-nr">A.1</span> <span class="sec-title">library(aggregate):
	235	<h2 id="sec:aggregate"><a id="sec:A.1"><span class="sec-nr">A.1</span> <span class="sec-title">library(aggregate):
195	236	Aggregation operators on backtrackable predicates</span></a></h2>
196	237
197		<p><a name="sec:aggregate"></a>
	238	<p><a id="sec:aggregate"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">Compatibility</dt>

312	353	<p><i>The development of this library was sponsored by SecuritEase, <a class="url" href="http://www.securitease.com">http://www.securitease.com</a></i>
313	354
314	355	<dl class="latex">
315		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="aggregate/3"><strong>aggregate</strong>(<var>+Template,
	356	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="aggregate/3"><strong>aggregate</strong>(<var>+Template,
316	357	:Goal, -Result</var>)</a></dt>
317	358	<dd class="defbody">
318	359	Aggregate bindings in <var>Goal</var> according to <var>Template</var>.
319	360	The <a class="pred" href="aggregate.html#aggregate/3">aggregate/3</a>
320	361	version performs <a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
321	362	on <var>Goal</var>.</dd>
322		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="aggregate/4"><strong>aggregate</strong>(<var>+Template,
	363	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="aggregate/4"><strong>aggregate</strong>(<var>+Template,
323	364	+Discriminator, :Goal, -Result</var>)</a></dt>
324	365	<dd class="defbody">
325	366	Aggregate bindings in <var>Goal</var> according to <var>Template</var>.
326	367	The <a class="pred" href="aggregate.html#aggregate/4">aggregate/4</a>
327	368	version performs <a class="pred" href="allsolutions.html#setof/3">setof/3</a>
328	369	on <var>Goal</var>.</dd>
329		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="aggregate_all/3"><strong>aggregate_all</strong>(<var>+Template,
	370	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="aggregate_all/3"><strong>aggregate_all</strong>(<var>+Template,
330	371	:Goal, -Result</var>)</a></dt>
331	372	<dd class="defbody">
332	373	Aggregate bindings in <var>Goal</var> according to <var>Template</var>.

338	379	<code>max(X)</code>, <code>min(X,Witness)</code> or <code>max(X,Witness)</code>
339	380	and <var>Goal</var> has no solutions, i.e., the minumum and maximum of
340	381	an empty set is undefined.</dd>
341		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="aggregate_all/4"><strong>aggregate_all</strong>(<var>+Template,
	382	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="aggregate_all/4"><strong>aggregate_all</strong>(<var>+Template,
342	383	+Discriminator, :Goal, -Result</var>)</a></dt>
343	384	<dd class="defbody">
344	385	Aggregate bindings in <var>Goal</var> according to <var>Template</var>.

348	389	followed by <a class="pred" href="builtinlist.html#sort/2">sort/2</a> on
349	390	<var>Goal</var>. See <a class="pred" href="aggregate.html#aggregate_all/3">aggregate_all/3</a>
350	391	to understand why this predicate can fail.</dd>
351		<dt class="pubdef"><a name="foreach/2"><strong>foreach</strong>(<var>:Generator,
	392	<dt class="pubdef"><a id="foreach/2"><strong>foreach</strong>(<var>:Generator,
352	393	:Goal</var>)</a></dt>
353	394	<dd class="defbody">
354	395	True if conjunction of results is true. Unlike <a class="pred" href="forall2.html#forall/2">forall/2</a>,

381	422	</dl>
382	423
383	424	</dd>
384		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="free_variables/4"><strong>free_variables</strong>(<var>:Generator,
	425	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="free_variables/4"><strong>free_variables</strong>(<var>:Generator,
385	426	+Template, +VarList0, -VarList</var>)</a></dt>
386	427	<dd class="defbody">
387	428	Find free variables in bagof/setof template. In order to handle

417	458	</dl>
418	459
419	460	</dd>
420		<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a name="sandbox:safe_meta/2"><span class="module">sandbox</span>:<strong>safe_meta</strong>(<var>+Goal,
	461	<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="sandbox:safe_meta/2"><span class="module">sandbox</span>:<strong>safe_meta</strong>(<var>+Goal,
421	462	-Called</var>)</a></dt>
422	463	<dd class="defbody">
423	464	Declare the aggregate meta-calls safe. This cannot be proven due to the

+83

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 4.30</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.30</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="builtinlist.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:allsolutions"><a name="sec:4.30"><span class="sec-nr">4.30</span> <span class="sec-title">Finding
	235	<h2 id="sec:allsolutions"><a id="sec:4.30"><span class="sec-nr">4.30</span> <span class="sec-title">Finding
195	236	all Solutions to a Goal</span></a></h2>
196	237
197		<a name="sec:allsolutions"></a>
	238	<a id="sec:allsolutions"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="findall/3"><strong>findall</strong>(<var>+Template,
	241	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="findall/3"><strong>findall</strong>(<var>+Template,
201	242	:Goal, -Bag</var>)</a></dt>
202	243	<dd class="defbody">
203	244	Create a list of the instantiations <var>Template</var> gets
204	245	successively on backtracking over <var>Goal</var> and unify the result
205	246	with <var>Bag</var>. Succeeds with an empty list if <var>Goal</var> has
206		no solutions. <a name="idx:findall3:1361"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
207		is equivalent to <a name="idx:bagof3:1362"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
	247	no solutions. <a id="idx:findall3:1361"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
	248	is equivalent to <a id="idx:bagof3:1362"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
208	249	with all free variables bound with the existential operator (<strong><code>^</code></strong>),
209		except that <a name="idx:bagof3:1363"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
	250	except that <a id="idx:bagof3:1363"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
210	251	fails when <var>Goal</var> has no solutions.</dd>
211		<dt class="pubdef"><a name="findall/4"><strong>findall</strong>(<var>+Template,
	252	<dt class="pubdef"><a id="findall/4"><strong>findall</strong>(<var>+Template,
212	253	:Goal, -Bag, +Tail</var>)</a></dt>
213	254	<dd class="defbody">
214		As <a name="idx:findall3:1364"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>,
	255	As <a id="idx:findall3:1364"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>,
215	256	but returns the result as the difference list
216	257	<var>Bag</var>-<var>Tail</var>. The 3-argument version is defined as
217	258

221	262	</pre>
222	263
223	264	</dd>
224		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="findnsols/4"><strong>findnsols</strong>(<var>+N,
	265	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="findnsols/4"><strong>findnsols</strong>(<var>+N,
225	266	@Template, :Goal, -List</var>)</a></dt>
226		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="findnsols/5"><strong>findnsols</strong>(<var>+N,
	267	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="findnsols/5"><strong>findnsols</strong>(<var>+N,
227	268	@Template, :Goal, -List, ?Tail</var>)</a></dt>
228	269	<dd class="defbody">
229		As <a name="idx:findall3:1365"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
230		and <a name="idx:findall4:1366"></a><a class="pred" href="allsolutions.html#findall/4">findall/4</a>,
	270	As <a id="idx:findall3:1365"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
	271	and <a id="idx:findall4:1366"></a><a class="pred" href="allsolutions.html#findall/4">findall/4</a>,
231	272	but generates at most <var>N</var> solutions. If
232	273	<var>N</var> solutions are returned, this predicate succeeds with a
233	274	choice point if <var>Goal</var> has a choice point. Backtracking returns
234	275	the next chunk of (at most) <var>N</var> solutions. In addition to
235	276	passing a plain integer for <var>N</var>, a term of the form <code>count(N)</code>
236	277	is accepted. Using <code>count(N)</code>, the size of the next chunk can
237		be controlled using <a name="idx:nbsetarg3:1367"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
	278	be controlled using <a id="idx:nbsetarg3:1367"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
238	279	The non-deterministic behaviour used to implement the
239	280	<em>chunk</em> option in <code>library(pengines)</code>. Based on Ciao,
240	281	but the Ciao version is deterministic. Portability can be achieved by
241		wrapping the goal in <a name="idx:once1:1368"></a><a class="pred" href="metacall.html#once/1">once/1</a>.
	282	wrapping the goal in <a id="idx:once1:1368"></a><a class="pred" href="metacall.html#once/1">once/1</a>.
242	283	Below are three examples. The first illustrates standard chunking of
243	284	answers. The second illustrates that the chunk size can be adjusted
244	285	dynamically and the last illustrates that no choice point is left if <var>Goal</var>

262	303	</pre>
263	304
264	305	</dd>
265		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="bagof/3"><strong>bagof</strong>(<var>+Template,
	306	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="bagof/3"><strong>bagof</strong>(<var>+Template,
266	307	:Goal, -Bag</var>)</a></dt>
267	308	<dd class="defbody">
268	309	Unify <var>Bag</var> with the alternatives of <var>Template</var>. If <var>Goal</var>
269		has free variables besides the one sharing with <var>Template</var>, <a name="idx:bagof3:1369"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
	310	has free variables besides the one sharing with <var>Template</var>, <a id="idx:bagof3:1369"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
270	311	will backtrack over the alternatives of these free variables, unifying
271	312	<var>Bag</var> with the corresponding alternatives of <var>Template</var>.
272	313	The construct <code>+<var>Var</var><code>^</code><var>Goal</var></code>
273		tells <a name="idx:bagof3:1370"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
	314	tells <a id="idx:bagof3:1370"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
274	315	not to bind
275		<var>Var</var> in <var>Goal</var>. <a name="idx:bagof3:1371"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
	316	<var>Var</var> in <var>Goal</var>. <a id="idx:bagof3:1371"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
276	317	fails if <var>Goal</var> has no solutions.
277	318
278		<p>The example below illustrates <a name="idx:bagof3:1372"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
	319	<p>The example below illustrates <a id="idx:bagof3:1372"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>
279	320	and the <strong><code>^</code></strong> operator. The variable bindings
280	321	are printed together on one line to save paper.
281	322

301	342	</pre>
302	343
303	344	</dd>
304		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="setof/3"><strong>setof</strong>(<var>+Template,
	345	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="setof/3"><strong>setof</strong>(<var>+Template,
305	346	+Goal, -Set</var>)</a></dt>
306	347	<dd class="defbody">
307		Equivalent to <a name="idx:bagof3:1373"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>,
308		but sorts the result using <a name="idx:sort2:1374"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>
	348	Equivalent to <a id="idx:bagof3:1373"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>,
	349	but sorts the result using <a id="idx:sort2:1374"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>
309	350	to get a sorted list of alternatives without duplicates.
310	351	</dd>
311	352	</dl>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 6.11</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:altmoduleapi"><a name="sec:6.11"><span class="sec-nr">6.11</span> <span class="sec-title">An
	235	<h2 id="sec:altmoduleapi"><a id="sec:6.11"><span class="sec-nr">6.11</span> <span class="sec-title">An
195	236	alternative import/export interface</span></a></h2>
196	237
197		<a name="sec:altmoduleapi"></a>
198
199		<p>The <a name="idx:usemodule1:1726"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
200		predicate from <a class="sec" href="import.html">section 6.3</a> defines
201		import and export relations based on the filename from which a module is
202		loaded. If modules are created differently, such as by asserting
203		predicates into a new module as described in <a class="sec" href="dynamic-modules.html">section
	238	<a id="sec:altmoduleapi"></a>
	239
	240	<p>The <a id="idx:usemodule1:1730"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	241	predicate from <a class="sec" href="import.html#sec:6.3">section 6.3</a>
	242	defines import and export relations based on the filename from which a
	243	module is loaded. If modules are created differently, such as by
	244	asserting predicates into a new module as described in <a class="sec" href="dynamic-modules.html#sec:6.12">section
204	245	6.12</a>, this interface cannot be used. The interface below provides
205	246	for import/export from modules that are not created using a module file.
206	247
207	248	<dl class="latex">
208		<dt class="pubdef"><a name="export/1"><strong>export</strong>(<var>+PredicateIndicator,
	249	<dt class="pubdef"><a id="export/1"><strong>export</strong>(<var>+PredicateIndicator,
209	250	...</var>)</a></dt>
210	251	<dd class="defbody">
211	252	Add predicates to the public list of the context module. This implies
212	253	the predicate will be imported into another module if this module is
213		imported with <a name="idx:usemodule12:1727"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.
214		Note that predicates are normally exported using the directive <a name="idx:module2:1728"></a><a class="pred" href="defmodule.html#module/2">module/2</a>. <a name="idx:export1:1729"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>
	254	imported with <a id="idx:usemodule12:1731"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.
	255	Note that predicates are normally exported using the directive <a id="idx:module2:1732"></a><a class="pred" href="defmodule.html#module/2">module/2</a>. <a id="idx:export1:1733"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>
215	256	is meant to handle export from dynamically created modules.</dd>
216		<dt class="pubdef"><a name="import/1"><strong>import</strong>(<var>+PredicateIndicator,
	257	<dt class="pubdef"><a id="import/1"><strong>import</strong>(<var>+PredicateIndicator,
217	258	...</var>)</a></dt>
218	259	<dd class="defbody">
219	260	Import predicates <var>PredicateIndicator</var> into the current context
220	261	module. <var>PredicateIndicator</var> must specify the source module
221	262	using the <<var>module</var>>:<<var>pi</var>> construct.
222		Note that predicates are normally imported using one of the directives <a name="idx:usemodule12:1730"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.
223		The <a name="idx:import1:1731"></a><a class="pred" href="altmoduleapi.html#import/1">import/1</a>
	263	Note that predicates are normally imported using one of the directives <a id="idx:usemodule12:1734"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.
	264	The <a id="idx:import1:1735"></a><a class="pred" href="altmoduleapi.html#import/1">import/1</a>
224	265	alternative is meant for handling imports into dynamically created
225		modules. See also <a name="idx:export1:1732"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>
226		and <a name="idx:exportlist2:1733"></a><span class="pred-ext">export_list/2</span>.
	266	modules. See also <a id="idx:export1:1736"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>
	267	and <a id="idx:exportlist2:1737"></a><span class="pred-ext">export_list/2</span>.
227	268	</dd>
228	269	</dl>
229	270

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193	234	</div>
194		<h2 id="sec:ancestral-cut"><a name="sec:B.2"><span class="sec-nr">B.2</span> <span class="sec-title">Ancestral
	235	<h2 id="sec:ancestral-cut"><a id="sec:B.2"><span class="sec-nr">B.2</span> <span class="sec-title">Ancestral
195	236	cuts</span></a></h2>
196	237
197		<a name="sec:ancestral-cut"></a>
	238	<a id="sec:ancestral-cut"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="prolog_cut_to/1"><strong>prolog_cut_to</strong>(<var>+Choice</var>)</a></dt>
	241	<dt class="pubdef"><a id="prolog_cut_to/1"><strong>prolog_cut_to</strong>(<var>+Choice</var>)</a></dt>
201	242	<dd class="defbody">
202	243	Prunes all choice points created since <var>Choice</var>. Can be used
203		together with <a name="idx:prologcurrentchoice1:2187"></a><a class="pred" href="manipstack.html#prolog_current_choice/1">prolog_current_choice/1</a>
	244	together with <a id="idx:prologcurrentchoice1:2191"></a><a class="pred" href="manipstack.html#prolog_current_choice/1">prolog_current_choice/1</a>
204	245	to implement <em>ancestral</em> cuts. This predicate is in the hackers
205	246	corner because it should not be used in normal Prolog code. It may be
206	247	used to create new high level control structures, particularly for

210	251	environment frames are <em>not</em> reclaimed. As a consequence, where
211	252	predicates that are deterministic due to clause indexing, normal cuts or
212	253	<code>(if\send{then};else)</code> and and tail recursive run in bounded
213		local stack space, predicates using <a name="idx:prologcutto1:2188"></a><a class="pred" href="ancestral-cut.html#prolog_cut_to/1">prolog_cut_to/1</a>
	254	local stack space, predicates using <a id="idx:prologcutto1:2192"></a><a class="pred" href="ancestral-cut.html#prolog_cut_to/1">prolog_cut_to/1</a>
214	255	will run out of stack.
215	256	</dd>
216	257	</dl>

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193	234	</div>
194		<h2 id="sec:apply"><a name="sec:A.2"><span class="sec-nr">A.2</span> <span class="sec-title">library(apply):
	235	<h2 id="sec:apply"><a id="sec:A.2"><span class="sec-nr">A.2</span> <span class="sec-title">library(apply):
195	236	Apply predicates on a list</span></a></h2>
196	237
197		<p><a name="sec:apply"></a>
	238	<p><a id="sec:apply"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="mtag">See also</dt>

213	254	members of a list.
214	255
215	256	<dl class="latex">
216		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="include/3"><strong>include</strong>(<var>:Goal,
	257	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="include/3"><strong>include</strong>(<var>:Goal,
217	258	+List1, ?List2</var>)</a></dt>
218	259	<dd class="defbody">
219	260	Filter elements for which <var>Goal</var> succeeds. True if <var>List2</var>

229	270	</dl>
230	271
231	272	</dd>
232		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="exclude/3"><strong>exclude</strong>(<var>:Goal,
	273	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="exclude/3"><strong>exclude</strong>(<var>:Goal,
233	274	+List1, ?List2</var>)</a></dt>
234	275	<dd class="defbody">
235	276	Filter elements for which <var>Goal</var> fails. True if <var>List2</var>
236	277	contains those elements Xi of <var>List1</var> for which <code>call(Goal, Xi)</code>
237	278	fails.</dd>
238		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="partition/4"><strong>partition</strong>(<var>:Pred,
	279	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="partition/4"><strong>partition</strong>(<var>:Pred,
239	280	+List, ?Included, ?Excluded</var>)</a></dt>
240	281	<dd class="defbody">
241	282	Filter elements of <var>List</var> according to <var>Pred</var>. True if <var>Included</var>
242	283	contains all elements for which <code>call(Pred, X)</code> succeeds and
243	284	<var>Excluded</var> contains the remaining elements.</dd>
244		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="partition/5"><strong>partition</strong>(<var>:Pred,
	285	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="partition/5"><strong>partition</strong>(<var>:Pred,
245	286	+List, ?Less, ?Equal, ?Greater</var>)</a></dt>
246	287	<dd class="defbody">
247	288	Filter <var>List</var> according to <var>Pred</var> in three sets. For

249	290	where Place must be unified to one of <code><</code>, <code>=</code>
250	291	or <code>></code>.
251	292	<var>Pred</var> must be deterministic.</dd>
252		<dt class="pubdef"><a name="maplist/2"><strong>maplist</strong>(<var>:Goal,
	293	<dt class="pubdef"><a id="maplist/2"><strong>maplist</strong>(<var>:Goal,
253	294	?List</var>)</a></dt>
254	295	<dd class="defbody">
255	296	True if <var>Goal</var> can successfully be applied on all elements of
256	297	<var>List</var>. Arguments are reordered to gain performance as well as
257	298	to make the predicate deterministic under normal circumstances.</dd>
258		<dt class="pubdef"><a name="maplist/3"><strong>maplist</strong>(<var>:Goal,
	299	<dt class="pubdef"><a id="maplist/3"><strong>maplist</strong>(<var>:Goal,
259	300	?List1, ?List2</var>)</a></dt>
260	301	<dd class="defbody">
261	302	As <a class="pred" href="apply.html#maplist/2">maplist/2</a>, operating
262	303	on pairs of elements from two lists.</dd>
263		<dt class="pubdef"><a name="maplist/4"><strong>maplist</strong>(<var>:Goal,
	304	<dt class="pubdef"><a id="maplist/4"><strong>maplist</strong>(<var>:Goal,
264	305	?List1, ?List2, ?List3</var>)</a></dt>
265	306	<dd class="defbody">
266	307	As <a class="pred" href="apply.html#maplist/2">maplist/2</a>, operating
267	308	on triples of elements from three lists.</dd>
268		<dt class="pubdef"><a name="maplist/5"><strong>maplist</strong>(<var>:Goal,
	309	<dt class="pubdef"><a id="maplist/5"><strong>maplist</strong>(<var>:Goal,
269	310	?List1, ?List2, ?List3, ?List4</var>)</a></dt>
270	311	<dd class="defbody">
271	312	As <a class="pred" href="apply.html#maplist/2">maplist/2</a>, operating
272	313	on quadruples of elements from four lists.</dd>
273		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="convlist/3"><strong>convlist</strong>(<var>:Goal,
	314	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="convlist/3"><strong>convlist</strong>(<var>:Goal,
274	315	+ListIn, -ListOut</var>)</a></dt>
275	316	<dd class="defbody">
276	317	Similar to <a class="pred" href="apply.html#maplist/3">maplist/3</a>,

292	333	</dl>
293	334
294	335	</dd>
295		<dt class="pubdef"><a name="foldl/4"><strong>foldl</strong>(<var>:Goal,
	336	<dt class="pubdef"><a id="foldl/4"><strong>foldl</strong>(<var>:Goal,
296	337	+List, +V0, -V</var>)</a></dt>
297		<dt class="pubdef"><a name="foldl/5"><strong>foldl</strong>(<var>:Goal,
	338	<dt class="pubdef"><a id="foldl/5"><strong>foldl</strong>(<var>:Goal,
298	339	+List1, +List2, +V0, -V</var>)</a></dt>
299		<dt class="pubdef"><a name="foldl/6"><strong>foldl</strong>(<var>:Goal,
	340	<dt class="pubdef"><a id="foldl/6"><strong>foldl</strong>(<var>:Goal,
300	341	+List1, +List2, +List3, +V0, -V</var>)</a></dt>
301		<dt class="pubdef"><a name="foldl/7"><strong>foldl</strong>(<var>:Goal,
	342	<dt class="pubdef"><a id="foldl/7"><strong>foldl</strong>(<var>:Goal,
302	343	+List1, +List2, +List3, +List4, +V0, -V</var>)</a></dt>
303	344	<dd class="defbody">
304	345	Fold a list, using arguments of the list as left argument. The foldl

312	353	</pre>
313	354
314	355	</dd>
315		<dt class="pubdef"><a name="scanl/4"><strong>scanl</strong>(<var>:Goal,
	356	<dt class="pubdef"><a id="scanl/4"><strong>scanl</strong>(<var>:Goal,
316	357	+List, +V0, -Values</var>)</a></dt>
317		<dt class="pubdef"><a name="scanl/5"><strong>scanl</strong>(<var>:Goal,
	358	<dt class="pubdef"><a id="scanl/5"><strong>scanl</strong>(<var>:Goal,
318	359	+List1, +List2, +V0, -Values</var>)</a></dt>
319		<dt class="pubdef"><a name="scanl/6"><strong>scanl</strong>(<var>:Goal,
	360	<dt class="pubdef"><a id="scanl/6"><strong>scanl</strong>(<var>:Goal,
320	361	+List1, +List2, +List3, +V0, -Values</var>)</a></dt>
321		<dt class="pubdef"><a name="scanl/7"><strong>scanl</strong>(<var>:Goal,
	362	<dt class="pubdef"><a id="scanl/7"><strong>scanl</strong>(<var>:Goal,
322	363	+List1, +List2, +List3, +List4, +V0, -Values</var>)</a></dt>
323	364	<dd class="defbody">
324	365	Left scan of list. The scanl family of higher order list operations is

+235

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193	234	</div>
194		<h2 id="sec:arith"><a name="sec:4.27"><span class="sec-nr">4.27</span> <span class="sec-title">Arithmetic</span></a></h2>
195
196		<a name="sec:arith"></a>
	235	<h2 id="sec:arith"><a id="sec:4.27"><span class="sec-nr">4.27</span> <span class="sec-title">Arithmetic</span></a></h2>
	236
	237	<a id="sec:arith"></a>
197	238
198	239	<p>Arithmetic can be divided into some special purpose integer
199	240	predicates and a series of general predicates for integer, floating
200	241	point and rational arithmetic as appropriate. The general arithmetic
201	242	predicates all handle <var>expressions</var>. An expression is either a
202	243	simple number or a <var>function</var>. The arguments of a function are
203		expressions. The functions are described in <a class="sec" href="arith.html">section
	244	expressions. The functions are described in <a class="sec" href="arith.html#sec:4.27.2.3">section
204	245	4.27.2.3</a>.
205	246
206		<p><h3 id="sec:logic-int-arith"><a name="sec:4.27.1"><span class="sec-nr">4.27.1</span> <span class="sec-title">Special
	247	<p><h3 id="sec:logic-int-arith"><a id="sec:4.27.1"><span class="sec-nr">4.27.1</span> <span class="sec-title">Special
207	248	purpose integer arithmetic</span></a></h3>
208	249
209		<a name="sec:logic-int-arith"></a>
	250	<a id="sec:logic-int-arith"></a>
210	251
211	252	<p>The predicates in this section provide more logical operations
212	253	between integers. They are not covered by the ISO standard, although

214	255	in many other Prolog systems.
215	256
216	257	<dl class="latex">
217		<dt class="pubdef"><a name="between/3"><strong>between</strong>(<var>+Low,
	258	<dt class="pubdef"><a id="between/3"><strong>between</strong>(<var>+Low,
218	259	+High, ?Value</var>)</a></dt>
219	260	<dd class="defbody">
220	261	<var>Low</var> and <var>High</var> are integers, <var><var>High</var> >=<var>Low</var></var>.

226	267	<code>infinite</code><sup class="fn">106<span class="fn-text">We prefer <code>infinite</code>,
227	268	but some other Prolog systems already use <code>inf</code> for infinity;
228	269	we accept both for the time being.</span></sup>
229		<a name="idx:between3:1321"></a><a class="pred" href="arith.html#between/3">between/3</a>
	270	<a id="idx:between3:1321"></a><a class="pred" href="arith.html#between/3">between/3</a>
230	271	is true iff <var><var>Value</var> >=<var>Low</var></var>, a feature
231	272	that is particularly interesting for generating integers from a certain
232	273	value.</dd>
233		<dt class="pubdef"><a name="succ/2"><strong>succ</strong>(<var>?Int1,
	274	<dt class="pubdef"><a id="succ/2"><strong>succ</strong>(<var>?Int1,
234	275	?Int2</var>)</a></dt>
235	276	<dd class="defbody">
236	277	True if <var><var>Int2</var> = <var>Int1</var> + 1</var> and <var><var>Int1</var>

240	281	silently and <code>succ(X, -1)</code> raises a domain error.<sup class="fn">107<span class="fn-text">The
241	282	behaviour to deal with natural numbers only was defined by Richard
242	283	O'Keefe to support the common count-down-to-zero in a natural way. Up to
243		5.1.8, <a name="idx:succ2:1322"></a><a class="pred" href="arith.html#succ/2">succ/2</a>
	284	5.1.8, <a id="idx:succ2:1322"></a><a class="pred" href="arith.html#succ/2">succ/2</a>
244	285	also accepted negative integers.</span></sup></dd>
245		<dt class="pubdef"><a name="plus/3"><strong>plus</strong>(<var>?Int1,
	286	<dt class="pubdef"><a id="plus/3"><strong>plus</strong>(<var>?Int1,
246	287	?Int2, ?Int3</var>)</a></dt>
247	288	<dd class="defbody">
248	289	True if <var><var>Int3</var> = <var>Int1</var> + <var>Int2</var></var>.
249	290	At least two of the three arguments must be instantiated to integers.</dd>
250		<dt class="pubdef"><a name="divmod/4"><strong>divmod</strong>(<var>+Dividend,
	291	<dt class="pubdef"><a id="divmod/4"><strong>divmod</strong>(<var>+Dividend,
251	292	+Divisor, -Quotient, -Remainder</var>)</a></dt>
252	293	<dd class="defbody">
253	294	This predicate is a shorthand for computing both the <var>Quotient</var>

256	297	for exploiting the fact that the low level implementation for computing
257	298	the quotient also produces the remainder. Timing confirms that this
258	299	predicate is almost twice as fast as performing the steps independently.
259		Semantically, <a name="idx:divmod4:1323"></a><a class="pred" href="arith.html#divmod/4">divmod/4</a>
	300	Semantically, <a id="idx:divmod4:1323"></a><a class="pred" href="arith.html#divmod/4">divmod/4</a>
260	301	is defined as below.
261	302
262	303	<pre class="code">

268	309	<p>Note that this predicate is only available if SWI-Prolog is compiled
269	310	with unbounded integer support. This is the case for all packaged
270	311	versions.</dd>
271		<dt class="pubdef"><a name="nth_integer_root_and_remainder/4"><strong>nth_integer_root_and_remainder</strong>(<var>+N,
	312	<dt class="pubdef"><a id="nth_integer_root_and_remainder/4"><strong>nth_integer_root_and_remainder</strong>(<var>+N,
272	313	+I, -Root, -Remainder</var>)</a></dt>
273	314	<dd class="defbody">
274	315	True when <var>Root ** N + Remainder = I</var>. <var>N</var> and <var>I</var>

296	337	<p></dd>
297	338	</dl>
298	339
299		<p><h3 id="sec:arithpreds"><a name="sec:4.27.2"><span class="sec-nr">4.27.2</span> <span class="sec-title">General
	340	<p><h3 id="sec:arithpreds"><a id="sec:4.27.2"><span class="sec-nr">4.27.2</span> <span class="sec-title">General
300	341	purpose arithmetic</span></a></h3>
301	342
302		<a name="sec:arithpreds"></a>
	343	<a id="sec:arithpreds"></a>
303	344
304	345	<p>The general arithmetic predicates are optionally compiled (see
305		<a name="idx:setprologflag2:1324"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
	346	<a id="idx:setprologflag2:1324"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
306	347	and the <strong>-O</strong> command line option). Compiled arithmetic
307	348	reduces global stack requirements and improves performance.
308	349	Unfortunately compiled arithmetic cannot be traced, which is why it is
309	350	optional.
310	351
311	352	<dl class="latex">
312		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name=">/2"><var>+Expr1</var> <strong>></strong> <var>+Expr2</var></a></dt>
	353	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id=">/2"><var>+Expr1</var> <strong>></strong> <var>+Expr2</var></a></dt>
313	354	<dd class="defbody">
314	355	True if expression <var>Expr1</var> evaluates to a larger number than <var>Expr2</var>.</dd>
315		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="</2"><var>+Expr1</var> <strong><</strong> <var>+Expr2</var></a></dt>
	356	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="</2"><var>+Expr1</var> <strong><</strong> <var>+Expr2</var></a></dt>
316	357	<dd class="defbody">
317	358	True if expression <var>Expr1</var> evaluates to a smaller number than <var>Expr2</var>.</dd>
318		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="=</2"><var>+Expr1</var> <strong>=<</strong> <var>+Expr2</var></a></dt>
	359	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="=</2"><var>+Expr1</var> <strong>=<</strong> <var>+Expr2</var></a></dt>
319	360	<dd class="defbody">
320	361	True if expression <var>Expr1</var> evaluates to a smaller or equal
321	362	number to <var>Expr2</var>.</dd>
322		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name=">=/2"><var>+Expr1</var> <strong>>=</strong> <var>+Expr2</var></a></dt>
	363	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id=">=/2"><var>+Expr1</var> <strong>>=</strong> <var>+Expr2</var></a></dt>
323	364	<dd class="defbody">
324	365	True if expression <var>Expr1</var> evaluates to a larger or equal
325	366	number to <var>Expr2</var>.</dd>
326		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="=\=/2"><var>+Expr1</var> <strong>=\=</strong> <var>+Expr2</var></a></dt>
	367	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="=\=/2"><var>+Expr1</var> <strong>=\=</strong> <var>+Expr2</var></a></dt>
327	368	<dd class="defbody">
328	369	True if expression <var>Expr1</var> evaluates to a number non-equal to
329	370	<var>Expr2</var>.</dd>
330		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="=:=/2"><var>+Expr1</var> <strong>=:=</strong> <var>+Expr2</var></a></dt>
	371	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="=:=/2"><var>+Expr1</var> <strong>=:=</strong> <var>+Expr2</var></a></dt>
331	372	<dd class="defbody">
332	373	True if expression <var>Expr1</var> evaluates to a number equal to <var>
333	374	Expr2</var>.</dd>
334		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="is/2"><var>-Number</var> <strong>is</strong> <var>+Expr</var></a></dt>
	375	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="is/2"><var>-Number</var> <strong>is</strong> <var>+Expr</var></a></dt>
335	376	<dd class="defbody">
336	377	True when <var>Number</var> is the value to which <var>Expr</var>
337		evaluates. Typically, <a name="idx:is2:1325"></a><a class="pred" href="arith.html#is/2">is/2</a>
	378	evaluates. Typically, <a id="idx:is2:1325"></a><a class="pred" href="arith.html#is/2">is/2</a>
338	379	should be used with unbound left operand. If equality is to be tested, <a class="pred" href="arith.html#=:=/2">=:=/2</a>
339	380	should be used. For example:
340		<div style="text-align:center"><table border="0" frame="void" rules="groups">
341		<tr valign="top"><td><code>?- 1 is sin(pi/2).</code> </td><td>Fails!
342		sin(pi/2) evaluates to the float 1.0, which does not unify with the
343		integer 1. </td></tr>
344		<tr valign="top"><td><code>?- 1 =:= sin(pi/2).</code> </td><td>Succeeds
345		as expected.</td></tr>
	381
	382	<p><table class="latex frame-void center">
	383	<tr><td><code>?- 1 is sin(pi/2).</code> </td><td>Fails! sin(pi/2)
	384	evaluates to the float 1.0, which does not unify with the integer 1. </td></tr>
	385	<tr><td><code>?- 1 =:= sin(pi/2).</code> </td><td>Succeeds as expected.</td></tr>
346	386	</table>
347		</div>
348	387	</dd>
349	388	</dl>
350	389
351		<p><h4 id="sec:artypes"><a name="sec:4.27.2.1"><span class="sec-nr">4.27.2.1</span> <span class="sec-title">Arithmetic
	390	<p><h4 id="sec:artypes"><a id="sec:4.27.2.1"><span class="sec-nr">4.27.2.1</span> <span class="sec-title">Arithmetic
352	391	types</span></a></h4>
353	392
354		<a name="sec:artypes"></a>
355
356		<p><a name="idx:integerunbounded:1326"></a><a name="idx:rationalnumber:1327"></a><a name="idx:numberrational:1328"></a>SWI-Prolog
	393	<a id="sec:artypes"></a>
	394
	395	<p><a id="idx:integerunbounded:1326"></a><a id="idx:rationalnumber:1327"></a><a id="idx:numberrational:1328"></a>SWI-Prolog
357	396	defines the following numeric types:
358	397
359	398	<p>
360	399	<ul class="latex">
361	400	<li><i>integer</i><br>
362	401	If SWI-Prolog is built using the <em>GNU multiple precision arithmetic
363		library</em> <a name="idx:GMP:1329"></a>(GMP), integer arithmetic is <em>unbounded</em>,
	402	library</em> <a id="idx:GMP:1329"></a>(GMP), integer arithmetic is <em>unbounded</em>,
364	403	which means that the size of integers is limited by available memory
365	404	only. Without GMP, SWI-Prolog integers are 64-bits, regardless of the
366	405	native integer size of the platform. The type of integer support can be

382	421	arithmetic is only provided if GMP is used (see above). Rational numbers
383	422	are currently not supported by a Prolog type. They are represented by
384	423	the compound term <code>rdiv(N,M)</code>. Rational numbers that are
385		returned from <a name="idx:is2:1330"></a><a class="pred" href="arith.html#is/2">is/2</a>
	424	returned from <a id="idx:is2:1330"></a><a class="pred" href="arith.html#is/2">is/2</a>
386	425	are <em>canonical</em>, which means <var>M</var> is positive and <var>N</var>
387	426	and
388	427	<var>M</var> have no common divisors. Rational numbers are introduced in

390	429	or the <a class="function" href="arith.html#f-rdiv/2">rdiv/2</a>
391	430	(rational division) function. Using the same functor for rational
392	431	division and for representing rational numbers allows for passing
393		rational numbers between computations as well as for using <a name="idx:format3:1331"></a><a class="pred" href="format.html#format/3">format/3</a>
	432	rational numbers between computations as well as for using <a id="idx:format3:1331"></a><a class="pred" href="format.html#format/3">format/3</a>
394	433	for printing.
395	434
396	435	<p>In the long term, it is likely that rational numbers will become
397	436	<em>atomic</em> as well as a subtype of <em>number</em>. User code that
398	437	creates or inspects the <code>rdiv(M,N)</code> terms will not be
399	438	portable to future versions. Rationals are created using one of the
400		functions mentioned above and inspected using <a name="idx:rational3:1332"></a><a class="pred" href="typetest.html#rational/3">rational/3</a>.
	439	functions mentioned above and inspected using <a id="idx:rational3:1332"></a><a class="pred" href="typetest.html#rational/3">rational/3</a>.
401	440
402	441	<p>
403	442	<li><i>float</i><br>

416	455	floating point number
417	456	</blockquote>
418	457
419		<p><h4 id="sec:rational"><a name="sec:4.27.2.2"><span class="sec-nr">4.27.2.2</span> <span class="sec-title">Rational
	458	<p><h4 id="sec:rational"><a id="sec:4.27.2.2"><span class="sec-nr">4.27.2.2</span> <span class="sec-title">Rational
420	459	number examples</span></a></h4>
421	460
422		<a name="sec:rational"></a>
	461	<a id="sec:rational"></a>
423	462
424	463	<p>The use of rational numbers with unbounded integers allows for exact
425	464	integer or <em>fixed point</em> arithmetic under addition, subtraction,

430	469	on floats will convert a rational operand to float and continue the
431	470	arithmetic using floating point numbers. Here are some examples.
432	471
433		<p><table border="0" frame="void" rules="groups" style="margin:auto">
434		<tr valign="top"><td>A is 2 rdiv 6</td><td>A = 1 rdiv 3 </td></tr>
435		<tr valign="top"><td>A is 4 rdiv 3 + 1</td><td>A = 7 rdiv 3 </td></tr>
436		<tr valign="top"><td>A is 4 rdiv 3 + 1.5</td><td>A = 2.83333 </td></tr>
437		<tr valign="top"><td>A is 4 rdiv 3 + rational(1.5)</td><td>A = 17 rdiv 6 </td></tr>
	472	<p><table class="latex frame-void center">
	473	<tr><td>A is 2 rdiv 6</td><td>A = 1 rdiv 3 </td></tr>
	474	<tr><td>A is 4 rdiv 3 + 1</td><td>A = 7 rdiv 3 </td></tr>
	475	<tr><td>A is 4 rdiv 3 + 1.5</td><td>A = 2.83333 </td></tr>
	476	<tr><td>A is 4 rdiv 3 + rational(1.5)</td><td>A = 17 rdiv 6 </td></tr>
438	477	</table>
439	478
440	479	<p>Note that floats cannot represent all decimal numbers exactly. The

445	484	for details and examples.
446	485
447	486	<p>Rational numbers can be printed as decimal numbers with arbitrary
448		precision using the <a name="idx:format3:1333"></a><a class="pred" href="format.html#format/3">format/3</a>
	487	precision using the <a id="idx:format3:1333"></a><a class="pred" href="format.html#format/3">format/3</a>
449	488	floating point conversion:
450	489
451	490	<pre class="code">

456	495	A = 17 rdiv 6
457	496	</pre>
458	497
459		<p><h4 id="sec:functions"><a name="sec:4.27.2.3"><span class="sec-nr">4.27.2.3</span> <span class="sec-title">Arithmetic
	498	<p><h4 id="sec:functions"><a id="sec:4.27.2.3"><span class="sec-nr">4.27.2.3</span> <span class="sec-title">Arithmetic
460	499	Functions</span></a></h4>
461	500
462		<a name="sec:functions"></a>
	501	<a id="sec:functions"></a>
463	502
464	503	<p>Arithmetic functions are terms which are evaluated by the arithmetic
465		predicates described in <a class="sec" href="arith.html">section 4.27.2</a>.
466		There are four types of arguments to functions:
467		<div style="text-align:center"><table border="0" frame="void" rules="groups">
468		<tr valign="top"><td><var>Expr</var> </td><td>Arbitrary expression,
469		returning either a floating point value or an integer. </td></tr>
470		<tr valign="top"><td><var>IntExpr</var> </td><td>Arbitrary expression
471		that must evaluate to an integer. </td></tr>
472		<tr valign="top"><td><var>RatExpr</var> </td><td>Arbitrary expression
473		that must evaluate to a rational number. </td></tr>
474		<tr valign="top"><td><var>FloatExpr</var> </td><td>Arbitrary expression
475		that must evaluate to a floating point.</td></tr>
	504	predicates described in <a class="sec" href="arith.html#sec:4.27.2">section
	505	4.27.2</a>. There are four types of arguments to functions:
	506
	507	<p><table class="latex frame-void center">
	508	<tr><td><var>Expr</var> </td><td>Arbitrary expression, returning either
	509	a floating point value or an integer. </td></tr>
	510	<tr><td><var>IntExpr</var> </td><td>Arbitrary expression that must
	511	evaluate to an integer. </td></tr>
	512	<tr><td><var>RatExpr</var> </td><td>Arbitrary expression that must
	513	evaluate to a rational number. </td></tr>
	514	<tr><td><var>FloatExpr</var> </td><td>Arbitrary expression that must
	515	evaluate to a floating point.</td></tr>
476	516	</table>
477		</div>
478	517
479	518	<p>For systems using bounded integer arithmetic (default is unbounded,
480		see <a class="sec" href="arith.html">section 4.27.2.1</a> for details),
481		integer operations that would cause overflow automatically convert to
482		floating point arithmetic.
	519	see <a class="sec" href="arith.html#sec:4.27.2.1">section 4.27.2.1</a>
	520	for details), integer operations that would cause overflow automatically
	521	convert to floating point arithmetic.
483	522
484	523	<p>SWI-Prolog provides many extensions to the set of floating point
485	524	functions defined by the ISO standard. The current policy is to provide
486	525	such functions on `as-needed' basis if the function is widely supported
487	526	elsewhere and notably if it is part of the
488		http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdfC99
489		mathematical library. In addition, we try to maintain compatibility with
490		http://www.dcc.fc.up.pt/ vsc/Yap/YAP.
	527	<a class="url" href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf">C99</a>
	528	mathematical library. In addition, we try to maintain compatibility with <a class="url" href="http://www.dcc.fc.up.pt/~vsc/Yap/">YAP</a>.
491	529
492	530	<dl class="latex">
493		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f--/1"><strong>-</strong> <var>+Expr</var></a></dt>
	531	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f--/1"><strong>-</strong> <var>+Expr</var></a></dt>
494	532	<dd class="defbody">
495	533	<var><var>Result</var> = -<var>Expr</var></var></dd>
496		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-+/1"><strong>+</strong> <var>+Expr</var></a></dt>
	534	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-+/1"><strong>+</strong> <var>+Expr</var></a></dt>
497	535	<dd class="defbody">
498	536	<var><var>Result</var> = <var>Expr</var></var>. Note that if <code><code>+</code></code>
499	537	is followed by a number, the parser discards the <code><code>+</code></code>.
500	538	I.e. <code>?- integer(+1)</code> succeeds.</dd>
501		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-+/2"><var>+Expr1</var> <strong>+</strong> <var>+Expr2</var></a></dt>
	539	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-+/2"><var>+Expr1</var> <strong>+</strong> <var>+Expr2</var></a></dt>
502	540	<dd class="defbody">
503	541	<var><var>Result</var> = <var>Expr1</var> + <var>Expr2</var></var></dd>
504		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f--/2"><var>+Expr1</var> <strong>-</strong> <var>+Expr2</var></a></dt>
	542	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f--/2"><var>+Expr1</var> <strong>-</strong> <var>+Expr2</var></a></dt>
505	543	<dd class="defbody">
506	544	<var><var>Result</var> = <var>Expr1</var> - <var>Expr2</var></var></dd>
507		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-/2"><var>+Expr1</var> <strong></strong> <var>+Expr2</var></a></dt>
	545	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-/2"><var>+Expr1</var> <strong></strong> <var>+Expr2</var></a></dt>
508	546	<dd class="defbody">
509	547	<var><var>Result</var> = <var>Expr1</var> × <var>Expr2</var></var></dd>
510		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-//2"><var>+Expr1</var> <strong>/</strong> <var>+Expr2</var></a></dt>
	548	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-//2"><var>+Expr1</var> <strong>/</strong> <var>+Expr2</var></a></dt>
511	549	<dd class="defbody">
512	550	<var><var>Result</var> = <var>Expr1</var>/<var>Expr2</var></var>. If the
513	551	flag <a class="flag" href="flags.html#flag:iso">iso</a> is <code>true</code>,

518	556	returns a rational number. In all other cases the return value is a
519	557	float. See also <a class="function" href="arith.html#f-///2">///2</a>
520	558	and <a class="function" href="arith.html#f-rdiv/2">rdiv/2</a>.</dd>
521		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-mod/2"><var>+IntExpr1</var> <strong>mod</strong> <var>+IntExpr2</var></a></dt>
	559	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-mod/2"><var>+IntExpr1</var> <strong>mod</strong> <var>+IntExpr2</var></a></dt>
522	560	<dd class="defbody">
523	561	Modulo, defined as <var>Result</var> = <var>IntExpr1</var> - (<var>IntExpr1</var>
524	562	div <var>IntExpr2</var>) <var> × </var> <var>IntExpr2</var>, where <code>div</code>
525	563	is
526	564	<em>floored</em> division.</dd>
527		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-rem/2"><var>+IntExpr1</var> <strong>rem</strong> <var>+IntExpr2</var></a></dt>
	565	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-rem/2"><var>+IntExpr1</var> <strong>rem</strong> <var>+IntExpr2</var></a></dt>
528	566	<dd class="defbody">
529	567	Remainder of integer division. Behaves as if defined by
530	568	<var>Result</var> is <var>IntExpr1</var> - (<var>IntExpr1</var> // <var>IntExpr2</var>) <var> × </var> <var>IntExpr2</var></dd>
531		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-///2"><var>+IntExpr1</var> <strong>//</strong> <var>+IntExpr2</var></a></dt>
	569	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-///2"><var>+IntExpr1</var> <strong>//</strong> <var>+IntExpr2</var></a></dt>
532	570	<dd class="defbody">
533	571	Integer division, defined as <var>Result</var> is <var>rnd_I</var>(<var>Expr1</var>/<var>Expr2</var>)
534	572	. The function <var>rnd_I</var> is the default rounding used by the C

536	574	<a class="flag" href="flags.html#flag:integer_rounding_function">integer_rounding_function</a>.
537	575	In the C99 standard, C-rounding is defined as <code>towards_zero</code>.<sup class="fn">109<span class="fn-text">Future
538	576	versions might guarantee rounding towards zero.</span></sup></dd>
539		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-div/2"><strong>div</strong>(<var>+IntExpr1,
	577	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-div/2"><strong>div</strong>(<var>+IntExpr1,
540	578	+IntExpr2</var>)</a></dt>
541	579	<dd class="defbody">
542	580	Integer division, defined as <var>Result</var> is (<var>IntExpr1</var> - <var>IntExpr1</var> <var>mod</var> <var>IntExpr2</var>)

554	592	</pre>
555	593
556	594	</dd>
557		<dt class="pubdef"><a name="f-rdiv/2"><var>+RatExpr</var> <strong>rdiv</strong> <var>+RatExpr</var></a></dt>
	595	<dt class="pubdef"><a id="f-rdiv/2"><var>+RatExpr</var> <strong>rdiv</strong> <var>+RatExpr</var></a></dt>
558	596	<dd class="defbody">
559	597	Rational number division. This function is only available if SWI-Prolog
560	598	has been compiled with rational number support. See
561		<a class="sec" href="arith.html">section 4.27.2.2</a> for details.</dd>
562		<dt class="pubdef"><a name="f-gcd/2"><var>+IntExpr1</var> <strong>gcd</strong> <var>+IntExpr2</var></a></dt>
	599	<a class="sec" href="arith.html#sec:4.27.2.2">section 4.27.2.2</a> for
	600	details.</dd>
	601	<dt class="pubdef"><a id="f-gcd/2"><var>+IntExpr1</var> <strong>gcd</strong> <var>+IntExpr2</var></a></dt>
563	602	<dd class="defbody">
564	603	Result is the greatest common divisor of <var>IntExpr1</var>, <var>IntExpr2</var>.</dd>
565		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-abs/1"><strong>abs</strong>(<var>+Expr</var>)</a></dt>
	604	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-abs/1"><strong>abs</strong>(<var>+Expr</var>)</a></dt>
566	605	<dd class="defbody">
567	606	Evaluate <var>Expr</var> and return the absolute value of it.</dd>
568		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-sign/1"><strong>sign</strong>(<var>+Expr</var>)</a></dt>
	607	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-sign/1"><strong>sign</strong>(<var>+Expr</var>)</a></dt>
569	608	<dd class="defbody">
570	609	Evaluate to -1 if <var><var>Expr</var> < 0</var>, 1 if <var><var>Expr</var>
571	610	> 0</var> and 0 if
572	611	<var><var>Expr</var> = 0</var>. If <var>Expr</var> evaluates to a float,
573	612	the return value is a float (e.g., -1.0, 0.0 or 1.0). In particular,
574	613	note that sign(-0.0) evaluates to 0.0. See also <a class="function" href="arith.html#f-copysign/2">copysign/2</a></dd>
575		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-copysign/2"><strong>copysign</strong>(<var>+Expr1,
	614	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-copysign/2"><strong>copysign</strong>(<var>+Expr1,
576	615	+Expr2</var>)</a></dt>
577	616	<dd class="defbody">
578	617	Evaluate to <var>X</var>, where the absolute value of <var>X</var>

585	624	-<var>Expr1</var> if the signs do not match. Here, we use the extended
586	625	notion of signs for floating point numbers, where the sign of -0.0 and
587	626	other special floats is negative.</dd>
588		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-max/2"><strong>max</strong>(<var>+Expr1,
	627	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-max/2"><strong>max</strong>(<var>+Expr1,
589	628	+Expr2</var>)</a></dt>
590	629	<dd class="defbody">
591	630	Evaluate to the larger of <var>Expr1</var> and <var>Expr2</var>. Both
592	631	arguments are compared after converting to the same type, but the return
593	632	value is in the original type. For example, max(2.5, 3) compares the two
594	633	values after converting to float, but returns the integer 3.</dd>
595		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-min/2"><strong>min</strong>(<var>+Expr1,
	634	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-min/2"><strong>min</strong>(<var>+Expr1,
596	635	+Expr2</var>)</a></dt>
597	636	<dd class="defbody">
598	637	Evaluate to the smaller of <var>Expr1</var> and <var>Expr2</var>. See
599	638	<a class="function" href="arith.html#f-max/2">max/2</a> for a
600	639	description of type handling.</dd>
601		<dt class="pubdef"><a name="f-./2"><strong>.</strong>(<var>+Int,[]</var>)</a></dt>
	640	<dt class="pubdef"><a id="f-./2"><strong>.</strong>(<var>+Int,[]</var>)</a></dt>
602	641	<dd class="defbody">
603	642	A list of one element evaluates to the element. This implies <code>"a"</code>
604	643	evaluates to the character code of the letter `a' (97) using the
605	644	traditional mapping of double quoted string to a list of character
606	645	codes. Arithmetic evaluation also translates a string object (see
607		<a class="sec" href="strings.html">section 5.2</a>) of one character
608		length into the character code for that character. This implies that
609		expression <code>"a"</code> also works of the Prolog flag <a class="flag" href="flags.html#flag:double_quotes">double_quotes</a>
	646	<a class="sec" href="strings.html#sec:5.2">section 5.2</a>) of one
	647	character length into the character code for that character. This
	648	implies that expression <code>"a"</code> also works of the Prolog flag <a class="flag" href="flags.html#flag:double_quotes">double_quotes</a>
610	649	is set to <code>string</code>. The recommended way to specify the
611	650	character code of the letter `a' is
612	651	<code>0'a</code>.</dd>
613		<dt class="pubdef"><a name="f-random/1"><strong>random</strong>(<var>+IntExpr</var>)</a></dt>
	652	<dt class="pubdef"><a id="f-random/1"><strong>random</strong>(<var>+IntExpr</var>)</a></dt>
614	653	<dd class="defbody">
615	654	Evaluate to a random integer <var>i</var> for which <var>0 =< i < <var>IntExpr</var></var>.
616	655	The system has two implementations. If it is compiled with support for

622	661	Windows the state is initialised from CryptGenRandom().</span></sup>
623	662	Otherwise it is set from the system clock. If unbounded arithmetic is
624	663	not supported, random numbers are shared between threads and the seed is
625		initialised from the clock when SWI-Prolog was started. The predicate <a name="idx:setrandom1:1334"></a><a class="pred" href="miscarith.html#set_random/1">set_random/1</a>
	664	initialised from the clock when SWI-Prolog was started. The predicate <a id="idx:setrandom1:1334"></a><a class="pred" href="miscarith.html#set_random/1">set_random/1</a>
626	665	can be used to control the random number generator.
627	666
628	667	<p><b>Warning!</b> Although properly seeded (if supported on the OS),
629	668	the Mersenne Twister algorithm does <em>not</em> produce
630	669	cryptographically secure random numbers. To generate cryptographically
631		secure random numbers, use <a name="idx:cryptonrandombytes2:1335"></a><span class="pred-ext">crypto_n_random_bytes/2</span>
	670	secure random numbers, use <a id="idx:cryptonrandombytes2:1335"></a><span class="pred-ext">crypto_n_random_bytes/2</span>
632	671	from library <code>library(crypto)</code> provided by the <code>ssl</code>
633	672	package.</dd>
634		<dt class="pubdef"><a name="f-random_float/0"><strong>random_float</strong></a></dt>
	673	<dt class="pubdef"><a id="f-random_float/0"><strong>random_float</strong></a></dt>
635	674	<dd class="defbody">
636	675	Evaluate to a random float <var>I</var> for which <var>0.0 < i <
637	676	1.0</var>. This function shares the random state with <a class="function" href="arith.html#f-random/1">random/1</a>.

647	686	expects [0.0,1.0) is going to be surprised when 0.0 fails to turn up in
648	687	a few millions of millions of trials, now is it? But a program that
649	688	expects (0.0,1.0) could be devastated if 0.0 did turn up.''</span></sup></dd>
650		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-round/1"><strong>round</strong>(<var>+Expr</var>)</a></dt>
	689	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-round/1"><strong>round</strong>(<var>+Expr</var>)</a></dt>
651	690	<dd class="defbody">
652	691	Evaluate <var>Expr</var> and round the result to the nearest integer.
653	692	According to ISO, <a class="function" href="arith.html#f-round/1">round/1</a>

657	696	<code>round(Expr) == -round(-Expr)</code> does not hold. SWI-Prolog
658	697	rounds <em>outward</em>, e.g., <code>round(1.5) =:= 2</code> and round
659	698	<code>round(-1.5) =:= -2</code>.</dd>
660		<dt class="pubdef"><a name="f-integer/1"><strong>integer</strong>(<var>+Expr</var>)</a></dt>
	699	<dt class="pubdef"><a id="f-integer/1"><strong>integer</strong>(<var>+Expr</var>)</a></dt>
661	700	<dd class="defbody">
662	701	Same as <a class="function" href="arith.html#f-round/1">round/1</a>
663	702	(backward compatibility).</dd>
664		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-float/1"><strong>float</strong>(<var>+Expr</var>)</a></dt>
	703	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-float/1"><strong>float</strong>(<var>+Expr</var>)</a></dt>
665	704	<dd class="defbody">
666	705	Translate the result to a floating point number. Normally, Prolog will
667	706	use integers whenever possible. When used around the 2nd argument of
668		<a name="idx:is2:1336"></a><a class="pred" href="arith.html#is/2">is/2</a>,
	707	<a id="idx:is2:1336"></a><a class="pred" href="arith.html#is/2">is/2</a>,
669	708	the result will be returned as a floating point number. In other
670	709	contexts, the operation has no effect.</dd>
671		<dt class="pubdef"><a name="f-rational/1"><strong>rational</strong>(<var>+Expr</var>)</a></dt>
	710	<dt class="pubdef"><a id="f-rational/1"><strong>rational</strong>(<var>+Expr</var>)</a></dt>
672	711	<dd class="defbody">
673	712	Convert the <var>Expr</var> to a rational number or integer. The
674	713	function returns the input on integers and rational numbers. For

677	716	numbers the results may be surprising. In the examples below, doubles
678	717	can represent 0.25 and the result is as expected, in contrast to the
679	718	result of <code>rational(0.1)</code>. The function <a class="function" href="arith.html#f-rationalize/1">rationalize/1</a>
680		remedies this. See <a class="sec" href="arith.html">section 4.27.2.2</a>
681		for more information on rational number support.
	719	remedies this. See <a class="sec" href="arith.html#sec:4.27.2.2">section
	720	4.27.2.2</a> for more information on rational number support.
682	721
683	722	<pre class="code">
684	723	?- A is rational(0.25).

689	728	</pre>
690	729
691	730	</dd>
692		<dt class="pubdef"><a name="f-rationalize/1"><strong>rationalize</strong>(<var>+Expr</var>)</a></dt>
	731	<dt class="pubdef"><a id="f-rationalize/1"><strong>rationalize</strong>(<var>+Expr</var>)</a></dt>
693	732	<dd class="defbody">
694	733	Convert the <var>Expr</var> to a rational number or integer. The
695	734	function is similar to <a class="function" href="arith.html#f-rational/1">rational/1</a>,

709	748	</pre>
710	749
711	750	</dd>
712		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-float_fractional_part/1"><strong>float_fractional_part</strong>(<var>+Expr</var>)</a></dt>
	751	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-float_fractional_part/1"><strong>float_fractional_part</strong>(<var>+Expr</var>)</a></dt>
713	752	<dd class="defbody">
714	753	Fractional part of a floating point number. Negative if <var>Expr</var>
715	754	is negative, rational if <var>Expr</var> is rational and 0 if <var>Expr</var>
716	755	is integer. The following relation is always true:
717	756	<var>X is float_fractional_part(X) + float_integer_part(X)</var>.</dd>
718		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-float_integer_part/1"><strong>float_integer_part</strong>(<var>+Expr</var>)</a></dt>
	757	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-float_integer_part/1"><strong>float_integer_part</strong>(<var>+Expr</var>)</a></dt>
719	758	<dd class="defbody">
720	759	Integer part of floating point number. Negative if <var>Expr</var> is
721	760	negative, <var>Expr</var> if <var>Expr</var> is integer.</dd>
722		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-truncate/1"><strong>truncate</strong>(<var>+Expr</var>)</a></dt>
	761	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-truncate/1"><strong>truncate</strong>(<var>+Expr</var>)</a></dt>
723	762	<dd class="defbody">
724	763	Truncate <var>Expr</var> to an integer. If <var><var>Expr</var> >= 0</var>
725	764	this is the same as <code>floor(Expr)</code>. For <var><var>Expr</var> <
726	765	0</var> this is the same as
727		<code>ceil(Expr)</code>. That is, <a name="idx:truncate1:1337"></a><span class="pred-ext">truncate/1</span>
	766	<code>ceil(Expr)</code>. That is, <a id="idx:truncate1:1337"></a><span class="pred-ext">truncate/1</span>
728	767	rounds towards zero.</dd>
729		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-floor/1"><strong>floor</strong>(<var>+Expr</var>)</a></dt>
	768	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-floor/1"><strong>floor</strong>(<var>+Expr</var>)</a></dt>
730	769	<dd class="defbody">
731	770	Evaluate <var>Expr</var> and return the largest integer smaller or equal
732	771	to the result of the evaluation.</dd>
733		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-ceiling/1"><strong>ceiling</strong>(<var>+Expr</var>)</a></dt>
	772	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-ceiling/1"><strong>ceiling</strong>(<var>+Expr</var>)</a></dt>
734	773	<dd class="defbody">
735	774	Evaluate <var>Expr</var> and return the smallest integer larger or equal
736	775	to the result of the evaluation.</dd>
737		<dt class="pubdef"><a name="f-ceil/1"><strong>ceil</strong>(<var>+Expr</var>)</a></dt>
	776	<dt class="pubdef"><a id="f-ceil/1"><strong>ceil</strong>(<var>+Expr</var>)</a></dt>
738	777	<dd class="defbody">
739	778	Same as <a class="function" href="arith.html#f-ceiling/1">ceiling/1</a>
740	779	(backward compatibility).</dd>
741		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f->>/2"><var>+IntExpr1</var> <strong>>></strong> <var>+IntExpr2</var></a></dt>
	780	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f->>/2"><var>+IntExpr1</var> <strong>>></strong> <var>+IntExpr2</var></a></dt>
742	781	<dd class="defbody">
743	782	Bitwise shift <var>IntExpr1</var> by <var>IntExpr2</var> bits to the
744	783	right. The operation performs <em>arithmetic shift</em>, which implies
745	784	that the inserted most significant bits are copies of the original most
746	785	significant bits.</dd>
747		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-<</2"><var>+IntExpr1</var> <strong><<</strong> <var>+IntExpr2</var></a></dt>
	786	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-<</2"><var>+IntExpr1</var> <strong><<</strong> <var>+IntExpr2</var></a></dt>
748	787	<dd class="defbody">
749	788	Bitwise shift <var>IntExpr1</var> by <var>IntExpr2</var> bits to the
750	789	left.</dd>
751		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-\//2"><var>+IntExpr1</var> <strong>\/</strong> <var>+IntExpr2</var></a></dt>
	790	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-\//2"><var>+IntExpr1</var> <strong>\/</strong> <var>+IntExpr2</var></a></dt>
752	791	<dd class="defbody">
753	792	Bitwise `or' <var>IntExpr1</var> and <var>IntExpr2</var>.</dd>
754		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-/\/2"><var>+IntExpr1</var> <strong>/\</strong> <var>+IntExpr2</var></a></dt>
	793	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-/\/2"><var>+IntExpr1</var> <strong>/\</strong> <var>+IntExpr2</var></a></dt>
755	794	<dd class="defbody">
756	795	Bitwise `and' <var>IntExpr1</var> and <var>IntExpr2</var>.</dd>
757		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-xor/2"><var>+IntExpr1</var> <strong>xor</strong> <var>+IntExpr2</var></a></dt>
	796	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-xor/2"><var>+IntExpr1</var> <strong>xor</strong> <var>+IntExpr2</var></a></dt>
758	797	<dd class="defbody">
759	798	Bitwise `exclusive or' <var>IntExpr1</var> and <var>IntExpr2</var>.</dd>
760		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-\/1"><strong>\</strong> <var>+IntExpr</var></a></dt>
	799	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-\/1"><strong>\</strong> <var>+IntExpr</var></a></dt>
761	800	<dd class="defbody">
762	801	Bitwise negation. The returned value is the one's complement of
763	802	<var>IntExpr</var>.</dd>
764		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-sqrt/1"><strong>sqrt</strong>(<var>+Expr</var>)</a></dt>
	803	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-sqrt/1"><strong>sqrt</strong>(<var>+Expr</var>)</a></dt>
765	804	<dd class="defbody">
766	805	<var><var>Result</var> = sqrt(<var>Expr</var>)</var>
767	806	</dd>
768		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-sin/1"><strong>sin</strong>(<var>+Expr</var>)</a></dt>
	807	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-sin/1"><strong>sin</strong>(<var>+Expr</var>)</a></dt>
769	808	<dd class="defbody">
770	809	<var><var>Result</var> = sin(<var>Expr</var>)</var>. <var>Expr</var> is
771	810	the angle in radians.
772	811	</dd>
773		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-cos/1"><strong>cos</strong>(<var>+Expr</var>)</a></dt>
	812	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-cos/1"><strong>cos</strong>(<var>+Expr</var>)</a></dt>
774	813	<dd class="defbody">
775	814	<var><var>Result</var> = cos(<var>Expr</var>)</var>. <var>Expr</var> is
776	815	the angle in radians.
777	816	</dd>
778		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-tan/1"><strong>tan</strong>(<var>+Expr</var>)</a></dt>
	817	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-tan/1"><strong>tan</strong>(<var>+Expr</var>)</a></dt>
779	818	<dd class="defbody">
780	819	<var><var>Result</var> = tan(<var>Expr</var>)</var>. <var>Expr</var> is
781	820	the angle in radians.
782	821	</dd>
783		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-asin/1"><strong>asin</strong>(<var>+Expr</var>)</a></dt>
	822	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-asin/1"><strong>asin</strong>(<var>+Expr</var>)</a></dt>
784	823	<dd class="defbody">
785	824	<var><var>Result</var> = arcsin(<var>Expr</var>)</var>. <var>Result</var>
786	825	is the angle in radians.
787	826	</dd>
788		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-acos/1"><strong>acos</strong>(<var>+Expr</var>)</a></dt>
	827	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-acos/1"><strong>acos</strong>(<var>+Expr</var>)</a></dt>
789	828	<dd class="defbody">
790	829	<var><var>Result</var> = arccos(<var>Expr</var>)</var>. <var>Result</var>
791	830	is the angle in radians.
792	831	</dd>
793		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-atan/1"><strong>atan</strong>(<var>+Expr</var>)</a></dt>
	832	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-atan/1"><strong>atan</strong>(<var>+Expr</var>)</a></dt>
794	833	<dd class="defbody">
795	834	<var><var>Result</var> = arctan(<var>Expr</var>)</var>. <var>Result</var>
796	835	is the angle in radians.
797	836	</dd>
798		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-atan2/2"><strong>atan2</strong>(<var>+YExpr,
	837	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-atan2/2"><strong>atan2</strong>(<var>+YExpr,
799	838	+XExpr</var>)</a></dt>
800	839	<dd class="defbody">
801	840	<var><var>Result</var> = arctan(<var>YExpr</var>/<var>XExpr</var>)</var>. <var>Result</var>

807	846	to raise an evaluation error, whereas the C99 and POSIX standards demand
808	847	this to evaluate to 0.0. SWI-Prolog follows C99 and POSIX.
809	848	</dd>
810		<dt class="pubdef"><a name="f-atan/2"><strong>atan</strong>(<var>+YExpr,
	849	<dt class="pubdef"><a id="f-atan/2"><strong>atan</strong>(<var>+YExpr,
811	850	+XExpr</var>)</a></dt>
812	851	<dd class="defbody">
813	852	Same as <a class="function" href="arith.html#f-atan2/2">atan2/2</a>
814	853	(backward compatibility).</dd>
815		<dt class="pubdef"><a name="f-sinh/1"><strong>sinh</strong>(<var>+Expr</var>)</a></dt>
	854	<dt class="pubdef"><a id="f-sinh/1"><strong>sinh</strong>(<var>+Expr</var>)</a></dt>
816	855	<dd class="defbody">
817	856	<var><var>Result</var> = sinh(<var>Expr</var>)</var>. The hyperbolic
818	857	sine of <var>X</var> is defined as <var>e X - e -X / 2</var>.
819	858	</dd>
820		<dt class="pubdef"><a name="f-cosh/1"><strong>cosh</strong>(<var>+Expr</var>)</a></dt>
	859	<dt class="pubdef"><a id="f-cosh/1"><strong>cosh</strong>(<var>+Expr</var>)</a></dt>
821	860	<dd class="defbody">
822	861	<var><var>Result</var> = cosh(<var>Expr</var>)</var>. The hyperbolic
823	862	cosine of <var>X</var> is defined as <var>e X + e -X / 2</var>.
824	863	</dd>
825		<dt class="pubdef"><a name="f-tanh/1"><strong>tanh</strong>(<var>+Expr</var>)</a></dt>
	864	<dt class="pubdef"><a id="f-tanh/1"><strong>tanh</strong>(<var>+Expr</var>)</a></dt>
826	865	<dd class="defbody">
827	866	<var><var>Result</var> = tanh(<var>Expr</var>)</var>. The hyperbolic
828	867	tangent of <var>X</var> is defined as <var>sinh( X ) / cosh( X )</var>.</dd>
829		<dt class="pubdef"><a name="f-asinh/1"><strong>asinh</strong>(<var>+Expr</var>)</a></dt>
	868	<dt class="pubdef"><a id="f-asinh/1"><strong>asinh</strong>(<var>+Expr</var>)</a></dt>
830	869	<dd class="defbody">
831	870	<var><var>Result</var> = arcsinh(<var>Expr</var>)</var> (inverse
832	871	hyperbolic sine).
833	872	</dd>
834		<dt class="pubdef"><a name="f-acosh/1"><strong>acosh</strong>(<var>+Expr</var>)</a></dt>
	873	<dt class="pubdef"><a id="f-acosh/1"><strong>acosh</strong>(<var>+Expr</var>)</a></dt>
835	874	<dd class="defbody">
836	875	<var><var>Result</var> = arccosh(<var>Expr</var>)</var> (inverse
837	876	hyperbolic cosine).
838	877	</dd>
839		<dt class="pubdef"><a name="f-atanh/1"><strong>atanh</strong>(<var>+Expr</var>)</a></dt>
	878	<dt class="pubdef"><a id="f-atanh/1"><strong>atanh</strong>(<var>+Expr</var>)</a></dt>
840	879	<dd class="defbody">
841	880	<var><var>Result</var> = arctanh(<var>Expr</var>)</var>. (inverse
842	881	hyperbolic tangent).</dd>
843		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-log/1"><strong>log</strong>(<var>+Expr</var>)</a></dt>
	882	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-log/1"><strong>log</strong>(<var>+Expr</var>)</a></dt>
844	883	<dd class="defbody">
845	884	Natural logarithm. <var><var>Result</var> = ln(<var>Expr</var>)</var>
846	885	</dd>
847		<dt class="pubdef"><a name="f-log10/1"><strong>log10</strong>(<var>+Expr</var>)</a></dt>
	886	<dt class="pubdef"><a id="f-log10/1"><strong>log10</strong>(<var>+Expr</var>)</a></dt>
848	887	<dd class="defbody">
849	888	Base-10 logarithm. <var><var>Result</var> = log10(<var>Expr</var>)</var>
850	889	</dd>
851		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-exp/1"><strong>exp</strong>(<var>+Expr</var>)</a></dt>
	890	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-exp/1"><strong>exp</strong>(<var>+Expr</var>)</a></dt>
852	891	<dd class="defbody">
853	892	<var><var>Result</var> = e **<var>Expr</var></var></dd>
854		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-/2"><var>+Expr1</var> <strong></strong> <var>+Expr2</var></a></dt>
	893	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-/2"><var>+Expr1</var> <strong></strong> <var>+Expr2</var></a></dt>
855	894	<dd class="defbody">
856	895	<var><var>Result</var> = <var>Expr1</var>**<var>Expr2</var></var>. The
857	896	result is a float, unless SWI-Prolog is compiled with unbounded integer

869	908	casting the <em>input</em> result in a floating point computation, while
870	909	casting the <em>output</em> performs integer exponentiation followed by
871	910	a conversion to float.</dd>
872		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-^/2"><var>+Expr1</var> <strong>^</strong> <var>+Expr2</var></a></dt>
	911	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-^/2"><var>+Expr1</var> <strong>^</strong> <var>+Expr2</var></a></dt>
873	912	<dd class="defbody">
874	913	In SWI-Prolog, <a class="function" href="arith.html#f-^/2">^/2</a> is
875	914	equivalent to <a class="function" href="arith.html#f-/2">/2</a>. The

879	918	an integer. The table below illustrates the behaviour of the
880	919	exponentiation functions in ISO and SWI.
881	920
882		<p><table border="2" frame="box" rules="groups" style="margin:auto">
883		<tr valign="top"><td><var>Expr1</var> </td><td><var>Expr2</var> </td><td>Function</td><td>SWI</td><td>ISO </td></tr>
884		<tbody>
885		<tr valign="top"><td>Int</td><td>Int</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Int
	921	<p><table class="latex frame-box center">
	922	<tr><td><var>Expr1</var> </td><td><var>Expr2</var> </td><td>Function</td><td>SWI</td><td>ISO </td></tr>
	923	<tr class="hline"><td>Int</td><td>Int</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Int
886	924	or Float</td><td>Float </td></tr>
887		<tr valign="top"><td>Int</td><td>Float</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Float</td><td>Float </td></tr>
888		<tr valign="top"><td>Rational</td><td>Int</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Rational</td><td>- </td></tr>
889		<tr valign="top"><td>Float</td><td>Int</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Float</td><td>Float </td></tr>
890		<tr valign="top"><td>Float</td><td>Float</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Float</td><td>Float </td></tr>
891		<tbody>
892		<tr valign="top"><td>Int</td><td>Int</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Int
	925	<tr><td>Int</td><td>Float</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Float</td><td>Float </td></tr>
	926	<tr><td>Rational</td><td>Int</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Rational</td><td>- </td></tr>
	927	<tr><td>Float</td><td>Int</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Float</td><td>Float </td></tr>
	928	<tr><td>Float</td><td>Float</td><td><a class="function" href="arith.html#f-/2">/2</a> </td><td>Float</td><td>Float </td></tr>
	929	<tr class="hline"><td>Int</td><td>Int</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Int
893	930	or Float</td><td>Int or error </td></tr>
894		<tr valign="top"><td>Int</td><td>Float</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Float</td><td>Float </td></tr>
895		<tr valign="top"><td>Rational</td><td>Int</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Rational</td><td>- </td></tr>
896		<tr valign="top"><td>Float</td><td>Int</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Float</td><td>Float </td></tr>
897		<tr valign="top"><td>Float</td><td>Float</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Float</td><td>Float </td></tr>
	931	<tr><td>Int</td><td>Float</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Float</td><td>Float </td></tr>
	932	<tr><td>Rational</td><td>Int</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Rational</td><td>- </td></tr>
	933	<tr><td>Float</td><td>Int</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Float</td><td>Float </td></tr>
	934	<tr><td>Float</td><td>Float</td><td><a class="function" href="arith.html#f-^/2">^/2</a> </td><td>Float</td><td>Float </td></tr>
898	935	</table>
899	936	</dd>
900		<dt class="pubdef"><a name="f-powm/3"><strong>powm</strong>(<var>+IntExprBase,
	937	<dt class="pubdef"><a id="f-powm/3"><strong>powm</strong>(<var>+IntExprBase,
901	938	+IntExprExp, +IntExprMod</var>)</a></dt>
902	939	<dd class="defbody">
903	940	<var><var>Result</var> = (<var>IntExprBase</var>**<var>IntExprExp</var>)

911	948	conditions. As the conditions are expensive to pre-compute, error
912	949	handling from GMP is non-trivial and negative values are not needed for
913	950	Diffie-Hellman key-exchange we do not support these.</span></sup></dd>
914		<dt class="pubdef"><a name="f-lgamma/1"><strong>lgamma</strong>(<var>+Expr</var>)</a></dt>
	951	<dt class="pubdef"><a id="f-lgamma/1"><strong>lgamma</strong>(<var>+Expr</var>)</a></dt>
915	952	<dd class="defbody">
916	953	Return the natural logarithm of the absolute value of the Gamma
917	954	function.<sup class="fn">114<span class="fn-text">Some interfaces also
918	955	provide the sign of the Gamma function. We canot do that in an
919	956	arithmetic function. Future versions may provide a <em>predicate</em>
920	957	lgamma/3 that returns both the value and the sign.</span></sup></dd>
921		<dt class="pubdef"><a name="f-erf/1"><strong>erf</strong>(<var>+Expr</var>)</a></dt>
922		<dd class="defbody">
923		https://en.wikipedia.org/wiki/Error_functionWikipedia: ``In mathematics,
924		the error function (also called the Gauss error function) is a special
925		function (non-elementary) of sigmoid shape which occurs in probability,
926		statistics and partial differential equations.''</dd>
927		<dt class="pubdef"><a name="f-erfc/1"><strong>erfc</strong>(<var>+Expr</var>)</a></dt>
928		<dd class="defbody">
929		https://en.wikipedia.org/wiki/Error_functionWikipedia: ``The
930		complementary error function.''</dd>
931		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="f-pi/0"><strong>pi</strong></a></dt>
	958	<dt class="pubdef"><a id="f-erf/1"><strong>erf</strong>(<var>+Expr</var>)</a></dt>
	959	<dd class="defbody">
	960	<a class="url" href="https://en.wikipedia.org/wiki/Error_function">Wikipedia</a>:
	961	``In mathematics, the error function (also called the Gauss error
	962	function) is a special function (non-elementary) of sigmoid shape which
	963	occurs in probability, statistics and partial differential equations.''</dd>
	964	<dt class="pubdef"><a id="f-erfc/1"><strong>erfc</strong>(<var>+Expr</var>)</a></dt>
	965	<dd class="defbody">
	966	<a class="url" href="https://en.wikipedia.org/wiki/Error_function">Wikipedia</a>:
	967	``The complementary error function.''</dd>
	968	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="f-pi/0"><strong>pi</strong></a></dt>
932	969	<dd class="defbody">
933	970	Evaluate to the mathematical constant <var>pi</var> (3.14159 ... ).
934	971	</dd>
935		<dt class="pubdef"><a name="f-e/0"><strong>e</strong></a></dt>
	972	<dt class="pubdef"><a id="f-e/0"><strong>e</strong></a></dt>
936	973	<dd class="defbody">
937	974	Evaluate to the mathematical constant <var>e</var> (2.71828 ... ).
938	975	</dd>
939		<dt class="pubdef"><a name="f-epsilon/0"><strong>epsilon</strong></a></dt>
	976	<dt class="pubdef"><a id="f-epsilon/0"><strong>epsilon</strong></a></dt>
940	977	<dd class="defbody">
941	978	Evaluate to the difference between the float 1.0 and the first larger
942	979	floating point number.
943	980	</dd>
944		<dt class="pubdef"><a name="f-inf/0"><strong>inf</strong></a></dt>
945		<dd class="defbody">
946		Evaluate to positive infinity. See <a class="sec" href="syntax.html">section
	981	<dt class="pubdef"><a id="f-inf/0"><strong>inf</strong></a></dt>
	982	<dd class="defbody">
	983	Evaluate to positive infinity. See <a class="sec" href="syntax.html#sec:2.16.1.6">section
947	984	2.16.1.6</a>. This value can be negated using <a class="function" href="arith.html#f--/1">-/1</a>.
948	985	</dd>
949		<dt class="pubdef"><a name="f-nan/0"><strong>nan</strong></a></dt>
950		<dd class="defbody">
951		Evaluate to <em>Not a Number</em>. See <a class="sec" href="syntax.html">section
	986	<dt class="pubdef"><a id="f-nan/0"><strong>nan</strong></a></dt>
	987	<dd class="defbody">
	988	Evaluate to <em>Not a Number</em>. See <a class="sec" href="syntax.html#sec:2.16.1.6">section
952	989	2.16.1.6</a>.
953	990	</dd>
954		<dt class="pubdef"><a name="f-cputime/0"><strong>cputime</strong></a></dt>
	991	<dt class="pubdef"><a id="f-cputime/0"><strong>cputime</strong></a></dt>
955	992	<dd class="defbody">
956	993	Evaluate to a floating point number expressing the <span style="font-variant:small-caps">CPU</span>
957		time (in seconds) used by Prolog up till now. See also <a name="idx:statistics2:1338"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>
958		and <a name="idx:time1:1339"></a><a class="pred" href="statistics.html#time/1">time/1</a>.</dd>
959		<dt class="pubdef"><a name="f-eval/1"><strong>eval</strong>(<var>+Expr</var>)</a></dt>
	994	time (in seconds) used by Prolog up till now. See also <a id="idx:statistics2:1338"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>
	995	and <a id="idx:time1:1339"></a><a class="pred" href="statistics.html#time/1">time/1</a>.</dd>
	996	<dt class="pubdef"><a id="f-eval/1"><strong>eval</strong>(<var>+Expr</var>)</a></dt>
960	997	<dd class="defbody">
961	998	Evaluate <var>Expr</var>. Although ISO standard dictates that `<var>A</var>=1+2, <var>B</var>
962	999	is

980	1017	bit-vectors.
981	1018
982	1019	<dl class="latex">
983		<dt class="pubdef"><a name="f-msb/1"><strong>msb</strong>(<var>+IntExpr</var>)</a></dt>
	1020	<dt class="pubdef"><a id="f-msb/1"><strong>msb</strong>(<var>+IntExpr</var>)</a></dt>
984	1021	<dd class="defbody">
985	1022	Return the largest integer <var>N</var> such that <code>(IntExpr >> N) /\ 1 =:= 1</code>.
986	1023	This is the (zero-origin) index of the most significant 1 bit in the
987	1024	value of <var>IntExpr</var>, which must evaluate to a positive integer.
988	1025	Errors for 0, negative integers, and non-integers.</dd>
989		<dt class="pubdef"><a name="f-lsb/1"><strong>lsb</strong>(<var>+IntExpr</var>)</a></dt>
	1026	<dt class="pubdef"><a id="f-lsb/1"><strong>lsb</strong>(<var>+IntExpr</var>)</a></dt>
990	1027	<dd class="defbody">
991	1028	Return the smallest integer <var>N</var> such that <code>(IntExpr >> N) /\ 1 =:= 1</code>.
992	1029	This is the (zero-origin) index of the least significant 1 bit in the
993	1030	value of <var>IntExpr</var>, which must evaluate to a positive integer.
994	1031	Errors for 0, negative integers, and non-integers.</dd>
995		<dt class="pubdef"><a name="f-popcount/1"><strong>popcount</strong>(<var>+IntExpr</var>)</a></dt>
	1032	<dt class="pubdef"><a id="f-popcount/1"><strong>popcount</strong>(<var>+IntExpr</var>)</a></dt>
996	1033	<dd class="defbody">
997	1034	Return the number of 1s in the binary representation of the non-negative
998	1035	integer <var>IntExpr</var>.</dd>
999		<dt class="pubdef"><a name="f-getbit/2"><strong>getbit</strong>(<var>+IntExprV,
	1036	<dt class="pubdef"><a id="f-getbit/2"><strong>getbit</strong>(<var>+IntExprV,
1000	1037	+IntExprI</var>)</a></dt>
1001	1038	<dd class="defbody">
1002	1039	Evaluates to the bit value (0 or 1) of the <var>IntExprI</var>-th bit of

+99

-58

man/Manual/assoc.html less more

1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.3</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.3</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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22		}
23
24		dt.multidef
25		{ background-color: #c8ffc7;
26		}
	20	dt.pubdef, dt.multidef
	21	{ color: #fff;
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	25	vertical-align: middle;
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27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
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122	126
123	127	div.caption

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128	132
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130
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141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
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191	232	<a class="nav" href="apply.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="broadcast.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:assoc"><a name="sec:A.3"><span class="sec-nr">A.3</span> <span class="sec-title">library(assoc):
	235	<h2 id="sec:assoc"><a id="sec:A.3"><span class="sec-nr">A.3</span> <span class="sec-title">library(assoc):
195	236	Association lists</span></a></h2>
196	237
197		<a name="sec:assoc"></a>
198		<a name="sec:lib:assoc"></a>
199
200		<p>Authors: <em>Richard A. O'Keefe, L.Damas, V.S.Costa and https://www.metalevel.atMarkus
201		Triska</em>
202
203		<p><h3 id="sec:assoc-introduction"><a name="sec:A.3.1"><span class="sec-nr">A.3.1</span> <span class="sec-title">Introduction</span></a></h3>
204
205		<p><a name="sec:assoc-introduction"></a>
	238	<a id="sec:assoc"></a>
	239	<a id="sec:lib:assoc"></a>
	240
	241	<p>Authors: <em>Richard A. O'Keefe, L.Damas, V.S.Costa and <a class="url" href="https://www.metalevel.at">Markus
	242	Triska</a></em>
	243
	244	<p><h3 id="sec:assoc-introduction"><a id="sec:A.3.1"><span class="sec-nr">A.3.1</span> <span class="sec-title">Introduction</span></a></h3>
	245
	246	<p><a id="sec:assoc-introduction"></a>
206	247
207	248	<p>An <i>association list</i> as implemented by this library is a
208	249	collection of unique <i>keys</i> that are associated to <i>values</i>.

239	280	arrays efficiently.
240	281	</ul>
241	282
242		<p><h3 id="sec:assoc-creation"><a name="sec:A.3.2"><span class="sec-nr">A.3.2</span> <span class="sec-title">Creating
	283	<p><h3 id="sec:assoc-creation"><a id="sec:A.3.2"><span class="sec-nr">A.3.2</span> <span class="sec-title">Creating
243	284	association lists</span></a></h3>
244	285
245		<p><a name="sec:assoc-creation"></a>
	286	<p><a id="sec:assoc-creation"></a>
246	287
247	288	<p>An assocation list is <i>created</i> with one of the following
248	289	predicates:
249	290
250	291	<dl class="latex">
251		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="empty_assoc/1"><strong>empty_assoc</strong>(<var>?Assoc</var>)</a></dt>
	292	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="empty_assoc/1"><strong>empty_assoc</strong>(<var>?Assoc</var>)</a></dt>
252	293	<dd class="defbody">
253	294	Is true if <var>Assoc</var> is the empty association list.</dd>
254		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_to_assoc/2"><strong>list_to_assoc</strong>(<var>+Pairs,
	295	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_to_assoc/2"><strong>list_to_assoc</strong>(<var>+Pairs,
255	296	-Assoc</var>)</a></dt>
256	297	<dd class="defbody">
257	298	Create an association from a list <var>Pairs</var> of Key-Value pairs.

266	307	</dl>
267	308
268	309	</dd>
269		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_list_to_assoc/2"><strong>ord_list_to_assoc</strong>(<var>+Pairs,
	310	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_list_to_assoc/2"><strong>ord_list_to_assoc</strong>(<var>+Pairs,
270	311	-Assoc</var>)</a></dt>
271	312	<dd class="defbody">
272	313	<var>Assoc</var> is created from an ordered list <var>Pairs</var> of

284	325	</dd>
285	326	</dl>
286	327
287		<p><h3 id="sec:assoc-querying"><a name="sec:A.3.3"><span class="sec-nr">A.3.3</span> <span class="sec-title">Querying
	328	<p><h3 id="sec:assoc-querying"><a id="sec:A.3.3"><span class="sec-nr">A.3.3</span> <span class="sec-title">Querying
288	329	association lists</span></a></h3>
289	330
290		<p><a name="sec:assoc-querying"></a>
	331	<p><a id="sec:assoc-querying"></a>
291	332
292	333	<p>An association list can be <i>queried</i> with:
293	334
294	335	<dl class="latex">
295		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="get_assoc/3"><strong>get_assoc</strong>(<var>+Key,
	336	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="get_assoc/3"><strong>get_assoc</strong>(<var>+Key,
296	337	+Assoc, -Value</var>)</a></dt>
297	338	<dd class="defbody">
298	339	True if <var>Key</var>-<var>Value</var> is an association in <var>Assoc</var>.

306	347	</dl>
307	348
308	349	</dd>
309		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="get_assoc/5"><strong>get_assoc</strong>(<var>+Key,
	350	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="get_assoc/5"><strong>get_assoc</strong>(<var>+Key,
310	351	+Assoc0, ?Val0, ?Assoc, ?Val</var>)</a></dt>
311	352	<dd class="defbody">
312	353	True if <var>Key</var>-<var>Val0</var> is in <var>Assoc0</var> and <var>Key</var>-<var>Val</var>
313	354	is in <var>Assoc</var>.</dd>
314		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="max_assoc/3"><strong>max_assoc</strong>(<var>+Assoc,
	355	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="max_assoc/3"><strong>max_assoc</strong>(<var>+Assoc,
315	356	-Key, -Value</var>)</a></dt>
316	357	<dd class="defbody">
317	358	True if <var>Key</var>-<var>Value</var> is in <var>Assoc</var> and <var>Key</var>
318	359	is the largest key.</dd>
319		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="min_assoc/3"><strong>min_assoc</strong>(<var>+Assoc,
	360	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="min_assoc/3"><strong>min_assoc</strong>(<var>+Assoc,
320	361	-Key, -Value</var>)</a></dt>
321	362	<dd class="defbody">
322	363	True if <var>Key</var>-<var>Value</var> is in assoc and <var>Key</var>
323	364	is the smallest key.</dd>
324		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="gen_assoc/3"><strong>gen_assoc</strong>(<var>?Key,
	365	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="gen_assoc/3"><strong>gen_assoc</strong>(<var>?Key,
325	366	+Assoc, ?Value</var>)</a></dt>
326	367	<dd class="defbody">
327	368	True if <var>Key</var>-<var>Value</var> is an association in <var>Assoc</var>.

337	378	</dd>
338	379	</dl>
339	380
340		<p><h3 id="sec:assoc-modifications"><a name="sec:A.3.4"><span class="sec-nr">A.3.4</span> <span class="sec-title">Modifying
	381	<p><h3 id="sec:assoc-modifications"><a id="sec:A.3.4"><span class="sec-nr">A.3.4</span> <span class="sec-title">Modifying
341	382	association lists</span></a></h3>
342	383
343		<p><a name="sec:assoc-modifications"></a>
	384	<p><a id="sec:assoc-modifications"></a>
344	385
345	386	<p>Elements of an association list can be changed and inserted with:
346	387
347	388	<dl class="latex">
348		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="put_assoc/4"><strong>put_assoc</strong>(<var>+Key,
	389	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="put_assoc/4"><strong>put_assoc</strong>(<var>+Key,
349	390	+Assoc0, +Value, -Assoc</var>)</a></dt>
350	391	<dd class="defbody">
351	392	<var>Assoc</var> is <var>Assoc0</var>, except that <var>Key</var> is
352	393	associated with
353	394	<var>Value</var>. This can be used to insert and change associations.</dd>
354		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="del_assoc/4"><strong>del_assoc</strong>(<var>+Key,
	395	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="del_assoc/4"><strong>del_assoc</strong>(<var>+Key,
355	396	+Assoc0, ?Value, -Assoc</var>)</a></dt>
356	397	<dd class="defbody">
357	398	True if <var>Key</var>-<var>Value</var> is in <var>Assoc0</var>. <var>Assoc</var>
358	399	is <var>Assoc0</var> with
359	400	<var>Key</var>-<var>Value</var> removed.</dd>
360		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="del_min_assoc/4"><strong>del_min_assoc</strong>(<var>+Assoc0,
	401	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="del_min_assoc/4"><strong>del_min_assoc</strong>(<var>+Assoc0,
361	402	?Key, ?Val, -Assoc</var>)</a></dt>
362	403	<dd class="defbody">
363	404	True if <var>Key</var>-Value is in <var>Assoc0</var> and <var>Key</var>

365	406	<var>Assoc</var> is <var>Assoc0</var> with <var>Key</var>-Value removed.
366	407	Warning: This will succeed with <i>no</i> bindings for <var>Key</var> or <var>Val</var>
367	408	if <var>Assoc0</var> is empty.</dd>
368		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="del_max_assoc/4"><strong>del_max_assoc</strong>(<var>+Assoc0,
	409	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="del_max_assoc/4"><strong>del_max_assoc</strong>(<var>+Assoc0,
369	410	?Key, ?Val, -Assoc</var>)</a></dt>
370	411	<dd class="defbody">
371	412	True if <var>Key</var>-Value is in <var>Assoc0</var> and <var>Key</var>

376	417	</dd>
377	418	</dl>
378	419
379		<p><h3 id="sec:assoc-conversion"><a name="sec:A.3.5"><span class="sec-nr">A.3.5</span> <span class="sec-title">Conversion
	420	<p><h3 id="sec:assoc-conversion"><a id="sec:A.3.5"><span class="sec-nr">A.3.5</span> <span class="sec-title">Conversion
380	421	predicates</span></a></h3>
381	422
382		<p><a name="sec:assoc-conversion"></a>
	423	<p><a id="sec:assoc-conversion"></a>
383	424
384	425	<p>Conversion of (parts of) an association list to <i>lists</i> is
385	426	possible with:
386	427
387	428	<dl class="latex">
388		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="assoc_to_list/2"><strong>assoc_to_list</strong>(<var>+Assoc,
	429	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="assoc_to_list/2"><strong>assoc_to_list</strong>(<var>+Assoc,
389	430	-Pairs</var>)</a></dt>
390	431	<dd class="defbody">
391	432	Translate <var>Assoc</var> to a list <var>Pairs</var> of Key-Value
392	433	pairs. The keys in <var>Pairs</var> are sorted in ascending order.</dd>
393		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="assoc_to_keys/2"><strong>assoc_to_keys</strong>(<var>+Assoc,
	434	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="assoc_to_keys/2"><strong>assoc_to_keys</strong>(<var>+Assoc,
394	435	-Keys</var>)</a></dt>
395	436	<dd class="defbody">
396	437	True if <var>Keys</var> is the list of keys in <var>Assoc</var>. The
397	438	keys are sorted in ascending order.</dd>
398		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="assoc_to_values/2"><strong>assoc_to_values</strong>(<var>+Assoc,
	439	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="assoc_to_values/2"><strong>assoc_to_values</strong>(<var>+Assoc,
399	440	-Values</var>)</a></dt>
400	441	<dd class="defbody">
401	442	True if <var>Values</var> is the list of values in <var>Assoc</var>. <var>Values</var>

404	445	</dd>
405	446	</dl>
406	447
407		<p><h3 id="sec:assoc-reasoning"><a name="sec:A.3.6"><span class="sec-nr">A.3.6</span> <span class="sec-title">Reasoning
	448	<p><h3 id="sec:assoc-reasoning"><a id="sec:A.3.6"><span class="sec-nr">A.3.6</span> <span class="sec-title">Reasoning
408	449	about association lists and their elements</span></a></h3>
409	450
410		<p><a name="sec:assoc-reasoning"></a>
	451	<p><a id="sec:assoc-reasoning"></a>
411	452
412	453	<p>Further inspection predicates of an association list and its elements
413	454	are:
414	455
415	456	<dl class="latex">
416		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="is_assoc/1"><strong>is_assoc</strong>(<var>+Assoc</var>)</a></dt>
	457	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="is_assoc/1"><strong>is_assoc</strong>(<var>+Assoc</var>)</a></dt>
417	458	<dd class="defbody">
418	459	True if <var>Assoc</var> is an association list. This predicate checks
419	460	that the structure is valid, elements are in order, and tree is balanced
420	461	to the extent guaranteed by AVL trees. I.e., branches of each subtree
421	462	differ in depth by at most 1.</dd>
422		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="map_assoc/2"><strong>map_assoc</strong>(<var>:Pred,
	463	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="map_assoc/2"><strong>map_assoc</strong>(<var>:Pred,
423	464	+Assoc</var>)</a></dt>
424	465	<dd class="defbody">
425	466	True if <var>Pred</var>(Value) is true for all values in <var>Assoc</var>.</dd>
426		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="map_assoc/3"><strong>map_assoc</strong>(<var>:Pred,
	467	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="map_assoc/3"><strong>map_assoc</strong>(<var>:Pred,
427	468	+Assoc0, ?Assoc</var>)</a></dt>
428	469	<dd class="defbody">
429	470	Map corresponding values. True if <var>Assoc</var> is <var>Assoc0</var>

+117

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193	234	</div>
194		<h2 id="sec:attvar"><a name="sec:7.1"><span class="sec-nr">7.1</span> <span class="sec-title">Attributed
	235	<h2 id="sec:attvar"><a id="sec:7.1"><span class="sec-nr">7.1</span> <span class="sec-title">Attributed
195	236	variables</span></a></h2>
196	237
197		<a name="sec:attvar"></a>
	238	<a id="sec:attvar"></a>
198	239
199	240	<p><em>Attributed variables</em> provide a technique for extending the
200	241	Prolog unification algorithm <cite><a class="cite" href="Bibliography.html#holzbaur:1992">Holzbaur,

203	244	interface to attributed variables. The SWI-Prolog interface is identical
204	245	to the one realised by Bart Demoen for hProlog <cite><a class="cite" href="Bibliography.html#Demoen:CW350">Demoen,
205	246	2002</a></cite>. This interface is simple and available on all Prolog
206		systems that can run the Leuven CHR system (see <a class="sec" href="chr.html">chapter
207		8</a> and the Leuven https://dtai.cs.kuleuven.be/CHR/CHR page ).
	247	systems that can run the Leuven CHR system (see <a class="sec" href="chr.html#sec:8">chapter
	248	8</a> and the Leuven <a class="url" href="https://dtai.cs.kuleuven.be/CHR/">CHR
	249	page</a>).
208	250
209	251	<p>Binding an attributed variable schedules a goal to be executed at the
210	252	first possible opportunity. In the current implementation the hooks are
211	253	executed immediately after a successful unification of the clause-head
212	254	or successful completion of a foreign language (built-in) predicate.
213		Each attribute is associated to a module, and the hook (<a name="idx:attrunifyhook2:1771"></a><a class="pred" href="attvar.html#attr_unify_hook/2">attr_unify_hook/2</a>)
	255	Each attribute is associated to a module, and the hook (<a id="idx:attrunifyhook2:1775"></a><a class="pred" href="attvar.html#attr_unify_hook/2">attr_unify_hook/2</a>)
214	256	is executed in this module. The example below realises a very simple and
215	257	incomplete finite domain reasoner:
216	258

254	296
255	297	<p>Before explaining the code we give some example queries:
256	298	<blockquote>
257		<table border="0" frame="void" rules="groups">
258		<tr valign="top"><td><code>?- domain(X, [a,b]), X = c</code></td><td>fail </td></tr>
259		<tr valign="top"><td><code>?- domain(X, [a,b]), domain(X, [a,c]).</code></td><td>X
260		= a </td></tr>
261		<tr valign="top"><td><code>?- domain(X, [a,b,c]), domain(X, [a,c]).</code></td><td>domain(X,
	299	<table class="latex frame-void">
	300	<tr><td><code>?- domain(X, [a,b]), X = c</code></td><td>fail </td></tr>
	301	<tr><td><code>?- domain(X, [a,b]), domain(X, [a,c]).</code></td><td>X =
	302	a </td></tr>
	303	<tr><td><code>?- domain(X, [a,b,c]), domain(X, [a,c]).</code></td><td>domain(X,
262	304	[a, c]) </td></tr>
263	305	</table>
264	306	</blockquote>
265	307
266	308	<p>The predicate domain/2 fetches (first clause) or assigns (second
267	309	clause) the variable a <em>domain</em>, a set of values the variable can
268		be unified with. In the second clause, <a name="idx:domain2:1772"></a><span class="pred-ext">domain/2</span>
	310	be unified with. In the second clause, <a id="idx:domain2:1776"></a><span class="pred-ext">domain/2</span>
269	311	first associates the domain with a fresh variable (Y) and then unifies X
270	312	to this variable to deal with the possibility that X already has a
271		domain. The predicate <a name="idx:attrunifyhook2:1773"></a><a class="pred" href="attvar.html#attr_unify_hook/2">attr_unify_hook/2</a>
	313	domain. The predicate <a id="idx:attrunifyhook2:1777"></a><a class="pred" href="attvar.html#attr_unify_hook/2">attr_unify_hook/2</a>
272	314	(see below) is a hook called after a variable with a domain is assigned
273	315	a value. In the simple case where the variable is bound to a concrete
274	316	value, we simply check whether this value is in the domain. Otherwise we

276	318	is empty (first example), assign the value if there is only one value in
277	319	the intersection (second example), or assign the intersection as the new
278	320	domain of the variable (third example). The nonterminal
279		<a name="idx:attributegoals1:1774"></a><span class="pred-ext">attribute_goals/3</span>
	321	<a id="idx:attributegoals1:1778"></a><a class="pred" href="attvar.html#attribute_goals//1">attribute_goals//1</a>
280	322	is used to translate remaining attributes to user-readable goals that,
281	323	when called, reinstate these attributes or attributes that correspond to
282	324	equivalent constraints.
283	325
284		<p>Implementing constraint solvers (<a class="sec" href="clp.html">chapter
	326	<p>Implementing constraint solvers (<a class="sec" href="clp.html#sec:7">chapter
285	327	7</a>) is the most common, but not the only use case for attributed
286	328	variables: If you implement algorithms that require efficient
287	329	destructive modifications, then using attributed variables is often a
288		more convenient and somewhat more declarative alternative for <a name="idx:setarg3:1775"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	330	more convenient and somewhat more declarative alternative for <a id="idx:setarg3:1779"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
289	331	and related predicates whose sharing semantics are harder to understand.
290	332	In particular, attributed variables make it easy to express graph
291	333	networks and graph-oriented algorithms, since each variable can store

293	335	of attributed variables should be confined within a module that exposes
294	336	its functionality via more declarative interface predicates.
295	337
296		<p><h3 id="sec:attvar-predicates"><a name="sec:7.1.1"><span class="sec-nr">7.1.1</span> <span class="sec-title">Attribute
	338	<p><h3 id="sec:attvar-predicates"><a id="sec:7.1.1"><span class="sec-nr">7.1.1</span> <span class="sec-title">Attribute
297	339	manipulation predicates</span></a></h3>
298	340
299		<a name="sec:attvar-predicates"></a>
	341	<a id="sec:attvar-predicates"></a>
300	342
301	343	<dl class="latex">
302		<dt class="pubdef"><a name="attvar/1"><strong>attvar</strong>(<var>@Term</var>)</a></dt>
303		<dd class="defbody">
304		Succeeds if <var>Term</var> is an attributed variable. Note that <a name="idx:var1:1776"></a><a class="pred" href="typetest.html#var/1">var/1</a>
	344	<dt class="pubdef"><a id="attvar/1"><strong>attvar</strong>(<var>@Term</var>)</a></dt>
	345	<dd class="defbody">
	346	Succeeds if <var>Term</var> is an attributed variable. Note that <a id="idx:var1:1780"></a><a class="pred" href="typetest.html#var/1">var/1</a>
305	347	also succeeds on attributed variables. Attributed variables are created
306	348	with
307		<a name="idx:putattr3:1777"></a><a class="pred" href="attvar.html#put_attr/3">put_attr/3</a>.</dd>
308		<dt class="pubdef"><a name="put_attr/3"><strong>put_attr</strong>(<var>+Var,
	349	<a id="idx:putattr3:1781"></a><a class="pred" href="attvar.html#put_attr/3">put_attr/3</a>.</dd>
	350	<dt class="pubdef"><a id="put_attr/3"><strong>put_attr</strong>(<var>+Var,
309	351	+Module, +Value</var>)</a></dt>
310	352	<dd class="defbody">
311	353	If <var>Var</var> is a variable or attributed variable, set the value
312	354	for the attribute named <var>Module</var> to <var>Value</var>. If an
313	355	attribute with this name is already associated with <var>Var</var>, the
314	356	old value is replaced. Backtracking will restore the old value (i.e., an
315		attribute is a mutable term; see also <a name="idx:setarg3:1778"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>).
	357	attribute is a mutable term; see also <a id="idx:setarg3:1782"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>).
316	358	This predicate raises an uninstantiation error if
317	359	<var>Var</var> is not a variable, and a type error if <var>Module</var>
318	360	is not an atom.</dd>
319		<dt class="pubdef"><a name="get_attr/3"><strong>get_attr</strong>(<var>+Var,
	361	<dt class="pubdef"><a id="get_attr/3"><strong>get_attr</strong>(<var>+Var,
320	362	+Module, -Value</var>)</a></dt>
321	363	<dd class="defbody">
322	364	Request the current <var>value</var> for the attribute named <var>Module</var>.

324	366	<var>Var</var> is not an attributed variable or the named attribute is
325	367	not associated to <var>Var</var> this predicate fails silently. If <var>Module</var>
326	368	is not an atom, a type error is raised.</dd>
327		<dt class="pubdef"><a name="del_attr/2"><strong>del_attr</strong>(<var>+Var,
	369	<dt class="pubdef"><a id="del_attr/2"><strong>del_attr</strong>(<var>+Var,
328	370	+Module</var>)</a></dt>
329	371	<dd class="defbody">
330	372	Delete the named attribute. If <var>Var</var> loses its last attribute

335	377	</dd>
336	378	</dl>
337	379
338		<p><h3 id="sec:attvar-hooks"><a name="sec:7.1.2"><span class="sec-nr">7.1.2</span> <span class="sec-title">Attributed
	380	<p><h3 id="sec:attvar-hooks"><a id="sec:7.1.2"><span class="sec-nr">7.1.2</span> <span class="sec-title">Attributed
339	381	variable hooks</span></a></h3>
340	382
341		<a name="sec:attvar-hooks"></a>
	383	<a id="sec:attvar-hooks"></a>
342	384
343	385	<p>Attribute names are linked to modules. This means that certain
344	386	operations on attributed variables cause <em>hooks</em> to be called in
345	387	the module whose name matches the attribute name.
346	388
347	389	<dl class="latex">
348		<dt class="pubdef"><a name="attr_unify_hook/2"><strong>attr_unify_hook</strong>(<var>+AttValue,
	390	<dt class="pubdef"><a id="attr_unify_hook/2"><strong>attr_unify_hook</strong>(<var>+AttValue,
349	391	+VarValue</var>)</a></dt>
350	392	<dd class="defbody">
351	393	A hook that must be defined in the module to which an attributed

357	399	is another attributed variable the hook often combines the two
358	400	attributes and associates the combined attribute with <var>VarValue</var>
359	401	using
360		<a name="idx:putattr3:1779"></a><a class="pred" href="attvar.html#put_attr/3">put_attr/3</a>.
	402	<a id="idx:putattr3:1783"></a><a class="pred" href="attvar.html#put_attr/3">put_attr/3</a>.
361	403
362	404	<dl class="tags">
363	405	<dt class="tag">To be done</dt>

373	415	</dl>
374	416
375	417	</dd>
376		<dt class="pubdef"><a name="attribute_goals/1"><strong>attribute_goals</strong>(<var>+Var</var>)</a><code>//</code></dt>
	418	<dt class="pubdef"><a id="attribute_goals//1"><strong>attribute_goals</strong>(<var>+Var</var>)</a><code>//</code></dt>
377	419	<dd class="defbody">
378	420	This nonterminal is the main mechanism in which residual constraints are
379	421	obtained. It is called in every module where it is defined, and
380	422	<var>Var</var> has an attribute. Its argument is that variable. In each
381		module, <a name="idx:attributegoals1:1780"></a><span class="pred-ext">attribute_goals/3</span>
	423	module, <a id="idx:attributegoals1:1784"></a><a class="pred" href="attvar.html#attribute_goals//1">attribute_goals//1</a>
382	424	must describe a list of Prolog goals that are declaratively equivalent
383	425	to the goals that caused the attributes of that module to be present and
384	426	in their current state. It is always possible to do this (since these

404	446	constraint solvers by contrasting obtained residual goals with expected
405	447	answers.
406	448
407		<p>This nonterminal is used by <a name="idx:copyterm3:1781"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>,
	449	<p>This nonterminal is used by <a id="idx:copyterm3:1785"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>,
408	450	on which the Prolog top level relies to ensure the basic invariant of
409	451	pure Prolog programs: The answer is <i>declaratively equivalent</i> to
410	452	the query.

413	455	<i>list</i> is used to represent residual goals. This simplifies
414	456	processing and reasoning about residual goals throughout all programs
415	457	that need this functionality.</dd>
416		<dt class="pubdef"><a name="project_attributes/2"><strong>project_attributes</strong>(<var>+QueryVars,
	458	<dt class="pubdef"><a id="project_attributes/2"><strong>project_attributes</strong>(<var>+QueryVars,
417	459	+ResidualVars</var>)</a></dt>
418	460	<dd class="defbody">
419	461	A hook that can be defined in each module to project constraints on
420	462	newly introduced variables back to the query variables.
421	463	<var>QueryVars</var> is the list of variables occurring in the query and
422	464	<var>ResidualVars</var> is a list of variables that have attributes
423		attached. There may be variables that occur in both lists. If possible, <a name="idx:projectattributes2:1782"></a><a class="pred" href="attvar.html#project_attributes/2">project_attributes/2</a>
	465	attached. There may be variables that occur in both lists. If possible, <a id="idx:projectattributes2:1786"></a><a class="pred" href="attvar.html#project_attributes/2">project_attributes/2</a>
424	466	should change the attributes so that all constraints are expressed as
425	467	residual goals that refer only to
426	468	<var>QueryVars</var>, while other variables are existentially
427	469	quantified.</dd>
428		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="attr_portray_hook/2"><strong>attr_portray_hook</strong>(<var>+AttValue,
	470	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="attr_portray_hook/2"><strong>attr_portray_hook</strong>(<var>+AttValue,
429	471	+Var</var>)</a></dt>
430	472	<dd class="defbody">
431		Called by <a name="idx:writeterm2:1783"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	473	Called by <a id="idx:writeterm2:1787"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
432	474	and friends for each attribute if the option
433	475	<code>attributes(portray)</code> is in effect. If the hook succeeds the
434	476	attribute is considered printed. Otherwise <code>Module = ...</code> is
435	477	printed to indicate the existence of a variable. This predicate is
436	478	deprecated because it cannot work with pure interface predicates like
437		<a name="idx:copyterm3:1784"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>.
438		Use <a name="idx:attributegoals1:1785"></a><span class="pred-ext">attribute_goals/3</span>
	479	<a id="idx:copyterm3:1788"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>.
	480	Use <a id="idx:attributegoals1:1789"></a><a class="pred" href="attvar.html#attribute_goals//1">attribute_goals//1</a>
439	481	instead to map attributes to residual goals.
440	482	</dd>
441	483	</dl>
442	484
443		<p><h3 id="sec:terms-with-attvars"><a name="sec:7.1.3"><span class="sec-nr">7.1.3</span> <span class="sec-title">Operations
	485	<p><h3 id="sec:terms-with-attvars"><a id="sec:7.1.3"><span class="sec-nr">7.1.3</span> <span class="sec-title">Operations
444	486	on terms with attributed variables</span></a></h3>
445	487
446		<a name="sec:terms-with-attvars"></a>
	488	<a id="sec:terms-with-attvars"></a>
447	489
448	490	<dl class="latex">
449		<dt class="pubdef"><a name="copy_term/3"><strong>copy_term</strong>(<var>+Term,
	491	<dt class="pubdef"><a id="copy_term/3"><strong>copy_term</strong>(<var>+Term,
450	492	-Copy, -Gs</var>)</a></dt>
451	493	<dd class="defbody">
452	494	Create a regular term <var>Copy</var> as a copy of <var>Term</var>
453	495	(without any attributes), and a list <var>Gs</var> of goals that
454	496	represents the attributes. The goal <code>maplist(call, Gs)</code>
455		recreates the attributes for <var>Copy</var>. The nonterminal <a name="idx:attributegoals1:1786"></a><span class="pred-ext">attribute_goals/3</span>,
	497	recreates the attributes for <var>Copy</var>. The nonterminal <a id="idx:attributegoals1:1790"></a><a class="pred" href="attvar.html#attribute_goals//1">attribute_goals//1</a>,
456	498	as defined in the modules the attributes stem from, is used to convert
457	499	attributes to lists of goals.
458	500

463	505
464	506	<p>The form <code>copy_term(Term, Term, Gs)</code> can be used to reason
465	507	about the constraints in which <code>Term</code> is involved.</dd>
466		<dt class="pubdef"><a name="copy_term_nat/2"><strong>copy_term_nat</strong>(<var>+Term,
	508	<dt class="pubdef"><a id="copy_term_nat/2"><strong>copy_term_nat</strong>(<var>+Term,
467	509	-Copy</var>)</a></dt>
468	510	<dd class="defbody">
469		As <a name="idx:copyterm2:1787"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>.
	511	As <a id="idx:copyterm2:1791"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>.
470	512	Attributes, however, are <em>not</em> copied but replaced by fresh
471	513	variables.</dd>
472		<dt class="pubdef"><a name="term_attvars/2"><strong>term_attvars</strong>(<var>+Term,
	514	<dt class="pubdef"><a id="term_attvars/2"><strong>term_attvars</strong>(<var>+Term,
473	515	-AttVars</var>)</a></dt>
474	516	<dd class="defbody">
475	517	<var>AttVars</var> is a list of all attributed variables in <var>Term</var>
476		and its attributes. That is, <a name="idx:termattvars2:1788"></a><a class="pred" href="attvar.html#term_attvars/2">term_attvars/2</a>
	518	and its attributes. That is, <a id="idx:termattvars2:1792"></a><a class="pred" href="attvar.html#term_attvars/2">term_attvars/2</a>
477	519	works recursively through attributes. This predicate is cycle-safe. The
478	520	goal
479	521	<code>term_attvars(Term,[])</code> in an efficient test that <var>Term</var>

483	525	</dd>
484	526	</dl>
485	527
486		<p><h3 id="sec:attvar-low-level-preds"><a name="sec:7.1.4"><span class="sec-nr">7.1.4</span> <span class="sec-title">Special
	528	<p><h3 id="sec:attvar-low-level-preds"><a id="sec:7.1.4"><span class="sec-nr">7.1.4</span> <span class="sec-title">Special
487	529	purpose predicates for attributes</span></a></h3>
488	530
489		<a name="sec:attvar-low-level-preds"></a>
490
491		<p>Normal user code should deal with <a name="idx:putattr3:1789"></a><a class="pred" href="attvar.html#put_attr/3">put_attr/3</a>, <a name="idx:getattr3:1790"></a><a class="pred" href="attvar.html#get_attr/3">get_attr/3</a>
492		and <a name="idx:delattr2:1791"></a><a class="pred" href="attvar.html#del_attr/2">del_attr/2</a>.
	531	<a id="sec:attvar-low-level-preds"></a>
	532
	533	<p>Normal user code should deal with <a id="idx:putattr3:1793"></a><a class="pred" href="attvar.html#put_attr/3">put_attr/3</a>, <a id="idx:getattr3:1794"></a><a class="pred" href="attvar.html#get_attr/3">get_attr/3</a>
	534	and <a id="idx:delattr2:1795"></a><a class="pred" href="attvar.html#del_attr/2">del_attr/2</a>.
493	535	The routines in this section fetch or set the entire attribute list of a
494	536	variable. Use of these predicates is anticipated to be restricted to
495	537	printing and other special purpose operations.
496	538
497	539	<dl class="latex">
498		<dt class="pubdef"><a name="get_attrs/2"><strong>get_attrs</strong>(<var>+Var,
	540	<dt class="pubdef"><a id="get_attrs/2"><strong>get_attrs</strong>(<var>+Var,
499	541	-Attributes</var>)</a></dt>
500	542	<dd class="defbody">
501	543	Get all attributes of <var>Var</var>. <var>Attributes</var> is a term of

503	545	<code>att(Module, Value, MoreAttributes)</code>, where <var>MoreAttributes</var>
504	546	is
505	547	<code>[]</code> for the last attribute.</dd>
506		<dt class="pubdef"><a name="put_attrs/2"><strong>put_attrs</strong>(<var>+Var,
	548	<dt class="pubdef"><a id="put_attrs/2"><strong>put_attrs</strong>(<var>+Var,
507	549	-Attributes</var>)</a></dt>
508	550	<dd class="defbody">
509		Set all attributes of <var>Var</var>. See <a name="idx:getattrs2:1792"></a><a class="pred" href="attvar.html#get_attrs/2">get_attrs/2</a>
	551	Set all attributes of <var>Var</var>. See <a id="idx:getattrs2:1796"></a><a class="pred" href="attvar.html#get_attrs/2">get_attrs/2</a>
510	552	for a description of
511	553	<var>Attributes</var>.</dd>
512		<dt class="pubdef"><a name="del_attrs/1"><strong>del_attrs</strong>(<var>+Var</var>)</a></dt>
	554	<dt class="pubdef"><a id="del_attrs/1"><strong>del_attrs</strong>(<var>+Var</var>)</a></dt>
513	555	<dd class="defbody">
514	556	If <var>Var</var> is an attributed variable, delete <em>all</em> its
515	557	attributes. In all other cases, this predicate succeeds without

+88

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193	234	</div>
194		<h2 id="sec:autoload"><a name="sec:2.13"><span class="sec-nr">2.13</span> <span class="sec-title">Automatic
	235	<h2 id="sec:autoload"><a id="sec:2.13"><span class="sec-nr">2.13</span> <span class="sec-title">Automatic
195	236	loading of libraries</span></a></h2>
196	237
197		<a name="sec:autoload"></a>
	238	<a id="sec:autoload"></a>
198	239
199	240	<p>If ---at runtime--- an undefined predicate is trapped, the system
200	241	will first try to import the predicate from the module's default module
201	242	(see
202		<a class="sec" href="importmodule.html">section 6.9</a>. If this fails
203		the <em>auto loader</em> is activated.<sup class="fn">23<span class="fn-text">Actually,
	243	<a class="sec" href="importmodule.html#sec:6.9">section 6.9</a>. If this
	244	fails the <em>auto loader</em> is activated.<sup class="fn">23<span class="fn-text">Actually,
204	245	the hook user:exception/3 is called; only if this hook fails does it
205	246	call the autoloader.</span></sup> On first activation an index to all
206		library files in all library directories is loaded in core (see <a name="idx:librarydirectory1:189"></a><a class="pred" href="consulting.html#library_directory/1">library_directory/1</a>, <a name="idx:filesearchpath2:190"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	247	library files in all library directories is loaded in core (see <a id="idx:librarydirectory1:189"></a><a class="pred" href="consulting.html#library_directory/1">library_directory/1</a>, <a id="idx:filesearchpath2:190"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
207	248	and
208		<a name="idx:reloadlibraryindex0:191"></a><a class="pred" href="autoload.html#reload_library_index/0">reload_library_index/0</a>).
	249	<a id="idx:reloadlibraryindex0:191"></a><a class="pred" href="autoload.html#reload_library_index/0">reload_library_index/0</a>).
209	250	If the undefined predicate can be located in one of the libraries, that
210	251	library file is automatically loaded and the call to the (previously
211	252	undefined) predicate is restarted. By default this mechanism loads the
212		file silently. The <a name="idx:currentprologflag2:192"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
	253	file silently. The <a id="idx:currentprologflag2:192"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
213	254	key <a class="flag" href="flags.html#flag:verbose_autoload">verbose_autoload</a>
214	255	is provided to get verbose loading. The Prolog flag <a class="flag" href="flags.html#flag:autoload">autoload</a>
215	256	can be used to enable/disable the autoload system.
216	257
217	258	<p>Autoloading only handles (library) source files that use the module
218		mechanism described in <a class="sec" href="modules.html">chapter 6</a>.
219		The files are loaded with <a name="idx:usemodule2:193"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
	259	mechanism described in <a class="sec" href="modules.html#sec:6">chapter
	260	6</a>. The files are loaded with <a id="idx:usemodule2:193"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
220	261	and only the trapped undefined predicate is imported into the module
221	262	where the undefined predicate was called. Each library directory must
222	263	hold a file <code>INDEX.pl</code> that contains an index to all library

227	268	index(Name, Arity, Module, File).
228	269	</pre>
229	270
230		<p>The predicate <a name="idx:make0:194"></a><a class="pred" href="consulting.html#make/0">make/0</a>
231		updates the autoload index. It searches for all library directories (see <a name="idx:librarydirectory1:195"></a><a class="pred" href="consulting.html#library_directory/1">library_directory/1</a>
232		and <a name="idx:filesearchpath2:196"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>)
	271	<p>The predicate <a id="idx:make0:194"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	272	updates the autoload index. It searches for all library directories (see <a id="idx:librarydirectory1:195"></a><a class="pred" href="consulting.html#library_directory/1">library_directory/1</a>
	273	and <a id="idx:filesearchpath2:196"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>)
233	274	holding the file <code>MKINDEX.pl</code> or <code>INDEX.pl</code>. If
234	275	the current user can write or create the file <code>INDEX.pl</code> and
235	276	it does not exist or is older than the directory or one of its files,
236	277	the index for this directory is updated. If the file <code>MKINDEX.pl</code>
237	278	exists, updating is achieved by loading this file, normally containing a
238	279	directive calling
239		<a name="idx:makelibraryindex2:197"></a><a class="pred" href="autoload.html#make_library_index/2">make_library_index/2</a>.
240		Otherwise <a name="idx:makelibraryindex1:198"></a><a class="pred" href="autoload.html#make_library_index/1">make_library_index/1</a>
	280	<a id="idx:makelibraryindex2:197"></a><a class="pred" href="autoload.html#make_library_index/2">make_library_index/2</a>.
	281	Otherwise <a id="idx:makelibraryindex1:198"></a><a class="pred" href="autoload.html#make_library_index/1">make_library_index/1</a>
241	282	is called, creating an index for all <code>*.pl</code> files containing
242	283	a module.
243	284

257	298	<li>If there is a library file that defines the module in which the
258	299	undefined predicate is trapped, this file is used.
259	300	<li>Otherwise library files are considered in the order they appear in
260		the <a name="idx:librarydirectory1:199"></a><a class="pred" href="consulting.html#library_directory/1">library_directory/1</a>
	301	the <a id="idx:librarydirectory1:199"></a><a class="pred" href="consulting.html#library_directory/1">library_directory/1</a>
261	302	predicate and within the directory alphabetically.
262	303	</ol>
263	304
264	305	<dl class="latex">
265		<dt class="pubdef"><a name="autoload_path/1"><strong>autoload_path</strong>(<var>+DirAlias</var>)</a></dt>
	306	<dt class="pubdef"><a id="autoload_path/1"><strong>autoload_path</strong>(<var>+DirAlias</var>)</a></dt>
266	307	<dd class="defbody">
267	308	Add <var>DirAlias</var> to the libraries that are used by the
268	309	autoloader. This extends the search path <code>autoload</code> and

274	315
275	316	<p>If this call appears as a directive, it is term-expanded into a
276	317	clause for user:file_search_path/2 and a directive calling
277		<a name="idx:reloadlibraryindex0:200"></a><a class="pred" href="autoload.html#reload_library_index/0">reload_library_index/0</a>.
	318	<a id="idx:reloadlibraryindex0:200"></a><a class="pred" href="autoload.html#reload_library_index/0">reload_library_index/0</a>.
278	319	This keeps source information and allows for removing this directive.</dd>
279		<dt class="pubdef"><a name="make_library_index/1"><strong>make_library_index</strong>(<var>+Directory</var>)</a></dt>
	320	<dt class="pubdef"><a id="make_library_index/1"><strong>make_library_index</strong>(<var>+Directory</var>)</a></dt>
280	321	<dd class="defbody">
281	322	Create an index for this directory. The index is written to the file
282	323	'INDEX.pl' in the specified directory. Fails with a warning if the
283	324	directory does not exist or is write protected.</dd>
284		<dt class="pubdef"><a name="make_library_index/2"><strong>make_library_index</strong>(<var>+Directory,
	325	<dt class="pubdef"><a id="make_library_index/2"><strong>make_library_index</strong>(<var>+Directory,
285	326	+ListOfPatterns</var>)</a></dt>
286	327	<dd class="defbody">
287	328	Normally used in <code>MKINDEX.pl</code>, this predicate creates <code>INDEX.pl</code>

305	346	</pre>
306	347
307	348	</dd>
308		<dt class="pubdef"><a name="reload_library_index/0"><strong>reload_library_index</strong></a></dt>
	349	<dt class="pubdef"><a id="reload_library_index/0"><strong>reload_library_index</strong></a></dt>
309	350	<dd class="defbody">
310	351	Force reloading the index after modifying the set of library directories
311		by changing the rules for <a name="idx:librarydirectory1:201"></a><a class="pred" href="consulting.html#library_directory/1">library_directory/1</a>, <a name="idx:filesearchpath2:202"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>,
	352	by changing the rules for <a id="idx:librarydirectory1:201"></a><a class="pred" href="consulting.html#library_directory/1">library_directory/1</a>, <a id="idx:filesearchpath2:202"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>,
312	353	adding or deleting <code>INDEX.pl</code> files. This predicate does <em>not</em>
313		update the <code>INDEX.pl</code> files. Check <a name="idx:makelibraryindex12:203"></a><a class="pred" href="autoload.html#make_library_index/1">make_library_index/[1,2]</a>
	354	update the <code>INDEX.pl</code> files. Check <a id="idx:makelibraryindex12:203"></a><a class="pred" href="autoload.html#make_library_index/1">make_library_index/[1,2]</a>
314	355	and
315		<a name="idx:make0:204"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	356	<a id="idx:make0:204"></a><a class="pred" href="consulting.html#make/0">make/0</a>
316	357	for updating the index files.
317	358
318	359	<p>Normally, the index is reloaded automatically if a predicate cannot
319	360	be found in the index and the set of library directories has changed.
320	361	Using
321		<a name="idx:reloadlibraryindex0:205"></a><a class="pred" href="autoload.html#reload_library_index/0">reload_library_index/0</a>
	362	<a id="idx:reloadlibraryindex0:205"></a><a class="pred" href="autoload.html#reload_library_index/0">reload_library_index/0</a>
322	363	is necessary if directories are removed or the order of the library
323	364	directories is changed.
324	365	</dd>
325	366	</dl>
326	367
327		<p>When creating an executable using either <a name="idx:qsaveprogram2:206"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
	368	<p>When creating an executable using either <a id="idx:qsaveprogram2:206"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
328	369	or the
329	370	<strong>-c</strong> command line options, it is necessarry to load all
330	371	predicates that would normally be autoloaded explicitly. This is
331		discussed in <a class="sec" href="runtime.html">section 12</a>. See <a name="idx:autoload0:207"></a><a class="pred" href="runtime.html#autoload/0">autoload/0</a>.
	372	discussed in <a class="sec" href="runtime.html#sec:12">section 12</a>.
	373	See <a id="idx:autoload0:207"></a><a class="pred" href="runtime.html#autoload/0">autoload/0</a>.
332	374
333	375	<p></body></html>⏎

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section B.4</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:breakpoint"><a name="sec:B.4"><span class="sec-nr">B.4</span> <span class="sec-title">Breakpoint
	235	<h2 id="sec:breakpoint"><a id="sec:B.4"><span class="sec-nr">B.4</span> <span class="sec-title">Breakpoint
195	236	and watchpoint handling</span></a></h2>
196	237
197		<a name="sec:breakpoint"></a>
	238	<a id="sec:breakpoint"></a>
198	239
199	240	<p>SWI-Prolog support <em>breakpoints</em>. Breakpoints can be
200	241	manipulated with the library <code>library(prolog_breakpoints)</code>.

204	245	describes this callback, called prolog:break_hook/6.
205	246
206	247	<dl class="latex">
207		<dt class="pubdef"><span class="pred-tag">[hook,semidet]</span><a name="prolog:break_hook/6"><strong>prolog:break_hook</strong>(<var>+Clause,
	248	<dt class="pubdef"><span class="pred-tag">[hook,semidet]</span><a id="prolog:break_hook/6"><strong>prolog:break_hook</strong>(<var>+Clause,
208	249	+PC, +FR, +BFR, +Expression, -Action</var>)</a></dt>
209	250	<dd class="defbody">
210	251	<em>Experimental</em> This hook is called if the virtual machine
211		executes a <code>D_BREAK</code>, set using <a name="idx:setbreakpoint4:2199"></a><span class="pred-ext">set_breakpoint/4</span>. <var>Clause</var>
	252	executes a <code>D_BREAK</code>, set using <a id="idx:setbreakpoint4:2203"></a><span class="pred-ext">set_breakpoint/4</span>. <var>Clause</var>
212	253	and <var>PC</var> identify the breakpoint. <var>FR</var> and <var>BFR</var>
213	254	provide the environment frame and current choicepoint. <var>Expression</var>
214	255	identifies the action that is interrupted, and is one of the following:

243	284	<dd class="defbody">
244	285	The breakpoint is on the completion of an in-lined unification while the
245	286	system is not in debug mode. If the system is in debug mode, inlined
246		unification is returned as call(Var=Term).<sup class="fn">186<span class="fn-text">This
	287	unification is returned as call(Var=Term).<sup class="fn">187<span class="fn-text">This
247	288	hack will disappear if we find a good solution for applying D_BREAK to
248	289	inlined unification. Only option might be to place the break on both the
249	290	unification start and end instructions.</span></sup>

260	301	Just continue as if no breakpoint was present.</dd>
261	302	<dt><strong>debug</strong></dt>
262	303	<dd class="defbody">
263		Continue in <em>debug mode</em>. See <a name="idx:debug0:2200"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.</dd>
	304	Continue in <em>debug mode</em>. See <a id="idx:debug0:2204"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.</dd>
264	305	<dt><strong>trace</strong></dt>
265	306	<dd class="defbody">
266		Continue in <em>trace mode</em>. See <a name="idx:trace0:2201"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>.</dd>
	307	Continue in <em>trace mode</em>. See <a id="idx:trace0:2205"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>.</dd>
267	308	<dt><strong>call</strong>(<var>Goal</var>)</dt>
268	309	<dd class="defbody">
269	310	Execute <var>Goal</var> instead of the goal that would be executed.
270		<var>Goal</var> is executed as <a name="idx:call1:2202"></a><a class="pred" href="metacall.html#call/1">call/1</a>,
	311	<var>Goal</var> is executed as <a id="idx:call1:2206"></a><a class="pred" href="metacall.html#call/1">call/1</a>,
271	312	preserving (non-)determinism and exceptions.
272	313	</dd>
273	314	</dl>

289	330	before deciding the return <code>trace</code>.
290	331	<li>Watch variables at a specific point in the execution. Note that
291	332	binding of these variables can be monitored using <em>attributed
292		variables</em>, see <a class="sec" href="attvar.html">section 7.1</a>.
293		<li>Dynamically add <em>assertions</em> on variables using <a name="idx:assertion1:2203"></a><a class="pred" href="debug.html#assertion/1">assertion/1</a>.
	333	variables</em>, see <a class="sec" href="attvar.html#sec:7.1">section
	334	7.1</a>.
	335	<li>Dynamically add <em>assertions</em> on variables using <a id="idx:assertion1:2207"></a><a class="pred" href="debug.html#assertion/1">assertion/1</a>.
294	336	<li>Wrap the <var>Goal</var> into a meta-call that traces progress of
295	337	the <var>Goal</var>.
296	338	</ul>

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193	234	</div>
194		<h2 id="sec:broadcast"><a name="sec:A.4"><span class="sec-nr">A.4</span> <span class="sec-title">library(broadcast):
	235	<h2 id="sec:broadcast"><a id="sec:A.4"><span class="sec-nr">A.4</span> <span class="sec-title">library(broadcast):
195	236	Broadcast and receive event notifications</span></a></h2>
196	237
197		<a name="sec:broadcast"></a>
198
199		<p><a name="idx:broadcast:2132"></a><a name="idx:messageservice:2133"></a><a name="idx:blackboard:2134"></a><a name="idx:agent:2135"></a><a name="idx:daemon:2136"></a>The <code>library(broadcast)</code>
	238	<a id="sec:broadcast"></a>
	239
	240	<p><a id="idx:broadcast:2136"></a><a id="idx:messageservice:2137"></a><a id="idx:blackboard:2138"></a><a id="idx:agent:2139"></a><a id="idx:daemon:2140"></a>The <code>library(broadcast)</code>
200	241	library was invented to realise GUI applications consisting of
201	242	stand-alone components that use the Prolog database for storing the
202	243	application data. <a class="fig" href="broadcast.html#fig:broadcast">Figure
203	244	12</a> illustrates the flow of information using this design
204	245
205		<p><a name="fig:broadcast"></a><div style="text-align:center"><img src="broadcast.gif"></div>
	246	<p><a id="fig:broadcast"></a><div style="text-align:center"><img src="broadcast.gif"></div>
206	247	<div class="caption"><b>Figure 12 : </b>Information-flow using
207	248	broadcasting service</div>
208	249

221	262	showing <var>X</var>?''.
222	263
223	264	<dl class="latex">
224		<dt class="pubdef"><a name="broadcast/1"><strong>broadcast</strong>(<var>+Term</var>)</a></dt>
	265	<dt class="pubdef"><a id="broadcast/1"><strong>broadcast</strong>(<var>+Term</var>)</a></dt>
225	266	<dd class="defbody">
226	267	Broadcast <var>Term</var>. There are no limitations to <var>Term</var>,
227	268	though being a global service, it is good practice to use a descriptive
228	269	and unique principal functor. All associated goals are started and
229		regardless of their success or failure, <a name="idx:broadcast1:2137"></a><a class="pred" href="broadcast.html#broadcast/1">broadcast/1</a>
	270	regardless of their success or failure, <a id="idx:broadcast1:2141"></a><a class="pred" href="broadcast.html#broadcast/1">broadcast/1</a>
230	271	always succeeds. Exceptions are passed.</dd>
231		<dt class="pubdef"><a name="broadcast_request/1"><strong>broadcast_request</strong>(<var>+Term</var>)</a></dt>
232		<dd class="defbody">
233		Unlike <a name="idx:broadcast1:2138"></a><a class="pred" href="broadcast.html#broadcast/1">broadcast/1</a>,
	272	<dt class="pubdef"><a id="broadcast_request/1"><strong>broadcast_request</strong>(<var>+Term</var>)</a></dt>
	273	<dd class="defbody">
	274	Unlike <a id="idx:broadcast1:2142"></a><a class="pred" href="broadcast.html#broadcast/1">broadcast/1</a>,
234	275	this predicate stops if an associated goal succeeds. Backtracking causes
235	276	it to try other listeners. A broadcast request is used to fetch
236	277	information without knowing the identity of the agent providing it. C.f. ``Is

244	285	<p>If there is an agent (<em>listener</em>) that registered an `age-of'
245	286	service and knows about the age of `John' this question will be
246	287	answered.</dd>
247		<dt class="pubdef"><a name="listen/2"><strong>listen</strong>(<var>+Template,
	288	<dt class="pubdef"><a id="listen/2"><strong>listen</strong>(<var>+Template,
248	289	:Goal</var>)</a></dt>
249	290	<dd class="defbody">
250	291	Register a <em>listen</em> channel. Whenever a term unifying

260	301	</pre>
261	302
262	303	</dd>
263		<dt class="pubdef"><a name="listen/3"><strong>listen</strong>(<var>+Listener,
	304	<dt class="pubdef"><a id="listen/3"><strong>listen</strong>(<var>+Listener,
264	305	+Template, :Goal</var>)</a></dt>
265	306	<dd class="defbody">
266	307	Declare <var>Listener</var> as the owner of the channel. Unlike a
267		channel opened using <a name="idx:listen2:2139"></a><a class="pred" href="broadcast.html#listen/2">listen/2</a>,
	308	channel opened using <a id="idx:listen2:2143"></a><a class="pred" href="broadcast.html#listen/2">listen/2</a>,
268	309	channels that have an owner can terminate the channel. This is commonly
269	310	used if an object is listening to broadcast messages. In the example
270	311	below we define a `name-item' displaying the name of an identifier
271		represented by the predicate <a name="idx:nameof2:2140"></a><span class="pred-ext">name_of/2</span>.
	312	represented by the predicate <a id="idx:nameof2:2144"></a><span class="pred-ext">name_of/2</span>.
272	313
273	314	<pre class="code">
274	315	:- pce_begin_class(name_item, text_item).

297	338	</pre>
298	339
299	340	</dd>
300		<dt class="pubdef"><a name="unlisten/1"><strong>unlisten</strong>(<var>+Listener</var>)</a></dt>
301		<dd class="defbody">
302		Deregister all entries created with <a name="idx:listen3:2141"></a><a class="pred" href="broadcast.html#listen/3">listen/3</a>
	341	<dt class="pubdef"><a id="unlisten/1"><strong>unlisten</strong>(<var>+Listener</var>)</a></dt>
	342	<dd class="defbody">
	343	Deregister all entries created with <a id="idx:listen3:2145"></a><a class="pred" href="broadcast.html#listen/3">listen/3</a>
303	344	whose <var>Listener</var> unify.</dd>
304		<dt class="pubdef"><a name="unlisten/2"><strong>unlisten</strong>(<var>+Listener,
	345	<dt class="pubdef"><a id="unlisten/2"><strong>unlisten</strong>(<var>+Listener,
305	346	+Template</var>)</a></dt>
306	347	<dd class="defbody">
307		Deregister all entries created with <a name="idx:listen3:2142"></a><a class="pred" href="broadcast.html#listen/3">listen/3</a>
	348	Deregister all entries created with <a id="idx:listen3:2146"></a><a class="pred" href="broadcast.html#listen/3">listen/3</a>
308	349	whose <var>Listener</var> and <var>Template</var> unify.</dd>
309		<dt class="pubdef"><a name="unlisten/3"><strong>unlisten</strong>(<var>+Listener,
	350	<dt class="pubdef"><a id="unlisten/3"><strong>unlisten</strong>(<var>+Listener,
310	351	+Template, :Goal</var>)</a></dt>
311	352	<dd class="defbody">
312		Deregister all entries created with <a name="idx:listen3:2143"></a><a class="pred" href="broadcast.html#listen/3">listen/3</a>
	353	Deregister all entries created with <a id="idx:listen3:2147"></a><a class="pred" href="broadcast.html#listen/3">listen/3</a>
313	354	whose <var>Listener</var>,
314	355	<var>Template</var> and <var>Goal</var> unify.</dd>
315		<dt class="pubdef"><a name="listening/3"><strong>listening</strong>(<var>?Listener,
	356	<dt class="pubdef"><a id="listening/3"><strong>listening</strong>(<var>?Listener,
316	357	?Template, ?Goal</var>)</a></dt>
317	358	<dd class="defbody">
318	359	Examine the current listeners. This predicate is useful for debugging

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194		<h1 id="sec:builtin"><a name="sec:4"><span class="sec-nr">4</span> <span class="sec-title">Built-in
	235	<h1 id="sec:builtin"><a id="sec:4"><span class="sec-nr">4</span> <span class="sec-title">Built-in
195	236	Predicates</span></a></h1>
196	237
197		<a name="sec:builtin"></a>
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198	239
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193	234	</div>
194		<h2 id="sec:builtinlist"><a name="sec:4.29"><span class="sec-nr">4.29</span> <span class="sec-title">Built-in
	235	<h2 id="sec:builtinlist"><a id="sec:4.29"><span class="sec-nr">4.29</span> <span class="sec-title">Built-in
195	236	list operations</span></a></h2>
196	237
197		<a name="sec:builtinlist"></a>
	238	<a id="sec:builtinlist"></a>
198	239
199	240	<p>Most list operations are defined in the library <code>library(lists)</code>
200		described in <a class="sec" href="lists.html">section A.15</a>. Some
201		that are implemented with more low-level primitives are built-in and
202		described here.
	241	described in <a class="sec" href="lists.html#sec:A.15">section A.15</a>.
	242	Some that are implemented with more low-level primitives are built-in
	243	and described here.
203	244
204	245	<dl class="latex">
205		<dt class="pubdef"><a name="is_list/1"><strong>is_list</strong>(<var>+Term</var>)</a></dt>
	246	<dt class="pubdef"><a id="is_list/1"><strong>is_list</strong>(<var>+Term</var>)</a></dt>
206	247	<dd class="defbody">
207	248	True if <var>Term</var> is bound to the empty list (<code>[]</code>) or
208	249	a term with functor `<code>'[\|]'</code>'<sup class="fn">118<span class="fn-text">The
209	250	traditional list functor is the dot (<code>'.'</code>). This is still
210	251	the case of the command line option <strong>--traditional</strong> is
211		given. See also <a class="sec" href="ext-lists.html">section 5.1</a>.</span></sup>
	252	given. See also <a class="sec" href="ext-lists.html#sec:5.1">section 5.1</a>.</span></sup>
212	253	and arity 2 and the second argument is a list.<sup class="fn">119<span class="fn-text">In
213		versions before 5.0.1, <a name="idx:islist1:1342"></a><a class="pred" href="builtinlist.html#is_list/1">is_list/1</a>
	254	versions before 5.0.1, <a id="idx:islist1:1342"></a><a class="pred" href="builtinlist.html#is_list/1">is_list/1</a>
214	255	just checked for <code>[]</code> or <code>[_\|_]</code> and proper_list/1
215		had the role of the current <a name="idx:islist1:1343"></a><a class="pred" href="builtinlist.html#is_list/1">is_list/1</a>.
	256	had the role of the current <a id="idx:islist1:1343"></a><a class="pred" href="builtinlist.html#is_list/1">is_list/1</a>.
216	257	The current definition conforms to the de facto standard. Assuming
217	258	proper coding standards, there should only be very few cases where a
218		quick-and-dirty <a name="idx:islist1:1344"></a><a class="pred" href="builtinlist.html#is_list/1">is_list/1</a>
	259	quick-and-dirty <a id="idx:islist1:1344"></a><a class="pred" href="builtinlist.html#is_list/1">is_list/1</a>
219	260	is a good choice. Richard O'Keefe pointed at this issue.</span></sup>
220	261	This predicate acts as if defined by the definition below on
221	262	<em>acyclic</em> terms. The implementation <em>fails</em> safely if

231	272	</pre>
232	273
233	274	</dd>
234		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="memberchk/2"><strong>memberchk</strong>(<var>?Elem,
	275	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="memberchk/2"><strong>memberchk</strong>(<var>?Elem,
235	276	+List</var>)</a></dt>
236	277	<dd class="defbody">
237	278	True when <var>Elem</var> is an element of <var>List</var>. This `chk'
238	279	variant of
239		<a name="idx:member2:1345"></a><a class="pred" href="lists.html#member/2">member/2</a>
	280	<a id="idx:member2:1345"></a><a class="pred" href="lists.html#member/2">member/2</a>
240	281	is semi deterministic and typically used to test membership of a list.
241	282	Raises a <code>type</code> error if scanning <var>List</var> encounters
242		a non-list. Note that <a name="idx:memberchk2:1346"></a><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a>
	283	a non-list. Note that <a id="idx:memberchk2:1346"></a><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a>
243	284	does <em>not</em> perform a full list typecheck. For example, <code>memberchk(a,
244	285	[a\|b])</code> succeeds without error. If <var>List</var> is cyclic and <var>Elem</var>
245	286	is not a member of
246		<var>List</var>, <a name="idx:memberchk2:1347"></a><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a>
	287	<var>List</var>, <a id="idx:memberchk2:1347"></a><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a>
247	288	eventually raises a <code>type</code> error.<sup class="fn">120<span class="fn-text"><i>Eventually</i>
248	289	here means it will scan as many elements as the longest list that may
249	290	exist given the current stack usage before raising the exception.</span></sup></dd>
250		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="length/2"><strong>length</strong>(<var>?List,
	291	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="length/2"><strong>length</strong>(<var>?List,
251	292	?Int</var>)</a></dt>
252	293	<dd class="defbody">
253	294	True if <var>Int</var> represents the number of elements in <var>List</var>.

272	313	is logically correct. An exception would be more appropriate, but to our
273	314	best knowledge, current practice in Prolog does not describe a suitable
274	315	candidate exception term.</span></sup></dd>
275		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="sort/2"><strong>sort</strong>(<var>+List,
	316	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="sort/2"><strong>sort</strong>(<var>+List,
276	317	-Sorted</var>)</a></dt>
277	318	<dd class="defbody">
278	319	True if <var>Sorted</var> can be unified with a list holding the
279	320	elements of <var>List</var>, sorted to the standard order of terms (see
280		<a class="sec" href="compare.html">section 4.7</a>). Duplicates are
281		removed. The implementation is in C, using <em>natural merge sort</em>.<sup class="fn">123<span class="fn-text">Contributed
282		by Richard O'Keefe.</span></sup> The <a name="idx:sort2:1348"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>
	321	<a class="sec" href="compare.html#sec:4.7">section 4.7</a>). Duplicates
	322	are removed. The implementation is in C, using <em>natural merge sort</em>.<sup class="fn">123<span class="fn-text">Contributed
	323	by Richard O'Keefe.</span></sup> The <a id="idx:sort2:1348"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>
283	324	predicate can sort a cyclic list, returning a non-cyclic version with
284	325	the same elements.
285	326

289	330	However, unifying a variable in <var>Sorted</var> may cause this
290	331	relation to become invalid,
291	332	<em>even</em> unifying a variable in <var>Sorted</var> with another
292		(older) variable. See also <a class="sec" href="compare.html">section
	333	(older) variable. See also <a class="sec" href="compare.html#sec:4.7.1">section
293	334	4.7.1</a>.</dd>
294		<dt class="pubdef"><a name="sort/4"><strong>sort</strong>(<var>+Key,
	335	<dt class="pubdef"><a id="sort/4"><strong>sort</strong>(<var>+Key,
295	336	+Order, +List, -Sorted</var>)</a></dt>
296	337	<dd class="defbody">
297	338	True when <var>Sorted</var> can be unified with a list holding the

309	350	<p>If <var>Key</var> is the integer zero (0), the entire term is used to
310	351	compare two elements. Using <var>Key</var>=0 can be used to sort
311	352	arbitrary Prolog terms. Other values for <var>Key</var> can only be used
312		with compound terms or dicts (see <a class="sec" href="dicts.html">section
	353	with compound terms or dicts (see <a class="sec" href="dicts.html#sec:5.4">section
313	354	5.4</a>). An integer key extracts the <var>Key</var>-th argument from a
314	355	compound term. An integer or atom key extracts the value from a dict
315	356	that is associated with the given key. A type_error is raised if the

324	365	compatibility with ECLiPSe, the values <code><code><</code></code>, <code><code>=<</code></code>, <code><code>></code></code>
325	366	and <code><code>>=</code></code> are allowed as synonyms.</span></sup>
326	367
327		<p><table border="0" frame="void" rules="groups" style="margin:auto">
328		<tr valign="top"><td>Order</td><td>Ordering</td><td>Duplicate handling </td></tr>
329		<tbody>
330		<tr valign="top"><td><code><code>@<</code></code> </td><td>ascending</td><td>remove </td></tr>
331		<tr valign="top"><td><code><code>@=<</code></code> </td><td>ascending</td><td>keep </td></tr>
332		<tr valign="top"><td><code><code>@></code></code> </td><td>descending</td><td>remove </td></tr>
333		<tr valign="top"><td><code><code>@>=</code></code> </td><td>descending</td><td>keep </td></tr>
	368	<p><table class="latex frame-void center">
	369	<tr><td>Order</td><td>Ordering</td><td>Duplicate handling </td></tr>
	370	<tr class="hline"><td><code><code>@<</code></code> </td><td>ascending</td><td>remove </td></tr>
	371	<tr><td><code><code>@=<</code></code> </td><td>ascending</td><td>keep </td></tr>
	372	<tr><td><code><code>@></code></code> </td><td>descending</td><td>remove </td></tr>
	373	<tr><td><code><code>@>=</code></code> </td><td>descending</td><td>keep </td></tr>
334	374	</table>
335	375
336	376	<p>The sort is <em>stable</em>, which implies that, if duplicates are

348	388
349	389	<p>The following example sorts a list of rows, for example resulting
350	390	from
351		<a name="idx:csvreadfile2:1349"></a><a class="pred" href="csv.html#csv_read_file/2">csv_read_file/2</a>)
	391	<a id="idx:csvreadfile2:1349"></a><a class="pred" href="csv.html#csv_read_file/2">csv_read_file/2</a>)
352	392	ascending on the 3th column and descending on the 4th column:
353	393
354	394	<pre class="code">

356	396	sort(3, @=<, Rows1, Sorted).
357	397	</pre>
358	398
359		<p>See also <a name="idx:sort2:1350"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>
360		(ISO), <a name="idx:msort2:1351"></a><a class="pred" href="builtinlist.html#msort/2">msort/2</a>, <a name="idx:keysort2:1352"></a><a class="pred" href="builtinlist.html#keysort/2">keysort/2</a>, <a name="idx:predsort3:1353"></a><a class="pred" href="builtinlist.html#predsort/3">predsort/3</a>
361		and <a name="idx:orderby2:1354"></a><a class="pred" href="solutionsequences.html#order_by/2">order_by/2</a>.</dd>
362		<dt class="pubdef"><a name="msort/2"><strong>msort</strong>(<var>+List,
	399	<p>See also <a id="idx:sort2:1350"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>
	400	(ISO), <a id="idx:msort2:1351"></a><a class="pred" href="builtinlist.html#msort/2">msort/2</a>, <a id="idx:keysort2:1352"></a><a class="pred" href="builtinlist.html#keysort/2">keysort/2</a>, <a id="idx:predsort3:1353"></a><a class="pred" href="builtinlist.html#predsort/3">predsort/3</a>
	401	and <a id="idx:orderby2:1354"></a><a class="pred" href="solutionsequences.html#order_by/2">order_by/2</a>.</dd>
	402	<dt class="pubdef"><a id="msort/2"><strong>msort</strong>(<var>+List,
363	403	-Sorted</var>)</a></dt>
364	404	<dd class="defbody">
365		Equivalent to <a name="idx:sort2:1355"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>,
	405	Equivalent to <a id="idx:sort2:1355"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>,
366	406	but does not remove duplicates. Raises a
367	407	<code>type_error</code> if <var>List</var> is a cyclic list or not a
368	408	list.</dd>
369		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="keysort/2"><strong>keysort</strong>(<var>+List,
	409	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="keysort/2"><strong>keysort</strong>(<var>+List,
370	410	-Sorted</var>)</a></dt>
371	411	<dd class="defbody">
372	412	Sort a list of <em>pairs</em>. <var>List</var> must be a list of
373	413	<code><var>Key</var>-<var>Value</var></code> pairs, terms whose
374	414	principal functor is (-)/2. <var>List</var> is sorted on <var>Key</var>
375		according to the standard order of terms (see <a class="sec" href="compare.html">section
	415	according to the standard order of terms (see <a class="sec" href="compare.html#sec:4.7.1">section
376	416	4.7.1</a>). Duplicates are <em>not</em> removed. Sorting is <em>stable</em>
377	417	with regard to the order of the
378	418	<var>Values</var>, i.e., the order of multiple elements that have the
379	419	same
380	420	<var>Key</var> is not changed.
381	421
382		<p>The <a name="idx:keysort2:1356"></a><a class="pred" href="builtinlist.html#keysort/2">keysort/2</a>
	422	<p>The <a id="idx:keysort2:1356"></a><a class="pred" href="builtinlist.html#keysort/2">keysort/2</a>
383	423	predicate is often used together with library
384	424	<code>library(pairs)</code>. It can be used to sort lists on different
385	425	or multiple criteria. For example, the following predicates sorts a list

396	436	</pre>
397	437
398	438	</dd>
399		<dt class="pubdef"><a name="predsort/3"><strong>predsort</strong>(<var>+Pred,
	439	<dt class="pubdef"><a id="predsort/3"><strong>predsort</strong>(<var>+Pred,
400	440	+List, -Sorted</var>)</a></dt>
401	441	<dd class="defbody">
402		Sorts similar to <a name="idx:sort2:1357"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>,
	442	Sorts similar to <a id="idx:sort2:1357"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>,
403	443	but determines the order of two terms by calling <var>Pred</var>(-<var>Delta</var>,
404	444	+<var>E1</var>, +<var>E2</var>) . This call must unify <var>Delta</var>
405	445	with one of <code><code><</code></code>, <code><code>></code></code>
406	446	or
407		<code><code>=</code></code>. If the built-in predicate <a name="idx:compare3:1358"></a><a class="pred" href="compare.html#compare/3">compare/3</a>
408		is used, the result is the same as <a name="idx:sort2:1359"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>.
409		See also <a name="idx:keysort2:1360"></a><a class="pred" href="builtinlist.html#keysort/2">keysort/2</a>.
	447	<code><code>=</code></code>. If the built-in predicate <a id="idx:compare3:1358"></a><a class="pred" href="compare.html#compare/3">compare/3</a>
	448	is used, the result is the same as <a id="idx:sort2:1359"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>.
	449	See also <a id="idx:keysort2:1360"></a><a class="pred" href="builtinlist.html#keysort/2">keysort/2</a>.
410	450	</dd>
411	451	</dl>
412	452

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3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 4.26</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.26</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="operators.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="arith.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:charconv"><a name="sec:4.26"><span class="sec-nr">4.26</span> <span class="sec-title">Character
	235	<h2 id="sec:charconv"><a id="sec:4.26"><span class="sec-nr">4.26</span> <span class="sec-title">Character
195	236	Conversion</span></a></h2>
196	237
197		<a name="sec:charconv"></a>
	238	<a id="sec:charconv"></a>
198	239
199	240	<p>Although I wouldn't really know why you would like to use these
200	241	features, they are provided for ISO compliance.
201	242
202	243	<dl class="latex">
203		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="char_conversion/2"><strong>char_conversion</strong>(<var>+CharIn,
	244	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="char_conversion/2"><strong>char_conversion</strong>(<var>+CharIn,
204	245	+CharOut</var>)</a></dt>
205	246	<dd class="defbody">
206		Define that term input (see <a name="idx:readterm3:1318"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>)
	247	Define that term input (see <a id="idx:readterm3:1318"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>)
207	248	maps each character read as
208	249	<var>CharIn</var> to the character <var>CharOut</var>. Character
209	250	conversion is only executed if the Prolog flag <a class="flag" href="flags.html#flag:char_conversion">char_conversion</a>
210	251	is set to
211	252	<code>true</code> and not inside quoted atoms or strings. The initial
212		table maps each character onto itself. See also <a name="idx:currentcharconversion2:1319"></a><a class="pred" href="charconv.html#current_char_conversion/2">current_char_conversion/2</a>.
	253	table maps each character onto itself. See also <a id="idx:currentcharconversion2:1319"></a><a class="pred" href="charconv.html#current_char_conversion/2">current_char_conversion/2</a>.
213	254	</dd>
214		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="current_char_conversion/2"><strong>current_char_conversion</strong>(<var>?CharIn,
	255	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="current_char_conversion/2"><strong>current_char_conversion</strong>(<var>?CharIn,
215	256	?CharOut</var>)</a></dt>
216	257	<dd class="defbody">
217		Queries the current character conversion table. See <a name="idx:charconversion2:1320"></a><a class="pred" href="charconv.html#char_conversion/2">char_conversion/2</a>
	258	Queries the current character conversion table. See <a id="idx:charconversion2:1320"></a><a class="pred" href="charconv.html#char_conversion/2">char_conversion/2</a>
218	259	for details.
219	260	</dd>
220	261	</dl>

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2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 4.19</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.19</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
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27	31
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191	232	<a class="nav" href="streamstat.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="termrw.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:chario"><a name="sec:4.19"><span class="sec-nr">4.19</span> <span class="sec-title">Primitive
	235	<h2 id="sec:chario"><a id="sec:4.19"><span class="sec-nr">4.19</span> <span class="sec-title">Primitive
195	236	character I/O</span></a></h2>
196	237
197		<a name="sec:chario"></a>
198
199		<p>See <a class="sec" href="chars.html">section 4.2</a> for an overview
200		of supported character representations.
	238	<a id="sec:chario"></a>
	239
	240	<p>See <a class="sec" href="chars.html#sec:4.2">section 4.2</a> for an
	241	overview of supported character representations.
201	242
202	243	<dl class="latex">
203		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="nl/0"><strong>nl</strong></a></dt>
	244	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="nl/0"><strong>nl</strong></a></dt>
204	245	<dd class="defbody">
205	246	Write a newline character to the current output stream. On Unix systems
206		<a name="idx:nl0:1074"></a><a class="pred" href="chario.html#nl/0">nl/0</a>
	247	<a id="idx:nl0:1074"></a><a class="pred" href="chario.html#nl/0">nl/0</a>
207	248	is equivalent to <code>put(10)</code>.</dd>
208		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="nl/1"><strong>nl</strong>(<var>+Stream</var>)</a></dt>
	249	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="nl/1"><strong>nl</strong>(<var>+Stream</var>)</a></dt>
209	250	<dd class="defbody">
210	251	Write a newline to <var>Stream</var>.</dd>
211		<dt class="pubdef"><a name="put/1"><strong>put</strong>(<var>+Char</var>)</a></dt>
	252	<dt class="pubdef"><a id="put/1"><strong>put</strong>(<var>+Char</var>)</a></dt>
212	253	<dd class="defbody">
213	254	Write <var>Char</var> to the current output stream. <var>Char</var> is
214	255	either an integer expression evaluating to a character code or an atom
215		of one character. Deprecated. New code should use <a name="idx:putchar1:1075"></a><a class="pred" href="chario.html#put_char/1">put_char/1</a>
216		or <a name="idx:putcode1:1076"></a><a class="pred" href="chario.html#put_code/1">put_code/1</a>.</dd>
217		<dt class="pubdef"><a name="put/2"><strong>put</strong>(<var>+Stream,
	256	of one character. Deprecated. New code should use <a id="idx:putchar1:1075"></a><a class="pred" href="chario.html#put_char/1">put_char/1</a>
	257	or <a id="idx:putcode1:1076"></a><a class="pred" href="chario.html#put_code/1">put_code/1</a>.</dd>
	258	<dt class="pubdef"><a id="put/2"><strong>put</strong>(<var>+Stream,
218	259	+Char</var>)</a></dt>
219	260	<dd class="defbody">
220		Write <var>Char</var> to <var>Stream</var>. See <a name="idx:put1:1077"></a><a class="pred" href="chario.html#put/1">put/1</a>
	261	Write <var>Char</var> to <var>Stream</var>. See <a id="idx:put1:1077"></a><a class="pred" href="chario.html#put/1">put/1</a>
221	262	for details.</dd>
222		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="put_byte/1"><strong>put_byte</strong>(<var>+Byte</var>)</a></dt>
	263	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="put_byte/1"><strong>put_byte</strong>(<var>+Byte</var>)</a></dt>
223	264	<dd class="defbody">
224	265	Write a single byte to the output. <var>Byte</var> must be an integer
225	266	between 0 and 255.</dd>
226		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="put_byte/2"><strong>put_byte</strong>(<var>+Stream,
	267	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="put_byte/2"><strong>put_byte</strong>(<var>+Stream,
227	268	+Byte</var>)</a></dt>
228	269	<dd class="defbody">
229	270	Write a single byte to <var>Stream</var>. <var>Byte</var> must be an
230	271	integer between 0 and 255.</dd>
231		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="put_char/1"><strong>put_char</strong>(<var>+Char</var>)</a></dt>
	272	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="put_char/1"><strong>put_char</strong>(<var>+Char</var>)</a></dt>
232	273	<dd class="defbody">
233	274	Write a character to the current output, obeying the encoding defined
234	275	for the current output stream. Note that this may raise an exception if
235	276	the encoding of the output stream cannot represent <var>Char</var>.</dd>
236		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="put_char/2"><strong>put_char</strong>(<var>+Stream,
	277	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="put_char/2"><strong>put_char</strong>(<var>+Stream,
237	278	+Char</var>)</a></dt>
238	279	<dd class="defbody">
239	280	Write a character to <var>Stream</var>, obeying the encoding defined for
240	281	<var>Stream</var>. Note that this may raise an exception if the encoding
241	282	of <var>Stream</var> cannot represent <var>Char</var>.</dd>
242		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="put_code/1"><strong>put_code</strong>(<var>+Code</var>)</a></dt>
243		<dd class="defbody">
244		Similar to <a name="idx:putchar1:1078"></a><a class="pred" href="chario.html#put_char/1">put_char/1</a>,
	283	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="put_code/1"><strong>put_code</strong>(<var>+Code</var>)</a></dt>
	284	<dd class="defbody">
	285	Similar to <a id="idx:putchar1:1078"></a><a class="pred" href="chario.html#put_char/1">put_char/1</a>,
245	286	but using a <em>character code</em>. <var>Code</var> is a non-negative
246	287	integer. Note that this may raise an exception if the encoding of the
247	288	output stream cannot represent <var>Code</var>.</dd>
248		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="put_code/2"><strong>put_code</strong>(<var>+Stream,
	289	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="put_code/2"><strong>put_code</strong>(<var>+Stream,
249	290	+Code</var>)</a></dt>
250	291	<dd class="defbody">
251		Same as <a name="idx:putcode1:1079"></a><a class="pred" href="chario.html#put_code/1">put_code/1</a>
	292	Same as <a id="idx:putcode1:1079"></a><a class="pred" href="chario.html#put_code/1">put_code/1</a>
252	293	but directing <var>Code</var> to <var>Stream</var>.</dd>
253		<dt class="pubdef"><a name="tab/1"><strong>tab</strong>(<var>+Amount</var>)</a></dt>
	294	<dt class="pubdef"><a id="tab/1"><strong>tab</strong>(<var>+Amount</var>)</a></dt>
254	295	<dd class="defbody">
255	296	Write <var>Amount</var> spaces on the current output stream. <var>Amount</var>
256	297	should be an expression that evaluates to a positive integer (see
257		<a class="sec" href="arith.html">section 4.27</a>).</dd>
258		<dt class="pubdef"><a name="tab/2"><strong>tab</strong>(<var>+Stream,
	298	<a class="sec" href="arith.html#sec:4.27">section 4.27</a>).</dd>
	299	<dt class="pubdef"><a id="tab/2"><strong>tab</strong>(<var>+Stream,
259	300	+Amount</var>)</a></dt>
260	301	<dd class="defbody">
261	302	Write <var>Amount</var> spaces to <var>Stream</var>.</dd>
262		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="flush_output/0"><strong>flush_output</strong></a></dt>
263		<dd class="defbody">
264		Flush pending output on current output stream. <a name="idx:flushoutput0:1080"></a><a class="pred" href="chario.html#flush_output/0">flush_output/0</a>
265		is automatically generated by <a name="idx:read1:1081"></a><a class="pred" href="termrw.html#read/1">read/1</a>
	303	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="flush_output/0"><strong>flush_output</strong></a></dt>
	304	<dd class="defbody">
	305	Flush pending output on current output stream. <a id="idx:flushoutput0:1080"></a><a class="pred" href="chario.html#flush_output/0">flush_output/0</a>
	306	is automatically generated by <a id="idx:read1:1081"></a><a class="pred" href="termrw.html#read/1">read/1</a>
266	307	and derivatives if the current input stream is <code>user</code> and the
267	308	cursor is not at the left margin.</dd>
268		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="flush_output/1"><strong>flush_output</strong>(<var>+Stream</var>)</a></dt>
	309	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="flush_output/1"><strong>flush_output</strong>(<var>+Stream</var>)</a></dt>
269	310	<dd class="defbody">
270	311	Flush output on the specified stream. The stream must be open for
271	312	writing.</dd>
272		<dt class="pubdef"><a name="ttyflush/0"><strong>ttyflush</strong></a></dt>
273		<dd class="defbody">
274		Flush pending output on stream <code>user</code>. See also <a name="idx:flushoutput01:1082"></a><a class="pred" href="chario.html#flush_output/0">flush_output/[0,1]</a>.
	313	<dt class="pubdef"><a id="ttyflush/0"><strong>ttyflush</strong></a></dt>
	314	<dd class="defbody">
	315	Flush pending output on stream <code>user</code>. See also <a id="idx:flushoutput01:1082"></a><a class="pred" href="chario.html#flush_output/0">flush_output/[0,1]</a>.
275	316	</dd>
276		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="get_byte/1"><strong>get_byte</strong>(<var>-Byte</var>)</a></dt>
	317	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="get_byte/1"><strong>get_byte</strong>(<var>-Byte</var>)</a></dt>
277	318	<dd class="defbody">
278	319	Read the current input stream and unify the next byte with <var>Byte</var>
279	320	(an integer between 0 and 255). <var>Byte</var> is unified with -1 on
280	321	end of file.</dd>
281		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="get_byte/2"><strong>get_byte</strong>(<var>+Stream,
	322	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="get_byte/2"><strong>get_byte</strong>(<var>+Stream,
282	323	-Byte</var>)</a></dt>
283	324	<dd class="defbody">
284	325	Read the next byte from <var>Stream</var> and unify <var>Byte</var> with
285	326	an integer between 0 and 255.</dd>
286		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="get_code/1"><strong>get_code</strong>(<var>-Code</var>)</a></dt>
	327	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="get_code/1"><strong>get_code</strong>(<var>-Code</var>)</a></dt>
287	328	<dd class="defbody">
288	329	Read the current input stream and unify <var>Code</var> with the
289	330	character code of the next character. <var>Code</var> is unified with -1
290		on end of file. See also <a name="idx:getchar1:1083"></a><a class="pred" href="chario.html#get_char/1">get_char/1</a>.</dd>
291		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="get_code/2"><strong>get_code</strong>(<var>+Stream,
	331	on end of file. See also <a id="idx:getchar1:1083"></a><a class="pred" href="chario.html#get_char/1">get_char/1</a>.</dd>
	332	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="get_code/2"><strong>get_code</strong>(<var>+Stream,
292	333	-Code</var>)</a></dt>
293	334	<dd class="defbody">
294	335	Read the next character code from <var>Stream</var>.</dd>
295		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="get_char/1"><strong>get_char</strong>(<var>-Char</var>)</a></dt>
	336	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="get_char/1"><strong>get_char</strong>(<var>-Char</var>)</a></dt>
296	337	<dd class="defbody">
297	338	Read the current input stream and unify <var>Char</var> with the next
298		character as a one-character atom. See also <a name="idx:atomchars2:1084"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>.
	339	character as a one-character atom. See also <a id="idx:atomchars2:1084"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>.
299	340	On end-of-file, <var>Char</var> is unified to the atom <code>end_of_file</code>.</dd>
300		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="get_char/2"><strong>get_char</strong>(<var>+Stream,
	341	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="get_char/2"><strong>get_char</strong>(<var>+Stream,
301	342	-Char</var>)</a></dt>
302	343	<dd class="defbody">
303	344	Unify <var>Char</var> with the next character from <var>Stream</var> as
304		a one-character atom. See also <a name="idx:getchar2:1085"></a><a class="pred" href="chario.html#get_char/2">get_char/2</a>, <a name="idx:getbyte2:1086"></a><a class="pred" href="chario.html#get_byte/2">get_byte/2</a>
305		and <a name="idx:getcode2:1087"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>.</dd>
306		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="get0/1"><strong>get0</strong>(<var>-Char</var>)</a></dt>
307		<dd class="defbody">
308		Edinburgh version of the ISO <a name="idx:getcode1:1088"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>
	345	a one-character atom. See also <a id="idx:getchar2:1085"></a><a class="pred" href="chario.html#get_char/2">get_char/2</a>, <a id="idx:getbyte2:1086"></a><a class="pred" href="chario.html#get_byte/2">get_byte/2</a>
	346	and <a id="idx:getcode2:1087"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>.</dd>
	347	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="get0/1"><strong>get0</strong>(<var>-Char</var>)</a></dt>
	348	<dd class="defbody">
	349	Edinburgh version of the ISO <a id="idx:getcode1:1088"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>
309	350	predicate. Note that Edinburgh Prolog didn't support wide characters and
310	351	therefore technically speaking
311		<a name="idx:get01:1089"></a><a class="pred" href="chario.html#get0/1">get0/1</a>
312		should have been mapped to <a name="idx:getbyte1:1090"></a><a class="pred" href="chario.html#get_byte/1">get_byte/1</a>.
313		The intention of <a name="idx:get01:1091"></a><a class="pred" href="chario.html#get0/1">get0/1</a>,
	352	<a id="idx:get01:1089"></a><a class="pred" href="chario.html#get0/1">get0/1</a>
	353	should have been mapped to <a id="idx:getbyte1:1090"></a><a class="pred" href="chario.html#get_byte/1">get_byte/1</a>.
	354	The intention of <a id="idx:get01:1091"></a><a class="pred" href="chario.html#get0/1">get0/1</a>,
314	355	however, is to read character codes.</dd>
315		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="get0/2"><strong>get0</strong>(<var>+Stream,
	356	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="get0/2"><strong>get0</strong>(<var>+Stream,
316	357	-Char</var>)</a></dt>
317	358	<dd class="defbody">
318		Edinburgh version of the ISO <a name="idx:getcode2:1092"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>
319		predicate. See also <a name="idx:get01:1093"></a><a class="pred" href="chario.html#get0/1">get0/1</a>.</dd>
320		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="get/1"><strong>get</strong>(<var>-Char</var>)</a></dt>
	359	Edinburgh version of the ISO <a id="idx:getcode2:1092"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>
	360	predicate. See also <a id="idx:get01:1093"></a><a class="pred" href="chario.html#get0/1">get0/1</a>.</dd>
	361	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="get/1"><strong>get</strong>(<var>-Char</var>)</a></dt>
321	362	<dd class="defbody">
322	363	Read the current input stream and unify the next non-blank character
323	364	with <var>Char</var>. <var>Char</var> is unified with -1 on end of file.
324		The predicate <a name="idx:get1:1094"></a><a class="pred" href="chario.html#get/1">get/1</a>
325		operates on character <em>codes</em>. See also <a name="idx:get01:1095"></a><a class="pred" href="chario.html#get0/1">get0/1</a>.</dd>
326		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="get/2"><strong>get</strong>(<var>+Stream,
	365	The predicate <a id="idx:get1:1094"></a><a class="pred" href="chario.html#get/1">get/1</a>
	366	operates on character <em>codes</em>. See also <a id="idx:get01:1095"></a><a class="pred" href="chario.html#get0/1">get0/1</a>.</dd>
	367	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="get/2"><strong>get</strong>(<var>+Stream,
327	368	-Char</var>)</a></dt>
328	369	<dd class="defbody">
329	370	Read the next non-blank character from <var>Stream</var>. See also
330		<a name="idx:get1:1096"></a><a class="pred" href="chario.html#get/1">get/1</a>, <a name="idx:get01:1097"></a><a class="pred" href="chario.html#get0/1">get0/1</a>
331		and <a name="idx:get02:1098"></a><a class="pred" href="chario.html#get0/2">get0/2</a>.</dd>
332		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="peek_byte/1"><strong>peek_byte</strong>(<var>-Byte</var>)</a></dt>
333		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="peek_byte/2"><strong>peek_byte</strong>(<var>+Stream,
	371	<a id="idx:get1:1096"></a><a class="pred" href="chario.html#get/1">get/1</a>, <a id="idx:get01:1097"></a><a class="pred" href="chario.html#get0/1">get0/1</a>
	372	and <a id="idx:get02:1098"></a><a class="pred" href="chario.html#get0/2">get0/2</a>.</dd>
	373	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="peek_byte/1"><strong>peek_byte</strong>(<var>-Byte</var>)</a></dt>
	374	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="peek_byte/2"><strong>peek_byte</strong>(<var>+Stream,
334	375	-Byte</var>)</a></dt>
335		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="peek_code/1"><strong>peek_code</strong>(<var>-Code</var>)</a></dt>
336		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="peek_code/2"><strong>peek_code</strong>(<var>+Stream,
	376	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="peek_code/1"><strong>peek_code</strong>(<var>-Code</var>)</a></dt>
	377	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="peek_code/2"><strong>peek_code</strong>(<var>+Stream,
337	378	-Code</var>)</a></dt>
338		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="peek_char/1"><strong>peek_char</strong>(<var>-Char</var>)</a></dt>
339		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="peek_char/2"><strong>peek_char</strong>(<var>+Stream,
	379	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="peek_char/1"><strong>peek_char</strong>(<var>-Char</var>)</a></dt>
	380	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="peek_char/2"><strong>peek_char</strong>(<var>+Stream,
340	381	-Char</var>)</a></dt>
341	382	<dd class="defbody">
342	383	Read the next byte/code/char from the input without removing it. These
343	384	predicates do not modify the stream's position or end-of-file status.
344		These predicates require a buffered stream (see <a name="idx:setstream2:1099"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>)
	385	These predicates require a buffered stream (see <a id="idx:setstream2:1099"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>)
345	386	and raise a permission error if the stream is unbuffered or the buffer
346	387	is too small to hold the longest multi-byte sequence that might need to
347	388	be buffered.</dd>
348		<dt class="pubdef"><a name="peek_string/3"><strong>peek_string</strong>(<var>+Stream,
	389	<dt class="pubdef"><a id="peek_string/3"><strong>peek_string</strong>(<var>+Stream,
349	390	+Len, -String</var>)</a></dt>
350	391	<dd class="defbody">
351	392	Read the next <var>Len</var> characters (if the stream is a text stream)

355	396	shorter than <var>Len</var> if the stream contains less data. This
356	397	predicate is intended to guess the content type of data read from
357	398	non-repositionable streams.</dd>
358		<dt class="pubdef"><a name="skip/1"><strong>skip</strong>(<var>+Code</var>)</a></dt>
	399	<dt class="pubdef"><a id="skip/1"><strong>skip</strong>(<var>+Code</var>)</a></dt>
359	400	<dd class="defbody">
360	401	Read the input until <var>Code</var> or the end of the file is
361		encountered. A subsequent call to <a name="idx:getcode1:1100"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>
	402	encountered. A subsequent call to <a id="idx:getcode1:1100"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>
362	403	will read the first character after
363	404	<var>Code</var>.</dd>
364		<dt class="pubdef"><a name="skip/2"><strong>skip</strong>(<var>+Stream,
	405	<dt class="pubdef"><a id="skip/2"><strong>skip</strong>(<var>+Stream,
365	406	+Code</var>)</a></dt>
366	407	<dd class="defbody">
367		Skip input (as <a name="idx:skip1:1101"></a><a class="pred" href="chario.html#skip/1">skip/1</a>)
	408	Skip input (as <a id="idx:skip1:1101"></a><a class="pred" href="chario.html#skip/1">skip/1</a>)
368	409	on <var>Stream</var>.</dd>
369		<dt class="pubdef"><a name="get_single_char/1"><strong>get_single_char</strong>(<var>-Code</var>)</a></dt>
	410	<dt class="pubdef"><a id="get_single_char/1"><strong>get_single_char</strong>(<var>-Code</var>)</a></dt>
370	411	<dd class="defbody">
371	412	Get a single character from input stream `user' (regardless of the
372		current input stream). Unlike <a name="idx:getcode1:1102"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>,
	413	current input stream). Unlike <a id="idx:getcode1:1102"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>,
373	414	this predicate does not wait for a return. The character is not echoed
374	415	to the user's terminal. This predicate is meant for keyboard menu
375	416	selection, etc. If SWI-Prolog was started with the <strong>-tty</strong>
376	417	option this predicate reads an entire line of input and returns the
377	418	first non-blank character on this line, or the character code of the
378	419	newline (10) if the entire line consisted of blank characters.</dd>
379		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="at_end_of_stream/0"><strong>at_end_of_stream</strong></a></dt>
	420	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="at_end_of_stream/0"><strong>at_end_of_stream</strong></a></dt>
380	421	<dd class="defbody">
381	422	Succeeds after the last character of the current input stream has been
382	423	read. Also succeeds if there is no valid current input stream.</dd>
383		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="at_end_of_stream/1"><strong>at_end_of_stream</strong>(<var>+Stream</var>)</a></dt>
	424	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="at_end_of_stream/1"><strong>at_end_of_stream</strong>(<var>+Stream</var>)</a></dt>
384	425	<dd class="defbody">
385	426	Succeeds after the last character of the named stream is read, or
386	427	<var>Stream</var> is not a valid input stream. The end-of-stream test is
387	428	only available on buffered input streams (unbuffered input streams are
388		rarely used; see <a name="idx:open4:1103"></a><a class="pred" href="IO.html#open/4">open/4</a>).</dd>
389		<dt class="pubdef"><a name="set_end_of_stream/1"><strong>set_end_of_stream</strong>(<var>+Stream</var>)</a></dt>
	429	rarely used; see <a id="idx:open4:1103"></a><a class="pred" href="IO.html#open/4">open/4</a>).</dd>
	430	<dt class="pubdef"><a id="set_end_of_stream/1"><strong>set_end_of_stream</strong>(<var>+Stream</var>)</a></dt>
390	431	<dd class="defbody">
391	432	Set the size of the file opened as <var>Stream</var> to the current file
392	433	position. This is typically used in combination with the open-mode <code>update</code>.</dd>
393		<dt class="pubdef"><a name="copy_stream_data/3"><strong>copy_stream_data</strong>(<var>+StreamIn,
	434	<dt class="pubdef"><a id="copy_stream_data/3"><strong>copy_stream_data</strong>(<var>+StreamIn,
394	435	+StreamOut, +Len</var>)</a></dt>
395	436	<dd class="defbody">
396	437	Copy <var>Len</var> codes from <var>StreamIn</var> to <var>StreamOut</var>.
397		Note that the copy is done using the semantics of <a name="idx:getcode2:1104"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>
	438	Note that the copy is done using the semantics of <a id="idx:getcode2:1104"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>
398	439	and
399		<a name="idx:putcode2:1105"></a><a class="pred" href="chario.html#put_code/2">put_code/2</a>,
	440	<a id="idx:putcode2:1105"></a><a class="pred" href="chario.html#put_code/2">put_code/2</a>,
400	441	taking care of possibly recoding that needs to take place between two
401		text files. See <a class="sec" href="widechars.html">section 2.19.1</a>.</dd>
402		<dt class="pubdef"><a name="copy_stream_data/2"><strong>copy_stream_data</strong>(<var>+StreamIn,
	442	text files. See <a class="sec" href="widechars.html#sec:2.19.1">section
	443	2.19.1</a>.</dd>
	444	<dt class="pubdef"><a id="copy_stream_data/2"><strong>copy_stream_data</strong>(<var>+StreamIn,
403	445	+StreamOut</var>)</a></dt>
404	446	<dd class="defbody">
405	447	Copy all (remaining) data from <var>StreamIn</var> to
406	448	<var>StreamOut</var>.</dd>
407		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="fill_buffer/1"><strong>fill_buffer</strong>(<var>+Stream</var>)</a></dt>
	449	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="fill_buffer/1"><strong>fill_buffer</strong>(<var>+Stream</var>)</a></dt>
408	450	<dd class="defbody">
409	451	Fill the <var>Stream</var>'s input buffer. Subsequent calls try to read
410	452	more input until the buffer is completely filled. This predicate is used
411		together with <a name="idx:readpendingcodes3:1106"></a><a class="pred" href="chario.html#read_pending_codes/3">read_pending_codes/3</a>
	453	together with <a id="idx:readpendingcodes3:1106"></a><a class="pred" href="chario.html#read_pending_codes/3">read_pending_codes/3</a>
412	454	to process input with minimal buffering.</dd>
413		<dt class="pubdef"><a name="read_pending_codes/3"><strong>read_pending_codes</strong>(<var>+StreamIn,
	455	<dt class="pubdef"><a id="read_pending_codes/3"><strong>read_pending_codes</strong>(<var>+StreamIn,
414	456	-Codes, ?Tail</var>)</a></dt>
415	457	<dd class="defbody">
416	458	Read input pending in the input buffer of <var>StreamIn</var> and return

425	467	input from files and streams using a DCG.
426	468
427	469	<p>The following code fragment realises efficient non-blocking copying
428		of data from an input to an output stream. The <a name="idx:atendofstream1:1107"></a><a class="pred" href="chario.html#at_end_of_stream/1">at_end_of_stream/1</a>
	470	of data from an input to an output stream. The <a id="idx:atendofstream1:1107"></a><a class="pred" href="chario.html#at_end_of_stream/1">at_end_of_stream/1</a>
429	471	call checks for end-of-stream and fills the input buffer. Note that the
430		use of a <a name="idx:getcode2:1108"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>
431		and <a name="idx:putcode2:1109"></a><a class="pred" href="chario.html#put_code/2">put_code/2</a>
432		based loop requires a <a name="idx:flushoutput1:1110"></a><a class="pred" href="chario.html#flush_output/1">flush_output/1</a>
433		call after <em>each</em> <a name="idx:putcode2:1111"></a><a class="pred" href="chario.html#put_code/2">put_code/2</a>.
434		The <a name="idx:copystreamdata2:1112"></a><a class="pred" href="chario.html#copy_stream_data/2">copy_stream_data/2</a>
	472	use of a <a id="idx:getcode2:1108"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>
	473	and <a id="idx:putcode2:1109"></a><a class="pred" href="chario.html#put_code/2">put_code/2</a>
	474	based loop requires a <a id="idx:flushoutput1:1110"></a><a class="pred" href="chario.html#flush_output/1">flush_output/1</a>
	475	call after <em>each</em> <a id="idx:putcode2:1111"></a><a class="pred" href="chario.html#put_code/2">put_code/2</a>.
	476	The <a id="idx:copystreamdata2:1112"></a><a class="pred" href="chario.html#copy_stream_data/2">copy_stream_data/2</a>
435	477	does not allow for inspection of the copied data and suffers from the
436	478	same buffering issues.
437	479

451	493	</pre>
452	494
453	495	</dd>
454		<dt class="pubdef"><a name="read_pending_chars/3"><strong>read_pending_chars</strong>(<var>+StreamIn,
	496	<dt class="pubdef"><a id="read_pending_chars/3"><strong>read_pending_chars</strong>(<var>+StreamIn,
455	497	-Chars, ?Tail</var>)</a></dt>
456	498	<dd class="defbody">
457		As <a name="idx:readpendingcodes3:1113"></a><a class="pred" href="chario.html#read_pending_codes/3">read_pending_codes/3</a>,
	499	As <a id="idx:readpendingcodes3:1113"></a><a class="pred" href="chario.html#read_pending_codes/3">read_pending_codes/3</a>,
458	500	but returns a difference list of one-character atoms.
459	501	</dd>
460	502	</dl>

+76

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 4.2</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.2</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

17	17	{ margin-bottom: 1em;
18	18	}
19	19
20		dt.pubdef
21		{ background-color: #c5e1ff;
22		}
23
24		dt.multidef
25		{ background-color: #c8ffc7;
26		}
	20	dt.pubdef, dt.multidef
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	26	overflow: hidden;
	27	}
	28
	29	dt.pubdef { background-color: #0c3d6e; }
	30	dt.multidef { background-color: #ef9439; }
27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
	124	color: #fff;
121	125	}
122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
135		{ display: block !important;
136		position: absolute; top: auto; left: auto; width: 80%;
137		color: #000; background: white;
138		border: 2px solid;
139		padding: 5px; margin: 10px; z-index: 100;
140		font-size: smaller;
	134	.fn {
	135	color: red;
	136	font-size: 70%;
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	138
	139	.fn-text, .fnp {
	140	position: absolute;
	141	top: auto;
	142	left: 10%;
	143	border: 1px solid #000;
	144	box-shadow: 5px 5px 5px #888;
	145	display: none;
	146	background: #fff;
	147	color: #000;
	148	margin-top: 25px;
	149	padding: 8px 12px;
	150	font-size: larger;
	151	}
	152
	153	sup:hover span.fn-text
	154	{ display: block;
141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
	200
	201	table.center
	202	{ margin: auto;
	203	}
	204
	205	table.latex
	206	{ border-collapse:collapse;
	207	}
	208
	209	table.latex tr
	210	{ vertical-align: text-top;
	211	}
	212
	213	table.latex td,th
	214	{ padding: 2px 1em;
	215	}
	216
	217	table.latex tr.hline td,th
	218	{ border-top: 1px solid black;
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	220
	221	table.frame-box
	222	{ border: 2px solid black;
	223	}
	224
184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="preddesc.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="consulting.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:chars"><a name="sec:4.2"><span class="sec-nr">4.2</span> <span class="sec-title">Character
	235	<h2 id="sec:chars"><a id="sec:4.2"><span class="sec-nr">4.2</span> <span class="sec-title">Character
195	236	representation</span></a></h2>
196	237
197		<a name="sec:chars"></a>
	238	<a id="sec:chars"></a>
198	239
199	240	<p>In traditional (Edinburgh) Prolog, characters are represented using
200	241	<em>character codes</em>. Character codes are integer indices into a

204	245	8859-1) is applicable to many Western languages.
205	246
206	247	<p>ISO Prolog introduces three types, two of which are used for
207		characters and one for accessing binary streams (see <a name="idx:open4:340"></a><a class="pred" href="IO.html#open/4">open/4</a>).
	248	characters and one for accessing binary streams (see <a id="idx:open4:340"></a><a class="pred" href="IO.html#open/4">open/4</a>).
208	249	These types are:
209	250
210	251	<p>

212	253	<li><i>code</i><br>
213	254	A <em>character code</em> is an integer representing a single character.
214	255	As files may use multi-byte encoding for supporting different character
215		sets (<a name="idx:utf8:341">utf-8</a> encoding for example), reading a
	256	sets (<a id="idx:utf8:341">utf-8</a> encoding for example), reading a
216	257	code from a text file is in general not the same as reading a byte.
217	258	<li><i>char</i><br>
218	259	Alternatively, characters may be represented as

224	265	</ul>
225	266
226	267	<p>In SWI-Prolog, character codes are <em>always</em> the Unicode
227		equivalent of the encoding. That is, if <a name="idx:getcode1:342"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>
	268	equivalent of the encoding. That is, if <a id="idx:getcode1:342"></a><a class="pred" href="chario.html#get_code/1">get_code/1</a>
228	269	reads from a stream encoded as
229	270	<code>KOI8-R</code> (used for the Cyrillic alphabet), it returns the
230	271	corresponding Unicode code points. Similarly, assembling or
231		disassembling atoms using <a name="idx:atomcodes2:343"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
	272	disassembling atoms using <a id="idx:atomcodes2:343"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
232	273	interprets the codes as Unicode points. See
233		<a class="sec" href="widechars.html">section 2.19.1</a> for details.
	274	<a class="sec" href="widechars.html#sec:2.19.1">section 2.19.1</a> for
	275	details.
234	276
235	277	<p>To ease the pain of the two character representations (code and
236	278	char), SWI-Prolog's built-in predicates dealing with character data work

247	289
248	290	<p>The two character representations are handled by a large number of
249	291	built-in predicates, all of which are ISO-compatible. For converting
250		between code and character there is <a name="idx:charcode2:344"></a><a class="pred" href="manipatom.html#char_code/2">char_code/2</a>.
251		For breaking atoms and numbers into characters there are <a name="idx:atomchars2:345"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>, <a name="idx:atomcodes2:346"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>,
252		<a name="idx:numberchars2:347"></a><a class="pred" href="manipatom.html#number_chars/2">number_chars/2</a>
253		and <a name="idx:numbercodes2:348"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>.
	292	between code and character there is <a id="idx:charcode2:344"></a><a class="pred" href="manipatom.html#char_code/2">char_code/2</a>.
	293	For breaking atoms and numbers into characters there are <a id="idx:atomchars2:345"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>, <a id="idx:atomcodes2:346"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>,
	294	<a id="idx:numberchars2:347"></a><a class="pred" href="manipatom.html#number_chars/2">number_chars/2</a>
	295	and <a id="idx:numbercodes2:348"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>.
254	296	For character I/O on streams there are
255		<a name="idx:getchar12:349"></a><a class="pred" href="chario.html#get_char/1">get_char/[1,2]</a>, <a name="idx:getcode12:350"></a><a class="pred" href="chario.html#get_code/1">get_code/[1,2]</a>, <a name="idx:getbyte12:351"></a><a class="pred" href="chario.html#get_byte/1">get_byte/[1,2]</a>, <a name="idx:peekchar12:352"></a><a class="pred" href="chario.html#peek_char/1">peek_char/[1,2]</a>,
256		<a name="idx:peekcode12:353"></a><a class="pred" href="chario.html#peek_code/1">peek_code/[1,2]</a>, <a name="idx:peekbyte12:354"></a><a class="pred" href="chario.html#peek_byte/1">peek_byte/[1,2]</a>, <a name="idx:putcode12:355"></a><a class="pred" href="chario.html#put_code/1">put_code/[1,2]</a>, <a name="idx:putchar12:356"></a><a class="pred" href="chario.html#put_char/1">put_char/[1,2]</a>
	297	<a id="idx:getchar12:349"></a><a class="pred" href="chario.html#get_char/1">get_char/[1,2]</a>, <a id="idx:getcode12:350"></a><a class="pred" href="chario.html#get_code/1">get_code/[1,2]</a>, <a id="idx:getbyte12:351"></a><a class="pred" href="chario.html#get_byte/1">get_byte/[1,2]</a>, <a id="idx:peekchar12:352"></a><a class="pred" href="chario.html#peek_char/1">peek_char/[1,2]</a>,
	298	<a id="idx:peekcode12:353"></a><a class="pred" href="chario.html#peek_code/1">peek_code/[1,2]</a>, <a id="idx:peekbyte12:354"></a><a class="pred" href="chario.html#peek_byte/1">peek_byte/[1,2]</a>, <a id="idx:putcode12:355"></a><a class="pred" href="chario.html#put_code/1">put_code/[1,2]</a>, <a id="idx:putchar12:356"></a><a class="pred" href="chario.html#put_char/1">put_char/[1,2]</a>
257	299	and
258		<a name="idx:putbyte12:357"></a><a class="pred" href="chario.html#put_byte/1">put_byte/[1,2]</a>.
	300	<a id="idx:putbyte12:357"></a><a class="pred" href="chario.html#put_byte/1">put_byte/[1,2]</a>.
259	301	The Prolog flag <a class="flag" href="flags.html#flag:double_quotes">double_quotes</a>
260	302	controls how text between double quotes is interpreted.
261	303

+77

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man/Manual/charsio.html less more

1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.5</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.5</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

17	17	{ margin-bottom: 1em;
18	18	}
19	19
20		dt.pubdef
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23
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	28
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27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
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121	125	}
122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
135		{ display: block !important;
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137		color: #000; background: white;
138		border: 2px solid;
139		padding: 5px; margin: 10px; z-index: 100;
140		font-size: smaller;
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	147	color: #000;
	148	margin-top: 25px;
	149	padding: 8px 12px;
	150	font-size: larger;
	151	}
	152
	153	sup:hover span.fn-text
	154	{ display: block;
141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
	200
	201	table.center
	202	{ margin: auto;
	203	}
	204
	205	table.latex
	206	{ border-collapse:collapse;
	207	}
	208
	209	table.latex tr
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	212
	213	table.latex td,th
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	224
184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="broadcast.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="check.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:charsio"><a name="sec:A.5"><span class="sec-nr">A.5</span> <span class="sec-title">library(charsio):
	235	<h2 id="sec:charsio"><a id="sec:A.5"><span class="sec-nr">A.5</span> <span class="sec-title">library(charsio):
195	236	I/O on Lists of Character Codes</span></a></h2>
196	237
197		<p><a name="sec:charsio"></a>
	238	<p><a id="sec:charsio"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">Compatibility</dt>

211	252	can even be replaced by ISO standard predicates.
212	253
213	254	<dl class="latex">
214		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="format_to_chars/3"><strong>format_to_chars</strong>(<var>+Format,
	255	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="format_to_chars/3"><strong>format_to_chars</strong>(<var>+Format,
215	256	+Args, -Codes</var>)</a></dt>
216	257	<dd class="defbody">
217	258	Use <a class="pred" href="format.html#format/2">format/2</a> to write to
218	259	a list of character codes.</dd>
219		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="format_to_chars/4"><strong>format_to_chars</strong>(<var>+Format,
	260	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="format_to_chars/4"><strong>format_to_chars</strong>(<var>+Format,
220	261	+Args, -Codes, ?Tail</var>)</a></dt>
221	262	<dd class="defbody">
222	263	Use <a class="pred" href="format.html#format/2">format/2</a> to write to
223	264	a difference list of character codes.</dd>
224		<dt class="pubdef"><a name="write_to_chars/2"><strong>write_to_chars</strong>(<var>+Term,
	265	<dt class="pubdef"><a id="write_to_chars/2"><strong>write_to_chars</strong>(<var>+Term,
225	266	-Codes</var>)</a></dt>
226	267	<dd class="defbody">
227	268	Write a term to a code list. True when <var>Codes</var> is a list of
228	269	character codes written by <a class="pred" href="termrw.html#write/1">write/1</a>
229	270	on <var>Term</var>.</dd>
230		<dt class="pubdef"><a name="write_to_chars/3"><strong>write_to_chars</strong>(<var>+Term,
	271	<dt class="pubdef"><a id="write_to_chars/3"><strong>write_to_chars</strong>(<var>+Term,
231	272	-Codes, ?Tail</var>)</a></dt>
232	273	<dd class="defbody">
233	274	Write a term to a code list. <var>Codes</var><code>\</code><var>Tail</var>
234	275	is a difference list of character codes produced by <a class="pred" href="termrw.html#write/1">write/1</a>
235	276	on <var>Term</var>.</dd>
236		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="atom_to_chars/2"><strong>atom_to_chars</strong>(<var>+Atom,
	277	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="atom_to_chars/2"><strong>atom_to_chars</strong>(<var>+Atom,
237	278	-Codes</var>)</a></dt>
238	279	<dd class="defbody">
239	280	Convert <var>Atom</var> into a list of character codes.

246	287	</dl>
247	288
248	289	</dd>
249		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="atom_to_chars/3"><strong>atom_to_chars</strong>(<var>+Atom,
	290	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="atom_to_chars/3"><strong>atom_to_chars</strong>(<var>+Atom,
250	291	-Codes, ?Tail</var>)</a></dt>
251	292	<dd class="defbody">
252	293	Convert <var>Atom</var> into a difference list of character codes.</dd>
253		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="number_to_chars/2"><strong>number_to_chars</strong>(<var>+Number,
	294	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="number_to_chars/2"><strong>number_to_chars</strong>(<var>+Number,
254	295	-Codes</var>)</a></dt>
255	296	<dd class="defbody">
256	297	Convert Atom into a list of character codes.

263	304	</dl>
264	305
265	306	</dd>
266		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="number_to_chars/3"><strong>number_to_chars</strong>(<var>+Number,
	307	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="number_to_chars/3"><strong>number_to_chars</strong>(<var>+Number,
267	308	-Codes, ?Tail</var>)</a></dt>
268	309	<dd class="defbody">
269	310	Convert <var>Number</var> into a difference list of character codes.</dd>
270		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="read_from_chars/2"><strong>read_from_chars</strong>(<var>+Codes,
	311	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="read_from_chars/2"><strong>read_from_chars</strong>(<var>+Codes,
271	312	-Term</var>)</a></dt>
272	313	<dd class="defbody">
273	314	Read <var>Codes</var> into <var>Term</var>.

281	322	</dl>
282	323
283	324	</dd>
284		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="read_term_from_chars/3"><strong>read_term_from_chars</strong>(<var>+Codes,
	325	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="read_term_from_chars/3"><strong>read_term_from_chars</strong>(<var>+Codes,
285	326	-Term, +Options</var>)</a></dt>
286	327	<dd class="defbody">
287	328	Read <var>Codes</var> into <var>Term</var>. <var>Options</var> are

295	336	</dl>
296	337
297	338	</dd>
298		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="open_chars_stream/2"><strong>open_chars_stream</strong>(<var>+Codes,
	339	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="open_chars_stream/2"><strong>open_chars_stream</strong>(<var>+Codes,
299	340	-Stream</var>)</a></dt>
300	341	<dd class="defbody">
301	342	Open <var>Codes</var> as an input stream.

308	349	</dl>
309	350
310	351	</dd>
311		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="with_output_to_chars/2"><strong>with_output_to_chars</strong>(<var>:Goal,
	352	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="with_output_to_chars/2"><strong>with_output_to_chars</strong>(<var>:Goal,
312	353	-Codes</var>)</a></dt>
313	354	<dd class="defbody">
314	355	Run <var>Goal</var> as with <a class="pred" href="metacall.html#once/1">once/1</a>.
315	356	Output written to <code>current_output</code> is collected in <var>Codes</var>.</dd>
316		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="with_output_to_chars/3"><strong>with_output_to_chars</strong>(<var>:Goal,
	357	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="with_output_to_chars/3"><strong>with_output_to_chars</strong>(<var>:Goal,
317	358	-Codes, ?Tail</var>)</a></dt>
318	359	<dd class="defbody">
319	360	Run <var>Goal</var> as with <a class="pred" href="metacall.html#once/1">once/1</a>.
320	361	Output written to <code>current_output</code> is collected in <var>Codes</var><code>\</code><var>Tail</var>.</dd>
321		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="with_output_to_chars/4"><strong>with_output_to_chars</strong>(<var>:Goal,
	362	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="with_output_to_chars/4"><strong>with_output_to_chars</strong>(<var>:Goal,
322	363	-Stream, -Codes, ?Tail</var>)</a></dt>
323	364	<dd class="defbody">
324	365	Same as <a class="pred" href="charsio.html#with_output_to_chars/3">with_output_to_chars/3</a>

+98

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man/Manual/chartype.html less more

1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 4.24</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.24</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

17	17	{ margin-bottom: 1em;
18	18	}
19	19
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	28
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27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

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118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
	124	color: #fff;
121	125	}
122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
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140		font-size: smaller;
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	138
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	152
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141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
	200
	201	table.center
	202	{ margin: auto;
	203	}
	204
	205	table.latex
	206	{ border-collapse:collapse;
	207	}
	208
	209	table.latex tr
	210	{ vertical-align: text-top;
	211	}
	212
	213	table.latex td,th
	214	{ padding: 2px 1em;
	215	}
	216
	217	table.latex tr.hline td,th
	218	{ border-top: 1px solid black;
	219	}
	220
	221	table.frame-box
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	224
184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="locale.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="operators.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:chartype"><a name="sec:4.24"><span class="sec-nr">4.24</span> <span class="sec-title">Character
	235	<h2 id="sec:chartype"><a id="sec:4.24"><span class="sec-nr">4.24</span> <span class="sec-title">Character
195	236	properties</span></a></h2>
196	237
197		<a name="sec:chartype"></a>
	238	<a id="sec:chartype"></a>
198	239
199	240	<p>SWI-Prolog offers two comprehensive predicates for classifying
200	241	characters and character codes. These predicates are defined as built-in

204	245
205	246	<p>In addition, there is the library <code>library(ctypes)</code>
206	247	providing compatibility with some other Prolog systems. The predicates
207		of this library are defined in terms of <a name="idx:codetype2:1292"></a><a class="pred" href="chartype.html#code_type/2">code_type/2</a>.
	248	of this library are defined in terms of <a id="idx:codetype2:1292"></a><a class="pred" href="chartype.html#code_type/2">code_type/2</a>.
208	249
209	250	<dl class="latex">
210		<dt class="pubdef"><a name="char_type/2"><strong>char_type</strong>(<var>?Char,
	251	<dt class="pubdef"><a id="char_type/2"><strong>char_type</strong>(<var>?Char,
211	252	?Type</var>)</a></dt>
212	253	<dd class="defbody">
213	254	Tests or generates alternative <var>Type</var>s or <var>Char</var>s. The

285	326	<dd class="defbody">
286	327	<var>Char</var> is a lowercase version of <var>Upper</var>. For
287	328	non-letters, or letter without case, <var>Char</var> and <var>Lower</var>
288		are the same. See also <a name="idx:upcaseatom2:1293"></a><a class="pred" href="chartype.html#upcase_atom/2">upcase_atom/2</a>
289		and <a name="idx:downcaseatom2:1294"></a><a class="pred" href="chartype.html#downcase_atom/2">downcase_atom/2</a>.
	329	are the same. See also <a id="idx:upcaseatom2:1293"></a><a class="pred" href="chartype.html#upcase_atom/2">upcase_atom/2</a>
	330	and <a id="idx:downcaseatom2:1294"></a><a class="pred" href="chartype.html#downcase_atom/2">downcase_atom/2</a>.
290	331	</dd>
291	332	<dt><strong>upper</strong></dt>
292	333	<dd class="defbody">

302	343	<dd class="defbody">
303	344	<var>Char</var> is an uppercase version of <var>Lower</var>. For
304	345	non-letters, or letter without case, <var>Char</var> and <var>Lower</var>
305		are the same. See also <a name="idx:upcaseatom2:1295"></a><a class="pred" href="chartype.html#upcase_atom/2">upcase_atom/2</a>
306		and <a name="idx:downcaseatom2:1296"></a><a class="pred" href="chartype.html#downcase_atom/2">downcase_atom/2</a>.
	346	are the same. See also <a id="idx:upcaseatom2:1295"></a><a class="pred" href="chartype.html#upcase_atom/2">upcase_atom/2</a>
	347	and <a id="idx:downcaseatom2:1296"></a><a class="pred" href="chartype.html#downcase_atom/2">downcase_atom/2</a>.
307	348	</dd>
308	349	<dt><strong>punct</strong></dt>
309	350	<dd class="defbody">

361	402	</dl>
362	403
363	404	</dd>
364		<dt class="pubdef"><a name="code_type/2"><strong>code_type</strong>(<var>?Code,
	405	<dt class="pubdef"><a id="code_type/2"><strong>code_type</strong>(<var>?Code,
365	406	?Type</var>)</a></dt>
366	407	<dd class="defbody">
367		As <a name="idx:chartype2:1297"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>,
	408	As <a id="idx:chartype2:1297"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>,
368	409	but uses character codes rather than one-character atoms. Please note
369	410	that both predicates are as flexible as possible. They handle either
370	411	representation if the argument is instantiated and will instantiate only
371	412	with an integer code or a one-character atom, depending of the version
372	413	used. See also the Prolog flag
373		<a class="flag" href="flags.html#flag:double_quotes">double_quotes</a>, <a name="idx:atomchars2:1298"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
374		and <a name="idx:atomcodes2:1299"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>.
	414	<a class="flag" href="flags.html#flag:double_quotes">double_quotes</a>, <a id="idx:atomchars2:1298"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
	415	and <a id="idx:atomcodes2:1299"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>.
375	416	</dd>
376	417	</dl>
377	418
378		<p><h3 id="sec:case"><a name="sec:4.24.1"><span class="sec-nr">4.24.1</span> <span class="sec-title">Case
	419	<p><h3 id="sec:case"><a id="sec:4.24.1"><span class="sec-nr">4.24.1</span> <span class="sec-title">Case
379	420	conversion</span></a></h3>
380	421
381		<a name="sec:case"></a>
	422	<a id="sec:case"></a>
382	423
383	424	<p>There is nothing in the Prolog standard for converting case in
384		textual data. The SWI-Prolog predicates <a name="idx:codetype2:1300"></a><a class="pred" href="chartype.html#code_type/2">code_type/2</a>
385		and <a name="idx:chartype2:1301"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>
	425	textual data. The SWI-Prolog predicates <a id="idx:codetype2:1300"></a><a class="pred" href="chartype.html#code_type/2">code_type/2</a>
	426	and <a id="idx:chartype2:1301"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>
386	427	can be used to test and convert individual characters. We have started
387	428	some additional support:
388	429
389	430	<dl class="latex">
390		<dt class="pubdef"><a name="downcase_atom/2"><strong>downcase_atom</strong>(<var>+AnyCase,
	431	<dt class="pubdef"><a id="downcase_atom/2"><strong>downcase_atom</strong>(<var>+AnyCase,
391	432	-LowerCase</var>)</a></dt>
392	433	<dd class="defbody">
393		Converts the characters of <var>AnyCase</var> into lowercase as <a name="idx:chartype2:1302"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>
	434	Converts the characters of <var>AnyCase</var> into lowercase as <a id="idx:chartype2:1302"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>
394	435	does (i.e. based on the defined <em>locale</em> if Prolog provides
395	436	locale support on the hosting platform) and unifies the lowercase atom
396	437	with <var>LowerCase</var>.</dd>
397		<dt class="pubdef"><a name="upcase_atom/2"><strong>upcase_atom</strong>(<var>+AnyCase,
	438	<dt class="pubdef"><a id="upcase_atom/2"><strong>upcase_atom</strong>(<var>+AnyCase,
398	439	-UpperCase</var>)</a></dt>
399	440	<dd class="defbody">
400		Converts, similar to <a name="idx:downcaseatom2:1303"></a><a class="pred" href="chartype.html#downcase_atom/2">downcase_atom/2</a>,
	441	Converts, similar to <a id="idx:downcaseatom2:1303"></a><a class="pred" href="chartype.html#downcase_atom/2">downcase_atom/2</a>,
401	442	an atom to uppercase.
402	443	</dd>
403	444	</dl>
404	445
405		<p><h3 id="sec:whitespace"><a name="sec:4.24.2"><span class="sec-nr">4.24.2</span> <span class="sec-title">White
	446	<p><h3 id="sec:whitespace"><a id="sec:4.24.2"><span class="sec-nr">4.24.2</span> <span class="sec-title">White
406	447	space normalization</span></a></h3>
407	448
408		<a name="sec:whitespace"></a>
	449	<a id="sec:whitespace"></a>
409	450
410	451	<dl class="latex">
411		<dt class="pubdef"><a name="normalize_space/2"><strong>normalize_space</strong>(<var>-Out,
	452	<dt class="pubdef"><a id="normalize_space/2"><strong>normalize_space</strong>(<var>-Out,
412	453	+In</var>)</a></dt>
413	454	<dd class="defbody">
414	455	Normalize white space in <var>In</var>. All leading and trailing white
415	456	space is removed. All non-empty sequences for Unicode white space
416	457	characters are replaced by a single space (<code>\u0020</code>)
417		character. <var>Out</var> uses the same conventions as <a name="idx:withoutputto2:1304"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
418		and <a name="idx:format3:1305"></a><a class="pred" href="format.html#format/3">format/3</a>.
	458	character. <var>Out</var> uses the same conventions as <a id="idx:withoutputto2:1304"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
	459	and <a id="idx:format3:1305"></a><a class="pred" href="format.html#format/3">format/3</a>.
419	460	</dd>
420	461	</dl>
421	462
422		<p><h3 id="sec:collate"><a name="sec:4.24.3"><span class="sec-nr">4.24.3</span> <span class="sec-title">Language-specific
	463	<p><h3 id="sec:collate"><a id="sec:4.24.3"><span class="sec-nr">4.24.3</span> <span class="sec-title">Language-specific
423	464	comparison</span></a></h3>
424	465
425		<a name="sec:collate"></a>
426
427		<p><a name="idx:locale:1306"></a><a name="idx:collate:1307"></a><a name="idx:comparelanguagespecific:1308"></a>This
	466	<a id="sec:collate"></a>
	467
	468	<p><a id="idx:locale:1306"></a><a id="idx:collate:1307"></a><a id="idx:comparelanguagespecific:1308"></a>This
428	469	section deals with predicates for language-specific string comparison
429	470	operations.
430	471
431	472	<dl class="latex">
432		<dt class="pubdef"><a name="collation_key/2"><strong>collation_key</strong>(<var>+Atom,
	473	<dt class="pubdef"><a id="collation_key/2"><strong>collation_key</strong>(<var>+Atom,
433	474	-Key</var>)</a></dt>
434	475	<dd class="defbody">
435	476	Create a <var>Key</var> from <var>Atom</var> for locale-specific

438	479	is alphabetically smaller than <var>B</var> using the sort order of the
439	480	current locale.
440	481
441		<p>The predicate <a name="idx:collationkey2:1309"></a><a class="pred" href="chartype.html#collation_key/2">collation_key/2</a>
442		is used by <a name="idx:localesort2:1310"></a><a class="pred" href="chartype.html#locale_sort/2">locale_sort/2</a>
443		from library(sort). Please examine the implementation of <a name="idx:localesort2:1311"></a><a class="pred" href="chartype.html#locale_sort/2">locale_sort/2</a>
	482	<p>The predicate <a id="idx:collationkey2:1309"></a><a class="pred" href="chartype.html#collation_key/2">collation_key/2</a>
	483	is used by <a id="idx:localesort2:1310"></a><a class="pred" href="chartype.html#locale_sort/2">locale_sort/2</a>
	484	from library(sort). Please examine the implementation of <a id="idx:localesort2:1311"></a><a class="pred" href="chartype.html#locale_sort/2">locale_sort/2</a>
444	485	as an example of using this call.
445	486
446	487	<p>The <var>Key</var> is an implementation-defined and generally
447	488	unreadable string. On systems that do not support locale handling, <var>Key</var>
448	489	is simply unified with <var>Atom</var>.</dd>
449		<dt class="pubdef"><a name="locale_sort/2"><strong>locale_sort</strong>(<var>+List,
	490	<dt class="pubdef"><a id="locale_sort/2"><strong>locale_sort</strong>(<var>+List,
450	491	-Sorted</var>)</a></dt>
451	492	<dd class="defbody">
452	493	Sort a list of atoms using the current locale. <var>List</var> is a list
453		of atoms or string objects (see <a class="sec" href="strings.html">section
	494	of atoms or string objects (see <a class="sec" href="strings.html#sec:5.2">section
454	495	5.2</a>). <var>Sorted</var> is unified with a list containing all atoms
455		of <var>List</var>, sorted to the rules of the current locale. See also <a name="idx:collationkey2:1312"></a><a class="pred" href="chartype.html#collation_key/2">collation_key/2</a>
	496	of <var>List</var>, sorted to the rules of the current locale. See also <a id="idx:collationkey2:1312"></a><a class="pred" href="chartype.html#collation_key/2">collation_key/2</a>
456	497	and
457		<a name="idx:setlocale3:1313"></a><a class="pred" href="system.html#setlocale/3">setlocale/3</a>.
	498	<a id="idx:setlocale3:1313"></a><a class="pred" href="system.html#setlocale/3">setlocale/3</a>.
458	499	</dd>
459	500	</dl>
460	501

+77

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.6</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.6</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
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130
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191	232	<a class="nav" href="charsio.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:check"><a name="sec:A.6"><span class="sec-nr">A.6</span> <span class="sec-title">library(check):
	235	<h2 id="sec:check"><a id="sec:A.6"><span class="sec-nr">A.6</span> <span class="sec-title">library(check):
195	236	Consistency checking</span></a></h2>
196	237
197		<p><a name="sec:check"></a>
	238	<p><a id="sec:check"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="mtag">See also</dt>

214	255	to find undefined predicates in `user' modules.
215	256
216	257	<dl class="latex">
217		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="check/0"><strong>check</strong></a></dt>
	258	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="check/0"><strong>check</strong></a></dt>
218	259	<dd class="defbody">
219	260	Run all consistency checks defined by <a class="pred" href="check.html#checker/2">checker/2</a>.
220	261	Checks enabled by default are:

233	274	lists predicates that will be defined at runtime using the autoloader.
234	275	</ul>
235	276	</dd>
236		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_undefined/0"><strong>list_undefined</strong></a></dt>
237		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_undefined/1"><strong>list_undefined</strong>(<var>+Options</var>)</a></dt>
	277	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_undefined/0"><strong>list_undefined</strong></a></dt>
	278	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_undefined/1"><strong>list_undefined</strong>(<var>+Options</var>)</a></dt>
238	279	<dd class="defbody">
239	280	Report undefined predicates. This predicate finds undefined predciates
240	281	by decompiling and analyzing the body of all clauses.

259	300	</dl>
260	301
261	302	</dd>
262		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_autoload/0"><strong>list_autoload</strong></a></dt>
	303	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_autoload/0"><strong>list_autoload</strong></a></dt>
263	304	<dd class="defbody">
264	305	Report predicates that may be auto-loaded. These are predicates that are
265	306	not defined, but will be loaded on demand if referenced.

277	318	</dl>
278	319
279	320	</dd>
280		<dt class="pubdef"><a name="list_redefined/0"><strong>list_redefined</strong></a></dt>
	321	<dt class="pubdef"><a id="list_redefined/0"><strong>list_redefined</strong></a></dt>
281	322	<dd class="defbody">
282	323	Lists predicates that are defined in the global module <code>user</code>
283	324	as well as in a normal module; that is, predicates for which the local
284	325	definition overrules the global default definition.</dd>
285		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_void_declarations/0"><strong>list_void_declarations</strong></a></dt>
	326	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_void_declarations/0"><strong>list_void_declarations</strong></a></dt>
286	327	<dd class="defbody">
287	328	List predicates that have declared attributes, but no clauses.</dd>
288		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_trivial_fails/0"><strong>list_trivial_fails</strong></a></dt>
289		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_trivial_fails/1"><strong>list_trivial_fails</strong>(<var>+Options</var>)</a></dt>
	329	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_trivial_fails/0"><strong>list_trivial_fails</strong></a></dt>
	330	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_trivial_fails/1"><strong>list_trivial_fails</strong>(<var>+Options</var>)</a></dt>
290	331	<dd class="defbody">
291	332	List goals that trivially fail because there is no matching clause. <var>Options</var>:
292	333

300	341	</dl>
301	342
302	343	</dd>
303		<dt class="multidef"><span class="pred-tag">[multifile]</span><a name="trivial_fail_goal/1"><strong>trivial_fail_goal</strong>(<var>:Goal</var>)</a></dt>
	344	<dt class="multidef"><span class="pred-tag">[multifile]</span><a id="trivial_fail_goal/1"><strong>trivial_fail_goal</strong>(<var>:Goal</var>)</a></dt>
304	345	<dd class="defbody">
305	346	Multifile hook that tells <a class="pred" href="check.html#list_trivial_fails/0">list_trivial_fails/0</a>
306	347	to accept <var>Goal</var> as valid.</dd>
307		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_strings/0"><strong>list_strings</strong></a></dt>
308		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_strings/1"><strong>list_strings</strong>(<var>+Options</var>)</a></dt>
	348	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_strings/0"><strong>list_strings</strong></a></dt>
	349	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_strings/1"><strong>list_strings</strong>(<var>+Options</var>)</a></dt>
309	350	<dd class="defbody">
310	351	List strings that appear in clauses. This predicate is used to find
311	352	portability issues for changing the Prolog flag

329	370	</dl>
330	371
331	372	</dd>
332		<dt class="multidef"><span class="pred-tag">[multifile]</span><a name="string_predicate/1"><strong>string_predicate</strong>(<var>:PredicateIndicator</var>)</a></dt>
	373	<dt class="multidef"><span class="pred-tag">[multifile]</span><a id="string_predicate/1"><strong>string_predicate</strong>(<var>:PredicateIndicator</var>)</a></dt>
333	374	<dd class="defbody">
334	375	Multifile hook to disable <a class="pred" href="strings.html#list_strings/0">list_strings/0</a>
335	376	on the given predicate. This is typically used for facts that store
336	377	strings.</dd>
337		<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a name="valid_string_goal/1"><strong>valid_string_goal</strong>(<var>+Goal</var>)</a></dt>
	378	<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="valid_string_goal/1"><strong>valid_string_goal</strong>(<var>+Goal</var>)</a></dt>
338	379	<dd class="defbody">
339	380	Multifile hook that qualifies <var>Goal</var> as valid for <a class="pred" href="strings.html#list_strings/0">list_strings/0</a>.
340	381	For example, <code>format("Hello world~n")</code> is considered proper
341	382	use of string constants.</dd>
342		<dt class="multidef"><span class="pred-tag">[multifile]</span><a name="checker/2"><strong>checker</strong>(<var>:Goal,
	383	<dt class="multidef"><span class="pred-tag">[multifile]</span><a id="checker/2"><strong>checker</strong>(<var>:Goal,
343	384	+Message:text</var>)</a></dt>
344	385	<dd class="defbody">
345	386	Register code validation routines. Each clause defines a <var>Goal</var>

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191	232	<a class="nav" href="coroutining.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h1 id="sec:chr"><a name="sec:8"><span class="sec-nr">8</span> <span class="sec-title">CHR:
	235	<h1 id="sec:chr"><a id="sec:8"><span class="sec-nr">8</span> <span class="sec-title">CHR:
195	236	Constraint Handling Rules</span></a></h1>
196	237
197		<a name="sec:chr"></a>
	238	<a id="sec:chr"></a>
198	239
199	240	<p>This chapter is written by Tom Schrijvers, K.U. Leuven, and
200	241	adjustments by Jan Wielemaker.

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 8.1</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="chr.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:chrintro"><a name="sec:8.1"><span class="sec-nr">8.1</span> <span class="sec-title">Introduction</span></a></h2>
195
196		<a name="sec:chrintro"></a> Constraint Handling Rules (CHR) is a
	235	<h2 id="sec:chrintro"><a id="sec:8.1"><span class="sec-nr">8.1</span> <span class="sec-title">Introduction</span></a></h2>
	236
	237	<a id="sec:chrintro"></a> Constraint Handling Rules (CHR) is a
197	238	committed-choice rule-based language embedded in Prolog. It is designed
198	239	for writing constraint solvers and is particularly useful for providing
199	240	application-specific constraints. It has been used in many kinds of

211	252	2009</a></cite>. More background on CHR can be found at
212	253	<cite><a class="cite" href="Bibliography.html#chrSite">Frühwirth,</a></cite>.
213	254
214		<p>In <a class="sec" href="SyntaxAndSemantics.html">section 8.2</a> we
215		present the syntax of CHR in Prolog and explain informally its
216		operational semantics. Next, <a class="sec" href="practical.html">section
	255	<p>In <a class="sec" href="SyntaxAndSemantics.html#sec:8.2">section 8.2</a>
	256	we present the syntax of CHR in Prolog and explain informally its
	257	operational semantics. Next, <a class="sec" href="practical.html#sec:8.3">section
217	258	8.3</a> deals with practical issues of writing and compiling Prolog
218		programs containing CHR. <a class="sec" href="debugging.html">Section
219		8.4</a> explains the (currently primitive) CHR debugging facilities. <a class="sec" href="debugging.html">Section
	259	programs containing CHR. <a class="sec" href="debugging.html#sec:8.4">Section
	260	8.4</a> explains the (currently primitive) CHR debugging facilities. <a class="sec" href="debugging.html#sec:8.4.3">Section
220	261	8.4.3</a> provides a few useful predicates to inspect the constraint
221		store, and <a class="sec" href="examples.html">section 8.5</a>
222		illustrates CHR with two example programs. <a class="sec" href="sicstus-chr.html">Section
	262	store, and <a class="sec" href="examples.html#sec:8.5">section 8.5</a>
	263	illustrates CHR with two example programs. <a class="sec" href="sicstus-chr.html#sec:8.6">Section
223	264	8.6</a> describes some compatibility issues with older versions of this
224		system and SICStus' CHR system. Finally, <a class="sec" href="guidelines.html">section
	265	system and SICStus' CHR system. Finally, <a class="sec" href="guidelines.html#sec:8.7">section
225	266	8.7</a> concludes with a few practical guidelines for using CHR.
226	267
227	268	<p></body></html>⏎

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193	234	</div>
194		<h1 id="sec:clp"><a name="sec:7"><span class="sec-nr">7</span> <span class="sec-title">Constraint
	235	<h1 id="sec:clp"><a id="sec:7"><span class="sec-nr">7</span> <span class="sec-title">Constraint
195	236	Logic Programming</span></a></h1>
196	237
197		<a name="sec:clp"></a>
198		<a name="idx:CLP:1759"></a><a name="idx:constraintprogramming:1760"></a>This
	238	<a id="sec:clp"></a>
	239	<a id="idx:CLP:1763"></a><a id="idx:constraintprogramming:1764"></a>This
199	240	chapter describes the extensions primarily designed to support
200	241	<b>constraint logic programming</b> (CLP), an important declarative
201	242	programming paradigm with countless practical applications.

203	244	<p>CLP(<var>X</var>) stands for constraint logic programming over the
204	245	domain <var>X</var>. Plain Prolog can be regarded as CLP(<var>H</var>),
205	246	where <var>H</var> stands for
206		<i>Herbrand terms</i><a name="idx:Herbrandterm:1761"></a>. Over
207		this domain,
208		<a class="pred" href="compare.html#=/2">=/2</a> and <a name="idx:dif2:1762"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
	247	<i>Herbrand terms</i><a id="idx:Herbrandterm:1765"></a>. Over this
	248	domain,
	249	<a class="pred" href="compare.html#=/2">=/2</a> and <a id="idx:dif2:1766"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
209	250	are the most important constraints that express, respectively, equality
210	251	and disequality of terms. Plain Prolog can thus be regarded as a
211	252	special case of CLP.

214	255
215	256	<p>
216	257	<ul class="latex">
217		<li>CLP(FD) for <b>integers</b> (<a class="sec" href="clpfd.html">section
	258	<li>CLP(FD) for <b>integers</b> (<a class="sec" href="clpfd.html#sec:A.8">section
218	259	A.8</a>)
219		<li>CLP(B) for <b>Boolean</b> variables (<a class="sec" href="clpb.html">section
	260	<li>CLP(B) for <b>Boolean</b> variables (<a class="sec" href="clpb.html#sec:A.7">section
220	261	A.7</a>)
221		<li>CLP(Q) for <b>rational</b> numbers (<a class="sec" href="clpqr.html">section
	262	<li>CLP(Q) for <b>rational</b> numbers (<a class="sec" href="clpqr.html#sec:A.9">section
222	263	A.9</a>)
223		<li>CLP(R) for <b>floating point</b> numbers (<a class="sec" href="clpqr.html">section
	264	<li>CLP(R) for <b>floating point</b> numbers (<a class="sec" href="clpqr.html#sec:A.9">section
224	265	A.9</a>).
225	266	</ul>
226	267
227		<p>In addition, CHR (<a class="sec" href="chr.html">chapter 8</a>)
	268	<p>In addition, CHR (<a class="sec" href="chr.html#sec:8">chapter 8</a>)
228	269	provides a general purpose constraint handling language to reason over
229	270	user-defined constraints.
230	271

246	287	it, both <i>before</i> and also <i>during</i> any search for concrete
247	288	solutions. Using available information to prune parts of the search
248	289	space is called constraint
249		<em>propagation</em><a name="idx:propagation:1763"></a>, and it is
	290	<em>propagation</em><a id="idx:propagation:1767"></a>, and it is
250	291	performed automatically by the available constraint solvers for their
251	292	respective domains. This feature can significantly increase the
252	293	<i>performance</i> of your programs.

264	305	the constraint solver combines the existing knowledge to infer that <var>X</var>
265	306	is either 1 or 2 (see below). To obtain concrete values for <var>X</var>,
266	307	you can ask the solver to <em>label</em> <var>X</var> and produce 1
267		and 2 on backtracking. See <a class="sec" href="clpfd.html">section
	308	and 2 on backtracking. See <a class="sec" href="clpfd.html#sec:A.8">section
268	309	A.8</a>.
269	310
270	311	<pre class="code">

288	329	two-dimensional space.
289	330
290	331	<p>Using constraints therefore makes your program more
291		<em>declarative</em><a name="idx:declarative:1764"></a> in that it frees
	332	<em>declarative</em><a id="idx:declarative:1768"></a> in that it frees
292	333	you from some procedural aspects and limitations of Prolog.
293	334
294	335	<p>When working with constraints, keep in mind the following:

300	341	goal that is delayed may prematurely prune the search space, because the
301	342	truth of delayed goals is not yet established. There are several ways to
302	343	avoid cuts in constraint logic programs, retaining both generality and
303		determinism of your programs. See for example <a name="idx:zcompare3:1765"></a><a class="pred" href="clpfd.html#zcompare/3">zcompare/3</a>.
304		<li>Term-copying operations (<a name="idx:assertz1:1766"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>, <a name="idx:retract1:1767"></a><a class="pred" href="db.html#retract/1">retract/1</a>, <a name="idx:findall3:1768"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>,
305		<a name="idx:copyterm2:1769"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>,
	344	determinism of your programs. See for example <a id="idx:zcompare3:1769"></a><a class="pred" href="clpfd.html#zcompare/3">zcompare/3</a>.
	345	<li>Term-copying operations (<a id="idx:assertz1:1770"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>, <a id="idx:retract1:1771"></a><a class="pred" href="db.html#retract/1">retract/1</a>, <a id="idx:findall3:1772"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>,
	346	<a id="idx:copyterm2:1773"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>,
306	347	etc.) generally also copy constraints. The effect varies from ok, silent
307	348	copying of huge constraint networks to violations of the internal
308	349	consistency of constraint networks. As a rule of thumb, copying terms
309	350	holding attributes must be deprecated. If you need to reason about a
310		term that is involved in constraints, use <a name="idx:copyterm3:1770"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>
	351	term that is involved in constraints, use <a id="idx:copyterm3:1774"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>
311	352	to obtain the constraints as Prolog goals, and use these goals for
312	353	further processing.
313	354	</ul>
314	355
315	356	<p>All of the mentioned constraint solvers are implemented using the
316		attributed variables interface described in <a class="sec" href="attvar.html">section
	357	attributed variables interface described in <a class="sec" href="attvar.html#sec:7.1">section
317	358	7.1</a>. These are lower-level predicates that are mainly intended for
318	359	library authors, not for typical Prolog programmers.
319	360

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193	234	</div>
194		<h2 id="sec:clpb"><a name="sec:A.7"><span class="sec-nr">A.7</span> <span class="sec-title">library(clpb):
	235	<h2 id="sec:clpb"><a id="sec:A.7"><span class="sec-nr">A.7</span> <span class="sec-title">library(clpb):
195	236	CLP(B): Constraint Logic Programming over Boolean Variables</span></a></h2>
196	237
197		<a name="sec:clpb"></a>
198
199		<p><a name="sec:clpb"></a>
	238	<a id="sec:clpb"></a>
	239
	240	<p><a id="sec:clpb"></a>
200	241
201	242	<dl class="tags">
202	243	<dt class="tag">author</dt>
203	244	<dd>
204		https://www.metalevel.atMarkus Triska
	245	<a class="url" href="https://www.metalevel.at">Markus Triska</a>
205	246	</dd>
206	247	</dl>
207	248
208		<p><h3 id="sec:clpb-intro"><a name="sec:A.7.1"><span class="sec-nr">A.7.1</span> <span class="sec-title">Introduction</span></a></h3>
209
210		<p><a name="sec:clpb-intro"></a>
	249	<p><h3 id="sec:clpb-intro"><a id="sec:A.7.1"><span class="sec-nr">A.7.1</span> <span class="sec-title">Introduction</span></a></h3>
	250
	251	<p><a id="sec:clpb-intro"></a>
211	252
212	253	<p>This library provides CLP(B), Constraint Logic Programming over
213	254	Boolean variables. It can be used to model and solve combinatorial
214	255	problems such as verification, allocation and covering tasks.
215	256
216		<p>CLP(B) is an instance of the general CLP(<i>X</i>) scheme (<a class="sec" href="clp.html">section
	257	<p>CLP(B) is an instance of the general CLP(<i>X</i>) scheme (<a class="sec" href="clp.html#sec:7">section
217	258	7</a>), extending logic programming with reasoning over specialised
218	259	domains.
219	260

221	262	Diagrams (BDDs).
222	263
223	264	<p>Benchmarks and usage examples of this library are available from:
224		https://www.metalevel.at/clpb/<b>https:<code>//</code>www.metalevel.at/clpb/</b>
	265	<a class="url" href="https://www.metalevel.at/clpb/"><b>https:<code>//</code>www.metalevel.at/clpb/</b></a>
225	266
226	267	<p>We recommend the following reference for citing this library in
227	268	scientific publications:

240	281	</pre>
241	282
242	283	<p>The paper is available from
243		https://www.metalevel.at/swiclpb.pdfhttps:<code>//</code>www.metalevel.at/swiclpb.pdf
244
245		<p><h3 id="sec:clpb-exprs"><a name="sec:A.7.2"><span class="sec-nr">A.7.2</span> <span class="sec-title">Boolean
	284	<a class="url" href="https://www.metalevel.at/swiclpb.pdf">https:<code>//</code>www.metalevel.at/swiclpb.pdf</a>
	285
	286	<p><h3 id="sec:clpb-exprs"><a id="sec:A.7.2"><span class="sec-nr">A.7.2</span> <span class="sec-title">Boolean
246	287	expressions</span></a></h3>
247	288
248		<p><a name="sec:clpb-exprs"></a>
	289	<p><a id="sec:clpb-exprs"></a>
249	290
250	291	<p>A <i>Boolean expression</i> is one of:
251	292	<blockquote>
252		<table border="2" frame="box" rules="groups">
253		<tr valign="top"><td><code>0</code> </td><td>false </td></tr>
254		<tr valign="top"><td><code>1</code> </td><td>true </td></tr>
255		<tr valign="top"><td><i>variable</i> </td><td>unknown truth value </td></tr>
256		<tr valign="top"><td><i>atom</i> </td><td>universally quantified
257		variable </td></tr>
258		<tr valign="top"><td><code>~</code> <i>Expr</i> </td><td>logical NOT </td></tr>
259		<tr valign="top"><td><i>Expr</i> + <i>Expr</i> </td><td>logical OR </td></tr>
260		<tr valign="top"><td><i>Expr</i> * <i>Expr</i> </td><td>logical AND </td></tr>
261		<tr valign="top"><td><i>Expr</i> # <i>Expr</i> </td><td>exclusive OR </td></tr>
262		<tr valign="top"><td><i>Var</i> <code>^</code> <i>Expr</i> </td><td>existential
	293	<table class="latex frame-box">
	294	<tr><td><code>0</code> </td><td>false </td></tr>
	295	<tr><td><code>1</code> </td><td>true </td></tr>
	296	<tr><td><i>variable</i> </td><td>unknown truth value </td></tr>
	297	<tr><td><i>atom</i> </td><td>universally quantified variable </td></tr>
	298	<tr><td><code>~</code> <i>Expr</i> </td><td>logical NOT </td></tr>
	299	<tr><td><i>Expr</i> + <i>Expr</i> </td><td>logical OR </td></tr>
	300	<tr><td><i>Expr</i> * <i>Expr</i> </td><td>logical AND </td></tr>
	301	<tr><td><i>Expr</i> # <i>Expr</i> </td><td>exclusive OR </td></tr>
	302	<tr><td><i>Var</i> <code>^</code> <i>Expr</i> </td><td>existential
263	303	quantification </td></tr>
264		<tr valign="top"><td><i>Expr</i> <code>=:=</code> <i>Expr</i> </td><td>equality </td></tr>
265		<tr valign="top"><td><i>Expr</i> <code>=\=</code> <i>Expr</i> </td><td>disequality
	304	<tr><td><i>Expr</i> <code>=:=</code> <i>Expr</i> </td><td>equality </td></tr>
	305	<tr><td><i>Expr</i> <code>=\=</code> <i>Expr</i> </td><td>disequality
266	306	(same as #) </td></tr>
267		<tr valign="top"><td><i>Expr</i> <code>=<</code> <i>Expr</i> </td><td>less
268		or equal (implication) </td></tr>
269		<tr valign="top"><td><i>Expr</i> <code>>=</code> <i>Expr</i> </td><td>greater
270		or equal </td></tr>
271		<tr valign="top"><td><i>Expr</i> <var><</var> <i>Expr</i> </td><td>less
272		than </td></tr>
273		<tr valign="top"><td><i>Expr</i> <var>></var> <i>Expr</i> </td><td>greater
274		than </td></tr>
275		<tr valign="top"><td><code>card(Is,Exprs)</code> </td><td><i>see below</i> </td></tr>
276		<tr valign="top"><td><code>+(Exprs)</code> </td><td><i>see below</i> </td></tr>
277		<tr valign="top"><td><code>*(Exprs)</code> </td><td><i>see below</i> </td></tr>
	307	<tr><td><i>Expr</i> <code>=<</code> <i>Expr</i> </td><td>less or
	308	equal (implication) </td></tr>
	309	<tr><td><i>Expr</i> <code>>=</code> <i>Expr</i> </td><td>greater or
	310	equal </td></tr>
	311	<tr><td><i>Expr</i> <var><</var> <i>Expr</i> </td><td>less than </td></tr>
	312	<tr><td><i>Expr</i> <var>></var> <i>Expr</i> </td><td>greater than </td></tr>
	313	<tr><td><code>card(Is,Exprs)</code> </td><td><i>see below</i> </td></tr>
	314	<tr><td><code>+(Exprs)</code> </td><td><i>see below</i> </td></tr>
	315	<tr><td><code>*(Exprs)</code> </td><td><i>see below</i> </td></tr>
278	316	</table>
279	317	</blockquote>
280	318

294	332	appear on the right-hand side of equations. Therefore, they can be used
295	333	to express functional dependencies on input variables.
296	334
297		<p><h3 id="sec:clpb-interface"><a name="sec:A.7.3"><span class="sec-nr">A.7.3</span> <span class="sec-title">Interface
	335	<p><h3 id="sec:clpb-interface"><a id="sec:A.7.3"><span class="sec-nr">A.7.3</span> <span class="sec-title">Interface
298	336	predicates</span></a></h3>
299	337
300		<p><a name="sec:clpb-interface"></a>
	338	<p><a id="sec:clpb-interface"></a>
301	339
302	340	<p>The most frequently used CLP(B) predicates are:
303	341

323	361	<p>The unification of a CLP(B) variable <i>X</i> with a term <i>T</i> is
324	362	equivalent to posting the constraint <code>sat(X=:=T)</code>.
325	363
326		<p><h3 id="sec:clpb-examples"><a name="sec:A.7.4"><span class="sec-nr">A.7.4</span> <span class="sec-title">Examples</span></a></h3>
327
328		<p><a name="sec:clpb-examples"></a>
	364	<p><h3 id="sec:clpb-examples"><a id="sec:A.7.4"><span class="sec-nr">A.7.4</span> <span class="sec-title">Examples</span></a></h3>
	365
	366	<p><a id="sec:clpb-examples"></a>
329	367
330	368	<p>Here is an example session with a few queries and their answers:
331	369

366	404	last example illustrates that when applicable, remaining variables are
367	405	expressed as functions of universally quantified variables.
368	406
369		<p><h3 id="sec:clpb-residual-goals"><a name="sec:A.7.5"><span class="sec-nr">A.7.5</span> <span class="sec-title">Obtaining
	407	<p><h3 id="sec:clpb-residual-goals"><a id="sec:A.7.5"><span class="sec-nr">A.7.5</span> <span class="sec-title">Obtaining
370	408	BDDs</span></a></h3>
371	409
372		<p><a name="sec:clpb-residual-goals"></a>
	410	<p><a id="sec:clpb-residual-goals"></a>
373	411
374	412	<p>By default, CLP(B) residual goals appear in (approximately) algebraic
375	413	normal form (ANF). This projection is often computationally expensive.

403	441	node(2)- (v(X, 1)->false;true).
404	442	</pre>
405	443
406		<p><h3 id="sec:clpb-monotonic"><a name="sec:A.7.6"><span class="sec-nr">A.7.6</span> <span class="sec-title">Enabling
	444	<p><h3 id="sec:clpb-monotonic"><a id="sec:A.7.6"><span class="sec-nr">A.7.6</span> <span class="sec-title">Enabling
407	445	monotonic CLP(B)</span></a></h3>
408	446
409		<p><a name="sec:clpb-monotonic"></a>
	447	<p><a id="sec:clpb-monotonic"></a>
410	448
411	449	<p>In the default execution mode, CLP(B) constraints are <i>not</i>
412	450	monotonic. This means that <i>adding</i> constraints can yield new

421	459	</pre>
422	460
423	461	<p>This behaviour is highly problematic from a logical point of view,
424		and it may render https://www.metalevel.at/prolog/debugging<b>declarative
425		debugging</b> techniques inapplicable.
	462	and it may render <a class="url" href="https://www.metalevel.at/prolog/debugging"><b>declarative
	463	debugging</b></a> techniques inapplicable.
426	464
427	465	<p>Set the flag <code>clpb_monotonic</code> to <code>true</code> to make
428	466	CLP(B) <b>monotonic</b>. If this mode is enabled, then you must wrap

436	474	X = 0.
437	475	</pre>
438	476
439		<p><h3 id="sec:clpb-pigeons"><a name="sec:A.7.7"><span class="sec-nr">A.7.7</span> <span class="sec-title">Example:
	477	<p><h3 id="sec:clpb-pigeons"><a id="sec:A.7.7"><span class="sec-nr">A.7.7</span> <span class="sec-title">Example:
440	478	Pigeons</span></a></h3>
441	479
442		<p><a name="sec:clpb-pigeons"></a>
	480	<p><a id="sec:clpb-pigeons"></a>
443	481
444	482	<p>In this example, we are attempting to place <i>I</i> pigeons into <i>J</i>
445	483	holes in such a way that each hole contains at most one pigeon. One

448	486	interesting aspect is that this task has no short resolution refutations
449	487	in general.
450	488
451		<p>In the following, we use https://www.metalevel.at/prolog/dcg<b>Prolog
452		DCG notation</b> to describe a list <var>Cs</var> of CLP(B) constraints
453		that must all be satisfied.
	489	<p>In the following, we use <a class="url" href="https://www.metalevel.at/prolog/dcg"><b>Prolog
	490	DCG notation</b></a> to describe a list <var>Cs</var> of CLP(B)
	491	constraints that must all be satisfied.
454	492
455	493	<pre class="code">
456	494	:- use_module(library(clpb)).

482	520	[0, 1, 0].
483	521	</pre>
484	522
485		<p><h3 id="sec:clpb-circuit"><a name="sec:A.7.8"><span class="sec-nr">A.7.8</span> <span class="sec-title">Example:
	523	<p><h3 id="sec:clpb-circuit"><a id="sec:A.7.8"><span class="sec-nr">A.7.8</span> <span class="sec-title">Example:
486	524	Boolean circuit</span></a></h3>
487	525
488		<p><a name="sec:clpb-circuit"></a>
	526	<p><a id="sec:clpb-circuit"></a>
489	527
490	528	<p>Consider a Boolean circuit that express the Boolean function <code>XOR</code>
491	529	with 4 <code>NAND</code> gates. We can model such a circuit with CLP(B)

511	549	sat(Z=:=x#y).
512	550	</pre>
513	551
514		<p><h3 id="sec:clpb-acknowledgments"><a name="sec:A.7.9"><span class="sec-nr">A.7.9</span> <span class="sec-title">Acknowledgments</span></a></h3>
515
516		<p><a name="sec:clpb-acknowledgments"></a>
	552	<p><h3 id="sec:clpb-acknowledgments"><a id="sec:A.7.9"><span class="sec-nr">A.7.9</span> <span class="sec-title">Acknowledgments</span></a></h3>
	553
	554	<p><a id="sec:clpb-acknowledgments"></a>
517	555
518	556	<p>The interface predicates of this library follow the example of
519		https://sicstus.sics.se<b>SICStus Prolog</b>.
	557	<a class="url" href="https://sicstus.sics.se"><b>SICStus Prolog</b></a>.
520	558
521	559	<p>Use SICStus Prolog for higher performance in many cases.
522	560
523		<p><h3 id="sec:clpb-predicates"><a name="sec:A.7.10"><span class="sec-nr">A.7.10</span> <span class="sec-title">CLP(B)
	561	<p><h3 id="sec:clpb-predicates"><a id="sec:A.7.10"><span class="sec-nr">A.7.10</span> <span class="sec-title">CLP(B)
524	562	predicate index</span></a></h3>
525	563
526		<p><a name="sec:clpb-predicates"></a>
	564	<p><a id="sec:clpb-predicates"></a>
527	565
528	566	<p>In the following, each CLP(B) predicate is described in more detail.
529	567

532	570	<p><a class="url" href="http://eu.swi-prolog.org/man/clpb.html">http://eu.swi-prolog.org/man/clpb.html</a>
533	571
534	572	<dl class="latex">
535		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="sat/1"><strong>sat</strong>(<var>+Expr</var>)</a></dt>
	573	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="sat/1"><strong>sat</strong>(<var>+Expr</var>)</a></dt>
536	574	<dd class="defbody">
537	575	True iff <var>Expr</var> is a satisfiable Boolean expression.</dd>
538		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="taut/2"><strong>taut</strong>(<var>+Expr,
	576	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="taut/2"><strong>taut</strong>(<var>+Expr,
539	577	-T</var>)</a></dt>
540	578	<dd class="defbody">
541	579	Tautology check. Succeeds with <var>T</var> = 0 if the Boolean
542	580	expression <var>Expr</var> cannot be satisfied, and with <var>T</var> =
543	581	1 if <var>Expr</var> is always true with respect to the current
544	582	constraints. Fails otherwise.</dd>
545		<dt class="pubdef"><span class="pred-tag">[multi]</span><a name="labeling/1"><strong>labeling</strong>(<var>+Vs</var>)</a></dt>
	583	<dt class="pubdef"><span class="pred-tag">[multi]</span><a id="labeling/1"><strong>labeling</strong>(<var>+Vs</var>)</a></dt>
546	584	<dd class="defbody">
547	585	Enumerate concrete solutions. Assigns truth values to the Boolean
548	586	variables <var>Vs</var> such that all stated constraints are satisfied.</dd>
549		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="sat_count/2"><strong>sat_count</strong>(<var>+Expr,
	587	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="sat_count/2"><strong>sat_count</strong>(<var>+Expr,
550	588	-Count</var>)</a></dt>
551	589	<dd class="defbody">
552	590	<var>Count</var> the number of admissible assignments. <var>Count</var>

575	613	</pre>
576	614
577	615	</dd>
578		<dt class="pubdef"><span class="pred-tag">[multi]</span><a name="weighted_maximum/3"><strong>weighted_maximum</strong>(<var>+Weights,
	616	<dt class="pubdef"><span class="pred-tag">[multi]</span><a id="weighted_maximum/3"><strong>weighted_maximum</strong>(<var>+Weights,
579	617	+Vs, -Maximum</var>)</a></dt>
580	618	<dd class="defbody">
581	619	Enumerate weighted optima over admissible assignments. Maximize a linear

598	636	</pre>
599	637
600	638	</dd>
601		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="random_labeling/2"><strong>random_labeling</strong>(<var>+Seed,
	639	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random_labeling/2"><strong>random_labeling</strong>(<var>+Seed,
602	640	+Vs</var>)</a></dt>
603	641	<dd class="defbody">
604	642	Select a single random solution. An admissible assignment of truth

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	21	{ color: #fff;
	22	padding: 2px 10px 0px 10px;
	23	margin-bottom: 5px;
	24	font-size: 18px;
	25	vertical-align: middle;
	26	overflow: hidden;
	27	}
	28
	29	dt.pubdef { background-color: #0c3d6e; }
	30	dt.multidef { background-color: #ef9439; }
27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
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121	125	}
122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
135		{ display: block !important;
136		position: absolute; top: auto; left: auto; width: 80%;
137		color: #000; background: white;
138		border: 2px solid;
139		padding: 5px; margin: 10px; z-index: 100;
140		font-size: smaller;
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	137	}
	138
	139	.fn-text, .fnp {
	140	position: absolute;
	141	top: auto;
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	144	box-shadow: 5px 5px 5px #888;
	145	display: none;
	146	background: #fff;
	147	color: #000;
	148	margin-top: 25px;
	149	padding: 8px 12px;
	150	font-size: larger;
	151	}
	152
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141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
	200
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	202	{ margin: auto;
	203	}
	204
	205	table.latex
	206	{ border-collapse:collapse;
	207	}
	208
	209	table.latex tr
	210	{ vertical-align: text-top;
	211	}
	212
	213	table.latex td,th
	214	{ padding: 2px 1em;
	215	}
	216
	217	table.latex tr.hline td,th
	218	{ border-top: 1px solid black;
	219	}
	220
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184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="clpb.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="clpqr.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:clpfd"><a name="sec:A.8"><span class="sec-nr">A.8</span> <span class="sec-title">library(clpfd):
	235	<h2 id="sec:clpfd"><a id="sec:A.8"><span class="sec-nr">A.8</span> <span class="sec-title">library(clpfd):
195	236	CLP(FD): Constraint Logic Programming over Finite Domains</span></a></h2>
196	237
197		<a name="sec:clpfd"></a>
198
199		<p><a name="sec:clpfd"></a>
	238	<a id="sec:clpfd"></a>
	239
	240	<p><a id="sec:clpfd"></a>
200	241
201	242	<dl class="tags">
202	243	<dt class="tag">author</dt>
203	244	<dd>
204		https://www.metalevel.atMarkus Triska
	245	<a class="url" href="https://www.metalevel.at">Markus Triska</a>
205	246	</dd>
206	247	</dl>
207	248
208	249	<p><b>Development of this library has moved to SICStus Prolog.</b><br>
209	250	Please see
210		https://github.com/triska/clpz<b>CLP(Z)</b> for more information.
211
212		<p><h3 id="sec:clpfd-intro"><a name="sec:A.8.1"><span class="sec-nr">A.8.1</span> <span class="sec-title">Introduction</span></a></h3>
213
214		<p><a name="sec:clpfd-intro"></a>
	251	<a class="url" href="https://github.com/triska/clpz"><b>CLP(Z)</b></a>
	252	for more information.
	253
	254	<p><h3 id="sec:clpfd-intro"><a id="sec:A.8.1"><span class="sec-nr">A.8.1</span> <span class="sec-title">Introduction</span></a></h3>
	255
	256	<p><a id="sec:clpfd-intro"></a>
215	257
216	258	<p>This library provides CLP(FD): Constraint Logic Programming over
217	259	Finite Domains. This is an instance of the general CLP(<i>X</i>) scheme
218		(<a class="sec" href="clp.html">section 7</a>), extending logic
	260	(<a class="sec" href="clp.html#sec:7">section 7</a>), extending logic
219	261	programming with reasoning over specialised domains. CLP(FD) lets us
220	262	reason about <b>integers</b> in a way that honors the relational nature
221	263	of Prolog.
222	264
223		<p>Read https://www.metalevel.at/prolog<b>The Power of Prolog</b> to
224		understand how this library is meant to be used in practice.
	265	<p>Read <a class="url" href="https://www.metalevel.at/prolog"><b>The
	266	Power of Prolog</b></a> to understand how this library is meant to be
	267	used in practice.
225	268
226	269	<p>There are two major use cases of CLP(FD) constraints:
227	270
228	271	<p>
229	272	<ol class="latex">
230		<li><b>declarative integer arithmetic</b> (<a class="sec" href="clpfd.html">section
	273	<li><b>declarative integer arithmetic</b> (<a class="sec" href="clpfd.html#sec:A.8.3">section
231	274	A.8.3</a>)
232	275	<li>solving <b>combinatorial problems</b> such as planning, scheduling
233	276	and allocation tasks.

238	281	<p>
239	282	<ul class="latex">
240	283	<li><i>arithmetic</i> constraints like <a class="pred" href="clpfd.html##=/2">#=/2</a>, <a class="pred" href="clpfd.html##>/2">#>/2</a>
241		and <a class="pred" href="clpfd.html##\=/2">#\=/2</a> (<a class="sec" href="clpfd.html">section
	284	and <a class="pred" href="clpfd.html##\=/2">#\=/2</a> (<a class="sec" href="clpfd.html#sec:A.8.17.1">section
242	285	A.8.17.1</a>)
243	286	<li>the <i>membership</i> constraints <a class="pred" href="clpfd.html#in/2">in/2</a>
244		and <a class="pred" href="clpfd.html#ins/2">ins/2</a> (<a class="sec" href="clpfd.html">section
	287	and <a class="pred" href="clpfd.html#ins/2">ins/2</a> (<a class="sec" href="clpfd.html#sec:A.8.17.2">section
245	288	A.8.17.2</a>)
246	289	<li>the <i>enumeration</i> predicates <a class="pred" href="clpfd.html#indomain/1">indomain/1</a>, <a class="pred" href="clpfd.html#label/1">label/1</a>
247		and <a class="pred" href="clpfd.html#labeling/2">labeling/2</a> (<a class="sec" href="clpfd.html">section
	290	and <a class="pred" href="clpfd.html#labeling/2">labeling/2</a> (<a class="sec" href="clpfd.html#sec:A.8.17.3">section
248	291	A.8.17.3</a>)
249	292	<li><i>combinatorial</i> constraints like <a class="pred" href="clpfd.html#all_distinct/1">all_distinct/1</a>
250	293	and <a class="pred" href="clpfd.html#global_cardinality/2">global_cardinality/2</a>
251		(<a class="sec" href="clpfd.html">section A.8.17.4</a>)
	294	(<a class="sec" href="clpfd.html#sec:A.8.17.4">section A.8.17.4</a>)
252	295	<li><i>reification</i> predicates such as <a class="pred" href="clpfd.html##<==>/2">#<==>/2</a>
253		(<a class="sec" href="clpfd.html">section A.8.17.5</a>)
	296	(<a class="sec" href="clpfd.html#sec:A.8.17.5">section A.8.17.5</a>)
254	297	<li><i>reflection</i> predicates such as <a class="pred" href="clpfd.html#fd_dom/2">fd_dom/2</a>
255		(<a class="sec" href="clpfd.html">section A.8.17.6</a>)
	298	(<a class="sec" href="clpfd.html#sec:A.8.17.6">section A.8.17.6</a>)
256	299	</ul>
257	300
258		<p>In most cases, <i>arithmetic constraints</i> (<a class="sec" href="clpfd.html">section
	301	<p>In most cases, <i>arithmetic constraints</i> (<a class="sec" href="clpfd.html#sec:A.8.2">section
259	302	A.8.2</a>) are the only predicates you will ever need from this library.
260	303	When reasoning over integers, simply replace low-level arithmetic
261	304	predicates like <code>(is)/2</code> and <code>(>)/2</code> by the

280	323
281	324	<p>Important concepts and principles of this library are illustrated by
282	325	means of usage examples that are available in a public git repository:
283		https://github.com/triska/clpfd<b>github.com/triska/clpfd</b>
	326	<a class="url" href="https://github.com/triska/clpfd"><b>github.com/triska/clpfd</b></a>
284	327
285	328	<p>If you are used to the complicated operational considerations that
286	329	low-level arithmetic primitives necessitate, then moving to CLP(FD)

300	343	advanced lectures.
301	344
302	345	<p>We recommend the following reference (PDF:
303		https://www.metalevel.at/swiclpfd.pdfmetalevel.at/swiclpfd.pdf) for
304		citing this library in scientific publications:
	346	<a class="url" href="https://www.metalevel.at/swiclpfd.pdf">metalevel.at/swiclpfd.pdf</a>)
	347	for citing this library in scientific publications:
305	348
306	349	<pre class="code">
307	350	@inproceedings{Triska12,

316	359	</pre>
317	360
318	361	<p>More information about CLP(FD) constraints and their implementation
319		is contained in: https://www.metalevel.at/drt.pdf<b>metalevel.at/drt.pdf</b>
	362	is contained in: <a class="url" href="https://www.metalevel.at/drt.pdf"><b>metalevel.at/drt.pdf</b></a>
320	363
321	364	<p>The best way to discuss applying, improving and extending CLP(FD)
322	365	constraints is to use the dedicated <code>clpfd</code> tag on
323		http://stackoverflow.comstackoverflow.com. Several of the world's
324		foremost CLP(FD) experts regularly participate in these discussions and
325		will help you for free on this platform.
326
327		<p><h3 id="sec:clpfd-arith-constraints"><a name="sec:A.8.2"><span class="sec-nr">A.8.2</span> <span class="sec-title">Arithmetic
	366	<a class="url" href="http://stackoverflow.com">stackoverflow.com</a>.
	367	Several of the world's foremost CLP(FD) experts regularly participate in
	368	these discussions and will help you for free on this platform.
	369
	370	<p><h3 id="sec:clpfd-arith-constraints"><a id="sec:A.8.2"><span class="sec-nr">A.8.2</span> <span class="sec-title">Arithmetic
328	371	constraints</span></a></h3>
329	372
330		<p><a name="sec:clpfd-arith-constraints"></a>
	373	<p><a id="sec:clpfd-arith-constraints"></a>
331	374
332	375	<p>In modern Prolog systems, <b>arithmetic constraints</b> subsume and
333	376	supersede low-level predicates over integers. The main advantage of

338	381	<p>The most important arithmetic constraint is <a class="pred" href="clpfd.html##=/2">#=/2</a>,
339	382	which subsumes both
340	383	<code>(is)/2</code> and <code>(=:=)/2</code> over integers. Use <a class="pred" href="clpfd.html##=/2">#=/2</a>
341		to make your programs more general. See declarative integer arithmetic (<a class="sec" href="clpfd.html">section
	384	to make your programs more general. See declarative integer arithmetic (<a class="sec" href="clpfd.html#sec:A.8.3">section
342	385	A.8.3</a>).
343	386
344	387	<p>In total, the arithmetic constraints are:
345	388	<blockquote>
346		<table border="2" frame="box" rules="groups">
347		<tr valign="top"><td>Expr1 <code>#=</code> Expr2</td><td>Expr1 equals
	389	<table class="latex frame-box">
	390	<tr><td>Expr1 <code>#=</code> Expr2</td><td>Expr1 equals Expr2 </td></tr>
	391	<tr><td>Expr1 <code>#\=</code> Expr2</td><td>Expr1 is not equal to Expr2 </td></tr>
	392	<tr><td>Expr1 <code>#>=</code> Expr2</td><td>Expr1 is greater than or
	393	equal to Expr2 </td></tr>
	394	<tr><td>Expr1 <code>#=<</code> Expr2</td><td>Expr1 is less than or
	395	equal to Expr2 </td></tr>
	396	<tr><td>Expr1 <code>#></code> Expr2</td><td>Expr1 is greater than
348	397	Expr2 </td></tr>
349		<tr valign="top"><td>Expr1 <code>#\=</code> Expr2</td><td>Expr1 is not
350		equal to Expr2 </td></tr>
351		<tr valign="top"><td>Expr1 <code>#>=</code> Expr2</td><td>Expr1 is
352		greater than or equal to Expr2 </td></tr>
353		<tr valign="top"><td>Expr1 <code>#=<</code> Expr2</td><td>Expr1 is
354		less than or equal to Expr2 </td></tr>
355		<tr valign="top"><td>Expr1 <code>#></code> Expr2</td><td>Expr1 is
356		greater than Expr2 </td></tr>
357		<tr valign="top"><td>Expr1 <code>#<</code> Expr2</td><td>Expr1 is
358		less than Expr2 </td></tr>
	398	<tr><td>Expr1 <code>#<</code> Expr2</td><td>Expr1 is less than Expr2 </td></tr>
359	399	</table>
360	400	</blockquote>
361	401
362	402	<p><var>Expr1</var> and <var>Expr2</var> denote <b>arithmetic
363	403	expressions</b>, which are:
364	404	<blockquote>
365		<table border="2" frame="box" rules="groups">
366		<tr valign="top"><td><i>integer</i> </td><td>Given value </td></tr>
367		<tr valign="top"><td><i>variable</i> </td><td>Unknown integer </td></tr>
368		<tr valign="top"><td>?(<i>variable</i>)</td><td>Unknown integer </td></tr>
369		<tr valign="top"><td>-Expr</td><td>Unary minus </td></tr>
370		<tr valign="top"><td>Expr + Expr</td><td>Addition </td></tr>
371		<tr valign="top"><td>Expr * Expr</td><td>Multiplication </td></tr>
372		<tr valign="top"><td>Expr - Expr</td><td>Subtraction </td></tr>
373		<tr valign="top"><td>Expr <code>^</code> Expr</td><td>Exponentiation </td></tr>
374		<tr valign="top"><td><code>min(Expr,Expr)</code> </td><td>Minimum of two
375		expressions </td></tr>
376		<tr valign="top"><td><code>max(Expr,Expr)</code> </td><td>Maximum of two
377		expressions </td></tr>
378		<tr valign="top"><td>Expr <code>mod</code> Expr</td><td>Modulo induced
379		by floored division </td></tr>
380		<tr valign="top"><td>Expr <code>rem</code> Expr</td><td>Modulo induced
381		by truncated division </td></tr>
382		<tr valign="top"><td><code>abs(Expr)</code> </td><td>Absolute value </td></tr>
383		<tr valign="top"><td>Expr <code>//</code> Expr</td><td>Truncated integer
	405	<table class="latex frame-box">
	406	<tr><td><i>integer</i> </td><td>Given value </td></tr>
	407	<tr><td><i>variable</i> </td><td>Unknown integer </td></tr>
	408	<tr><td>?(<i>variable</i>)</td><td>Unknown integer </td></tr>
	409	<tr><td>-Expr</td><td>Unary minus </td></tr>
	410	<tr><td>Expr + Expr</td><td>Addition </td></tr>
	411	<tr><td>Expr * Expr</td><td>Multiplication </td></tr>
	412	<tr><td>Expr - Expr</td><td>Subtraction </td></tr>
	413	<tr><td>Expr <code>^</code> Expr</td><td>Exponentiation </td></tr>
	414	<tr><td><code>min(Expr,Expr)</code> </td><td>Minimum of two expressions </td></tr>
	415	<tr><td><code>max(Expr,Expr)</code> </td><td>Maximum of two expressions </td></tr>
	416	<tr><td>Expr <code>mod</code> Expr</td><td>Modulo induced by floored
384	417	division </td></tr>
385		<tr valign="top"><td>Expr div Expr</td><td>Floored integer division </td></tr>
	418	<tr><td>Expr <code>rem</code> Expr</td><td>Modulo induced by truncated
	419	division </td></tr>
	420	<tr><td><code>abs(Expr)</code> </td><td>Absolute value </td></tr>
	421	<tr><td>Expr <code>//</code> Expr</td><td>Truncated integer division </td></tr>
	422	<tr><td>Expr div Expr</td><td>Floored integer division </td></tr>
386	423	</table>
387	424	</blockquote>
388	425

392	429	<code>(<<)/2</code>, <code>lsb/1</code>, <code>msb/1</code>, <code>popcount/1</code>
393	430	and <code>(xor)/2</code> are also supported.
394	431
395		<p><h3 id="sec:clpfd-integer-arith"><a name="sec:A.8.3"><span class="sec-nr">A.8.3</span> <span class="sec-title">Declarative
	432	<p><h3 id="sec:clpfd-integer-arith"><a id="sec:A.8.3"><span class="sec-nr">A.8.3</span> <span class="sec-title">Declarative
396	433	integer arithmetic</span></a></h3>
397	434
398		<p><a name="sec:clpfd-integer-arith"></a>
399
400		<p>The <i>arithmetic constraints</i> (<a class="sec" href="clpfd.html">section
	435	<p><a id="sec:clpfd-integer-arith"></a>
	436
	437	<p>The <i>arithmetic constraints</i> (<a class="sec" href="clpfd.html#sec:A.8.2">section
401	438	A.8.2</a>) <a class="pred" href="clpfd.html##=/2">#=/2</a>, <a class="pred" href="clpfd.html##>/2">#>/2</a>
402	439	etc. are meant to be used <i>instead</i> of the primitives <code>(is)/2</code>,
403	440	<code>(=:=)/2</code>, <code>(>)/2</code> etc. over integers. Almost

449	486
450	487	<p>For supported expressions, CLP(FD) constraints are drop-in
451	488	replacements of these low-level arithmetic predicates, often yielding
452		more general programs. See <code>n_factorial/2</code> (<a class="sec" href="clpfd.html">section
	489	more general programs. See <code>n_factorial/2</code> (<a class="sec" href="clpfd.html#sec:A.8.4">section
453	490	A.8.4</a>) for an example.
454	491
455	492	<p>This library uses <a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>

485	522	primitives by providing declarative alternatives that are meant to be
486	523	used instead.
487	524
488		<p><h3 id="sec:clpfd-factorial"><a name="sec:A.8.4"><span class="sec-nr">A.8.4</span> <span class="sec-title">Example:
	525	<p><h3 id="sec:clpfd-factorial"><a id="sec:A.8.4"><span class="sec-nr">A.8.4</span> <span class="sec-title">Example:
489	526	Factorial relation</span></a></h3>
490	527
491		<p><a name="sec:clpfd-factorial"></a>
	528	<p><a id="sec:clpfd-factorial"></a>
492	529
493	530	<p>We illustrate the benefit of using <a class="pred" href="clpfd.html##=/2">#=/2</a>
494	531	for more generality with a simple example.

550	587	freeing us from <i>all</i> procedural phenomena. For example, the two
551	588	programs do not even have the same <i>termination properties</i> in all
552	589	cases. Instead, the primary benefit of CLP(FD) constraints is that they
553		allow you to try different execution orders and apply https://www.metalevel.at/prolog/debugging<b>declarative
554		debugging</b> techniques <i>at all</i>! Reordering goals (and clauses)
555		can significantly impact the performance of Prolog programs, and you are
556		free to try different variants if you use declarative approaches.
557		Moreover, since all CLP(FD) constraints <i>always terminate</i>, placing
558		them earlier can at most <i>improve</i>, never worsen, the termination
559		properties of your programs. An additional benefit of CLP(FD)
560		constraints is that they eliminate the complexity of introducing <code>(is)/2</code>
	590	allow you to try different execution orders and apply <a class="url" href="https://www.metalevel.at/prolog/debugging"><b>declarative
	591	debugging</b></a> techniques <i>at all</i>! Reordering goals (and
	592	clauses) can significantly impact the performance of Prolog programs,
	593	and you are free to try different variants if you use declarative
	594	approaches. Moreover, since all CLP(FD) constraints <i>always terminate</i>,
	595	placing them earlier can at most <i>improve</i>, never worsen, the
	596	termination properties of your programs. An additional benefit of
	597	CLP(FD) constraints is that they eliminate the complexity of introducing <code>(is)/2</code>
561	598	and <code>(=:=)/2</code> to beginners, since <i>both</i> predicates are
562	599	subsumed by <a class="pred" href="clpfd.html##=/2">#=/2</a> when
563	600	reasoning over integers.

571	608	the symbolic outcome (<code><</code>, <code>=</code>, <code>></code>)
572	609	of 0 compared to N.
573	610
574		<p><h3 id="sec:clpfd-combinatorial"><a name="sec:A.8.5"><span class="sec-nr">A.8.5</span> <span class="sec-title">Combinatorial
	611	<p><h3 id="sec:clpfd-combinatorial"><a id="sec:A.8.5"><span class="sec-nr">A.8.5</span> <span class="sec-title">Combinatorial
575	612	constraints</span></a></h3>
576	613
577		<p><a name="sec:clpfd-combinatorial"></a>
	614	<p><a id="sec:clpfd-combinatorial"></a>
578	615
579	616	<p>In addition to subsuming and replacing low-level arithmetic
580	617	predicates, CLP(FD) constraints are often used to solve combinatorial

586	623	and <a class="pred" href="clpfd.html#automaton/8">automaton/8</a>, which
587	624	are useful in more specialized applications.
588	625
589		<p><h3 id="sec:clpfd-domains"><a name="sec:A.8.6"><span class="sec-nr">A.8.6</span> <span class="sec-title">Domains</span></a></h3>
590
591		<p><a name="sec:clpfd-domains"></a>
	626	<p><h3 id="sec:clpfd-domains"><a id="sec:A.8.6"><span class="sec-nr">A.8.6</span> <span class="sec-title">Domains</span></a></h3>
	627
	628	<p><a id="sec:clpfd-domains"></a>
592	629
593	630	<p>Each CLP(FD) variable has an associated set of admissible integers,
594	631	which we call the variable's <b>domain</b>. Initially, the domain of

606	643	<p>Domains are taken into account when further constraints are stated,
607	644	and by enumeration predicates like <a class="pred" href="clpfd.html#labeling/2">labeling/2</a>.
608	645
609		<p><h3 id="sec:clpfd-sudoku"><a name="sec:A.8.7"><span class="sec-nr">A.8.7</span> <span class="sec-title">Example:
	646	<p><h3 id="sec:clpfd-sudoku"><a id="sec:A.8.7"><span class="sec-nr">A.8.7</span> <span class="sec-title">Example:
610	647	Sudoku</span></a></h3>
611	648
612		<p><a name="sec:clpfd-sudoku"></a>
	649	<p><a id="sec:clpfd-sudoku"></a>
613	650
614	651	<p>As another example, consider <i>Sudoku</i>: It is a popular puzzle
615	652	over integers that can be easily solved with CLP(FD) constraints.

661	698	<p>In this concrete case, the constraint solver is strong enough to find
662	699	the unique solution without any search.
663	700
664		<p><h3 id="sec:clpfd-residual-goals"><a name="sec:A.8.8"><span class="sec-nr">A.8.8</span> <span class="sec-title">Residual
	701	<p><h3 id="sec:clpfd-residual-goals"><a id="sec:A.8.8"><span class="sec-nr">A.8.8</span> <span class="sec-title">Residual
665	702	goals</span></a></h3>
666	703
667		<p><a name="sec:clpfd-residual-goals"></a>
	704	<p><a id="sec:clpfd-residual-goals"></a>
668	705
669	706	<p>Here is an example session with a few queries and their answers:
670	707

717	754	which we can inspect a variable's current domain. These predicates can
718	755	be useful if you want to implement your own labeling strategies.
719	756
720		<p><h3 id="sec:clpfd-search"><a name="sec:A.8.9"><span class="sec-nr">A.8.9</span> <span class="sec-title">Core
	757	<p><h3 id="sec:clpfd-search"><a id="sec:A.8.9"><span class="sec-nr">A.8.9</span> <span class="sec-title">Core
721	758	relations and search</span></a></h3>
722	759
723		<p><a name="sec:clpfd-search"></a>
	760	<p><a id="sec:clpfd-search"></a>
724	761
725	762	<p>Using CLP(FD) constraints to solve combinatorial tasks typically
726	763	consists of two phases:

797	834	general though, it is necessary to label all variables to obtain ground
798	835	solutions.
799	836
800		<p><h3 id="sec:clpfd-n-queens"><a name="sec:A.8.10"><span class="sec-nr">A.8.10</span> <span class="sec-title">Example:
	837	<p><h3 id="sec:clpfd-n-queens"><a id="sec:A.8.10"><span class="sec-nr">A.8.10</span> <span class="sec-title">Example:
801	838	Eight queens puzzle</span></a></h3>
802	839
803		<p><a name="sec:clpfd-n-queens"></a>
	840	<p><a id="sec:clpfd-n-queens"></a>
804	841
805	842	<p>We illustrate the concepts of the preceding sections by means of the
806	843	so-called <i>eight queens puzzle</i>. The task is to place 8 queens on

876	913	<p>Experimenting with different search strategies is easy because we
877	914	have separated the core relation from the actual search.
878	915
879		<p><h3 id="sec:clpfd-optimisation"><a name="sec:A.8.11"><span class="sec-nr">A.8.11</span> <span class="sec-title">Optimisation</span></a></h3>
880
881		<p><a name="sec:clpfd-optimisation"></a>
	916	<p><h3 id="sec:clpfd-optimisation"><a id="sec:A.8.11"><span class="sec-nr">A.8.11</span> <span class="sec-title">Optimisation</span></a></h3>
	917
	918	<p><a id="sec:clpfd-optimisation"></a>
882	919
883	920	<p>We can use <a class="pred" href="clpfd.html#labeling/2">labeling/2</a>
884	921	to minimize or maximize the value of a CLP(FD) expression, and generate

897	934	optimal solution. However, it is often very valuable to see alternative
898	935	solutions that are <i>also</i> optimal, so that we can choose among
899	936	optimal solutions by other criteria. For the sake of
900		https://www.metalevel.at/prolog/purity<b>purity</b> and completeness, we
901		recommend to avoid <code>once/1</code> and other constructs that lead to
902		impurities in CLP(FD) programs.
	937	<a class="url" href="https://www.metalevel.at/prolog/purity"><b>purity</b></a>
	938	and completeness, we recommend to avoid <code>once/1</code> and other
	939	constructs that lead to impurities in CLP(FD) programs.
903	940
904	941	<p>Related to optimisation with CLP(FD) constraints are
905		http://eu.swi-prolog.org/man/simplex.html<code>library(simplex)</code>
	942	<a class="url" href="http://eu.swi-prolog.org/man/simplex.html"><code>library(simplex)</code></a>
906	943	and CLP(Q) which reason about <i>linear</i> constraints over rational
907	944	numbers.
908	945
909		<p><h3 id="sec:clpfd-reification"><a name="sec:A.8.12"><span class="sec-nr">A.8.12</span> <span class="sec-title">Reification</span></a></h3>
910
911		<p><a name="sec:clpfd-reification"></a>
	946	<p><h3 id="sec:clpfd-reification"><a id="sec:A.8.12"><span class="sec-nr">A.8.12</span> <span class="sec-title">Reification</span></a></h3>
	947
	948	<p><a id="sec:clpfd-reification"></a>
912	949
913	950	<p>The constraints <a class="pred" href="clpfd.html#in/2">in/2</a>, <a class="pred" href="clpfd.html##=/2">#=/2</a>, <a class="pred" href="clpfd.html##\=/2">#\=/2</a>, <a class="pred" href="clpfd.html##</2">#</2</a>, <a class="pred" href="clpfd.html##>/2">#>/2</a>, <a class="pred" href="clpfd.html##=</2">#=</2</a>,
914	951	and <a class="pred" href="clpfd.html##>=/2">#>=/2</a> can be

916	953	values represented by the integers 0 and 1. Let P and Q denote reifiable
917	954	constraints or Boolean variables, then:
918	955	<blockquote>
919		<table border="2" frame="box" rules="groups">
920		<tr valign="top"><td><code>#\</code> Q</td><td>True iff Q is false </td></tr>
921		<tr valign="top"><td>P <code>#\/</code> Q</td><td>True iff either P or Q </td></tr>
922		<tr valign="top"><td>P <code>#/\</code> Q</td><td>True iff both P and Q </td></tr>
923		<tr valign="top"><td>P <code>#\</code> Q</td><td>True iff either P or Q,
924		but not both </td></tr>
925		<tr valign="top"><td>P <code>#<==></code> Q</td><td>True iff P and
926		Q are equivalent </td></tr>
927		<tr valign="top"><td>P <code>#==></code> Q</td><td>True iff P implies
928		Q </td></tr>
929		<tr valign="top"><td>P <code>#<==</code> Q</td><td>True iff Q implies
930		P </td></tr>
	956	<table class="latex frame-box">
	957	<tr><td><code>#\</code> Q</td><td>True iff Q is false </td></tr>
	958	<tr><td>P <code>#\/</code> Q</td><td>True iff either P or Q </td></tr>
	959	<tr><td>P <code>#/\</code> Q</td><td>True iff both P and Q </td></tr>
	960	<tr><td>P <code>#\</code> Q</td><td>True iff either P or Q, but not both </td></tr>
	961	<tr><td>P <code>#<==></code> Q</td><td>True iff P and Q are
	962	equivalent </td></tr>
	963	<tr><td>P <code>#==></code> Q</td><td>True iff P implies Q </td></tr>
	964	<tr><td>P <code>#<==</code> Q</td><td>True iff Q implies P </td></tr>
931	965	</table>
932	966	</blockquote>
933	967

935	969
936	970	<p>When reasoning over Boolean variables, also consider using CLP(B)
937	971	constraints as provided by
938		http://eu.swi-prolog.org/man/clpb.html<code>library(clpb)</code>.
939
940		<p><h3 id="sec:clpfd-monotonicity"><a name="sec:A.8.13"><span class="sec-nr">A.8.13</span> <span class="sec-title">Enabling
	972	<a class="url" href="http://eu.swi-prolog.org/man/clpb.html"><code>library(clpb)</code></a>.
	973
	974	<p><h3 id="sec:clpfd-monotonicity"><a id="sec:A.8.13"><span class="sec-nr">A.8.13</span> <span class="sec-title">Enabling
941	975	monotonic CLP(FD)</span></a></h3>
942	976
943		<p><a name="sec:clpfd-monotonicity"></a>
	977	<p><a id="sec:clpfd-monotonicity"></a>
944	978
945	979	<p>In the default execution mode, CLP(FD) constraints still exhibit some
946	980	non-relational properties. For example, <i>adding</i> constraints can

978	1012	<p>The wrapper can be omitted for variables that are already constrained
979	1013	to integers.
980	1014
981		<p><h3 id="sec:clpfd-custom-constraints"><a name="sec:A.8.14"><span class="sec-nr">A.8.14</span> <span class="sec-title">Custom
	1015	<p><h3 id="sec:clpfd-custom-constraints"><a id="sec:A.8.14"><span class="sec-nr">A.8.14</span> <span class="sec-title">Custom
982	1016	constraints</span></a></h3>
983	1017
984		<p><a name="sec:clpfd-custom-constraints"></a>
	1018	<p><a id="sec:clpfd-custom-constraints"></a>
985	1019
986	1020	<p>We can define custom constraints. The mechanism to do this is not yet
987	1021	finalised, and we welcome suggestions and descriptions of use cases that

1031	1065	X in inf..sup.
1032	1066	</pre>
1033	1067
1034		<p><h3 id="sec:clpfd-applications"><a name="sec:A.8.15"><span class="sec-nr">A.8.15</span> <span class="sec-title">Applications</span></a></h3>
1035
1036		<p><a name="sec:clpfd-applications"></a>
	1068	<p><h3 id="sec:clpfd-applications"><a id="sec:A.8.15"><span class="sec-nr">A.8.15</span> <span class="sec-title">Applications</span></a></h3>
	1069
	1070	<p><a id="sec:clpfd-applications"></a>
1037	1071
1038	1072	<p>CLP(FD) applications that we find particularly impressive and worth
1039	1073	studying include:

1042	1076	<ul class="latex">
1043	1077	<li>Michael Hendricks uses CLP(FD) constraints for flexible reasoning
1044	1078	about <i>dates</i> and <i>times</i> in the
1045		http://www.swi-prolog.org/pack/list?p=julian<code>julian</code> package.
	1079	<a class="url" href="http://www.swi-prolog.org/pack/list?p=julian"><code>julian</code></a>
	1080	package.
1046	1081	<li>Julien Cumin uses CLP(FD) constraints for integer arithmetic in
1047		https://github.com/JCumin/Brachylog<code>Brachylog</code>.
	1082	<a class="url" href="https://github.com/JCumin/Brachylog"><code>Brachylog</code></a>.
1048	1083	</ul>
1049	1084
1050		<p><h3 id="sec:clpfd-acknowledgments"><a name="sec:A.8.16"><span class="sec-nr">A.8.16</span> <span class="sec-title">Acknowledgments</span></a></h3>
1051
1052		<p><a name="sec:clpfd-acknowledgments"></a>
1053
1054		<p>This library gives you a glimpse of what https://sicstus.sics.se/<b>SICStus
1055		Prolog</b> can do. The API is intentionally mostly compatible with that
1056		of SICStus Prolog, so that you can easily switch to a much more
1057		feature-rich and much faster CLP(FD) system when you need it. I thank
1058		https://www.sics.se/ matsc/ Mats Carlsson , the designer and main
1059		implementor of SICStus Prolog, for his elegant example. I first
1060		encountered his system as part of the excellent
1061		http://www.complang.tuwien.ac.at/ulrich/gupu/<b>GUPU</b> teaching
1062		environment by http://www.complang.tuwien.ac.at/ulrich/Ulrich Neumerkel
1063		. Ulrich was also the first and most determined tester of the present
1064		system, filing hundreds of comments and suggestions for improvement.
1065		https://people.cs.kuleuven.be/ tom.schrijvers/ Tom Schrijvers has
1066		contributed several constraint libraries to SWI-Prolog, and I learned a
1067		lot from his coding style and implementation examples.
1068		https://people.cs.kuleuven.be/ bart.demoen/ Bart Demoen was a
1069		driving force behind the implementation of attributed variables in
1070		SWI-Prolog, and this library could not even have started without his
1071		prior work and contributions. Thank you all!
1072
1073		<p><h3 id="sec:clpfd-predicate-index"><a name="sec:A.8.17"><span class="sec-nr">A.8.17</span> <span class="sec-title">CLP(FD)
	1085	<p><h3 id="sec:clpfd-acknowledgments"><a id="sec:A.8.16"><span class="sec-nr">A.8.16</span> <span class="sec-title">Acknowledgments</span></a></h3>
	1086
	1087	<p><a id="sec:clpfd-acknowledgments"></a>
	1088
	1089	<p>This library gives you a glimpse of what <a class="url" href="https://sicstus.sics.se/"><b>SICStus
	1090	Prolog</b></a> can do. The API is intentionally mostly compatible with
	1091	that of SICStus Prolog, so that you can easily switch to a much more
	1092	feature-rich and much faster CLP(FD) system when you need it. I thank <a class="url" href="https://www.sics.se/~matsc/">Mats
	1093	Carlsson</a>, the designer and main implementor of SICStus Prolog, for
	1094	his elegant example. I first encountered his system as part of the
	1095	excellent
	1096	<a class="url" href="http://www.complang.tuwien.ac.at/ulrich/gupu/"><b>GUPU</b></a>
	1097	teaching environment by <a class="url" href="http://www.complang.tuwien.ac.at/ulrich/">Ulrich
	1098	Neumerkel</a>. Ulrich was also the first and most determined tester of
	1099	the present system, filing hundreds of comments and suggestions for
	1100	improvement. <a class="url" href="https://people.cs.kuleuven.be/~tom.schrijvers/">Tom
	1101	Schrijvers</a> has contributed several constraint libraries to
	1102	SWI-Prolog, and I learned a lot from his coding style and implementation
	1103	examples. <a class="url" href="https://people.cs.kuleuven.be/~bart.demoen/">Bart
	1104	Demoen</a> was a driving force behind the implementation of attributed
	1105	variables in SWI-Prolog, and this library could not even have started
	1106	without his prior work and contributions. Thank you all!
	1107
	1108	<p><h3 id="sec:clpfd-predicate-index"><a id="sec:A.8.17"><span class="sec-nr">A.8.17</span> <span class="sec-title">CLP(FD)
1074	1109	predicate index</span></a></h3>
1075	1110
1076		<p><a name="sec:clpfd-predicate-index"></a>
	1111	<p><a id="sec:clpfd-predicate-index"></a>
1077	1112
1078	1113	<p>In the following, each CLP(FD) predicate is described in more detail.
1079	1114

1081	1116
1082	1117	<p><a class="url" href="http://eu.swi-prolog.org/man/clpfd.html">http://eu.swi-prolog.org/man/clpfd.html</a>
1083	1118
1084		<p><h4 id="sec:clpfd-arithmetic"><a name="sec:A.8.17.1"><span class="sec-nr">A.8.17.1</span> <span class="sec-title">Arithmetic
	1119	<p><h4 id="sec:clpfd-arithmetic"><a id="sec:A.8.17.1"><span class="sec-nr">A.8.17.1</span> <span class="sec-title">Arithmetic
1085	1120	constraints</span></a></h4>
1086	1121
1087		<p><a name="sec:clpfd-arithmetic"></a>
	1122	<p><a id="sec:clpfd-arithmetic"></a>
1088	1123
1089	1124	<p><i>Arithmetic</i> constraints are the most basic use of CLP(FD).
1090	1125	Every time you use <code>(is)/2</code> or one of the low-level
1091	1126	arithmetic comparisons (<code>(<)/2</code>, <code>(>)/2</code>
1092	1127	etc.) over integers, consider using CLP(FD) constraints <i>instead</i>.
1093	1128	This can at most <i>increase</i> the generality of your programs. See
1094		declarative integer arithmetic (<a class="sec" href="clpfd.html">section
	1129	declarative integer arithmetic (<a class="sec" href="clpfd.html#sec:A.8.3">section
1095	1130	A.8.3</a>).
1096	1131
1097	1132	<dl class="latex">
1098		<dt class="pubdef"><a name="#=/2"><var>?X</var> <strong>#=</strong> <var>?Y</var></a></dt>
	1133	<dt class="pubdef"><a id="#=/2"><var>?X</var> <strong>#=</strong> <var>?Y</var></a></dt>
1099	1134	<dd class="defbody">
1100	1135	The arithmetic expression <var>X</var> equals <var>Y</var>. This is the
1101		most important arithmetic constraint (<a class="sec" href="clpfd.html">section
	1136	most important arithmetic constraint (<a class="sec" href="clpfd.html#sec:A.8.2">section
1102	1137	A.8.2</a>), subsuming and replacing both <code>(is)/2</code> <i>and</i> <code>(=:=)/2</code>
1103		over integers. See declarative integer arithmetic (<a class="sec" href="clpfd.html">section
	1138	over integers. See declarative integer arithmetic (<a class="sec" href="clpfd.html#sec:A.8.3">section
1104	1139	A.8.3</a>).</dd>
1105		<dt class="pubdef"><a name="#\=/2"><var>?X</var> <strong>#\=</strong> <var>?Y</var></a></dt>
	1140	<dt class="pubdef"><a id="#\=/2"><var>?X</var> <strong>#\=</strong> <var>?Y</var></a></dt>
1106	1141	<dd class="defbody">
1107	1142	The arithmetic expressions <var>X</var> and <var>Y</var> evaluate to
1108	1143	distinct integers. When reasoning over integers, replace <code>(=\=)/2</code>
1109	1144	by <a class="pred" href="clpfd.html##\=/2">#\=/2</a> to obtain more
1110		general relations. See declarative integer arithmetic (<a class="sec" href="clpfd.html">section
	1145	general relations. See declarative integer arithmetic (<a class="sec" href="clpfd.html#sec:A.8.3">section
1111	1146	A.8.3</a>).</dd>
1112		<dt class="pubdef"><a name="#>=/2"><var>?X</var> <strong>#>=</strong> <var>?Y</var></a></dt>
	1147	<dt class="pubdef"><a id="#>=/2"><var>?X</var> <strong>#>=</strong> <var>?Y</var></a></dt>
1113	1148	<dd class="defbody">
1114	1149	Same as <var>Y</var> <code>#=<</code> <var>X</var>. When reasoning
1115	1150	over integers, replace <code>(>=)/2</code> by
1116	1151	<a class="pred" href="clpfd.html##>=/2">#>=/2</a> to obtain more
1117		general relations. See declarative integer arithmetic (<a class="sec" href="clpfd.html">section
	1152	general relations. See declarative integer arithmetic (<a class="sec" href="clpfd.html#sec:A.8.3">section
1118	1153	A.8.3</a>).</dd>
1119		<dt class="pubdef"><a name="#=</2"><var>?X</var> <strong>#=<</strong> <var>?Y</var></a></dt>
	1154	<dt class="pubdef"><a id="#=</2"><var>?X</var> <strong>#=<</strong> <var>?Y</var></a></dt>
1120	1155	<dd class="defbody">
1121	1156	The arithmetic expression <var>X</var> is less than or equal to <var>Y</var>.
1122	1157	When reasoning over integers, replace <code>(=<)/2</code> by <a class="pred" href="clpfd.html##=</2">#=</2</a>
1123		to obtain more general relations. See declarative integer arithmetic (<a class="sec" href="clpfd.html">section
	1158	to obtain more general relations. See declarative integer arithmetic (<a class="sec" href="clpfd.html#sec:A.8.3">section
1124	1159	A.8.3</a>).</dd>
1125		<dt class="pubdef"><a name="#>/2"><var>?X</var> <strong>#></strong> <var>?Y</var></a></dt>
	1160	<dt class="pubdef"><a id="#>/2"><var>?X</var> <strong>#></strong> <var>?Y</var></a></dt>
1126	1161	<dd class="defbody">
1127	1162	Same as <var>Y</var> <code>#<</code> <var>X</var>. When reasoning
1128	1163	over integers, replace <code>(>)/2</code> by
1129	1164	<a class="pred" href="clpfd.html##>/2">#>/2</a> to obtain more
1130		general relations See declarative integer arithmetic (<a class="sec" href="clpfd.html">section
	1165	general relations See declarative integer arithmetic (<a class="sec" href="clpfd.html#sec:A.8.3">section
1131	1166	A.8.3</a>).</dd>
1132		<dt class="pubdef"><a name="#</2"><var>?X</var> <strong>#<</strong> <var>?Y</var></a></dt>
	1167	<dt class="pubdef"><a id="#</2"><var>?X</var> <strong>#<</strong> <var>?Y</var></a></dt>
1133	1168	<dd class="defbody">
1134	1169	The arithmetic expression <var>X</var> is less than <var>Y</var>. When
1135	1170	reasoning over integers, replace <code>(<)/2</code> by <a class="pred" href="clpfd.html##</2">#</2</a>
1136		to obtain more general relations. See declarative integer arithmetic (<a class="sec" href="clpfd.html">section
	1171	to obtain more general relations. See declarative integer arithmetic (<a class="sec" href="clpfd.html#sec:A.8.3">section
1137	1172	A.8.3</a>).
1138	1173
1139	1174	<p>In addition to its regular use in tasks that require it, this

1154	1189	<p></dd>
1155	1190	</dl>
1156	1191
1157		<p><h4 id="sec:clpfd-membership"><a name="sec:A.8.17.2"><span class="sec-nr">A.8.17.2</span> <span class="sec-title">Membership
	1192	<p><h4 id="sec:clpfd-membership"><a id="sec:A.8.17.2"><span class="sec-nr">A.8.17.2</span> <span class="sec-title">Membership
1158	1193	constraints</span></a></h4>
1159	1194
1160		<p><a name="sec:clpfd-membership"></a>
	1195	<p><a id="sec:clpfd-membership"></a>
1161	1196
1162	1197	<p>If you are using CLP(FD) to model and solve combinatorial tasks, then
1163	1198	you typically need to specify the admissible domains of variables. The <i>membership

1165	1200	are useful in such cases.
1166	1201
1167	1202	<dl class="latex">
1168		<dt class="pubdef"><a name="in/2"><var>?Var</var> <strong>in</strong> <var>+Domain</var></a></dt>
	1203	<dt class="pubdef"><a id="in/2"><var>?Var</var> <strong>in</strong> <var>+Domain</var></a></dt>
1169	1204	<dd class="defbody">
1170	1205	<var>Var</var> is an element of <var>Domain</var>. <var>Domain</var> is
1171	1206	one of:

1189	1224	</dl>
1190	1225
1191	1226	</dd>
1192		<dt class="pubdef"><a name="ins/2"><var>+Vars</var> <strong>ins</strong> <var>+Domain</var></a></dt>
	1227	<dt class="pubdef"><a id="ins/2"><var>+Vars</var> <strong>ins</strong> <var>+Domain</var></a></dt>
1193	1228	<dd class="defbody">
1194	1229	The variables in the list <var>Vars</var> are elements of <var>Domain</var>.
1195	1230	See <a class="pred" href="clpfd.html#in/2">in/2</a> for the syntax of <var>Domain</var>.
1196	1231	</dd>
1197	1232	</dl>
1198	1233
1199		<p><h4 id="sec:clpfd-enumeration"><a name="sec:A.8.17.3"><span class="sec-nr">A.8.17.3</span> <span class="sec-title">Enumeration
	1234	<p><h4 id="sec:clpfd-enumeration"><a id="sec:A.8.17.3"><span class="sec-nr">A.8.17.3</span> <span class="sec-title">Enumeration
1200	1235	predicates</span></a></h4>
1201	1236
1202		<p><a name="sec:clpfd-enumeration"></a>
	1237	<p><a id="sec:clpfd-enumeration"></a>
1203	1238
1204	1239	<p>When modeling combinatorial tasks, the actual search for solutions is
1205	1240	typically performed by <i>enumeration predicates</i> like <a class="pred" href="clpfd.html#labeling/2">labeling/2</a>.

1207	1242	information.
1208	1243
1209	1244	<dl class="latex">
1210		<dt class="pubdef"><a name="indomain/1"><strong>indomain</strong>(<var>?Var</var>)</a></dt>
	1245	<dt class="pubdef"><a id="indomain/1"><strong>indomain</strong>(<var>?Var</var>)</a></dt>
1211	1246	<dd class="defbody">
1212	1247	Bind <var>Var</var> to all feasible values of its domain on
1213	1248	backtracking. The domain of <var>Var</var> must be finite.</dd>
1214		<dt class="pubdef"><a name="label/1"><strong>label</strong>(<var>+Vars</var>)</a></dt>
	1249	<dt class="pubdef"><a id="label/1"><strong>label</strong>(<var>+Vars</var>)</a></dt>
1215	1250	<dd class="defbody">
1216	1251	Equivalent to <code>labeling([], Vars)</code>. See <a class="pred" href="clpfd.html#labeling/2">labeling/2</a>.</dd>
1217		<dt class="pubdef"><a name="labeling/2"><strong>labeling</strong>(<var>+Options,
	1252	<dt class="pubdef"><a id="labeling/2"><strong>labeling</strong>(<var>+Options,
1218	1253	+Vars</var>)</a></dt>
1219	1254	<dd class="defbody">
1220	1255	Assign a value to each variable in <var>Vars</var>. Labeling means

1321	1356	</pre>
1322	1357
1323	1358	<p>Labeling is always complete, always terminates, and yields no
1324		redundant solutions. See core relations and search (<a class="sec" href="clpfd.html">section
	1359	redundant solutions. See core relations and search (<a class="sec" href="clpfd.html#sec:A.8.9">section
1325	1360	A.8.9</a>) for usage advice.
1326	1361	</dd>
1327	1362	</dl>
1328	1363
1329		<p><h4 id="sec:clpfd-global"><a name="sec:A.8.17.4"><span class="sec-nr">A.8.17.4</span> <span class="sec-title">Global
	1364	<p><h4 id="sec:clpfd-global"><a id="sec:A.8.17.4"><span class="sec-nr">A.8.17.4</span> <span class="sec-title">Global
1330	1365	constraints</span></a></h4>
1331	1366
1332		<p><a name="sec:clpfd-global"></a>
	1367	<p><a id="sec:clpfd-global"></a>
1333	1368
1334	1369	<p>A <i>global constraint</i> expresses a relation that involves many
1335	1370	variables at once. The most frequently used global constraints of this

1338	1373	and <a class="pred" href="clpfd.html#cumulative/2">cumulative/2</a>.
1339	1374
1340	1375	<dl class="latex">
1341		<dt class="pubdef"><a name="all_distinct/1"><strong>all_distinct</strong>(<var>+Vars</var>)</a></dt>
	1376	<dt class="pubdef"><a id="all_distinct/1"><strong>all_distinct</strong>(<var>+Vars</var>)</a></dt>
1342	1377	<dd class="defbody">
1343	1378	True iff <var>Vars</var> are pairwise distinct. For example, <a class="pred" href="clpfd.html#all_distinct/1">all_distinct/1</a>
1344	1379	can detect that not all variables can assume distinct values given the

1352	1387	</pre>
1353	1388
1354	1389	</dd>
1355		<dt class="pubdef"><a name="all_different/1"><strong>all_different</strong>(<var>+Vars</var>)</a></dt>
	1390	<dt class="pubdef"><a id="all_different/1"><strong>all_different</strong>(<var>+Vars</var>)</a></dt>
1356	1391	<dd class="defbody">
1357	1392	Like <a class="pred" href="clpfd.html#all_distinct/1">all_distinct/1</a>,
1358	1393	but with weaker propagation. Consider using
1359	1394	<a class="pred" href="clpfd.html#all_distinct/1">all_distinct/1</a>
1360	1395	instead, since <a class="pred" href="clpfd.html#all_distinct/1">all_distinct/1</a>
1361	1396	is typically acceptably efficient and propagates much more strongly.</dd>
1362		<dt class="pubdef"><a name="sum/3"><strong>sum</strong>(<var>+Vars,
1363		+Rel, ?Expr</var>)</a></dt>
	1397	<dt class="pubdef"><a id="sum/3"><strong>sum</strong>(<var>+Vars, +Rel,
	1398	?Expr</var>)</a></dt>
1364	1399	<dd class="defbody">
1365	1400	The sum of elements of the list <var>Vars</var> is in relation <var>Rel</var>
1366	1401	to <var>Expr</var>.

1376	1411	</pre>
1377	1412
1378	1413	</dd>
1379		<dt class="pubdef"><a name="scalar_product/4"><strong>scalar_product</strong>(<var>+Cs,
	1414	<dt class="pubdef"><a id="scalar_product/4"><strong>scalar_product</strong>(<var>+Cs,
1380	1415	+Vs, +Rel, ?Expr</var>)</a></dt>
1381	1416	<dd class="defbody">
1382	1417	True iff the scalar product of <var>Cs</var> and <var>Vs</var> is in

1385	1420	variables and integers.
1386	1421	<var>Rel</var> is #=, #<code>\</code>=, #<var><</var>, #<var>></var>, <code>#=<</code>
1387	1422	or #<var>></var>=.</dd>
1388		<dt class="pubdef"><a name="lex_chain/1"><strong>lex_chain</strong>(<var>+Lists</var>)</a></dt>
	1423	<dt class="pubdef"><a id="lex_chain/1"><strong>lex_chain</strong>(<var>+Lists</var>)</a></dt>
1389	1424	<dd class="defbody">
1390	1425	<var>Lists</var> are lexicographically non-decreasing.</dd>
1391		<dt class="pubdef"><a name="tuples_in/2"><strong>tuples_in</strong>(<var>+Tuples,
	1426	<dt class="pubdef"><a id="tuples_in/2"><strong>tuples_in</strong>(<var>+Tuples,
1392	1427	+Relation</var>)</a></dt>
1393	1428	<dd class="defbody">
1394	1429	True iff all <var>Tuples</var> are elements of <var>Relation</var>. Each

1434	1469	</pre>
1435	1470
1436	1471	</dd>
1437		<dt class="pubdef"><a name="serialized/2"><strong>serialized</strong>(<var>+Starts,
	1472	<dt class="pubdef"><a id="serialized/2"><strong>serialized</strong>(<var>+Starts,
1438	1473	+Durations</var>)</a></dt>
1439	1474	<dd class="defbody">
1440	1475	Describes a set of non-overlapping tasks.

1464	1499	</dl>
1465	1500
1466	1501	</dd>
1467		<dt class="pubdef"><a name="element/3"><strong>element</strong>(<var>?N,
	1502	<dt class="pubdef"><a id="element/3"><strong>element</strong>(<var>?N,
1468	1503	+Vs, ?V</var>)</a></dt>
1469	1504	<dd class="defbody">
1470	1505	The <var>N</var>-th element of the list of finite domain variables <var>Vs</var>
1471	1506	is <var>V</var>. Analogous to <a class="pred" href="lists.html#nth1/3">nth1/3</a>.</dd>
1472		<dt class="pubdef"><a name="global_cardinality/2"><strong>global_cardinality</strong>(<var>+Vs,
	1507	<dt class="pubdef"><a id="global_cardinality/2"><strong>global_cardinality</strong>(<var>+Vs,
1473	1508	+Pairs</var>)</a></dt>
1474	1509	<dd class="defbody">
1475	1510	Global Cardinality constraint. Equivalent to

1485	1520	</pre>
1486	1521
1487	1522	</dd>
1488		<dt class="pubdef"><a name="global_cardinality/3"><strong>global_cardinality</strong>(<var>+Vs,
	1523	<dt class="pubdef"><a id="global_cardinality/3"><strong>global_cardinality</strong>(<var>+Vs,
1489	1524	+Pairs, +Options</var>)</a></dt>
1490	1525	<dd class="defbody">
1491	1526	Global Cardinality constraint. <var>Vs</var> is a list of finite domain

1511	1546	</dl>
1512	1547
1513	1548	</dd>
1514		<dt class="pubdef"><a name="circuit/1"><strong>circuit</strong>(<var>+Vs</var>)</a></dt>
	1549	<dt class="pubdef"><a id="circuit/1"><strong>circuit</strong>(<var>+Vs</var>)</a></dt>
1515	1550	<dd class="defbody">
1516	1551	True iff the list <var>Vs</var> of finite domain variables induces a
1517	1552	Hamiltonian circuit. The k-th element of <var>Vs</var> denotes the

1528	1563	</pre>
1529	1564
1530	1565	</dd>
1531		<dt class="pubdef"><a name="cumulative/1"><strong>cumulative</strong>(<var>+Tasks</var>)</a></dt>
	1566	<dt class="pubdef"><a id="cumulative/1"><strong>cumulative</strong>(<var>+Tasks</var>)</a></dt>
1532	1567	<dd class="defbody">
1533	1568	Equivalent to <code>cumulative(Tasks, [limit(1)])</code>. See <a class="pred" href="clpfd.html#cumulative/2">cumulative/2</a>.</dd>
1534		<dt class="pubdef"><a name="cumulative/2"><strong>cumulative</strong>(<var>+Tasks,
	1569	<dt class="pubdef"><a id="cumulative/2"><strong>cumulative</strong>(<var>+Tasks,
1535	1570	+Options</var>)</a></dt>
1536	1571	<dd class="defbody">
1537	1572	Schedule with a limited resource. <var>Tasks</var> is a list of tasks,

1572	1607	</pre>
1573	1608
1574	1609	</dd>
1575		<dt class="pubdef"><a name="disjoint2/1"><strong>disjoint2</strong>(<var>+Rectangles</var>)</a></dt>
	1610	<dt class="pubdef"><a id="disjoint2/1"><strong>disjoint2</strong>(<var>+Rectangles</var>)</a></dt>
1576	1611	<dd class="defbody">
1577	1612	True iff <var>Rectangles</var> are not overlapping. <var>Rectangles</var>
1578	1613	is a list of terms of the form F(X_i, W_i, Y_i, H_i), where F is any
1579	1614	functor, and the arguments are finite domain variables or integers that
1580	1615	denote, respectively, the X coordinate, width, Y coordinate and height
1581	1616	of each rectangle.</dd>
1582		<dt class="pubdef"><a name="automaton/3"><strong>automaton</strong>(<var>+Vs,
	1617	<dt class="pubdef"><a id="automaton/3"><strong>automaton</strong>(<var>+Vs,
1583	1618	+Nodes, +Arcs</var>)</a></dt>
1584	1619	<dd class="defbody">
1585	1620	Describes a list of finite domain variables with a finite automaton.

1606	1641	</pre>
1607	1642
1608	1643	</dd>
1609		<dt class="pubdef"><a name="automaton/8"><strong>automaton</strong>(<var>+Sequence,
	1644	<dt class="pubdef"><a id="automaton/8"><strong>automaton</strong>(<var>+Sequence,
1610	1645	?Template, +Signature, +Nodes, +Arcs, +Counters, +Initials, ?Finals</var>)</a></dt>
1611	1646	<dd class="defbody">
1612	1647	Describes a list of finite domain variables with a finite automaton.

1678	1713	</pre>
1679	1714
1680	1715	</dd>
1681		<dt class="pubdef"><a name="chain/2"><strong>chain</strong>(<var>+Zs,
	1716	<dt class="pubdef"><a id="chain/2"><strong>chain</strong>(<var>+Zs,
1682	1717	+Relation</var>)</a></dt>
1683	1718	<dd class="defbody">
1684	1719	<var>Zs</var> form a chain with respect to <var>Relation</var>. <var>Zs</var>

1698	1733	<p></dd>
1699	1734	</dl>
1700	1735
1701		<p><h4 id="sec:clpfd-reification-predicates"><a name="sec:A.8.17.5"><span class="sec-nr">A.8.17.5</span> <span class="sec-title">Reification
	1736	<p><h4 id="sec:clpfd-reification-predicates"><a id="sec:A.8.17.5"><span class="sec-nr">A.8.17.5</span> <span class="sec-title">Reification
1702	1737	predicates</span></a></h4>
1703	1738
1704		<p><a name="sec:clpfd-reification-predicates"></a>
	1739	<p><a id="sec:clpfd-reification-predicates"></a>
1705	1740
1706	1741	<p>Many CLP(FD) constraints can be <i>reified</i>. This means that their
1707	1742	truth value is itself turned into a CLP(FD) variable, so that we can
1708	1743	explicitly reason about whether a constraint holds or not. See
1709		reification (<a class="sec" href="clpfd.html">section A.8.12</a>).
	1744	reification (<a class="sec" href="clpfd.html#sec:A.8.12">section A.8.12</a>).
1710	1745
1711	1746	<dl class="latex">
1712		<dt class="pubdef"><a name="#\/1"><strong>#\</strong> <var>+Q</var></a></dt>
1713		<dd class="defbody">
1714		<var>Q</var> does <i>not</i> hold. See reification (<a class="sec" href="clpfd.html">section
	1747	<dt class="pubdef"><a id="#\/1"><strong>#\</strong> <var>+Q</var></a></dt>
	1748	<dd class="defbody">
	1749	<var>Q</var> does <i>not</i> hold. See reification (<a class="sec" href="clpfd.html#sec:A.8.12">section
1715	1750	A.8.12</a>).
1716	1751
1717	1752	<p>For example, to obtain the complement of a domain:

1722	1757	</pre>
1723	1758
1724	1759	</dd>
1725		<dt class="pubdef"><a name="#<==>/2"><var>?P</var> <strong>#<==></strong> <var>?Q</var></a></dt>
1726		<dd class="defbody">
1727		<var>P</var> and <var>Q</var> are equivalent. See reification (<a class="sec" href="clpfd.html">section
	1760	<dt class="pubdef"><a id="#<==>/2"><var>?P</var> <strong>#<==></strong> <var>?Q</var></a></dt>
	1761	<dd class="defbody">
	1762	<var>P</var> and <var>Q</var> are equivalent. See reification (<a class="sec" href="clpfd.html#sec:A.8.12">section
1728	1763	A.8.12</a>).
1729	1764
1730	1765	<p>For example:

1763	1798	</pre>
1764	1799
1765	1800	</dd>
1766		<dt class="pubdef"><a name="#==>/2"><var>?P</var> <strong>#==></strong> <var>?Q</var></a></dt>
1767		<dd class="defbody">
1768		<var>P</var> implies <var>Q</var>. See reification (<a class="sec" href="clpfd.html">section
	1801	<dt class="pubdef"><a id="#==>/2"><var>?P</var> <strong>#==></strong> <var>?Q</var></a></dt>
	1802	<dd class="defbody">
	1803	<var>P</var> implies <var>Q</var>. See reification (<a class="sec" href="clpfd.html#sec:A.8.12">section
1769	1804	A.8.12</a>).</dd>
1770		<dt class="pubdef"><a name="#<==/2"><var>?P</var> <strong>#<==</strong> <var>?Q</var></a></dt>
1771		<dd class="defbody">
1772		<var>Q</var> implies <var>P</var>. See reification (<a class="sec" href="clpfd.html">section
	1805	<dt class="pubdef"><a id="#<==/2"><var>?P</var> <strong>#<==</strong> <var>?Q</var></a></dt>
	1806	<dd class="defbody">
	1807	<var>Q</var> implies <var>P</var>. See reification (<a class="sec" href="clpfd.html#sec:A.8.12">section
1773	1808	A.8.12</a>).</dd>
1774		<dt class="pubdef"><a name="#/\/2"><var>?P</var> <strong>#/\</strong> <var>?Q</var></a></dt>
1775		<dd class="defbody">
1776		<var>P</var> and <var>Q</var> hold. See reification (<a class="sec" href="clpfd.html">section
	1809	<dt class="pubdef"><a id="#/\/2"><var>?P</var> <strong>#/\</strong> <var>?Q</var></a></dt>
	1810	<dd class="defbody">
	1811	<var>P</var> and <var>Q</var> hold. See reification (<a class="sec" href="clpfd.html#sec:A.8.12">section
1777	1812	A.8.12</a>).</dd>
1778		<dt class="pubdef"><a name="#\//2"><var>?P</var> <strong>#\/</strong> <var>?Q</var></a></dt>
1779		<dd class="defbody">
1780		<var>P</var> or <var>Q</var> holds. See reification (<a class="sec" href="clpfd.html">section
	1813	<dt class="pubdef"><a id="#\//2"><var>?P</var> <strong>#\/</strong> <var>?Q</var></a></dt>
	1814	<dd class="defbody">
	1815	<var>P</var> or <var>Q</var> holds. See reification (<a class="sec" href="clpfd.html#sec:A.8.12">section
1781	1816	A.8.12</a>).
1782	1817
1783	1818	<p>For example, the sum of natural numbers below 1000 that are multiples

1793	1828	</pre>
1794	1829
1795	1830	</dd>
1796		<dt class="pubdef"><a name="#\/2"><var>?P</var> <strong>#\</strong> <var>?Q</var></a></dt>
	1831	<dt class="pubdef"><a id="#\/2"><var>?P</var> <strong>#\</strong> <var>?Q</var></a></dt>
1797	1832	<dd class="defbody">
1798	1833	Either <var>P</var> holds or <var>Q</var> holds, but not both. See
1799		reification (<a class="sec" href="clpfd.html">section A.8.12</a>).</dd>
1800		<dt class="pubdef"><a name="zcompare/3"><strong>zcompare</strong>(<var>?Order,
	1834	reification (<a class="sec" href="clpfd.html#sec:A.8.12">section A.8.12</a>).</dd>
	1835	<dt class="pubdef"><a id="zcompare/3"><strong>zcompare</strong>(<var>?Order,
1801	1836	?A, ?B</var>)</a></dt>
1802	1837	<dd class="defbody">
1803	1838	Analogous to <a class="pred" href="compare.html#compare/3">compare/3</a>,

1856	1891	ensures that the respective ordering between N and 0 holds in each case.
1857	1892
1858	1893	<p>The truth value of a comparison can also be reified with (<code>#<==></code>)/2
1859		in combination with one of the <i>arithmetic constraints</i> (<a class="sec" href="clpfd.html">section
1860		A.8.2</a>). See reification (<a class="sec" href="clpfd.html">section
	1894	in combination with one of the <i>arithmetic constraints</i> (<a class="sec" href="clpfd.html#sec:A.8.2">section
	1895	A.8.2</a>). See reification (<a class="sec" href="clpfd.html#sec:A.8.12">section
1861	1896	A.8.12</a>). However, <a class="pred" href="clpfd.html#zcompare/3">zcompare/3</a>
1862	1897	lets you more conveniently distinguish the cases.
1863	1898	</dd>
1864	1899	</dl>
1865	1900
1866		<p><h4 id="sec:clpfd-reflection-predicates"><a name="sec:A.8.17.6"><span class="sec-nr">A.8.17.6</span> <span class="sec-title">Reflection
	1901	<p><h4 id="sec:clpfd-reflection-predicates"><a id="sec:A.8.17.6"><span class="sec-nr">A.8.17.6</span> <span class="sec-title">Reflection
1867	1902	predicates</span></a></h4>
1868	1903
1869		<p><a name="sec:clpfd-reflection-predicates"></a>
	1904	<p><a id="sec:clpfd-reflection-predicates"></a>
1870	1905
1871	1906	<p>Reflection predicates let us obtain, in a well-defined way,
1872	1907	information that is normally internal to this library. In addition to

1877	1912	useful in program analyzers and declarative debuggers.
1878	1913
1879	1914	<dl class="latex">
1880		<dt class="pubdef"><a name="fd_var/1"><strong>fd_var</strong>(<var>+Var</var>)</a></dt>
	1915	<dt class="pubdef"><a id="fd_var/1"><strong>fd_var</strong>(<var>+Var</var>)</a></dt>
1881	1916	<dd class="defbody">
1882	1917	True iff <var>Var</var> is a CLP(FD) variable.</dd>
1883		<dt class="pubdef"><a name="fd_inf/2"><strong>fd_inf</strong>(<var>+Var,
	1918	<dt class="pubdef"><a id="fd_inf/2"><strong>fd_inf</strong>(<var>+Var,
1884	1919	-Inf</var>)</a></dt>
1885	1920	<dd class="defbody">
1886	1921	<var>Inf</var> is the infimum of the current domain of <var>Var</var>.</dd>
1887		<dt class="pubdef"><a name="fd_sup/2"><strong>fd_sup</strong>(<var>+Var,
	1922	<dt class="pubdef"><a id="fd_sup/2"><strong>fd_sup</strong>(<var>+Var,
1888	1923	-Sup</var>)</a></dt>
1889	1924	<dd class="defbody">
1890	1925	<var>Sup</var> is the supremum of the current domain of <var>Var</var>.</dd>
1891		<dt class="pubdef"><a name="fd_size/2"><strong>fd_size</strong>(<var>+Var,
	1926	<dt class="pubdef"><a id="fd_size/2"><strong>fd_size</strong>(<var>+Var,
1892	1927	-Size</var>)</a></dt>
1893	1928	<dd class="defbody">
1894	1929	Reflect the current size of a domain. <var>Size</var> is the number of
1895	1930	elements of the current domain of <var>Var</var>, or the atom <b>sup</b>
1896	1931	if the domain is unbounded.</dd>
1897		<dt class="pubdef"><a name="fd_dom/2"><strong>fd_dom</strong>(<var>+Var,
	1932	<dt class="pubdef"><a id="fd_dom/2"><strong>fd_dom</strong>(<var>+Var,
1898	1933	-Dom</var>)</a></dt>
1899	1934	<dd class="defbody">
1900	1935	<var>Dom</var> is the current domain (see <a class="pred" href="clpfd.html#in/2">in/2</a>)

1928	1963	<p></dd>
1929	1964	</dl>
1930	1965
1931		<p><h3 id="sec:clpfd-closing-opening"><a name="sec:A.8.18"><span class="sec-nr">A.8.18</span> <span class="sec-title">Closing
	1966	<p><h3 id="sec:clpfd-closing-opening"><a id="sec:A.8.18"><span class="sec-nr">A.8.18</span> <span class="sec-title">Closing
1932	1967	and opening words about CLP(FD)</span></a></h3>
1933	1968
1934		<p><a name="sec:clpfd-closing-opening"></a>
	1969	<p><a id="sec:clpfd-closing-opening"></a>
1935	1970
1936	1971	<p>CLP(FD) constraints are one of the main reasons why logic programming
1937	1972	approaches are picked over other paradigms for solving many tasks of

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191	232	<a class="nav" href="clpfd.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:clpqr"><a name="sec:A.9"><span class="sec-nr">A.9</span> <span class="sec-title">library(clpqr):
	235	<h2 id="sec:clpqr"><a id="sec:A.9"><span class="sec-nr">A.9</span> <span class="sec-title">library(clpqr):
195	236	Constraint Logic Programming over Rationals and Reals</span></a></h2>
196	237
197		<a name="sec:clpqr"></a>
198		<a name="sec:lib:clpqr"></a>
	238	<a id="sec:clpqr"></a>
	239	<a id="sec:lib:clpqr"></a>
199	240	<blockquote> Author: <em>Christian Holzbaur</em>, ported to SWI-Prolog
200	241	by <em>Leslie De Koninck</em>, K.U. Leuven
201	242	</blockquote>

203	244	<p>This CLP(Q,R) system is a port of the CLP(Q,R) system of Sicstus
204	245	Prolog by Christian Holzbaur: Holzbaur C.: OFAI clp(q,r) Manual, Edition
205	246	1.3.3, Austrian Research Institute for Artificial Intelligence, Vienna,
206		TR-95-09, 1995.<sup class="fn">181<span class="fn-text">http://www.ai.univie.ac.at/cgi-bin/tr-online?number+95-09</span></sup>
	247	TR-95-09, 1995.<sup class="fn">182<span class="fn-text">http://www.ai.univie.ac.at/cgi-bin/tr-online?number+95-09</span></sup>
207	248	This manual is roughly based on the manual of the above mentioned
208	249	CLP(Q,R) implementation.
209	250

232	273	:- use_module(library(clpr)).
233	274	</pre>
234	275
235		<p><h3 id="sec:clpqr-predicates"><a name="sec:A.9.1"><span class="sec-nr">A.9.1</span> <span class="sec-title">Solver
	276	<p><h3 id="sec:clpqr-predicates"><a id="sec:A.9.1"><span class="sec-nr">A.9.1</span> <span class="sec-title">Solver
236	277	predicates</span></a></h3>
237	278
238		<a name="sec:clpqr-predicates"></a> The following predicates are
239		provided to work with constraints:
	279	<a id="sec:clpqr-predicates"></a> The following predicates are provided
	280	to work with constraints:
240	281
241	282	<dl class="latex">
242		<dt class="pubdef"><a name="{}/1"><strong>{}</strong>(<var>+Constraints</var>)</a></dt>
	283	<dt class="pubdef"><a id="{}/1"><strong>{}</strong>(<var>+Constraints</var>)</a></dt>
243	284	<dd class="defbody">
244	285	Adds the constraints given by <var>Constraints</var> to the constraint
245	286	store.</dd>
246		<dt class="pubdef"><a name="entailed/1"><strong>entailed</strong>(<var>+Constraint</var>)</a></dt>
	287	<dt class="pubdef"><a id="entailed/1"><strong>entailed</strong>(<var>+Constraint</var>)</a></dt>
247	288	<dd class="defbody">
248	289	Succeeds if <var>Constraint</var> is necessarily true within the current
249	290	constraint store. This means that adding the negation of the constraint
250	291	to the store results in failure.</dd>
251		<dt class="pubdef"><a name="inf/2"><strong>inf</strong>(<var>+Expression,
	292	<dt class="pubdef"><a id="inf/2"><strong>inf</strong>(<var>+Expression,
252	293	-Inf</var>)</a></dt>
253	294	<dd class="defbody">
254	295	Computes the infimum of <var>Expression</var> within the current state
255	296	of the constraint store and returns that infimum in <var>Inf</var>. This
256	297	predicate does not change the constraint store.</dd>
257		<dt class="pubdef"><a name="sup/2"><strong>sup</strong>(<var>+Expression,
	298	<dt class="pubdef"><a id="sup/2"><strong>sup</strong>(<var>+Expression,
258	299	-Sup</var>)</a></dt>
259	300	<dd class="defbody">
260	301	Computes the supremum of <var>Expression</var> within the current state
261	302	of the constraint store and returns that supremum in <var>Sup</var>.
262	303	This predicate does not change the constraint store.</dd>
263		<dt class="pubdef"><a name="minimize/1"><strong>minimize</strong>(<var>+Expression</var>)</a></dt>
	304	<dt class="pubdef"><a id="minimize/1"><strong>minimize</strong>(<var>+Expression</var>)</a></dt>
264	305	<dd class="defbody">
265	306	Minimizes <var>Expression</var> within the current constraint store.
266	307	This is the same as computing the infimum and equating the expression to
267	308	that infimum.</dd>
268		<dt class="pubdef"><a name="maximize/1"><strong>maximize</strong>(<var>+Expression</var>)</a></dt>
	309	<dt class="pubdef"><a id="maximize/1"><strong>maximize</strong>(<var>+Expression</var>)</a></dt>
269	310	<dd class="defbody">
270	311	Maximizes <var>Expression</var> within the current constraint store.
271	312	This is the same as computing the supremum and equating the expression
272	313	to that supremum.</dd>
273		<dt class="pubdef"><a name="bb_inf/5"><strong>bb_inf</strong>(<var>+Ints,
	314	<dt class="pubdef"><a id="bb_inf/5"><strong>bb_inf</strong>(<var>+Ints,
274	315	+Expression, -Inf, -Vertex, +Eps</var>)</a></dt>
275	316	<dd class="defbody">
276	317	This predicate is offered in CLP(R) only. It computes the infimum of

281	322	an integer to be considered an integer. E.g. when
282	323	<var>Eps</var> = 0.001, then X = 4.999 will be considered as an integer
283	324	(5 in this case). <var>Eps</var> should be between 0 and 0.5.</dd>
284		<dt class="pubdef"><a name="bb_inf/4"><strong>bb_inf</strong>(<var>+Ints,
	325	<dt class="pubdef"><a id="bb_inf/4"><strong>bb_inf</strong>(<var>+Ints,
285	326	+Expression, -Inf, -Vertex</var>)</a></dt>
286	327	<dd class="defbody">
287	328	This predicate is offered in CLP(Q) only. It behaves the same as
288	329	<a class="pred" href="clpqr.html#bb_inf/5">bb_inf/5</a> but does not use
289	330	an error margin.</dd>
290		<dt class="pubdef"><a name="bb_inf/3"><strong>bb_inf</strong>(<var>+Ints,
	331	<dt class="pubdef"><a id="bb_inf/3"><strong>bb_inf</strong>(<var>+Ints,
291	332	+Expression, -Inf</var>)</a></dt>
292	333	<dd class="defbody">
293	334	The same as <a class="pred" href="clpqr.html#bb_inf/5">bb_inf/5</a> or <a class="pred" href="clpqr.html#bb_inf/4">bb_inf/4</a>
294	335	but without returning the values of the integers. In CLP(R), an error
295	336	margin of 0.001 is used.</dd>
296		<dt class="pubdef"><a name="dump/3"><strong>dump</strong>(<var>+Target,
	337	<dt class="pubdef"><a id="dump/3"><strong>dump</strong>(<var>+Target,
297	338	+Newvars, -CodedAnswer</var>)</a></dt>
298	339	<dd class="defbody">
299	340	Returns the constraints on <var>Target</var> in the list <var>CodedAnswer</var>

310	351	<p></dd>
311	352	</dl>
312	353
313		<p><h3 id="sec:clpqr-arg-syntax"><a name="sec:A.9.2"><span class="sec-nr">A.9.2</span> <span class="sec-title">Syntax
	354	<p><h3 id="sec:clpqr-arg-syntax"><a id="sec:A.9.2"><span class="sec-nr">A.9.2</span> <span class="sec-title">Syntax
314	355	of the predicate arguments</span></a></h3>
315	356
316		<a name="sec:clpqr-arg-syntax"></a> The arguments of the predicates
	357	<a id="sec:clpqr-arg-syntax"></a> The arguments of the predicates
317	358	defined in the subsection above are defined in <a class="tab" href="clpqr.html#tab:clpqrbnf">table
318	359	10</a>. Failing to meet the syntax rules will result in an exception.
319	360	<div style="text-align:center">
320		<table border="2" frame="box" rules="groups">
321		<tr valign="top"><td><<var>Constraints</var>> </td><td align=right>::=</td><td><<var>Constraint</var>> </td><td>single
	361	<table class="latex frame-box">
	362	<tr><td><<var>Constraints</var>> </td><td align=right>::=</td><td><<var>Constraint</var>> </td><td>single
322	363	constraint </td></tr>
323		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Constraint</var>>
324		, <<var>Constraints</var>> </td><td>conjunction </td></tr>
325		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Constraint</var>>
326		; <<var>Constraints</var>> </td><td>disjunction </td></tr>
327		<tr valign="top"><td>
	364	<tr><td></td><td align=right>\|</td><td><<var>Constraint</var>> , <<var>Constraints</var>> </td><td>conjunction </td></tr>
	365	<tr><td></td><td align=right>\|</td><td><<var>Constraint</var>> ; <<var>Constraints</var>> </td><td>disjunction </td></tr>
	366	<tr><td>
328	367
329	368	<p><<var>Constraint</var>> </td><td align=right>::=</td><td><<var>Expression</var>> <code><</code> <<var>Expression</var>> </td><td>less
330	369	than </td></tr>
331		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>></code> <<var>Expression</var>> </td><td>greater
	370	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>></code> <<var>Expression</var>> </td><td>greater
332	371	than </td></tr>
333		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>=<</code> <<var>Expression</var>> </td><td>less
	372	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>=<</code> <<var>Expression</var>> </td><td>less
334	373	or equal </td></tr>
335		<tr valign="top"><td></td><td align=right>\|</td><td><code><=</code>(<<var>Expression</var>>, <<var>Expression</var>>)</td><td>less
	374	<tr><td></td><td align=right>\|</td><td><code><=</code>(<<var>Expression</var>>, <<var>Expression</var>>)</td><td>less
336	375	or equal </td></tr>
337		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>>=</code> <<var>Expression</var>> </td><td>greater
	376	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>>=</code> <<var>Expression</var>> </td><td>greater
338	377	or equal </td></tr>
339		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>=\=</code> <<var>Expression</var>> </td><td>not
	378	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>=\=</code> <<var>Expression</var>> </td><td>not
340	379	equal </td></tr>
341		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>>
342		=:= <<var>Expression</var>> </td><td>equal </td></tr>
343		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>>
344		= <<var>Expression</var>> </td><td>equal </td></tr>
345		<tr valign="top"><td>
	380	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> =:= <<var>Expression</var>> </td><td>equal </td></tr>
	381	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> = <<var>Expression</var>> </td><td>equal </td></tr>
	382	<tr><td>
346	383
347	384	<p><<var>Expression</var>> </td><td align=right>::=</td><td><<var>Variable</var>> </td><td>Prolog
348	385	variable </td></tr>
349		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Number</var>> </td><td>Prolog
	386	<tr><td></td><td align=right>\|</td><td><<var>Number</var>> </td><td>Prolog
350	387	number </td></tr>
351		<tr valign="top"><td></td><td align=right>\|</td><td>+<<var>Expression</var>> </td><td>unary
	388	<tr><td></td><td align=right>\|</td><td>+<<var>Expression</var>> </td><td>unary
352	389	plus </td></tr>
353		<tr valign="top"><td></td><td align=right>\|</td><td>-<<var>Expression</var>> </td><td>unary
	390	<tr><td></td><td align=right>\|</td><td>-<<var>Expression</var>> </td><td>unary
354	391	minus </td></tr>
355		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>>
356		+ <<var>Expression</var>> </td><td>addition </td></tr>
357		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>>
358		- <<var>Expression</var>> </td><td>substraction </td></tr>
359		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>>
360		* <<var>Expression</var>> </td><td>multiplication </td></tr>
361		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>>
362		/ <<var>Expression</var>> </td><td>division </td></tr>
363		<tr valign="top"><td></td><td align=right>\|</td><td>abs(<<var>Expression</var>>)</td><td>absolute
	392	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> + <<var>Expression</var>> </td><td>addition </td></tr>
	393	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> - <<var>Expression</var>> </td><td>substraction </td></tr>
	394	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> * <<var>Expression</var>> </td><td>multiplication </td></tr>
	395	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> / <<var>Expression</var>> </td><td>division </td></tr>
	396	<tr><td></td><td align=right>\|</td><td>abs(<<var>Expression</var>>)</td><td>absolute
364	397	value </td></tr>
365		<tr valign="top"><td></td><td align=right>\|</td><td>sin(<<var>Expression</var>>)</td><td>sine </td></tr>
366		<tr valign="top"><td></td><td align=right>\|</td><td>cos(<<var>Expression</var>>)</td><td>cosine </td></tr>
367		<tr valign="top"><td></td><td align=right>\|</td><td>tan(<<var>Expression</var>>)</td><td>tangent </td></tr>
368		<tr valign="top"><td></td><td align=right>\|</td><td>exp(<<var>Expression</var>>)</td><td>exponent </td></tr>
369		<tr valign="top"><td></td><td align=right>\|</td><td>pow(<<var>Expression</var>>)</td><td>exponent </td></tr>
370		<tr valign="top"><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>^</code> <<var>Expression</var>> </td><td>exponent </td></tr>
371		<tr valign="top"><td></td><td align=right>\|</td><td>min(<<var>Expression</var>>, <<var>Expression</var>>)</td><td>minimum </td></tr>
372		<tr valign="top"><td></td><td align=right>\|</td><td>max(<<var>Expression</var>>, <<var>Expression</var>>)</td><td>maximum </td></tr>
	398	<tr><td></td><td align=right>\|</td><td>sin(<<var>Expression</var>>)</td><td>sine </td></tr>
	399	<tr><td></td><td align=right>\|</td><td>cos(<<var>Expression</var>>)</td><td>cosine </td></tr>
	400	<tr><td></td><td align=right>\|</td><td>tan(<<var>Expression</var>>)</td><td>tangent </td></tr>
	401	<tr><td></td><td align=right>\|</td><td>exp(<<var>Expression</var>>)</td><td>exponent </td></tr>
	402	<tr><td></td><td align=right>\|</td><td>pow(<<var>Expression</var>>)</td><td>exponent </td></tr>
	403	<tr><td></td><td align=right>\|</td><td><<var>Expression</var>> <code>^</code> <<var>Expression</var>> </td><td>exponent </td></tr>
	404	<tr><td></td><td align=right>\|</td><td>min(<<var>Expression</var>>, <<var>Expression</var>>)</td><td>minimum </td></tr>
	405	<tr><td></td><td align=right>\|</td><td>max(<<var>Expression</var>>, <<var>Expression</var>>)</td><td>maximum </td></tr>
373	406	</table>
374	407	<div class="caption"><b>Table 10 : </b>CLP(Q,R) constraint BNF</div>
375		<a name="tab:clpqrbnf"></a>
	408	<a id="tab:clpqrbnf"></a>
376	409	</div>
377	410
378		<p><h3 id="sec:clpqr-unification"><a name="sec:A.9.3"><span class="sec-nr">A.9.3</span> <span class="sec-title">Use
	411	<p><h3 id="sec:clpqr-unification"><a id="sec:A.9.3"><span class="sec-nr">A.9.3</span> <span class="sec-title">Use
379	412	of unification</span></a></h3>
380	413
381		<a name="sec:clpqr-unification"></a>
	414	<a id="sec:clpqr-unification"></a>
382	415
383	416	<p>Instead of using the <a class="pred" href="clpqr.html#{}/1">{}/1</a>
384	417	predicate, you can also use the standard unification mechanism to store

406	439	<p>
407	440	</ul>
408	441
409		<p><h3 id="sec:clpqr-non-linear"><a name="sec:A.9.4"><span class="sec-nr">A.9.4</span> <span class="sec-title">Non-linear
	442	<p><h3 id="sec:clpqr-non-linear"><a id="sec:A.9.4"><span class="sec-nr">A.9.4</span> <span class="sec-title">Non-linear
410	443	constraints</span></a></h3>
411	444
412		<a name="sec:clpqr-non-linear"></a> The CLP(Q,R) system deals only
	445	<a id="sec:clpqr-non-linear"></a> The CLP(Q,R) system deals only
413	446	passively with non-linear constraints. They remain in a passive state
414	447	until certain conditions are satisfied. These conditions, which are
415	448	called the isolation axioms, are given in
416	449	<a class="tab" href="clpqr.html#tab:clpqraxioms">table 11</a>.
417	450	<div style="text-align:center">
418		<table border="2" frame="box" rules="groups">
419		<tr valign="top"><td><var>A = B * C</var> </td><td>B or C is ground</td><td>A
420		= 5 * C or A = B * 4 </td></tr>
421		<tr valign="top"><td></td><td>A and (B or C) are ground</td><td>20 = 5 *
422		C or 20 = B * 4 </td></tr>
423		<tbody>
424		<tr valign="top"><td><var>A = B / C</var> </td><td>C is ground</td><td>A
	451	<table class="latex frame-box">
	452	<tr><td><var>A = B * C</var> </td><td>B or C is ground</td><td>A = 5 * C
	453	or A = B * 4 </td></tr>
	454	<tr><td></td><td>A and (B or C) are ground</td><td>20 = 5 * C or 20 = B
	455	* 4 </td></tr>
	456	<tr class="hline"><td><var>A = B / C</var> </td><td>C is ground</td><td>A
425	457	= B / 3 </td></tr>
426		<tr valign="top"><td></td><td>A and B are ground</td><td>4 = 12 / C </td></tr>
427		<tbody>
428		<tr valign="top"><td><var>X = min(Y,Z)</var> </td><td>Y and Z are ground</td><td>X
429		= min(4,3) </td></tr>
430		<tr valign="top"><td><var>X = max(Y,Z)</var> </td><td>Y and Z are ground</td><td>X
431		= max(4,3) </td></tr>
432		<tr valign="top"><td><var>X = abs(Y)</var> </td><td>Y is ground</td><td>X
433		= abs(-7) </td></tr>
434		<tbody>
435		<tr valign="top"><td><var>X = pow(Y,Z)</var> </td><td>X and Y are ground</td><td>8
436		= 2 <code>^</code> Z </td></tr>
437		<tr valign="top"><td><var>X = exp(Y,Z)</var> </td><td>X and Z are ground</td><td>8
438		= Y <code>^</code> 3 </td></tr>
439		<tr valign="top"><td><var>X = Y</var> <code>^</code> <var>Z</var> </td><td>Y
440		and Z are ground</td><td>X = 2 <code>^</code> 3 </td></tr>
441		<tbody>
442		<tr valign="top"><td><var>X = sin(Y)</var> </td><td>X is ground</td><td>1
	458	<tr><td></td><td>A and B are ground</td><td>4 = 12 / C </td></tr>
	459	<tr class="hline"><td><var>X = min(Y,Z)</var> </td><td>Y and Z are
	460	ground</td><td>X = min(4,3) </td></tr>
	461	<tr><td><var>X = max(Y,Z)</var> </td><td>Y and Z are ground</td><td>X =
	462	max(4,3) </td></tr>
	463	<tr><td><var>X = abs(Y)</var> </td><td>Y is ground</td><td>X = abs(-7) </td></tr>
	464	<tr class="hline"><td><var>X = pow(Y,Z)</var> </td><td>X and Y are
	465	ground</td><td>8 = 2 <code>^</code> Z </td></tr>
	466	<tr><td><var>X = exp(Y,Z)</var> </td><td>X and Z are ground</td><td>8 =
	467	Y <code>^</code> 3 </td></tr>
	468	<tr><td><var>X = Y</var> <code>^</code> <var>Z</var> </td><td>Y and Z
	469	are ground</td><td>X = 2 <code>^</code> 3 </td></tr>
	470	<tr class="hline"><td><var>X = sin(Y)</var> </td><td>X is ground</td><td>1
443	471	= sin(Y) </td></tr>
444		<tr valign="top"><td><var>X = cos(Y)</var> </td><td>Y is ground</td><td>X
445		= sin(1.5707) </td></tr>
446		<tr valign="top"><td><var>X = tan(Y)</var> </td><td></td></tr>
	472	<tr><td><var>X = cos(Y)</var> </td><td>Y is ground</td><td>X =
	473	sin(1.5707) </td></tr>
	474	<tr><td><var>X = tan(Y)</var> </td><td></td></tr>
447	475	</table>
448	476	<div class="caption"><b>Table 11 : </b>CLP(Q,R) isolating axioms</div>
449		<a name="tab:clpqraxioms"></a>
	477	<a id="tab:clpqraxioms"></a>
450	478	</div>
451	479
452		<p><h3 id="sec:clpqr-status"><a name="sec:A.9.5"><span class="sec-nr">A.9.5</span> <span class="sec-title">Status
	480	<p><h3 id="sec:clpqr-status"><a id="sec:A.9.5"><span class="sec-nr">A.9.5</span> <span class="sec-title">Status
453	481	and known problems</span></a></h3>
454	482
455		<a name="sec:clpqr-status"></a>
	483	<a id="sec:clpqr-status"></a>
456	484
457	485	<p>The clpq and clpr libraries are `orphaned', i.e., they currently have
458	486	no maintainer.

475	503
476	504	<p>
477	505	<li><i>Dumping constraints</i><br>
478		The first argument of <a name="idx:dump3:2144"></a><a class="pred" href="clpqr.html#dump/3">dump/3</a>
	506	The first argument of <a id="idx:dump3:2148"></a><a class="pred" href="clpqr.html#dump/3">dump/3</a>
479	507	has to be a list of free variables at call-time:
480	508
481	509	<pre class="code">

+125

-83

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191	232	<a class="nav" href="initgoal.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="gemacs.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:cmdline"><a name="sec:2.4"><span class="sec-nr">2.4</span> <span class="sec-title">Command
	235	<h2 id="sec:cmdline"><a id="sec:2.4"><span class="sec-nr">2.4</span> <span class="sec-title">Command
195	236	line options</span></a></h2>
196	237
197		<a name="sec:cmdline"></a>
	238	<a id="sec:cmdline"></a>
198	239
199	240	<p>SWI-Prolog can be executed in one of the following modes:
200	241

205	246	<dt><b><code>swipl --dump-runtime-variables</code></b></dt>
206	247	<dd class="defbody">
207	248	These options must appear as only option. They cause Prolog to print an
208		informational message and exit. See <a class="sec" href="cmdline.html">section
	249	informational message and exit. See <a class="sec" href="cmdline.html#sec:2.4.1">section
209	250	2.4.1</a>.</dd>
210	251	<dt><b><code>swipl</code> [<var>option</var> ...] <var>script-file</var>
211	252	[<var>arg</var> ...]</b></dt>

217	258	... [[<code>--</code>] <var>arg</var> ...]</b></dt>
218	259	<dd class="defbody">
219	260	This is the normal way to start Prolog. The options are described in
220		<a class="sec" href="cmdline.html">section 2.4.2</a>, <a class="sec" href="cmdline.html">section
221		2.4.3</a> and <a class="sec" href="cmdline.html">section 2.4.4</a>. The
222		Prolog flag <a class="flag" href="flags.html#flag:argv">argv</a>
	261	<a class="sec" href="cmdline.html#sec:2.4.2">section 2.4.2</a>, <a class="sec" href="cmdline.html#sec:2.4.3">section
	262	2.4.3</a> and <a class="sec" href="cmdline.html#sec:2.4.4">section 2.4.4</a>.
	263	The Prolog flag <a class="flag" href="flags.html#flag:argv">argv</a>
223	264	provides access to <var>arg</var> ... If the <var>options</var> are
224	265	followed by one or more Prolog file names (i.e., names with extension <code>.pl</code>, <code>.prolog</code>
225	266	or (on Windows) the user preferred extension registered during

227	268	the Prolog flag
228	269	<a class="flag" href="flags.html#flag:associated_file">associated_file</a>.
229	270	In addition, <b>pl-win[.exe]</b> switches to the directory in which this
230		primary source file is located using <a name="idx:workingdirectory2:24"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>.</dd>
	271	primary source file is located using <a id="idx:workingdirectory2:24"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>.</dd>
231	272	<dt><b><code>swipl</code> -o <var>output</var> -c <var>prolog-file</var>
232	273	...</b></dt>
233	274	<dd class="defbody">
234	275	The <strong>-c</strong> option is used to compile a set of Prolog files
235		into an executable. See <a class="sec" href="cmdline.html">section 2.4.5</a>.</dd>
	276	into an executable. See <a class="sec" href="cmdline.html#sec:2.4.5">section
	277	2.4.5</a>.</dd>
236	278	<dt><b><code>swipl</code> -o <var>output</var> -b <var>bootfile</var> <var>prolog-file</var>
237	279	...</b></dt>
238	280	<dd class="defbody">
239		Bootstrap compilation. See <a class="sec" href="cmdline.html">section
	281	Bootstrap compilation. See <a class="sec" href="cmdline.html#sec:2.4.6">section
240	282	2.4.6</a>.
241	283	</dd>
242	284	</dl>
243	285
244		<p><h3 id="sec:info-options"><a name="sec:2.4.1"><span class="sec-nr">2.4.1</span> <span class="sec-title">Informational
	286	<p><h3 id="sec:info-options"><a id="sec:2.4.1"><span class="sec-nr">2.4.1</span> <span class="sec-title">Informational
245	287	command line options</span></a></h3>
246	288
247		<a name="sec:info-options"></a>
	289	<a id="sec:info-options"></a>
248	290
249	291	<dl class="latex">
250	292	<dt><strong>--arch</strong> <var></var></dt>

258	300	<dd class="defbody">
259	301	When given as the only option, it prints a sequence of variable settings
260	302	that can be used in shell scripts to deal with Prolog parameters. This
261		feature is also used by <b>swipl-ld</b> (see <a class="sec" href="plld.html">section
	303	feature is also used by <b>swipl-ld</b> (see <a class="sec" href="plld.html#sec:11.5">section
262	304	11.5</a>). Below is a typical example of using this feature.
263	305
264	306	<pre class="code">

280	322	</dd>
281	323	</dl>
282	324
283		<p><h3 id="sec:running-options"><a name="sec:2.4.2"><span class="sec-nr">2.4.2</span> <span class="sec-title">Command
	325	<p><h3 id="sec:running-options"><a id="sec:2.4.2"><span class="sec-nr">2.4.2</span> <span class="sec-title">Command
284	326	line options for running Prolog</span></a></h3>
285	327
286		<a name="sec:running-options"></a>
	328	<a id="sec:running-options"></a>
287	329
288	330	<dl class="latex">
289	331	<dt><strong>--home=DIR</strong> <var></var></dt>
290	332	<dd class="defbody">
291		Use DIR as home directory. See <a class="sec" href="findhome.html">section
	333	Use DIR as home directory. See <a class="sec" href="findhome.html#sec:11.6">section
292	334	11.6</a> for details.</dd>
293	335	<dt><strong>--quiet</strong> <var></var></dt>
294	336	<dd class="defbody">
295		<a name="idx:verbose:25"></a><a name="idx:quiet:26"></a>Set the Prolog
296		flag <a class="flag" href="flags.html#flag:verbose">verbose</a> to <code>silent</code>,
297		suppressing informational and banner messages. Also available as <strong>-q</strong>.</dd>
	337	<a id="idx:verbose:25"></a><a id="idx:quiet:26"></a>Set the Prolog flag <a class="flag" href="flags.html#flag:verbose">verbose</a>
	338	to <code>silent</code>, suppressing informational and banner messages.
	339	Also available as <strong>-q</strong>.</dd>
298	340	<dt><strong>--nodebug</strong> <var></var></dt>
299	341	<dd class="defbody">
300		Disable debugging. See the <a name="idx:currentprologflag2:27"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
	342	Disable debugging. See the <a id="idx:currentprologflag2:27"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
301	343	flag
302	344	<a class="flag" href="flags.html#flag:generate_debug_info">generate_debug_info</a>
303	345	for details.</dd>

306	348	Inhibit any signal handling by Prolog, a property that is sometimes
307	349	desirable for embedded applications. This option sets the flag
308	350	<a class="flag" href="flags.html#flag:signals">signals</a> to <code>false</code>.
309		See <a class="sec" href="foreigninclude.html">section 11.4.21.1</a> for
310		details. Note that the handler to unblock system calls is still
311		installed. This can be prevented using <code>--sigalert=0</code>
	351	See <a class="sec" href="foreigninclude.html#sec:11.4.21.1">section
	352	11.4.21.1</a> for details. Note that the handler to unblock system calls
	353	is still installed. This can be prevented using <code>--sigalert=0</code>
312	354	additionally. See <strong>--sigalert</strong>. This flag also sets
313	355	<b>gc_thread</b> to <code>false</code> as synchronization with the
314	356	garbage collect thread is based on signals.</dd>

321	363	<dt><strong>--sigalert=NUM</strong> <var></var></dt>
322	364	<dd class="defbody">
323	365	Use signal <var>NUM</var> (1 ... 31) for alerting a thread. This is
324		needed to make <a name="idx:threadsignal2:28"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>,
	366	needed to make <a id="idx:threadsignal2:28"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>,
325	367	and derived Prolog signal handling act immediately when the target
326		thread is blocked on an interruptable system call (e.g., <a name="idx:sleep1:29"></a><a class="pred" href="miscpreds.html#sleep/1">sleep/1</a>,
	368	thread is blocked on an interruptable system call (e.g., <a id="idx:sleep1:29"></a><a class="pred" href="miscpreds.html#sleep/1">sleep/1</a>,
327	369	read/write to most devices). The default is to use <code>SIGUSR2</code>.
328	370	If <var>NUM</var> is 0 (zero), this handler is not installed.</dd>
329	371	<dt><strong>-tty</strong> <var></var></dt>
330	372	<dd class="defbody">
331	373	Unix only. Switches controlling the terminal for allowing
332		single-character commands to the tracer and <a name="idx:getsinglechar1:30"></a><a class="pred" href="chario.html#get_single_char/1">get_single_char/1</a>.
	374	single-character commands to the tracer and <a id="idx:getsinglechar1:30"></a><a class="pred" href="chario.html#get_single_char/1">get_single_char/1</a>.
333	375	By default, manipulating the terminal is enabled unless the system
334	376	detects it is not connected to a terminal or it is running as a
335	377	GNU-Emacs inferior process. See also <a class="flag" href="flags.html#flag:tty_control">tty_control</a>.</dd>

338	380	This option is available only in <b>swipl-win.exe</b> and is used for
339	381	the start-menu item. If causes <b>plwin</b> to start in the folder
340	382	<code>...\My Documents\Prolog</code> or local equivalent thereof (see
341		<a name="idx:winfolder2:31"></a><a class="pred" href="system.html#win_folder/2">win_folder/2</a>).
	383	<a id="idx:winfolder2:31"></a><a class="pred" href="system.html#win_folder/2">win_folder/2</a>).
342	384	The <code>Prolog</code> subdirectory is created if it does not exist.</dd>
343	385	<dt><strong>-O</strong> <var></var></dt>
344	386	<dd class="defbody">
345		Optimised compilation. See <a name="idx:currentprologflag2:32"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
	387	Optimised compilation. See <a id="idx:currentprologflag2:32"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
346	388	flag
347	389	<a class="flag" href="flags.html#flag:optimise">optimise</a> for
348	390	details.</dd>

351	393	Load <var>file</var>. This flag provides compatibility with some other
352	394	Prolog systems.<sup class="fn">10<span class="fn-text">YAP, SICStus</span></sup>
353	395	It is used in SWI-Prolog to skip the program initialization specified
354		using <a name="idx:initialization2:33"></a><a class="pred" href="consulting.html#initialization/2">initialization/2</a>
355		directives. See also <a class="sec" href="compilation.html">section
356		2.10.2.1</a>, and <a name="idx:initialize0:34"></a><span class="pred-ext">initialize/0</span>.</dd>
	396	using <a id="idx:initialization2:33"></a><a class="pred" href="consulting.html#initialization/2">initialization/2</a>
	397	directives. See also <a class="sec" href="compilation.html#sec:2.10.2.1">section
	398	2.10.2.1</a>, and <a id="idx:initialize0:34"></a><span class="pred-ext">initialize/0</span>.</dd>
357	399	<dt><strong>-s</strong> <var>file</var></dt>
358	400	<dd class="defbody">
359	401	Use <var>file</var> as a script file. The script file is loaded after

366	408	<code>.swiplrc</code> (Unix) or <code>swipl.ini</code> (Windows). `<strong>-f</strong> <var>none</var>'
367	409	stops SWI-Prolog from searching for a startup file. This option can be
368	410	used as an alternative to <strong>-s</strong> <var>file</var> that stops
369		Prolog from loading the personal initialisation file. See also <a class="sec" href="initfile.html">section
	411	Prolog from loading the personal initialisation file. See also <a class="sec" href="initfile.html#sec:2.2">section
370	412	2.2</a>.</dd>
371	413	<dt><strong>-F</strong> <var>script</var></dt>
372	414	<dd class="defbody">

386	428	A boot file is a file resulting from a Prolog compilation using the
387	429	<strong>-b</strong> or <strong>-c</strong> option or a program saved
388	430	using
389		<a name="idx:qsaveprogram12:35"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>.</dd>
	431	<a id="idx:qsaveprogram12:35"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>.</dd>
390	432	<dt><strong>-p</strong> <var>alias=path1[:path2 ... ]</var></dt>
391	433	<dd class="defbody">
392	434	Define a path alias for file_search_path. <var>alias</var> is the name
393	435	of the alias, and arg path1 ... is a list of values for the alias. On
394	436	Windows the list separator is <code><code>;</code></code>. On other
395	437	systems it is <code><code>:</code></code>. A value is either a term of
396		the form alias(value) or pathname. The computed aliases are added to <a name="idx:filesearchpath2:36"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
397		using <a name="idx:asserta1:37"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>,
398		so they precede predefined values for the alias. See <a name="idx:filesearchpath2:38"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	438	the form alias(value) or pathname. The computed aliases are added to <a id="idx:filesearchpath2:36"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	439	using <a id="idx:asserta1:37"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>,
	440	so they precede predefined values for the alias. See <a id="idx:filesearchpath2:38"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
399	441	for details on using this file location mechanism.</dd>
400	442	<dt><strong>--traditional</strong> <var></var></dt>
401	443	<dd class="defbody">
402	444	This flag disables the most important extensions of SWI-Prolog version 7
403		(see <a class="sec" href="extensions.html">section 5</a>) that introduce
404		incompatibilities with earlier versions. In particular, lists are
405		represented in the traditional way, double quoted text is represented by
406		a list of character codes and the functional notation on dicts is not
407		supported. Dicts as a syntactic entity, and the predicates that act on
408		them, are still supported if this flag is present.</dd>
	445	(see <a class="sec" href="extensions.html#sec:5">section 5</a>) that
	446	introduce incompatibilities with earlier versions. In particular, lists
	447	are represented in the traditional way, double quoted text is
	448	represented by a list of character codes and the functional notation on
	449	dicts is not supported. Dicts as a syntactic entity, and the predicates
	450	that act on them, are still supported if this flag is present.</dd>
409	451	<dt><strong>--</strong> <var></var></dt>
410	452	<dd class="defbody">
411		<a name="idx:commandlinearguments:39"></a>Stops scanning for more
	453	<a id="idx:commandlinearguments:39"></a>Stops scanning for more
412	454	arguments, so you can pass arguments for your application after this
413		one. See <a name="idx:currentprologflag2:40"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
	455	one. See <a id="idx:currentprologflag2:40"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
414	456	using the flag <a class="flag" href="flags.html#flag:argv">argv</a> for
415	457	obtaining the command line arguments.
416	458	</dd>
417	459	</dl>
418	460
419		<p><h3 id="sec:stacksizes"><a name="sec:2.4.3"><span class="sec-nr">2.4.3</span> <span class="sec-title">Controlling
	461	<p><h3 id="sec:stacksizes"><a id="sec:2.4.3"><span class="sec-nr">2.4.3</span> <span class="sec-title">Controlling
420	462	the stack sizes</span></a></h3>
421	463
422		<a name="sec:stacksizes"></a>
	464	<a id="sec:stacksizes"></a>
423	465
424	466	<p>The default limit for the Prolog stacks is 128 MB on 32-bit and
425	467	256 MB on 64-bit hardware. The 128 MB limit on 32-bit systems
426	468	is the highest possible value and the command line options can thus only
427	469	be used to lower the limit. On 64-bit systems, the limit can both be
428		reduced and enlarged. See <a class="sec" href="limits.html">section 2.20</a>.
429		Below are two examples, the first reducing the local stack limit to
430		catch unbounded recursion quickly and the second using a big (32 GB)
431		global limit, which is only possible on 64-bit hardware. Note that
432		setting the limit using the command line only sets a <em>soft</em>
	470	reduced and enlarged. See <a class="sec" href="limits.html#sec:2.20">section
	471	2.20</a>. Below are two examples, the first reducing the local stack
	472	limit to catch unbounded recursion quickly and the second using a big
	473	(32 GB) global limit, which is only possible on 64-bit hardware.
	474	Note that setting the limit using the command line only sets a <em>soft</em>
433	475	limit. Stack parameters can be changed (both reduced and enlarged) at
434		any time using the predicate <a name="idx:setprologstack2:41"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>.
	476	any time using the predicate <a id="idx:setprologstack2:41"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>.
435	477
436	478	<pre class="code">
437	479	$ swipl -L8m

464	506	</dd>
465	507	</dl>
466	508
467		<p><h3 id="sec:runoptions"><a name="sec:2.4.4"><span class="sec-nr">2.4.4</span> <span class="sec-title">Running
	509	<p><h3 id="sec:runoptions"><a id="sec:2.4.4"><span class="sec-nr">2.4.4</span> <span class="sec-title">Running
468	510	goals from the command line</span></a></h3>
469	511
470		<a name="sec:runoptions"></a>
	512	<a id="sec:runoptions"></a>
471	513
472	514	<dl class="latex">
473	515	<dt><strong>-g</strong> <var>goal</var></dt>
474	516	<dd class="defbody">
475	517	<var>Goal</var> is executed just before entering the top level. This
476		option may appear multiple times. See <a class="sec" href="initgoal.html">section
	518	option may appear multiple times. See <a class="sec" href="initgoal.html#sec:2.3">section
477	519	2.3</a> for details. If no initialization goal is present the system
478		calls <a name="idx:version0:42"></a><a class="pred" href="exception.html#version/0">version/0</a>
	520	calls <a id="idx:version0:42"></a><a class="pred" href="exception.html#version/0">version/0</a>
479	521	to print the welcome message. The welcome message can be suppressed with
480	522	<strong>--quiet</strong>, but also with <strong>-g</strong> <var>true</var>. <var>goal</var>
481	523	can be a complex term. In this case quotes are normally needed to

493	535	<dt><strong>-t</strong> <var>goal</var></dt>
494	536	<dd class="defbody">
495	537	Use <var>goal</var> as interactive top level instead of the default goal
496		<a name="idx:prolog0:43"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>.
	538	<a id="idx:prolog0:43"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>.
497	539	The <var>goal</var> can be a complex term. If the top-level goal
498	540	succeeds SWI-Prolog exits with status 0. If it fails the exit status is
499	541	1. If the top level raises an exception, this is printed as an uncaught
500	542	error and the top level is <em>restarted</em>. This flag also determines
501		the goal started by <a name="idx:break0:44"></a><a class="pred" href="toplevel.html#break/0">break/0</a>
502		and <a name="idx:abort0:45"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
	543	the goal started by <a id="idx:break0:44"></a><a class="pred" href="toplevel.html#break/0">break/0</a>
	544	and <a id="idx:abort0:45"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
503	545	If you want to prevent the user from entering interactive mode, start
504	546	the application with `<strong>-g</strong> <var>goal</var> <strong>-t</strong> <var>halt</var>'.
505	547	</dd>
506	548	</dl>
507	549
508		<p><h3 id="sec:compoptions"><a name="sec:2.4.5"><span class="sec-nr">2.4.5</span> <span class="sec-title">Compilation
	550	<p><h3 id="sec:compoptions"><a id="sec:2.4.5"><span class="sec-nr">2.4.5</span> <span class="sec-title">Compilation
509	551	options</span></a></h3>
510	552
511		<a name="sec:compoptions"></a>
	553	<a id="sec:compoptions"></a>
512	554
513	555	<dl class="latex">
514	556	<dt><strong>-c</strong> <var>file ...</var></dt>
515	557	<dd class="defbody">
516		Compile files into an `intermediate code file'. See <a class="sec" href="compilation.html">section
	558	Compile files into an `intermediate code file'. See <a class="sec" href="compilation.html#sec:2.10">section
517	559	2.10</a>.</dd>
518	560	<dt><strong>-o</strong> <var>output</var></dt>
519	561	<dd class="defbody">

522	564	</dd>
523	565	</dl>
524	566
525		<p><h3 id="sec:maintoptions"><a name="sec:2.4.6"><span class="sec-nr">2.4.6</span> <span class="sec-title">Maintenance
	567	<p><h3 id="sec:maintoptions"><a id="sec:2.4.6"><span class="sec-nr">2.4.6</span> <span class="sec-title">Maintenance
526	568	options</span></a></h3>
527	569
528		<a name="sec:maintoptions"></a>
	570	<a id="sec:maintoptions"></a>
529	571
530	572	<p>The following options are for system maintenance. They are given for
531	573	reference only.

+111

-76

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.7</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="typetest.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="control.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:compare"><a name="sec:4.7"><span class="sec-nr">4.7</span> <span class="sec-title">Comparison
	235	<h2 id="sec:compare"><a id="sec:4.7"><span class="sec-nr">4.7</span> <span class="sec-title">Comparison
195	236	and Unification of Terms</span></a></h2>
196	237
197		<a name="sec:compare"></a>
	238	<a id="sec:compare"></a>
198	239
199	240	<p>Although unification is mostly done implicitly while matching the
200	241	head of a predicate, it is also provided by the predicate =/2.
201	242
202	243	<dl class="latex">
203		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="=/2"><var>?Term1</var> <strong>=</strong> <var>?Term2</var></a></dt>
	244	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="=/2"><var>?Term1</var> <strong>=</strong> <var>?Term2</var></a></dt>
204	245	<dd class="defbody">
205	246	Unify <var>Term1</var> with <var>Term2</var>. True if the unification
206	247	succeeds. For behaviour on cyclic terms see the Prolog flag

212	253	</pre>
213	254
214	255	</dd>
215		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="\=/2"><var>@Term1</var> <strong>\=</strong> <var>@Term2</var></a></dt>
	256	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="\=/2"><var>@Term1</var> <strong>\=</strong> <var>@Term2</var></a></dt>
216	257	<dd class="defbody">
217	258	Equivalent to <code><code>\+</code>Term1 = Term2</code>.
218	259

222	263	incomplete nature of <a class="pred" href="control.html#\+/1">\+/1</a>.
223	264
224	265	<p>To make your programs work correctly also in situations where the
225		arguments are not yet sufficiently instantiated, use <a name="idx:dif2:624"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
	266	arguments are not yet sufficiently instantiated, use <a id="idx:dif2:624"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
226	267	instead.
227	268	</dd>
228	269	</dl>
229	270
230		<p><h3 id="sec:standardorder"><a name="sec:4.7.1"><span class="sec-nr">4.7.1</span> <span class="sec-title">Standard
	271	<p><h3 id="sec:standardorder"><a id="sec:4.7.1"><span class="sec-nr">4.7.1</span> <span class="sec-title">Standard
231	272	Order of Terms</span></a></h3>
232	273
233		<a name="sec:standardorder"></a>
	274	<a id="sec:standardorder"></a>
234	275
235	276	<p>Comparison and unification of arbitrary terms. Terms are ordered in
236	277	the so-called ``standard order''. This order is defined as follows:

253	294
254	295	<p>Although variables are ordered, there are some unexpected properties
255	296	one should keep in mind when relying on variable ordering. This applies
256		to the predicates below as to predicate such as <a name="idx:sort2:625"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>
	297	to the predicates below as to predicate such as <a id="idx:sort2:625"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>
257	298	as well as libraries that reply on ordering such as library <code>library(assoc)</code>
258	299	and library
259	300	<code>library(ordsets)</code>. Obviously, an established relation <var>A</var> <code><code>@<</code></code> <var>B</var>

266	307	`newer' variables. If two variables are unified their `shared' age is
267	308	the age of oldest variable. This implies we can examine a list of sorted
268	309	variables with `newer' (fresh) variables without invalidating the order.
269		Attaching an <em>attribute</em>, see <a class="sec" href="attvar.html">section
	310	Attaching an <em>attribute</em>, see <a class="sec" href="attvar.html#sec:7.1">section
270	311	7.1</a>, turns an `old' variable into a `new' one as illustrated below.
271	312	Note that the first always succeeds as the first argument of a term is
272	313	always the oldest. This only applies for the <em>first</em> attribute,

288	329	attributes to register information about variables.
289	330
290	331	<dl class="latex">
291		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="==/2"><var>@Term1</var> <strong>==</strong> <var>@Term2</var></a></dt>
	332	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="==/2"><var>@Term1</var> <strong>==</strong> <var>@Term2</var></a></dt>
292	333	<dd class="defbody">
293	334	True if <var>Term1</var> is equivalent to <var>Term2</var>. A variable
294	335	is only identical to a sharing variable.</dd>
295		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="\==/2"><var>@Term1</var> <strong>\==</strong> <var>@Term2</var></a></dt>
	336	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="\==/2"><var>@Term1</var> <strong>\==</strong> <var>@Term2</var></a></dt>
296	337	<dd class="defbody">
297	338	Equivalent to <code><code>\+</code>Term1 == Term2</code>.</dd>
298		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="@</2"><var>@Term1</var> <strong>@<</strong> <var>@Term2</var></a></dt>
	339	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="@</2"><var>@Term1</var> <strong>@<</strong> <var>@Term2</var></a></dt>
299	340	<dd class="defbody">
300	341	True if <var>Term1</var> is before <var>Term2</var> in the standard
301	342	order of terms.</dd>
302		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="@=</2"><var>@Term1</var> <strong>@=<</strong> <var>@Term2</var></a></dt>
	343	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="@=</2"><var>@Term1</var> <strong>@=<</strong> <var>@Term2</var></a></dt>
303	344	<dd class="defbody">
304	345	True if both terms are equal (<a class="pred" href="compare.html#==/2">==/2</a>)
305	346	or <var>Term1</var> is before <var>Term2</var> in the standard order of
306	347	terms.</dd>
307		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="@>/2"><var>@Term1</var> <strong>@></strong> <var>@Term2</var></a></dt>
	348	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="@>/2"><var>@Term1</var> <strong>@></strong> <var>@Term2</var></a></dt>
308	349	<dd class="defbody">
309	350	True if <var>Term1</var> is after <var>Term2</var> in the standard order
310	351	of terms.</dd>
311		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="@>=/2"><var>@Term1</var> <strong>@>=</strong> <var>@Term2</var></a></dt>
	352	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="@>=/2"><var>@Term1</var> <strong>@>=</strong> <var>@Term2</var></a></dt>
312	353	<dd class="defbody">
313	354	True if both terms are equal (<a class="pred" href="compare.html#==/2">==/2</a>)
314	355	or <var>Term1</var> is after <var>Term2</var> in the standard order of
315	356	terms.</dd>
316		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="compare/3"><strong>compare</strong>(<var>?Order,
	357	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="compare/3"><strong>compare</strong>(<var>?Order,
317	358	@Term1, @Term2</var>)</a></dt>
318	359	<dd class="defbody">
319	360	Determine or test the <var>Order</var> between two terms in the standard

322	363	</dd>
323	364	</dl>
324	365
325		<p><h3 id="sec:unifyspecial"><a name="sec:4.7.2"><span class="sec-nr">4.7.2</span> <span class="sec-title">Special
	366	<p><h3 id="sec:unifyspecial"><a id="sec:4.7.2"><span class="sec-nr">4.7.2</span> <span class="sec-title">Special
326	367	unification and comparison predicates</span></a></h3>
327	368
328		<a name="sec:unifyspecial"></a>
	369	<a id="sec:unifyspecial"></a>
329	370
330	371	<p>This section describes special purpose variations on Prolog
331		unification. The predicate <a name="idx:unifywithoccurscheck2:626"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>
	372	unification. The predicate <a id="idx:unifywithoccurscheck2:626"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>
332	373	provides sound unification and is part of the ISO standard. The
333		predicate <a name="idx:subsumesterm2:627"></a><a class="pred" href="compare.html#subsumes_term/2">subsumes_term/2</a>
	374	predicate <a id="idx:subsumesterm2:627"></a><a class="pred" href="compare.html#subsumes_term/2">subsumes_term/2</a>
334	375	defines `one-sided unification' and is part of the ISO proposal
335		established in Edinburgh (2010). Finally, <a name="idx:unifiable3:628"></a><a class="pred" href="compare.html#unifiable/3">unifiable/3</a>
	376	established in Edinburgh (2010). Finally, <a id="idx:unifiable3:628"></a><a class="pred" href="compare.html#unifiable/3">unifiable/3</a>
336	377	is a `what-if' version of unification that is often used as a building
337	378	block in constraint reasoners.
338	379
339	380	<dl class="latex">
340		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="unify_with_occurs_check/2"><strong>unify_with_occurs_check</strong>(<var>+Term1,
	381	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="unify_with_occurs_check/2"><strong>unify_with_occurs_check</strong>(<var>+Term1,
341	382	+Term2</var>)</a></dt>
342	383	<dd class="defbody">
343	384	As <a class="pred" href="compare.html#=/2">=/2</a>, but using <em>sound

352	393	false.
353	394	</pre>
354	395
355		<p><a name="idx:occurscheck:629"></a>The first statement creates a <em>cyclic
	396	<p><a id="idx:occurscheck:629"></a>The first statement creates a <em>cyclic
356	397	term</em>, also called a
357	398	<em>rational tree</em>. The second executes logically sound unification
358	399	and thus fails. Note that the behaviour of unification through
359	400	<a class="pred" href="compare.html#=/2">=/2</a> as well as implicit
360	401	unification in the head can be changed using the Prolog flag <a class="flag" href="flags.html#flag:occurs_check">occurs_check</a>.
361	402
362		<p>The SWI-Prolog implementation of <a name="idx:unifywithoccurscheck2:630"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>
	403	<p>The SWI-Prolog implementation of <a id="idx:unifywithoccurscheck2:630"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>
363	404	is cycle-safe and only guards against <em>creating</em> cycles, not
364	405	against cycles that may already be present in one of the arguments. This
365	406	is illustrated in the following two queries:

371	412	X = Y, Y = f(Y).
372	413	</pre>
373	414
374		<p>Some other Prolog systems interpret <a name="idx:unifywithoccurscheck2:631"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>
	415	<p>Some other Prolog systems interpret <a id="idx:unifywithoccurscheck2:631"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>
375	416	as if defined by the clause below, causing failure on the above two
376		queries. Direct use of <a name="idx:acyclicterm1:632"></a><a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a>
	417	queries. Direct use of <a id="idx:acyclicterm1:632"></a><a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a>
377	418	is portable and more appropriate for such applications.
378	419
379	420	<pre class="code">

381	422	</pre>
382	423
383	424	</dd>
384		<dt class="pubdef"><a name="=@=/2"><var>+Term1</var> <strong>=@=</strong> <var>+Term2</var></a></dt>
385		<dd class="defbody">
386		<a name="idx:variant:633"></a>True if <var>Term1</var> is a <em>variant</em>
	425	<dt class="pubdef"><a id="=@=/2"><var>+Term1</var> <strong>=@=</strong> <var>+Term2</var></a></dt>
	426	<dd class="defbody">
	427	<a id="idx:variant:633"></a>True if <var>Term1</var> is a <em>variant</em>
387	428	of (or <em>structurally equivalent</em> to) <var>Term2</var>. Testing
388	429	for a variant is weaker than equivalence (<a class="pred" href="compare.html#==/2">==/2</a>),
389	430	but stronger than unification (<a class="pred" href="compare.html#=/2">=/2</a>).

398	439	E.g., after binding the first argument in row 8 to a value, both
399	440	terms are no longer variant.</span></sup> Examples:
400	441	<blockquote>
401		<table border="0" frame="void" rules="groups">
402		<tr valign="top"><td align=right>1</td><td align=center><code>a =@= A</code></td><td align=center>false </td></tr>
403		<tr valign="top"><td align=right>2</td><td align=center><code>A =@= B</code></td><td align=center>true </td></tr>
404		<tr valign="top"><td align=right>3</td><td align=center><code>x(A,A) =@=
405		x(B,C)</code></td><td align=center>false </td></tr>
406		<tr valign="top"><td align=right>4</td><td align=center><code>x(A,A) =@=
407		x(B,B)</code></td><td align=center>true </td></tr>
408		<tr valign="top"><td align=right>5</td><td align=center><code>x(A,A) =@=
409		x(A,B)</code></td><td align=center>false </td></tr>
410		<tr valign="top"><td align=right>6</td><td align=center><code>x(A,B) =@=
411		x(C,D)</code></td><td align=center>true </td></tr>
412		<tr valign="top"><td align=right>7</td><td align=center><code>x(A,B) =@=
413		x(B,A)</code></td><td align=center>true </td></tr>
414		<tr valign="top"><td align=right>8</td><td align=center><code>x(A,B) =@=
415		x(C,A)</code></td><td align=center>true </td></tr>
	442	<table class="latex frame-void">
	443	<tr><td align=right>1</td><td align=center><code>a =@= A</code></td><td align=center>false </td></tr>
	444	<tr><td align=right>2</td><td align=center><code>A =@= B</code></td><td align=center>true </td></tr>
	445	<tr><td align=right>3</td><td align=center><code>x(A,A) =@= x(B,C)</code></td><td align=center>false </td></tr>
	446	<tr><td align=right>4</td><td align=center><code>x(A,A) =@= x(B,B)</code></td><td align=center>true </td></tr>
	447	<tr><td align=right>5</td><td align=center><code>x(A,A) =@= x(A,B)</code></td><td align=center>false </td></tr>
	448	<tr><td align=right>6</td><td align=center><code>x(A,B) =@= x(C,D)</code></td><td align=center>true </td></tr>
	449	<tr><td align=right>7</td><td align=center><code>x(A,B) =@= x(B,A)</code></td><td align=center>true </td></tr>
	450	<tr><td align=right>8</td><td align=center><code>x(A,B) =@= x(C,A)</code></td><td align=center>true </td></tr>
416	451	</table>
417	452	</blockquote>
418	453
419	454	<p>A term is always a variant of a copy of itself. Term copying takes
420		place in, e.g., <a name="idx:copyterm2:634"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>, <a name="idx:findall3:635"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
	455	place in, e.g., <a id="idx:copyterm2:634"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>, <a id="idx:findall3:635"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
421	456	or proving a clause added with
422		<a name="idx:asserta1:636"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>.
	457	<a id="idx:asserta1:636"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>.
423	458	In the pure Prolog world (i.e., without attributed variables), <a class="pred" href="compare.html#=@=/2">=@=/2</a>
424	459	behaves as if defined below. With attributed variables, variant of the
425	460	attributes is tested rather than trying to satisfy the constraints.

444	479	in some other Prolog systems. Be aware of possible differences in
445	480	semantics if the arguments contain attributed variables or share
446	481	variables.<sup class="fn">61<span class="fn-text">In many systems
447		variant is implemented using two calls to <a name="idx:subsumesterm2:637"></a><a class="pred" href="compare.html#subsumes_term/2">subsumes_term/2</a>.</span></sup></dd>
448		<dt class="pubdef"><a name="\=@=/2"><var>+Term1</var> <strong>\=@=</strong> <var>+Term2</var></a></dt>
	482	variant is implemented using two calls to <a id="idx:subsumesterm2:637"></a><a class="pred" href="compare.html#subsumes_term/2">subsumes_term/2</a>.</span></sup></dd>
	483	<dt class="pubdef"><a id="\=@=/2"><var>+Term1</var> <strong>\=@=</strong> <var>+Term2</var></a></dt>
449	484	<dd class="defbody">
450	485	Equivalent to <code>`<code>\+</code>Term1 =@= Term2'</code>. See <a class="pred" href="compare.html#=@=/2">=@=/2</a>
451	486	for details.</dd>
452		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="subsumes_term/2"><strong>subsumes_term</strong>(<var>@Generic, @Specific</var>)</a></dt>
	487	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="subsumes_term/2"><strong>subsumes_term</strong>(<var>@Generic, @Specific</var>)</a></dt>
453	488	<dd class="defbody">
454	489	True if <var>Generic</var> can be made equivalent to <var>Specific</var>
455	490	by only binding variables in <var>Generic</var>. The current
456	491	implementation performs the unification and ensures that the variable
457	492	set of <var>Specific</var> is not changed by the unification. On
458	493	success, the bindings are undone.<sup class="fn">62<span class="fn-text">This
459		predicate is often named <a name="idx:subsumeschk2:638"></a><span class="pred-ext">subsumes_chk/2</span>
	494	predicate is often named <a id="idx:subsumeschk2:638"></a><span class="pred-ext">subsumes_chk/2</span>
460	495	in older Prolog dialects. The current name was established in the ISO
461	496	WG17 meeting in Edinburgh (2010). The <code>chk</code> postfix was
462		considered to refer to determinism as in e.g., <a name="idx:memberchk2:639"></a><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a>.</span></sup>
	497	considered to refer to determinism as in e.g., <a id="idx:memberchk2:639"></a><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a>.</span></sup>
463	498	This predicate respects constraints.</dd>
464		<dt class="pubdef"><a name="term_subsumer/3"><strong>term_subsumer</strong>(<var>+Special1,
	499	<dt class="pubdef"><a id="term_subsumer/3"><strong>term_subsumer</strong>(<var>+Special1,
465	500	+Special2, -General</var>)</a></dt>
466	501	<dd class="defbody">
467	502	<var>General</var> is the most specific term that is a generalisation of
468	503	<var>Special1</var> and <var>Special2</var>. The implementation can
469	504	handle cyclic terms.</dd>
470		<dt class="pubdef"><a name="unifiable/3"><strong>unifiable</strong>(<var>@X, @Y,
	505	<dt class="pubdef"><a id="unifiable/3"><strong>unifiable</strong>(<var>@X, @Y,
471	506	-Unifier</var>)</a></dt>
472	507	<dd class="defbody">
473	508	If <var>X</var> and <var>Y</var> can unify, unify <var>Unifier</var>
474	509	with a list of
475	510	<var>Var</var> = <var>Value</var>, representing the bindings required to
476	511	make <var>X</var> and <var>Y</var> equivalent.<sup class="fn">63<span class="fn-text">This
477		predicate was introduced for the implementation of <a name="idx:dif2:640"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
478		and <a name="idx:when2:641"></a><a class="pred" href="coroutining.html#when/2">when/2</a>
	512	predicate was introduced for the implementation of <a id="idx:dif2:640"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
	513	and <a id="idx:when2:641"></a><a class="pred" href="coroutining.html#when/2">when/2</a>
479	514	after discussion with Tom Schrijvers and Bart Demoen. None of us is
480	515	really happy with the name and therefore suggestions for a new name are
481	516	welcome.</span></sup> This predicate can handle cyclic terms. Attributed
482	517	variables are handled as normal variables. Associated hooks are <em>not</em>
483	518	executed.</dd>
484		<dt class="pubdef"><a name="?=/2"><strong>?=</strong>(<var>@Term1, @Term2</var>)</a></dt>
	519	<dt class="pubdef"><a id="?=/2"><strong>?=</strong>(<var>@Term1, @Term2</var>)</a></dt>
485	520	<dd class="defbody">
486	521	Succeeds if the syntactic equality of <var>Term1</var> and <var>Term2</var>
487	522	can be decided safely, i.e. if the result of <code>Term1 == Term2</code>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 2.10</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="debugoverview.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:compilation"><a name="sec:2.10"><span class="sec-nr">2.10</span> <span class="sec-title">Compilation</span></a></h2>
195
196		<a name="sec:compilation"></a>
197
198		<p><h3 id="sec:develcomp"><a name="sec:2.10.1"><span class="sec-nr">2.10.1</span> <span class="sec-title">During
	235	<h2 id="sec:compilation"><a id="sec:2.10"><span class="sec-nr">2.10</span> <span class="sec-title">Compilation</span></a></h2>
	236
	237	<a id="sec:compilation"></a>
	238
	239	<p><h3 id="sec:develcomp"><a id="sec:2.10.1"><span class="sec-nr">2.10.1</span> <span class="sec-title">During
199	240	program development</span></a></h3>
200	241
201		<a name="sec:develcomp"></a>
	242	<a id="sec:develcomp"></a>
202	243
203	244	<p>During program development, programs are normally loaded using the
204	245	list abbreviation (<code>?- [load].</code>). It is common practice to
205	246	organise a project as a collection of source files and a <em>load file</em>,
206		a Prolog file containing only <a name="idx:usemodule12:71"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>
207		or <a name="idx:ensureloaded1:72"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>
	247	a Prolog file containing only <a id="idx:usemodule12:71"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>
	248	or <a id="idx:ensureloaded1:72"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>
208	249	directives, possibly with a definition of the <em>entry point</em> of
209	250	the program, the predicate that is normally used to start the program.
210	251	This file is often called <code>load.pl</code>. If the entry point is

229	270	before entering the top level. If Prolog is started from an interactive
230	271	shell, one may choose the type <code>swipl -s load.pl</code>.
231	272
232		<p><h3 id="sec:runcomp"><a name="sec:2.10.2"><span class="sec-nr">2.10.2</span> <span class="sec-title">For
	273	<p><h3 id="sec:runcomp"><a id="sec:2.10.2"><span class="sec-nr">2.10.2</span> <span class="sec-title">For
233	274	running the result</span></a></h3>
234	275
235		<a name="sec:runcomp"></a>
	276	<a id="sec:runcomp"></a>
236	277
237	278	<p>There are various options if you want to make your program ready for
238	279	real usage. The best choice depends on whether the program is to be used
239	280	only on machines holding the SWI-Prolog development system, the size of
240	281	the program, and the operating system (Unix vs. Windows).
241	282
242		<p><h4 id="sec:plscript"><a name="sec:2.10.2.1"><span class="sec-nr">2.10.2.1</span> <span class="sec-title">Using
	283	<p><h4 id="sec:plscript"><a id="sec:2.10.2.1"><span class="sec-nr">2.10.2.1</span> <span class="sec-title">Using
243	284	PrologScript</span></a></h4>
244	285
245		<a name="sec:plscript"></a>
	286	<a id="sec:plscript"></a>
246	287
247	288	<p>A Prolog source file can be used directly as a Unix program using the
248	289	Unix <code>#!</code> magic start. The Unix <code>#!</code> magic is

267	308	spaces. When started this way, the Prolog flag <a class="flag" href="flags.html#flag:argv">argv</a>
268	309	contains the command line arguments that follow the script invocation.
269	310
270		<p>Starting with version 7.5.8, <a name="idx:initialization2:73"></a><a class="pred" href="consulting.html#initialization/2">initialization/2</a>
	311	<p>Starting with version 7.5.8, <a id="idx:initialization2:73"></a><a class="pred" href="consulting.html#initialization/2">initialization/2</a>
271	312	support the <var>When</var> options <code>program</code> and <code>main</code>,
272	313	allowing for the following definition of a Prolog script that evaluates
273		an arithmetic expression on the command line. Note that <a name="idx:main0:74"></a><a class="pred" href="main.html#main/0">main/0</a>
	314	an arithmetic expression on the command line. Note that <a id="idx:main0:74"></a><a class="pred" href="main.html#main/0">main/0</a>
274	315	is defined lib the library
275		<code>library(main)</code>. It calls <a name="idx:main1:75"></a><span class="pred-ext">main/1</span>
	316	<code>library(main)</code>. It calls <a id="idx:main1:75"></a><span class="pred-ext">main/1</span>
276	317	with the command line arguments after disabling signal handling.
277	318
278	319	<pre class="code">

328	369	Due to the compatibility issues around <em>HashBang</em> line
329	370	processing, we decided to remove it completely.</span></sup>
330	371
331		<p><h4 id="sec:shellscript"><a name="sec:2.10.2.2"><span class="sec-nr">2.10.2.2</span> <span class="sec-title">Creating
	372	<p><h4 id="sec:shellscript"><a id="sec:2.10.2.2"><span class="sec-nr">2.10.2.2</span> <span class="sec-title">Creating
332	373	a shell script</span></a></h4>
333	374
334		<a name="sec:shellscript"></a>
335
336		<p>With the introduction of <em>PrologScript</em> (see <a class="sec" href="compilation.html">section
	375	<a id="sec:shellscript"></a>
	376
	377	<p>With the introduction of <em>PrologScript</em> (see <a class="sec" href="compilation.html#sec:2.10.2.1">section
337	378	2.10.2.1</a>), using shell scripts as explained in this section has
338	379	become redundant for most applications.
339	380

366	407	shortcut to Prolog, passing the proper options or writing a <code>.bat</code>
367	408	file.
368	409
369		<p><h4 id="sec:makestate"><a name="sec:2.10.2.3"><span class="sec-nr">2.10.2.3</span> <span class="sec-title">Creating
	410	<p><h4 id="sec:makestate"><a id="sec:2.10.2.3"><span class="sec-nr">2.10.2.3</span> <span class="sec-title">Creating
370	411	a saved state</span></a></h4>
371	412
372		<a name="sec:makestate"></a>
	413	<a id="sec:makestate"></a>
373	414
374	415	<p>For larger programs, as well as for programs that are required to run
375	416	on systems that do not have the SWI-Prolog development system installed,
376	417	creating a saved state is the best solution. A saved state is created
377		using <a name="idx:qsaveprogram12:76"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>
	418	using <a id="idx:qsaveprogram12:76"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>
378	419	or the <strong>-c</strong> command line option. A saved state is a file
379	420	containing machine-independent<sup class="fn">16<span class="fn-text">The
380	421	saved state does not depend on the CPU instruction set or endianness.

383	424	created.</span></sup> intermediate code in a format dedicated for fast
384	425	loading. Optionally, the emulator may be integrated in the saved state,
385	426	creating a single file, but machine-dependent, executable. This process
386		is described in <a class="sec" href="runtime.html">chapter 12</a>.
387
388		<p><h4 id="sec:cmdlinecomp"><a name="sec:2.10.2.4"><span class="sec-nr">2.10.2.4</span> <span class="sec-title">Compilation
	427	is described in <a class="sec" href="runtime.html#sec:12">chapter 12</a>.
	428
	429	<p><h4 id="sec:cmdlinecomp"><a id="sec:2.10.2.4"><span class="sec-nr">2.10.2.4</span> <span class="sec-title">Compilation
389	430	using the -c command line option</span></a></h4>
390	431
391		<a name="sec:cmdlinecomp"></a>
	432	<a id="sec:cmdlinecomp"></a>
392	433
393	434	<p>This mechanism loads a series of Prolog source files and then creates
394		a saved state as <a name="idx:qsaveprogram2:77"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
	435	a saved state as <a id="idx:qsaveprogram2:77"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
395	436	does. The command syntax is:
396	437
397	438	<pre class="code">
398	439	% swipl [option ...] [-o output] -c file.pl ...
399	440	</pre>
400	441
401		<p>The <var>options</var> argument are options to <a name="idx:qsaveprogram2:78"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
	442	<p>The <var>options</var> argument are options to <a id="idx:qsaveprogram2:78"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
402	443	written in the format below. The option names and their values are
403	444	described with
404		<a name="idx:qsaveprogram2:79"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
	445	<a id="idx:qsaveprogram2:79"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
405	446	<blockquote>
406	447	<code>--</code><em>option-name</em><code>=</code><em>option-value
407	448	</em></blockquote>

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27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
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121	125	}
122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
135		{ display: block !important;
136		position: absolute; top: auto; left: auto; width: 80%;
137		color: #000; background: white;
138		border: 2px solid;
139		padding: 5px; margin: 10px; z-index: 100;
140		font-size: smaller;
	134	.fn {
	135	color: red;
	136	font-size: 70%;
	137	}
	138
	139	.fn-text, .fnp {
	140	position: absolute;
	141	top: auto;
	142	left: 10%;
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	144	box-shadow: 5px 5px 5px #888;
	145	display: none;
	146	background: #fff;
	147	color: #000;
	148	margin-top: 25px;
	149	padding: 8px 12px;
	150	font-size: larger;
	151	}
	152
	153	sup:hover span.fn-text
	154	{ display: block;
141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
	200
	201	table.center
	202	{ margin: auto;
	203	}
	204
	205	table.latex
	206	{ border-collapse:collapse;
	207	}
	208
	209	table.latex tr
	210	{ vertical-align: text-top;
	211	}
	212
	213	table.latex td,th
	214	{ padding: 2px 1em;
	215	}
	216
	217	table.latex tr.hline td,th
	218	{ border-top: 1px solid black;
	219	}
	220
	221	table.frame-box
	222	{ border: 2px solid black;
	223	}
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184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="chars.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="edit.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:consulting"><a name="sec:4.3"><span class="sec-nr">4.3</span> <span class="sec-title">Loading
	235	<h2 id="sec:consulting"><a id="sec:4.3"><span class="sec-nr">4.3</span> <span class="sec-title">Loading
195	236	Prolog source files</span></a></h2>
196	237
197		<a name="sec:consulting"></a>
	238	<a id="sec:consulting"></a>
198	239
199	240	<p>This section deals with loading Prolog source files. A Prolog source
200	241	file is a plain text file containing a Prolog program or part thereof.

205	246	<dd>
206	247	Prolog source file contains Prolog clauses and directives, but no <em>module
207	248	declaration</em> (see
208		<a name="idx:module1:358"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>).
209		They are normally loaded using <a name="idx:consult1:359"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
210		or <a name="idx:ensureloaded1:360"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>.
	249	<a id="idx:module1:358"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>).
	250	They are normally loaded using <a id="idx:consult1:359"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	251	or <a id="idx:ensureloaded1:360"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>.
211	252	Currently, a non-module file can only be loaded into a single module.<sup class="fn">45<span class="fn-text">This
212	253	limitation may be lifted in the future. Existing limitations in
213	254	SWI-Prolog's source code administration make this non-trivial.</span></sup></dd>

216	257	Prolog source file starts with a module declaration. The subsequent
217	258	Prolog code is loaded into the specified module, and only the <em>exported</em>
218	259	predicates are made available to the context loading the module. Module
219		files are normally loaded with <a name="idx:usemodule12:361"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.
220		See <a class="sec" href="modules.html">chapter 6</a> for details.</dd>
	260	files are normally loaded with <a id="idx:usemodule12:361"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.
	261	See <a class="sec" href="modules.html#sec:6">chapter 6</a> for details.</dd>
221	262	<dt><b> An include</b></dt>
222	263	<dd>
223		Prolog source file is loaded using the <a name="idx:include1:362"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	264	Prolog source file is loaded using the <a id="idx:include1:362"></a><a class="pred" href="consulting.html#include/1">include/1</a>
224	265	directive, textually including Prolog text into another Prolog source. A
225	266	file may be included into multiple source files and is typically used to
226	267	share <em>declarations</em> such as multifile or dynamic between source

228	269	</dd>
229	270	</dl>
230	271
231		<p>Prolog source files are located using <a name="idx:absolutefilename3:363"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	272	<p>Prolog source files are located using <a id="idx:absolutefilename3:363"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
232	273	with the following options:
233	274
234	275	<pre class="code">

241	282	</pre>
242	283
243	284	<p>The <code>file_type(prolog)</code> option is used to determine the
244		extension of the file using <a name="idx:prologfiletype2:364"></a><a class="pred" href="consulting.html#prolog_file_type/2">prolog_file_type/2</a>.
	285	extension of the file using <a id="idx:prologfiletype2:364"></a><a class="pred" href="consulting.html#prolog_file_type/2">prolog_file_type/2</a>.
245	286	The default extension is
246	287	<code>.pl</code>. <var>Spec</var> allows for the <em>path alias</em>
247		construct defined by <a name="idx:absolutefilename3:365"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
	288	construct defined by <a id="idx:absolutefilename3:365"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
248	289	The most commonly used path alias is <code>library(LibraryFile)</code>.
249	290	The example below loads the library file <code>ordsets.pl</code>
250	291	(containing predicates for manipulating ordered sets).

253	294	:- use_module(library(ordsets)).
254	295	</pre>
255	296
256		<p>SWI-Prolog recognises grammar rules (<a name="idx:DCG:366">DCG</a>)
257		as defined in
	297	<p>SWI-Prolog recognises grammar rules (<a id="idx:DCG:366">DCG</a>) as
	298	defined in
258	299	<cite><a class="cite" href="Bibliography.html#Clocksin:87">Clocksin &
259	300	Melish, 1987</a></cite>. The user may define additional compilation of
260	301	the source file by defining the dynamic multifile predicates
261		<a name="idx:termexpansion2:367"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>, <a name="idx:termexpansion4:368"></a><a class="pred" href="consulting.html#term_expansion/4">term_expansion/4</a>, <a name="idx:goalexpansion2:369"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	302	<a id="idx:termexpansion2:367"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>, <a id="idx:termexpansion4:368"></a><a class="pred" href="consulting.html#term_expansion/4">term_expansion/4</a>, <a id="idx:goalexpansion2:369"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
262	303	and
263		<a name="idx:goalexpansion4:370"></a><a class="pred" href="consulting.html#goal_expansion/4">goal_expansion/4</a>.
264		It is not allowed to use <a name="idx:assert1:371"></a><a class="pred" href="db.html#assert/1">assert/1</a>, <a name="idx:retract1:372"></a><a class="pred" href="db.html#retract/1">retract/1</a>
265		or any other database predicate in <a name="idx:termexpansion2:373"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	304	<a id="idx:goalexpansion4:370"></a><a class="pred" href="consulting.html#goal_expansion/4">goal_expansion/4</a>.
	305	It is not allowed to use <a id="idx:assert1:371"></a><a class="pred" href="db.html#assert/1">assert/1</a>, <a id="idx:retract1:372"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	306	or any other database predicate in <a id="idx:termexpansion2:373"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
266	307	other than for local computational purposes.<sup class="fn">46<span class="fn-text">It
267		does work for normal loading, but not for <a name="idx:qcompile1:374"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>.</span></sup>
268		Code that needs to create additional clauses must use <a name="idx:compileauxclauses1:375"></a><a class="pred" href="consulting.html#compile_aux_clauses/1">compile_aux_clauses/1</a>.
	308	does work for normal loading, but not for <a id="idx:qcompile1:374"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>.</span></sup>
	309	Code that needs to create additional clauses must use <a id="idx:compileauxclauses1:375"></a><a class="pred" href="consulting.html#compile_aux_clauses/1">compile_aux_clauses/1</a>.
269	310	See <code>library(library(apply_macros))</code> for an example.
270	311
271	312	<p>A <em>directive</em> is an instruction to the compiler. Directives
272		are used to set (predicate) properties (see <a class="sec" href="dynamic.html">section
273		4.15</a>), set flags (see <a name="idx:setprologflag2:376"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>)
	313	are used to set (predicate) properties (see <a class="sec" href="dynamic.html#sec:4.15">section
	314	4.15</a>), set flags (see <a id="idx:setprologflag2:376"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>)
274	315	and load files (this section). Directives are terms of the form <code><code>:-</code></code> <<var>term</var>>.
275	316	. Here are some examples:
276	317

280	321	store/2. % Name, Value
281	322	</pre>
282	323
283		<p>The directive <a name="idx:initialization1:377"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	324	<p>The directive <a id="idx:initialization1:377"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
284	325	can be used to run arbitrary Prolog goals. The specified goal is started <em>after</em>
285	326	loading the file in which it appears has completed.
286	327

290	331	appears. It also accepts <code><code>?-</code></code> <<var>term</var>>.
291	332	as a synonym.
292	333
293		<p><a name="idx:reconsult:378"></a>SWI-Prolog does not have a separate
	334	<p><a id="idx:reconsult:378"></a>SWI-Prolog does not have a separate
294	335	reconsult/1 predicate. Reconsulting is implied automatically by the fact
295	336	that a file is consulted which is already loaded.
296	337
297	338	<p>Advanced topics are handled in subsequent sections: mutually
298		dependent files (<a class="sec" href="consulting.html">section 4.3.2.1</a>),
299		multithreaded loading (<a class="sec" href="consulting.html">section
300		4.3.2.2</a>) and reloading running code (<a class="sec" href="consulting.html">section
	339	dependent files (<a class="sec" href="consulting.html#sec:4.3.2.1">section
	340	4.3.2.1</a>), multithreaded loading (<a class="sec" href="consulting.html#sec:4.3.2.2">section
	341	4.3.2.2</a>) and reloading running code (<a class="sec" href="consulting.html#sec:4.3.2">section
301	342	4.3.2</a>).
302	343
303		<p>The core of the family of loading predicates is <a name="idx:loadfiles2:379"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
	344	<p>The core of the family of loading predicates is <a id="idx:loadfiles2:379"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
304	345	The predicates
305		<a name="idx:consult1:380"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>, <a name="idx:ensureloaded1:381"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>, <a name="idx:usemodule1:382"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>, <a name="idx:usemodule2:383"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
306		and <a name="idx:reexport1:384"></a><a class="pred" href="reexport.html#reexport/1">reexport/1</a>
307		pass the file argument directly to <a name="idx:loadfiles2:385"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	346	<a id="idx:consult1:380"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>, <a id="idx:ensureloaded1:381"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>, <a id="idx:usemodule1:382"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>, <a id="idx:usemodule2:383"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
	347	and <a id="idx:reexport1:384"></a><a class="pred" href="reexport.html#reexport/1">reexport/1</a>
	348	pass the file argument directly to <a id="idx:loadfiles2:385"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
308	349	and pass additional options as expressed in the <a class="tab" href="consulting.html#tab:loadpreds">table
309	350	4</a>:
310	351
311		<p><table border="2" frame="hsides" rules="groups" style="margin:auto">
312		<tr valign="top"><td><b>Predicate</b></td><td align=center><b>if</b></td><td align=center><b>must_be_module</b></td><td align=center><b>import </b></td></tr>
313		<tbody>
314		<tr valign="top"><td><a name="idx:consult1:386"></a><a class="pred" href="consulting.html#consult/1">consult/1</a> </td><td align=center><code>true</code> </td><td align=center><code>false</code> </td><td align=center>all </td></tr>
315		<tr valign="top"><td><a name="idx:ensureloaded1:387"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>false</code> </td><td align=center>all </td></tr>
316		<tr valign="top"><td><a name="idx:usemodule1:388"></a><a class="pred" href="import.html#use_module/1">use_module/1</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>true</code> </td><td align=center>all</td></tr>
317		<tr valign="top"><td><a name="idx:usemodule2:389"></a><a class="pred" href="import.html#use_module/2">use_module/2</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>true</code> </td><td align=center>specified </td></tr>
318		<tr valign="top"><td><a name="idx:reexport1:390"></a><a class="pred" href="reexport.html#reexport/1">reexport/1</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>true</code> </td><td align=center>all </td></tr>
319		<tr valign="top"><td><a name="idx:reexport2:391"></a><a class="pred" href="reexport.html#reexport/2">reexport/2</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>true</code> </td><td align=center>specified </td></tr>
	352	<p><table class="latex frame-hsides center">
	353	<tr><td><b>Predicate</b></td><td align=center><b>if</b></td><td align=center><b>must_be_module</b></td><td align=center><b>import </b></td></tr>
	354	<tr class="hline"><td><a id="idx:consult1:386"></a><a class="pred" href="consulting.html#consult/1">consult/1</a> </td><td align=center><code>true</code> </td><td align=center><code>false</code> </td><td align=center>all </td></tr>
	355	<tr><td><a id="idx:ensureloaded1:387"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>false</code> </td><td align=center>all </td></tr>
	356	<tr><td><a id="idx:usemodule1:388"></a><a class="pred" href="import.html#use_module/1">use_module/1</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>true</code> </td><td align=center>all</td></tr>
	357	<tr><td><a id="idx:usemodule2:389"></a><a class="pred" href="import.html#use_module/2">use_module/2</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>true</code> </td><td align=center>specified </td></tr>
	358	<tr><td><a id="idx:reexport1:390"></a><a class="pred" href="reexport.html#reexport/1">reexport/1</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>true</code> </td><td align=center>all </td></tr>
	359	<tr><td><a id="idx:reexport2:391"></a><a class="pred" href="reexport.html#reexport/2">reexport/2</a> </td><td align=center><code>not_loaded</code> </td><td align=center><code>true</code> </td><td align=center>specified </td></tr>
320	360	</table>
321	361	<div class="caption"><b>Table 4 : </b>Properties of the file-loading
322	362	predicates. The <i>import</i> column specifies what is imported if the
323	363	loaded file is a module file.</div>
324		<a name="tab:loadpreds"></a>
	364	<a id="tab:loadpreds"></a>
325	365
326	366	<dl class="latex">
327		<dt class="pubdef"><a name="load_files/1"><strong>load_files</strong>(<var>:Files</var>)</a></dt>
328		<dd class="defbody">
329		Equivalent to <code>load_files(Files,[])</code>. Same as <a name="idx:consult1:392"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
330		See <a name="idx:loadfiles2:393"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	367	<dt class="pubdef"><a id="load_files/1"><strong>load_files</strong>(<var>:Files</var>)</a></dt>
	368	<dd class="defbody">
	369	Equivalent to <code>load_files(Files,[])</code>. Same as <a id="idx:consult1:392"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
	370	See <a id="idx:loadfiles2:393"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
331	371	for supported options.
332	372	</dd>
333		<dt class="pubdef"><a name="load_files/2"><strong>load_files</strong>(<var>:Files,
	373	<dt class="pubdef"><a id="load_files/2"><strong>load_files</strong>(<var>:Files,
334	374	+Options</var>)</a></dt>
335	375	<dd class="defbody">
336		The predicate <a name="idx:loadfiles2:394"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
337		is the parent of all the other loading predicates except for <a name="idx:include1:395"></a><a class="pred" href="consulting.html#include/1">include/1</a>.
338		It currently supports a subset of the options of Quintus <a name="idx:loadfiles2:396"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>. <var>Files</var>
	376	The predicate <a id="idx:loadfiles2:394"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	377	is the parent of all the other loading predicates except for <a id="idx:include1:395"></a><a class="pred" href="consulting.html#include/1">include/1</a>.
	378	It currently supports a subset of the options of Quintus <a id="idx:loadfiles2:396"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>. <var>Files</var>
339	379	is either a single source file or a list of source files. The
340		specification for a source file is handed to <a name="idx:absolutefilename2:397"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>.
	380	specification for a source file is handed to <a id="idx:absolutefilename2:397"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>.
341	381	See this predicate for the supported expansions. <var>Options</var> is a
342	382	list of options using the format <var>OptionName</var>(<var>OptionValue</var>).
343	383

351	391	<em>demand</em> load. This implies that, depending on the setting of the
352	392	Prolog flag <a class="flag" href="flags.html#flag:verbose_autoload">verbose_autoload</a>,
353	393	the load action is printed at level <code>informational</code> or <code>silent</code>.
354		See also <a name="idx:printmessage2:398"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
355		and <a name="idx:currentprologflag2:399"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>.</dd>
	394	See also <a id="idx:printmessage2:398"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	395	and <a id="idx:currentprologflag2:399"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>.</dd>
356	396	<dt><strong>check_script</strong>(<var>Bool</var>)</dt>
357	397	<dd class="defbody">
358	398	If <code>false</code> (default <code>true</code>), do not check the

361	401	<dt><strong>derived_from</strong>(<var>File</var>)</dt>
362	402	<dd class="defbody">
363	403	Indicate that the loaded file is derived from <var>File</var>. Used by
364		<a name="idx:make0:400"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	404	<a id="idx:make0:400"></a><a class="pred" href="consulting.html#make/0">make/0</a>
365	405	to time-check and load the original file rather than the derived file.</dd>
366	406	<dt><strong>dialect</strong>(<var>+Dialect</var>)</dt>
367	407	<dd class="defbody">
368	408	Load <var>Files</var> with enhanced compatibility with the target Prolog
369		system identified by <var>Dialect</var>. See <a name="idx:expectsdialect1:401"></a><a class="pred" href="dialect.html#expects_dialect/1">expects_dialect/1</a>
	409	system identified by <var>Dialect</var>. See <a id="idx:expectsdialect1:401"></a><a class="pred" href="dialect.html#expects_dialect/1">expects_dialect/1</a>
370	410	and
371		<a class="sec" href="dialect.html">section C</a> for details.</dd>
	411	<a class="sec" href="dialect.html#sec:C">section C</a> for details.</dd>
372	412	<dt><strong>encoding</strong>(<var>Encoding</var>)</dt>
373	413	<dd class="defbody">
374	414	Specify the way characters are encoded in the file. Default is taken
375	415	from the Prolog flag <a class="flag" href="flags.html#flag:encoding">encoding</a>.
376		See <a class="sec" href="widechars.html">section 2.19.1</a> for details.</dd>
	416	See <a class="sec" href="widechars.html#sec:2.19.1">section 2.19.1</a>
	417	for details.</dd>
377	418	<dt><strong>expand</strong>(<var>Bool</var>)</dt>
378	419	<dd class="defbody">
379		If <code>true</code>, run the filenames through <a name="idx:expandfilename2:402"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>
380		and load the returned files. Default is <code>false</code>, except for <a name="idx:consult1:403"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	420	If <code>true</code>, run the filenames through <a id="idx:expandfilename2:402"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>
	421	and load the returned files. Default is <code>false</code>, except for <a id="idx:consult1:403"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
381	422	which is intended for interactive use. Flexible location of files is
382		defined by <a name="idx:filesearchpath2:404"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.</dd>
	423	defined by <a id="idx:filesearchpath2:404"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.</dd>
383	424	<dt><strong>format</strong>(<var>+Format</var>)</dt>
384	425	<dd class="defbody">
385	426	Used to specify the file format if data is loaded from a stream using
386	427	the <code>stream(Stream)</code> option. Default is <code>source</code>,
387		loading Prolog source text. If <code>qlf</code>, load QLF data (see <a name="idx:qcompile1:405"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>).</dd>
	428	loading Prolog source text. If <code>qlf</code>, load QLF data (see <a id="idx:qcompile1:405"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>).</dd>
388	429	<dt><strong>if</strong>(<var>Condition</var>)</dt>
389	430	<dd class="defbody">
390	431	Load the file only if the specified condition is satisfied. The value

395	436	<dt><strong>imports</strong>(<var>Import</var>)</dt>
396	437	<dd class="defbody">
397	438	Specify what to import from the loaded module. The default for
398		<a name="idx:usemodule1:406"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	439	<a id="idx:usemodule1:406"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
399	440	is <code>all</code>. <var>Import</var> is passed from the second
400		argument of <a name="idx:usemodule2:407"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>.
	441	argument of <a id="idx:usemodule2:407"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>.
401	442	Traditionally it is a list of predicate indicators to import. As part of
402	443	the SWI-Prolog/YAP integration, we also support <var>Pred</var> as <var>Name</var>
403	444	to import a predicate under another name. Finally, <var>Import</var> can
404	445	be the term <code>except(Exceptions)</code>, where <var>Exceptions</var>
405	446	is a list of predicate indicators that specify predicates that are <em>not</em>
406	447	imported or <var>Pred</var> as <var>Name</var> terms to denote renamed
407		predicates. See also <a name="idx:reexport2:408"></a><a class="pred" href="reexport.html#reexport/2">reexport/2</a>
	448	predicates. See also <a id="idx:reexport2:408"></a><a class="pred" href="reexport.html#reexport/2">reexport/2</a>
408	449	and
409		<a name="idx:usemodule2:409"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>.<sup class="fn">bug<span class="fn-text"><var>Name</var>/<var>Arity</var>
	450	<a id="idx:usemodule2:409"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>.<sup class="fn">bug<span class="fn-text"><var>Name</var>/<var>Arity</var>
410	451	as <var>NewName</var> is currently implemented using a <em>link clause</em>.
411	452	This harms efficiency and does not allow for querying the relation
412		through <a name="idx:predicateproperty2:410"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.</span></sup>
	453	through <a id="idx:predicateproperty2:410"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.</span></sup>
413	454
414	455	<p>If <var>Import</var> equals <code>all</code>, all operators are
415	456	imported as well. Otherwise, operators are <em>not</em> imported.

438	479	<dd class="defbody">
439	480	If <code>true</code>, raise an error if the file is not a module file.
440	481	Used by
441		<a name="idx:usemodule12:411"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.</dd>
	482	<a id="idx:usemodule12:411"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.</dd>
442	483	<dt><strong>qcompile</strong>(<var>Atom</var>)</dt>
443	484	<dd class="defbody">
444		How to deal with quick-load-file compilation by <a name="idx:qcompile1:412"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>.
	485	How to deal with quick-load-file compilation by <a id="idx:qcompile1:412"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>.
445	486	Values are:
446	487
447	488	<dl class="latex">

460	501	</dd>
461	502	<dt><strong>part</strong></dt>
462	503	<dd class="defbody">
463		If <a name="idx:loadfiles2:413"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	504	If <a id="idx:loadfiles2:413"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
464	505	appears in a directive of a file that is compiled into Quick Load Format
465		using <a name="idx:qcompile1:414"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>,
	506	using <a id="idx:qcompile1:414"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>,
466	507	the contents of the argument files are included in the <code>.qlf</code>
467	508	file instead of the loading directive.
468	509	</dd>

475	516	Defines what to do if a file is loaded that provides a module that is
476	517	already loaded from another file. <var>Action</var> is one of <code>false</code>
477	518	(default), which prints an error and refuses to load the file, or
478		<code>true</code>, which uses <a name="idx:unloadfile1:415"></a><a class="pred" href="consulting.html#unload_file/1">unload_file/1</a>
	519	<code>true</code>, which uses <a id="idx:unloadfile1:415"></a><a class="pred" href="consulting.html#unload_file/1">unload_file/1</a>
479	520	on the old file and then proceeds loading the new file. Finally, there
480	521	is <code>ask</code>, which starts interaction with the user. <code>ask</code>
481	522	is only provided if the stream <code>user_input</code> is associated
482	523	with a terminal.</dd>
483	524	<dt><strong>reexport</strong>(<var>Bool</var>)</dt>
484	525	<dd class="defbody">
485		If <code>true</code> re-export the imported predicate. Used by <a name="idx:reexport1:416"></a><a class="pred" href="reexport.html#reexport/1">reexport/1</a>
486		and <a name="idx:reexport2:417"></a><a class="pred" href="reexport.html#reexport/2">reexport/2</a>.</dd>
	526	If <code>true</code> re-export the imported predicate. Used by <a id="idx:reexport1:416"></a><a class="pred" href="reexport.html#reexport/1">reexport/1</a>
	527	and <a id="idx:reexport2:417"></a><a class="pred" href="reexport.html#reexport/2">reexport/2</a>.</dd>
487	528	<dt><strong>register</strong>(<var>Bool</var>)</dt>
488	529	<dd class="defbody">
489	530	If <code>false</code>, do not register the load location and options.
490		This option is used by <a name="idx:make0:418"></a><a class="pred" href="consulting.html#make/0">make/0</a>
491		and load_hotfixes1 to avoid polluting the load-context database. See <a name="idx:sourcefileproperty2:419"></a><a class="pred" href="consulting.html#source_file_property/2">source_file_property/2</a>.</dd>
	531	This option is used by <a id="idx:make0:418"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	532	and load_hotfixes/1 to avoid polluting the load-context database. See <a id="idx:sourcefileproperty2:419"></a><a class="pred" href="consulting.html#source_file_property/2">source_file_property/2</a>.</dd>
492	533	<dt><strong>sandboxed</strong>(<var>Bool</var>)</dt>
493	534	<dd class="defbody">
494	535	Load the file in <em>sandboxed</em> mode. This option controls the flag <a class="flag" href="flags.html#flag:sandboxed_load">sandboxed_load</a>.

497	538	Prolog flag is set to <code>true</code> raises a permission error.</dd>
498	539	<dt><strong>scope_settings</strong>(<var>Bool</var>)</dt>
499	540	<dd class="defbody">
500		Scope <a name="idx:stylecheck1:420"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>
501		and <a name="idx:expectsdialect1:421"></a><a class="pred" href="dialect.html#expects_dialect/1">expects_dialect/1</a>
	541	Scope <a id="idx:stylecheck1:420"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>
	542	and <a id="idx:expectsdialect1:421"></a><a class="pred" href="dialect.html#expects_dialect/1">expects_dialect/1</a>
502	543	to the file and files loaded from the file after the directive. Default
503	544	is <code>true</code>. The system and user initialization files (see <strong>-f</strong>
504	545	and

518	559	clauses as well as to remove all clauses if the data is reconsulted.
519	560
520	561	<p>This option is added to allow compiling from non-file locations such
521		as databases, the web, the <em>user</em> (see <a name="idx:consult1:422"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>)
	562	as databases, the web, the <em>user</em> (see <a id="idx:consult1:422"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>)
522	563	or other servers. It can be combined with <code>format(qlf)</code> to
523	564	load QLF data from a stream.
524	565	</dd>
525	566	</dl>
526	567
527		<p>The <a name="idx:loadfiles2:423"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	568	<p>The <a id="idx:loadfiles2:423"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
528	569	predicate can be hooked to load other data or data from objects other
529		than files. See <a name="idx:prologloadfile2:424"></a><a class="pred" href="loadfilehook.html#prolog_load_file/2">prolog_load_file/2</a>
	570	than files. See <a id="idx:prologloadfile2:424"></a><a class="pred" href="loadfilehook.html#prolog_load_file/2">prolog_load_file/2</a>
530	571	for a description and
531		<code>library(http/http_load)</code> for an example. All hooks for <a name="idx:loadfiles2:425"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
532		are documented in <a class="sec" href="loadfilehook.html">section B.8</a>.</dd>
533		<dt class="pubdef"><a name="consult/1"><strong>consult</strong>(<var>:File</var>)</a></dt>
534		<dd class="defbody">
535		Read <var>File</var> as a Prolog source file. Calls to <a name="idx:consult1:426"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	572	<code>library(http/http_load)</code> for an example. All hooks for <a id="idx:loadfiles2:425"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	573	are documented in <a class="sec" href="loadfilehook.html#sec:B.8">section
	574	B.8</a>.</dd>
	575	<dt class="pubdef"><a id="consult/1"><strong>consult</strong>(<var>:File</var>)</a></dt>
	576	<dd class="defbody">
	577	Read <var>File</var> as a Prolog source file. Calls to <a id="idx:consult1:426"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
536	578	may be abbreviated by just typing a number of filenames in a list.
537	579	Examples:
538		<div style="text-align:center"><table border="0" frame="void" rules="groups">
539		<tr valign="top"><td><code>?- consult(load).</code> </td><td>% consult <code>load</code>
	580
	581	<p><table class="latex frame-void center">
	582	<tr><td><code>?- consult(load).</code> </td><td>% consult <code>load</code>
540	583	or <code>load.pl</code> </td></tr>
541		<tr valign="top"><td><code>?- [library(lists)].</code> </td><td>% load
542		library lists </td></tr>
543		<tr valign="top"><td><code>?- [user].</code> </td><td>% Type program on
544		the terminal </td></tr>
	584	<tr><td><code>?- [library(lists)].</code> </td><td>% load library lists </td></tr>
	585	<tr><td><code>?- [user].</code> </td><td>% Type program on the terminal </td></tr>
545	586	</table>
546		</div>
547
548		<p>The predicate <a name="idx:consult1:427"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	587
	588	<p>The predicate <a id="idx:consult1:427"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
549	589	is equivalent to <code>load_files(File, [])</code>, except for handling
550	590	the special file <code>user</code>, which reads clauses from the
551	591	terminal. See also the <code>stream(Input)</code> option of
552		<a name="idx:loadfiles2:428"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
	592	<a id="idx:loadfiles2:428"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
553	593	Abbreviation using <code>?- [file1,file2].</code> does
554	594	<em>not</em> work for the empty list (<code>[]</code>). This facility is
555	595	implemented by defining the list as a predicate. Applications may only
556	596	rely on using the list abbreviation at the Prolog toplevel and in
557	597	directives.</dd>
558		<dt class="pubdef"><a name="ensure_loaded/1"><strong>ensure_loaded</strong>(<var>:File</var>)</a></dt>
559		<dd class="defbody">
560		If the file is not already loaded, this is equivalent to <a name="idx:consult1:429"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>.
	598	<dt class="pubdef"><a id="ensure_loaded/1"><strong>ensure_loaded</strong>(<var>:File</var>)</a></dt>
	599	<dd class="defbody">
	600	If the file is not already loaded, this is equivalent to <a id="idx:consult1:429"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>.
561	601	Otherwise, if the file defines a module, import all public predicates.
562	602	Finally, if the file is already loaded, is not a module file, and the
563		context module is not the global user module, <a name="idx:ensureloaded1:430"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>
564		will call <a name="idx:consult1:431"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>.
	603	context module is not the global user module, <a id="idx:ensureloaded1:430"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>
	604	will call <a id="idx:consult1:431"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>.
565	605
566	606	<p>With this semantics, we hope to get as close as possible to the clear
567	607	semantics without the presence of a module system. Applications using
568		modules should consider using <a name="idx:usemodule12:432"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.
	608	modules should consider using <a id="idx:usemodule12:432"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.
569	609
570	610	<p>Equivalent to <code>load_files(Files, [if(not_loaded)]).</code><sup class="fn">47<span class="fn-text">On
571	611	older versions the condition used to be <code>if(changed)</code>. Poor
572		time management on some machines or copying often caused problems. The <a name="idx:make0:433"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	612	time management on some machines or copying often caused problems. The <a id="idx:make0:433"></a><a class="pred" href="consulting.html#make/0">make/0</a>
573	613	predicate deals with updating the running system after changing the
574	614	source code.</span></sup></dd>
575		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="include/1"><strong>include</strong>(<var>+File</var>)</a></dt>
	615	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="include/1"><strong>include</strong>(<var>+File</var>)</a></dt>
576	616	<dd class="defbody">
577	617	Textually include the content of <var>File</var> at the position where
578	618	the
579	619	<em>directive</em> <code>:- include(File).</code> appears. The include
580	620	construct is only honoured if it appears as a directive in a source
581	621	file. <em>Textual</em> include (similar to C/C++ #include) is obviously
582		useful for sharing declarations such as <a name="idx:dynamic1:434"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
	622	useful for sharing declarations such as <a id="idx:dynamic1:434"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
583	623	or
584		<a name="idx:multifile1:435"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>
	624	<a id="idx:multifile1:435"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>
585	625	by including a file with directives from multiple files that use these
586	626	predicates.
587	627

590	630	in which they are defined. This information is used to <em>replace</em>
591	631	the old definition after the file has been modified and is reloaded by,
592	632	e.g.,
593		<a name="idx:make0:436"></a><a class="pred" href="consulting.html#make/0">make/0</a>.
594		As we understand it, <a name="idx:include1:437"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	633	<a id="idx:make0:436"></a><a class="pred" href="consulting.html#make/0">make/0</a>.
	634	As we understand it, <a id="idx:include1:437"></a><a class="pred" href="consulting.html#include/1">include/1</a>
595	635	is intended to include the same file multiple times. Including a file
596	636	holding clauses multiple times into the same module is rather
597	637	meaningless as it just duplicates the same clauses. Including a file
598	638	holding clauses in multiple modules does not suffer from this problem,
599	639	but leads to multiple equivalent
600		<em>copies</em> of predicates. Using <a name="idx:usemodule1:438"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	640	<em>copies</em> of predicates. Using <a id="idx:usemodule1:438"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
601	641	can achieve the same result while <em>sharing</em> the predicates.
602	642
603		<p>If <a name="idx:include1:439"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	643	<p>If <a id="idx:include1:439"></a><a class="pred" href="consulting.html#include/1">include/1</a>
604	644	is used to load files holding clauses, and if these files are loaded
605		only once, then these <a name="idx:include1:440"></a><a class="pred" href="consulting.html#include/1">include/1</a>
606		directives can be replaced by other predicates (such as <a name="idx:consult1:441"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>).
607		However, there are several cases where either <a name="idx:include1:442"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	645	only once, then these <a id="idx:include1:440"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	646	directives can be replaced by other predicates (such as <a id="idx:consult1:441"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>).
	647	However, there are several cases where either <a id="idx:include1:442"></a><a class="pred" href="consulting.html#include/1">include/1</a>
608	648	has no alternative, or using any alternative also requires other
609		changes. An example of the former is using <a name="idx:include1:443"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	649	changes. An example of the former is using <a id="idx:include1:443"></a><a class="pred" href="consulting.html#include/1">include/1</a>
610	650	to share directives. An example of the latter are cases where clauses of
611	651	different predicates are distributed over multiple files: If these files
612		are loaded with <a name="idx:include1:444"></a><a class="pred" href="consulting.html#include/1">include/1</a>,
613		the directive <a name="idx:discontiguous1:445"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a>
	652	are loaded with <a id="idx:include1:444"></a><a class="pred" href="consulting.html#include/1">include/1</a>,
	653	the directive <a id="idx:discontiguous1:445"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a>
614	654	is appropriate, whereas if they are consulted, one must use the
615		directive <a name="idx:multifile1:446"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.
	655	directive <a id="idx:multifile1:446"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.
616	656
617	657	<p>To accommodate included files holding clauses, SWI-Prolog
618	658	distinguishes between the source location of a clause (in this case the
619	659	included file) and the <em>owner</em> of a clause (the file that
620	660	includes the file holding the clause). The source location is used by,
621		e.g., <a name="idx:edit1:447"></a><a class="pred" href="edit.html#edit/1">edit/1</a>,
	661	e.g., <a id="idx:edit1:447"></a><a class="pred" href="edit.html#edit/1">edit/1</a>,
622	662	the graphical tracer, etc., while the owner is used to determine which
623	663	clauses are removed if the file is modified. Relevant information is
624	664	found with the following predicates:
625	665
626	666	<p>
627	667	<ul class="latex">
628		<li><a name="idx:sourcefile2:448"></a><a class="pred" href="consulting.html#source_file/2">source_file/2</a>
	668	<li><a id="idx:sourcefile2:448"></a><a class="pred" href="consulting.html#source_file/2">source_file/2</a>
629	669	describes the owner relation.
630		<li><a name="idx:predicateproperty2:449"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
	670	<li><a id="idx:predicateproperty2:449"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
631	671	describes the source location (of the first clause).
632		<li><a name="idx:clauseproperty2:450"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>
	672	<li><a id="idx:clauseproperty2:450"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>
633	673	provides access to both source and ownership.
634		<li><a name="idx:sourcefileproperty2:451"></a><a class="pred" href="consulting.html#source_file_property/2">source_file_property/2</a>
	674	<li><a id="idx:sourcefileproperty2:451"></a><a class="pred" href="consulting.html#source_file_property/2">source_file_property/2</a>
635	675	can be used to query include relationships between files.
636	676	</ul>
637	677	</dd>
638		<dt class="pubdef"><a name="require/1"><strong>require</strong>(<var>+ListOfNameAndArity</var>)</a></dt>
	678	<dt class="pubdef"><a id="require/1"><strong>require</strong>(<var>+ListOfNameAndArity</var>)</a></dt>
639	679	<dd class="defbody">
640	680	Declare that this file/module requires the specified predicates to be
641	681	defined ``with their commonly accepted definition''. This predicate

649	689
650	690	<p>SWI-Prolog, having autoloading, does <b>not</b> load the library.
651	691	Instead it creates a procedure header for the predicate if it does not
652		exist. This will flag the predicate as `undefined'. See also <a name="idx:check0:452"></a><a class="pred" href="check.html#check/0">check/0</a>
	692	exist. This will flag the predicate as `undefined'. See also <a id="idx:check0:452"></a><a class="pred" href="check.html#check/0">check/0</a>
653	693	and
654		<a name="idx:autoload0:453"></a><a class="pred" href="runtime.html#autoload/0">autoload/0</a>.</dd>
655		<dt class="pubdef"><a name="encoding/1"><strong>encoding</strong>(<var>+Encoding</var>)</a></dt>
	694	<a id="idx:autoload0:453"></a><a class="pred" href="runtime.html#autoload/0">autoload/0</a>.</dd>
	695	<dt class="pubdef"><a id="encoding/1"><strong>encoding</strong>(<var>+Encoding</var>)</a></dt>
656	696	<dd class="defbody">
657	697	This directive can appear anywhere in a source file to define how
658	698	characters are encoded in the remainder of the file. It can be used in
659	699	files that are encoded with a superset of US-ASCII, currently UTF-8 and
660		ISO Latin-1. See also <a class="sec" href="widechars.html">section
	700	ISO Latin-1. See also <a class="sec" href="widechars.html#sec:2.19.1">section
661	701	2.19.1</a>.</dd>
662		<dt class="pubdef"><a name="make/0"><strong>make</strong></a></dt>
	702	<dt class="pubdef"><a id="make/0"><strong>make</strong></a></dt>
663	703	<dd class="defbody">
664	704	Consult all source files that have been changed since they were
665	705	consulted. It checks <var>all</var> loaded source files: files loaded
666	706	into a compiled state using <code>pl -c ...</code> and files loaded
667		using <a name="idx:consult1:454"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
668		or one of its derivatives. The predicate <a name="idx:make0:455"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	707	using <a id="idx:consult1:454"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	708	or one of its derivatives. The predicate <a id="idx:make0:455"></a><a class="pred" href="consulting.html#make/0">make/0</a>
669	709	is called after
670		<a name="idx:edit1:456"></a><a class="pred" href="edit.html#edit/1">edit/1</a>,
	710	<a id="idx:edit1:456"></a><a class="pred" href="edit.html#edit/1">edit/1</a>,
671	711	automatically reloading all modified files. If the user uses an external
672		editor (in a separate window), <a name="idx:make0:457"></a><a class="pred" href="consulting.html#make/0">make/0</a>
673		is normally used to update the program after editing. In addition, <a name="idx:make0:458"></a><a class="pred" href="consulting.html#make/0">make/0</a>
674		updates the autoload indices (see <a class="sec" href="autoload.html">section
675		2.13</a>) and runs <a name="idx:listundefined0:459"></a><a class="pred" href="check.html#list_undefined/0">list_undefined/0</a>
	712	editor (in a separate window), <a id="idx:make0:457"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	713	is normally used to update the program after editing. In addition, <a id="idx:make0:458"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	714	updates the autoload indices (see <a class="sec" href="autoload.html#sec:2.13">section
	715	2.13</a>) and runs <a id="idx:listundefined0:459"></a><a class="pred" href="check.html#list_undefined/0">list_undefined/0</a>
676	716	from the <code>library(check)</code> library to report on undefined
677	717	predicates.</dd>
678		<dt class="pubdef"><a name="library_directory/1"><strong>library_directory</strong>(<var>?Atom</var>)</a></dt>
	718	<dt class="pubdef"><a id="library_directory/1"><strong>library_directory</strong>(<var>?Atom</var>)</a></dt>
679	719	<dd class="defbody">
680	720	Dynamic predicate used to specify library directories. Default
681	721	<code>./lib</code>, <code> /lib/prolog</code> and the system's library
682	722	(in this order) are defined. The user may add library directories using
683		<a name="idx:assertz1:460"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>, <a name="idx:asserta1:461"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
684		or remove system defaults using <a name="idx:retract1:462"></a><a class="pred" href="db.html#retract/1">retract/1</a>.
685		Deprecated. New code should use <a name="idx:filesearchpath2:463"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.</dd>
686		<dt class="pubdef"><a name="file_search_path/2"><strong>file_search_path</strong>(<var>+Alias,
	723	<a id="idx:assertz1:460"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>, <a id="idx:asserta1:461"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
	724	or remove system defaults using <a id="idx:retract1:462"></a><a class="pred" href="db.html#retract/1">retract/1</a>.
	725	Deprecated. New code should use <a id="idx:filesearchpath2:463"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.</dd>
	726	<dt class="pubdef"><a id="file_search_path/2"><strong>file_search_path</strong>(<var>+Alias,
687	727	-Path</var>)</a></dt>
688	728	<dd class="defbody">
689	729	Dynamic multifile hook predicate used to specify `path aliases'. This
690		hook is called by <a name="idx:absolutefilename3:464"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	730	hook is called by <a id="idx:absolutefilename3:464"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
691	731	to search files specified as
692	732	<code>Alias(Name)</code>, e.g., <code>library(lists)</code>. This
693	733	feature is best described using an example. Given the definition:

698	738
699	739	<p>the file specification <code>demo(myfile)</code> will be expanded to
700	740	<code>/usr/lib/prolog/demo/myfile</code>. The second argument of
701		<a name="idx:filesearchpath2:465"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	741	<a id="idx:filesearchpath2:465"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
702	742	may be another alias.
703	743
704	744	<p>Below is the initial definition of the file search path. This path

706	746	in the SWI-Prolog home directory. The alias <code>foreign(<<var>Path</var>>)</code>
707	747	is intended for storing shared libraries (<code>.so</code> or <code>.DLL</code>
708	748	files). See also
709		<a name="idx:useforeignlibrary1:466"></a><a class="pred" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a>.
	749	<a id="idx:useforeignlibrary1:466"></a><a class="pred" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a>.
710	750
711	751	<pre class="code">
712	752	user:file_search_path(library, X) :-

726	766	member(Dir, Dirs).
727	767	</pre>
728	768
729		<p>The <a name="idx:filesearchpath2:467"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
730		expansion is used by all loading predicates as well as by <a name="idx:absolutefilename23:468"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/[2,3]</a>.
	769	<p>The <a id="idx:filesearchpath2:467"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	770	expansion is used by all loading predicates as well as by <a id="idx:absolutefilename23:468"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/[2,3]</a>.
731	771
732	772	<p>The Prolog flag <a class="flag" href="flags.html#flag:verbose_file_search">verbose_file_search</a>
733	773	can be set to <code>true</code> to help debugging Prolog's search for
734	774	files.</dd>
735		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="expand_file_search_path/2"><strong>expand_file_search_path</strong>(<var>+Spec,
	775	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="expand_file_search_path/2"><strong>expand_file_search_path</strong>(<var>+Spec,
736	776	-Path</var>)</a></dt>
737	777	<dd class="defbody">
738	778	Unifies <var>Path</var> with all possible expansions of the filename
739		specification <var>Spec</var>. See also <a name="idx:absolutefilename3:469"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.</dd>
740		<dt class="pubdef"><a name="prolog_file_type/2"><strong>prolog_file_type</strong>(<var>?Extension,
	779	specification <var>Spec</var>. See also <a id="idx:absolutefilename3:469"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.</dd>
	780	<dt class="pubdef"><a id="prolog_file_type/2"><strong>prolog_file_type</strong>(<var>?Extension,
741	781	?Type</var>)</a></dt>
742	782	<dd class="defbody">
743	783	This dynamic multifile predicate defined in module <code>user</code>
744		determines the extensions considered by <a name="idx:filesearchpath2:470"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
	784	determines the extensions considered by <a id="idx:filesearchpath2:470"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
745	785	<var>Extension</var> is the filename extension without the leading dot,
746	786	and
747	787	<var>Type</var> denotes the type as used by the <code>file_type(Type)</code>
748		option of <a name="idx:filesearchpath2:471"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
	788	option of <a id="idx:filesearchpath2:471"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
749	789	Here is the initial definition of
750		<a name="idx:prologfiletype2:472"></a><a class="pred" href="consulting.html#prolog_file_type/2">prolog_file_type/2</a>:
	790	<a id="idx:prologfiletype2:472"></a><a class="pred" href="consulting.html#prolog_file_type/2">prolog_file_type/2</a>:
751	791
752	792	<pre class="code">
753	793	user:prolog_file_type(pl, prolog).

764	804	Prolog implementation. We suggest using <code>.pro</code> for avoiding
765	805	conflicts with <b>perl</b>. Overriding the system definitions can stop
766	806	the system from finding libraries.</dd>
767		<dt class="pubdef"><a name="source_file/1"><strong>source_file</strong>(<var>?File</var>)</a></dt>
	807	<dt class="pubdef"><a id="source_file/1"><strong>source_file</strong>(<var>?File</var>)</a></dt>
768	808	<dd class="defbody">
769	809	True if <var>File</var> is a loaded Prolog source file. <var>File</var>
770	810	is the absolute and canonical path to the source file.</dd>
771		<dt class="pubdef"><a name="source_file/2"><strong>source_file</strong>(<var>:Pred,
	811	<dt class="pubdef"><a id="source_file/2"><strong>source_file</strong>(<var>:Pred,
772	812	?File</var>)</a></dt>
773	813	<dd class="defbody">
774	814	True if the predicate specified by <var>Pred</var> is owned by file
775	815	<var>File</var>, where <var>File</var> is an absolute path name (see
776		<a name="idx:absolutefilename2:473"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>).
	816	<a id="idx:absolutefilename2:473"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>).
777	817	Can be used with any instantiation pattern, but the database only
778	818	maintains the source file for each predicate. If
779	819	<var>Pred</var> is a <em>multifile</em> predicate this predicate
780	820	succeeds for all files that contribute clauses to <var>Pred</var>.<sup class="fn">48<span class="fn-text">The
781	821	current implementation performs a linear scan through all clauses to
782		establish this set of files.</span></sup> See also <a name="idx:clauseproperty2:474"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>.
	822	establish this set of files.</span></sup> See also <a id="idx:clauseproperty2:474"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>.
783	823	Note that the relation between files and predicates is more complicated
784		if <a name="idx:include1:475"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	824	if <a id="idx:include1:475"></a><a class="pred" href="consulting.html#include/1">include/1</a>
785	825	is used. The predicate describes the <em>owner</em> of the predicate.
786	826	See
787		<a name="idx:include1:476"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	827	<a id="idx:include1:476"></a><a class="pred" href="consulting.html#include/1">include/1</a>
788	828	for details.</dd>
789		<dt class="pubdef"><a name="source_file_property/2"><strong>source_file_property</strong>(<var>?File,
	829	<dt class="pubdef"><a id="source_file_property/2"><strong>source_file_property</strong>(<var>?File,
790	830	?Property</var>)</a></dt>
791	831	<dd class="defbody">
792	832	True when <var>Property</var> is a property of the loaded file <var>File</var>.
793	833	If <var>File</var> is non-var, it can be a file specification that is
794		valid for <a name="idx:loadfiles2:477"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
	834	valid for <a id="idx:loadfiles2:477"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
795	835	Defined properties are:
796	836
797	837	<dl class="latex">

801	841	was last modified at time <var>OriginalModified</var> at the time it was
802	842	loaded. This property is available if <var>File</var> was loaded using
803	843	the
804		<code>derived_from(Original)</code> option to <a name="idx:loadfiles2:478"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.</dd>
	844	<code>derived_from(Original)</code> option to <a id="idx:loadfiles2:478"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.</dd>
805	845	<dt><strong>includes</strong>(<var>IncludedFile, IncludedFileModified</var>)</dt>
806	846	<dd class="defbody">
807		<var>File</var> used <a name="idx:include1:479"></a><a class="pred" href="consulting.html#include/1">include/1</a>
	847	<var>File</var> used <a id="idx:include1:479"></a><a class="pred" href="consulting.html#include/1">include/1</a>
808	848	to include <var>IncludedFile</var>. The last modified time of <var>IncludedFile</var>
809	849	was <var>IncludedFileModified</var> at the time it was included.</dd>
810	850	<dt><strong>included_in</strong>(<var>MasterFile, Line</var>)</dt>

820	860	the file was loaded. It is either a term <<var>file</var>>:<<var>line</var>>
821	861	or the atom
822	862	<code>user</code> if the file was loaded from the terminal or another
823		unknown source. <var>Options</var> are the options passed to <a name="idx:loadfiles2:480"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
824		Note that all predicates to load files are mapped to <a name="idx:loadfiles2:481"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>,
	863	unknown source. <var>Options</var> are the options passed to <a id="idx:loadfiles2:480"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
	864	Note that all predicates to load files are mapped to <a id="idx:loadfiles2:481"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>,
825	865	using the option argument to specify the exact behaviour.</dd>
826	866	<dt><strong>load_count</strong>(<var>-Count</var>)</dt>
827	867	<dd class="defbody">

830	870	<dt><strong>modified</strong>(<var>Stamp</var>)</dt>
831	871	<dd class="defbody">
832	872	File modification time when <var>File</var> was loaded. This is used by
833		<a name="idx:make0:482"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	873	<a id="idx:make0:482"></a><a class="pred" href="consulting.html#make/0">make/0</a>
834	874	to find files whose modification time is different from when it was
835	875	loaded.</dd>
836	876	<dt><strong>module</strong>(<var>Module</var>)</dt>

848	888	</dl>
849	889
850	890	</dd>
851		<dt class="pubdef"><a name="unload_file/1"><strong>unload_file</strong>(<var>+File</var>)</a></dt>
	891	<dt class="pubdef"><a id="unload_file/1"><strong>unload_file</strong>(<var>+File</var>)</a></dt>
852	892	<dd class="defbody">
853	893	Remove all clauses loaded from <var>File</var>. If <var>File</var>
854	894	loaded a module, clear the module's export list and disassociate it from
855	895	the file. <var>File</var> is a canonical filename or a file indicator
856		that is valid for <a name="idx:loadfiles2:483"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
	896	that is valid for <a id="idx:loadfiles2:483"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
857	897
858	898	<p>This predicate should be used with care. The multithreaded nature of
859	899	SWI-Prolog makes removing static code unsafe. Attempts to do this should
860	900	be reserved for development or situations where the application can
861	901	guarantee that none of the clauses associated to <var>File</var> are
862	902	active.</dd>
863		<dt class="pubdef"><a name="prolog_load_context/2"><strong>prolog_load_context</strong>(<var>?Key,
	903	<dt class="pubdef"><a id="prolog_load_context/2"><strong>prolog_load_context</strong>(<var>?Key,
864	904	?Value</var>)</a></dt>
865	905	<dd class="defbody">
866	906	Obtain context information during compilation. This predicate can be
867	907	used from directives appearing in a source file to get information about
868		the file being loaded as well as by the <a name="idx:termexpansion2:484"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	908	the file being loaded as well as by the <a id="idx:termexpansion2:484"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
869	909	and
870		<a name="idx:goalexpansion2:485"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
871		hooks. See also <a name="idx:sourcelocation2:486"></a><a class="pred" href="consulting.html#source_location/2">source_location/2</a>
872		and <a name="idx:if1:487"></a><a class="pred" href="consulting.html#if/1">if/1</a>.
	910	<a id="idx:goalexpansion2:485"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	911	hooks. See also <a id="idx:sourcelocation2:486"></a><a class="pred" href="consulting.html#source_location/2">source_location/2</a>
	912	and <a id="idx:if1:487"></a><a class="pred" href="consulting.html#if/1">if/1</a>.
873	913	The following keys are defined:
874	914
875		<p><table border="2" frame="box" rules="groups" style="margin:auto">
876		<tr valign="top"><td><b>Key</b></td><td><b>Description </b></td></tr>
877		<tbody>
878		<tr valign="top"><td><code>directory</code> </td><td>Directory in which <code>source</code>
	915	<p><table class="latex frame-box center">
	916	<tr><td><b>Key</b></td><td><b>Description </b></td></tr>
	917	<tr class="hline"><td><code>directory</code> </td><td>Directory in which <code>source</code>
879	918	lives </td></tr>
880		<tr valign="top"><td><code>dialect</code> </td><td>Compatibility mode.
881		See <a name="idx:expectsdialect1:488"></a><a class="pred" href="dialect.html#expects_dialect/1">expects_dialect/1</a>. </td></tr>
882		<tr valign="top"><td><code>file</code> </td><td>Similar to <code>source</code>,
883		but returns the file being included when called while an include file is
	919	<tr><td><code>dialect</code> </td><td>Compatibility mode. See <a id="idx:expectsdialect1:488"></a><a class="pred" href="dialect.html#expects_dialect/1">expects_dialect/1</a>. </td></tr>
	920	<tr><td><code>file</code> </td><td>Similar to <code>source</code>, but
	921	returns the file being included when called while an include file is
884	922	being processed </td></tr>
885		<tr valign="top"><td><code>module</code> </td><td>Module into which file
886		is loaded </td></tr>
887		<tr valign="top"><td><code>reload</code> </td><td><code>true</code> if
888		the file is being
	923	<tr><td><code>module</code> </td><td>Module into which file is loaded </td></tr>
	924	<tr><td><code>reload</code> </td><td><code>true</code> if the file is
	925	being
889	926	<b>re</b>loaded. Not present on first load </td></tr>
890		<tr valign="top"><td><code>script</code> </td><td>Boolean that indicates
891		whether the file is loaded as a script file (see
	927	<tr><td><code>script</code> </td><td>Boolean that indicates whether the
	928	file is loaded as a script file (see
892	929	<strong>-s</strong>) </td></tr>
893		<tr valign="top"><td><code>source</code> </td><td>File being loaded. If
894		the system is processing an included file, the value is the <em>main</em>
895		file. Returns the original Prolog file when loading a
	930	<tr><td><code>source</code> </td><td>File being loaded. If the system is
	931	processing an included file, the value is the <em>main</em> file.
	932	Returns the original Prolog file when loading a
896	933	<code>.qlf</code> file. </td></tr>
897		<tr valign="top"><td><code>stream</code> </td><td>Stream identifier (see <a name="idx:currentinput1:489"></a><a class="pred" href="IO.html#current_input/1">current_input/1</a>) </td></tr>
898		<tr valign="top"><td><code>term_position</code> </td><td>Start position
899		of last term read. See also
900		<a name="idx:streamproperty2:490"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
	934	<tr><td><code>stream</code> </td><td>Stream identifier (see <a id="idx:currentinput1:489"></a><a class="pred" href="IO.html#current_input/1">current_input/1</a>) </td></tr>
	935	<tr><td><code>term_position</code> </td><td>Start position of last term
	936	read. See also
	937	<a id="idx:streamproperty2:490"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>
901	938	(<code>position</code> property and
902		<a name="idx:streampositiondata3:491"></a><a class="pred" href="IO.html#stream_position_data/3">stream_position_data/3</a>.<sup class="fn">49<span class="fn-text">Up
	939	<a id="idx:streampositiondata3:491"></a><a class="pred" href="IO.html#stream_position_data/3">stream_position_data/3</a>.<sup class="fn">49<span class="fn-text">Up
903	940	to version 7.1.22, the position term carried fake data except for the <code>line_count</code>
904	941	and had <b>five</b> arguments, where the position property of a stream
905	942	only has <b>four</b>.</span></sup> </td></tr>
906		<tr valign="top"><td><code>term</code> </td><td>Term being expanded by <a name="idx:expandterm2:492"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>. </td></tr>
907		<tr valign="top"><td><code>variable_names</code></td><td>A list of `<var>Name</var>
908		= <var>Var</var>' of the last term read. See <a name="idx:readterm2:493"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	943	<tr><td><code>term</code> </td><td>Term being expanded by <a id="idx:expandterm2:492"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>. </td></tr>
	944	<tr><td><code>variable_names</code></td><td>A list of `<var>Name</var> = <var>Var</var>'
	945	of the last term read. See <a id="idx:readterm2:493"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
909	946	for details. </td></tr>
910	947	</table>
911	948
912		<p>The <code>directory</code> is commonly used to add rules to <a name="idx:filesearchpath2:494"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>,
913		setting up a search path for finding files with <a name="idx:absolutefilename3:495"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
	949	<p>The <code>directory</code> is commonly used to add rules to <a id="idx:filesearchpath2:494"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>,
	950	setting up a search path for finding files with <a id="idx:absolutefilename3:495"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
914	951	For example:
915	952
916	953	<pre class="code">

927	964	</pre>
928	965
929	966	</dd>
930		<dt class="pubdef"><a name="source_location/2"><strong>source_location</strong>(<var>-File,
	967	<dt class="pubdef"><a id="source_location/2"><strong>source_location</strong>(<var>-File,
931	968	-Line</var>)</a></dt>
932	969	<dd class="defbody">
933	970	If the last term has been read from a physical file (i.e., not from the
934	971	file <code>user</code> or a string), unify <var>File</var> with an
935	972	absolute path to the file and <var>Line</var> with the line number in
936		the file. New code should use <a name="idx:prologloadcontext2:496"></a><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a>.</dd>
937		<dt class="pubdef"><a name="at_halt/1"><strong>at_halt</strong>(<var>:Goal</var>)</a></dt>
	973	the file. New code should use <a id="idx:prologloadcontext2:496"></a><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a>.</dd>
	974	<dt class="pubdef"><a id="at_halt/1"><strong>at_halt</strong>(<var>:Goal</var>)</a></dt>
938	975	<dd class="defbody">
939	976	Register <var>Goal</var> to be run from <a class="func" href="foreigninclude.html#PL_cleanup()">PL_cleanup()</a>,
940	977	which is called when the system halts. The hooks are run in the reverse
941	978	order they were registered (FIFO). Success or failure executing a hook
942		is ignored. If the hook raises an exception this is printed using <a name="idx:printmessage2:497"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
943		An attempt to call <a name="idx:halt01:498"></a><a class="pred" href="toplevel.html#halt/0">halt/[0,1]</a>
	979	is ignored. If the hook raises an exception this is printed using <a id="idx:printmessage2:497"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
	980	An attempt to call <a id="idx:halt01:498"></a><a class="pred" href="toplevel.html#halt/0">halt/[0,1]</a>
944	981	from a hook is ignored. Hooks may call
945		<a name="idx:cancelhalt1:499"></a><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a>,
946		causing <a name="idx:halt0:500"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>
	982	<a id="idx:cancelhalt1:499"></a><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a>,
	983	causing <a id="idx:halt0:500"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>
947	984	and <a class="func" href="foreigninclude.html#PL_halt()">PL_halt(0)</a>
948	985	to print a message indicating that halting the system has been
949	986	cancelled.</dd>
950		<dt class="pubdef"><a name="cancel_halt/1"><strong>cancel_halt</strong>(<var>+Reason</var>)</a></dt>
951		<dd class="defbody">
952		If this predicate is called from a hook registered with <a name="idx:athalt1:501"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>,
	987	<dt class="pubdef"><a id="cancel_halt/1"><strong>cancel_halt</strong>(<var>+Reason</var>)</a></dt>
	988	<dd class="defbody">
	989	If this predicate is called from a hook registered with <a id="idx:athalt1:501"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>,
953	990	halting Prolog is cancelled and an informational message is printed that
954	991	includes <var>Reason</var>. This is used by the development tools to
955	992	cancel halting the system if the editor has unsafed data and the user
956	993	decides to cancel.</dd>
957		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="initialization/1">:- <strong>initialization</strong>(<var>:Goal</var>)</a></dt>
	994	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="initialization/1">:- <strong>initialization</strong>(<var>:Goal</var>)</a></dt>
958	995	<dd class="defbody">
959	996	Call <var>Goal</var> <em>after</em> loading the source file in which
960	997	this directive appears has been completed. In addition, <var>Goal</var>
961		is executed if a saved state created using <a name="idx:qsaveprogram1:502"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/1</a>
	998	is executed if a saved state created using <a id="idx:qsaveprogram1:502"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/1</a>
962	999	is restored.
963	1000
964	1001	<p>The ISO standard only allows for using <code>:- Term</code> if <var>Term</var>
965	1002	is a
966	1003	<em>directive</em>. This means that arbitrary goals can only be called
967		from a directive by means of the <a name="idx:initialization1:503"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	1004	from a directive by means of the <a id="idx:initialization1:503"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
968	1005	directive. SWI-Prolog does not enforce this rule.
969	1006
970		<p>The <a name="idx:initialization1:504"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
971		directive must be used to do program initialization in saved states (see <a name="idx:qsaveprogram1:505"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/1</a>).
	1007	<p>The <a id="idx:initialization1:504"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	1008	directive must be used to do program initialization in saved states (see <a id="idx:qsaveprogram1:505"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/1</a>).
972	1009	A saved state contains the predicates, Prolog flags and operators
973	1010	present at the moment the state was created. Other resources (records,
974		foreign resources, etc.) must be recreated using <a name="idx:initialization1:506"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	1011	foreign resources, etc.) must be recreated using <a id="idx:initialization1:506"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
975	1012	directives or from the entry goal of the saved state.
976	1013
977	1014	<p>Up to SWI-Prolog 5.7.11, <var>Goal</var> was executed immediately
978	1015	rather than after loading the program text in which the directive
979	1016	appears as dictated by the ISO standard. In many cases the exact moment
980	1017	of execution is irrelevant, but there are exceptions. For example,
981		<a name="idx:loadforeignlibrary1:507"></a><a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>
	1018	<a id="idx:loadforeignlibrary1:507"></a><a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>
982	1019	must be executed immediately to make the loaded foreign predicates
983		available for exporting. SWI-Prolog now provides the directive <a name="idx:useforeignlibrary1:508"></a><a class="pred" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a>
	1020	available for exporting. SWI-Prolog now provides the directive <a id="idx:useforeignlibrary1:508"></a><a class="pred" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a>
984	1021	to ensure immediate loading as well as loading after restoring a saved
985	1022	state. If the system encounters a directive <code>:-
986	1023	initialization(load_foreign_library(...))</code>, it will load the

988	1025	This behaviour can be extended by providing clauses for the multifile
989	1026	hook predicate <code>prolog:initialize_now(Term, Advice)</code>, where <var>Advice</var>
990	1027	is an atom that gives advice on how to resolve the compatibility issue.</dd>
991		<dt class="pubdef"><a name="initialization/2"><strong>initialization</strong>(<var>:Goal,
	1028	<dt class="pubdef"><a id="initialization/2"><strong>initialization</strong>(<var>:Goal,
992	1029	+When</var>)</a></dt>
993	1030	<dd class="defbody">
994		Similar to <a name="idx:initialization1:509"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>,
	1031	Similar to <a id="idx:initialization1:509"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>,
995	1032	but allows for specifying when <var>Goal</var> is executed while loading
996	1033	the program text:
997	1034

1003	1040	<dd class="defbody">
1004	1041	Execute <var>Goal</var> after loading the program text in which the
1005	1042	directive appears. This is the same as
1006		<a name="idx:initialization1:510"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>.</dd>
	1043	<a id="idx:initialization1:510"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>.</dd>
1007	1044	<dt><strong>restore</strong></dt>
1008	1045	<dd class="defbody">
1009	1046	Do not execute <var>Goal</var> while loading the program, but <em>only</em>

1015	1052	encountered and a failure or exception causes the Prolog to exit with
1016	1053	non-zero exit status. These goals are <em>not</em> executed if the
1017	1054	<strong>-l</strong> is given to merely <em>load</em> files. In that case
1018		they may be executed explicitly using <a name="idx:initialize0:511"></a><span class="pred-ext">initialize/0</span>.
	1055	they may be executed explicitly using <a id="idx:initialize0:511"></a><span class="pred-ext">initialize/0</span>.
1019	1056	See also
1020		<a class="sec" href="compilation.html">section 2.10.2.1</a>.</dd>
	1057	<a class="sec" href="compilation.html#sec:2.10.2.1">section 2.10.2.1</a>.</dd>
1021	1058	<dt><strong>main</strong></dt>
1022	1059	<dd class="defbody">
1023	1060	When Prolog starts, the last goal registered using
1024	1061	<code>initialization(Goal, main)</code> is executed as main goal. If
1025	1062	<var>Goal</var> fails or raises an exception, the process terminates
1026	1063	with non-zero exit code. If not explicitly specified using the
1027		<strong>-t</strong> the <em>toplevel goal</em> is set to <a name="idx:halt0:512"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>,
	1064	<strong>-t</strong> the <em>toplevel goal</em> is set to <a id="idx:halt0:512"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>,
1028	1065	causing the process to exit with status 0. An explicitly specified
1029	1066	toplevel is executed normally. This implies that <code>-t prolog</code>
1030	1067	causes the application to start the normal interactive toplevel after
1031	1068	completing
1032	1069	<var>Goal</var>. See also the Prolog flag <a class="flag" href="flags.html#flag:toplevel_goal">toplevel_goal</a>
1033	1070	and
1034		<a class="sec" href="compilation.html">section 2.10.2.1</a>.
	1071	<a class="sec" href="compilation.html#sec:2.10.2.1">section 2.10.2.1</a>.
1035	1072	</dd>
1036	1073	</dl>
1037	1074
1038	1075	</dd>
1039		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="initialization/0"><strong>initialization</strong></a></dt>
	1076	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="initialization/0"><strong>initialization</strong></a></dt>
1040	1077	<dd class="defbody">
1041	1078	Run all initialization goals registered using
1042	1079	<code>initialization(Goal, program)</code>. Raises an error
1043	1080	<code>initialization_error(Reason, Goal, File:Line)</code> if <var>Goal</var>
1044	1081	fails or raises an exception. <var>Reason</var> is <code>failed</code>
1045	1082	or the exception raised.</dd>
1046		<dt class="pubdef"><a name="compiling/0"><strong>compiling</strong></a></dt>
	1083	<dt class="pubdef"><a id="compiling/0"><strong>compiling</strong></a></dt>
1047	1084	<dd class="defbody">
1048	1085	True if the system is compiling source files with the <strong>-c</strong>
1049		option or <a name="idx:qcompile1:513"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>
	1086	option or <a id="idx:qcompile1:513"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>
1050	1087	into an intermediate code file. Can be used to perform conditional code
1051		optimisations in <a name="idx:termexpansion2:514"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	1088	optimisations in <a id="idx:termexpansion2:514"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
1052	1089	(see also the
1053	1090	<strong>-O</strong> option) or to omit execution of directives during
1054	1091	compilation.
1055	1092	</dd>
1056	1093	</dl>
1057	1094
1058		<p><h3 id="sec:progtransform"><a name="sec:4.3.1"><span class="sec-nr">4.3.1</span> <span class="sec-title">Conditional
	1095	<p><h3 id="sec:progtransform"><a id="sec:4.3.1"><span class="sec-nr">4.3.1</span> <span class="sec-title">Conditional
1059	1096	compilation and program transformation</span></a></h3>
1060	1097
1061		<a name="sec:progtransform"></a>
1062
1063		<p><a name="idx:transformationofprogram:515"></a>ISO Prolog defines no
1064		way for program transformations such as macro expansion or conditional
1065		compilation. Expansion through <a name="idx:termexpansion2:516"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
1066		and <a name="idx:expandterm2:517"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>
	1098	<a id="sec:progtransform"></a>
	1099
	1100	<p><a id="idx:transformationofprogram:515"></a>ISO Prolog defines no way
	1101	for program transformations such as macro expansion or conditional
	1102	compilation. Expansion through <a id="idx:termexpansion2:516"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	1103	and <a id="idx:expandterm2:517"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>
1067	1104	can be seen as part of the de-facto standard. This mechanism can do
1068	1105	arbitrary translation between valid Prolog terms read from the source
1069	1106	file to Prolog terms handed to the compiler. As
1070		<a name="idx:termexpansion2:518"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	1107	<a id="idx:termexpansion2:518"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
1071	1108	can return a list, the transformation does not need to be term-to-term.
1072	1109
1073		<p>Various Prolog dialects provide the analogous <a name="idx:goalexpansion2:519"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1110	<p>Various Prolog dialects provide the analogous <a id="idx:goalexpansion2:519"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1074	1111	and
1075		<a name="idx:expandgoal2:520"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>
	1112	<a id="idx:expandgoal2:520"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>
1076	1113	that allow for translation of individual body terms, freeing the user of
1077	1114	the task to disassemble each clause.
1078	1115
1079	1116	<dl class="latex">
1080		<dt class="pubdef"><a name="term_expansion/2"><strong>term_expansion</strong>(<var>+Term1,
	1117	<dt class="pubdef"><a id="term_expansion/2"><strong>term_expansion</strong>(<var>+Term1,
1081	1118	-Term2</var>)</a></dt>
1082	1119	<dd class="defbody">
1083	1120	Dynamic and multifile predicate, normally not defined. When defined by

1093	1130	<code>'$source_location'(<<var>File</var>>, <<var>Line</var>>):<<var>Clause</var>></code>
1094	1131	</blockquote>
1095	1132
1096		<p>When compiling a module (see <a class="sec" href="modules.html">chapter
1097		6</a> and the directive <a name="idx:module2:521"></a><a class="pred" href="defmodule.html#module/2">module/2</a>),
1098		<a name="idx:expandterm2:522"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>
1099		will first try <a name="idx:termexpansion2:523"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	1133	<p>When compiling a module (see <a class="sec" href="modules.html#sec:6">chapter
	1134	6</a> and the directive <a id="idx:module2:521"></a><a class="pred" href="defmodule.html#module/2">module/2</a>),
	1135	<a id="idx:expandterm2:522"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>
	1136	will first try <a id="idx:termexpansion2:523"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
1100	1137	in the module being compiled to allow for term expansion rules that are
1101	1138	local to a module. If there is no local definition, or the local
1102		definition fails to translate the term, <a name="idx:expandterm2:524"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>
1103		will try <a name="idx:termexpansion2:525"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	1139	definition fails to translate the term, <a id="idx:expandterm2:524"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>
	1140	will try <a id="idx:termexpansion2:525"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
1104	1141	in module
1105	1142	<code>user</code>. For compatibility with SICStus and Quintus Prolog,
1106		this feature should not be used. See also <a name="idx:expandterm2:526"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>, <a name="idx:goalexpansion2:527"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1143	this feature should not be used. See also <a id="idx:expandterm2:526"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>, <a id="idx:goalexpansion2:527"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1107	1144	and
1108		<a name="idx:expandgoal2:528"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>.</dd>
1109		<dt class="pubdef"><a name="expand_term/2"><strong>expand_term</strong>(<var>+Term1,
	1145	<a id="idx:expandgoal2:528"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>.</dd>
	1146	<dt class="pubdef"><a id="expand_term/2"><strong>expand_term</strong>(<var>+Term1,
1110	1147	-Term2</var>)</a></dt>
1111	1148	<dd class="defbody">
1112	1149	This predicate is normally called by the compiler on terms read from the

1116	1153	<p>
1117	1154	<ol class="latex">
1118	1155	<li>Test conditional compilation directives and translate all input to <code>[]</code>
1119		if we are in a `false branch' of the conditional compilation. See <a class="sec" href="consulting.html">section
	1156	if we are in a `false branch' of the conditional compilation. See <a class="sec" href="consulting.html#sec:4.3.1.2">section
1120	1157	4.3.1.2</a>.
1121	1158
1122	1159	<p>
1123		<li>Call <a name="idx:termexpansion2:529"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>.
	1160	<li>Call <a id="idx:termexpansion2:529"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>.
1124	1161	This predicate is first tried in the module that is being compiled and
1125	1162	then in the module
1126	1163	<code>user</code>.
1127	1164
1128	1165	<p>
1129		<li>Call DCG expansion (<a name="idx:dcgtranslaterule2:530"></a><a class="pred" href="consulting.html#dcg_translate_rule/2">dcg_translate_rule/2</a>).
	1166	<li>Call DCG expansion (<a id="idx:dcgtranslaterule2:530"></a><a class="pred" href="consulting.html#dcg_translate_rule/2">dcg_translate_rule/2</a>).
1130	1167
1131	1168	<p>
1132		<li>Call <a name="idx:expandgoal2:531"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>
	1169	<li>Call <a id="idx:expandgoal2:531"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>
1133	1170	on each body term that appears in the output of the previous steps.
1134	1171	</ol>
1135	1172	</dd>
1136		<dt class="pubdef"><a name="goal_expansion/2"><strong>goal_expansion</strong>(<var>+Goal1,
	1173	<dt class="pubdef"><a id="goal_expansion/2"><strong>goal_expansion</strong>(<var>+Goal1,
1137	1174	-Goal2</var>)</a></dt>
1138	1175	<dd class="defbody">
1139		Like <a name="idx:termexpansion2:532"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>, <a name="idx:goalexpansion2:533"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1140		provides for macro expansion of Prolog source code. Between <a name="idx:expandterm2:534"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>
	1176	Like <a id="idx:termexpansion2:532"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>, <a id="idx:goalexpansion2:533"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1177	provides for macro expansion of Prolog source code. Between <a id="idx:expandterm2:534"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>
1141	1178	and the actual compilation, the body of clauses analysed and the goals
1142		are handed to <a name="idx:expandgoal2:535"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>,
1143		which uses the <a name="idx:goalexpansion2:536"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1179	are handed to <a id="idx:expandgoal2:535"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>,
	1180	which uses the <a id="idx:goalexpansion2:536"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1144	1181	hook to do user-defined expansion.
1145	1182
1146		<p>The predicate <a name="idx:goalexpansion2:537"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1183	<p>The predicate <a id="idx:goalexpansion2:537"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1147	1184	is first called in the module that is being compiled, and then follows
1148		the module inheritance path as defined by <a name="idx:defaultmodule2:538"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>,
	1185	the module inheritance path as defined by <a id="idx:defaultmodule2:538"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>,
1149	1186	i.e., by default <code>user</code> and <code>system</code>. If <var>Goal</var>
1150	1187	is of the form <var>Module</var>:<var>Goal</var> where <var>Module</var>
1151		is instantiated, <a name="idx:goalexpansion2:539"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1188	is instantiated, <a id="idx:goalexpansion2:539"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1152	1189	is called on <var>Goal</var> using rules from module <var>Module</var>
1153	1190	followed by default modules for <var>Module</var>.
1154	1191
1155	1192	<p>Only goals appearing in the body of clauses when reading a source
1156	1193	file are expanded using this mechanism, and only if they appear
1157	1194	literally in the clause, or as an argument to a defined meta-predicate
1158		that is annotated using `0' (see <a name="idx:metapredicate1:540"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>).
	1195	that is annotated using `0' (see <a id="idx:metapredicate1:540"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>).
1159	1196	Other cases need a real predicate definition.
1160	1197
1161		<p>The expansion hook can use <a name="idx:prologloadcontext2:541"></a><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a>
	1198	<p>The expansion hook can use <a id="idx:prologloadcontext2:541"></a><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a>
1162	1199	to obtain information about the context in which the goal is exanded
1163	1200	such as the module, variable names or the encapsulating term.</dd>
1164		<dt class="pubdef"><a name="expand_goal/2"><strong>expand_goal</strong>(<var>+Goal1,
	1201	<dt class="pubdef"><a id="expand_goal/2"><strong>expand_goal</strong>(<var>+Goal1,
1165	1202	-Goal2</var>)</a></dt>
1166	1203	<dd class="defbody">
1167	1204	This predicate is normally called by the compiler to perform
1168		preprocessing using <a name="idx:goalexpansion2:542"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>.
	1205	preprocessing using <a id="idx:goalexpansion2:542"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>.
1169	1206	The predicate computes a fixed-point by applying transformations until
1170	1207	there are no more changes. If optimisation is enabled (see <strong>-O</strong>
1171	1208	and
1172		<a class="flag" href="flags.html#flag:optimise">optimise</a>), <a name="idx:expandgoal2:543"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>
1173		simplifies the result by removing unneeded calls to <a name="idx:true0:544"></a><a class="pred" href="control.html#true/0">true/0</a>
1174		and <a name="idx:fail0:545"></a><a class="pred" href="control.html#fail/0">fail/0</a>
	1209	<a class="flag" href="flags.html#flag:optimise">optimise</a>), <a id="idx:expandgoal2:543"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>
	1210	simplifies the result by removing unneeded calls to <a id="idx:true0:544"></a><a class="pred" href="control.html#true/0">true/0</a>
	1211	and <a id="idx:fail0:545"></a><a class="pred" href="control.html#fail/0">fail/0</a>
1175	1212	as well as unreachable branches.</dd>
1176		<dt class="pubdef"><a name="compile_aux_clauses/1"><strong>compile_aux_clauses</strong>(<var>+Clauses</var>)</a></dt>
1177		<dd class="defbody">
1178		Compile clauses on behalf of <a name="idx:goalexpansion2:546"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>.
	1213	<dt class="pubdef"><a id="compile_aux_clauses/1"><strong>compile_aux_clauses</strong>(<var>+Clauses</var>)</a></dt>
	1214	<dd class="defbody">
	1215	Compile clauses on behalf of <a id="idx:goalexpansion2:546"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>.
1179	1216	This predicate compiles the argument clauses into static predicates,
1180	1217	associating the predicates with the current file but avoids changing the
1181	1218	notion of current predicate and therefore discontiguous warnings.
1182	1219
1183	1220	<p>Note that in some cases multiple expansions of similar goals can
1184	1221	share the same compiled auxiliary predicate. In such cases, the
1185		implementation of <a name="idx:goalexpansion2:547"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1186		can use <a name="idx:predicateproperty2:548"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
	1222	implementation of <a id="idx:goalexpansion2:547"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1223	can use <a id="idx:predicateproperty2:548"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
1187	1224	using the property
1188	1225	<code>defined</code> to test whether the predicate is already defined in
1189	1226	the current context.</dd>
1190		<dt class="pubdef"><a name="dcg_translate_rule/2"><strong>dcg_translate_rule</strong>(<var>+In,
	1227	<dt class="pubdef"><a id="dcg_translate_rule/2"><strong>dcg_translate_rule</strong>(<var>+In,
1191	1228	-Out</var>)</a></dt>
1192	1229	<dd class="defbody">
1193	1230	This predicate performs the translation of a term <code>Head-->Body</code>
1194	1231	into a normal Prolog clause. Normally this functionality should be
1195		accessed using <a name="idx:expandterm2:549"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>.</dd>
1196		<dt class="pubdef"><a name="var_property/2"><strong>var_property</strong>(<var>+Var,
	1232	accessed using <a id="idx:expandterm2:549"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>.</dd>
	1233	<dt class="pubdef"><a id="var_property/2"><strong>var_property</strong>(<var>+Var,
1197	1234	?Property</var>)</a></dt>
1198	1235	<dd class="defbody">
1199	1236	True when <var>Property</var> is a property of <var>Var</var>. These
1200	1237	properties are available during goal- and term-expansion. Defined
1201	1238	properties are below. Future versions are likely to provide more
1202	1239	properties, such as whether the variable is a singleton or whether the
1203		variable is referenced in the remainder of the term. See also <a name="idx:goalexpansion2:550"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>.
	1240	variable is referenced in the remainder of the term. See also <a id="idx:goalexpansion2:550"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>.
1204	1241
1205	1242	<dl class="latex">
1206	1243	<dt><strong>fresh</strong>(<var>Bool</var>)</dt>

1219	1256	</dd>
1220	1257	</dl>
1221	1258
1222		<p><h4 id="sec:progtransform-layout"><a name="sec:4.3.1.1"><span class="sec-nr">4.3.1.1</span> <span class="sec-title">Program
	1259	<p><h4 id="sec:progtransform-layout"><a id="sec:4.3.1.1"><span class="sec-nr">4.3.1.1</span> <span class="sec-title">Program
1223	1260	transformation with source layout info</span></a></h4>
1224	1261
1225		<a name="sec:progtransform-layout"></a>
	1262	<a id="sec:progtransform-layout"></a>
1226	1263
1227	1264	<p>This sections documents extended versions of the program
1228	1265	transformation predicates that also transform the source layout

1237	1274	</ul>
1238	1275
1239	1276	<dl class="latex">
1240		<dt class="pubdef"><a name="expand_goal/4"><strong>expand_goal</strong>(<var>+Goal1,
	1277	<dt class="pubdef"><a id="expand_goal/4"><strong>expand_goal</strong>(<var>+Goal1,
1241	1278	?Layout1, -Goal2, -Layout2</var>)</a></dt>
1242		<dt class="pubdef"><a name="goal_expansion/4"><strong>goal_expansion</strong>(<var>+Goal1,
	1279	<dt class="pubdef"><a id="goal_expansion/4"><strong>goal_expansion</strong>(<var>+Goal1,
1243	1280	?Layout1, -Goal2, -Layout2</var>)</a></dt>
1244		<dt class="pubdef"><a name="expand_term/4"><strong>expand_term</strong>(<var>+Term1,
	1281	<dt class="pubdef"><a id="expand_term/4"><strong>expand_term</strong>(<var>+Term1,
1245	1282	?Layout1, -Term2, -Layout2</var>)</a></dt>
1246		<dt class="pubdef"><a name="term_expansion/4"><strong>term_expansion</strong>(<var>+Term1,
	1283	<dt class="pubdef"><a id="term_expansion/4"><strong>term_expansion</strong>(<var>+Term1,
1247	1284	?Layout1, -Term2, -Layout2</var>)</a></dt>
1248		<dt class="pubdef"><a name="dcg_translate_rule/4"><strong>dcg_translate_rule</strong>(<var>+In,
	1285	<dt class="pubdef"><a id="dcg_translate_rule/4"><strong>dcg_translate_rule</strong>(<var>+In,
1249	1286	?LayoutIn, -Out, -LayoutOut</var>)</a></dt>
1250	1287	<dd class="defbody">
1251	1288	These versions are called <em>before</em> their 2-argument counterparts.
1252	1289	The input layout term is either a variable (if no layout information is
1253	1290	available) or a term carrying detailed layout information as returned by
1254		the <code>subterm_positions</code> of <a name="idx:readterm2:551"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.
	1291	the <code>subterm_positions</code> of <a id="idx:readterm2:551"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.
1255	1292	</dd>
1256	1293	</dl>
1257	1294
1258		<p><h4 id="sec:conditionalcompilation"><a name="sec:4.3.1.2"><span class="sec-nr">4.3.1.2</span> <span class="sec-title">Conditional
	1295	<p><h4 id="sec:conditionalcompilation"><a id="sec:4.3.1.2"><span class="sec-nr">4.3.1.2</span> <span class="sec-title">Conditional
1259	1296	compilation</span></a></h4>
1260	1297
1261		<a name="sec:conditionalcompilation"></a>
1262
1263		<p><a name="idx:ifdirective:552"></a>Conditional compilation builds on
1264		the same principle as
1265		<a name="idx:termexpansion2:553"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>, <a name="idx:goalexpansion2:554"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1298	<a id="sec:conditionalcompilation"></a>
	1299
	1300	<p><a id="idx:ifdirective:552"></a>Conditional compilation builds on the
	1301	same principle as
	1302	<a id="idx:termexpansion2:553"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>, <a id="idx:goalexpansion2:554"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1266	1303	and the expansion of grammar rules to compile sections of the source
1267	1304	code conditionally. One of the reasons for introducing conditional
1268		compilation is to simplify writing portable code. See <a class="sec" href="dialect.html">section
	1305	compilation is to simplify writing portable code. See <a class="sec" href="dialect.html#sec:C">section
1269	1306	C</a> for more information. Here is a simple example:
1270	1307
1271	1308	<pre class="code">

1290	1327	</ul>
1291	1328
1292	1329	<dl class="latex">
1293		<dt class="pubdef"><a name="if/1">:- <strong>if</strong>(<var>:Goal</var>)</a></dt>
	1330	<dt class="pubdef"><a id="if/1">:- <strong>if</strong>(<var>:Goal</var>)</a></dt>
1294	1331	<dd class="defbody">
1295	1332	Compile subsequent code only if <var>Goal</var> succeeds. For enhanced
1296		portability, <var>Goal</var> is processed by <a name="idx:expandgoal2:555"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>
	1333	portability, <var>Goal</var> is processed by <a id="idx:expandgoal2:555"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>
1297	1334	before execution. If an error occurs, the error is printed and
1298	1335	processing proceeds as if
1299	1336	<var>Goal</var> has failed.</dd>
1300		<dt class="pubdef"><a name="elif/1">:- <strong>elif</strong>(<var>:Goal</var>)</a></dt>
	1337	<dt class="pubdef"><a id="elif/1">:- <strong>elif</strong>(<var>:Goal</var>)</a></dt>
1301	1338	<dd class="defbody">
1302	1339	Equivalent to <code>:- else. :-if(Goal).</code> ... <code>:- endif.</code>
1303	1340	In a sequence as below, the section below the first matching <code>elif</code>

1316	1353	</pre>
1317	1354
1318	1355	</dd>
1319		<dt class="pubdef"><a name="else/0">:- <strong>else</strong></a></dt>
	1356	<dt class="pubdef"><a id="else/0">:- <strong>else</strong></a></dt>
1320	1357	<dd class="defbody">
1321	1358	Start `else' branch.</dd>
1322		<dt class="pubdef"><a name="endif/0">:- <strong>endif</strong></a></dt>
	1359	<dt class="pubdef"><a id="endif/0">:- <strong>endif</strong></a></dt>
1323	1360	<dd class="defbody">
1324	1361	End of conditional compilation.
1325	1362	</dd>
1326	1363	</dl>
1327	1364
1328		<p><h3 id="sec:loadrunningcode"><a name="sec:4.3.2"><span class="sec-nr">4.3.2</span> <span class="sec-title">Reloading
	1365	<p><h3 id="sec:loadrunningcode"><a id="sec:4.3.2"><span class="sec-nr">4.3.2</span> <span class="sec-title">Reloading
1329	1366	files, active code and threads</span></a></h3>
1330	1367
1331		<a name="sec:loadrunningcode"></a>
	1368	<a id="sec:loadrunningcode"></a>
1332	1369
1333	1370	<p>Traditionally, Prolog environments allow for reloading files holding
1334	1371	currently active code. In particular, the following sequence is a valid

1339	1376	<li>Trace a goal
1340	1377	<li>Find unexpected behaviour of a predicate
1341	1378	<li>Enter a <em>break</em> using the <b>b</b> command
1342		<li>Fix the sources and reload them using <a name="idx:make0:556"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	1379	<li>Fix the sources and reload them using <a id="idx:make0:556"></a><a class="pred" href="consulting.html#make/0">make/0</a>
1343	1380	<li>Exit the break, <em>retry</em> executing the now fixed predicate
1344	1381	using the <b>r</b> command
1345	1382	</ul>

1349	1386	<em>thread</em>. Executing threads switch atomically to the new
1350	1387	definition of modified predicates, while clauses that belong to the old
1351	1388	definition are (eventually) reclaimed by
1352		<a name="idx:garbagecollectclauses0:557"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>.<sup class="fn">50<span class="fn-text">As
	1389	<a id="idx:garbagecollectclauses0:557"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>.<sup class="fn">50<span class="fn-text">As
1353	1390	of version 7.3.12. Older versions wipe all clauses originating from the
1354	1391	file before loading the new clauses. This causes threads that executes
1355	1392	the code to (typically) die with an <em>undefined predicate</em>

1388	1425	after the file completes loading. Currently, <code>dynamic</code> and
1389	1426	<code>thread_local</code> are applied immediately.
1390	1427	<li>New modules are recorded in the reload context. Export declarations
1391		(the module's public list and <a name="idx:export1:558"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>
	1428	(the module's public list and <a id="idx:export1:558"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>
1392	1429	calls) are both applied and recorded.
1393	1430	<li>When the end-of-file is reached, the following fixup steps are taken
1394	1431	<ol class="latex">

1400	1437	by changing their `erased' or `created'
1401	1438	<em>generation</em>. Erased clauses are (eventually) reclaimed by the <em>clause
1402	1439	garbage collector</em>, see
1403		<a name="idx:garbagecollectclauses0:559"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>.
	1440	<a id="idx:garbagecollectclauses0:559"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>.
1404	1441	<li>Pending predicate property changes are applied.
1405	1442	</ol>
1406	1443	<li>For each module

1412	1449	</ol>
1413	1450
1414	1451	<p>The above generally ensures that changes to the <em>content</em> of
1415		source files can typically be activated safely using <a name="idx:make0:560"></a><a class="pred" href="consulting.html#make/0">make/0</a>.
	1452	source files can typically be activated safely using <a id="idx:make0:560"></a><a class="pred" href="consulting.html#make/0">make/0</a>.
1416	1453	Global changes such as operator changes, changes of module names,
1417	1454	changes to multi-file predicates, etc. sometimes require a restart. In
1418	1455	almost all cases, the need for restart is indicated by permission or

1420	1457	program.
1421	1458
1422	1459	<p>In some cases the content of a source file refers `to itself'. This
1423		is notably the case if local rules for <a name="idx:goalexpansion2:561"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1424		or <a name="idx:termexpansion2:562"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	1460	is notably the case if local rules for <a id="idx:goalexpansion2:561"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1461	or <a id="idx:termexpansion2:562"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
1425	1462	are defined or goals are executed using
1426		<em>directives</em>.<sup class="fn">51<span class="fn-text">Note that <a name="idx:initialization1:563"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	1463	<em>directives</em>.<sup class="fn">51<span class="fn-text">Note that <a id="idx:initialization1:563"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
1427	1464	directives are executed <em>after</em> loading the file. SWI-Prolog
1428	1465	allows for directives that are executed <em>while</em> loading the file
1429		using <code>:- Goal.</code> or <a name="idx:initialization2:564"></a><a class="pred" href="consulting.html#initialization/2">initialization/2</a></span></sup>.
	1466	using <code>:- Goal.</code> or <a id="idx:initialization2:564"></a><a class="pred" href="consulting.html#initialization/2">initialization/2</a></span></sup>.
1430	1467	Up to version 7.5.12 it was typically needed to reload the file <em>twice</em>,
1431	1468	once for updating the code that was used for compiling the remainder of
1432	1469	the file and once to effectuate this. As of version 7.5.13, conventional <em>transaction

1437	1474	implemented by Keri Harris.</span></sup>
1438	1475
1439	1476	<dl class="latex">
1440		<dt class="pubdef"><a name="garbage_collect_clauses/0"><strong>garbage_collect_clauses</strong></a></dt>
	1477	<dt class="pubdef"><a id="garbage_collect_clauses/0"><strong>garbage_collect_clauses</strong></a></dt>
1441	1478	<dd class="defbody">
1442	1479	Reclaim retracted clauses. During normal operation, retracting a clause
1443	1480	implies setting the <em>erased generation</em> to the current

1467	1504	</dd>
1468	1505	</dl>
1469	1506
1470		<p><h4 id="sec:depload"><a name="sec:4.3.2.1"><span class="sec-nr">4.3.2.1</span> <span class="sec-title">Compilation
	1507	<p><h4 id="sec:depload"><a id="sec:4.3.2.1"><span class="sec-nr">4.3.2.1</span> <span class="sec-title">Compilation
1471	1508	of mutually dependent code</span></a></h4>
1472	1509
1473		<a name="sec:depload"></a>
	1510	<a id="sec:depload"></a>
1474	1511
1475	1512	<p>Large programs are generally split into multiple files. If file <var>A</var>
1476	1513	accesses predicates from file <var>B</var> which accesses predicates
1477	1514	from file
1478	1515	<var>A</var>, we consider this a mutual or circular dependency. If
1479		traditional load predicates (e.g., <a name="idx:consult1:565"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>)
	1516	traditional load predicates (e.g., <a id="idx:consult1:565"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>)
1480	1517	are used to include file <var>B</var> from <var>A</var> and <var>A</var>
1481	1518	from <var>B</var>, loading either file results in a loop. This is
1482	1519	because
1483		<a name="idx:consult1:566"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
1484		is mapped to <a name="idx:loadfiles2:567"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	1520	<a id="idx:consult1:566"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	1521	is mapped to <a id="idx:loadfiles2:567"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
1485	1522	using the option <code>if(true)(if(true))</code> Such programs are
1486	1523	typically loaded using a <em>load file</em> that consults all required
1487	1524	(non-module) files. If modules are used, the dependencies are made
1488		explicit using <a name="idx:usemodule1:568"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	1525	explicit using <a id="idx:usemodule1:568"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
1489	1526	statements. The
1490		<a name="idx:usemodule1:569"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
1491		predicate, however, maps to <a name="idx:loadfiles2:570"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	1527	<a id="idx:usemodule1:569"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	1528	predicate, however, maps to <a id="idx:loadfiles2:570"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
1492	1529	with the option
1493		<code>if(not_loaded)(if(not_loaded))</code> A <a name="idx:usemodule1:571"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	1530	<code>if(not_loaded)(if(not_loaded))</code> A <a id="idx:usemodule1:571"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
1494	1531	on an already loaded file merely makes the public predicates of the used
1495	1532	module available.
1496	1533
1497	1534	<p>Summarizing, mutual dependency of source files is fully supported
1498	1535	with no precautions when using modules. Modules can use each other in an
1499		arbitrary dependency graph. When using <a name="idx:consult1:572"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
	1536	arbitrary dependency graph. When using <a id="idx:consult1:572"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
1500	1537	predicate dependencies between loaded files can still be arbitrary, but
1501	1538	the consult relations between files must be a proper tree.
1502	1539
1503		<p><h4 id="sec:mtload"><a name="sec:4.3.2.2"><span class="sec-nr">4.3.2.2</span> <span class="sec-title">Compilation
	1540	<p><h4 id="sec:mtload"><a id="sec:4.3.2.2"><span class="sec-nr">4.3.2.2</span> <span class="sec-title">Compilation
1504	1541	with multiple threads</span></a></h4>
1505	1542
1506		<a name="sec:mtload"></a>
	1543	<a id="sec:mtload"></a>
1507	1544
1508	1545	<p>This section discusses compiling files for the first time. For
1509		reloading, see <a class="sec" href="consulting.html">section 4.3.2</a>.
	1546	reloading, see <a class="sec" href="consulting.html#sec:4.3.2">section
	1547	4.3.2</a>.
1510	1548
1511	1549	<p>In older versions, compilation was thread-safe due to a global
1512		<em>lock</em> in <a name="idx:loadfiles2:573"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	1550	<em>lock</em> in <a id="idx:loadfiles2:573"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
1513	1551	and the code dealing with
1514		<em>autoloading</em> (see <a class="sec" href="autoload.html">section
	1552	<em>autoloading</em> (see <a class="sec" href="autoload.html#sec:2.13">section
1515	1553	2.13</a>). Besides unnecessary stalling when multiple threads trap
1516	1554	unrelated undefined predicates, this easily leads to deadlocks, notably
1517	1555	if threads are started from an
1518		<a name="idx:initialization1:574"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	1556	<a id="idx:initialization1:574"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
1519	1557	directive.<sup class="fn">54<span class="fn-text">Although such goals
1520	1558	are started after loading the file in which they appear, the calling
1521	1559	thread is still likely to hold the `load' lock because it is compiling

1524	1562	<p>Starting with version 5.11.27, the autoloader is no longer locked and
1525	1563	multiple threads can compile files concurrently. This requires special
1526	1564	precautions only if multiple threads wish to load the same file at the
1527		same time. Therefore, <a name="idx:loadfiles2:575"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	1565	same time. Therefore, <a id="idx:loadfiles2:575"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
1528	1566	checks automatically whether some other thread is already loading the
1529	1567	file. If not, it starts loading the file. If another thread is already
1530	1568	loading the file, the thread blocks until the other thread finishes

1532	1570	will make the public predicates available.
1533	1571
1534	1572	<p>Note that this schema does not prevent deadlocks under all
1535		situations. Consider two mutually dependent (see <a class="sec" href="consulting.html">section
	1573	situations. Consider two mutually dependent (see <a class="sec" href="consulting.html#sec:4.3.2.1">section
1536	1574	4.3.2.1</a>) module files <var>A</var> and <var>B</var>, where thread 1
1537	1575	starts loading <var>A</var> and thread 2 starts loading
1538	1576	<var>B</var> at the same time. Both threads will deadlock when trying to

1542	1580	involved threads will freeze. This problem can be avoided if a mutually
1543	1581	dependent collection of files is always loaded from the same start file.
1544	1582
1545		<p><h3 id="sec:qlf"><a name="sec:4.3.3"><span class="sec-nr">4.3.3</span> <span class="sec-title">Quick
	1583	<p><h3 id="sec:qlf"><a id="sec:4.3.3"><span class="sec-nr">4.3.3</span> <span class="sec-title">Quick
1546	1584	load files</span></a></h3>
1547	1585
1548		<a name="sec:qlf"></a>
	1586	<a id="sec:qlf"></a>
1549	1587
1550	1588	<p>SWI-Prolog supports compilation of individual or multiple Prolog
1551	1589	source files into `Quick Load Files'. A `Quick Load File' (<code>.qlf</code>

1557	1595	are stored as virtual machine instructions. Changes to the compiler will
1558	1596	generally make old compiled files unusable.
1559	1597
1560		<p>Quick Load Files are created using <a name="idx:qcompile1:576"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>.
	1598	<p>Quick Load Files are created using <a id="idx:qcompile1:576"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>.
1561	1599	They are loaded using
1562		<a name="idx:consult1:577"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	1600	<a id="idx:consult1:577"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
1563	1601	or one of the other file-loading predicates described in
1564		<a class="sec" href="consulting.html">section 4.3</a>. If <a name="idx:consult1:578"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	1602	<a class="sec" href="consulting.html#sec:4.3">section 4.3</a>. If <a id="idx:consult1:578"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
1565	1603	is given an explicit <code>.pl</code> file, it will load the Prolog
1566	1604	source. When given a <code>.qlf</code> file, it will load the file. When
1567	1605	no extension is specified, it will load the

1569	1607	otherwise.
1570	1608
1571	1609	<dl class="latex">
1572		<dt class="pubdef"><a name="qcompile/1"><strong>qcompile</strong>(<var>:File</var>)</a></dt>
1573		<dd class="defbody">
1574		Takes a file specification as <a name="idx:consult1:579"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
	1610	<dt class="pubdef"><a id="qcompile/1"><strong>qcompile</strong>(<var>:File</var>)</a></dt>
	1611	<dd class="defbody">
	1612	Takes a file specification as <a id="idx:consult1:579"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
1575	1613	etc., and, in addition to the normal compilation, creates a <em>Quick
1576	1614	Load File</em> from <var>File</var>. The file extension of this file is <code>.qlf</code>.
1577	1615	The basename of the Quick Load File is the same as the input file.

1585	1623	the
1586	1624	<code>.pl</code> file.
1587	1625
1588		<p>For <a name="idx:termexpansion2:580"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>,
	1626	<p>For <a id="idx:termexpansion2:580"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>,
1589	1627	the same rules as described in
1590		<a class="sec" href="compilation.html">section 2.10</a> apply.
	1628	<a class="sec" href="compilation.html#sec:2.10">section 2.10</a> apply.
1591	1629
1592	1630	<p>Conditional execution or optimisation may test the predicate
1593		<a name="idx:compiling0:581"></a><a class="pred" href="consulting.html#compiling/0">compiling/0</a>.
1594
1595		<p>Source references (<a name="idx:sourcefile2:582"></a><a class="pred" href="consulting.html#source_file/2">source_file/2</a>)
	1631	<a id="idx:compiling0:581"></a><a class="pred" href="consulting.html#compiling/0">compiling/0</a>.
	1632
	1633	<p>Source references (<a id="idx:sourcefile2:582"></a><a class="pred" href="consulting.html#source_file/2">source_file/2</a>)
1596	1634	in the Quick Load File refer to the Prolog source file from which the
1597	1635	compiled code originates.</dd>
1598		<dt class="pubdef"><a name="qcompile/2"><strong>qcompile</strong>(<var>:File,
	1636	<dt class="pubdef"><a id="qcompile/2"><strong>qcompile</strong>(<var>:File,
1599	1637	+Options</var>)</a></dt>
1600	1638	<dd class="defbody">
1601		As <a name="idx:qcompile1:583"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>,
	1639	As <a id="idx:qcompile1:583"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>,
1602	1640	but processes additional options as defined by
1603		<a name="idx:loadfiles2:584"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.<sup class="fn">bug<span class="fn-text">Option
	1641	<a id="idx:loadfiles2:584"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.<sup class="fn">bug<span class="fn-text">Option
1604	1642	processing is currently incomplete.</span></sup>
1605	1643	</dd>
1606	1644	</dl>

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2	2	<html>
3	3	<head>
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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section E.1</title><link rel="home" href="index.html">
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123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
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132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
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	140	position: absolute;
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	144	box-shadow: 5px 5px 5px #888;
	145	display: none;
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	147	color: #000;
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	150	font-size: larger;
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	154	{ display: block;
141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
	200
	201	table.center
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	205	table.latex
	206	{ border-collapse:collapse;
	207	}
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	209	table.latex tr
	210	{ vertical-align: text-top;
	211	}
	212
	213	table.latex td,th
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191	232	<a class="nav" href="license.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="softlicense.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:contrib"><a name="sec:E.1"><span class="sec-nr">E.1</span> <span class="sec-title">Contributing
	235	<h2 id="sec:contrib"><a id="sec:E.1"><span class="sec-nr">E.1</span> <span class="sec-title">Contributing
195	236	to the SWI-Prolog project</span></a></h2>
196	237
197		<a name="sec:contrib"></a>
	238	<a id="sec:contrib"></a>
198	239
199	240	<p>To reach maximal coherence we will, as a rule of thumb, only accept
200	241	new code that has the Simplified BSD license and existing code with a
201	242	<em>permissive</em> license such as MIT, Apache, BSD-3, etc. In
202	243	exceptional cases we may accept code with GPL or LGPL conditions. Such
203		code must be tagged using a <a name="idx:license1:2339"></a><a class="pred" href="softlicense.html#license/1">license/1</a>
	244	code must be tagged using a <a id="idx:license1:2343"></a><a class="pred" href="softlicense.html#license/1">license/1</a>
204	245	directive (Prolog) or a call to
205	246	<a class="func" href="softlicense.html#PL_license()">PL_license()</a>
206	247	for foreign code and, if they are part of the core, the code must be

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	124	color: #fff;
121	125	}
122	126
123	127	div.caption

127	131	}
128	132
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130
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193	234	</div>
194		<h2 id="sec:control"><a name="sec:4.8"><span class="sec-nr">4.8</span> <span class="sec-title">Control
	235	<h2 id="sec:control"><a id="sec:4.8"><span class="sec-nr">4.8</span> <span class="sec-title">Control
195	236	Predicates</span></a></h2>
196	237
197		<a name="sec:control"></a>
	238	<a id="sec:control"></a>
198	239
199	240	<p>The predicates of this section implement control structures. Normally
200		the constructs in this section, except for <a name="idx:repeat0:642"></a><a class="pred" href="control.html#repeat/0">repeat/0</a>,
	241	the constructs in this section, except for <a id="idx:repeat0:642"></a><a class="pred" href="control.html#repeat/0">repeat/0</a>,
201	242	are translated by the compiler. Please note that complex goals passed as
202		arguments to meta-predicates such as <a name="idx:findall3:643"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
	243	arguments to meta-predicates such as <a id="idx:findall3:643"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
203	244	below cause the goal to be compiled to a temporary location before
204	245	execution. It is faster to define a sub-predicate (i.e. one_character_atoms/1
205	246	in the example below) and make a call to this simple predicate.

210	251	</pre>
211	252
212	253	<dl class="latex">
213		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="fail/0"><strong>fail</strong></a></dt>
214		<dd class="defbody">
215		Always fail. The predicate <a name="idx:fail0:644"></a><a class="pred" href="control.html#fail/0">fail/0</a>
	254	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="fail/0"><strong>fail</strong></a></dt>
	255	<dd class="defbody">
	256	Always fail. The predicate <a id="idx:fail0:644"></a><a class="pred" href="control.html#fail/0">fail/0</a>
216	257	is translated into a single virtual machine instruction.
217	258	</dd>
218		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="false/0"><strong>false</strong></a></dt>
	259	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="false/0"><strong>false</strong></a></dt>
219	260	<dd class="defbody">
220	261	Same as fail, but the name has a more declarative connotation.
221	262	</dd>
222		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="true/0"><strong>true</strong></a></dt>
223		<dd class="defbody">
224		Always succeed. The predicate <a name="idx:true0:645"></a><a class="pred" href="control.html#true/0">true/0</a>
	263	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="true/0"><strong>true</strong></a></dt>
	264	<dd class="defbody">
	265	Always succeed. The predicate <a id="idx:true0:645"></a><a class="pred" href="control.html#true/0">true/0</a>
225	266	is translated into a single virtual machine instruction.
226	267	</dd>
227		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="repeat/0"><strong>repeat</strong></a></dt>
	268	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="repeat/0"><strong>repeat</strong></a></dt>
228	269	<dd class="defbody">
229	270	Always succeed, provide an infinite number of choice points.</dd>
230		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="!/0"><strong>!</strong></a></dt>
	271	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="!/0"><strong>!</strong></a></dt>
231	272	<dd class="defbody">
232	273	Cut. Discard all choice points created since entering the predicate in
233	274	which the cut appears. In other words, <em>commit</em> to the clause in
234	275	which the cut appears <em>and</em> discard choice points that have been
235	276	created by goals to the left of the cut in the current clause. Meta
236	277	calling is opaque to the cut. This implies that cuts that appear in a
237		term that is subject to meta-calling (<a name="idx:call1:646"></a><a class="pred" href="metacall.html#call/1">call/1</a>)
	278	term that is subject to meta-calling (<a id="idx:call1:646"></a><a class="pred" href="metacall.html#call/1">call/1</a>)
238	279	only affect choice points created by the meta-called term. The following
239		control structures are transparent to the cut: <a class="pred" href="control.html#;/2">;/2</a>, <a class="pred" href="control.html#send_arrow/2">->/2</a>
	280	control structures are transparent to the cut: <a class="pred" href="control.html#;/2">;/2</a>, <a class="pred" href="control.html#->/2">->/2</a>
240	281	and
241	282	<a class="pred" href="control.html#->/2">->/2</a>. Cuts appearing
242	283	in the <em>condition</em> part of
243		<a class="pred" href="control.html#send_arrow/2">->/2</a> and <a class="pred" href="control.html#->/2">->/2</a>
	284	<a class="pred" href="control.html#->/2">->/2</a> and <a class="pred" href="control.html#->/2">->/2</a>
244	285	are opaque to the cut. The table below explains the scope of the cut
245	286	with examples. <i>Prunes</i> here means ``prunes <var>X</var> choice
246	287	point created by <var>X</var>''.
247		<div style="text-align:center"><table border="0" frame="void" rules="groups">
248		<tr valign="top"><td><code>t0 :- (a, !, b).</code> </td><td>% prunes a/0
249		and t0/0 </td></tr>
250		<tr valign="top"><td><code>t1 :- (a, !, fail ; b).</code> </td><td>%
251		prunes a/0 and t1/0 </td></tr>
252		<tr valign="top"><td><code>t2 :- (a -> b, ! ; c).</code> </td><td>%
253		prunes b/0 and t2/0 </td></tr>
254		<tr valign="top"><td><code>t3 :- call((a, !, fail ; b)).</code> </td><td>%
255		prunes a/0 </td></tr>
256		<tr valign="top"><td><code>t4 :- <code>\+</code>(a, !, fail).</code> </td><td>%
	288
	289	<p><table class="latex frame-void center">
	290	<tr><td><code>t0 :- (a, !, b).</code> </td><td>% prunes a/0 and t0/0 </td></tr>
	291	<tr><td><code>t1 :- (a, !, fail ; b).</code> </td><td>% prunes a/0 and t1/0 </td></tr>
	292	<tr><td><code>t2 :- (a -> b, ! ; c).</code> </td><td>% prunes b/0 and t2/0 </td></tr>
	293	<tr><td><code>t3 :- call((a, !, fail ; b)).</code> </td><td>% prunes a/0 </td></tr>
	294	<tr><td><code>t4 :- <code>\+</code>(a, !, fail).</code> </td><td>%
257	295	prunes a/0 </td></tr>
258	296	</table>
259		</div>
260		</dd>
261		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name=",/2"><var>:Goal1</var> <strong>,</strong> <var>:Goal2</var></a></dt>
	297	</dd>
	298	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id=",/2"><var>:Goal1</var> <strong>,</strong> <var>:Goal2</var></a></dt>
262	299	<dd class="defbody">
263	300	Conjunction. True if both `Goal1' and `Goal2' can be proved. It is
264	301	defined as follows (this definition does not lead to a loop as the

269	306	</pre>
270	307
271	308	</dd>
272		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name=";/2"><var>:Goal1</var> <strong>;</strong> <var>:Goal2</var></a></dt>
	309	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id=";/2"><var>:Goal1</var> <strong>;</strong> <var>:Goal2</var></a></dt>
273	310	<dd class="defbody">
274	311	The `or' predicate is defined as:
275	312

279	316	</pre>
280	317
281	318	</dd>
282		<dt class="pubdef"><a name="\|/2"><var>:Goal1</var> <strong>\|</strong> <var>:Goal2</var></a></dt>
	319	<dt class="pubdef"><a id="\|/2"><var>:Goal1</var> <strong>\|</strong> <var>:Goal2</var></a></dt>
283	320	<dd class="defbody">
284	321	Equivalent to <a class="pred" href="control.html#;/2">;/2</a>. Retained
285	322	for compatibility only. New code should use <a class="pred" href="control.html#;/2">;/2</a>.</dd>
286		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="send_arrow/2"><var>:Condition</var> <strong>-></strong> <var>:Action</var></a></dt>
287		<dd class="defbody">
288		If-then and If-Then-Else. The <a class="pred" href="control.html#send_arrow/2">->/2</a>
	323	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="->/2"><var>:Condition</var> <strong>-></strong> <var>:Action</var></a></dt>
	324	<dd class="defbody">
	325	If-then and If-Then-Else. The <a class="pred" href="control.html#->/2">->/2</a>
289	326	construct commits to the choices made at its left-hand side, destroying
290	327	choice points created inside the clause (by <a class="pred" href="control.html#;/2">;/2</a>),
291	328	or by goals called by this clause. Unlike <a class="pred" href="control.html#!/0">!/0</a>,
292	329	the choice point of the predicate as a whole (due to multiple clauses)
293	330	is <strong>not</strong> destroyed. The combination <a class="pred" href="control.html#;/2">;/2</a>
294		and <a class="pred" href="control.html#send_arrow/2">->/2</a> acts as
295		if defined as:
	331	and <a class="pred" href="control.html#->/2">->/2</a> acts as if
	332	defined as:
296	333
297	334	<pre class="code">
298	335	If -> Then; _Else :- If, !, Then.

310	347	and that the <em>combined</em> semantics of this syntactic construct as
311	348	defined above is <em>different</em> from the simple nesting of the two
312	349	individual constructs, i.e., the semantics of
313		<a class="pred" href="control.html#send_arrow/2">->/2</a> <em>changes</em>
	350	<a class="pred" href="control.html#->/2">->/2</a> <em>changes</em>
314	351	when embedded in <a class="pred" href="control.html#;/2">;/2</a>. See
315	352	also
316		<a name="idx:once1:647"></a><a class="pred" href="metacall.html#once/1">once/1</a>.</dd>
317		<dt class="pubdef"><a name="->/2"><var>:Condition</var> <strong>-></strong> <var>:Action
	353	<a id="idx:once1:647"></a><a class="pred" href="metacall.html#once/1">once/1</a>.</dd>
	354	<dt class="pubdef"><a id="->/2"><var>:Condition</var> <strong>-></strong> <var>:Action
318	355	; :Else</var></a></dt>
319	356	<dd class="defbody">
320	357	This construct implements the so-called `soft-cut'. The control is

331	368	without an
332	369	<var>Else</var> branch, is translated as the normal conjunction <var>A</var>,
333	370	<var>B</var>.<sup class="fn">bug<span class="fn-text">The decompiler
334		implemented by <a name="idx:clause2:648"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>
	371	implemented by <a id="idx:clause2:648"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>
335	372	returns this construct as a normal conjunction too.</span></sup>
336	373
337	374	<p>This construct is rarely used. An example use case is the

352	389	solutions
353	390	<var>X=a</var> and <var>X=b</var>, while <code>optional(member(X,[]))</code>
354	391	succeeds without binding <var>X</var>.</dd>
355		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="\+/1"><strong>\+</strong> <var>:Goal</var></a></dt>
	392	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="\+/1"><strong>\+</strong> <var>:Goal</var></a></dt>
356	393	<dd class="defbody">
357	394	True if `Goal' cannot be proven (mnemonic: <code><code>+</code></code>
358	395	refers to <em>provable</em> and the backslash (<code><code>\</code></code>)

+91

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193	234	</div>
194		<h2 id="sec:coroutining"><a name="sec:7.2"><span class="sec-nr">7.2</span> <span class="sec-title">Coroutining</span></a></h2>
195
196		<a name="sec:coroutining"></a>
	235	<h2 id="sec:coroutining"><a id="sec:7.2"><span class="sec-nr">7.2</span> <span class="sec-title">Coroutining</span></a></h2>
	236
	237	<a id="sec:coroutining"></a>
197	238
198	239	<p>Coroutining allows us to delay the execution of Prolog goals until
199	240	their truth can be safely decided.
200	241
201		<p>Among the most important coroutining predicates is <a name="idx:dif2:1793"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>,
	242	<p>Among the most important coroutining predicates is <a id="idx:dif2:1797"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>,
202	243	which expresses <i>disequality</i> of terms in a sound way. The actual
203	244	test is delayed until the terms are sufficiently different, or have
204	245	become identical. For example:

214	255
215	256	<p>There are also lower-level coroutining predicates that are intended
216	257	as building blocks for higher-level constraints. For example, we can use
217		<a name="idx:freeze2:1794"></a><a class="pred" href="coroutining.html#freeze/2">freeze/2</a>
	258	<a id="idx:freeze2:1798"></a><a class="pred" href="coroutining.html#freeze/2">freeze/2</a>
218	259	to define a variable that can only be assigned an atom:
219	260
220	261	<pre class="code">

222	263	X = a.
223	264	</pre>
224	265
225		<p>In this case, calling <a name="idx:atom1:1795"></a><a class="pred" href="typetest.html#atom/1">atom/1</a>
	266	<p>In this case, calling <a id="idx:atom1:1799"></a><a class="pred" href="typetest.html#atom/1">atom/1</a>
226	267	earlier causes the whole query to fail:
227	268
228	269	<pre class="code">

249	290	</pre>
250	291
251	292	<p>Remaining constraints, such as <code>X mod 2#=0</code> in the example
252		above, are called <em>residual</em><a name="idx:residual:1796"></a>
253		goals. They are said to
254		<em>flounder</em><a name="idx:flounder:1797"></a>, because their truth
255		is not yet decided. Declaratively, the query is only true if all
256		residual goals are satisfiable. Use <a name="idx:callresiduevars2:1798"></a><a class="pred" href="coroutining.html#call_residue_vars/2">call_residue_vars/2</a>
	293	above, are called <em>residual</em><a id="idx:residual:1800"></a> goals.
	294	They are said to
	295	<em>flounder</em><a id="idx:flounder:1801"></a>, because their truth is
	296	not yet decided. Declaratively, the query is only true if all residual
	297	goals are satisfiable. Use <a id="idx:callresiduevars2:1802"></a><a class="pred" href="coroutining.html#call_residue_vars/2">call_residue_vars/2</a>
257	298	to collect all variables that are involved in constraints.
258	299
259	300	<dl class="latex">
260		<dt class="pubdef"><a name="dif/2"><strong>dif</strong>(<var>@A, @B</var>)</a></dt>
261		<dd class="defbody">
262		The <a name="idx:dif2:1799"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
	301	<dt class="pubdef"><a id="dif/2"><strong>dif</strong>(<var>@A, @B</var>)</a></dt>
	302	<dd class="defbody">
	303	The <a id="idx:dif2:1803"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
263	304	predicate is a <i>constraint</i> that is true if and only if <var>A</var>
264	305	and <var>B</var> are different terms. If <var>A</var> and <var>B</var>
265		can never unify, <a name="idx:dif2:1800"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
	306	can never unify, <a id="idx:dif2:1804"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
266	307	succeeds deterministically. If <var>A</var> and <var>B</var> are
267	308	identical, it fails immediately. Finally, if <var>A</var> and <var>B</var>
268	309	can unify, goals are delayed that prevent <var>A</var> and <var>B</var>
269		to become equal. It is this last property that makes <a name="idx:dif2:1801"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
	310	to become equal. It is this last property that makes <a id="idx:dif2:1805"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
270	311	a more general and more declarative alternative for <a class="pred" href="compare.html#\=/2">\=/2</a>
271	312	and related predicates.
272	313

274	315	<code>dif(X, Y) :- when(?=(X,Y), X \== Y)</code>. See also <a class="pred" href="compare.html#?=/2">?=/2</a>.
275	316	The implementation can deal with cyclic terms.
276	317
277		<p>The <a name="idx:dif2:1802"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
	318	<p>The <a id="idx:dif2:1806"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>
278	319	predicate is realised using attributed variables associated with the
279	320	module <code>dif</code>. It is an autoloaded predicate that is defined
280	321	in the library <code>library(dif)</code>.</dd>
281		<dt class="pubdef"><a name="freeze/2"><strong>freeze</strong>(<var>+Var,
	322	<dt class="pubdef"><a id="freeze/2"><strong>freeze</strong>(<var>+Var,
282	323	:Goal</var>)</a></dt>
283	324	<dd class="defbody">
284	325	Delay the execution of <var>Goal</var> until <var>Var</var> is bound
285	326	(i.e. is not a variable or attributed variable). If <var>Var</var> is
286	327	bound on entry
287		<a name="idx:freeze2:1803"></a><a class="pred" href="coroutining.html#freeze/2">freeze/2</a>
288		is equivalent to <a name="idx:call1:1804"></a><a class="pred" href="metacall.html#call/1">call/1</a>.
289		The <a name="idx:freeze2:1805"></a><a class="pred" href="coroutining.html#freeze/2">freeze/2</a>
	328	<a id="idx:freeze2:1807"></a><a class="pred" href="coroutining.html#freeze/2">freeze/2</a>
	329	is equivalent to <a id="idx:call1:1808"></a><a class="pred" href="metacall.html#call/1">call/1</a>.
	330	The <a id="idx:freeze2:1809"></a><a class="pred" href="coroutining.html#freeze/2">freeze/2</a>
290	331	predicate is realised using an attributed variable associated with the
291	332	module <code>freeze</code>. Use <code>frozen(Var, Goal)</code> to find
292	333	out whether and which goals are delayed on <var>Var</var>.</dd>
293		<dt class="pubdef"><a name="frozen/2"><strong>frozen</strong>(<var>@Var,
	334	<dt class="pubdef"><a id="frozen/2"><strong>frozen</strong>(<var>@Var,
294	335	-Goal</var>)</a></dt>
295	336	<dd class="defbody">
296	337	Unify <var>Goal</var> with the goal or conjunction of goals delayed on
297	338	<var>Var</var>. If no goals are frozen on <var>Var</var>, <var>Goal</var>
298	339	is unified to <code>true</code>.</dd>
299		<dt class="pubdef"><a name="when/2"><strong>when</strong>(<var>@Condition,
	340	<dt class="pubdef"><a id="when/2"><strong>when</strong>(<var>@Condition,
300	341	:Goal</var>)</a></dt>
301	342	<dd class="defbody">
302	343	Execute <var>Goal</var> when <var>Condition</var> becomes true. <var>Condition</var>
303	344	is one of <code>?=(X, Y)</code>, <code>nonvar(X)</code>, <code>ground(X)</code>,
304	345	<code><code>,</code>(Cond1, Cond2)</code> or <code><code>;</code>(Cond1,
305		Cond2)</code>. See also <a name="idx:freeze2:1806"></a><a class="pred" href="coroutining.html#freeze/2">freeze/2</a>
306		and <a name="idx:dif2:1807"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>.
	346	Cond2)</code>. See also <a id="idx:freeze2:1810"></a><a class="pred" href="coroutining.html#freeze/2">freeze/2</a>
	347	and <a id="idx:dif2:1811"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>.
307	348	The implementation can deal with cyclic terms in <var>X</var> and <var>Y</var>.
308	349
309		<p>The <a name="idx:when2:1808"></a><a class="pred" href="coroutining.html#when/2">when/2</a>
	350	<p>The <a id="idx:when2:1812"></a><a class="pred" href="coroutining.html#when/2">when/2</a>
310	351	predicate is realised using attributed variables associated with the
311	352	module <code>when</code>. It is defined in the autoload library
312	353	<code>library(when)</code>.</dd>
313		<dt class="pubdef"><a name="call_residue_vars/2"><strong>call_residue_vars</strong>(<var>:Goal,
	354	<dt class="pubdef"><a id="call_residue_vars/2"><strong>call_residue_vars</strong>(<var>:Goal,
314	355	-Vars</var>)</a></dt>
315	356	<dd class="defbody">
316	357	Find residual attributed variables left by <var>Goal</var>. This

323	364	because the constraint solver is too weak to detect the contradiction.
324	365	Ideally, delayed goals and constraints are all executed at the end of
325	366	the computation. The meta predicate
326		<a name="idx:callresiduevars2:1809"></a><a class="pred" href="coroutining.html#call_residue_vars/2">call_residue_vars/2</a>
	367	<a id="idx:callresiduevars2:1813"></a><a class="pred" href="coroutining.html#call_residue_vars/2">call_residue_vars/2</a>
327	368	finds variables that are given attributes or whose attributes are
328	369	modified by <var>Goal</var>, regardless of whether or not these
329	370	variables are reachable from the arguments of
330		<var>Goal</var>.<sup class="fn">153<span class="fn-text">The
331		implementation of <a name="idx:callresiduevars2:1810"></a><a class="pred" href="coroutining.html#call_residue_vars/2">call_residue_vars/2</a>
	371	<var>Goal</var>.<sup class="fn">154<span class="fn-text">The
	372	implementation of <a id="idx:callresiduevars2:1814"></a><a class="pred" href="coroutining.html#call_residue_vars/2">call_residue_vars/2</a>
332	373	is completely redone in version 7.3.2 (7.2.1) after discussion with Bart
333	374	Demoen. The current implementation no longer performs full scans of the
334	375	stacks. The overhead is proportional to the number of attributed

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193	234	</div>
194		<h2 id="sec:csv"><a name="sec:A.10"><span class="sec-nr">A.10</span> <span class="sec-title">library(csv):
	235	<h2 id="sec:csv"><a id="sec:A.10"><span class="sec-nr">A.10</span> <span class="sec-title">library(csv):
195	236	Process CSV (Comma-Separated Values) data</span></a></h2>
196	237
197		<p><a name="sec:csv"></a>
	238	<p><a id="sec:csv"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">See also</dt>

214	255	have the same name and arity.
215	256
216	257	<dl class="latex">
217		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv_read_file/2"><strong>csv_read_file</strong>(<var>+File,
	258	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_read_file/2"><strong>csv_read_file</strong>(<var>+File,
218	259	-Rows</var>)</a></dt>
219		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv_read_file/3"><strong>csv_read_file</strong>(<var>+File,
	260	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_read_file/3"><strong>csv_read_file</strong>(<var>+File,
220	261	-Rows, +Options</var>)</a></dt>
221	262	<dd class="defbody">
222	263	Read a CSV file into a list of rows. Each row is a Prolog term with the
223		same arity. <var>Options</var> is handed to <span class="pred-ext">csv/4</span>.
	264	same arity. <var>Options</var> is handed to <a class="pred" href="csv.html#csv//2">csv//2</a>.
224	265	Remaining options are processed by <a class="pred" href="pio.html#phrase_from_file/3">phrase_from_file/3</a>.
225	266	The default separator depends on the file name extension and is <code>\t</code>
226	267	for

238	279	</pre>
239	280
240	281	</dd>
241		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv/1"><strong>csv</strong>(<var>?Rows</var>)</a><code>//</code></dt>
242		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv/2"><strong>csv</strong>(<var>?Rows,
	282	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv//1"><strong>csv</strong>(<var>?Rows</var>)</a><code>//</code></dt>
	283	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv//2"><strong>csv</strong>(<var>?Rows,
243	284	+Options</var>)</a><code>//</code></dt>
244	285	<dd class="defbody">
245	286	Prolog DCG to `read/write' CSV data. <var>Options</var>:

289	330	</dl>
290	331
291	332	</dd>
292		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="csv_read_file_row/3"><strong>csv_read_file_row</strong>(<var>+File,
	333	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="csv_read_file_row/3"><strong>csv_read_file_row</strong>(<var>+File,
293	334	-Row, +Options</var>)</a></dt>
294	335	<dd class="defbody">
295	336	True when <var>Row</var> is a row in <var>File</var>. First unifies <var>Row</var>

322	363	</dl>
323	364
324	365	</dd>
325		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv_read_row/3"><strong>csv_read_row</strong>(<var>+Stream,
	366	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_read_row/3"><strong>csv_read_row</strong>(<var>+Stream,
326	367	-Row, +CompiledOptions</var>)</a></dt>
327	368	<dd class="defbody">
328	369	Read the next CSV record from <var>Stream</var> and unify the result
329	370	with <var>Row</var>.
330		<var>CompiledOptions</var> is created from options defined for <span class="pred-ext">csv/4</span>
	371	<var>CompiledOptions</var> is created from options defined for <a class="pred" href="csv.html#csv//2">csv//2</a>
331	372	using
332	373	<a class="pred" href="csv.html#csv_options/2">csv_options/2</a>. <var>Row</var>
333	374	is unified with <code>end_of_file</code> upon reaching the end of the
334	375	input.</dd>
335		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv_options/2"><strong>csv_options</strong>(<var>-Compiled,
	376	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_options/2"><strong>csv_options</strong>(<var>-Compiled,
336	377	+Options</var>)</a></dt>
337	378	<dd class="defbody">
338	379	<var>Compiled</var> is the compiled representation of the CSV processing
339		options as they may be passed into <span class="pred-ext">csv/4</span>,
	380	options as they may be passed into <a class="pred" href="csv.html#csv//2">csv//2</a>,
340	381	etc. This predicate is used in combination with <a class="pred" href="csv.html#csv_read_row/3">csv_read_row/3</a>
341	382	to avoid repeated processing of the options.</dd>
342		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv_write_file/2"><strong>csv_write_file</strong>(<var>+File,
	383	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_write_file/2"><strong>csv_write_file</strong>(<var>+File,
343	384	+Data</var>)</a></dt>
344		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv_write_file/3"><strong>csv_write_file</strong>(<var>+File,
	385	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_write_file/3"><strong>csv_write_file</strong>(<var>+File,
345	386	+Data, +Options</var>)</a></dt>
346	387	<dd class="defbody">
347	388	Write a list of Prolog terms to a CSV file. <var>Options</var> are given
348		to <span class="pred-ext">csv/4</span>. Remaining options are given to <a class="pred" href="IO.html#open/4">open/4</a>.
349		The default separator depends on the file name extension and is <code>\t</code>
	389	to <a class="pred" href="csv.html#csv//2">csv//2</a>. Remaining options
	390	are given to <a class="pred" href="IO.html#open/4">open/4</a>. The
	391	default separator depends on the file name extension and is <code>\t</code>
350	392	for
351	393	<code>.tsv</code> files and <code>,</code> otherwise.</dd>
352		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="csv_write_stream/3"><strong>csv_write_stream</strong>(<var>+Stream,
	394	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="csv_write_stream/3"><strong>csv_write_stream</strong>(<var>+Stream,
353	395	+Data, +Options</var>)</a></dt>
354	396	<dd class="defbody">
355	397	Write the rows in <var>Data</var> to <var>Stream</var>. This is similar

+80

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193	234	</div>
194		<h2 id="sec:ctxmodule"><a name="sec:6.13"><span class="sec-nr">6.13</span> <span class="sec-title">Transparent
	235	<h2 id="sec:ctxmodule"><a id="sec:6.13"><span class="sec-nr">6.13</span> <span class="sec-title">Transparent
195	236	predicates: definition and context module</span></a></h2>
196	237
197		<a name="sec:ctxmodule"></a>
	238	<a id="sec:ctxmodule"></a>
198	239
199	240	<p><i>The `module-transparent' mechanism is still underlying the actual
200		implementation. Direct usage by programmers is deprecated. Please use <a name="idx:metapredicate1:1736"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	241	implementation. Direct usage by programmers is deprecated. Please use <a id="idx:metapredicate1:1740"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
201	242	to deal with meta-predicates.</i>
202	243
203		<p>The qualification of module-sensitive arguments described in <a class="sec" href="metapred.html">section
	244	<p>The qualification of module-sensitive arguments described in <a class="sec" href="metapred.html#sec:6.4">section
204	245	6.4</a> is realised using <em>transparent</em> predicates. It is now
205	246	deprecated to use this mechanism directly. However, studying the
206	247	underlying mechanism helps to understand SWI-Prolog's modules. In some

217	258	default, the context module is the definition module of the predicate
218	259	running the goal. For transparent predicates, however, this is the
219	260	context module of the goal inherited from the parent goal. Below, we
220		implement <a name="idx:maplist3:1737"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
	261	implement <a id="idx:maplist3:1741"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
221	262	using the transparent mechanism. The code of
222		<a name="idx:maplist3:1738"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
223		and <a name="idx:maplist3:1739"></a><span class="pred-ext">maplist_/3</span>
224		is the same as in <a class="sec" href="metapred.html">section 6.4</a>,
225		but now we must declare both the main predicate and the helper as
226		transparent to avoid changing the context module when calling the
	263	<a id="idx:maplist3:1742"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
	264	and <a id="idx:maplist3:1743"></a><span class="pred-ext">maplist_/3</span>
	265	is the same as in <a class="sec" href="metapred.html#sec:6.4">section
	266	6.4</a>, but now we must declare both the main predicate and the helper
	267	as transparent to avoid changing the context module when calling the
227	268	helper.
228	269
229	270	<pre class="code">

247	288	module-sensitive arguments. For example, the module below counts the
248	289	number of unique atoms returned as bindings for a variable. It works as
249	290	expected. If we use the directive
250		<code>:- module_transparent <a name="idx:countatomresults3:1740"></a><span class="pred-ext">count_atom_results/3</span>.</code>
	291	<code>:- module_transparent <a id="idx:countatomresults3:1744"></a><span class="pred-ext">count_atom_results/3</span>.</code>
251	292	instead,
252		<a name="idx:atomresult2:1741"></a><span class="pred-ext">atom_result/2</span>
	293	<a id="idx:atomresult2:1745"></a><span class="pred-ext">atom_result/2</span>
253	294	is called wrongly in the module <em>calling</em>
254		<a name="idx:countatomresults3:1742"></a><span class="pred-ext">count_atom_results/3</span>.
255		This can be solved using <a name="idx:stripmodule3:1743"></a><a class="pred" href="ctxmodule.html#strip_module/3">strip_module/3</a>
	295	<a id="idx:countatomresults3:1746"></a><span class="pred-ext">count_atom_results/3</span>.
	296	This can be solved using <a id="idx:stripmodule3:1747"></a><a class="pred" href="ctxmodule.html#strip_module/3">strip_module/3</a>
256	297	to create a qualified goal and a non-transparent helper predicate that
257	298	is defined in the same module.
258	299

275	316	<p>The following predicates support the module-transparent interface:
276	317
277	318	<dl class="latex">
278		<dt class="pubdef"><a name="module_transparent/1">:- <strong>module_transparent</strong>(<var>+Preds</var>)</a></dt>
	319	<dt class="pubdef"><a id="module_transparent/1">:- <strong>module_transparent</strong>(<var>+Preds</var>)</a></dt>
279	320	<dd class="defbody">
280	321	<var>Preds</var> is a comma-separated list of name/arity pairs (like
281		<a name="idx:dynamic1:1744"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>).
	322	<a id="idx:dynamic1:1748"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>).
282	323	Each goal associated with a transparent-declared predicate will inherit
283	324	the <em>context module</em> from its parent goal.</dd>
284		<dt class="pubdef"><a name="context_module/1"><strong>context_module</strong>(<var>-Module</var>)</a></dt>
	325	<dt class="pubdef"><a id="context_module/1"><strong>context_module</strong>(<var>-Module</var>)</a></dt>
285	326	<dd class="defbody">
286	327	Unify <var>Module</var> with the context module of the current goal.
287		<a name="idx:contextmodule1:1745"></a><a class="pred" href="ctxmodule.html#context_module/1">context_module/1</a>
	328	<a id="idx:contextmodule1:1749"></a><a class="pred" href="ctxmodule.html#context_module/1">context_module/1</a>
288	329	itself is, of course, transparent.</dd>
289		<dt class="pubdef"><a name="strip_module/3"><strong>strip_module</strong>(<var>+Term,
	330	<dt class="pubdef"><a id="strip_module/3"><strong>strip_module</strong>(<var>+Term,
290	331	-Module, -Plain</var>)</a></dt>
291	332	<dd class="defbody">
292	333	Used in module-transparent predicates or meta-predicates to extract the

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 2.17</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 2.17</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="syntax.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:cyclic"><a name="sec:2.17"><span class="sec-nr">2.17</span> <span class="sec-title">Rational
	235	<h2 id="sec:cyclic"><a id="sec:2.17"><span class="sec-nr">2.17</span> <span class="sec-title">Rational
195	236	trees (cyclic terms)</span></a></h2>
196	237
197		<a name="sec:cyclic"></a>
198
199		<p><a name="idx:rationaltrees:228"></a><a name="idx:infinitetrees:229"></a><a name="idx:cyclicterms:230"></a><a name="idx:termscyclic:231"></a>SWI-Prolog
	238	<a id="sec:cyclic"></a>
	239
	240	<p><a id="idx:rationaltrees:228"></a><a id="idx:infinitetrees:229"></a><a id="idx:cyclicterms:230"></a><a id="idx:termscyclic:231"></a>SWI-Prolog
200	241	supports rational trees, also known as cyclic terms. `Supports' is so
201	242	defined that most relevant built-in predicates terminate when faced with
202	243	rational trees. Almost all SWI-Prolog's built-in term manipulation

214	255	<a class="pred" href="compare.html#\==/2">\==/2</a>,
215	256	<a class="pred" href="compare.html#\=@=/2">\=@=/2</a>,
216	257	<a class="pred" href="compare.html#\=/2">\=/2</a>,
217		<a name="idx:acyclicterm1:232"></a><a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a>,
218		<a name="idx:bagof3:233"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>,
219		<a name="idx:compare3:234"></a><a class="pred" href="compare.html#compare/3">compare/3</a>,
220		<a name="idx:copyterm2:235"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>,
221		<a name="idx:cyclicterm1:236"></a><a class="pred" href="typetest.html#cyclic_term/1">cyclic_term/1</a>,
222		<a name="idx:dif2:237"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>,
223		<a name="idx:duplicateterm2:238"></a><a class="pred" href="manipterm.html#duplicate_term/2">duplicate_term/2</a>,
224		<a name="idx:findall3:239"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>,
225		<a name="idx:ground1:240"></a><a class="pred" href="typetest.html#ground/1">ground/1</a>,
226		<a name="idx:termhash2:241"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>,
227		<a name="idx:numbervars3:242"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>,
228		<a name="idx:numbervars4:243"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>,
229		<a name="idx:recorda3:244"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>,
230		<a name="idx:recordz3:245"></a><a class="pred" href="db.html#recordz/3">recordz/3</a>,
231		<a name="idx:setof3:246"></a><a class="pred" href="allsolutions.html#setof/3">setof/3</a>,
232		<a name="idx:subsumesterm2:247"></a><a class="pred" href="compare.html#subsumes_term/2">subsumes_term/2</a>,
233		<a name="idx:termvariables2:248"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>,
234		<a name="idx:throw1:249"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
235		<a name="idx:unifywithoccurscheck2:250"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>,
236		<a name="idx:unifiable3:251"></a><a class="pred" href="compare.html#unifiable/3">unifiable/3</a>,
237		<a name="idx:when2:252"></a><a class="pred" href="coroutining.html#when/2">when/2</a>,
238		<a name="idx:write1:253"></a><a class="pred" href="termrw.html#write/1">write/1</a>
	258	<a id="idx:acyclicterm1:232"></a><a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a>,
	259	<a id="idx:bagof3:233"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>,
	260	<a id="idx:compare3:234"></a><a class="pred" href="compare.html#compare/3">compare/3</a>,
	261	<a id="idx:copyterm2:235"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>,
	262	<a id="idx:cyclicterm1:236"></a><a class="pred" href="typetest.html#cyclic_term/1">cyclic_term/1</a>,
	263	<a id="idx:dif2:237"></a><a class="pred" href="coroutining.html#dif/2">dif/2</a>,
	264	<a id="idx:duplicateterm2:238"></a><a class="pred" href="manipterm.html#duplicate_term/2">duplicate_term/2</a>,
	265	<a id="idx:findall3:239"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>,
	266	<a id="idx:ground1:240"></a><a class="pred" href="typetest.html#ground/1">ground/1</a>,
	267	<a id="idx:termhash2:241"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>,
	268	<a id="idx:numbervars3:242"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>,
	269	<a id="idx:numbervars4:243"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>,
	270	<a id="idx:recorda3:244"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>,
	271	<a id="idx:recordz3:245"></a><a class="pred" href="db.html#recordz/3">recordz/3</a>,
	272	<a id="idx:setof3:246"></a><a class="pred" href="allsolutions.html#setof/3">setof/3</a>,
	273	<a id="idx:subsumesterm2:247"></a><a class="pred" href="compare.html#subsumes_term/2">subsumes_term/2</a>,
	274	<a id="idx:termvariables2:248"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>,
	275	<a id="idx:throw1:249"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
	276	<a id="idx:unifywithoccurscheck2:250"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>,
	277	<a id="idx:unifiable3:251"></a><a class="pred" href="compare.html#unifiable/3">unifiable/3</a>,
	278	<a id="idx:when2:252"></a><a class="pred" href="coroutining.html#when/2">when/2</a>,
	279	<a id="idx:write1:253"></a><a class="pred" href="termrw.html#write/1">write/1</a>
239	280	(and related predicates) .
240	281
241	282	<p>In addition, some built-ins recognise rational trees and raise an
242	283	appropriate exception. Arithmetic evaluation belongs to this group. The
243		compiler (<a name="idx:asserta1:254"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>,
	284	compiler (<a id="idx:asserta1:254"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>,
244	285	etc.) also raises an exception. Future versions may support rational
245	286	trees. Predicates that could provide meaningful processing of rational
246	287	trees raise a <code>representation_error</code>. Predicates for which

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.14</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="DCG.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:db"><a name="sec:4.14"><span class="sec-nr">4.14</span> <span class="sec-title">Database</span></a></h2>
195
196		<a name="sec:db"></a>
	235	<h2 id="sec:db"><a id="sec:4.14"><span class="sec-nr">4.14</span> <span class="sec-title">Database</span></a></h2>
	236
	237	<a id="sec:db"></a>
197	238
198	239	<p>SWI-Prolog offers several ways to store data in globally accessible
199	240	memory, i.e., outside the Prolog <em>stacks</em>. Data stored this way

202	243	variables that can be assigned to. Typically, first consider
203	244	representing data processed by your program as terms passed around as
204	245	predicate arguments. If you need to reason over multiple solutions to a
205		goal, consider <a name="idx:findall3:792"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>, <a name="idx:aggregate3:793"></a><a class="pred" href="aggregate.html#aggregate/3">aggregate/3</a>
	246	goal, consider <a id="idx:findall3:792"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>, <a id="idx:aggregate3:793"></a><a class="pred" href="aggregate.html#aggregate/3">aggregate/3</a>
206	247	and related predicates.
207	248
208	249	<p>Nevertheless, there are scenarios where storing data outside the

213	254	<dt><b>Using dynamic predicates</b></dt>
214	255	<dd>
215	256	Dynamic predicates are predicates for which the list of clauses is
216		modified at runtime using <a name="idx:asserta1:794"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>, <a name="idx:assertz1:795"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>, <a name="idx:retract1:796"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	257	modified at runtime using <a id="idx:asserta1:794"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>, <a id="idx:assertz1:795"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>, <a id="idx:retract1:796"></a><a class="pred" href="db.html#retract/1">retract/1</a>
217	258	or
218		<a name="idx:retractall1:797"></a><a class="pred" href="db.html#retractall/1">retractall/1</a>.
	259	<a id="idx:retractall1:797"></a><a class="pred" href="db.html#retractall/1">retractall/1</a>.
219	260	Following the ISO standard, predicates that are modified this way need
220		to be declared using the <a name="idx:dynamic1:798"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a> <em>directive</em>.
	261	to be declared using the <a id="idx:dynamic1:798"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a> <em>directive</em>.
221	262	These facilities are defined by the ISO standard and widely supported.
222	263	The mechanism is often considered slow in the literature. Performance
223	264	depends on the Prolog implementation. In SWI-Prolog, querying dynamic
224	265	predicates has the same performance as static ones. The manipulation
225		predicates are fast. Using <a name="idx:retract1:799"></a><a class="pred" href="db.html#retract/1">retract/1</a>
226		or <a name="idx:retractall1:800"></a><a class="pred" href="db.html#retractall/1">retractall/1</a>
	266	predicates are fast. Using <a id="idx:retract1:799"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	267	or <a id="idx:retractall1:800"></a><a class="pred" href="db.html#retractall/1">retractall/1</a>
227	268	on a predicate registers the predicate as `dirty'. Dirty predicates are
228	269	cleaned by
229		<a name="idx:garbagecollectclauses0:801"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>,
	270	<a id="idx:garbagecollectclauses0:801"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>,
230	271	which is normally automatically invoked. Some workloads may result in
231	272	significant performance reduction due to skipping retracted clauses
232	273	and/or clause garbage collection.

235	276	to maintain a backup of the data on disk. Dynamic predicates come in two
236	277	flavours, <em>shared</em> between threads and <em>local</em> to each
237	278	thread. The latter version is created using the directive
238		<a name="idx:threadlocal1:802"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>.</dd>
	279	<a id="idx:threadlocal1:802"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>.</dd>
239	280	<dt><b>The recorded database</b></dt>
240	281	<dd>
241	282	The `recorded database' registers a list of terms with a <em>key</em>,
242		an atom or compound term. The list is managed using <a name="idx:recorda3:803"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>, <a name="idx:recordz3:804"></a><a class="pred" href="db.html#recordz/3">recordz/3</a>
243		and <a name="idx:erase1:805"></a><a class="pred" href="db.html#erase/1">erase/1</a>.
244		It is queried using <a name="idx:recorded3:806"></a><a class="pred" href="db.html#recorded/3">recorded/3</a>.
	283	an atom or compound term. The list is managed using <a id="idx:recorda3:803"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>, <a id="idx:recordz3:804"></a><a class="pred" href="db.html#recordz/3">recordz/3</a>
	284	and <a id="idx:erase1:805"></a><a class="pred" href="db.html#erase/1">erase/1</a>.
	285	It is queried using <a id="idx:recorded3:806"></a><a class="pred" href="db.html#recorded/3">recorded/3</a>.
245	286	The recorded database is not part of the ISO standard but fairly widely
246	287	supported, notably in implementations building on the `Edinburgh
247	288	tradition'. There are few reasons to use this database in SWI-Prolog due
248	289	to the good performance of dynamic predicates. Advantages are (1) the
249	290	handle provides a direct reference to a term, (2) cyclic terms can be
250		stored and (3) attributes (<a class="sec" href="attvar.html">section 7.1</a>)
251		are preserved. Disadvantages are (1) the terms in a list associated with
252		a key are not indexed, (2) the poorly specified
253		<em>immediate update semantics</em> (see <a class="sec" href="db.html">section
	291	stored and (3) attributes (<a class="sec" href="attvar.html#sec:7.1">section
	292	7.1</a>) are preserved. Disadvantages are (1) the terms in a list
	293	associated with a key are not indexed, (2) the poorly specified
	294	<em>immediate update semantics</em> (see <a class="sec" href="db.html#sec:4.14.5">section
254	295	4.14.5</a> applies to the recorded database and (3) reduced portability.</dd>
255		<dt><b>The <a name="idx:flag3:807"></a><a class="pred" href="db.html#flag/3">flag/3</a>
	296	<dt><b>The <a id="idx:flag3:807"></a><a class="pred" href="db.html#flag/3">flag/3</a>
256	297	predicate</b></dt>
257	298	<dd>
258		The predicate <a name="idx:flag3:808"></a><a class="pred" href="db.html#flag/3">flag/3</a>
	299	The predicate <a id="idx:flag3:808"></a><a class="pred" href="db.html#flag/3">flag/3</a>
259	300	associates one simple value (number or atom) with a key (atom, integer
260	301	or compound). It is an old SWI-Prolog specific predicate that should be
261	302	considered deprecated, although there is no plan to remove it.</dd>
262	303	<dt><b>Using global variables</b></dt>
263	304	<dd>
264		The predicates <a name="idx:bsetval2:809"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>
265		and <a name="idx:nbsetval2:810"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
	305	The predicates <a id="idx:bsetval2:809"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>
	306	and <a id="idx:nbsetval2:810"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
266	307	associate a term living on the Prolog stack with a name, either
267	308	backtrackable or non-backtrackable. Backtrackable and non-backtrackable
268		assignment without using a global name can be realised with <a name="idx:setarg3:811"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
269		and <a name="idx:nbsetarg3:812"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
270		Notably the latter are used to realise aggregation as e.g., <a name="idx:aggregateall3:813"></a><a class="pred" href="aggregate.html#aggregate_all/3">aggregate_all/3</a>
	309	assignment without using a global name can be realised with <a id="idx:setarg3:811"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	310	and <a id="idx:nbsetarg3:812"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
	311	Notably the latter are used to realise aggregation as e.g., <a id="idx:aggregateall3:813"></a><a class="pred" href="aggregate.html#aggregate_all/3">aggregate_all/3</a>
271	312	performs.</dd>
272	313	<dt><b>Tries</b></dt>
273	314	<dd>
274	315	As of version 7.3.21, SWI-Prolog provides <em>tries</em> (prefix trees)
275	316	to associate a term <em>variant</em> with a value. Tries have been
276		introduced to support <var>tabling</var> and are described in <a class="sec" href="db.html">section
	317	introduced to support <var>tabling</var> and are described in <a class="sec" href="db.html#sec:4.14.4">section
277	318	4.14.4</a>.
278	319	</dd>
279	320	</dl>
280	321
281		<p><h3 id="sec:dynpreds"><a name="sec:4.14.1"><span class="sec-nr">4.14.1</span> <span class="sec-title">Managing
	322	<p><h3 id="sec:dynpreds"><a id="sec:4.14.1"><span class="sec-nr">4.14.1</span> <span class="sec-title">Managing
282	323	(dynamic) predicates</span></a></h3>
283	324
284		<a name="sec:dynpreds"></a>
	325	<a id="sec:dynpreds"></a>
285	326
286	327	<dl class="latex">
287		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="abolish/1"><strong>abolish</strong>(<var>:PredicateIndicator</var>)</a></dt>
	328	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="abolish/1"><strong>abolish</strong>(<var>:PredicateIndicator</var>)</a></dt>
288	329	<dd class="defbody">
289	330	Removes all clauses of a predicate with functor <var>Functor</var> and
290	331	arity

293	334	imported predicate only removes the import link; the predicate will keep
294	335	its old definition in its definition module.
295	336
296		<p>According to the ISO standard, <a name="idx:abolish1:814"></a><a class="pred" href="db.html#abolish/1">abolish/1</a>
	337	<p>According to the ISO standard, <a id="idx:abolish1:814"></a><a class="pred" href="db.html#abolish/1">abolish/1</a>
297	338	can only be applied to dynamic procedures. This is odd, as for dealing
298		with dynamic procedures there is already <a name="idx:retract1:815"></a><a class="pred" href="db.html#retract/1">retract/1</a>
299		and <a name="idx:retractall1:816"></a><a class="pred" href="db.html#retractall/1">retractall/1</a>.
300		The <a name="idx:abolish1:817"></a><a class="pred" href="db.html#abolish/1">abolish/1</a>
	339	with dynamic procedures there is already <a id="idx:retract1:815"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	340	and <a id="idx:retractall1:816"></a><a class="pred" href="db.html#retractall/1">retractall/1</a>.
	341	The <a id="idx:abolish1:817"></a><a class="pred" href="db.html#abolish/1">abolish/1</a>
301	342	predicate was introduced in DEC-10 Prolog precisely for dealing with
302		static procedures. In SWI-Prolog, <a name="idx:abolish1:818"></a><a class="pred" href="db.html#abolish/1">abolish/1</a>
	343	static procedures. In SWI-Prolog, <a id="idx:abolish1:818"></a><a class="pred" href="db.html#abolish/1">abolish/1</a>
303	344	works on static procedures, unless the Prolog flag <a class="flag" href="flags.html#flag:iso">iso</a>
304	345	is set to <code>true</code>.
305	346
306		<p>It is advised to use <a name="idx:retractall1:819"></a><a class="pred" href="db.html#retractall/1">retractall/1</a>
	347	<p>It is advised to use <a id="idx:retractall1:819"></a><a class="pred" href="db.html#retractall/1">retractall/1</a>
307	348	for erasing all clauses of a dynamic predicate.</dd>
308		<dt class="pubdef"><a name="abolish/2"><strong>abolish</strong>(<var>+Name,
	349	<dt class="pubdef"><a id="abolish/2"><strong>abolish</strong>(<var>+Name,
309	350	+Arity</var>)</a></dt>
310	351	<dd class="defbody">
311		Same as <code>abolish(Name/Arity)</code>. The predicate <a name="idx:abolish2:820"></a><a class="pred" href="db.html#abolish/2">abolish/2</a>
312		conforms to the Edinburgh standard, while <a name="idx:abolish1:821"></a><a class="pred" href="db.html#abolish/1">abolish/1</a>
	352	Same as <code>abolish(Name/Arity)</code>. The predicate <a id="idx:abolish2:820"></a><a class="pred" href="db.html#abolish/2">abolish/2</a>
	353	conforms to the Edinburgh standard, while <a id="idx:abolish1:821"></a><a class="pred" href="db.html#abolish/1">abolish/1</a>
313	354	is ISO compliant.</dd>
314		<dt class="pubdef"><a name="copy_predicate_clauses/2"><strong>copy_predicate_clauses</strong>(<var>:From,
	355	<dt class="pubdef"><a id="copy_predicate_clauses/2"><strong>copy_predicate_clauses</strong>(<var>:From,
315	356	:To</var>)</a></dt>
316	357	<dd class="defbody">
317	358	Copy all clauses of predicate <var>From</var> to <var>To</var>. The

320	361	undefined, it is created as a dynamic predicate holding a copy of the
321	362	clauses of
322	363	<var>From</var>. If <var>To</var> is a dynamic predicate, the clauses of
323		<var>From</var> are added (as in <a name="idx:assertz1:822"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>)
	364	<var>From</var> are added (as in <a id="idx:assertz1:822"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>)
324	365	to the clauses of <var>To</var>.
325	366	<var>To</var> and <var>From</var> must have the same arity. Acts as if
326	367	defined by the program below, but at a much better performance by

341	382	</pre>
342	383
343	384	</dd>
344		<dt class="pubdef"><a name="redefine_system_predicate/1"><strong>redefine_system_predicate</strong>(<var>+Head</var>)</a></dt>
	385	<dt class="pubdef"><a id="redefine_system_predicate/1"><strong>redefine_system_predicate</strong>(<var>+Head</var>)</a></dt>
345	386	<dd class="defbody">
346	387	This directive may be used both in module <code>user</code> and in
347	388	normal modules to redefine any system predicate. If the system

352	393
353	394	<p>Redefining system predicate facilitates the definition of
354	395	compatibility packages. Use in other contexts is discouraged.</dd>
355		<dt class="pubdef"><span class="pred-tag">[ISO,nondet]</span><a name="retract/1"><strong>retract</strong>(<var>+Term</var>)</a></dt>
	396	<dt class="pubdef"><span class="pred-tag">[ISO,nondet]</span><a id="retract/1"><strong>retract</strong>(<var>+Term</var>)</a></dt>
356	397	<dd class="defbody">
357	398	When <var>Term</var> is an atom or a term it is unified with the first
358	399	unifying fact or clause in the database. The fact or clause is removed
359		from the database. The <a name="idx:retract1:823"></a><a class="pred" href="db.html#retract/1">retract/1</a>
360		predicate respects the <em>logical update view</em>. This implies that <a name="idx:retract1:824"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	400	from the database. The <a id="idx:retract1:823"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	401	predicate respects the <em>logical update view</em>. This implies that <a id="idx:retract1:824"></a><a class="pred" href="db.html#retract/1">retract/1</a>
361	402	succeeds for all clauses that match <var>Term</var> when the predicate
362	403	was <em>called</em>. The example below illustrates that the first call
363		to <a name="idx:retract1:825"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	404	to <a id="idx:retract1:825"></a><a class="pred" href="db.html#retract/1">retract/1</a>
364	405	succeeds on <code>bee</code> on backtracking despite the fact that <code>bee</code>
365	406	is already retracted.<sup class="fn">74<span class="fn-text">Example by
366	407	Jan Burse</span></sup>.

384	425	time their notion of the <em>entry generation</em> is adjusted such that
385	426	they do not retract the same first clause. This implies that, if
386	427	multiple threads use <code>once(retract(Term))</code>, no two threads
387		will retract the same clause. Note that on backtracking over <a name="idx:retract1:826"></a><a class="pred" href="db.html#retract/1">retract/1</a>,
	428	will retract the same clause. Note that on backtracking over <a id="idx:retract1:826"></a><a class="pred" href="db.html#retract/1">retract/1</a>,
388	429	multiple threads may retract the same clause as both threads respect the
389	430	logical update view.</dd>
390		<dt class="pubdef"><span class="pred-tag">[ISO,det]</span><a name="retractall/1"><strong>retractall</strong>(<var>+Head</var>)</a></dt>
	431	<dt class="pubdef"><span class="pred-tag">[ISO,det]</span><a id="retractall/1"><strong>retractall</strong>(<var>+Head</var>)</a></dt>
391	432	<dd class="defbody">
392	433	All facts or clauses in the database for which the <var>head</var>
393	434	unifies with <var>Head</var> are removed. If <var>Head</var> refers to a
394	435	predicate that is not defined, it is implicitly created as a dynamic
395		predicate. See also <a name="idx:dynamic1:827"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>.<sup class="fn">75<span class="fn-text">The
396		ISO standard only allows using <a name="idx:dynamic1:828"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
	436	predicate. See also <a id="idx:dynamic1:827"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>.<sup class="fn">75<span class="fn-text">The
	437	ISO standard only allows using <a id="idx:dynamic1:828"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
397	438	as a <em>directive</em>.</span></sup></dd>
398		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="asserta/1"><strong>asserta</strong>(<var>+Term</var>)</a></dt>
399		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="assertz/1"><strong>assertz</strong>(<var>+Term</var>)</a></dt>
400		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="assert/1"><strong>assert</strong>(<var>+Term</var>)</a></dt>
	439	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="asserta/1"><strong>asserta</strong>(<var>+Term</var>)</a></dt>
	440	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="assertz/1"><strong>assertz</strong>(<var>+Term</var>)</a></dt>
	441	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="assert/1"><strong>assert</strong>(<var>+Term</var>)</a></dt>
401	442	<dd class="defbody">
402	443	Assert a clause (fact or rule) into the database. The predicate
403		<a name="idx:asserta1:829"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
	444	<a id="idx:asserta1:829"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
404	445	asserts the clause as first clause of the predicate while
405		<a name="idx:assertz1:830"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
406		assert the clause as last clause. The deprecated <a name="idx:assert1:831"></a><a class="pred" href="db.html#assert/1">assert/1</a>
407		is equivalent to <a name="idx:assertz1:832"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>.
408		If the program space for the target module is limited (see <a name="idx:setmodule1:833"></a><a class="pred" href="manipmodule.html#set_module/1">set_module/1</a>), <a name="idx:asserta1:834"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
	446	<a id="idx:assertz1:830"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
	447	assert the clause as last clause. The deprecated <a id="idx:assert1:831"></a><a class="pred" href="db.html#assert/1">assert/1</a>
	448	is equivalent to <a id="idx:assertz1:832"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>.
	449	If the program space for the target module is limited (see <a id="idx:setmodule1:833"></a><a class="pred" href="manipmodule.html#set_module/1">set_module/1</a>), <a id="idx:asserta1:834"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
409	450	can raise a
410	451	<code>resource_error(program_space)</code> exception. The example below
411	452	adds two facts and a rule. Note the double parentheses around the rule.

419	460	</pre>
420	461
421	462	</dd>
422		<dt class="pubdef"><a name="asserta/2"><strong>asserta</strong>(<var>+Term,
	463	<dt class="pubdef"><a id="asserta/2"><strong>asserta</strong>(<var>+Term,
423	464	-Reference</var>)</a></dt>
424		<dt class="pubdef"><a name="assertz/2"><strong>assertz</strong>(<var>+Term,
	465	<dt class="pubdef"><a id="assertz/2"><strong>assertz</strong>(<var>+Term,
425	466	-Reference</var>)</a></dt>
426		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="assert/2"><strong>assert</strong>(<var>+Term,
	467	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="assert/2"><strong>assert</strong>(<var>+Term,
427	468	-Reference</var>)</a></dt>
428	469	<dd class="defbody">
429		Equivalent to <a name="idx:asserta1:835"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>, <a name="idx:assertz1:836"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>, <a name="idx:assert1:837"></a><a class="pred" href="db.html#assert/1">assert/1</a>,
	470	Equivalent to <a id="idx:asserta1:835"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>, <a id="idx:assertz1:836"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>, <a id="idx:assert1:837"></a><a class="pred" href="db.html#assert/1">assert/1</a>,
430	471	but in addition unifies
431	472	<var>Reference</var> with a handle to the asserted clauses. The handle
432		can be used to access this clause with <a name="idx:clause3:838"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>
433		and <a name="idx:erase1:839"></a><a class="pred" href="db.html#erase/1">erase/1</a>.
	473	can be used to access this clause with <a id="idx:clause3:838"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>
	474	and <a id="idx:erase1:839"></a><a class="pred" href="db.html#erase/1">erase/1</a>.
434	475	</dd>
435	476	</dl>
436	477
437		<p><h3 id="sec:recdb"><a name="sec:4.14.2"><span class="sec-nr">4.14.2</span> <span class="sec-title">The
	478	<p><h3 id="sec:recdb"><a id="sec:4.14.2"><span class="sec-nr">4.14.2</span> <span class="sec-title">The
438	479	recorded database</span></a></h3>
439	480
440		<a name="sec:recdb"></a>
	481	<a id="sec:recdb"></a>
441	482
442	483	<dl class="latex">
443		<dt class="pubdef"><a name="recorda/3"><strong>recorda</strong>(<var>+Key,
	484	<dt class="pubdef"><a id="recorda/3"><strong>recorda</strong>(<var>+Key,
444	485	+Term, -Reference</var>)</a></dt>
445	486	<dd class="defbody">
446	487	Assert <var>Term</var> in the recorded database under key <var>Key</var>.

449	490	atom or compound term. If the key is a compound term, only the name and
450	491	arity define the key.
451	492	<var>Reference</var> is unified with an opaque handle to the record (see
452		<a name="idx:erase1:840"></a><a class="pred" href="db.html#erase/1">erase/1</a>).</dd>
453		<dt class="pubdef"><a name="recorda/2"><strong>recorda</strong>(<var>+Key,
	493	<a id="idx:erase1:840"></a><a class="pred" href="db.html#erase/1">erase/1</a>).</dd>
	494	<dt class="pubdef"><a id="recorda/2"><strong>recorda</strong>(<var>+Key,
454	495	+Term</var>)</a></dt>
455	496	<dd class="defbody">
456	497	Equivalent to <code>recorda(<var>Key</var>, <var>Term</var>, _)</code>.</dd>
457		<dt class="pubdef"><a name="recordz/3"><strong>recordz</strong>(<var>+Key,
	498	<dt class="pubdef"><a id="recordz/3"><strong>recordz</strong>(<var>+Key,
458	499	+Term, -Reference</var>)</a></dt>
459	500	<dd class="defbody">
460		Equivalent to <a name="idx:recorda3:841"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>,
	501	Equivalent to <a id="idx:recorda3:841"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>,
461	502	but puts the <var>Term</var> at the tail of the terms recorded under <var>Key</var>.</dd>
462		<dt class="pubdef"><a name="recordz/2"><strong>recordz</strong>(<var>+Key,
	503	<dt class="pubdef"><a id="recordz/2"><strong>recordz</strong>(<var>+Key,
463	504	+Term</var>)</a></dt>
464	505	<dd class="defbody">
465	506	Equivalent to <code>recordz(<var>Key</var>, <var>Term</var>, _)</code>.</dd>
466		<dt class="pubdef"><a name="recorded/3"><strong>recorded</strong>(<var>?Key,
	507	<dt class="pubdef"><a id="recorded/3"><strong>recorded</strong>(<var>?Key,
467	508	?Value, ?Reference</var>)</a></dt>
468	509	<dd class="defbody">
469	510	True if <var>Value</var> is recorded under <var>Key</var> and has the

472	513	non-deterministic. If neither <var>Reference</var> nor <var>Key</var> is
473	514	given, the triples are generated as in the code snippet below.<sup class="fn">76<span class="fn-text">Note
474	515	that, without a given <var>Key</var>, some implementations return
475		triples in the order defined by <a name="idx:recorda2:842"></a><a class="pred" href="db.html#recorda/2">recorda/2</a>
476		and <a name="idx:recordz2:843"></a><a class="pred" href="db.html#recordz/2">recordz/2</a>.</span></sup>
477		See also <a name="idx:currentkey1:844"></a><a class="pred" href="examineprog.html#current_key/1">current_key/1</a>.
	516	triples in the order defined by <a id="idx:recorda2:842"></a><a class="pred" href="db.html#recorda/2">recorda/2</a>
	517	and <a id="idx:recordz2:843"></a><a class="pred" href="db.html#recordz/2">recordz/2</a>.</span></sup>
	518	See also <a id="idx:currentkey1:844"></a><a class="pred" href="examineprog.html#current_key/1">current_key/1</a>.
478	519
479	520	<pre class="code">
480	521	current_key(Key),

482	523	</pre>
483	524
484	525	</dd>
485		<dt class="pubdef"><a name="recorded/2"><strong>recorded</strong>(<var>+Key,
	526	<dt class="pubdef"><a id="recorded/2"><strong>recorded</strong>(<var>+Key,
486	527	-Value</var>)</a></dt>
487	528	<dd class="defbody">
488	529	Equivalent to <code>recorded(<var>Key</var>, <var>Value</var>, _)</code>.</dd>
489		<dt class="pubdef"><a name="erase/1"><strong>erase</strong>(<var>+Reference</var>)</a></dt>
	530	<dt class="pubdef"><a id="erase/1"><strong>erase</strong>(<var>+Reference</var>)</a></dt>
490	531	<dd class="defbody">
491	532	Erase a record or clause from the database. <var>Reference</var> is a
492		db-reference returned by <a name="idx:recorda3:845"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>, <a name="idx:recordz3:846"></a><a class="pred" href="db.html#recordz/3">recordz/3</a>
493		or <a name="idx:recorded3:847"></a><a class="pred" href="db.html#recorded/3">recorded/3</a>, <a name="idx:clause3:848"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>,
494		<a name="idx:assert2:849"></a><a class="pred" href="db.html#assert/2">assert/2</a>, <a name="idx:asserta2:850"></a><a class="pred" href="db.html#asserta/2">asserta/2</a>
495		or <a name="idx:assertz2:851"></a><a class="pred" href="db.html#assertz/2">assertz/2</a>.
	533	db-reference returned by <a id="idx:recorda3:845"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>, <a id="idx:recordz3:846"></a><a class="pred" href="db.html#recordz/3">recordz/3</a>
	534	or <a id="idx:recorded3:847"></a><a class="pred" href="db.html#recorded/3">recorded/3</a>, <a id="idx:clause3:848"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>,
	535	<a id="idx:assert2:849"></a><a class="pred" href="db.html#assert/2">assert/2</a>, <a id="idx:asserta2:850"></a><a class="pred" href="db.html#asserta/2">asserta/2</a>
	536	or <a id="idx:assertz2:851"></a><a class="pred" href="db.html#assertz/2">assertz/2</a>.
496	537	Fail silently if the referenced object no longer exists. Notably, if
497	538	multiple threads attempt to erase the same clause one will succeed and
498	539	the others will fail.</dd>
499		<dt class="pubdef"><a name="instance/2"><strong>instance</strong>(<var>+Reference,
	540	<dt class="pubdef"><a id="instance/2"><strong>instance</strong>(<var>+Reference,
500	541	-Term</var>)</a></dt>
501	542	<dd class="defbody">
502	543	Unify <var>Term</var> with the referenced clause or database record.

504	545	</dd>
505	546	</dl>
506	547
507		<p><h3 id="sec:flag"><a name="sec:4.14.3"><span class="sec-nr">4.14.3</span> <span class="sec-title">Flags</span></a></h3>
508
509		<a name="sec:flag"></a>
510
511		<p>The predicate <a name="idx:flag3:852"></a><a class="pred" href="db.html#flag/3">flag/3</a>
	548	<p><h3 id="sec:flag"><a id="sec:4.14.3"><span class="sec-nr">4.14.3</span> <span class="sec-title">Flags</span></a></h3>
	549
	550	<a id="sec:flag"></a>
	551
	552	<p>The predicate <a id="idx:flag3:852"></a><a class="pred" href="db.html#flag/3">flag/3</a>
512	553	is the oldest way to store global non-backtrackable data in SWI-Prolog.
513	554	Flags are global and shared by all threads. Their value is limited to
514	555	atoms, small (64-bit) integers and floating point numbers. Flags are
515	556	thread-safe. The flags described in this section must not be confused
516	557	with <em>Prolog flags</em> described in
517		<a class="sec" href="flags.html">section 2.11</a>.
	558	<a class="sec" href="flags.html#sec:2.11">section 2.11</a>.
518	559
519	560	<dl class="latex">
520		<dt class="pubdef"><a name="get_flag/2"><strong>get_flag</strong>(<var>+Key,
	561	<dt class="pubdef"><a id="get_flag/2"><strong>get_flag</strong>(<var>+Key,
521	562	-Value</var>)</a></dt>
522	563	<dd class="defbody">
523	564	True when <var>Value</var> is the value currently associated with <var>Key</var>.
524	565	If <var>Key</var> does not exist, a new flag with value `0' (zero) is
525	566	created.
526	567	</dd>
527		<dt class="pubdef"><a name="set_flag/2"><strong>set_flag</strong>(<var>+Key,
	568	<dt class="pubdef"><a id="set_flag/2"><strong>set_flag</strong>(<var>+Key,
528	569	Value</var>)</a></dt>
529	570	<dd class="defbody">
530	571	Set flag <var>Key</var> to <var>Value</var>. Value must be an atom,
531	572	small (64-bit) integer or float.
532	573	</dd>
533		<dt class="pubdef"><a name="flag/3"><strong>flag</strong>(<var>+Key,
534		-Old, +New</var>)</a></dt>
	574	<dt class="pubdef"><a id="flag/3"><strong>flag</strong>(<var>+Key, -Old,
	575	+New</var>)</a></dt>
535	576	<dd class="defbody">
536	577	True when <var>Old</var> is the current value of the flag <var>Key</var>
537	578	and the flag has been set to <var>New</var>. <var>New</var> can be an

547	588	<p></dd>
548	589	</dl>
549	590
550		<p><h3 id="sec:trie"><a name="sec:4.14.4"><span class="sec-nr">4.14.4</span> <span class="sec-title">Tries</span></a></h3>
551
552		<a name="sec:trie"></a>
	591	<p><h3 id="sec:trie"><a id="sec:4.14.4"><span class="sec-nr">4.14.4</span> <span class="sec-title">Tries</span></a></h3>
	592
	593	<a id="sec:trie"></a>
553	594
554	595	<p>Tries (also called <em>digital tree</em>, <em>radix tree</em> or
555	596	<em>prefix tree</em> maintain a mapping between a variant of a term (see

562	603	<ul class="compact">
563	604	<li>Tries are not thread-safe.
564	605	<li>Tries should not be modified while non-deterministic predicates such
565		as <a name="idx:triegen3:853"></a><a class="pred" href="db.html#trie_gen/3">trie_gen/3</a>
	606	as <a id="idx:triegen3:853"></a><a class="pred" href="db.html#trie_gen/3">trie_gen/3</a>
566	607	are running on the trie.
567	608	<li>Terms cannot have <em>attributed variables</em>.
568	609	<li>Terms cannot be <em>cyclic</em>. Possibly this will not change

576	617	considered stable.</b>
577	618
578	619	<dl class="latex">
579		<dt class="pubdef"><a name="trie_new/1"><strong>trie_new</strong>(<var>-Trie</var>)</a></dt>
	620	<dt class="pubdef"><a id="trie_new/1"><strong>trie_new</strong>(<var>-Trie</var>)</a></dt>
580	621	<dd class="defbody">
581	622	Create a new trie and unify <var>Trie</var> with a handle to the trie.
582	623	The trie handle is a <em>blob</em>. Tries are subject to atom garbage
583	624	collection.</dd>
584		<dt class="pubdef"><a name="trie_destroy/1"><strong>trie_destroy</strong>(<var>+Trie</var>)</a></dt>
	625	<dt class="pubdef"><a id="trie_destroy/1"><strong>trie_destroy</strong>(<var>+Trie</var>)</a></dt>
585	626	<dd class="defbody">
586	627	Destroy <var>Trie</var>. This removes all nodes from the trie and causes
587	628	further access to <var>Trie</var> to raise an existence_error exception.
588	629	The handle itself is reclaimed by atom garbage collection.</dd>
589		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="is_trie/1"><strong>is_trie</strong>(<var>@Trie</var>)</a></dt>
590		<dd class="defbody">
591		True when <var>Trie</var> is a trie object. See also <a name="idx:currenttrie1:854"></a><a class="pred" href="db.html#current_trie/1">current_trie/1</a>.</dd>
592		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_trie/1"><strong>current_trie</strong>(<var>-Trie</var>)</a></dt>
	630	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="is_trie/1"><strong>is_trie</strong>(<var>@Trie</var>)</a></dt>
	631	<dd class="defbody">
	632	True when <var>Trie</var> is a trie object. See also <a id="idx:currenttrie1:854"></a><a class="pred" href="db.html#current_trie/1">current_trie/1</a>.</dd>
	633	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_trie/1"><strong>current_trie</strong>(<var>-Trie</var>)</a></dt>
593	634	<dd class="defbody">
594	635	True if <var>Trie</var> is a currently existing trie. As this enumerates
595	636	and then filters all known atoms this predicate is slow and should only
596		be used for debugging purposes. See also <a name="idx:istrie1:855"></a><a class="pred" href="db.html#is_trie/1">is_trie/1</a>.</dd>
597		<dt class="pubdef"><a name="trie_insert/3"><strong>trie_insert</strong>(<var>+Trie,
	637	be used for debugging purposes. See also <a id="idx:istrie1:855"></a><a class="pred" href="db.html#is_trie/1">is_trie/1</a>.</dd>
	638	<dt class="pubdef"><a id="trie_insert/3"><strong>trie_insert</strong>(<var>+Trie,
598	639	+Key, +Value</var>)</a></dt>
599	640	<dd class="defbody">
600	641	Insert the term <var>Key</var> into <var>Trie</var> and associate it

604	645	silently. If <var>Key</var> is in <var>Trie</var> associated with a
605	646	different value, a
606	647	<code>permission_error</code> is raised.</dd>
607		<dt class="pubdef"><a name="trie_update/3"><strong>trie_update</strong>(<var>+Trie,
	648	<dt class="pubdef"><a id="trie_update/3"><strong>trie_update</strong>(<var>+Trie,
608	649	+Key, +Value</var>)</a></dt>
609	650	<dd class="defbody">
610		As <a name="idx:trieinsert3:856"></a><a class="pred" href="db.html#trie_insert/3">trie_insert/3</a>,
	651	As <a id="idx:trieinsert3:856"></a><a class="pred" href="db.html#trie_insert/3">trie_insert/3</a>,
611	652	but if <var>Key</var> is in <var>Trie</var>, its associated value is <em>updated</em>.</dd>
612		<dt class="pubdef"><a name="trie_insert/4"><strong>trie_insert</strong>(<var>+Trie,
	653	<dt class="pubdef"><a id="trie_insert/4"><strong>trie_insert</strong>(<var>+Trie,
613	654	+Term, +Value, -Handle</var>)</a></dt>
614	655	<dd class="defbody">
615		As <a name="idx:trieinsert3:857"></a><a class="pred" href="db.html#trie_insert/3">trie_insert/3</a>,
	656	As <a id="idx:trieinsert3:857"></a><a class="pred" href="db.html#trie_insert/3">trie_insert/3</a>,
616	657	returning a handle to the trie node. This predicate is currently unsafe
617	658	as <var>Handle</var> is an integer used to encode a pointer. It was used
618	659	to implement a pure Prolog version of the <code>library(tabling)</code>
619	660	library.</dd>
620		<dt class="pubdef"><a name="trie_delete/3"><strong>trie_delete</strong>(<var>+Trie,
	661	<dt class="pubdef"><a id="trie_delete/3"><strong>trie_delete</strong>(<var>+Trie,
621	662	+Key, ?Value</var>)</a></dt>
622	663	<dd class="defbody">
623	664	Delete <var>Key</var> from <var>Trie</var> if the value associated with <var>Key</var>
624	665	unifies with <var>Value</var>.</dd>
625		<dt class="pubdef"><a name="trie_lookup/3"><strong>trie_lookup</strong>(<var>+Trie,
	666	<dt class="pubdef"><a id="trie_lookup/3"><strong>trie_lookup</strong>(<var>+Trie,
626	667	+Key, -Value</var>)</a></dt>
627	668	<dd class="defbody">
628	669	True if the term <var>Key</var> is in <var>Trie</var> and associated
629	670	with
630	671	<var>Value</var>.</dd>
631		<dt class="pubdef"><a name="trie_term/2"><strong>trie_term</strong>(<var>+Handle,
	672	<dt class="pubdef"><a id="trie_term/2"><strong>trie_term</strong>(<var>+Handle,
632	673	-Term</var>)</a></dt>
633	674	<dd class="defbody">
634	675	True when <var>Term</var> is a copy of the term associated with <var>Handle</var>.
635	676	The result is undefined (including crashes) if <var>Handle</var> is not
636		a handle returned by <a name="idx:trieinsertnew3:858"></a><span class="pred-ext">trie_insert_new/3</span>
	677	a handle returned by <a id="idx:trieinsertnew3:858"></a><span class="pred-ext">trie_insert_new/3</span>
637	678	or the node has been removed afterwards.</dd>
638		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="trie_gen/3"><strong>trie_gen</strong>(<var>+Trie,
	679	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="trie_gen/3"><strong>trie_gen</strong>(<var>+Trie,
639	680	?Key, -Value</var>)</a></dt>
640	681	<dd class="defbody">
641	682	True when <var>Key</var> is associated with <var>Value</var> in <var>Trie</var>.
642	683	Backtracking retrieves all pairs. Currently scans the entire trie, even
643	684	if <var>Key</var> is partly known. Currently unsafe if <var>Trie</var>
644	685	is modified while the values are being enumerated.</dd>
645		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="trie_property/2"><strong>trie_property</strong>(<var>?Trie,
	686	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="trie_property/2"><strong>trie_property</strong>(<var>?Trie,
646	687	?Property</var>)</a></dt>
647	688	<dd class="defbody">
648	689	True if <var>Trie</var> exists with <var>Property</var>. Intended for

671	712	</dd>
672	713	</dl>
673	714
674		<p><h3 id="sec:update"><a name="sec:4.14.5"><span class="sec-nr">4.14.5</span> <span class="sec-title">Update
	715	<p><h3 id="sec:update"><a id="sec:4.14.5"><span class="sec-nr">4.14.5</span> <span class="sec-title">Update
675	716	view</span></a></h3>
676	717
677		<a name="sec:update"></a>
678
679		<p><a name="idx:logicalupdateview:859"></a><a name="idx:immediateupdateview:860"></a><a name="idx:updateview:861"></a>Traditionally,
	718	<a id="sec:update"></a>
	719
	720	<p><a id="idx:logicalupdateview:859"></a><a id="idx:immediateupdateview:860"></a><a id="idx:updateview:861"></a>Traditionally,
680	721	Prolog systems used the <em>immediate update view</em>: new clauses
681	722	became visible to predicates backtracking over dynamic predicates
682	723	immediately, and retracted clauses became invisible immediately.
683	724
684	725	<p>Starting with SWI-Prolog 3.3.0 we adhere to the <em>logical update
685	726	view</em>, where backtrackable predicates that enter the definition of a
686		predicate will not see any changes (either caused by <a name="idx:assert1:862"></a><a class="pred" href="db.html#assert/1">assert/1</a>
	727	predicate will not see any changes (either caused by <a id="idx:assert1:862"></a><a class="pred" href="db.html#assert/1">assert/1</a>
687	728	or
688		<a name="idx:retract1:863"></a><a class="pred" href="db.html#retract/1">retract/1</a>)
	729	<a id="idx:retract1:863"></a><a class="pred" href="db.html#retract/1">retract/1</a>)
689	730	to the predicate. This view is the ISO standard, the most commonly used
690	731	and the most `safe'.<sup class="fn">77<span class="fn-text">For example,
691	732	using the immediate update view, no call to a dynamic predicate is

698	739	with a `created' ... `erased' interval that encloses the generation of
699	740	the current goal are considered visible.
700	741
701		<p><h3 id="sec:hashterm"><a name="sec:4.14.6"><span class="sec-nr">4.14.6</span> <span class="sec-title">Indexing
	742	<p><h3 id="sec:hashterm"><a id="sec:4.14.6"><span class="sec-nr">4.14.6</span> <span class="sec-title">Indexing
702	743	databases</span></a></h3>
703	744
704		<a name="sec:hashterm"></a>
705
706		<p><a name="idx:indexingtermhashes:864"></a>The indexing capabilities of
	745	<a id="sec:hashterm"></a>
	746
	747	<p><a id="idx:indexingtermhashes:864"></a>The indexing capabilities of
707	748	SWI-Prolog are described in
708		<a class="sec" href="jitindex.html">section 2.18</a>. Summarizing,
709		SWI-Prolog creates indexes for any applicable argument, but only on one
710		argument, and does not index on arguments of compound terms. The
711		predicates below provide building blocks to circumvent the limitations
712		of the current indexing system.
713
714		<p>Programs that aim at portability should consider using <a name="idx:termhash2:865"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>
	749	<a class="sec" href="jitindex.html#sec:2.18">section 2.18</a>.
	750	Summarizing, SWI-Prolog creates indexes for any applicable argument, but
	751	only on one argument, and does not index on arguments of compound terms.
	752	The predicates below provide building blocks to circumvent the
	753	limitations of the current indexing system.
	754
	755	<p>Programs that aim at portability should consider using <a id="idx:termhash2:865"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>
715	756	and
716		<a name="idx:termhash4:866"></a><a class="pred" href="db.html#term_hash/4">term_hash/4</a>
	757	<a id="idx:termhash4:866"></a><a class="pred" href="db.html#term_hash/4">term_hash/4</a>
717	758	to design their database such that indexing on constant or functor
718	759	(name/arity reference) on the first argument is sufficient.
719	760
720	761	<dl class="latex">
721		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="term_hash/2"><strong>term_hash</strong>(<var>+Term,
	762	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="term_hash/2"><strong>term_hash</strong>(<var>+Term,
722	763	-HashKey</var>)</a></dt>
723	764	<dd class="defbody">
724		If <var>Term</var> is a ground term (see <a name="idx:ground1:867"></a><a class="pred" href="typetest.html#ground/1">ground/1</a>), <var>HashKey</var>
	765	If <var>Term</var> is a ground term (see <a id="idx:ground1:867"></a><a class="pred" href="typetest.html#ground/1">ground/1</a>), <var>HashKey</var>
725	766	is unified with a positive integer value that may be used as a hash key
726	767	to the value. If <var>Term</var> is not ground, the predicate leaves <var>HashKey</var>
727	768	an unbound variable. Hash keys are in the range <var>0 ... 16,777,215</var>,

735	776	atoms and may be assumed constant over different invocations and
736	777	versions of SWI-Prolog.<sup class="fn">78<span class="fn-text">Last
737	778	change: version 5.10.4</span></sup> Hashes differ between big and little
738		endian machines. The <a name="idx:termhash2:868"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>
	779	endian machines. The <a id="idx:termhash2:868"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>
739	780	predicate is cycle-safe.<sup class="fn">bug<span class="fn-text">All
740	781	arguments that (indirectly) lead to a cycle have the same hash key.</span></sup></dd>
741		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="term_hash/4"><strong>term_hash</strong>(<var>+Term,
	782	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="term_hash/4"><strong>term_hash</strong>(<var>+Term,
742	783	+Depth, +Range, -HashKey</var>)</a></dt>
743	784	<dd class="defbody">
744		As <a name="idx:termhash2:869"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>,
	785	As <a id="idx:termhash2:869"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>,
745	786	but only considers <var>Term</var> to the specified
746	787	<var>Depth</var>. The top-level term has depth 1, its arguments have
747	788	depth 2, etc. That is, <var><var>Depth</var> = 0</var> hashes nothing; <var><var>Depth</var>

751	792
752	793	<p><var>HashKey</var> is in the range <var>[0 ...<var>Range</var>-1]</var>. <var>Range</var>
753	794	must be in the range <var>[1 ... 2147483647]</var></dd>
754		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="variant_sha1/2"><strong>variant_sha1</strong>(<var>+Term,
	795	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="variant_sha1/2"><strong>variant_sha1</strong>(<var>+Term,
755	796	-SHA1</var>)</a></dt>
756	797	<dd class="defbody">
757	798	Compute a SHA1-hash from <var>Term</var>. The hash is represented as a
758		40-byte hexadecimal atom. Unlike <a name="idx:termhash2:870"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>
	799	40-byte hexadecimal atom. Unlike <a id="idx:termhash2:870"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>
759	800	and friends, this predicate produces a hash key for non-ground terms.
760	801	The hash is invariant over variable-renaming (see <a class="pred" href="compare.html#=@=/2">=@=/2</a>)
761	802	and constants over different invocations of Prolog.<sup class="fn">bug<span class="fn-text">The

764	805
765	806	<p>This predicate raises an exception when trying to compute the hash on
766	807	a cyclic term or attributed term. Attributed terms are not handled
767		because <a name="idx:subsumeschk2:871"></a><span class="pred-ext">subsumes_chk/2</span>
	808	because <a id="idx:subsumeschk2:871"></a><span class="pred-ext">subsumes_chk/2</span>
768	809	is not considered well defined for attributed terms. Cyclic terms are
769	810	not supported because this would require establishing a canonical cycle.
770	811	That is, given A=[a\|A] and B=[a,a\|B],

775	816	table. By using a cryptographic hash, heuristic algorithms can often
776	817	ignore the possibility of hash collisions and thus avoid storing the
777	818	goal term itself as well as testing using <a class="pred" href="compare.html#=@=/2">=@=/2</a>.</dd>
778		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="variant_hash/2"><strong>variant_hash</strong>(<var>+Term,
	819	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="variant_hash/2"><strong>variant_hash</strong>(<var>+Term,
779	820	-HashKey</var>)</a></dt>
780	821	<dd class="defbody">
781		Similar to <a name="idx:variantsha12:872"></a><a class="pred" href="db.html#variant_sha1/2">variant_sha1/2</a>,
782		but using a non-cryptographic hash and produces an integer result like <a name="idx:termhash2:873"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>.
	822	Similar to <a id="idx:variantsha12:872"></a><a class="pred" href="db.html#variant_sha1/2">variant_sha1/2</a>,
	823	but using a non-cryptographic hash and produces an integer result like <a id="idx:termhash2:873"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>.
783	824	This version does deal with attributed variables, processing them as
784	825	normal variables. This hash is primarily intended to speedup finding
785	826	variant terms in a set of terms.
786		<sup class="fn">bug<span class="fn-text">As <a name="idx:variantsha12:874"></a><a class="pred" href="db.html#variant_sha1/2">variant_sha1/2</a>,
	827	<sup class="fn">bug<span class="fn-text">As <a id="idx:variantsha12:874"></a><a class="pred" href="db.html#variant_sha1/2">variant_sha1/2</a>,
787	828	cyclic terms result in an exception.</span></sup>
788	829	</dd>
789	830	</dl>

+74

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.11</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.11</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:debug"><a name="sec:A.11"><span class="sec-nr">A.11</span> <span class="sec-title">library(debug):
	235	<h2 id="sec:debug"><a id="sec:A.11"><span class="sec-nr">A.11</span> <span class="sec-title">library(debug):
195	236	Print debug messages and test assertions</span></a></h2>
196	237
197		<p><a name="sec:debug"></a>
	238	<p><a id="sec:debug"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">author</dt>

221	262	debugger if the condition does not hold.
222	263
223	264	<dl class="latex">
224		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="debugging/1"><strong>debugging</strong>(<var>+Topic</var>)</a></dt>
225		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="debugging/1"><strong>debugging</strong>(<var>-Topic</var>)</a></dt>
226		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="debugging/2"><strong>debugging</strong>(<var>?Topic,
	265	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="debugging/1"><strong>debugging</strong>(<var>+Topic</var>)</a></dt>
	266	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="debugging/1"><strong>debugging</strong>(<var>-Topic</var>)</a></dt>
	267	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="debugging/2"><strong>debugging</strong>(<var>?Topic,
227	268	?Bool</var>)</a></dt>
228	269	<dd class="defbody">
229	270	Examine debug topics. The form <code>debugging(+Topic)</code> may be

240	281
241	282	<p>The other two calls are intended to examine existing and enabled
242	283	debugging tokens and are typically not used in user programs.</dd>
243		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="debug/1"><strong>debug</strong>(<var>+Topic</var>)</a></dt>
244		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="nodebug/1"><strong>nodebug</strong>(<var>+Topic</var>)</a></dt>
	284	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="debug/1"><strong>debug</strong>(<var>+Topic</var>)</a></dt>
	285	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="nodebug/1"><strong>nodebug</strong>(<var>+Topic</var>)</a></dt>
245	286	<dd class="defbody">
246	287	Add/remove a topic from being printed. <code>nodebug(_)</code> removes
247	288	all topics. Gives a warning if the topic is not defined unless it is

252	293	can be a term <var>Topic</var> <var>></var> Out, where Out is either
253	294	a stream or stream-alias or a filename (atom). This redirects debug
254	295	information on this topic to the given output.</dd>
255		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_debug_topics/0"><strong>list_debug_topics</strong></a></dt>
	296	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_debug_topics/0"><strong>list_debug_topics</strong></a></dt>
256	297	<dd class="defbody">
257	298	List currently known debug topics and their setting.</dd>
258		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="debug_message_context/1"><strong>debug_message_context</strong>(<var>+What</var>)</a></dt>
	299	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="debug_message_context/1"><strong>debug_message_context</strong>(<var>+What</var>)</a></dt>
259	300	<dd class="defbody">
260	301	Specify additional context for debug messages. <var>What</var> is one of
261	302	+Context or -Context, and Context is one of <code>thread</code>, <code>time</code>

264	305	<a class="pred" href="system.html#format_time/3">format_time/3</a>
265	306	(default is <code>%T.%3f</code>). Initially, <a class="pred" href="debug.html#debug/3">debug/3</a>
266	307	shows only thread information.</dd>
267		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="debug/3"><strong>debug</strong>(<var>+Topic,
	308	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="debug/3"><strong>debug</strong>(<var>+Topic,
268	309	+Format, :Args</var>)</a></dt>
269	310	<dd class="defbody">
270	311	<var>Format</var> a message if debug topic is enabled. Similar to <a class="pred" href="format.html#format/3">format/3</a>

291	332	</dl>
292	333
293	334	</dd>
294		<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a name="prolog:debug_print_hook/3"><span class="module">prolog</span>:<strong>debug_print_hook</strong>(<var>+Topic,
	335	<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="prolog:debug_print_hook/3"><span class="module">prolog</span>:<strong>debug_print_hook</strong>(<var>+Topic,
295	336	+Format, +Args</var>)</a></dt>
296	337	<dd class="defbody">
297	338	Hook called by <a class="pred" href="debug.html#debug/3">debug/3</a>.

302	343	</pre>
303	344
304	345	</dd>
305		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="assertion/1"><strong>assertion</strong>(<var>:Goal</var>)</a></dt>
	346	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="assertion/1"><strong>assertion</strong>(<var>:Goal</var>)</a></dt>
306	347	<dd class="defbody">
307	348	Acts similar to C <code>assert()</code> macro. It has no effect if <var>Goal</var>
308	349	succeeds. If <var>Goal</var> fails or throws an exception, the following

323	364	</ul>
324	365	</ul>
325	366	</dd>
326		<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a name="prolog:assertion_failed/2"><span class="module">prolog</span>:<strong>assertion_failed</strong>(<var>+Reason,
	367	<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="prolog:assertion_failed/2"><span class="module">prolog</span>:<strong>assertion_failed</strong>(<var>+Reason,
327	368	+Goal</var>)</a></dt>
328	369	<dd class="defbody">
329	370	This hook is called if the <var>Goal</var> of <a class="pred" href="debug.html#assertion/1">assertion/1</a>

+121

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.39</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:debugger"><a name="sec:4.39"><span class="sec-nr">4.39</span> <span class="sec-title">Debugging
	235	<h2 id="sec:debugger"><a id="sec:4.39"><span class="sec-nr">4.39</span> <span class="sec-title">Debugging
195	236	and Tracing Programs</span></a></h2>
196	237
197		<a name="sec:debugger"></a>
	238	<a id="sec:debugger"></a>
198	239
199	240	<p>This section is a reference to the debugger interaction predicates. A
200		more use-oriented overview of the debugger is in <a class="sec" href="debugoverview.html">section
	241	more use-oriented overview of the debugger is in <a class="sec" href="debugoverview.html#sec:2.9">section
201	242	2.9</a>.
202	243
203	244	<p>If you have installed XPCE, you can use the graphical front-end of
204		the tracer. This front-end is installed using the predicate <a name="idx:guitracer0:1541"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>.
	245	the tracer. This front-end is installed using the predicate <a id="idx:guitracer0:1541"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>.
205	246
206	247	<dl class="latex">
207		<dt class="pubdef"><a name="trace/0"><strong>trace</strong></a></dt>
208		<dd class="defbody">
209		Start the tracer. <a name="idx:trace0:1542"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	248	<dt class="pubdef"><a id="trace/0"><strong>trace</strong></a></dt>
	249	<dd class="defbody">
	250	Start the tracer. <a id="idx:trace0:1542"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
210	251	itself cannot be seen in the tracer. Note that the Prolog top level
211		treats <a name="idx:trace0:1543"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	252	treats <a id="idx:trace0:1543"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
212	253	special; it means `trace the next goal'.
213	254	</dd>
214		<dt class="pubdef"><a name="tracing/0"><strong>tracing</strong></a></dt>
215		<dd class="defbody">
216		True if the tracer is currently switched on. <a name="idx:tracing0:1544"></a><a class="pred" href="debugger.html#tracing/0">tracing/0</a>
	255	<dt class="pubdef"><a id="tracing/0"><strong>tracing</strong></a></dt>
	256	<dd class="defbody">
	257	True if the tracer is currently switched on. <a id="idx:tracing0:1544"></a><a class="pred" href="debugger.html#tracing/0">tracing/0</a>
217	258	itself cannot be seen in the tracer.
218	259	</dd>
219		<dt class="pubdef"><a name="notrace/0"><strong>notrace</strong></a></dt>
220		<dd class="defbody">
221		Stop the tracer. <a name="idx:notrace0:1545"></a><a class="pred" href="debugger.html#notrace/0">notrace/0</a>
	260	<dt class="pubdef"><a id="notrace/0"><strong>notrace</strong></a></dt>
	261	<dd class="defbody">
	262	Stop the tracer. <a id="idx:notrace0:1545"></a><a class="pred" href="debugger.html#notrace/0">notrace/0</a>
222	263	itself cannot be seen in the tracer.
223	264	</dd>
224		<dt class="pubdef"><a name="guitracer/0"><strong>guitracer</strong></a></dt>
225		<dd class="defbody">
226		Installs hooks (see <a name="idx:prologtraceinterception4:1546"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>)
	265	<dt class="pubdef"><a id="guitracer/0"><strong>guitracer</strong></a></dt>
	266	<dd class="defbody">
	267	Installs hooks (see <a id="idx:prologtraceinterception4:1546"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>)
227	268	into the system that redirect tracing information to a GUI front-end
228	269	providing structured access to variable bindings, graphical overview of
229	270	the stack and highlighting of relevant source code.
230	271	</dd>
231		<dt class="pubdef"><a name="noguitracer/0"><strong>noguitracer</strong></a></dt>
	272	<dt class="pubdef"><a id="noguitracer/0"><strong>noguitracer</strong></a></dt>
232	273	<dd class="defbody">
233	274	Revert back to the textual tracer.
234	275	</dd>
235		<dt class="pubdef"><a name="trace/1"><strong>trace</strong>(<var>+Pred</var>)</a></dt>
	276	<dt class="pubdef"><a id="trace/1"><strong>trace</strong>(<var>+Pred</var>)</a></dt>
236	277	<dd class="defbody">
237	278	Equivalent to <code>trace(<var>Pred</var>, +all)</code>.
238	279	</dd>
239		<dt class="pubdef"><a name="trace/2"><strong>trace</strong>(<var>+Pred,
	280	<dt class="pubdef"><a id="trace/2"><strong>trace</strong>(<var>+Pred,
240	281	+Ports</var>)</a></dt>
241	282	<dd class="defbody">
242	283	Put a trace point on all predicates satisfying the predicate

247	288	sign, the trace point is cleared for the port. If it is preceded by a <code><code>+</code></code>,
248	289	the trace point is set.
249	290
250		<p>The predicate <a name="idx:trace2:1547"></a><a class="pred" href="debugger.html#trace/2">trace/2</a>
251		activates debug mode (see <a name="idx:debug0:1548"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>).
	291	<p>The predicate <a id="idx:trace2:1547"></a><a class="pred" href="debugger.html#trace/2">trace/2</a>
	292	activates debug mode (see <a id="idx:debug0:1548"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>).
252	293	Each time a port (of the 4-port model) is passed that has a trace point
253		set, the goal is printed as with <a name="idx:trace0:1549"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>.
254		Unlike <a name="idx:trace0:1550"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>,
	294	set, the goal is printed as with <a id="idx:trace0:1549"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>.
	295	Unlike <a id="idx:trace0:1550"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>,
255	296	however, the execution is continued without asking for further
256	297	information. Examples:
257	298
258		<p><table border="0" frame="void" rules="groups" style="margin:auto">
259		<tr valign="top"><td><code>?- trace(hello).</code> </td><td>Trace all
260		ports of hello with any arity in any module. </td></tr>
261		<tr valign="top"><td><code>?- trace(foo/2, +fail).</code> </td><td>Trace
262		failures of foo/2 in any module. </td></tr>
263		<tr valign="top"><td><code>?- trace(bar/1, -all).</code> </td><td>Stop
264		tracing bar/1.</td></tr>
	299	<p><table class="latex frame-void center">
	300	<tr><td><code>?- trace(hello).</code> </td><td>Trace all ports of hello
	301	with any arity in any module. </td></tr>
	302	<tr><td><code>?- trace(foo/2, +fail).</code> </td><td>Trace failures of foo/2
	303	in any module. </td></tr>
	304	<tr><td><code>?- trace(bar/1, -all).</code> </td><td>Stop tracing bar/1.</td></tr>
265	305	</table>
266	306
267		<p>The predicate <a name="idx:debugging0:1551"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a>
	307	<p>The predicate <a id="idx:debugging0:1551"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a>
268	308	shows all currently defined trace points.</dd>
269		<dt class="pubdef"><a name="notrace/1"><strong>notrace</strong>(<var>:Goal</var>)</a></dt>
	309	<dt class="pubdef"><a id="notrace/1"><strong>notrace</strong>(<var>:Goal</var>)</a></dt>
270	310	<dd class="defbody">
271	311	Call <var>Goal</var>, but suspend the debugger while <var>Goal</var> is
272	312	executing. The current implementation cuts the choice points of <var>Goal</var>
273		after successful completion. See <a name="idx:once1:1552"></a><a class="pred" href="metacall.html#once/1">once/1</a>.
274		Later implementations may have the same semantics as <a name="idx:call1:1553"></a><a class="pred" href="metacall.html#call/1">call/1</a>.</dd>
275		<dt class="pubdef"><a name="debug/0"><strong>debug</strong></a></dt>
	313	after successful completion. See <a id="idx:once1:1552"></a><a class="pred" href="metacall.html#once/1">once/1</a>.
	314	Later implementations may have the same semantics as <a id="idx:call1:1553"></a><a class="pred" href="metacall.html#call/1">call/1</a>.</dd>
	315	<dt class="pubdef"><a id="debug/0"><strong>debug</strong></a></dt>
276	316	<dd class="defbody">
277	317	Start debugger. In debug mode, Prolog stops at spy and trace points,
278	318	disables last-call optimisation and aggressive destruction of choice

283	323	enlarged to 8 K cells if debugging is switched off in order to
284	324	avoid excessive GC. GC complicates tracing because it renames the <i>_G<NNN></i>
285	325	variables and replaces unreachable variables with the atom
286		<code><garbage_collected></code>. Calling <a name="idx:nodebug0:1554"></a><a class="pred" href="debugger.html#nodebug/0">nodebug/0</a>
	326	<code><garbage_collected></code>. Calling <a id="idx:nodebug0:1554"></a><a class="pred" href="debugger.html#nodebug/0">nodebug/0</a>
287	327	does <em>not</em> reset the initial free-margin because several parts of
288	328	the top level and debugger disable debugging of system code regions. See
289		also <a name="idx:setprologstack2:1555"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>.</dd>
290		<dt class="pubdef"><a name="nodebug/0"><strong>nodebug</strong></a></dt>
	329	also <a id="idx:setprologstack2:1555"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>.</dd>
	330	<dt class="pubdef"><a id="nodebug/0"><strong>nodebug</strong></a></dt>
291	331	<dd class="defbody">
292	332	Stop debugger. Implemented by the Prolog flag <a class="flag" href="flags.html#flag:debug">debug</a>.
293		See also <a name="idx:debug0:1556"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.</dd>
294		<dt class="pubdef"><a name="debugging/0"><strong>debugging</strong></a></dt>
	333	See also <a id="idx:debug0:1556"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.</dd>
	334	<dt class="pubdef"><a id="debugging/0"><strong>debugging</strong></a></dt>
295	335	<dd class="defbody">
296	336	Print debug status and spy points on current output stream. See also the
297	337	Prolog flag <a class="flag" href="flags.html#flag:debug">debug</a>.
298	338	</dd>
299		<dt class="pubdef"><a name="spy/1"><strong>spy</strong>(<var>+Pred</var>)</a></dt>
	339	<dt class="pubdef"><a id="spy/1"><strong>spy</strong>(<var>+Pred</var>)</a></dt>
300	340	<dd class="defbody">
301	341	Put a spy point on all predicates meeting the predicate specification
302		<var>Pred</var>. See <a class="sec" href="listing.html">section 4.5</a>.
303		</dd>
304		<dt class="pubdef"><a name="nospy/1"><strong>nospy</strong>(<var>+Pred</var>)</a></dt>
	342	<var>Pred</var>. See <a class="sec" href="listing.html#sec:4.5">section
	343	4.5</a>.
	344	</dd>
	345	<dt class="pubdef"><a id="nospy/1"><strong>nospy</strong>(<var>+Pred</var>)</a></dt>
305	346	<dd class="defbody">
306	347	Remove spy point from all predicates meeting the predicate specification
307	348	<var>Pred</var>.
308	349	</dd>
309		<dt class="pubdef"><a name="nospyall/0"><strong>nospyall</strong></a></dt>
	350	<dt class="pubdef"><a id="nospyall/0"><strong>nospyall</strong></a></dt>
310	351	<dd class="defbody">
311	352	Remove all spy points from the entire program.
312	353	</dd>
313		<dt class="pubdef"><a name="leash/1"><strong>leash</strong>(<var>?Ports</var>)</a></dt>
	354	<dt class="pubdef"><a id="leash/1"><strong>leash</strong>(<var>?Ports</var>)</a></dt>
314	355	<dd class="defbody">
315	356	Set/query leashing (ports which allow for user interaction). <var>Ports</var>
316	357	is one of <var>+Name</var>, <var>-Name</var>, <var>?Name</var> or a list

326	367	(default).
327	368	<code>half</code> refers to the <code>call</code>, <code>redo</code> and <code>fail</code>
328	369	port.</dd>
329		<dt class="pubdef"><a name="visible/1"><strong>visible</strong>(<var>+Ports</var>)</a></dt>
330		<dd class="defbody">
331		Set the ports shown by the debugger. See <a name="idx:leash1:1557"></a><a class="pred" href="debugger.html#leash/1">leash/1</a>
	370	<dt class="pubdef"><a id="visible/1"><strong>visible</strong>(<var>+Ports</var>)</a></dt>
	371	<dd class="defbody">
	372	Set the ports shown by the debugger. See <a id="idx:leash1:1557"></a><a class="pred" href="debugger.html#leash/1">leash/1</a>
332	373	for a description of the <var>Ports</var> specification. Default is <code>full</code>.</dd>
333		<dt class="pubdef"><a name="unknown/2"><strong>unknown</strong>(<var>-Old,
	374	<dt class="pubdef"><a id="unknown/2"><strong>unknown</strong>(<var>-Old,
334	375	+New</var>)</a></dt>
335	376	<dd class="defbody">
336	377	Edinburgh-Prolog compatibility predicate, interfacing to the ISO Prolog

338	379	are <code>trace</code> (meaning <code>error</code>) and <code>fail</code>.
339	380	If the <a class="flag" href="flags.html#flag:unknown">unknown</a> flag
340	381	is set to
341		<code>warning</code>, <a name="idx:unknown2:1558"></a><a class="pred" href="debugger.html#unknown/2">unknown/2</a>
	382	<code>warning</code>, <a id="idx:unknown2:1558"></a><a class="pred" href="debugger.html#unknown/2">unknown/2</a>
342	383	reports the value as <code>trace</code>.</dd>
343		<dt class="pubdef"><a name="style_check/1"><strong>style_check</strong>(<var>+Spec</var>)</a></dt>
	384	<dt class="pubdef"><a id="style_check/1"><strong>style_check</strong>(<var>+Spec</var>)</a></dt>
344	385	<dd class="defbody">
345	386	Modify/query style checking options. <var>Spec</var> is one of the terms
346	387	below or a list of these.

353	394	is unbound, all active style check options are returned on backtracking.
354	395	</ul>
355	396
356		<p>Loading a file using <a name="idx:loadfiles2:1559"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	397	<p>Loading a file using <a id="idx:loadfiles2:1559"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
357	398	or one of its derived predicates reset the style checking options to
358	399	their value before loading the file, scoping the option to the remainder
359	400	of the file and all files loaded

362	403	<dl class="latex">
363	404	<dt><strong>singleton</strong>(<var>true</var>)</dt>
364	405	<dd class="defbody">
365		The predicate <a name="idx:readclause3:1560"></a><a class="pred" href="termrw.html#read_clause/3">read_clause/3</a>
	406	The predicate <a id="idx:readclause3:1560"></a><a class="pred" href="termrw.html#read_clause/3">read_clause/3</a>
366	407	(used by the compiler to read source code) warns on variables appearing
367	408	only once in a term (clause) which have a name not starting with an
368		underscore. See <a class="sec" href="syntax.html">section 2.16.1.9</a>
369		for details on variable handling and warnings.</dd>
	409	underscore. See <a class="sec" href="syntax.html#sec:2.16.1.9">section
	410	2.16.1.9</a> for details on variable handling and warnings.</dd>
370	411	<dt><strong>no_effect</strong>(<var>true</var>)</dt>
371	412	<dd class="defbody">
372	413	This warning is generated by the compiler for BIPs (built-in predicates)

415	456	<dd class="defbody">
416	457	Warn if the clauses for a predicate are not together in the same source
417	458	file. It is advised to disable the warning for discontiguous predicates
418		using the <a name="idx:discontiguous1:1561"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a>
	459	using the <a id="idx:discontiguous1:1561"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a>
419	460	directive.</dd>
420	461	<dt><strong>charset</strong>(<var>false</var>)</dt>
421	462	<dd class="defbody">
422	463	Warn on atoms and variable names holding non-ASCII characters that are
423		not quoted. See also <a class="sec" href="syntax.html">section 2.16.1.1</a>.
	464	not quoted. See also <a class="sec" href="syntax.html#sec:2.16.1.1">section
	465	2.16.1.1</a>.
424	466	</dd>
425	467	</dl>
426	468

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191	232	<a class="nav" href="practical.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:debugging"><a name="sec:8.4"><span class="sec-nr">8.4</span> <span class="sec-title">Debugging</span></a></h2>
195
196		<a name="sec:debugging"></a> The CHR debugging facilities are currently
	235	<h2 id="sec:debugging"><a id="sec:8.4"><span class="sec-nr">8.4</span> <span class="sec-title">Debugging</span></a></h2>
	236
	237	<a id="sec:debugging"></a> The CHR debugging facilities are currently
197	238	rather limited. Only tracing is currently available. To use the CHR
198	239	debugging facilities for a CHR file it must be compiled for debugging.
199	240	Generating debug info is controlled by the CHR option <a class="flag" href="flags.html#flag:debug">debug</a>,

201	242	Therefore debug info is provided unless the <strong>-nodebug</strong> is
202	243	used.
203	244
204		<p><h3 id="sec:chrports"><a name="sec:8.4.1"><span class="sec-nr">8.4.1</span> <span class="sec-title">Ports</span></a></h3>
205
206		<a name="sec:chrports"></a> For CHR constraints the four standard ports
	245	<p><h3 id="sec:chrports"><a id="sec:8.4.1"><span class="sec-nr">8.4.1</span> <span class="sec-title">Ports</span></a></h3>
	246
	247	<a id="sec:chrports"></a> For CHR constraints the four standard ports
207	248	are defined:
208	249
209	250	<dl class="latex">

256	297	</dd>
257	298	</dl>
258	299
259		<p><h3 id="sec:chr-tracing"><a name="sec:8.4.2"><span class="sec-nr">8.4.2</span> <span class="sec-title">Tracing</span></a></h3>
260
261		<a name="sec:chr-tracing"></a> Tracing is enabled with the <a name="idx:chrtrace0:1814"></a><a class="pred" href="debugging.html#chr_trace/0">chr_trace/0</a>
262		predicate and disabled with the <a name="idx:chrnotrace0:1815"></a><a class="pred" href="debugging.html#chr_notrace/0">chr_notrace/0</a>
	300	<p><h3 id="sec:chr-tracing"><a id="sec:8.4.2"><span class="sec-nr">8.4.2</span> <span class="sec-title">Tracing</span></a></h3>
	301
	302	<a id="sec:chr-tracing"></a> Tracing is enabled with the <a id="idx:chrtrace0:1818"></a><a class="pred" href="debugging.html#chr_trace/0">chr_trace/0</a>
	303	predicate and disabled with the <a id="idx:chrnotrace0:1819"></a><a class="pred" href="debugging.html#chr_notrace/0">chr_notrace/0</a>
263	304	predicate.
264	305
265	306	<p>When enabled the tracer will step through the <code>call</code>,

302	343	</dd>
303	344	<dt><strong>break</strong></dt>
304	345	<dd class="defbody">
305		Enter a recursive Prolog top level. See <a name="idx:break0:1816"></a><a class="pred" href="toplevel.html#break/0">break/0</a>.
	346	Enter a recursive Prolog top level. See <a id="idx:break0:1820"></a><a class="pred" href="toplevel.html#break/0">break/0</a>.
306	347	</dd>
307	348	<dt><strong>abort</strong></dt>
308	349	<dd class="defbody">
309		Exit to the top level. See <a name="idx:abort0:1817"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
	350	Exit to the top level. See <a id="idx:abort0:1821"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
310	351	</dd>
311	352	<dt><strong>fail</strong></dt>
312	353	<dd class="defbody">

318	359	</dd>
319	360	</dl>
320	361
321		<p><h3 id="sec:predicates"><a name="sec:8.4.3"><span class="sec-nr">8.4.3</span> <span class="sec-title">CHR
	362	<p><h3 id="sec:predicates"><a id="sec:8.4.3"><span class="sec-nr">8.4.3</span> <span class="sec-title">CHR
322	363	Debugging Predicates</span></a></h3>
323	364
324		<a name="sec:predicates"></a> The <code>library(chr)</code> module
	365	<a id="sec:predicates"></a> The <code>library(chr)</code> module
325	366	contains several predicates that allow inspecting and printing the
326	367	content of the constraint store.
327	368
328	369	<dl class="latex">
329		<dt class="pubdef"><a name="chr_trace/0"><strong>chr_trace</strong></a></dt>
	370	<dt class="pubdef"><a id="chr_trace/0"><strong>chr_trace</strong></a></dt>
330	371	<dd class="defbody">
331	372	Activate the CHR tracer. By default the CHR tracer is activated and
332		deactivated automatically by the Prolog predicates <a name="idx:trace0:1818"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	373	deactivated automatically by the Prolog predicates <a id="idx:trace0:1822"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
333	374	and
334		<a name="idx:notrace0:1819"></a><a class="pred" href="debugger.html#notrace/0">notrace/0</a>.</dd>
335		<dt class="pubdef"><a name="chr_notrace/0"><strong>chr_notrace</strong></a></dt>
	375	<a id="idx:notrace0:1823"></a><a class="pred" href="debugger.html#notrace/0">notrace/0</a>.</dd>
	376	<dt class="pubdef"><a id="chr_notrace/0"><strong>chr_notrace</strong></a></dt>
336	377	<dd class="defbody">
337	378	Deactivate the CHR tracer. By default the CHR tracer is activated and
338		deactivated automatically by the Prolog predicates <a name="idx:trace0:1820"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	379	deactivated automatically by the Prolog predicates <a id="idx:trace0:1824"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
339	380	and
340		<a name="idx:notrace0:1821"></a><a class="pred" href="debugger.html#notrace/0">notrace/0</a>.</dd>
341		<dt class="pubdef"><a name="chr_leash/1"><strong>chr_leash</strong>(<var>+Spec</var>)</a></dt>
	381	<a id="idx:notrace0:1825"></a><a class="pred" href="debugger.html#notrace/0">notrace/0</a>.</dd>
	382	<dt class="pubdef"><a id="chr_leash/1"><strong>chr_leash</strong>(<var>+Spec</var>)</a></dt>
342	383	<dd class="defbody">
343	384	Define the set of CHR ports on which the CHR tracer asks for user
344	385	intervention (i.e. stops). <var>Spec</var> is either a list of ports as
345		defined in <a class="sec" href="debugging.html">section 8.4.1</a> or a
346		predefined `alias'. Defined aliases are: <code>full</code> to stop at
347		all ports, <code>none</code> or <code>off</code> to never stop, and <code>default</code>
	386	defined in <a class="sec" href="debugging.html#sec:8.4.1">section 8.4.1</a>
	387	or a predefined `alias'. Defined aliases are: <code>full</code> to stop
	388	at all ports, <code>none</code> or <code>off</code> to never stop, and <code>default</code>
348	389	to stop at the <code>call</code>,
349	390	<code>exit</code>, <code>fail</code>, <code>wake</code> and <code>apply</code>
350		ports. See also <a name="idx:leash1:1822"></a><a class="pred" href="debugger.html#leash/1">leash/1</a>.</dd>
351		<dt class="pubdef"><a name="chr_show_store/1"><strong>chr_show_store</strong>(<var>+Mod</var>)</a></dt>
	391	ports. See also <a id="idx:leash1:1826"></a><a class="pred" href="debugger.html#leash/1">leash/1</a>.</dd>
	392	<dt class="pubdef"><a id="chr_show_store/1"><strong>chr_show_store</strong>(<var>+Mod</var>)</a></dt>
352	393	<dd class="defbody">
353	394	Prints all suspended constraints of module <var>Mod</var> to the
354	395	standard output. This predicate is automatically called by the

357	398	<code>chr_toplevel_show_store</code> controls whether the top level
358	399	shows the constraint stores. The value <code>true</code> enables it. Any
359	400	other value disables it.</dd>
360		<dt class="pubdef"><a name="find_chr_constraint/1"><strong>find_chr_constraint</strong>(<var>-Constraint</var>)</a></dt>
	401	<dt class="pubdef"><a id="find_chr_constraint/1"><strong>find_chr_constraint</strong>(<var>-Constraint</var>)</a></dt>
361	402	<dd class="defbody">
362	403	Returns a constraint in the constraint store. Via backtracking, all
363	404	constraints in the store can be enumerated.

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	213	table.latex td,th
	214	{ padding: 2px 1em;
	215	}
	216
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	218	{ border-top: 1px solid black;
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	222	{ border: 2px solid black;
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186	227	<body style="background:white">

191	232	<a class="nav" href="topvars.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="compilation.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:debugoverview"><a name="sec:2.9"><span class="sec-nr">2.9</span> <span class="sec-title">Overview
	235	<h2 id="sec:debugoverview"><a id="sec:2.9"><span class="sec-nr">2.9</span> <span class="sec-title">Overview
195	236	of the Debugger</span></a></h2>
196	237
197		<a name="sec:debugoverview"></a>
	238	<a id="sec:debugoverview"></a>
198	239
199	240	<p>SWI-Prolog has a 6-port tracer, extending the standard 4-port tracer
200	241	<cite><a class="cite" href="Bibliography.html#Byrd:80">Byrd, 1980</a>, <a class="cite" href="Bibliography.html#Clocksin:87">Clocksin &
201	242	Melish, 1987</a></cite> with two additional ports. The optional
202	243	<var>unify</var> port allows the user to inspect the result after
203	244	unification of the head. The <var>exception</var> port shows exceptions
204		raised by <a name="idx:throw1:54"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
205		or one of the built-in predicates. See <a class="sec" href="exception.html">section
	245	raised by <a id="idx:throw1:54"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
	246	or one of the built-in predicates. See <a class="sec" href="exception.html#sec:4.11">section
206	247	4.11</a>.
207	248
208	249	<p>The standard ports are called <code>call</code>, <code>exit</code>, <code>redo</code>,
209		<code>fail</code> and <code>unify</code>. The tracer is started by the <a name="idx:trace0:55"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	250	<code>fail</code> and <code>unify</code>. The tracer is started by the <a id="idx:trace0:55"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
210	251	command, when a spy point is reached and the system is in debugging mode
211		(see <a name="idx:spy1:56"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
212		and <a name="idx:debug0:57"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>),
	252	(see <a id="idx:spy1:56"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
	253	and <a id="idx:debug0:57"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>),
213	254	or when an exception is raised that is not caught.
214	255
215		<p>The interactive top-level goal <a name="idx:trace0:58"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	256	<p>The interactive top-level goal <a id="idx:trace0:58"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
216	257	means ``trace the next query''. The tracer shows the port, displaying
217	258	the port name, the current depth of the recursion and the goal. The goal
218		is printed using the Prolog predicate <a name="idx:writeterm2:59"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>.
	259	is printed using the Prolog predicate <a id="idx:writeterm2:59"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>.
219	260	The style is defined by the Prolog flag
220	261	<a class="flag" href="flags.html#flag:debugger_write_options">debugger_write_options</a>
221	262	and can be modified using this flag or using the <code>w</code>, <code>p</code>

252	293
253	294	<div class="caption"><b>Figure 2 : </b>Example trace of the program
254	295	above showing all ports. The lines marked <code><code>^</code></code>
255		indicate calls to <em>transparent</em> predicates. See <a class="sec" href="modules.html">section
	296	indicate calls to <em>transparent</em> predicates. See <a class="sec" href="modules.html#sec:6">section
256	297	6</a>.</div>
257		<a name="fig:tracer"></a>
258
259		<p>On <em>leashed ports</em> (set with the predicate <a name="idx:leash1:60"></a><a class="pred" href="debugger.html#leash/1">leash/1</a>,
	298	<a id="fig:tracer"></a>
	299
	300	<p>On <em>leashed ports</em> (set with the predicate <a id="idx:leash1:60"></a><a class="pred" href="debugger.html#leash/1">leash/1</a>,
260	301	default are
261	302	<code>call</code>, <code>exit</code>, <code>redo</code> and <code>fail</code>)
262	303	the user is prompted for an action. All actions are single-character

266	307	<dl class="latex">
267	308	<dt><strong>Spy</strong> (<code>+</code>)</dt>
268	309	<dd class="defbody">
269		Set a spy point (see <a name="idx:spy1:61"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>)
	310	Set a spy point (see <a id="idx:spy1:61"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>)
270	311	on the current predicate.
271	312	</dd>
272	313	<dt><strong>No spy</strong> (<code>-</code>)</dt>
273	314	<dd class="defbody">
274		Remove the spy point (see <a name="idx:nospy1:62"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>)
	315	Remove the spy point (see <a id="idx:nospy1:62"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>)
275	316	from the current predicate.
276	317	</dd>
277	318	<dt><strong>Find</strong> (<code>/</code>)</dt>

282	323	unify with the goal run by the port. If no term is specified it is taken
283	324	as a variable, searching for any port of the specified type. If an atom
284	325	is given, any goal whose functor has a name equal to that atom matches.
285		Examples:
286		<div style="text-align:center"><table border="0" frame="void" rules="groups">
287		<tr valign="top"><td><code>/f</code></td><td>Search for any fail port </td></tr>
288		<tr valign="top"><td><code>/fe solve</code></td><td>Search for a fail or
289		exit port of any goal with name <code>solve</code> </td></tr>
290		<tr valign="top"><td><code>/c solve(a, _)</code></td><td>Search for a
291		call to solve/2 whose first argument is a variable or the atom <code>a</code> </td></tr>
292		<tr valign="top"><td><code>/a member(_, _)</code></td><td>Search for any
293		port on <a name="idx:member2:63"></a><a class="pred" href="lists.html#member/2">member/2</a>.
294		This is equivalent to setting a spy point on <a name="idx:member2:64"></a><a class="pred" href="lists.html#member/2">member/2</a>. </td></tr>
	326	Examples: <table class="latex frame-void center">
	327	<tr><td><code>/f</code></td><td>Search for any fail port </td></tr>
	328	<tr><td><code>/fe solve</code></td><td>Search for a fail or exit port of
	329	any goal with name <code>solve</code> </td></tr>
	330	<tr><td><code>/c solve(a, _)</code></td><td>Search for a call to solve/2
	331	whose first argument is a variable or the atom <code>a</code> </td></tr>
	332	<tr><td><code>/a member(_, _)</code></td><td>Search for any port on <a id="idx:member2:63"></a><a class="pred" href="lists.html#member/2">member/2</a>.
	333	This is equivalent to setting a spy point on <a id="idx:member2:64"></a><a class="pred" href="lists.html#member/2">member/2</a>. </td></tr>
295	334	</table>
296		</div>
297	335	</dd>
298	336	<dt><strong>Repeat find</strong> (<code>.</code>)</dt>
299	337	<dd class="defbody">

306	344	<dt><strong>Context</strong> (<code>C</code>)</dt>
307	345	<dd class="defbody">
308	346	Toggle `Show Context'. If <code>on</code>, the context module of the
309		goal is displayed between square brackets (see <a class="sec" href="modules.html">section
	347	goal is displayed between square brackets (see <a class="sec" href="modules.html#sec:6">section
310	348	6</a>). Default is <code>off</code>.
311	349	</dd>
312	350	<dt><strong>Listing</strong> (<code>L</code>)</dt>
313	351	<dd class="defbody">
314		List the current predicate with <a name="idx:listing1:65"></a><a class="pred" href="listing.html#listing/1">listing/1</a>.
	352	List the current predicate with <a id="idx:listing1:65"></a><a class="pred" href="listing.html#listing/1">listing/1</a>.
315	353	</dd>
316	354	<dt><strong>Abort</strong> (<code>a</code>)</dt>
317	355	<dd class="defbody">
318		Abort Prolog execution (see <a name="idx:abort0:66"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>).
	356	Abort Prolog execution (see <a id="idx:abort0:66"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>).
319	357	</dd>
320	358	<dt><strong>Break</strong> (<code>b</code>)</dt>
321	359	<dd class="defbody">
322		Enter a Prolog break environment (see <a name="idx:break0:67"></a><a class="pred" href="toplevel.html#break/0">break/0</a>).
	360	Enter a Prolog break environment (see <a id="idx:break0:67"></a><a class="pred" href="toplevel.html#break/0">break/0</a>).
323	361	</dd>
324	362	<dt><strong>Creep</strong> (<code>c</code>)</dt>
325	363	<dd class="defbody">

333	371	</dd>
334	372	<dt><strong>Exit</strong> (<code>e</code>)</dt>
335	373	<dd class="defbody">
336		Terminate Prolog (see <a name="idx:halt0:68"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>).
	374	Terminate Prolog (see <a id="idx:halt0:68"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>).
337	375	</dd>
338	376	<dt><strong>Fail</strong> (<code>f</code>)</dt>
339	377	<dd class="defbody">

387	425	<dd class="defbody">
388	426	Set the Prolog flag <a class="flag" href="flags.html#flag:debugger_write_options">debugger_write_options</a>
389	427	to <code>[quoted(true), attributes(write), priority(699)]</code>,
390		bypassing <a name="idx:portray1:69"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>,
	428	bypassing <a id="idx:portray1:69"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>,
391	429	etc.
392	430	</dd>
393	431	</dl>

399	437	because code optimisation removes part of the choice and exit points.
400	438	Backtrack points are not shown if either the goal succeeded
401	439	deterministically or its alternatives were removed using the cut. When
402		running in debug mode (<a name="idx:debug0:70"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>)
	440	running in debug mode (<a id="idx:debug0:70"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>)
403	441	choice points are only destroyed when removed by the cut. In debug mode,
404	442	last call optimisation is switched off.<sup class="fn">13<span class="fn-text">This
405	443	implies the system can run out of stack in debug mode, while no problems
406	444	arise when running in non-debug mode.</span></sup>
407	445
408	446	<p>Reference information to all predicates available for manipulating
409		the debugger is in <a class="sec" href="debugger.html">section 4.39</a>.
	447	the debugger is in <a class="sec" href="debugger.html#sec:4.39">section
	448	4.39</a>.
410	449
411	450	<p></body></html>⏎

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193	234	</div>
194		<h2 id="sec:defmodule"><a name="sec:6.2"><span class="sec-nr">6.2</span> <span class="sec-title">Defining
	235	<h2 id="sec:defmodule"><a id="sec:6.2"><span class="sec-nr">6.2</span> <span class="sec-title">Defining
195	236	a Module</span></a></h2>
196	237
197		<a name="sec:defmodule"></a>
	238	<a id="sec:defmodule"></a>
198	239
199	240	<p>Modules are normally created by loading a <em>module file</em>. A
200		module file is a file holding a <a name="idx:module2:1660"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
	241	module file is a file holding a <a id="idx:module2:1664"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
201	242	directive as its first term. The
202		<a name="idx:module2:1661"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
	243	<a id="idx:module2:1665"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
203	244	directive declares the name and the public (i.e., externally visible)
204	245	predicates of the module. The rest of the file is loaded into the
205		module. Below is an example of a module file, defining <a name="idx:reverse2:1662"></a><a class="pred" href="lists.html#reverse/2">reverse/2</a>
206		and hiding the helper predicate <a name="idx:rev3:1663"></a><span class="pred-ext">rev/3</span>.
	246	module. Below is an example of a module file, defining <a id="idx:reverse2:1666"></a><a class="pred" href="lists.html#reverse/2">reverse/2</a>
	247	and hiding the helper predicate <a id="idx:rev3:1667"></a><span class="pred-ext">rev/3</span>.
207	248	A module can use all built-in predicates and, by default, cannot
208	249	redefine system predicates.
209	250

227	268	module explicitly in the source text.
228	269
229	270	<dl class="latex">
230		<dt class="pubdef"><a name="module/2">:- <strong>module</strong>(<var>+Module,
	271	<dt class="pubdef"><a id="module/2">:- <strong>module</strong>(<var>+Module,
231	272	+PublicList</var>)</a></dt>
232	273	<dd class="defbody">
233	274	This directive can only be used as the first term of a source file. It

237	278	is a list of predicate indicators (name/arity or name//arity pairs) or
238	279	operator declarations using the format <code>op(Precedence, Type, Name)</code>.
239	280	Operators defined in the export list are available inside the module as
240		well as to modules importing this module. See also <a class="sec" href="operators.html">section
	281	well as to modules importing this module. See also <a class="sec" href="operators.html#sec:4.25">section
241	282	4.25</a>.
242	283
243	284	<p>Compatible to Ciao Prolog, if <var>Module</var> is unbound, it is
244	285	unified with the basename without extension of the file being loaded.</dd>
245		<dt class="pubdef"><a name="module/3">:- <strong>module</strong>(<var>+Module,
	286	<dt class="pubdef"><a id="module/3">:- <strong>module</strong>(<var>+Module,
246	287	+PublicList, +Dialect</var>)</a></dt>
247	288	<dd class="defbody">
248		Same as <a name="idx:module2:1664"></a><a class="pred" href="defmodule.html#module/2">module/2</a>.
	289	Same as <a id="idx:module2:1668"></a><a class="pred" href="defmodule.html#module/2">module/2</a>.
249	290	The additional <var>Dialect</var> argument provides a list of <em>language
250		options</em>. Each atom in the list <var>Dialect</var> is mapped to a <a name="idx:usemodule1:1665"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
251		goal as given below. See also <a class="sec" href="dialect.html">section
	291	options</em>. Each atom in the list <var>Dialect</var> is mapped to a <a id="idx:usemodule1:1669"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	292	goal as given below. See also <a class="sec" href="dialect.html#sec:C">section
252	293	C</a>. The third argument is supported for compatibility with the
253		http://prolog-commons.org/Prolog Commons project .
	294	<a class="url" href="http://prolog-commons.org/">Prolog Commons project</a>.
254	295
255	296	<pre class="code">
256	297	:- use_module(library(dialect/LangOption)).

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193	234	</div>
194		<h2 id="sec:delcont"><a name="sec:4.10"><span class="sec-nr">4.10</span> <span class="sec-title">Delimited
	235	<h2 id="sec:delcont"><a id="sec:4.10"><span class="sec-nr">4.10</span> <span class="sec-title">Delimited
195	236	continuations</span></a></h2>
196	237
197		<a name="sec:delcont"></a>
198
199		<p>The predicates <a name="idx:reset3:678"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
200		and <a name="idx:shift1:679"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>
	238	<a id="sec:delcont"></a>
	239
	240	<p>The predicates <a id="idx:reset3:678"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
	241	and <a id="idx:shift1:679"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>
201	242	implement <em>delimited continuations</em> for Prolog. Delimited
202	243	continuation for Prolog is described in <cite><a class="cite" href="Bibliography.html#DBLP:journals/tplp/SchrijversDDW13">Schrijvers <em>et
203	244	al.</em>, 2013</a></cite>. The mechanism allows for proper <em>coroutines</em>,
204	245	two or more routines whose execution is interleaved, while they exchange
205	246	data. Note that coroutines in this sense differ from coroutines realised
206		using attributed variables as described in <a class="sec" href="clp.html">chapter
	247	using attributed variables as described in <a class="sec" href="clp.html#sec:7">chapter
207	248	7</a>.
208	249
209	250	<p>The suspension mechanism provided by delimited continuations is

212	253	al.</em>, 2015</a></cite>, see library <code>library(tabling)</code>.
213	254
214	255	<dl class="latex">
215		<dt class="pubdef"><a name="reset/3"><strong>reset</strong>(<var>:Goal,
	256	<dt class="pubdef"><a id="reset/3"><strong>reset</strong>(<var>:Goal,
216	257	?Ball, -Continuation</var>)</a></dt>
217	258	<dd class="defbody">
218		Call <var>Goal</var>. If <var>Goal</var> calls <a name="idx:shift1:680"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>
219		and the argument of <a name="idx:shift1:681"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>
	259	Call <var>Goal</var>. If <var>Goal</var> calls <a id="idx:shift1:680"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>
	260	and the argument of <a id="idx:shift1:681"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>
220	261	can be unified with <var>Ball</var>,<sup class="fn">67<span class="fn-text">The
221	262	argument order described in <cite><a class="cite" href="Bibliography.html#DBLP:journals/tplp/SchrijversDDW13">Schrijvers <em>et
222	263	al.</em>, 2013</a></cite> is <code>reset(Goal,Continuation,Ball)</code>.
223		We swapped the argument order for compatibility with <a name="idx:catch3:682"></a><a class="pred" href="exception.html#catch/3">catch/3</a></span></sup> <a name="idx:shift1:683"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>
224		causes <a name="idx:reset3:684"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
	264	We swapped the argument order for compatibility with <a id="idx:catch3:682"></a><a class="pred" href="exception.html#catch/3">catch/3</a></span></sup> <a id="idx:shift1:683"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>
	265	causes <a id="idx:reset3:684"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
225	266	to return, unifying
226	267	<var>Continuation</var> with a goal that represents the <em>continuation</em>
227		after <a name="idx:shift1:685"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>.
	268	after <a id="idx:shift1:685"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>.
228	269	In other words, meta-calling <var>Continuation</var> completes the
229		execution where shift left it. If <var>Goal</var> does not call <a name="idx:shift1:686"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>,
	270	execution where shift left it. If <var>Goal</var> does not call <a id="idx:shift1:686"></a><a class="pred" href="delcont.html#shift/1">shift/1</a>,
230	271	<var>Continuation</var> are unified with the integer <code>0</code>
231	272	(zero).<sup class="fn">68<span class="fn-text">Note that older versions
232	273	also unify <var>Ball</var> with <code>0</code>. Testing whether or not
233	274	shift happened on <var>Ball</var> however is <em>always</em> ambiguous.</span></sup></dd>
234		<dt class="pubdef"><a name="shift/1"><strong>shift</strong>(<var>+Ball</var>)</a></dt>
	275	<dt class="pubdef"><a id="shift/1"><strong>shift</strong>(<var>+Ball</var>)</a></dt>
235	276	<dd class="defbody">
236	277	Abandon the execution of the current goal, returning control to just
237		<em>after</em> the matching <a name="idx:reset3:687"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
238		call. This is similar to <a name="idx:throw1:688"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
	278	<em>after</em> the matching <a id="idx:reset3:687"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
	279	call. This is similar to <a id="idx:throw1:688"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
239	280	except that (1) nothing is `undone' and (2) the 3th argument of
240		<a name="idx:reset3:689"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
241		is unified with the <em>continuation</em>, which allows the code calling <a name="idx:reset3:690"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
	281	<a id="idx:reset3:689"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
	282	is unified with the <em>continuation</em>, which allows the code calling <a id="idx:reset3:690"></a><a class="pred" href="delcont.html#reset/3">reset/3</a>
242	283	to <em>resume</em> the current goal.
243	284	</dd>
244	285	</dl>

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191	232	<a class="nav" href="loadfilehook.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h1 id="sec:dialect"><a name="sec:C"><span class="sec-nr">C</span> <span class="sec-title">Compatibility
	235	<h1 id="sec:dialect"><a id="sec:C"><span class="sec-nr">C</span> <span class="sec-title">Compatibility
195	236	with other Prolog dialects</span></a></h1>
196	237
197		<a name="sec:dialect"></a>
198
199		<p><a name="idx:YAPprolog:2243"></a><a name="idx:portableprologcode:2244"></a>This
	238	<a id="sec:dialect"></a>
	239
	240	<p><a id="idx:YAPprolog:2247"></a><a id="idx:portableprologcode:2248"></a>This
200	241	chapter explains issues for writing portable Prolog programs. It was
201	242	started after discussion with Vitor Santos Costa, the leading developer
202		of YAP Prolog<sup class="fn">187<span class="fn-text"><a class="url" href="http://yap.sourceforge.net/">http://yap.sourceforge.net/</a></span></sup>
	243	of YAP Prolog<sup class="fn">188<span class="fn-text"><a class="url" href="http://yap.sourceforge.net/">http://yap.sourceforge.net/</a></span></sup>
203	244	YAP and SWI-Prolog have expressed the ambition to enhance the
204	245	portability beyond the trivial Prolog examples, including complex
205	246	libraries involving foreign code.

225	266
226	267	<p>
227	268	<li>Conditional compilation using <code>:- if(Condition)</code> ...<code>:-
228		endif</code> is supported. See <a class="sec" href="consulting.html">section
	269	endif</code> is supported. See <a class="sec" href="consulting.html#sec:4.3.1.2">section
229	270	4.3.1.2</a>.
230	271
231	272	<p>
232		<li>The predicate <a name="idx:expectsdialect1:2245"></a><a class="pred" href="dialect.html#expects_dialect/1">expects_dialect/1</a>
	273	<li>The predicate <a id="idx:expectsdialect1:2249"></a><a class="pred" href="dialect.html#expects_dialect/1">expects_dialect/1</a>
233	274	allows for specifying for which Prolog system the code was written.
234	275
235	276	<p>
236		<li>The predicates <a name="idx:existssource1:2246"></a><a class="pred" href="dialect.html#exists_source/1">exists_source/1</a>
237		and <a name="idx:sourceexports2:2247"></a><a class="pred" href="dialect.html#source_exports/2">source_exports/2</a>
238		can be used to query the library content. The <a name="idx:require1:2248"></a><a class="pred" href="consulting.html#require/1">require/1</a>
	277	<li>The predicates <a id="idx:existssource1:2250"></a><a class="pred" href="dialect.html#exists_source/1">exists_source/1</a>
	278	and <a id="idx:sourceexports2:2251"></a><a class="pred" href="dialect.html#source_exports/2">source_exports/2</a>
	279	can be used to query the library content. The <a id="idx:require1:2252"></a><a class="pred" href="consulting.html#require/1">require/1</a>
239	280	directive can be used to get access to predicates without knowing their
240	281	location.
241	282
242	283	<p>
243		<li>The module predicates <a name="idx:usemodule1:2249"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>, <a name="idx:usemodule2:2250"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
	284	<li>The module predicates <a id="idx:usemodule1:2253"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>, <a id="idx:usemodule2:2254"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
244	285	have been extended with a notion for `import-except' and `import-as'.
245		This is particularly useful together with <a name="idx:reexport1:2251"></a><a class="pred" href="reexport.html#reexport/1">reexport/1</a>
246		and <a name="idx:reexport2:2252"></a><a class="pred" href="reexport.html#reexport/2">reexport/2</a>
	286	This is particularly useful together with <a id="idx:reexport1:2255"></a><a class="pred" href="reexport.html#reexport/1">reexport/1</a>
	287	and <a id="idx:reexport2:2256"></a><a class="pred" href="reexport.html#reexport/2">reexport/2</a>
247	288	to compose modules from other modules and mapping names.
248	289
249	290	<p>

252	293	</ul>
253	294
254	295	<dl class="latex">
255		<dt class="pubdef"><a name="expects_dialect/1">:- <strong>expects_dialect</strong>(<var>+Dialect</var>)</a></dt>
	296	<dt class="pubdef"><a id="expects_dialect/1">:- <strong>expects_dialect</strong>(<var>+Dialect</var>)</a></dt>
256	297	<dd class="defbody">
257	298	This directive states that the code following the directive is written
258	299	for the given Prolog <var>Dialect</var>. See also <a class="flag" href="flags.html#flag:dialect">dialect</a>.
259	300	The declaration holds until the end of the file in which it appears. The
260		current dialect is available using <a name="idx:prologloadcontext2:2253"></a><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a>.
	301	current dialect is available using <a id="idx:prologloadcontext2:2257"></a><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a>.
261	302
262	303	<p>The exact behaviour of this predicate is still subject to discussion.
263	304	Of course, if <var>Dialect</var> matches the running dialect the

270	311	<li>Define system predicates of the requested dialect we do not have.
271	312
272	313	<p>
273		<li>Apply <a name="idx:goalexpansion2:2254"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	314	<li>Apply <a id="idx:goalexpansion2:2258"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
274	315	rules that map conflicting predicates to versions emulating the
275	316	requested dialect. These expansion rules reside in the dialect
276	317	compatibility module, but are applied if prolog_load_context(dialect,

284	325	<li>Setup support for the default filename extension of the dialect.
285	326	</ul>
286	327	</dd>
287		<dt class="pubdef"><a name="exists_source/1"><strong>exists_source</strong>(<var>+Spec</var>)</a></dt>
	328	<dt class="pubdef"><a id="exists_source/1"><strong>exists_source</strong>(<var>+Spec</var>)</a></dt>
288	329	<dd class="defbody">
289	330	Is true if <var>Spec</var> exists as a Prolog source. <var>Spec</var>
290		uses the same conventions as <a name="idx:loadfiles2:2255"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
	331	uses the same conventions as <a id="idx:loadfiles2:2259"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
291	332	Fails without error if <var>Spec</var> cannot be found.</dd>
292		<dt class="pubdef"><a name="source_exports/2"><strong>source_exports</strong>(<var>+Spec,
	333	<dt class="pubdef"><a id="source_exports/2"><strong>source_exports</strong>(<var>+Spec,
293	334	+Export</var>)</a></dt>
294	335	<dd class="defbody">
295	336	Is true if source <var>Spec</var> exports <var>Export</var>, a predicate

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193	234	</div>
194		<h2 id="sec:dicts"><a name="sec:5.4"><span class="sec-nr">5.4</span> <span class="sec-title">Dicts:
	235	<h2 id="sec:dicts"><a id="sec:5.4"><span class="sec-nr">5.4</span> <span class="sec-title">Dicts:
195	236	structures with named arguments</span></a></h2>
196	237
197		<a name="sec:dicts"></a>
	238	<a id="sec:dicts"></a>
198	239
199	240	<p>SWI-Prolog version 7 introduces dicts as an abstract object with
200	241	a concrete modern syntax and functional notation for accessing members

213	254	into an opaque internal representation that does <em>not</em> respect
214	255	the order in which the key-value pairs appear in the input text. If a
215	256	dict is written, the keys are written according to the standard order of
216		terms (see <a class="sec" href="compare.html">section 4.7.1</a>). Here
217		are some examples, where the second example illustrates that the order
218		is not maintained and the third illustrates an anonymous dict.
	257	terms (see <a class="sec" href="compare.html#sec:4.7.1">section 4.7.1</a>).
	258	Here are some examples, where the second example illustrates that the
	259	order is not maintained and the third illustrates an anonymous dict.
219	260
220	261	<pre class="code">
221	262	?- A = point{x:1, y:2}.

247	288	into a new dict that has the union of the keys of the two original
248	289	dicts.
249	290
250		<p><h3 id="sec:ext-dict-functions"><a name="sec:5.4.1"><span class="sec-nr">5.4.1</span> <span class="sec-title">Functions
	291	<p><h3 id="sec:ext-dict-functions"><a id="sec:5.4.1"><span class="sec-nr">5.4.1</span> <span class="sec-title">Functions
251	292	on dicts</span></a></h3>
252	293
253		<a name="sec:ext-dict-functions"></a>
	294	<a id="sec:ext-dict-functions"></a>
254	295
255	296	<p>The infix operator dot (<code>op(100, yfx, .)</code> is used to
256	297	extract values and evaluate functions on dicts. Functions are recognised

295	336
296	337	<p>Note that expansion of <code><code>.</code>/2</code> terms implies
297	338	that such terms cannot be created by writing them explicitly in your
298		source code. Such terms can still be created with <a name="idx:functor3:1631"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>, <a class="pred" href="manipterm.html#=../2">=../2</a>,
299		<a name="idx:compoundnamearity3:1632"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>
	339	source code. Such terms can still be created with <a id="idx:functor3:1631"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>, <a class="pred" href="manipterm.html#=../2">=../2</a>,
	340	<a id="idx:compoundnamearity3:1632"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>
300	341	and
301		<a name="idx:compoundnamearguments3:1633"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>.<sup class="fn">149<span class="fn-text">Traditional
	342	<a id="idx:compoundnamearguments3:1633"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>.<sup class="fn">149<span class="fn-text">Traditional
302	343	code is unlikely to use <code><code>.</code>/2</code> terms because they
303	344	were practically reserved for usage in lists. We do not provide a
304	345	quoting mechanism as found in functional languages because it would only

306	347	rare and term manipulation provides an escape route.</span></sup>
307	348
308	349	<dl class="latex">
309		<dt class="pubdef"><a name="./3"><strong>.</strong>(<var>+Dict,
310		+Function, -Result</var>)</a></dt>
	350	<dt class="pubdef"><a id="./3"><strong>.</strong>(<var>+Dict, +Function,
	351	-Result</var>)</a></dt>
311	352	<dd class="defbody">
312	353	This predicate is called to evaluate <code><code>.</code>/2</code> terms
313	354	found in the arguments of a goal. This predicate evaluates the field
314		extraction described above, which is mapped to <a name="idx:getdictex3:1634"></a><span class="pred-ext">get_dict_ex/3</span>.
	355	extraction described above, which is mapped to <a id="idx:getdictex3:1634"></a><span class="pred-ext">get_dict_ex/3</span>.
315	356	If <var>Function</var> is a compound term, it checks for the predefined
316		functions on dicts described in <a class="sec" href="dicts.html">section
317		5.4.1.2</a> or executes a user defined function as described in <a class="sec" href="dicts.html">section
	357	functions on dicts described in <a class="sec" href="dicts.html#sec:5.4.1.2">section
	358	5.4.1.2</a> or executes a user defined function as described in <a class="sec" href="dicts.html#sec:5.4.1.1">section
318	359	5.4.1.1</a>.
319	360	</dd>
320	361	</dl>
321	362
322		<p><h4 id="sec:ext-dict-user-functions"><a name="sec:5.4.1.1"><span class="sec-nr">5.4.1.1</span> <span class="sec-title">User
	363	<p><h4 id="sec:ext-dict-user-functions"><a id="sec:5.4.1.1"><span class="sec-nr">5.4.1.1</span> <span class="sec-title">User
323	364	defined functions on dicts</span></a></h4>
324	365
325		<a name="sec:ext-dict-user-functions"></a>
	366	<a id="sec:ext-dict-user-functions"></a>
326	367
327	368	<p>The tag of a dict associates the dict to a module. If the dot
328	369	notation uses a compound term, this calls the goal below.

336	377	predicates without worrying about the argument calling conventions. The
337	378	code below defines a function <code>multiply(Times)</code> on a point
338	379	that creates a new point by multiplying both coordinates. and <code>len()</code><sup class="fn">150<span class="fn-text">as <code>length()</code>
339		would result in a predicate <a name="idx:length2:1635"></a><a class="pred" href="builtinlist.html#length/2">length/2</a>,
	380	would result in a predicate <a id="idx:length2:1635"></a><a class="pred" href="builtinlist.html#length/2">length/2</a>,
340	381	this name cannot be used. This might change in future versions.</span></sup>
341	382	to compute the length from the origin. The . and <code>:=</code>
342	383	operators are used to abstract the location of the predicate arguments.

364	405	X = 4.47213595499958.
365	406	</pre>
366	407
367		<p><h4 id="sec:ext-dicts-predefined"><a name="sec:5.4.1.2"><span class="sec-nr">5.4.1.2</span> <span class="sec-title">Predefined
	408	<p><h4 id="sec:ext-dicts-predefined"><a id="sec:5.4.1.2"><span class="sec-nr">5.4.1.2</span> <span class="sec-title">Predefined
368	409	functions on dicts</span></a></h4>
369	410
370		<a name="sec:ext-dicts-predefined"></a>
	411	<a id="sec:ext-dicts-predefined"></a>
371	412
372	413	<p>Dicts currently define the following reserved functions:
373	414
374	415	<dl class="latex">
	416	<dt class="pubdef"><a id="m-get-1"><strong>get</strong>(<var>?Key</var>)</a></dt>
	417	<dd class="defbody">
	418	Same as <var>Dict</var>.<var>Key</var>, but maps to <a id="idx:getdict3:1636"></a><a class="pred" href="dicts.html#get_dict/3">get_dict/3</a>
	419	instead of
	420	<a id="idx:getdictex3:1637"></a><span class="pred-ext">get_dict_ex/3</span>.
	421	This implies that the function evaluation fails silently if <var>Key</var>
	422	does not appear in <var>Dict</var>. See also
	423	<a class="pred" href="dicts.html#:</2">:</2</a>, which can be used to
	424	test for existence and unify multiple key values from a dict. For
	425	example:
	426
	427	<pre class="code">
	428	?- write(t{a:x}.get(a)).
	429	x
	430	?- write(t{a:x}.get(b)).
	431	false.
	432	</pre>
	433
	434	</dd>
	435	<dt class="pubdef"><a id="m-put-1"><strong>put</strong>(<var>+New</var>)</a></dt>
	436	<dd class="defbody">
	437	Evaluates to a new dict where the key-values in <var>New</var> replace
	438	or extend the key-values in the original dict. See <a id="idx:putdict3:1638"></a><a class="pred" href="dicts.html#put_dict/3">put_dict/3</a>.</dd>
	439	<dt class="pubdef"><a id="m-put-2"><strong>put</strong>(<var>+KeyPath,
	440	+Value</var>)</a></dt>
	441	<dd class="defbody">
	442	Evaluates to a new dict where the <var>KeyPath</var>-<var>Value</var>
	443	replaces or extends the key-values in the original dict. <var>KeyPath</var>
	444	is either a key or a term <var>KeyPath</var>/<var>Key</var>,<sup class="fn">151<span class="fn-text">Note
	445	that we do not use the '.' functor here, because the <code><code>.</code>/2</code>
	446	would <em>evaluate</em>.</span></sup> replacing the value associated
	447	with <var>Key</var> in a sub-dict of the dict on which the function
	448	operates. See <a id="idx:putdict4:1639"></a><a class="pred" href="dicts.html#put_dict/4">put_dict/4</a>.
	449	Below are some examples:
	450
	451	<pre class="code">
	452	?- A = _{}.put(a, 1).
	453	A = _G7359{a:1}.
	454
	455	?- A = _{a:1}.put(a, 2).
	456	A = _G7377{a:2}.
	457
	458	?- A = _{a:1}.put(b/c, 2).
	459	A = _G1395{a:1, b:_G1584{c:2}}.
	460
	461	?- A = _{a:_{b:1}}.put(a/b, 2).
	462	A = _G1429{a:_G1425{b:2}}.
	463
	464	?- A = _{a:1}.put(a/b, 2).
	465	A = _G1395{a:_G1578{b:2}}.
	466	</pre>
	467
	468	<p></dd>
375	469	</dl>
376	470
377		<p><h3 id="sec:ext-dict-predicates"><a name="sec:5.4.2"><span class="sec-nr">5.4.2</span> <span class="sec-title">Predicates
	471	<p><h3 id="sec:ext-dict-predicates"><a id="sec:5.4.2"><span class="sec-nr">5.4.2</span> <span class="sec-title">Predicates
378	472	for managing dicts</span></a></h3>
379	473
380		<a name="sec:ext-dict-predicates"></a>
	474	<a id="sec:ext-dict-predicates"></a>
381	475
382	476	<p>This section documents the predicates that are defined on dicts. We
383	477	use the naming and argument conventions of the traditional <code>library(assoc)</code>.
384	478
385	479	<dl class="latex">
386		<dt class="pubdef"><a name="is_dict/1"><strong>is_dict</strong>(<var>@Term</var>)</a></dt>
	480	<dt class="pubdef"><a id="is_dict/1"><strong>is_dict</strong>(<var>@Term</var>)</a></dt>
387	481	<dd class="defbody">
388	482	True if <var>Term</var> is a dict. This is the same as <code>is_dict(Term,_)</code>.</dd>
389		<dt class="pubdef"><a name="is_dict/2"><strong>is_dict</strong>(<var>@Term,
	483	<dt class="pubdef"><a id="is_dict/2"><strong>is_dict</strong>(<var>@Term,
390	484	-Tag</var>)</a></dt>
391	485	<dd class="defbody">
392	486	True if <var>Term</var> is a dict of <var>Tag</var>.</dd>
393		<dt class="pubdef"><a name="get_dict/3"><strong>get_dict</strong>(<var>?Key,
	487	<dt class="pubdef"><a id="get_dict/3"><strong>get_dict</strong>(<var>?Key,
394	488	+Dict, -Value</var>)</a></dt>
395	489	<dd class="defbody">
396	490	Unify the value associated with <var>Key</var> in dict with <var>Value</var>.

398	492	<var>Key</var> is unbound, all associations in <var>Dict</var> are
399	493	returned on backtracking. The order in which the associations are
400	494	returned is undefined. This predicate is normally accessed using the
401		functional notation <code>Dict.Key</code>. See <a class="sec" href="dicts.html">section
	495	functional notation <code>Dict.Key</code>. See <a class="sec" href="dicts.html#sec:5.4.1">section
402	496	5.4.1</a>.
403	497
404	498	<p>Fails silently if Key does not appear in Dict. This is different from
405	499	the behavior of the functional `.`-notation, which throws an existence
406	500	error in that case.</dd>
407		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="get_dict/5"><strong>get_dict</strong>(<var>+Key,
	501	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="get_dict/5"><strong>get_dict</strong>(<var>+Key,
408	502	+Dict, -Value, -NewDict, +NewValue</var>)</a></dt>
409	503	<dd class="defbody">
410	504	Create a new dict after updating the value for <var>Key</var>. Fails if

421	515	</pre>
422	516
423	517	</dd>
424		<dt class="pubdef"><a name="dict_create/3"><strong>dict_create</strong>(<var>-Dict,
	518	<dt class="pubdef"><a id="dict_create/3"><strong>dict_create</strong>(<var>-Dict,
425	519	+Tag, +Data</var>)</a></dt>
426	520	<dd class="defbody">
427	521	Create a dict in <var>Tag</var> from <var>Data</var>. <var>Data</var> is

430	524	An exception is raised if <var>Data</var> is not a proper list, one of
431	525	the elements is not of the shape above, a key is neither an atom nor a
432	526	small integer or there is a duplicate key.</dd>
433		<dt class="pubdef"><a name="dict_pairs/3"><strong>dict_pairs</strong>(<var>?Dict,
	527	<dt class="pubdef"><a id="dict_pairs/3"><strong>dict_pairs</strong>(<var>?Dict,
434	528	?Tag, ?Pairs</var>)</a></dt>
435	529	<dd class="defbody">
436		Bi-directional mapping between a dict and an ordered list of pairs (see <a class="sec" href="pairs.html">section
	530	Bi-directional mapping between a dict and an ordered list of pairs (see <a class="sec" href="pairs.html#sec:A.22">section
437	531	A.22</a>).</dd>
438		<dt class="pubdef"><a name="put_dict/3"><strong>put_dict</strong>(<var>+New,
	532	<dt class="pubdef"><a id="put_dict/3"><strong>put_dict</strong>(<var>+New,
439	533	+DictIn, -DictOut</var>)</a></dt>
440	534	<dd class="defbody">
441	535	<var>DictOut</var> is a new dict created by replacing or adding
442	536	key-value pairs from <var>New</var> to <var>Dict</var>. <var>New</var>
443		is either a dict or a valid input for <a name="idx:dictcreate3:1636"></a><a class="pred" href="dicts.html#dict_create/3">dict_create/3</a>.
	537	is either a dict or a valid input for <a id="idx:dictcreate3:1640"></a><a class="pred" href="dicts.html#dict_create/3">dict_create/3</a>.
444	538	This predicate is normally accessed using the functional notation. Below
445	539	are some examples:
446	540

456	550	</pre>
457	551
458	552	</dd>
459		<dt class="pubdef"><a name="put_dict/4"><strong>put_dict</strong>(<var>+Key,
	553	<dt class="pubdef"><a id="put_dict/4"><strong>put_dict</strong>(<var>+Key,
460	554	+DictIn, +Value, -DictOut</var>)</a></dt>
461	555	<dd class="defbody">
462	556	<var>DictOut</var> is a new dict created by replacing or adding

476	570	</pre>
477	571
478	572	</dd>
479		<dt class="pubdef"><a name="del_dict/4"><strong>del_dict</strong>(<var>+Key,
	573	<dt class="pubdef"><a id="del_dict/4"><strong>del_dict</strong>(<var>+Key,
480	574	+DictIn, ?Value, -DictOut</var>)</a></dt>
481	575	<dd class="defbody">
482	576	True when <var>Key</var>-<var>Value</var> is in <var>DictIn</var> and <var>DictOut</var>
483	577	contains all associations of <var>DictIn</var> except for <var>Key</var>.</dd>
484		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name=":</2"><var>+Select</var> <strong>:<</strong> <var>+From</var></a></dt>
	578	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id=":</2"><var>+Select</var> <strong>:<</strong> <var>+From</var></a></dt>
485	579	<dd class="defbody">
486	580	True when <var>Select</var> is a `sub dict' of <var>From</var>: the
487	581	tages must unify and all keys in <var>Select</var> must appear with

501	595
502	596	<p>The goal <code>Select :< From</code> is equivalent to
503	597	<code>select_dict(Select, From, _)</code>.</dd>
504		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="select_dict/3"><strong>select_dict</strong>(<var>+Select,
	598	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="select_dict/3"><strong>select_dict</strong>(<var>+Select,
505	599	+From, -Rest</var>)</a></dt>
506	600	<dd class="defbody">
507	601	True when the tags of <var>Select</var> and <var>From</var> have been

517	611	R = _G1705{z:2}.
518	612	</pre>
519	613
520		<p>See also <a name="idx:selectdict2:1637"></a><span class="pred-ext">select_dict/2</span>
	614	<p>See also <a id="idx:selectdict2:1641"></a><span class="pred-ext">select_dict/2</span>
521	615	to ignore <var>Rest</var> and <a class="pred" href="dicts.html#>:</2">>:</2</a>
522	616	for a symmetric partial unification of two dicts.</dd>
523		<dt class="pubdef"><a name=">:</2"><var>+Dict1</var> <strong>>:<</strong> <var>+Dict2</var></a></dt>
	617	<dt class="pubdef"><a id=">:</2"><var>+Dict1</var> <strong>>:<</strong> <var>+Dict2</var></a></dt>
524	618	<dd class="defbody">
525	619	This operator specifies a <em>partial unification</em> between
526	620	<var>Dict1</var> and <var>Dict2</var>. It is true when the tags and the

534	628	Dict >:< point{x:0, y:Y}.
535	629	</pre>
536	630
537		<p>See also <a class="pred" href="dicts.html#:</2">:</2</a> and <a name="idx:selectdict3:1638"></a><a class="pred" href="dicts.html#select_dict/3">select_dict/3</a>.
	631	<p>See also <a class="pred" href="dicts.html#:</2">:</2</a> and <a id="idx:selectdict3:1642"></a><a class="pred" href="dicts.html#select_dict/3">select_dict/3</a>.
538	632	</dd>
539	633	</dl>
540	634
541		<p><h4 id="sec:ext-dict-assignment"><a name="sec:5.4.2.1"><span class="sec-nr">5.4.2.1</span> <span class="sec-title">Destructive
	635	<p><h4 id="sec:ext-dict-assignment"><a id="sec:5.4.2.1"><span class="sec-nr">5.4.2.1</span> <span class="sec-title">Destructive
542	636	assignment in dicts</span></a></h4>
543	637
544		<a name="sec:ext-dict-assignment"></a>
	638	<a id="sec:ext-dict-assignment"></a>
545	639
546	640	<p>This section describes the destructive update operations defined on
547	641	dicts. These actions can only <em>update</em> keys and not add or remove

553	647	with care because the system may copy or share identical Prolog terms at
554	648	any time. Some of this behaviour can be avoided by adding an additional
555	649	unbound value to the dict. This prevents unwanted sharing and ensures
556		that <a name="idx:copyterm2:1639"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>
	650	that <a id="idx:copyterm2:1643"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>
557	651	actually copies the dict. This pitfall is demonstrated in the example
558	652	below:
559	653

567	661	</pre>
568	662
569	663	<dl class="latex">
570		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="b_set_dict/3"><strong>b_set_dict</strong>(<var>+Key,
	664	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="b_set_dict/3"><strong>b_set_dict</strong>(<var>+Key,
571	665	!Dict, +Value</var>)</a></dt>
572	666	<dd class="defbody">
573	667	Destructively update the value associated with <var>Key</var> in <var>Dict</var>
574	668	to
575	669	<var>Value</var>. The update is trailed and undone on backtracking. This
576	670	predicate raises an existence error if <var>Key</var> does not appear in
577		<var>Dict</var>. The update semantics are equivalent to <a name="idx:setarg3:1640"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	671	<var>Dict</var>. The update semantics are equivalent to <a id="idx:setarg3:1644"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
578	672	and
579		<a name="idx:bsetval2:1641"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>.</dd>
580		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="nb_set_dict/3"><strong>nb_set_dict</strong>(<var>+Key,
	673	<a id="idx:bsetval2:1645"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>.</dd>
	674	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="nb_set_dict/3"><strong>nb_set_dict</strong>(<var>+Key,
581	675	!Dict, +Value</var>)</a></dt>
582	676	<dd class="defbody">
583	677	Destructively update the value associated with <var>Key</var> in <var>Dict</var>
584	678	to a copy of <var>Value</var>. The update is <em>not</em> undone on
585	679	backtracking. This predicate raises an existence error if <var>Key</var>
586	680	does not appear in
587		<var>Dict</var>. The update semantics are equivalent to <a name="idx:nbsetarg3:1642"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>
	681	<var>Dict</var>. The update semantics are equivalent to <a id="idx:nbsetarg3:1646"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>
588	682	and
589		<a name="idx:nbsetval2:1643"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>.</dd>
590		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="nb_link_dict/3"><strong>nb_link_dict</strong>(<var>+Key,
	683	<a id="idx:nbsetval2:1647"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>.</dd>
	684	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="nb_link_dict/3"><strong>nb_link_dict</strong>(<var>+Key,
591	685	!Dict, +Value</var>)</a></dt>
592	686	<dd class="defbody">
593	687	Destructively update the value associated with <var>Key</var> in <var>Dict</var>

595	689	<var>Value</var>. The update is <em>not</em> undone on backtracking.
596	690	This predicate raises an existence error if <var>Key</var> does not
597	691	appear in
598		<var>Dict</var>. The update semantics are equivalent to <a name="idx:nblinkarg3:1644"></a><a class="pred" href="manipterm.html#nb_linkarg/3">nb_linkarg/3</a>
	692	<var>Dict</var>. The update semantics are equivalent to <a id="idx:nblinkarg3:1648"></a><a class="pred" href="manipterm.html#nb_linkarg/3">nb_linkarg/3</a>
599	693	and
600		<a name="idx:nblinkval2:1645"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>.
	694	<a id="idx:nblinkval2:1649"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>.
601	695	Use with extreme care and consult the documentation of
602		<a name="idx:nblinkval2:1646"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>
	696	<a id="idx:nblinkval2:1650"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>
603	697	before use.
604	698	</dd>
605	699	</dl>
606	700
607		<p><h3 id="sec:ext-dicts-usage"><a name="sec:5.4.3"><span class="sec-nr">5.4.3</span> <span class="sec-title">When
	701	<p><h3 id="sec:ext-dicts-usage"><a id="sec:5.4.3"><span class="sec-nr">5.4.3</span> <span class="sec-title">When
608	702	to use dicts?</span></a></h3>
609	703
610		<a name="sec:ext-dicts-usage"></a>
	704	<a id="sec:ext-dicts-usage"></a>
611	705
612	706	<p>Dicts are a new type in the Prolog world. They compete with several
613	707	other types and libraries. In the list below we have a closer look at

691	785	code does not rely on ordered operations.</dd>
692	786	<dt><b>Library <code>library(option)</code></b></dt>
693	787	<dd>
694		Option lists are introduced by ISO Prolog, for example for <a name="idx:readterm3:1647"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>,
695		<a name="idx:open4:1648"></a><a class="pred" href="IO.html#open/4">open/4</a>,
	788	Option lists are introduced by ISO Prolog, for example for <a id="idx:readterm3:1651"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>,
	789	<a id="idx:open4:1652"></a><a class="pred" href="IO.html#open/4">open/4</a>,
696	790	etc. The <code>library(option)</code> library provides operations to
697	791	extract options, merge options lists, etc. Dicts are well suited to
698	792	replace option lists because they are cheaper, can be processed faster

701	795	<dd>
702	796	This library is commonly used to process large name-value associations.
703	797	In many cases this concerns short-lived datastructures that result from
704		<a name="idx:findall3:1649"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>, <a name="idx:maplist3:1650"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
	798	<a id="idx:findall3:1653"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>, <a id="idx:maplist3:1654"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
705	799	and similar list processing predicates. Dicts may play a role if
706	800	frequent random key lookups are needed on the resulting association. For
707	801	example, the skeleton `create a pairs list', `use
708		<a name="idx:listtoassoc2:1651"></a><a class="pred" href="assoc.html#list_to_assoc/2">list_to_assoc/2</a>
	802	<a id="idx:listtoassoc2:1655"></a><a class="pred" href="assoc.html#list_to_assoc/2">list_to_assoc/2</a>
709	803	to create an assoc', followed by frequent usage of
710		<a name="idx:getassoc3:1652"></a><a class="pred" href="assoc.html#get_assoc/3">get_assoc/3</a>
711		to extract key values can be replaced using <a name="idx:dictpairs3:1653"></a><a class="pred" href="dicts.html#dict_pairs/3">dict_pairs/3</a>
	804	<a id="idx:getassoc3:1656"></a><a class="pred" href="assoc.html#get_assoc/3">get_assoc/3</a>
	805	to extract key values can be replaced using <a id="idx:dictpairs3:1657"></a><a class="pred" href="dicts.html#dict_pairs/3">dict_pairs/3</a>
712	806	and the dict access functions. Using dicts in this scenario is more
713	807	efficient and provides a more pleasant access syntax.
714	808	</dd>
715	809	</dl>
716	810
717		<p><h3 id="sec:ext-dicts-motivation"><a name="sec:5.4.4"><span class="sec-nr">5.4.4</span> <span class="sec-title">A
	811	<p><h3 id="sec:ext-dicts-motivation"><a id="sec:5.4.4"><span class="sec-nr">5.4.4</span> <span class="sec-title">A
718	812	motivation for dicts as primary citizens</span></a></h3>
719	813
720		<a name="sec:ext-dicts-motivation"></a>
	814	<a id="sec:ext-dicts-motivation"></a>
721	815
722	816	<p>Dicts, or key-value associations, are a common data structure. A good
723	817	old example are <em>property lists</em> as found in Lisp, while a good

748	842	<code>library(assoc)</code> allows for efficient manipulation of
749	843	changing associations, but the syntactical representation of an assoc is
750	844	complex, which makes them unsuitable for e.g., <em>options lists</em> as
751		seen in predicates such as <a name="idx:open4:1654"></a><a class="pred" href="IO.html#open/4">open/4</a>.
752
753		<p><h3 id="sec:ext-dicts-implementation"><a name="sec:5.4.5"><span class="sec-nr">5.4.5</span> <span class="sec-title">Implementation
	845	seen in predicates such as <a id="idx:open4:1658"></a><a class="pred" href="IO.html#open/4">open/4</a>.
	846
	847	<p><h3 id="sec:ext-dicts-implementation"><a id="sec:5.4.5"><span class="sec-nr">5.4.5</span> <span class="sec-title">Implementation
754	848	notes about dicts</span></a></h3>
755	849
756		<a name="sec:ext-dicts-implementation"></a>
	850	<a id="sec:ext-dicts-implementation"></a>
757	851
758	852	<p>Although dicts are designed as an abstract data type and we
759	853	deliberately reserve the possibility to change the representation and

763	857	<p>Dicts are currently represented as a compound term using the functor
764	858	<code>`dict`</code>. The first argument is the tag. The remaining
765	859	arguments create an array of sorted key-value pairs. This representation
766		is compact and guarantees good locality. Lookup is order <var>N</var>,
	860	is compact and guarantees good locality. Lookup is order <var>log( N )</var>,
767	861	while adding values, deleting values and merging with other dicts has
768	862	order
769	863	<var>N</var>. The main disadvantage is that changing values in large

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193	234	</div>
194		<h2 id="sec:dynamic-modules"><a name="sec:6.12"><span class="sec-nr">6.12</span> <span class="sec-title">Dynamic
	235	<h2 id="sec:dynamic-modules"><a id="sec:6.12"><span class="sec-nr">6.12</span> <span class="sec-title">Dynamic
195	236	Modules</span></a></h2>
196	237
197		<a name="sec:dynamic-modules"></a>
	238	<a id="sec:dynamic-modules"></a>
198	239
199	240	<p>So far, we discussed modules that were created by loading a module
200	241	file. These modules have been introduced to facilitate the development

221	262
222	263	<p>Import and export from a dynamically created world can be achieved
223	264	using
224		<a name="idx:import1:1734"></a><a class="pred" href="altmoduleapi.html#import/1">import/1</a>
225		and <a name="idx:export1:1735"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>
	265	<a id="idx:import1:1738"></a><a class="pred" href="altmoduleapi.html#import/1">import/1</a>
	266	and <a id="idx:export1:1739"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>
226	267	or by specifying the import module as described in
227		<a class="sec" href="importmodule.html">section 6.9</a>.
	268	<a class="sec" href="importmodule.html#sec:6.9">section 6.9</a>.
228	269
229	270	<pre class="code">
230	271	?- world_b:export(solve/2). % exports solve/2 from world_b

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193	234	</div>
194		<h2 id="sec:declare"><a name="sec:4.15"><span class="sec-nr">4.15</span> <span class="sec-title">Declaring
	235	<h2 id="sec:declare"><a id="sec:4.15"><span class="sec-nr">4.15</span> <span class="sec-title">Declaring
195	236	predicate properties</span></a></h2>
196	237
197		<a name="ch:dynamic"></a>
198		<a name="sec:declare"></a>
	238	<a id="ch:dynamic"></a>
	239	<a id="sec:declare"></a>
199	240
200	241	<p>This section describes directives which manipulate attributes of
201		predicate definitions. The functors <a name="idx:dynamic1:875"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>, <a name="idx:multifile1:876"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>,
202		<a name="idx:discontiguous1:877"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a>
203		and <a name="idx:public1:878"></a><a class="pred" href="dynamic.html#public/1">public/1</a>
204		are operators of priority 1150 (see <a name="idx:op3:879"></a><a class="pred" href="operators.html#op/3">op/3</a>),
	242	predicate definitions. The functors <a id="idx:dynamic1:875"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>, <a id="idx:multifile1:876"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>,
	243	<a id="idx:discontiguous1:877"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a>
	244	and <a id="idx:public1:878"></a><a class="pred" href="dynamic.html#public/1">public/1</a>
	245	are operators of priority 1150 (see <a id="idx:op3:879"></a><a class="pred" href="operators.html#op/3">op/3</a>),
205	246	which implies that the list of predicates they involve can just be a
206	247	comma-separated list:
207	248

216	257	want to maintain portability to other Prolog implementations.
217	258
218	259	<dl class="latex">
219		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="dynamic/1"><strong>dynamic</strong> <var>:PredicateIndicator,
	260	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="dynamic/1"><strong>dynamic</strong> <var>:PredicateIndicator,
220	261	...</var></a></dt>
221	262	<dd class="defbody">
222	263	Informs the interpreter that the definition of the predicate(s) may
223		change during execution (using <a name="idx:assert1:880"></a><a class="pred" href="db.html#assert/1">assert/1</a>
224		and/or <a name="idx:retract1:881"></a><a class="pred" href="db.html#retract/1">retract/1</a>).
	264	change during execution (using <a id="idx:assert1:880"></a><a class="pred" href="db.html#assert/1">assert/1</a>
	265	and/or <a id="idx:retract1:881"></a><a class="pred" href="db.html#retract/1">retract/1</a>).
225	266	In the multithreaded version, the clauses of dynamic predicates are
226		shared between the threads. The directive <a name="idx:threadlocal1:882"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>
	267	shared between the threads. The directive <a id="idx:threadlocal1:882"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>
227	268	provides an alternative where each thread has its own clause list for
228	269	the predicate. Dynamic predicates can be turned into static ones using
229		<a name="idx:compilepredicates1:883"></a><a class="pred" href="dynamic.html#compile_predicates/1">compile_predicates/1</a>.</dd>
230		<dt class="pubdef"><a name="compile_predicates/1"><strong>compile_predicates</strong>(<var>:ListOfPredicateIndicators</var>)</a></dt>
231		<dd class="defbody">
232		Compile a list of specified dynamic predicates (see <a name="idx:dynamic1:884"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
	270	<a id="idx:compilepredicates1:883"></a><a class="pred" href="dynamic.html#compile_predicates/1">compile_predicates/1</a>.</dd>
	271	<dt class="pubdef"><a id="compile_predicates/1"><strong>compile_predicates</strong>(<var>:ListOfPredicateIndicators</var>)</a></dt>
	272	<dd class="defbody">
	273	Compile a list of specified dynamic predicates (see <a id="idx:dynamic1:884"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
233	274	and
234		<a name="idx:assert1:885"></a><a class="pred" href="db.html#assert/1">assert/1</a>)
	275	<a id="idx:assert1:885"></a><a class="pred" href="db.html#assert/1">assert/1</a>)
235	276	into normal static predicates. This call tells the Prolog environment
236		the definition will not change anymore and further calls to <a name="idx:assert1:886"></a><a class="pred" href="db.html#assert/1">assert/1</a>
237		or <a name="idx:retract1:887"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	277	the definition will not change anymore and further calls to <a id="idx:assert1:886"></a><a class="pred" href="db.html#assert/1">assert/1</a>
	278	or <a id="idx:retract1:887"></a><a class="pred" href="db.html#retract/1">retract/1</a>
238	279	on the named predicates raise a permission error. This predicate is
239	280	designed to deal with parts of the program that are generated at runtime
240	281	but do not change during the remainder of the program execution.<sup class="fn">79<span class="fn-text">The

243	284	implemented. In multithreaded Prolog, however, static code runs faster
244	285	as it does not require synchronisation. This is particularly true on SMP
245	286	hardware.</span></sup></dd>
246		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="multifile/1"><strong>multifile</strong> <var>:PredicateIndicator,
	287	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="multifile/1"><strong>multifile</strong> <var>:PredicateIndicator,
247	288	...</var></a></dt>
248	289	<dd class="defbody">
249	290	Informs the system that the specified predicate(s) may be defined over
250		more than one file. This stops <a name="idx:consult1:888"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
	291	more than one file. This stops <a id="idx:consult1:888"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>
251	292	from redefining a predicate when a new definition is found.</dd>
252		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="discontiguous/1"><strong>discontiguous</strong> <var>:PredicateIndicator,
	293	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="discontiguous/1"><strong>discontiguous</strong> <var>:PredicateIndicator,
253	294	...</var></a></dt>
254	295	<dd class="defbody">
255	296	Informs the system that the clauses of the specified predicate(s) might
256		not be together in the source file. See also <a name="idx:stylecheck1:889"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>.</dd>
257		<dt class="pubdef"><a name="public/1"><strong>public</strong> <var>:PredicateIndicator,
	297	not be together in the source file. See also <a id="idx:stylecheck1:889"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>.</dd>
	298	<dt class="pubdef"><a id="public/1"><strong>public</strong> <var>:PredicateIndicator,
258	299	...</var></a></dt>
259	300	<dd class="defbody">
260	301	Instructs the cross-referencer that the predicate can be called. It has
261	302	no semantics.<sup class="fn">80<span class="fn-text">This declaration is
262		compatible with SICStus. In YAP, <a name="idx:public1:890"></a><a class="pred" href="dynamic.html#public/1">public/1</a>
	303	compatible with SICStus. In YAP, <a id="idx:public1:890"></a><a class="pred" href="dynamic.html#public/1">public/1</a>
263	304	instructs the compiler to keep the source. As the source is always
264	305	available in SWI-Prolog, our current interpretation also enhances the
265	306	compatibility with YAP.</span></sup> The public declaration can be
266		queried using <a name="idx:predicateproperty2:891"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.
267		The <a name="idx:public1:892"></a><a class="pred" href="dynamic.html#public/1">public/1</a>
	307	queried using <a id="idx:predicateproperty2:891"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.
	308	The <a id="idx:public1:892"></a><a class="pred" href="dynamic.html#public/1">public/1</a>
268	309	directive does
269		<em>not</em> export the predicate (see <a name="idx:module1:893"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>
270		and <a name="idx:export1:894"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>).
	310	<em>not</em> export the predicate (see <a id="idx:module1:893"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>
	311	and <a id="idx:export1:894"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>).
271	312	The public directive is used for (1) direct calls into the module from,
272	313	e.g., foreign code, (2) direct calls into the module from other modules,
273	314	or (3) flag a predicate as being called if the call is generated by

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193	234	</div>
194		<h2 id="sec:edit"><a name="sec:4.4"><span class="sec-nr">4.4</span> <span class="sec-title">Editor
	235	<h2 id="sec:edit"><a id="sec:4.4"><span class="sec-nr">4.4</span> <span class="sec-title">Editor
195	236	Interface</span></a></h2>
196	237
197		<a name="sec:edit"></a>
	238	<a id="sec:edit"></a>
198	239
199	240	<p>SWI-Prolog offers an extensible interface which allows the user to
200	241	edit objects of the program: predicates, modules, files, etc. The editor
201		interface is implemented by <a name="idx:edit1:585"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	242	interface is implemented by <a id="idx:edit1:585"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
202	243	and consists of three parts:
203	244	<em>locating</em>, <em>selecting</em> and <em>starting</em> the editor.
204		Any of these parts may be customized. See <a class="sec" href="edit.html">section
	245	Any of these parts may be customized. See <a class="sec" href="edit.html#sec:4.4.1">section
205	246	4.4.1</a>.
206	247
207		<p>The built-in edit specifications for <a name="idx:edit1:586"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	248	<p>The built-in edit specifications for <a id="idx:edit1:586"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
208	249	(see prolog_edit:locate/3) are described in the table below:
209	250
210		<p><table border="2" frame="box" rules="groups" style="margin:auto">
211		<tr valign="top"><td colspan=2 align=center><b>Fully specified objects</b></tr>
212		<tbody>
213		<tr valign="top"><td><<var>Module</var>>:<<var>Name</var>>/<<var>Arity</var>> </td><td>Refers
	251	<p><table class="latex frame-box center">
	252	<tr><td colspan=2 align=center><b>Fully specified objects</b></tr>
	253	<tr class="hline"><td><<var>Module</var>>:<<var>Name</var>>/<<var>Arity</var>> </td><td>Refers
214	254	to a predicate </td></tr>
215		<tr valign="top"><td>module(<<var>Module</var>>)</td><td>Refers to
216		a module </td></tr>
217		<tr valign="top"><td>file(<<var>Path</var>>)</td><td>Refers to a
218		file </td></tr>
219		<tr valign="top"><td>source_file(<<var>Path</var>>)</td><td>Refers
220		to a loaded source file </td></tr>
221		<tbody>
222		<tr valign="top"><td colspan=2 align=center><b>Ambiguous specifications</b></tr>
223		<tbody>
224		<tr valign="top"><td><<var>Name</var>>/<<var>Arity</var>> </td><td>Refers
	255	<tr><td>module(<<var>Module</var>>)</td><td>Refers to a module </td></tr>
	256	<tr><td>file(<<var>Path</var>>)</td><td>Refers to a file </td></tr>
	257	<tr><td>source_file(<<var>Path</var>>)</td><td>Refers to a loaded
	258	source file </td></tr>
	259	<tr class="hline"><td colspan=2 align=center><b>Ambiguous specifications</b></tr>
	260	<tr class="hline"><td><<var>Name</var>>/<<var>Arity</var>> </td><td>Refers
225	261	to this predicate in any module </td></tr>
226		<tr valign="top"><td><<var>Name</var>> </td><td>Refers to (1) the
227		named predicate in any module with any arity, (2) a (source) file, or
228		(3) a module. </td></tr>
	262	<tr><td><<var>Name</var>> </td><td>Refers to (1) the named
	263	predicate in any module with any arity, (2) a (source) file, or (3) a
	264	module. </td></tr>
229	265	</table>
230	266
231	267	<dl class="latex">
232		<dt class="pubdef"><a name="edit/1"><strong>edit</strong>(<var>+Specification</var>)</a></dt>
	268	<dt class="pubdef"><a id="edit/1"><strong>edit</strong>(<var>+Specification</var>)</a></dt>
233	269	<dd class="defbody">
234	270	First, exploit <a class="pred" href="edit.html#prolog_edit:locate/3">prolog_edit:locate/3</a>
235	271	to translate
236	272	<var>Specification</var> into a list of <em>Locations</em>. If there is
237	273	more than one `hit', the user is asked to select from the locations
238	274	found. Finally, <a class="pred" href="edit.html#prolog_edit:edit_source/1">prolog_edit:edit_source/1</a>
239		is used to invoke the user's preferred editor. Typically, <a name="idx:edit1:587"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	275	is used to invoke the user's preferred editor. Typically, <a id="idx:edit1:587"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
240	276	can be handed the name of a predicate, module, basename of a file, XPCE
241	277	class, XPCE method, etc.</dd>
242		<dt class="pubdef"><a name="edit/0"><strong>edit</strong></a></dt>
243		<dd class="defbody">
244		Edit the `default' file using <a name="idx:edit1:588"></a><a class="pred" href="edit.html#edit/1">edit/1</a>.
	278	<dt class="pubdef"><a id="edit/0"><strong>edit</strong></a></dt>
	279	<dd class="defbody">
	280	Edit the `default' file using <a id="idx:edit1:588"></a><a class="pred" href="edit.html#edit/1">edit/1</a>.
245	281	The default file is the file loaded with the command line option <strong>-s</strong>
246	282	or, in Windows, the file loaded by double-clicking from the Windows
247	283	shell.
248	284	</dd>
249	285	</dl>
250	286
251		<p><h3 id="sec:customedit"><a name="sec:4.4.1"><span class="sec-nr">4.4.1</span> <span class="sec-title">Customizing
	287	<p><h3 id="sec:customedit"><a id="sec:4.4.1"><span class="sec-nr">4.4.1</span> <span class="sec-title">Customizing
252	288	the editor interface</span></a></h3>
253	289
254		<a name="sec:customedit"></a>
	290	<a id="sec:customedit"></a>
255	291
256	292	<p>The predicates described in this section are <em>hooks</em> that can
257		be defined to disambiguate specifications given to <a name="idx:edit1:589"></a><a class="pred" href="edit.html#edit/1">edit/1</a>,
	293	be defined to disambiguate specifications given to <a id="idx:edit1:589"></a><a class="pred" href="edit.html#edit/1">edit/1</a>,
258	294	find the related source, and open an editor at the given source
259	295	location.
260	296
261	297	<dl class="latex">
262		<dt class="pubdef"><a name="prolog_edit:locate/3"><strong>prolog_edit:locate</strong>(<var>+Spec,
	298	<dt class="pubdef"><a id="prolog_edit:locate/3"><strong>prolog_edit:locate</strong>(<var>+Spec,
263	299	-FullSpec, -Location</var>)</a></dt>
264	300	<dd class="defbody">
265		Where <var>Spec</var> is the specification provided through <a name="idx:edit1:590"></a><a class="pred" href="edit.html#edit/1">edit/1</a>.
	301	Where <var>Spec</var> is the specification provided through <a id="idx:edit1:590"></a><a class="pred" href="edit.html#edit/1">edit/1</a>.
266	302	This multifile predicate is used to enumerate locations where an object
267	303	satisfying the given <var>Spec</var> can be found. <var>FullSpec</var>
268	304	is unified with the complete specification for the object. This

274	310	<p><var>Location</var> is a list of attributes of the location.
275	311	Normally, this list will contain the term <code>file(File)</code> and,
276	312	if available, the term <code>line(Line)</code>.</dd>
277		<dt class="pubdef"><a name="prolog_edit:locate/2"><strong>prolog_edit:locate</strong>(<var>+Spec,
	313	<dt class="pubdef"><a id="prolog_edit:locate/2"><strong>prolog_edit:locate</strong>(<var>+Spec,
278	314	-Location</var>)</a></dt>
279	315	<dd class="defbody">
280	316	Same as prolog_edit:locate/3, but only deals with fully specified
281	317	objects.</dd>
282		<dt class="pubdef"><a name="prolog_edit:edit_source/1"><strong>prolog_edit:edit_source</strong>(<var>+Location</var>)</a></dt>
	318	<dt class="pubdef"><a id="prolog_edit:edit_source/1"><strong>prolog_edit:edit_source</strong>(<var>+Location</var>)</a></dt>
283	319	<dd class="defbody">
284	320	Start editor on <var>Location</var>. See prolog_edit:locate/3 for the
285	321	format of a location term. This multifile predicate is normally not
286		defined. If it succeeds, <a name="idx:edit1:591"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	322	defined. If it succeeds, <a id="idx:edit1:591"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
287	323	assumes the editor is started.
288	324
289		<p>If it fails, <a name="idx:edit1:592"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	325	<p>If it fails, <a id="idx:edit1:592"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
290	326	uses its internal defaults, which are defined by the Prolog flag <a class="flag" href="flags.html#flag:editor">editor</a>
291	327	and/or the environment variable
292	328	<code>EDITOR</code>. The following rules apply. If the Prolog flag <a class="flag" href="flags.html#flag:editor">editor</a>

301	337
302	338	<p>See the default user preferences file <code>dotfiles/dotswiplrc</code>
303	339	for examples.</dd>
304		<dt class="pubdef"><a name="prolog_edit:edit_command/2"><strong>prolog_edit:edit_command</strong>(<var>+Editor,
	340	<dt class="pubdef"><a id="prolog_edit:edit_command/2"><strong>prolog_edit:edit_command</strong>(<var>+Editor,
305	341	-Command</var>)</a></dt>
306	342	<dd class="defbody">
307		Determines how <var>Editor</var> is to be invoked using <a name="idx:shell1:593"></a><a class="pred" href="system.html#shell/1">shell/1</a>. <var>Editor</var>
	343	Determines how <var>Editor</var> is to be invoked using <a id="idx:shell1:593"></a><a class="pred" href="system.html#shell/1">shell/1</a>. <var>Editor</var>
308	344	is the determined editor (see qpredrefprolog_editedit_source1), without
309	345	the full path specification, and without a possible (<code>.exe</code>)
310	346	extension. <var>Command</var> is an atom describing the command. The
311	347	following %-sequences are replaced in <var>Command</var> before the
312		result is handed to <a name="idx:shell1:594"></a><a class="pred" href="system.html#shell/1">shell/1</a>:
313
314		<p><table border="2" frame="box" rules="groups" style="margin:auto">
315		<tr valign="top"><td>%e</td><td>Replaced by the (OS) command name of the
316		editor </td></tr>
317		<tr valign="top"><td>%f</td><td>Replaced by the (OS) full path name of
318		the file </td></tr>
319		<tr valign="top"><td>%d</td><td>Replaced by the line number </td></tr>
	348	result is handed to <a id="idx:shell1:594"></a><a class="pred" href="system.html#shell/1">shell/1</a>:
	349
	350	<p><table class="latex frame-box center">
	351	<tr><td>%e</td><td>Replaced by the (OS) command name of the editor </td></tr>
	352	<tr><td>%f</td><td>Replaced by the (OS) full path name of the file </td></tr>
	353	<tr><td>%d</td><td>Replaced by the line number </td></tr>
320	354	</table>
321	355
322	356	<p>If the editor can deal with starting at a specified line, two clauses

329	363	a given line number.
330	364
331	365	<p>Please contribute your specifications to <a class="url" href="mailto:bugs@swi-prolog.org">bugs@swi-prolog.org</a>.</dd>
332		<dt class="pubdef"><a name="prolog_edit:load/0"><strong>prolog_edit:load</strong></a></dt>
	366	<dt class="pubdef"><a id="prolog_edit:load/0"><strong>prolog_edit:load</strong></a></dt>
333	367	<dd class="defbody">
334	368	Normally an undefined multifile predicate. This predicate may be defined
335	369	to provide loading hooks for user extensions to the edit module. For

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 3.3</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="usingmodules.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:editreload"><a name="sec:3.3"><span class="sec-nr">3.3</span> <span class="sec-title">The
	235	<h2 id="sec:editreload"><a id="sec:3.3"><span class="sec-nr">3.3</span> <span class="sec-title">The
195	236	test-edit-reload cycle</span></a></h2>
196	237
197		<a name="sec:editreload"></a>
	238	<a id="sec:editreload"></a>
198	239
199	240	<p>SWI-Prolog does not enforce the use of a particular editor for
200	241	writing Prolog source code. Editors are complicated programs that must

206	247
207	248	<p>The use of a built-in editor, which is selected by setting the Prolog
208	249	flag <a class="flag" href="flags.html#flag:editor">editor</a> to <code>pce_emacs</code>,
209		has advantages. The XPCE object, around which the built-in PceEmacs is
210		built, can be opened as a Prolog stream allowing analysis of your source
211		by the real Prolog system.
212
213		<p><h3 id="sec:editfind"><a name="sec:3.3.1"><span class="sec-nr">3.3.1</span> <span class="sec-title">Locating
	250	has advantages. The XPCE <i>editor</i> object, around which the built-in
	251	PceEmacs is built, can be opened as a Prolog stream allowing analysis of
	252	your source by the real Prolog system.
	253
	254	<p><h3 id="sec:editfind"><a id="sec:3.3.1"><span class="sec-nr">3.3.1</span> <span class="sec-title">Locating
214	255	things to edit</span></a></h3>
215	256
216		<a name="sec:editfind"></a>
217
218		<p><a name="idx:TABcompletion:304"></a><a name="idx:completionTAB:305"></a>The
219		central predicate for editing something is <a name="idx:edit1:306"></a><a class="pred" href="edit.html#edit/1">edit/1</a>,
	257	<a id="sec:editfind"></a>
	258
	259	<p><a id="idx:TABcompletion:304"></a><a id="idx:completionTAB:305"></a>The
	260	central predicate for editing something is <a id="idx:edit1:306"></a><a class="pred" href="edit.html#edit/1">edit/1</a>,
220	261	an extensible front-end that searches for objects (files, predicates,
221	262	modules, as well as XPCE classes and methods) in the Prolog database. If
222	263	multiple matches are found it provides a choice. Together with the

233	274	Your choice?
234	275	</pre>
235	276
236		<p><h3 id="sec:editcompile"><a name="sec:3.3.2"><span class="sec-nr">3.3.2</span> <span class="sec-title">Editing
	277	<p><h3 id="sec:editcompile"><a id="sec:3.3.2"><span class="sec-nr">3.3.2</span> <span class="sec-title">Editing
237	278	and incremental compilation</span></a></h3>
238	279
239		<a name="sec:editcompile"></a>
	280	<a id="sec:editcompile"></a>
240	281
241	282	<p>One of the nice features of Prolog is that the code can be modified
242	283	while the program is running. Using pure Prolog you can trace a program,

247	288	understanding the misbehaviour, edit the source, reload it and try
248	289	again.
249	290
250		<p>One of the nice features of SWI-Prolog is the availability of <a name="idx:make0:307"></a><a class="pred" href="consulting.html#make/0">make/0</a>,
	291	<p>One of the nice features of SWI-Prolog is the availability of <a id="idx:make0:307"></a><a class="pred" href="consulting.html#make/0">make/0</a>,
251	292	a simple predicate that checks all loaded source files to see which ones
252	293	you have modified. It then reloads these files, considering the module
253	294	from which the file was loaded originally. This greatly simplifies the

259	300	</pre>
260	301
261	302	<p>Now edit the source, possibly switching to other files and making
262		multiple changes. After finishing, invoke <a name="idx:make0:308"></a><a class="pred" href="consulting.html#make/0">make/0</a>,
	303	multiple changes. After finishing, invoke <a id="idx:make0:308"></a><a class="pred" href="consulting.html#make/0">make/0</a>,
263	304	either through the editor UI (<strong>Compile/Make</strong> (<code>Control-C
264	305	Control-M</code>)) or on the top level, and watch the files being
265	306	reloaded.<sup class="fn">37<span class="fn-text">Watching these files is

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191	232	<a class="nav" href="engines.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="engine-resources.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:engine-examples"><a name="sec:10.1"><span class="sec-nr">10.1</span> <span class="sec-title">Examples
	235	<h2 id="sec:engine-examples"><a id="sec:10.1"><span class="sec-nr">10.1</span> <span class="sec-title">Examples
195	236	using engines</span></a></h2>
196	237
197		<a name="sec:engine-examples"></a>
	238	<a id="sec:engine-examples"></a>
198	239
199	240	<p>We introduce engines by describing application areas and providing
200	241	simple example programs. The predicates are defined in
201		<a class="sec" href="engine-predicates.html">section 10.3</a>. We
202		identify the following application areas for engines.
	242	<a class="sec" href="engine-predicates.html#sec:10.3">section 10.3</a>.
	243	We identify the following application areas for engines.
203	244
204	245	<p>
205	246	<ol class="latex">
206	247	<li>Aggregating solutions from one or more goals. See
207		<a class="sec" href="engine-examples.html">section 10.1.1</a>.
	248	<a class="sec" href="engine-examples.html#sec:10.1.1">section 10.1.1</a>.
208	249	<li>Access the terms produced in <em>forward execution</em> through
209		backtracking without collecting all of them first. <a class="sec" href="engine-examples.html">Section
	250	backtracking without collecting all of them first. <a class="sec" href="engine-examples.html#sec:10.1.1">Section
210	251	10.1.1</a> illustrates this as well.
211		<li>State accumulation and sharing. See <a class="sec" href="engine-examples.html">section
	252	<li>State accumulation and sharing. See <a class="sec" href="engine-examples.html#sec:10.1.2">section
212	253	10.1.2</a>.
213		<li>Scalable many-agent applications. See <a class="sec" href="engine-examples.html">section
	254	<li>Scalable many-agent applications. See <a class="sec" href="engine-examples.html#sec:10.1.3">section
214	255	10.1.3</a>.
215	256	</ol>
216	257
217		<p><h3 id="sec:engine-aggregation"><a name="sec:10.1.1"><span class="sec-nr">10.1.1</span> <span class="sec-title">Aggregation
	258	<p><h3 id="sec:engine-aggregation"><a id="sec:10.1.1"><span class="sec-nr">10.1.1</span> <span class="sec-title">Aggregation
218	259	using engines</span></a></h3>
219	260
220		<a name="sec:engine-aggregation"></a>
	261	<a id="sec:engine-aggregation"></a>
221	262
222	263	<p>Engines can be used to reason about solutions produced by a goal
223	264	through backtracking. In this scenario we create an engine with the goal
224		we wish to backtrack over and we enumerate all its solution using <a name="idx:enginenext1:1965"></a><span class="pred-ext">engine_next/1</span>.
225		This usage scenario competes with the all solution predicates (<a name="idx:findall3:1966"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>, <a name="idx:bagof3:1967"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>,
	265	we wish to backtrack over and we enumerate all its solution using <a id="idx:enginenext1:1969"></a><span class="pred-ext">engine_next/1</span>.
	266	This usage scenario competes with the all solution predicates (<a id="idx:findall3:1970"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>, <a id="idx:bagof3:1971"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>,
226	267	etc.) and the predicates from library
227		<code>library(aggregate)</code>. Below we implement <a name="idx:findall3:1968"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
	268	<code>library(aggregate)</code>. Below we implement <a id="idx:findall3:1972"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
228	269	using engines.
229	270
230	271	<pre class="code">

242	283
243	284	<p>The above is not a particularly attractive alternative for the
244	285	built-in
245		<a name="idx:findall3:1969"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>.
	286	<a id="idx:findall3:1973"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>.
246	287	It is mostly slower due to time required to create and destroy the
247		engine as well as the (currently<sup class="fn">165<span class="fn-text">The
	288	engine as well as the (currently<sup class="fn">166<span class="fn-text">The
248	289	current implementation of engines is built on top of primitives that are
249	290	not optimal for the engine use case. There is considerable opportunity
250	291	to reduce the overhead.</span></sup>) higher overhead of copying terms
251	292	between engines than the overhead required by the dedicated
252	293	representation used by
253		<a name="idx:findall3:1970"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>.
	294	<a id="idx:findall3:1974"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>.
254	295
255	296	<p>It gets more interesting if we wish to combine answers from multiple
256	297	backtracking predicates. Assume we have two predicates that, on

331	372	yield_remaining(S1, E).
332	373	</pre>
333	374
334		<p><h3 id="sec:engine-state"><a name="sec:10.1.2"><span class="sec-nr">10.1.2</span> <span class="sec-title">State
	375	<p><h3 id="sec:engine-state"><a id="sec:10.1.2"><span class="sec-nr">10.1.2</span> <span class="sec-title">State
335	376	accumulation using engines</span></a></h3>
336	377
337		<a name="sec:engine-state"></a>
	378	<a id="sec:engine-state"></a>
338	379
339	380	<p>Applications that need to manage a state can do so by passing the
340	381	state around in an additional argument, storing it in a global variable
341		or update it in the dynamic database using <a name="idx:assertz1:1971"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
342		and <a name="idx:retract1:1972"></a><a class="pred" href="db.html#retract/1">retract/1</a>.
343		Both using an additional argument and a global variable (see <a name="idx:bsetval2:1973"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>),
	382	or update it in the dynamic database using <a id="idx:assertz1:1975"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
	383	and <a id="idx:retract1:1976"></a><a class="pred" href="db.html#retract/1">retract/1</a>.
	384	Both using an additional argument and a global variable (see <a id="idx:bsetval2:1977"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>),
344	385	make the state subject to backtracking. This may or may not be
345	386	desirable. If having a state is that subject to backtracking is
346	387	required, using an additional argument or backtrackable global variable
347		is the right approach. Otherwise, non-backtrackable global variables (<a name="idx:nbsetval2:1974"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>)
	388	is the right approach. Otherwise, non-backtrackable global variables (<a id="idx:nbsetval2:1978"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>)
348	389	and dynamic database come into the picture, where global variables are
349	390	always local to a thread and the dynamic database may or may not be
350		shared between threads (see <a name="idx:threadlocal1:1975"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>).
	391	shared between threads (see <a id="idx:threadlocal1:1979"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>).
351	392
352	393	<p>Engines bring an alternative that packages a state inside the engine
353	394	where it is typically represented in a (threaded) Prolog variable. The

359	400	<p>
360	401	<ul class="latex">
361	402	<li>The programming style needed inside the engine is much more `Prolog
362		friendly', using <a name="idx:enginefetch1:1976"></a><a class="pred" href="engine-predicates.html#engine_fetch/1">engine_fetch/1</a>
	403	friendly', using <a id="idx:enginefetch1:1980"></a><a class="pred" href="engine-predicates.html#engine_fetch/1">engine_fetch/1</a>
363	404	to read a request and
364		<a name="idx:engineyield1:1977"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
	405	<a id="idx:engineyield1:1981"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
365	406	to reply to it.
366	407	<li>The state is packaged and subject to (atom) garbage collection.
367	408	<li>The state may be accessed from multiple threads. Access to the state

373	414	typical update loop for maintaining state inside an engine: fetch a
374	415	command, update the state, yield with the reply and call the updater
375	416	recursively. The update step is guarded against failure. For robustness
376		one may also guard it against exceptions using <a name="idx:catch3:1978"></a><a class="pred" href="exception.html#catch/3">catch/3</a>.
	417	one may also guard it against exceptions using <a id="idx:catch3:1982"></a><a class="pred" href="exception.html#catch/3">catch/3</a>.
377	418	Note that heap_get/2 passes the <var>Priority</var> and <var>Key</var>
378	419	it wishes to delete from the heap such that if the unification fails,
379	420	the heap remains unchanged.

412	453	engine_post(E, get(Priority, Key), Priority-Key).
413	454	</pre>
414	455
415		<p><h3 id="sec:engine-agents"><a name="sec:10.1.3"><span class="sec-nr">10.1.3</span> <span class="sec-title">Scalable
	456	<p><h3 id="sec:engine-agents"><a id="sec:10.1.3"><span class="sec-nr">10.1.3</span> <span class="sec-title">Scalable
416	457	many-agent applications</span></a></h3>
417	458
418		<a name="sec:engine-agents"></a>
	459	<a id="sec:engine-agents"></a>
419	460
420	461	<p>The final application area we touch are agent systems were we wish to
421	462	capture an agent in a Prolog goal. Such systems can be implemented using
422		threads (see <a class="sec" href="threads.html">section 9</a>) that use <a name="idx:threadsendmessage2:1979"></a><a class="pred" href="threadcom.html#thread_send_message/2">thread_send_message/2</a>
	463	threads (see <a class="sec" href="threads.html#sec:9">section 9</a>)
	464	that use <a id="idx:threadsendmessage2:1983"></a><a class="pred" href="threadcom.html#thread_send_message/2">thread_send_message/2</a>
423	465	and
424		<a name="idx:threadgetmessage1:1980"></a><a class="pred" href="threadcom.html#thread_get_message/1">thread_get_message/1</a>
	466	<a id="idx:threadgetmessage1:1984"></a><a class="pred" href="threadcom.html#thread_get_message/1">thread_get_message/1</a>
425	467	to communicate. The main problem is that each thread is associated by an
426	468	operating system thread. OS threads are, depending on the OS, relatively
427	469	expensive. Scalability of this design typically ends, depending on OS

430	472	<p>Engines provide an alternative. A detached Prolog engine currently
431	473	requires approximately 20 Kbytes memory on 64 bit hardware,
432	474	growing with the size of the Prolog stacks. The Prolog stacks may be
433		minimised by calling <a name="idx:garbagecollect0:1981"></a><a class="pred" href="memory.html#garbage_collect/0">garbage_collect/0</a>
434		followed by <a name="idx:trimstacks0:1982"></a><a class="pred" href="memory.html#trim_stacks/0">trim_stacks/0</a>,
	475	minimised by calling <a id="idx:garbagecollect0:1985"></a><a class="pred" href="memory.html#garbage_collect/0">garbage_collect/0</a>
	476	followed by <a id="idx:trimstacks0:1986"></a><a class="pred" href="memory.html#trim_stacks/0">trim_stacks/0</a>,
435	477	providing a
436	478	<em>deep sleep</em> mode. The set of agents, each represented by an
437	479	engine can be controlled by a static or dynamic pool of threads.

441	483	<blockquote> This section needs an example. Preferably something that
442	484	fits on one page and would not scale using threads. Engines might work
443	485	nice to implement <i>Antrank: An ant colony algorithm for ranking web
444		pages</i>.<sup class="fn">166<span class="fn-text"><a class="url" href="http://www.ijettcs.org/Volume3Issue2/IJETTCS-2014-04-23-113.pdf">http://www.ijettcs.org/Volume3Issue2/IJETTCS-2014-04-23-113.pdf</a></span></sup>
	486	pages</i>.<sup class="fn">167<span class="fn-text"><a class="url" href="http://www.ijettcs.org/Volume3Issue2/IJETTCS-2014-04-23-113.pdf">http://www.ijettcs.org/Volume3Issue2/IJETTCS-2014-04-23-113.pdf</a></span></sup>
445	487	</blockquote>
446	488
447	489	<p></body></html>⏎

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193	234	</div>
194		<h2 id="sec:engine-predicates"><a name="sec:10.3"><span class="sec-nr">10.3</span> <span class="sec-title">Engine
	235	<h2 id="sec:engine-predicates"><a id="sec:10.3"><span class="sec-nr">10.3</span> <span class="sec-title">Engine
195	236	predicate reference</span></a></h2>
196	237
197		<a name="sec:engine-predicates"></a>
	238	<a id="sec:engine-predicates"></a>
198	239
199	240	<p>This section documents the built-in predicates that deal with
200	241	engines. In addition to these, most predicates dealing with threads and
201	242	message queue can be used to access engines.
202	243
203	244	<dl class="latex">
204		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_create/3"><strong>engine_create</strong>(<var>+Template,
	245	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_create/3"><strong>engine_create</strong>(<var>+Template,
205	246	:Goal, ?Engine</var>)</a></dt>
206		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_create/4"><strong>engine_create</strong>(<var>+Template,
	247	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_create/4"><strong>engine_create</strong>(<var>+Template,
207	248	:Goal, -Engine, +Options</var>)</a></dt>
208	249	<dd class="defbody">
209	250	Create a new engine and unify <var>Engine</var> with a handle to it.
210		<var>Template</var> and <var>Goal</var> form a pair similar to <a name="idx:findall3:1990"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>:
211		the instantiation of <var>Template</var> becomes available though <a name="idx:enginenext2:1991"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>
	251	<var>Template</var> and <var>Goal</var> form a pair similar to <a id="idx:findall3:1994"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>:
	252	the instantiation of <var>Template</var> becomes available though <a id="idx:enginenext2:1995"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>
212	253	after <var>Goal</var> succeeds. <var>Options</var> is a list of the
213		following options. See <a name="idx:threadcreate3:1992"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>
	254	following options. See <a id="idx:threadcreate3:1996"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>
214	255	for details.
215	256
216	257	<dl class="latex">

234	275	</dd>
235	276	</dl>
236	277
237		The <var>Engine</var> argument of <a name="idx:enginecreate3:1993"></a><a class="pred" href="engine-predicates.html#engine_create/3">engine_create/3</a>
	278	The <var>Engine</var> argument of <a id="idx:enginecreate3:1997"></a><a class="pred" href="engine-predicates.html#engine_create/3">engine_create/3</a>
238	279	may be instantiated to an atom, creating an engine with the given alias.</dd>
239		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_destroy/1"><strong>engine_destroy</strong>(<var>+Engine</var>)</a></dt>
	280	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_destroy/1"><strong>engine_destroy</strong>(<var>+Engine</var>)</a></dt>
240	281	<dd class="defbody">
241	282	Destroy <var>Engine</var>.</dd>
242		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="engine_next/2"><strong>engine_next</strong>(<var>+Engine,
	283	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="engine_next/2"><strong>engine_next</strong>(<var>+Engine,
243	284	-Term</var>)</a></dt>
244	285	<dd class="defbody">
245	286	Ask the engine <var>Engine</var> to produce a next answer. On this first
246	287	call on a specific engine, the <var>Goal</var> of the engine is started.
247	288	If a previous call returned an answer through completion, this causes
248	289	the engine to backtrack and finally, if the engine produces a previous
249		result using <a name="idx:engineyield1:1994"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>,
250		execution proceeds after the <a name="idx:engineyield1:1995"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
	290	result using <a id="idx:engineyield1:1998"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>,
	291	execution proceeds after the <a id="idx:engineyield1:1999"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
251	292	call.</dd>
252		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_next_reified/2"><strong>engine_next_reified</strong>(<var>+Engine,
	293	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_next_reified/2"><strong>engine_next_reified</strong>(<var>+Engine,
253	294	-Term</var>)</a></dt>
254	295	<dd class="defbody">
255		Similar to <a name="idx:enginenext2:1996"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>,
	296	Similar to <a id="idx:enginenext2:2000"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>,
256	297	but instead of success, failure or or raising an exception, <var>Term</var>
257	298	is unified with one of terms below. This predicate is provided primarily
258	299	for compatibility with Lean Prolog.

274	315	</dl>
275	316
276	317	</dd>
277		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_post/2"><strong>engine_post</strong>(<var>+Engine,
	318	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_post/2"><strong>engine_post</strong>(<var>+Engine,
278	319	+Term</var>)</a></dt>
279	320	<dd class="defbody">
280		Make <var>Term</var> available to <a name="idx:enginefetch1:1997"></a><a class="pred" href="engine-predicates.html#engine_fetch/1">engine_fetch/1</a>
281		inside the <var>Engine</var>. This call must be followed by a call to <a name="idx:enginenext2:1998"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>
282		and the engine must call <a name="idx:enginefetch1:1999"></a><a class="pred" href="engine-predicates.html#engine_fetch/1">engine_fetch/1</a>.</dd>
283		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_post/3"><strong>engine_post</strong>(<var>+Engine,
	321	Make <var>Term</var> available to <a id="idx:enginefetch1:2001"></a><a class="pred" href="engine-predicates.html#engine_fetch/1">engine_fetch/1</a>
	322	inside the <var>Engine</var>. This call must be followed by a call to <a id="idx:enginenext2:2002"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>
	323	and the engine must call <a id="idx:enginefetch1:2003"></a><a class="pred" href="engine-predicates.html#engine_fetch/1">engine_fetch/1</a>.</dd>
	324	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_post/3"><strong>engine_post</strong>(<var>+Engine,
284	325	+Term, -Reply</var>)</a></dt>
285	326	<dd class="defbody">
286		Combines <a name="idx:enginepost2:2000"></a><a class="pred" href="engine-predicates.html#engine_post/2">engine_post/2</a>
287		and <a name="idx:enginenext2:2001"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>.</dd>
288		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_yield/1"><strong>engine_yield</strong>(<var>+Term</var>)</a></dt>
289		<dd class="defbody">
290		Called from within the engine, causing <a name="idx:enginenext2:2002"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>
291		in the caller to return with <var>Term</var>. A subsequent call to <a name="idx:enginenext2:2003"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>
	327	Combines <a id="idx:enginepost2:2004"></a><a class="pred" href="engine-predicates.html#engine_post/2">engine_post/2</a>
	328	and <a id="idx:enginenext2:2005"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>.</dd>
	329	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_yield/1"><strong>engine_yield</strong>(<var>+Term</var>)</a></dt>
	330	<dd class="defbody">
	331	Called from within the engine, causing <a id="idx:enginenext2:2006"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>
	332	in the caller to return with <var>Term</var>. A subsequent call to <a id="idx:enginenext2:2007"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>
292	333	causes
293		<a name="idx:engineyield1:2004"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
	334	<a id="idx:engineyield1:2008"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
294	335	to `return'. This predicate can only be called if the engine is not
295	336	involved in a callback from C, i.e., when the engine calls a predicate
296	337	defined in C that calls back Prolog it is not possible to use this
297	338	predicate. Trying to do so results in a
298	339	<code>permission_error</code> exception.</dd>
299		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_fetch/1"><strong>engine_fetch</strong>(<var>-Term</var>)</a></dt>
	340	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_fetch/1"><strong>engine_fetch</strong>(<var>-Term</var>)</a></dt>
300	341	<dd class="defbody">
301	342	Called from within the engine to fetch the term made available through
302		<a name="idx:enginepost2:2005"></a><a class="pred" href="engine-predicates.html#engine_post/2">engine_post/2</a>
303		or <a name="idx:enginepost3:2006"></a><a class="pred" href="engine-predicates.html#engine_post/3">engine_post/3</a>.
	343	<a id="idx:enginepost2:2009"></a><a class="pred" href="engine-predicates.html#engine_post/2">engine_post/2</a>
	344	or <a id="idx:enginepost3:2010"></a><a class="pred" href="engine-predicates.html#engine_post/3">engine_post/3</a>.
304	345	If no term is available an existence_error exception is raised.</dd>
305		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="engine_self/1"><strong>engine_self</strong>(<var>-Engine</var>)</a></dt>
	346	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="engine_self/1"><strong>engine_self</strong>(<var>-Engine</var>)</a></dt>
306	347	<dd class="defbody">
307	348	Called from within the engine to get access to the handle to the engine
308	349	itself.</dd>
309		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="is_engine/1"><strong>is_engine</strong>(<var>@Term</var>)</a></dt>
	350	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="is_engine/1"><strong>is_engine</strong>(<var>@Term</var>)</a></dt>
310	351	<dd class="defbody">
311	352	True if <var>Term</var> is a reference to or the alias name of an
312	353	existing engine.</dd>
313		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_engine/1"><strong>current_engine</strong>(<var>-Engine</var>)</a></dt>
	354	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_engine/1"><strong>current_engine</strong>(<var>-Engine</var>)</a></dt>
314	355	<dd class="defbody">
315	356	True when <var>Engine</var> is an existing engine.
316	357	</dd>

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193	234	</div>
194		<h2 id="sec:engine-resources"><a name="sec:10.2"><span class="sec-nr">10.2</span> <span class="sec-title">Engine
	235	<h2 id="sec:engine-resources"><a id="sec:10.2"><span class="sec-nr">10.2</span> <span class="sec-title">Engine
195	236	resource usage</span></a></h2>
196	237
197		<a name="sec:engine-resources"></a>
	238	<a id="sec:engine-resources"></a>
198	239
199	240	<p>A Prolog engine consists of a virtual machine state that includes the
200	241	Prolog stacks. An `empty' engine requires aout 20 KBytes of memory.
201	242	This grows when the engine requires additional stack space. Anonymous
202		engines are subject to atom garbage collection (see <a name="idx:garbagecollectatoms0:1983"></a><a class="pred" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a>).
203		Engines may be reclaimed immediately using <a name="idx:enginedestroy1:1984"></a><a class="pred" href="engine-predicates.html#engine_destroy/1">engine_destroy/1</a>.
	243	engines are subject to atom garbage collection (see <a id="idx:garbagecollectatoms0:1987"></a><a class="pred" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a>).
	244	Engines may be reclaimed immediately using <a id="idx:enginedestroy1:1988"></a><a class="pred" href="engine-predicates.html#engine_destroy/1">engine_destroy/1</a>.
204	245	Calling
205		<a name="idx:enginedestroy1:1985"></a><a class="pred" href="engine-predicates.html#engine_destroy/1">engine_destroy/1</a>
	246	<a id="idx:enginedestroy1:1989"></a><a class="pred" href="engine-predicates.html#engine_destroy/1">engine_destroy/1</a>
206	247	destroys the virtual machine state, while the handle itself is left to
207	248	atom garbage collection. The virtual machine is reclaimed as soon as an
208	249	engine produced its last result, failed or raised an exception. This
209	250	implies that it is only advantageous to call
210		<a name="idx:enginedestroy1:1986"></a><a class="pred" href="engine-predicates.html#engine_destroy/1">engine_destroy/1</a>
	251	<a id="idx:enginedestroy1:1990"></a><a class="pred" href="engine-predicates.html#engine_destroy/1">engine_destroy/1</a>
211	252	explicitly if you are not interested in further answers.
212	253
213	254	<p>Engines that are expected to be left in inactive state for a
214		prelonged time can be minimized by calling <a name="idx:garbagecollect0:1987"></a><a class="pred" href="memory.html#garbage_collect/0">garbage_collect/0</a>
215		and <a name="idx:trimmstacks0:1988"></a><span class="pred-ext">trimm_stacks/0</span>
216		(in that order) before calling <a name="idx:engineyield1:1989"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
	255	prelonged time can be minimized by calling <a id="idx:garbagecollect0:1991"></a><a class="pred" href="memory.html#garbage_collect/0">garbage_collect/0</a>
	256	and <a id="idx:trimmstacks0:1992"></a><span class="pred-ext">trimm_stacks/0</span>
	257	(in that order) before calling <a id="idx:engineyield1:1993"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
217	258	or succeeding.
218	259
219	260	<p></body></html>⏎

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193	234	</div>
194		<h1 id="sec:engines"><a name="sec:10"><span class="sec-nr">10</span> <span class="sec-title">Coroutining
	235	<h1 id="sec:engines"><a id="sec:10"><span class="sec-nr">10</span> <span class="sec-title">Coroutining
195	236	using Prolog engines</span></a></h1>
196	237
197		<a name="sec:engines"></a>
	238	<a id="sec:engines"></a>
198	239
199	240	<p>Where the term <em>coroutine</em> in Prolog typically refer to hooks
200		triggered by <em>attributed variables</em> (<a class="sec" href="attvar.html">section
	241	triggered by <em>attributed variables</em> (<a class="sec" href="attvar.html#sec:7.1">section
201	242	7.1</a>), SWI-Prolog provides two other forms of coroutines. Delimited
202	243	continuations (see
203		<a class="sec" href="delcont.html">section 4.10</a>) allow creating
204		coroutines that run in the same Prolog engine by capturing and
	244	<a class="sec" href="delcont.html#sec:4.10">section 4.10</a>) allow
	245	creating coroutines that run in the same Prolog engine by capturing and
205	246	restarting the <em>continuation</em>. This section discusses <em>engines</em>,
206	247	also known as <em>interactors</em>. The idea was pinned by Paul Tarau <cite><a class="cite" href="Bibliography.html#DBLP:conf/coordination/Tarau11">Tarau,
207	248	2011</a></cite>. The API described in this chapter has been established
208	249	together with Paul Tarau and Paulo Moura.
209	250
210		<p>Engines are closely related to <em>threads</em> (<a class="sec" href="threads.html">section
	251	<p>Engines are closely related to <em>threads</em> (<a class="sec" href="threads.html#sec:9">section
211	252	9</a>). An engine is a Prolog virtual machine that has its own stacks
212	253	and (virtual) machine state. Unlike normal Prolog threads though, they
213	254	are not associated with an operating system thread. Instead, you <em>ask</em>
214		an engine for a next answer (<a name="idx:enginenext2:1963"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>).
	255	an engine for a next answer (<a id="idx:enginenext2:1967"></a><a class="pred" href="engine-predicates.html#engine_next/2">engine_next/2</a>).
215	256	Asking an engine for the next answer attaches the engine to the calling
216		operating system thread and cause it to run until the engine calls <a name="idx:engineyield1:1964"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
	257	operating system thread and cause it to run until the engine calls <a id="idx:engineyield1:1968"></a><a class="pred" href="engine-predicates.html#engine_yield/1">engine_yield/1</a>
217	258	or its associated goal completes with an answer, failure or an
218	259	exception. After the engine yields or completes, it is detached from the
219	260	operating system thread and the answer term is made available to the

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191	232	<a class="nav" href="debug.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:error"><a name="sec:A.12"><span class="sec-nr">A.12</span> <span class="sec-title">library(error):
	235	<h2 id="sec:error"><a id="sec:A.12"><span class="sec-nr">A.12</span> <span class="sec-title">library(error):
195	236	Error generating support</span></a></h2>
196	237
197		<p><a name="sec:error"></a>
	238	<p><a id="sec:error"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="mtag">author</dt>

219	260	to simplify throwing the most common ISO error terms.
220	261
221	262	<dl class="latex">
222		<dt class="pubdef"><a name="type_error/2"><strong>type_error</strong>(<var>+Type,
	263	<dt class="pubdef"><a id="type_error/2"><strong>type_error</strong>(<var>+Type,
223	264	+Term</var>)</a></dt>
224	265	<dd class="defbody">
225	266	Tell the user that <var>Term</var> is not of the expected <var>Type</var>.

236	277	compound-term and any other compound term is a domain error. Most Prolog
237	278	programmers consider each compound as a type and would consider a
238	279	compoint that is not <code>point(_,_)</code> a <i>type_error</i>.</dd>
239		<dt class="pubdef"><a name="domain_error/2"><strong>domain_error</strong>(<var>+Type,
	280	<dt class="pubdef"><a id="domain_error/2"><strong>domain_error</strong>(<var>+Type,
240	281	+Term</var>)</a></dt>
241	282	<dd class="defbody">
242	283	The argument is of the proper type, but has a value that is outside the
243	284	supported values. See <a class="pred" href="error.html#type_error/2">type_error/2</a>
244	285	for a more elaborate discussion of the distinction between type- and
245	286	domain-errors.</dd>
246		<dt class="pubdef"><a name="existence_error/2"><strong>existence_error</strong>(<var>+Type,
	287	<dt class="pubdef"><a id="existence_error/2"><strong>existence_error</strong>(<var>+Type,
247	288	+Term</var>)</a></dt>
248	289	<dd class="defbody">
249	290	<var>Term</var> is of the correct type and correct domain, but there is
250	291	no existing (external) resource that is represented by it.</dd>
251		<dt class="pubdef"><a name="permission_error/3"><strong>permission_error</strong>(<var>+Action,
	292	<dt class="pubdef"><a id="permission_error/3"><strong>permission_error</strong>(<var>+Action,
252	293	+Type, +Term</var>)</a></dt>
253	294	<dd class="defbody">
254	295	It is not allowed to perform <var>Action</var> on the object <var>Term</var>
255	296	that is of the given <var>Type</var>.</dd>
256		<dt class="pubdef"><a name="instantiation_error/1"><strong>instantiation_error</strong>(<var>+Term</var>)</a></dt>
	297	<dt class="pubdef"><a id="instantiation_error/1"><strong>instantiation_error</strong>(<var>+Term</var>)</a></dt>
257	298	<dd class="defbody">
258	299	An argument is under-instantiated. I.e. it is not acceptable as it is,
259	300	but if some variables are bound to appropriate values it would be
260	301	acceptable.
261	302	<table class="arglist">
262		<tr valign="top"><td><var>Term</var> </td><td>is the term that needs
263		(further) instantiation. Unfortunately, the ISO error does not allow for
264		passing this term along with the error, but we pass it to this predicate
265		for documentation purposes and to allow for future enhancement. </td></tr>
	303	<tr><td><var>Term</var> </td><td>is the term that needs (further)
	304	instantiation. Unfortunately, the ISO error does not allow for passing
	305	this term along with the error, but we pass it to this predicate for
	306	documentation purposes and to allow for future enhancement. </td></tr>
266	307	</table>
267	308	</dd>
268		<dt class="pubdef"><a name="uninstantiation_error/1"><strong>uninstantiation_error</strong>(<var>+Term</var>)</a></dt>
	309	<dt class="pubdef"><a id="uninstantiation_error/1"><strong>uninstantiation_error</strong>(<var>+Term</var>)</a></dt>
269	310	<dd class="defbody">
270	311	An argument is over-instantiated. This error is used for output
271	312	arguments whose value cannot be known upfront. For example, the goal <code>open(File, read, input)</code>
272	313	cannot succeed because the system will allocate a new unique stream
273	314	handle that will never unify with <code>input</code>.</dd>
274		<dt class="pubdef"><a name="representation_error/1"><strong>representation_error</strong>(<var>+Reason</var>)</a></dt>
	315	<dt class="pubdef"><a id="representation_error/1"><strong>representation_error</strong>(<var>+Reason</var>)</a></dt>
275	316	<dd class="defbody">
276	317	A representation error indicates a limitation of the implementation.
277	318	SWI-Prolog has no such limits that are not covered by other errors, but
278	319	an example of a representation error in another Prolog implementation
279	320	could be an attempt to create a term with an arity higher than supported
280	321	by the system.</dd>
281		<dt class="pubdef"><a name="syntax_error/1"><strong>syntax_error</strong>(<var>+Culprit</var>)</a></dt>
	322	<dt class="pubdef"><a id="syntax_error/1"><strong>syntax_error</strong>(<var>+Culprit</var>)</a></dt>
282	323	<dd class="defbody">
283	324	A text has invalid syntax. The error is described by <var>Culprit</var>.
284	325

292	333	</dl>
293	334
294	335	</dd>
295		<dt class="pubdef"><a name="resource_error/1"><strong>resource_error</strong>(<var>+Culprit</var>)</a></dt>
	336	<dt class="pubdef"><a id="resource_error/1"><strong>resource_error</strong>(<var>+Culprit</var>)</a></dt>
296	337	<dd class="defbody">
297	338	A goal cannot be completed due to lack of resources.</dd>
298		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="must_be/2"><strong>must_be</strong>(<var>+Type,
	339	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="must_be/2"><strong>must_be</strong>(<var>+Type,
299	340	@Term</var>)</a></dt>
300	341	<dd class="defbody">
301	342	True if <var>Term</var> satisfies the type constraints for <var>Type</var>.

309	350	<p>Most of these types are defined by an arity-1 built-in predicate of
310	351	the same name. Below is a brief definition of the other types.
311	352	<blockquote>
312		<table border="2" frame="box" rules="groups">
313		<tr valign="top"><td>acyclic</td><td>Acyclic term (tree); see <a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a> </td></tr>
314		<tr valign="top"><td>any</td></tr>
315		<tr valign="top"><td><code>between(FloatL,FloatU)</code> </td><td>Number
	353	<table class="latex frame-box">
	354	<tr><td>acyclic</td><td>Acyclic term (tree); see <a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a> </td></tr>
	355	<tr><td>any</td></tr>
	356	<tr><td><code>between(FloatL,FloatU)</code> </td><td>Number
316	357	[FloatL..FloatU] </td></tr>
317		<tr valign="top"><td><code>between(IntL,IntU)</code> </td><td>Integer
318		[IntL..IntU] </td></tr>
319		<tr valign="top"><td>boolean</td><td>One of <code>true</code> or <code>false</code> </td></tr>
320		<tr valign="top"><td>char</td><td>Atom of length 1 </td></tr>
321		<tr valign="top"><td>chars</td><td>Proper list of 1-character atoms </td></tr>
322		<tr valign="top"><td>code</td><td>Representation Unicode code point </td></tr>
323		<tr valign="top"><td>codes</td><td>Proper list of Unicode character
324		codes </td></tr>
325		<tr valign="top"><td>constant</td><td>Same as <code>atomic</code> </td></tr>
326		<tr valign="top"><td>cyclic</td><td>Cyclic term (rational tree); see <a class="pred" href="typetest.html#cyclic_term/1">cyclic_term/1</a> </td></tr>
327		<tr valign="top"><td>dict</td><td>A dictionary term; see <a class="pred" href="dicts.html#is_dict/1">is_dict/1</a> </td></tr>
328		<tr valign="top"><td>encoding</td><td>Valid name for a character
329		encoding; see <span class="pred-ext">current_encoding/1</span> </td></tr>
330		<tr valign="top"><td>list</td><td>A (non-open) list; see <a class="pred" href="builtinlist.html#is_list/1">is_list/1</a> </td></tr>
331		<tr valign="top"><td>negative_integer</td><td>Integer <var><</var> 0 </td></tr>
332		<tr valign="top"><td>nonneg</td><td>Integer <code>>=</code> 0 </td></tr>
333		<tr valign="top"><td><code>oneof(L)</code> </td><td>Ground term that is
334		member of L </td></tr>
335		<tr valign="top"><td>positive_integer</td><td>Integer <var>></var> 0 </td></tr>
336		<tr valign="top"><td>proper_list</td><td>Same as list </td></tr>
337		<tr valign="top"><td><code>list(Type)</code> </td><td>Proper list with
338		elements of <var>Type</var> </td></tr>
339		<tr valign="top"><td>list_or_partial_list</td><td>A list or an open list
340		(ending in a variable); see <span class="pred-ext">is_list_or_partial_list/1</span> </td></tr>
341		<tr valign="top"><td>stream</td><td>A stream name or valid stream
342		handle; see <a class="pred" href="IO.html#is_stream/1">is_stream/1</a> </td></tr>
343		<tr valign="top"><td>symbol</td><td>Same as <code>atom</code> </td></tr>
344		<tr valign="top"><td>text</td><td>One of <code>atom</code>, <code>string</code>, <code>chars</code>
	358	<tr><td><code>between(IntL,IntU)</code> </td><td>Integer [IntL..IntU] </td></tr>
	359	<tr><td>boolean</td><td>One of <code>true</code> or <code>false</code> </td></tr>
	360	<tr><td>char</td><td>Atom of length 1 </td></tr>
	361	<tr><td>chars</td><td>Proper list of 1-character atoms </td></tr>
	362	<tr><td>code</td><td>Representation Unicode code point </td></tr>
	363	<tr><td>codes</td><td>Proper list of Unicode character codes </td></tr>
	364	<tr><td>constant</td><td>Same as <code>atomic</code> </td></tr>
	365	<tr><td>cyclic</td><td>Cyclic term (rational tree); see <a class="pred" href="typetest.html#cyclic_term/1">cyclic_term/1</a> </td></tr>
	366	<tr><td>dict</td><td>A dictionary term; see <a class="pred" href="dicts.html#is_dict/1">is_dict/1</a> </td></tr>
	367	<tr><td>encoding</td><td>Valid name for a character encoding; see <span class="pred-ext">current_encoding/1</span> </td></tr>
	368	<tr><td>list</td><td>A (non-open) list; see <a class="pred" href="builtinlist.html#is_list/1">is_list/1</a> </td></tr>
	369	<tr><td>negative_integer</td><td>Integer <var><</var> 0 </td></tr>
	370	<tr><td>nonneg</td><td>Integer <code>>=</code> 0 </td></tr>
	371	<tr><td><code>oneof(L)</code> </td><td>Ground term that is member of L </td></tr>
	372	<tr><td>positive_integer</td><td>Integer <var>></var> 0 </td></tr>
	373	<tr><td>proper_list</td><td>Same as list </td></tr>
	374	<tr><td><code>list(Type)</code> </td><td>Proper list with elements of <var>Type</var> </td></tr>
	375	<tr><td>list_or_partial_list</td><td>A list or an open list (ending in a
	376	variable); see <span class="pred-ext">is_list_or_partial_list/1</span> </td></tr>
	377	<tr><td>stream</td><td>A stream name or valid stream handle; see <a class="pred" href="IO.html#is_stream/1">is_stream/1</a> </td></tr>
	378	<tr><td>symbol</td><td>Same as <code>atom</code> </td></tr>
	379	<tr><td>text</td><td>One of <code>atom</code>, <code>string</code>, <code>chars</code>
345	380	or <code>codes</code> </td></tr>
346	381	</table>
347	382	</blockquote>

359	394	</dl>
360	395
361	396	</dd>
362		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="is_of_type/2"><strong>is_of_type</strong>(<var>+Type,
	397	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="is_of_type/2"><strong>is_of_type</strong>(<var>+Type,
363	398	@Term</var>)</a></dt>
364	399	<dd class="defbody">
365	400	True if <var>Term</var> satisfies <var>Type</var>.</dd>
366		<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a name="has_type/2"><strong>has_type</strong>(<var>+Type,
	401	<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="has_type/2"><strong>has_type</strong>(<var>+Type,
367	402	@Term</var>)</a></dt>
368	403	<dd class="defbody">
369	404	True if <var>Term</var> satisfies <var>Type</var>.</dd>
370		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_type/3"><strong>current_type</strong>(<var>?Type,
	405	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_type/3"><strong>current_type</strong>(<var>?Type,
371	406	@Var, -Body</var>)</a></dt>
372	407	<dd class="defbody">
373	408	True when <var>Type</var> is a currently defined type and <var>Var</var>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 8.8</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:errors"><a name="sec:8.8"><span class="sec-nr">8.8</span> <span class="sec-title">Compiler
	235	<h2 id="sec:errors"><a id="sec:8.8"><span class="sec-nr">8.8</span> <span class="sec-title">Compiler
195	236	Errors and Warnings</span></a></h2>
196	237
197		<a name="sec:errors"></a> In this section we summarize the most
198		important error and warning messages of the CHR compiler.
199
200		<p><h3 id="sec:chr-errors"><a name="sec:8.8.1"><span class="sec-nr">8.8.1</span> <span class="sec-title">CHR
	238	<a id="sec:errors"></a> In this section we summarize the most important
	239	error and warning messages of the CHR compiler.
	240
	241	<p><h3 id="sec:chr-errors"><a id="sec:8.8.1"><span class="sec-nr">8.8.1</span> <span class="sec-title">CHR
201	242	Compiler Errors</span></a></h3>
202	243
203		<a name="sec:chr-errors"></a>
	244	<a id="sec:chr-errors"></a>
204	245
205	246	<dl class="latex">
206	247	<dt><b>Type clash</b></dt>

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	216
	217	table.latex tr.hline td,th
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184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="dynamic.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="IO.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:examineprog"><a name="sec:4.16"><span class="sec-nr">4.16</span> <span class="sec-title">Examining
	235	<h2 id="sec:examineprog"><a id="sec:4.16"><span class="sec-nr">4.16</span> <span class="sec-title">Examining
195	236	the program</span></a></h2>
196	237
197		<a name="sec:examineprog"></a>
	238	<a id="sec:examineprog"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="current_atom/1"><strong>current_atom</strong>(<var>-Atom</var>)</a></dt>
	241	<dt class="pubdef"><a id="current_atom/1"><strong>current_atom</strong>(<var>-Atom</var>)</a></dt>
201	242	<dd class="defbody">
202	243	Successively unifies <var>Atom</var> with all atoms known to the system.
203		Note that <a name="idx:currentatom1:895"></a><a class="pred" href="examineprog.html#current_atom/1">current_atom/1</a>
	244	Note that <a id="idx:currentatom1:895"></a><a class="pred" href="examineprog.html#current_atom/1">current_atom/1</a>
204	245	always succeeds if <var>Atom</var> is instantiated to an atom.</dd>
205		<dt class="pubdef"><a name="current_blob/2"><strong>current_blob</strong>(<var>?Blob,
	246	<dt class="pubdef"><a id="current_blob/2"><strong>current_blob</strong>(<var>?Blob,
206	247	?Type</var>)</a></dt>
207	248	<dd class="defbody">
208	249	Examine the type or enumerate blobs of the given <var>Type</var>. Typed
209	250	blobs are supported through the foreign language interface for storing
210	251	arbitrary BLOBs (Binary Large Object) or handles to external entities.
211		See <a class="sec" href="foreigninclude.html">section 11.4.7</a> for
212		details.</dd>
213		<dt class="pubdef"><a name="current_functor/2"><strong>current_functor</strong>(<var>?Name,
	252	See <a class="sec" href="foreigninclude.html#sec:11.4.7">section 11.4.7</a>
	253	for details.</dd>
	254	<dt class="pubdef"><a id="current_functor/2"><strong>current_functor</strong>(<var>?Name,
214	255	?Arity</var>)</a></dt>
215	256	<dd class="defbody">
216	257	True when <var>Name</var>/<var>Arity</var> is a known functor. This

219	260	garbage collection. Due to timing, t/2 below with instantiated
220	261	<var>Name</var> and <var>Arity</var> can theoretically fail, i.e., a
221	262	functor may be visible in instantiated mode while it is not yet visible
222		in unbound mode. Considering that the only practical value of <a name="idx:currentfunctor2:896"></a><a class="pred" href="examineprog.html#current_functor/2">current_functor/2</a>
	263	in unbound mode. Considering that the only practical value of <a id="idx:currentfunctor2:896"></a><a class="pred" href="examineprog.html#current_functor/2">current_functor/2</a>
223	264	we are aware of is to analyse resource usage we accept this impure
224	265	behaviour.
225	266

232	273	</pre>
233	274
234	275	</dd>
235		<dt class="pubdef"><a name="current_flag/1"><strong>current_flag</strong>(<var>-FlagKey</var>)</a></dt>
	276	<dt class="pubdef"><a id="current_flag/1"><strong>current_flag</strong>(<var>-FlagKey</var>)</a></dt>
236	277	<dd class="defbody">
237	278	Successively unifies <var>FlagKey</var> with all keys used for flags
238	279	(see
239		<a name="idx:flag3:897"></a><a class="pred" href="db.html#flag/3">flag/3</a>).</dd>
240		<dt class="pubdef"><a name="current_key/1"><strong>current_key</strong>(<var>-Key</var>)</a></dt>
	280	<a id="idx:flag3:897"></a><a class="pred" href="db.html#flag/3">flag/3</a>).</dd>
	281	<dt class="pubdef"><a id="current_key/1"><strong>current_key</strong>(<var>-Key</var>)</a></dt>
241	282	<dd class="defbody">
242	283	Successively unifies <var>Key</var> with all keys used for records (see
243		<a name="idx:recorda3:898"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>,
	284	<a id="idx:recorda3:898"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>,
244	285	etc.).</dd>
245		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="current_predicate/1"><strong>current_predicate</strong>(<var>:PredicateIndicator</var>)</a></dt>
	286	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="current_predicate/1"><strong>current_predicate</strong>(<var>:PredicateIndicator</var>)</a></dt>
246	287	<dd class="defbody">
247	288	True if <var>PredicateIndicator</var> is a currently defined predicate.
248	289	A predicate is considered defined if it exists in the specified module,
249	290	is imported into the module or is defined in one of the modules from
250	291	which the predicate will be imported if it is called (see
251		<a class="sec" href="importmodule.html">section 6.9</a>). Note that <a name="idx:currentpredicate1:899"></a><a class="pred" href="examineprog.html#current_predicate/1">current_predicate/1</a>
	292	<a class="sec" href="importmodule.html#sec:6.9">section 6.9</a>). Note
	293	that <a id="idx:currentpredicate1:899"></a><a class="pred" href="examineprog.html#current_predicate/1">current_predicate/1</a>
252	294	does <em>not</em> succeed for predicates that can be <em>autoloaded</em>.
253	295	See also
254		<a name="idx:currentpredicate2:900"></a><a class="pred" href="examineprog.html#current_predicate/2">current_predicate/2</a>
255		and <a name="idx:predicateproperty2:901"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.
	296	<a id="idx:currentpredicate2:900"></a><a class="pred" href="examineprog.html#current_predicate/2">current_predicate/2</a>
	297	and <a id="idx:predicateproperty2:901"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.
256	298
257	299	<p>If <var>PredicateIndicator</var> is not fully specified, the
258	300	predicate only generates values that are defined in or already imported
259	301	into the target module. Generating all callable predicates therefore
260		requires enumerating modules using <a name="idx:currentmodule1:902"></a><a class="pred" href="manipmodule.html#current_module/1">current_module/1</a>.
	302	requires enumerating modules using <a id="idx:currentmodule1:902"></a><a class="pred" href="manipmodule.html#current_module/1">current_module/1</a>.
261	303	Generating predicates callable in a given module requires enumerating
262		the import modules using <a name="idx:importmodule2:903"></a><a class="pred" href="importmodule.html#import_module/2">import_module/2</a>
	304	the import modules using <a id="idx:importmodule2:903"></a><a class="pred" href="importmodule.html#import_module/2">import_module/2</a>
263	305	and the autoloadable predicates using the
264		<a name="idx:predicateproperty2:904"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a> <code>autoload</code>.</dd>
265		<dt class="pubdef"><a name="current_predicate/2"><strong>current_predicate</strong>(<var>?Name,
	306	<a id="idx:predicateproperty2:904"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a> <code>autoload</code>.</dd>
	307	<dt class="pubdef"><a id="current_predicate/2"><strong>current_predicate</strong>(<var>?Name,
266	308	:Head</var>)</a></dt>
267	309	<dd class="defbody">
268		Classical pre-ISO implementation of <a name="idx:currentpredicate1:905"></a><a class="pred" href="examineprog.html#current_predicate/1">current_predicate/1</a>,
	310	Classical pre-ISO implementation of <a id="idx:currentpredicate1:905"></a><a class="pred" href="examineprog.html#current_predicate/1">current_predicate/1</a>,
269	311	where the predicate is represented by the head term. The advantage is
270	312	that this can be used for checking the existence of a predicate before
271		calling it without the need for <a name="idx:functor3:906"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>:
	313	calling it without the need for <a id="idx:functor3:906"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>:
272	314
273	315	<pre class="code">
274	316	call_if_exists(G) :-

276	318	call(G).
277	319	</pre>
278	320
279		<p>Because of this intended usage, <a name="idx:currentpredicate2:907"></a><a class="pred" href="examineprog.html#current_predicate/2">current_predicate/2</a>
	321	<p>Because of this intended usage, <a id="idx:currentpredicate2:907"></a><a class="pred" href="examineprog.html#current_predicate/2">current_predicate/2</a>
280	322	also succeeds if the predicate can be autoloaded. Unfortunately,
281	323	checking the autoloader makes this predicate relatively slow, in
282	324	particular because a failed lookup of the autoloader will cause the
283	325	autoloader to verify that its index is up-to-date.</dd>
284		<dt class="pubdef"><a name="predicate_property/2"><strong>predicate_property</strong>(<var>:Head,
	326	<dt class="pubdef"><a id="predicate_property/2"><strong>predicate_property</strong>(<var>:Head,
285	327	?Property</var>)</a></dt>
286	328	<dd class="defbody">
287	329	True when <var>Head</var> refers to a predicate that has property
288	330	<var>Property</var>. With sufficiently instantiated <var>Head</var>,
289		<a name="idx:predicateproperty2:908"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
	331	<a id="idx:predicateproperty2:908"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
290	332	tries to resolve the predicate the same way as calling it would do: if
291		the predicate is not defined it scans the default modules (see <a name="idx:defaultmodule2:909"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>)
	333	the predicate is not defined it scans the default modules (see <a id="idx:defaultmodule2:909"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>)
292	334	and finally tries the autoloader. Unlike calling, failure to find the
293	335	target predicate causes
294		<a name="idx:predicateproperty2:910"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
	336	<a id="idx:predicateproperty2:910"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
295	337	to fail silently. If <var>Head</var> is not sufficiently bound, only
296	338	currently locally defined and already imported predicates are
297		enumerated. See <a name="idx:currentpredicate1:911"></a><a class="pred" href="examineprog.html#current_predicate/1">current_predicate/1</a>
	339	enumerated. See <a id="idx:currentpredicate1:911"></a><a class="pred" href="examineprog.html#current_predicate/1">current_predicate/1</a>
298	340	for enumerating all predicates. A common issue concerns <em>generating</em>
299	341	all built-in predicates. This can be achieved using the code below:
300	342

322	364	True if the predicate is defined. This property is aware of sources
323	365	being <em>reloaded</em>, in which case it claims the predicate defined
324	366	only if it is defined in another source or it has seen a definition in
325		the current source. See <a name="idx:compileauxclauses1:912"></a><a class="pred" href="consulting.html#compile_aux_clauses/1">compile_aux_clauses/1</a>.</dd>
	367	the current source. See <a id="idx:compileauxclauses1:912"></a><a class="pred" href="consulting.html#compile_aux_clauses/1">compile_aux_clauses/1</a>.</dd>
326	368	<dt><strong>dynamic</strong></dt>
327	369	<dd class="defbody">
328		True if <a name="idx:assert1:913"></a><a class="pred" href="db.html#assert/1">assert/1</a>
329		and <a name="idx:retract1:914"></a><a class="pred" href="db.html#retract/1">retract/1</a>
330		may be used to modify the predicate. This property is set using <a name="idx:dynamic1:915"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>.</dd>
	370	True if <a id="idx:assert1:913"></a><a class="pred" href="db.html#assert/1">assert/1</a>
	371	and <a id="idx:retract1:914"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	372	may be used to modify the predicate. This property is set using <a id="idx:dynamic1:915"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>.</dd>
331	373	<dt><strong>exported</strong></dt>
332	374	<dd class="defbody">
333	375	True if the predicate is in the public list of the context module.</dd>

337	379	<dt><strong>file</strong>(<var>FileName</var>)</dt>
338	380	<dd class="defbody">
339	381	Unify <var>FileName</var> with the name of the source file in which the
340		predicate is defined. See also <a name="idx:sourcefile2:916"></a><a class="pred" href="consulting.html#source_file/2">source_file/2</a>
	382	predicate is defined. See also <a id="idx:sourcefile2:916"></a><a class="pred" href="consulting.html#source_file/2">source_file/2</a>
341	383	and the property
342	384	<code>line_count</code>. Note that this reports the file of the first
343		clause of a predicate. A more robust interface can be achieved using <a name="idx:nthclause3:917"></a><a class="pred" href="examineprog.html#nth_clause/3">nth_clause/3</a>
344		and <a name="idx:clauseproperty2:918"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>.</dd>
	385	clause of a predicate. A more robust interface can be achieved using <a id="idx:nthclause3:917"></a><a class="pred" href="examineprog.html#nth_clause/3">nth_clause/3</a>
	386	and <a id="idx:clauseproperty2:918"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>.</dd>
345	387	<dt><strong>foreign</strong></dt>
346	388	<dd class="defbody">
347	389	True if the predicate is defined in the C language.</dd>

352	394	mechanism as when the an undefined predicate is encountered, but does
353	395	not perform any loading. It searches (1) the module inheritence
354	396	hierarchy (see
355		<a name="idx:defaultmodule2:919"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>)
	397	<a id="idx:defaultmodule2:919"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>)
356	398	and (2) the autoload index if the <a class="flag" href="flags.html#flag:unknown">unknown</a>
357	399	flag is not set to <code>fail</code> in the target module.</dd>
358	400	<dt><strong>indexed</strong>(<var>Indexes</var>)</dt>

381	423	<dd class="defbody">
382	424	Unify <var>LineNumber</var> with the line number of the first clause of
383	425	the predicate. Fails if the predicate is not associated with a file. See
384		also <a name="idx:sourcefile2:920"></a><a class="pred" href="consulting.html#source_file/2">source_file/2</a>.
385		See also the <code>file</code> property above, notably the reference to <a name="idx:clauseproperty2:921"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>.</dd>
	426	also <a id="idx:sourcefile2:920"></a><a class="pred" href="consulting.html#source_file/2">source_file/2</a>.
	427	See also the <code>file</code> property above, notably the reference to <a id="idx:clauseproperty2:921"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>.</dd>
386	428	<dt><strong>multifile</strong></dt>
387	429	<dd class="defbody">
388	430	True if there may be multiple (or no) files providing clauses for the
389		predicate. This property is set using <a name="idx:multifile1:922"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.</dd>
	431	predicate. This property is set using <a id="idx:multifile1:922"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.</dd>
390	432	<dt><strong>meta_predicate</strong>(<var>Head</var>)</dt>
391	433	<dd class="defbody">
392		If the predicate is declared as a meta-predicate using <a name="idx:metapredicate1:923"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>,
	434	If the predicate is declared as a meta-predicate using <a id="idx:metapredicate1:923"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>,
393	435	unify <var>Head</var> with the head-pattern. The head-pattern is a
394	436	compound term with the same name and arity as the predicate where each
395		argument of the term is a meta-predicate specifier. See <a name="idx:metapredicate1:924"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	437	argument of the term is a meta-predicate specifier. See <a id="idx:metapredicate1:924"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
396	438	for details.</dd>
397	439	<dt><strong>nodebug</strong></dt>
398	440	<dd class="defbody">

419	461	time. Intended to quickly assesses the validity of caches.</dd>
420	462	<dt><strong>public</strong></dt>
421	463	<dd class="defbody">
422		Predicate is declared public using <a name="idx:public1:925"></a><a class="pred" href="dynamic.html#public/1">public/1</a>.
	464	Predicate is declared public using <a id="idx:public1:925"></a><a class="pred" href="dynamic.html#public/1">public/1</a>.
423	465	Note that without further definition, public predicates are considered
424	466	undefined and this property is <em>not</em> reported.</dd>
425	467	<dt><strong>quasi_quotation_syntax</strong></dt>
426	468	<dd class="defbody">
427	469	The predicate (with arity 4) is declared to provide quasi quotation
428		syntax with <a name="idx:quasiquotationsyntax1:926"></a><a class="pred" href="quasiquotations.html#quasi_quotation_syntax/1">quasi_quotation_syntax/1</a>.</dd>
	470	syntax with <a id="idx:quasiquotationsyntax1:926"></a><a class="pred" href="quasiquotations.html#quasi_quotation_syntax/1">quasi_quotation_syntax/1</a>.</dd>
429	471	<dt><strong>static</strong></dt>
430	472	<dd class="defbody">
431		The definition can <em>not</em> be modified using <a name="idx:assertz1:927"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
	473	The definition can <em>not</em> be modified using <a id="idx:assertz1:927"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
432	474	and friends. This property is the opposite from <code>dynamic</code>,
433	475	i.e., for each defined predicate, either <code>static</code> or <code>dynamic</code>
434	476	is true but never both.</dd>

436	478	<dd class="defbody">
437	479	If true (only possible on the multithreaded version) each thread has its
438	480	own clauses for the predicate. This property is set using
439		<a name="idx:threadlocal1:928"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>.</dd>
	481	<a id="idx:threadlocal1:928"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>.</dd>
440	482	<dt><strong>transparent</strong></dt>
441	483	<dd class="defbody">
442	484	True if the predicate is declared transparent using the
443		<a name="idx:moduletransparent1:929"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>
444		or <a name="idx:metapredicate1:930"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	485	<a id="idx:moduletransparent1:929"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>
	486	or <a id="idx:metapredicate1:930"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
445	487	declaration. In the latter case the property <code>meta_predicate(Head)</code>
446		is also provided. See <a class="sec" href="modules.html">chapter 6</a>
	488	is also provided. See <a class="sec" href="modules.html#sec:6">chapter 6</a>
447	489	for details.</dd>
448	490	<dt><strong>undefined</strong></dt>
449	491	<dd class="defbody">

453	495	attempt to call it has been made via one of the meta-call predicates,
454	496	the predicate has been declared as e.g., a meta-predicate or the
455	497	predicate had a definition in the past. Originally used to find missing
456		predicate definitions. The current implementation of <a name="idx:listundefined0:931"></a><a class="pred" href="check.html#list_undefined/0">list_undefined/0</a>
	498	predicate definitions. The current implementation of <a id="idx:listundefined0:931"></a><a class="pred" href="check.html#list_undefined/0">list_undefined/0</a>
457	499	used cross-referencing. Deprecated.</dd>
458	500	<dt><strong>visible</strong></dt>
459	501	<dd class="defbody">
460	502	True when predicate can be called without raising a predicate existence
461	503	error. This means that the predicate is (1) defined, (2) can be
462		inherited from one of the default modules (see <a name="idx:defaultmodule2:932"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>)
	504	inherited from one of the default modules (see <a id="idx:defaultmodule2:932"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>)
463	505	or (3) can be autoloaded. The behaviour is logically consistent iff the
464	506	property
465	507	<code>visible</code> is provided explicitly. If the property is left
466	508	unbound, only defined predicates are enumerated.</dd>
467	509	<dt><strong>volatile</strong></dt>
468	510	<dd class="defbody">
469		If true, the clauses are not saved into a saved state by <a name="idx:qsaveprogram12:933"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>.
470		This property is set using <a name="idx:volatile1:934"></a><a class="pred" href="runtime.html#volatile/1">volatile/1</a>.
	511	If true, the clauses are not saved into a saved state by <a id="idx:qsaveprogram12:933"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>.
	512	This property is set using <a id="idx:volatile1:934"></a><a class="pred" href="runtime.html#volatile/1">volatile/1</a>.
471	513	</dd>
472	514	</dl>
473	515
474	516	</dd>
475		<dt class="pubdef"><a name="dwim_predicate/2"><strong>dwim_predicate</strong>(<var>+Term,
	517	<dt class="pubdef"><a id="dwim_predicate/2"><strong>dwim_predicate</strong>(<var>+Term,
476	518	-Dwim</var>)</a></dt>
477	519	<dd class="defbody">
478	520	`Do What I Mean' (`dwim') support predicate. <var>Term</var> is a term,

480	522	is instantiated with the most general term built from <var>Name</var>
481	523	and the arity of a defined predicate that matches the predicate
482	524	specified by
483		<var>Term</var> in the `Do What I Mean' sense. See <a name="idx:dwimmatch2:935"></a><a class="pred" href="miscpreds.html#dwim_match/2">dwim_match/2</a>
	525	<var>Term</var> in the `Do What I Mean' sense. See <a id="idx:dwimmatch2:935"></a><a class="pred" href="miscpreds.html#dwim_match/2">dwim_match/2</a>
484	526	for `Do What I Mean' string matching. Internal system predicates are not
485	527	generated, unless the access level is <code>system</code> (see
486	528	<a class="flag" href="flags.html#flag:access_level">access_level</a>).
487	529	Backtracking provides all alternative matches.</dd>
488		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="clause/2"><strong>clause</strong>(<var>:Head,
	530	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="clause/2"><strong>clause</strong>(<var>:Head,
489	531	?Body</var>)</a></dt>
490	532	<dd class="defbody">
491	533	True if <var>Head</var> can be unified with a clause head and <var>Body</var>
492	534	with the corresponding clause body. Gives alternative clauses on
493	535	backtracking. For facts, <var>Body</var> is unified with the atom <var>true</var>.</dd>
494		<dt class="pubdef"><a name="clause/3"><strong>clause</strong>(<var>:Head,
	536	<dt class="pubdef"><a id="clause/3"><strong>clause</strong>(<var>:Head,
495	537	?Body, ?Reference</var>)</a></dt>
496	538	<dd class="defbody">
497		Equivalent to <a name="idx:clause2:936"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>,
	539	Equivalent to <a id="idx:clause2:936"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>,
498	540	but unifies <var>Reference</var> with a unique reference to the clause
499		(see also <a name="idx:assert2:937"></a><a class="pred" href="db.html#assert/2">assert/2</a>, <a name="idx:erase1:938"></a><a class="pred" href="db.html#erase/1">erase/1</a>).
	541	(see also <a id="idx:assert2:937"></a><a class="pred" href="db.html#assert/2">assert/2</a>, <a id="idx:erase1:938"></a><a class="pred" href="db.html#erase/1">erase/1</a>).
500	542	If <var>Reference</var> is instantiated to a reference the clause's head
501	543	and body will be unified with <var>Head</var> and <var>Body</var>.</dd>
502		<dt class="pubdef"><a name="nth_clause/3"><strong>nth_clause</strong>(<var>?Pred,
	544	<dt class="pubdef"><a id="nth_clause/3"><strong>nth_clause</strong>(<var>?Pred,
503	545	?Index, ?Reference</var>)</a></dt>
504	546	<dd class="defbody">
505	547	Provides access to the clauses of a predicate using their index number.

510	552	is provided, <var>Reference</var> will be unified with the clause
511	553	reference. If <var>Index</var> is unbound, backtracking will yield both
512	554	the indexes and the references of all clauses of the predicate. The
513		following example finds the 2nd clause of <a name="idx:append3:939"></a><a class="pred" href="lists.html#append/3">append/3</a>:
	555	following example finds the 2nd clause of <a id="idx:append3:939"></a><a class="pred" href="lists.html#append/3">append/3</a>:
514	556
515	557	<pre class="code">
516	558	?- use_module(library(lists)).

522	564	</pre>
523	565
524	566	</dd>
525		<dt class="pubdef"><a name="clause_property/2"><strong>clause_property</strong>(<var>+ClauseRef,
	567	<dt class="pubdef"><a id="clause_property/2"><strong>clause_property</strong>(<var>+ClauseRef,
526	568	-Property</var>)</a></dt>
527	569	<dd class="defbody">
528	570	Queries properties of a clause. <var>ClauseRef</var> is a reference to a
529		clause as produced by <a name="idx:clause3:940"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>, <a name="idx:nthclause3:941"></a><a class="pred" href="examineprog.html#nth_clause/3">nth_clause/3</a>
	571	clause as produced by <a id="idx:clause3:940"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>, <a id="idx:nthclause3:941"></a><a class="pred" href="examineprog.html#nth_clause/3">nth_clause/3</a>
530	572	or
531		<a name="idx:prologframeattribute3:942"></a><a class="pred" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a>.
532		Unlike most other predicates that access clause references, <a name="idx:clauseproperty2:943"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>
	573	<a id="idx:prologframeattribute3:942"></a><a class="pred" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a>.
	574	Unlike most other predicates that access clause references, <a id="idx:clauseproperty2:943"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>
533	575	may be used to get information about erased clauses that have not yet
534	576	been reclaimed. <var>Property</var> is one of the following:
535	577

538	580	<dd class="defbody">
539	581	Unify <var>FileName</var> with the name of the file from which the
540	582	clause is loaded. Fails if the clause was not created by loading a file
541		(e.g., clauses added using <a name="idx:assertz1:944"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>).
	583	(e.g., clauses added using <a id="idx:assertz1:944"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>).
542	584	See also <code>source</code>.
543	585	</dd>
544	586	<dt><strong>line_count</strong>(<var>LineNumber</var>)</dt>

559	601	the clause. This is the same as the <code>file</code> property, unless
560	602	the file is loaded from a file that is textually included into source
561	603	using
562		<a name="idx:include1:945"></a><a class="pred" href="consulting.html#include/1">include/1</a>.
	604	<a id="idx:include1:945"></a><a class="pred" href="consulting.html#include/1">include/1</a>.
563	605	In this scenario, <code>file</code> is the included file, while the <code>source</code>
564	606	property refers to the <em>main</em> file.
565	607	</dd>

576	618	<dd class="defbody">
577	619	<var>PredicateIndicator</var> denotes the predicate to which this clause
578	620	belongs. This is needed to obtain information on erased clauses because
579		the usual way to obtain this information using <a name="idx:clause3:946"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>
	621	the usual way to obtain this information using <a id="idx:clause3:946"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>
580	622	fails for erased clauses.
581	623	</dd>
582	624	<dt><strong>module</strong>(<var>Module</var>)</dt>

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193	234	</div>
194		<h2 id="sec:examples"><a name="sec:8.5"><span class="sec-nr">8.5</span> <span class="sec-title">Examples</span></a></h2>
195
196		<a name="sec:examples"></a> Here are two example constraint solvers
	235	<h2 id="sec:examples"><a id="sec:8.5"><span class="sec-nr">8.5</span> <span class="sec-title">Examples</span></a></h2>
	236
	237	<a id="sec:examples"></a> Here are two example constraint solvers
197	238	written in CHR.
198	239
199	240	<p>

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193	234	</div>
194		<h2 id="sec:excepthook"><a name="sec:B.5"><span class="sec-nr">B.5</span> <span class="sec-title">Adding
	235	<h2 id="sec:excepthook"><a id="sec:B.5"><span class="sec-nr">B.5</span> <span class="sec-title">Adding
195	236	context to errors: prolog_exception_hook</span></a></h2>
196	237
197		<a name="sec:excepthook"></a>
198
199		<p>The hook <a name="idx:prologexceptionhook4:2204"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
	238	<a id="sec:excepthook"></a>
	239
	240	<p>The hook <a id="idx:prologexceptionhook4:2208"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
200	241	has been introduced in SWI-Prolog 5.6.5 to provide dedicated exception
201	242	handling facilities for application frameworks, for example
202	243	non-interactive server applications that wish to provide extensive
203	244	context for exceptions for offline debugging.
204	245
205	246	<dl class="latex">
206		<dt class="pubdef"><a name="prolog_exception_hook/4"><strong>prolog_exception_hook</strong>(<var>+ExceptionIn,
	247	<dt class="pubdef"><a id="prolog_exception_hook/4"><strong>prolog_exception_hook</strong>(<var>+ExceptionIn,
207	248	-ExceptionOut, +Frame, +CatcherFrame</var>)</a></dt>
208	249	<dd class="defbody">
209	250	This hook predicate, if defined in the module <code>user</code>, is
210	251	between raising an exception and handling it. It is intended to allow a
211	252	program adding additional context to an exception to simplify diagnosing
212		the problem. <var>ExceptionIn</var> is the exception term as raised by <a name="idx:throw1:2205"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
	253	the problem. <var>ExceptionIn</var> is the exception term as raised by <a id="idx:throw1:2209"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
213	254	or one of the built-in predicates. The output argument <var>ExceptionOut</var>
214	255	describes the exception that is actually raised. <var>Frame</var> is the
215		innermost frame. See <a name="idx:prologframeattribute3:2206"></a><a class="pred" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a>
	256	innermost frame. See <a id="idx:prologframeattribute3:2210"></a><a class="pred" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a>
216	257	and the library
217	258	<code>library(prolog_stack)</code> for getting information from this.
218	259	<var>CatcherFrame</var> is a reference to the frame calling the matching
219		<a name="idx:catch3:2207"></a><a class="pred" href="exception.html#catch/3">catch/3</a>, <code>none</code>
	260	<a id="idx:catch3:2211"></a><a class="pred" href="exception.html#catch/3">catch/3</a>, <code>none</code>
220	261	if the exception is not caught or <code>'C'</code> if the exception is
221	262	caught in C calling Prolog using the flag
222	263	<code>PL_Q_CATCH_EXCEPTION</code>.

227	268	recursively. The hook is <em>not</em> allowed to modify <var>ExceptionOut</var>
228	269	in such a way that it no longer unifies with the catching frame.
229	270
230		<p>Typically, <a name="idx:prologexceptionhook4:2208"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
	271	<p>Typically, <a id="idx:prologexceptionhook4:2212"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
231	272	is used to fill the second argument of <code>error(Formal, Context)</code>
232	273	exceptions. <var>Formal</var> is defined by the ISO standard, while
233	274	SWI-Prolog defines <var>Context</var> as a term <code>context(Location,

239	280	a quick test of the environment before starting expensive gathering
240	281	information on the state of the program.
241	282
242		<p>The hook can call <a name="idx:trace0:2209"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	283	<p>The hook can call <a id="idx:trace0:2213"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
243	284	to enter trace mode immediately. For example, imagine an application
244	285	performing an unwanted division by zero while all other errors are
245	286	expected and handled. We can force the debugger using the hook
246		definition below. Run the program in debug mode (see <a name="idx:debug0:2210"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>)
	287	definition below. Run the program in debug mode (see <a id="idx:debug0:2214"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>)
247	288	to preserve as much as possible of the error context.
248	289
249	290	<pre class="code">

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193	234	</div>
194		<h2 id="sec:exception"><a name="sec:4.11"><span class="sec-nr">4.11</span> <span class="sec-title">Exception
	235	<h2 id="sec:exception"><a id="sec:4.11"><span class="sec-nr">4.11</span> <span class="sec-title">Exception
195	236	handling</span></a></h2>
196	237
197		<a name="sec:exception"></a>
198
199		<p>The predicates <a name="idx:catch3:691"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
200		and <a name="idx:throw1:692"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
	238	<a id="sec:exception"></a>
	239
	240	<p>The predicates <a id="idx:catch3:691"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	241	and <a id="idx:throw1:692"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
201	242	provide ISO compliant raising and catching of exceptions.
202	243
203	244	<dl class="latex">
204		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="catch/3"><strong>catch</strong>(<var>:Goal,
	245	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="catch/3"><strong>catch</strong>(<var>:Goal,
205	246	+Catcher, :Recover</var>)</a></dt>
206	247	<dd class="defbody">
207		Behaves as <a name="idx:call1:693"></a><a class="pred" href="metacall.html#call/1">call/1</a>
	248	Behaves as <a id="idx:call1:693"></a><a class="pred" href="metacall.html#call/1">call/1</a>
208	249	if no exception is raised when executing <var>Goal</var>. If an
209		exception is raised using <a name="idx:throw1:694"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
	250	exception is raised using <a id="idx:throw1:694"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
210	251	while <var>Goal</var> executes, and the <var>Goal</var> is the innermost
211		goal for which <var>Catcher</var> unifies with the argument of <a name="idx:throw1:695"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
	252	goal for which <var>Catcher</var> unifies with the argument of <a id="idx:throw1:695"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
212	253	all choice points generated by <var>Goal</var> are cut, the system
213		backtracks to the start of <a name="idx:catch3:696"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	254	backtracks to the start of <a id="idx:catch3:696"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
214	255	while preserving the thrown exception term, and <var>Recover</var> is
215		called as in <a name="idx:call1:697"></a><a class="pred" href="metacall.html#call/1">call/1</a>.
216
217		<p>The overhead of calling a goal through <a name="idx:catch3:698"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	256	called as in <a id="idx:call1:697"></a><a class="pred" href="metacall.html#call/1">call/1</a>.
	257
	258	<p>The overhead of calling a goal through <a id="idx:catch3:698"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
218	259	is comparable to
219		<a name="idx:call1:699"></a><a class="pred" href="metacall.html#call/1">call/1</a>.
	260	<a id="idx:call1:699"></a><a class="pred" href="metacall.html#call/1">call/1</a>.
220	261	Recovery from an exception is much slower, especially if the exception
221	262	term is large due to the copying thereof or is decorated with a stack
222	263	trace using, e.g., the library <code>library(prolog_stack)</code> based
223	264	on the
224		<a name="idx:prologexceptionhook4:700"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
	265	<a id="idx:prologexceptionhook4:700"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
225	266	hook predicate to rewrite exceptions.</dd>
226		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="throw/1"><strong>throw</strong>(<var>+Exception</var>)</a></dt>
227		<dd class="defbody">
228		Raise an exception. The system looks for the innermost <a name="idx:catch3:701"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	267	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="throw/1"><strong>throw</strong>(<var>+Exception</var>)</a></dt>
	268	<dd class="defbody">
	269	Raise an exception. The system looks for the innermost <a id="idx:catch3:701"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
229	270	ancestor for which <var>Exception</var> unifies with the <var>Catcher</var>
230		argument of the <a name="idx:catch3:702"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
231		call. See <a name="idx:catch3:703"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	271	argument of the <a id="idx:catch3:702"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	272	call. See <a id="idx:catch3:703"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
232	273	for details.
233	274
234		<p>ISO demands that <a name="idx:throw1:704"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
235		make a copy of <var>Exception</var>, walk up the stack to a <a name="idx:catch3:705"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	275	<p>ISO demands that <a id="idx:throw1:704"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
	276	make a copy of <var>Exception</var>, walk up the stack to a <a id="idx:catch3:705"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
236	277	call, backtrack and try to unify the copy of
237	278	<var>Exception</var> with <var>Catcher</var>. SWI-Prolog delays
238		backtracking until it actually finds a matching <a name="idx:catch3:706"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	279	backtracking until it actually finds a matching <a id="idx:catch3:706"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
239	280	goal. The advantage is that we can start the debugger at the first
240	281	possible location while preserving the entire exception context if there
241		is no matching <a name="idx:catch3:707"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	282	is no matching <a id="idx:catch3:707"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
242	283	goal. This approach can lead to different behaviour if <var>Goal</var>
243		and <var>Catcher</var> of <a name="idx:catch3:708"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	284	and <var>Catcher</var> of <a id="idx:catch3:708"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
244	285	call shared variables. We assume this to be highly unlikely and could
245	286	not think of a scenario where this is useful.<sup class="fn">69<span class="fn-text">I'd
246	287	like to acknowledge Bart Demoen for his clarifications on these matters.</span></sup>
247	288
248		<p>In addition to explicit calls to <a name="idx:throw1:709"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
	289	<p>In addition to explicit calls to <a id="idx:throw1:709"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
249	290	many built-in predicates throw exceptions directly from C. If the <var>Exception</var>
250	291	term cannot be copied due to lack of stack space, the following actions
251	292	are tried in order:

256	297	ImplementationDefined)</code>, try to raise the exception without the <var>ImplementationDefined</var>
257	298	part.
258	299	<li>Try to raise <code>error(<code>resource_error(stack)</code>, global)</code>.
259		<li>Abort (see <a name="idx:abort0:710"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>).
	300	<li>Abort (see <a id="idx:abort0:710"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>).
260	301	</ol>
261	302
262		<p>If an exception is raised in a call-back from C (see <a class="sec" href="foreign.html">chapter
	303	<p>If an exception is raised in a call-back from C (see <a class="sec" href="foreign.html#sec:11">chapter
263	304	11</a>) and not caught in the same call-back, <a class="func" href="foreigninclude.html#PL_next_solution()">PL_next_solution()</a>
264	305	fails and the exception context can be retrieved using <a class="func" href="foreigninclude.html#PL_exception()">PL_exception()</a>.
265	306	</dd>
266	307	</dl>
267	308
268		<p><h3 id="sec:urgentexceptions"><a name="sec:4.11.1"><span class="sec-nr">4.11.1</span> <span class="sec-title">Urgency
	309	<p><h3 id="sec:urgentexceptions"><a id="sec:4.11.1"><span class="sec-nr">4.11.1</span> <span class="sec-title">Urgency
269	310	of exceptions</span></a></h3>
270	311
271		<a name="sec:urgentexceptions"></a>
	312	<a id="sec:urgentexceptions"></a>
272	313
273	314	<p>Under some conditions an exception may be raised as a result of
274	315	handling another exception. Below are some of the scenarios:
275	316
276	317	<p>
277	318	<ul class="latex">
278		<li>The predicate <a name="idx:setupcallcleanup3:711"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
	319	<li>The predicate <a id="idx:setupcallcleanup3:711"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
279	320	calls the cleanup handler as a result of an exception and the cleanup
280	321	handler raises an exception itself. In this case the most <em>urgent</em>
281	322	exception is propagated into the environment.

283	324	stack space to store the exception. In this case a resource exception is
284	325	raised. If that too fails the system tries to raise a resource exception
285	326	without (stack) context. If that fails it will raise the exception
286		<code>'$aborted'</code>, also raised by <a name="idx:abort0:712"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
	327	<code>'$aborted'</code>, also raised by <a id="idx:abort0:712"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
287	328	As no stack space is required for processing this atomic exception, this
288	329	should always succeed.
289	330	<li>Certain <em>callback</em> operations raise an exception while
290	331	processing another exception or a previous callback already raised an
291	332	exception before there was an opportunity to process the exception. The
292		most notable <em>callback</em> subject to this issue are <a name="idx:prologeventhook1:713"></a><span class="pred-ext">prolog_event_hook/1</span>
293		(supporting e.g., the graphical debugger), <a name="idx:prologexceptionhook4:714"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
294		(rewriting exceptions, e.g., by adding context) and <a name="idx:printmessage2:715"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	333	most notable <em>callback</em> subject to this issue are <a id="idx:prologeventhook1:713"></a><span class="pred-ext">prolog_event_hook/1</span>
	334	(supporting e.g., the graphical debugger), <a id="idx:prologexceptionhook4:714"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
	335	(rewriting exceptions, e.g., by adding context) and <a id="idx:printmessage2:715"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
295	336	when called from the core facilities such as the internal debugger. As
296	337	with
297		<a name="idx:setupcallcleanup3:716"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>,
	338	<a id="idx:setupcallcleanup3:716"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>,
298	339	the most <em>urgent</em> exception is preserved.
299	340	</ul>
300	341

303	344
304	345	<p>
305	346	<ol class="latex">
306		<li><code>'$aborted'</code> (<a name="idx:abort0:717"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>)
307		<li><code>time_limit_exceeded</code> (<a name="idx:callwithtimelimit2:718"></a><span class="pred-ext">call_with_time_limit/2</span>)
	347	<li><code>'$aborted'</code> (<a id="idx:abort0:717"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>)
	348	<li><code>time_limit_exceeded</code> (<a id="idx:callwithtimelimit2:718"></a><span class="pred-ext">call_with_time_limit/2</span>)
308	349	<li><code>error(<code>resource_error(Resource)</code>, Context)</code>
309	350	<li><code>error(Formal, Context)</code>
310	351	<li>All other exceptions

312	353
313	354	<p><b>Note</b> The above resolution is not described in the ISO
314	355	standard. This is not needed either because ISO does not specify
315		<a name="idx:setupcallcleanup3:719"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
	356	<a id="idx:setupcallcleanup3:719"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
316	357	and does not deal with environment management issues such as (debugger)
317		callbacks. Neither does it define <a name="idx:abort0:720"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
318		or timeout handling. Notably <a name="idx:abort0:721"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
	358	callbacks. Neither does it define <a id="idx:abort0:720"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
	359	or timeout handling. Notably <a id="idx:abort0:721"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
319	360	and timeout are non-logical control structures. They are implemented on
320	361	top of exceptions as they need to unwind the stack, destroy choice
321	362	points and call cleanup handlers in the same way. However, the pending
322	363	exception should not be replaced by another one before the intended
323	364	handler is reached. The abort exception cannot be caught, something
324		which is achieved by wrapping the <em>cleanup handler</em> of <a name="idx:catch3:722"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	365	which is achieved by wrapping the <em>cleanup handler</em> of <a id="idx:catch3:722"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
325	366	into
326	367	<code>call_cleanup(Handler, abort)</code>.
327	368
328		<p><h3 id="sec:debugexceptions"><a name="sec:4.11.2"><span class="sec-nr">4.11.2</span> <span class="sec-title">Debugging
	369	<p><h3 id="sec:debugexceptions"><a id="sec:4.11.2"><span class="sec-nr">4.11.2</span> <span class="sec-title">Debugging
329	370	and exceptions</span></a></h3>
330	371
331		<a name="sec:debugexceptions"></a>
332
333		<p><a name="idx:exceptionsdebugging:723"></a><a name="idx:debuggingexceptions:724"></a>Before
	372	<a id="sec:debugexceptions"></a>
	373
	374	<p><a id="idx:exceptionsdebugging:723"></a><a id="idx:debuggingexceptions:724"></a>Before
334	375	the introduction of exceptions in SWI-Prolog a runtime error was handled
335	376	by printing an error message, after which the predicate failed. If the
336	377	Prolog flag <a class="flag" href="flags.html#flag:debug_on_error">debug_on_error</a>

339	380	locate the error.
340	381
341	382	<p>With exception handling, things are different. A programmer may wish
342		to trap an exception using <a name="idx:catch3:725"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	383	to trap an exception using <a id="idx:catch3:725"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
343	384	to avoid it reaching the user. If the exception is not handled by user
344	385	code, the interactive top level will trap it to prevent termination.
345	386
346	387	<p>If we do not take special precautions, the context information
347	388	associated with an unexpected exception (i.e., a programming error) is
348	389	lost. Therefore, if an exception is raised which is not caught using
349		<a name="idx:catch3:726"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	390	<a id="idx:catch3:726"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
350	391	and the top level is running, the error will be printed, and the system
351	392	will enter trace mode.
352	393
353	394	<p>If the system is in a non-interactive call-back from foreign code and
354		there is no <a name="idx:catch3:727"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	395	there is no <a id="idx:catch3:727"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
355	396	active in the current context, it cannot determine whether or not the
356	397	exception will be caught by the external routine calling Prolog. It will
357	398	then base its behaviour on the Prolog flag

369	410	</ul>
370	411
371	412	<p>While looking for the context in which an exception takes place, it
372		is advised to switch on debug mode using the predicate <a name="idx:debug0:728"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.
	413	is advised to switch on debug mode using the predicate <a id="idx:debug0:728"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.
373	414	The hook
374		<a name="idx:prologexceptionhook4:729"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
	415	<a id="idx:prologexceptionhook4:729"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>
375	416	can be used to add more debugging facilities to exceptions. An example
376	417	is the library <code>library(http/http_error)</code>, generating a full
377	418	stack trace on errors in the HTTP server library.
378	419
379		<p><h3 id="sec:exceptterm"><a name="sec:4.11.3"><span class="sec-nr">4.11.3</span> <span class="sec-title">The
	420	<p><h3 id="sec:exceptterm"><a id="sec:4.11.3"><span class="sec-nr">4.11.3</span> <span class="sec-title">The
380	421	exception term</span></a></h3>
381	422
382		<a name="sec:exceptterm"></a>
	423	<a id="sec:exceptterm"></a>
383	424
384	425	<p>Built-in predicates generate exceptions using a term
385	426	<code>error(Formal, Context)</code>. The first argument is the `formal'

393	434	description of the error. Any part of this structure may be a variable
394	435	if no information was present.
395	436
396		<p><h3 id="sec:printmsg"><a name="sec:4.11.4"><span class="sec-nr">4.11.4</span> <span class="sec-title">Printing
	437	<p><h3 id="sec:printmsg"><a id="sec:4.11.4"><span class="sec-nr">4.11.4</span> <span class="sec-title">Printing
397	438	messages</span></a></h3>
398	439
399		<a name="sec:printmsg"></a>
400
401		<p>The predicate <a name="idx:printmessage2:730"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	440	<a id="sec:printmsg"></a>
	441
	442	<p>The predicate <a id="idx:printmessage2:730"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
402	443	is used to print a message term in a human-readable format. The other
403	444	predicates from this section allow the user to refine and extend the
404	445	message system. A common usage of
405		<a name="idx:printmessage2:731"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	446	<a id="idx:printmessage2:731"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
406	447	is to print error messages from exceptions. The code below prints errors
407	448	encountered during the execution of <var>Goal</var>, without further
408	449	propagating the exception and without starting the debugger.

416	457	...
417	458	</pre>
418	459
419		<p>Another common use is to define <a name="idx:messagehook3:732"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
	460	<p>Another common use is to define <a id="idx:messagehook3:732"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
420	461	for printing messages that are normally <em>silent</em>, suppressing
421	462	messages, redirecting messages or make something happen in addition to
422	463	printing the message.
423	464
424	465	<dl class="latex">
425		<dt class="pubdef"><a name="print_message/2"><strong>print_message</strong>(<var>+Kind,
	466	<dt class="pubdef"><a id="print_message/2"><strong>print_message</strong>(<var>+Kind,
426	467	+Term</var>)</a></dt>
427	468	<dd class="defbody">
428		The predicate <a name="idx:printmessage2:733"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	469	The predicate <a id="idx:printmessage2:733"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
429	470	is used by the system and libraries to print messages. <var>Kind</var>
430	471	describes the nature of the message, while
431	472	<var>Term</var> is a Prolog term that describes the content. Printing
432		messages through this indirection instead of using <a name="idx:format3:734"></a><a class="pred" href="format.html#format/3">format/3</a>
	473	messages through this indirection instead of using <a id="idx:format3:734"></a><a class="pred" href="format.html#format/3">format/3</a>
433	474	to the stream <code>user_error</code> allows displaying the message
434	475	appropriate to the application (terminal, logfile, graphics), acting on
435		messages based on their content instead of a string (see <a name="idx:messagehook3:735"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>)
	476	messages based on their content instead of a string (see <a id="idx:messagehook3:735"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>)
436	477	and creating language specific versions of the messages. See also
437		<a class="sec" href="exception.html">section 4.11.4.1</a>. The following
438		message kinds are known:
	478	<a class="sec" href="exception.html#sec:4.11.4.1">section 4.11.4.1</a>.
	479	The following message kinds are known:
439	480
440	481	<dl class="latex">
441	482	<dt><strong>banner</strong></dt>

445	486	to <code>silent</code>.</dd>
446	487	<dt><strong>debug</strong>(<var>Topic</var>)</dt>
447	488	<dd class="defbody">
448		Message from library(debug). See <a name="idx:debug3:736"></a><a class="pred" href="debug.html#debug/3">debug/3</a>.</dd>
	489	Message from library(debug). See <a id="idx:debug3:736"></a><a class="pred" href="debug.html#debug/3">debug/3</a>.</dd>
449	490	<dt><strong>error</strong></dt>
450	491	<dd class="defbody">
451	492	The message indicates an erroneous situation. This kind is used to print
452	493	uncaught exceptions of type <code>error(Formal, Context)</code>. See
453		section introduction (<a class="sec" href="exception.html">section
	494	section introduction (<a class="sec" href="exception.html#sec:4.11.4">section
454	495	4.11.4</a>).</dd>
455	496	<dt><strong>help</strong></dt>
456	497	<dd class="defbody">

458	499	prompt.</dd>
459	500	<dt><strong>information</strong></dt>
460	501	<dd class="defbody">
461		Information that is requested by the user. An example is <a name="idx:statistics0:737"></a><a class="pred" href="statistics.html#statistics/0">statistics/0</a>.</dd>
	502	Information that is requested by the user. An example is <a id="idx:statistics0:737"></a><a class="pred" href="statistics.html#statistics/0">statistics/0</a>.</dd>
462	503	<dt><strong>informational</strong></dt>
463	504	<dd class="defbody">
464	505	Typically messages of events are progres that are considered useful to a

467	508	<dt><strong>silent</strong></dt>
468	509	<dd class="defbody">
469	510	Message that is normally not printed. Applications may define
470		<a name="idx:messagehook3:738"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
	511	<a id="idx:messagehook3:738"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
471	512	to act upon such messages.</dd>
472	513	<dt><strong>trace</strong></dt>
473	514	<dd class="defbody">

475	516	<dt><strong>warning</strong></dt>
476	517	<dd class="defbody">
477	518	The message indicates something dubious that is not considered fatal.
478		For example, discontiguous predicates (see <a name="idx:discontiguous1:739"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a>).
	519	For example, discontiguous predicates (see <a id="idx:discontiguous1:739"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a>).
479	520	</dd>
480	521	</dl>
481	522
482		<p>The predicate <a name="idx:printmessage2:740"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
483		first translates the <var>Term</var> into a list of `message lines' (see <a name="idx:printmessagelines3:741"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a>
484		for details). Next, it calls the hook <a name="idx:messagehook3:742"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
485		to allow the user to intercept the message. If <a name="idx:messagehook3:743"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
	523	<p>The predicate <a id="idx:printmessage2:740"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	524	first translates the <var>Term</var> into a list of `message lines' (see <a id="idx:printmessagelines3:741"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a>
	525	for details). Next, it calls the hook <a id="idx:messagehook3:742"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
	526	to allow the user to intercept the message. If <a id="idx:messagehook3:743"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
486	527	fails it prints the message unless <var>Kind</var> is silent.
487	528
488		<p>The <a name="idx:printmessage2:744"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	529	<p>The <a id="idx:printmessage2:744"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
489	530	predicate and its rules are in the file
490	531	<code><<var>plhome</var>>/boot/messages.pl</code>, which may be
491	532	inspected for more information on the error messages and related error

494	535	existing message term is applicable, invent a fairly unique term that
495	536	represents the event and define a rule for the multifile predicate
496	537	prolog:message//1. See
497		<a class="sec" href="exception.html">section 4.11.4.1</a> for a deeper
498		discussion and examples.
499
500		<p>See also <a name="idx:messagetostring2:745"></a><a class="pred" href="exception.html#message_to_string/2">message_to_string/2</a>.</dd>
501		<dt class="pubdef"><a name="print_message_lines/3"><strong>print_message_lines</strong>(<var>+Stream,
	538	<a class="sec" href="exception.html#sec:4.11.4.1">section 4.11.4.1</a>
	539	for a deeper discussion and examples.
	540
	541	<p>See also <a id="idx:messagetostring2:745"></a><a class="pred" href="exception.html#message_to_string/2">message_to_string/2</a>.</dd>
	542	<dt class="pubdef"><a id="print_message_lines/3"><strong>print_message_lines</strong>(<var>+Stream,
502	543	+Prefix, +Lines</var>)</a></dt>
503	544	<dd class="defbody">
504		Print a message (see <a name="idx:printmessage2:746"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>)
	545	Print a message (see <a id="idx:printmessage2:746"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>)
505	546	that has been translated to a list of message elements. The elements of
506	547	this list are:
507	548

509	550	<dt><strong><<var>Format</var>>-<<var>Args</var>></strong></dt>
510	551	<dd class="defbody">
511	552	Where <var>Format</var> is an atom and <var>Args</var> is a list of
512		format arguments. Handed to <a name="idx:format3:747"></a><a class="pred" href="format.html#format/3">format/3</a>.
	553	format arguments. Handed to <a id="idx:format3:747"></a><a class="pred" href="format.html#format/3">format/3</a>.
513	554	</dd>
514	555	<dt><strong>flush</strong></dt>
515	556	<dd class="defbody">
516		If this appears as the last element, <var>Stream</var> is flushed (see <a name="idx:flushoutput1:748"></a><a class="pred" href="chario.html#flush_output/1">flush_output/1</a>)
	557	If this appears as the last element, <var>Stream</var> is flushed (see <a id="idx:flushoutput1:748"></a><a class="pred" href="chario.html#flush_output/1">flush_output/1</a>)
517	558	and no final newline is generated. This is combined with a subsequent
518	559	message that starts with
519	560	<code>at_same_line</code> to complete the line.

521	562	<dt><strong>at_same_line</strong></dt>
522	563	<dd class="defbody">
523	564	If this appears as first element, no prefix is printed for the first
524		line and the line position is not forced to 0 (see <a name="idx:format1:749"></a><a class="pred" href="format.html#format/1">format/1</a>, <code>~N</code>).
	565	line and the line position is not forced to 0 (see <a id="idx:format1:749"></a><a class="pred" href="format.html#format/1">format/1</a>, <code>~N</code>).
525	566	</dd>
526	567	<dt><strong>ansi</strong>(<var>+Attributes, +Format, +Args</var>)</dt>
527	568	<dd class="defbody">

544	585	</dd>
545	586	<dt><strong><<var>Format</var>></strong></dt>
546	587	<dd class="defbody">
547		Handed to <a name="idx:format3:750"></a><a class="pred" href="format.html#format/3">format/3</a>
	588	Handed to <a id="idx:format3:750"></a><a class="pred" href="format.html#format/3">format/3</a>
548	589	as <code>format(Stream, Format,[])</code>. Deprecated because it is
549	590	ambiguous if <var>Format</var> collides with one of the atomic commands.
550	591	</dd>
551	592	</dl>
552	593
553		<p>See also <a name="idx:printmessage2:751"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
554		and <a name="idx:messagehook3:752"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>.</dd>
555		<dt class="pubdef"><a name="message_hook/3"><strong>message_hook</strong>(<var>+Term,
	594	<p>See also <a id="idx:printmessage2:751"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	595	and <a id="idx:messagehook3:752"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>.</dd>
	596	<dt class="pubdef"><a id="message_hook/3"><strong>message_hook</strong>(<var>+Term,
556	597	+Kind, +Lines</var>)</a></dt>
557	598	<dd class="defbody">
558	599	Hook predicate that may be defined in the module <code>user</code> to
559		intercept messages from <a name="idx:printmessage2:753"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>. <var>Term</var>
560		and <var>Kind</var> are the same as passed to <a name="idx:printmessage2:754"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>. <var>Lines</var>
561		is a list of format statements as described with <a name="idx:printmessagelines3:755"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a>.
	600	intercept messages from <a id="idx:printmessage2:753"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>. <var>Term</var>
	601	and <var>Kind</var> are the same as passed to <a id="idx:printmessage2:754"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>. <var>Lines</var>
	602	is a list of format statements as described with <a id="idx:printmessagelines3:755"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a>.
562	603	See also
563		<a name="idx:messagetostring2:756"></a><a class="pred" href="exception.html#message_to_string/2">message_to_string/2</a>.
	604	<a id="idx:messagetostring2:756"></a><a class="pred" href="exception.html#message_to_string/2">message_to_string/2</a>.
564	605
565	606	<p>This predicate must be defined dynamic and multifile to allow other
566	607	modules defining clauses for it too.</dd>
567		<dt class="pubdef"><a name="thread_message_hook/3"><strong>thread_message_hook</strong>(<var>+Term,
	608	<dt class="pubdef"><a id="thread_message_hook/3"><strong>thread_message_hook</strong>(<var>+Term,
568	609	+Kind, +Lines</var>)</a></dt>
569	610	<dd class="defbody">
570		As <a name="idx:messagehook3:757"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>,
571		but this predicate is local to the calling thread (see <a name="idx:threadlocal1:758"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>).
572		This hook is called <em>before</em> <a name="idx:messagehook3:759"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>.
	611	As <a id="idx:messagehook3:757"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>,
	612	but this predicate is local to the calling thread (see <a id="idx:threadlocal1:758"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>).
	613	This hook is called <em>before</em> <a id="idx:messagehook3:759"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>.
573	614	The `pre-hook' is indented to catch messages they may be produced by
574	615	calling some goal without affecting other threads.</dd>
575		<dt class="pubdef"><a name="message_property/2"><strong>message_property</strong>(<var>+Kind,
	616	<dt class="pubdef"><a id="message_property/2"><strong>message_property</strong>(<var>+Kind,
576	617	?Property</var>)</a></dt>
577	618	<dd class="defbody">
578	619	This hook can be used to define additional message kinds and the way

581	622	<dl class="latex">
582	623	<dt><strong>color</strong>(<var>-Attributes</var>)</dt>
583	624	<dd class="defbody">
584		Print message using ANSI terminal attributes. See <a name="idx:ansiformat3:760"></a><span class="pred-ext">ansi_format/3</span>
	625	Print message using ANSI terminal attributes. See <a id="idx:ansiformat3:760"></a><span class="pred-ext">ansi_format/3</span>
585	626	for details. Here is an example, printing help messages in blue:
586	627
587	628	<pre class="code">

593	634	</dd>
594	635	<dt><strong>prefix</strong>(<var>-Prefix</var>)</dt>
595	636	<dd class="defbody">
596		Prefix printed before each line. This argument is handed to <a name="idx:format3:761"></a><a class="pred" href="format.html#format/3">format/3</a>.
	637	Prefix printed before each line. This argument is handed to <a id="idx:format3:761"></a><a class="pred" href="format.html#format/3">format/3</a>.
597	638	The default is <code>'~N'</code>. For example, messages of kind
598	639	<code>warning</code> use <code>'~NWarning: '</code>.</dd>
599	640	<dt><strong>location_prefix</strong>(<var>+Location, -FirstPrefix,

622	663	</dl>
623	664
624	665	</dd>
625		<dt class="pubdef"><a name="prolog:message_line_element/2"><strong>prolog:message_line_element</strong>(<var>+Stream,
	666	<dt class="pubdef"><a id="prolog:message_line_element/2"><strong>prolog:message_line_element</strong>(<var>+Stream,
626	667	+Term</var>)</a></dt>
627	668	<dd class="defbody">
628	669	This hook is called to print the individual elements of a message from
629		<a name="idx:printmessagelines3:762"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a>.
	670	<a id="idx:printmessagelines3:762"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a>.
630	671	This hook is used by e.g., library
631	672	<code>library(ansi_term)</code> to colour messages on ANSI-capable
632	673	terminals.</dd>
633		<dt class="pubdef"><a name="message_to_string/2"><strong>message_to_string</strong>(<var>+Term,
	674	<dt class="pubdef"><a id="message_to_string/2"><strong>message_to_string</strong>(<var>+Term,
634	675	-String</var>)</a></dt>
635	676	<dd class="defbody">
636		Translates a message term into a string object (see <a class="sec" href="strings.html">section
	677	Translates a message term into a string object (see <a class="sec" href="strings.html#sec:5.2">section
637	678	5.2</a>).</dd>
638		<dt class="pubdef"><a name="version/0"><strong>version</strong></a></dt>
	679	<dt class="pubdef"><a id="version/0"><strong>version</strong></a></dt>
639	680	<dd class="defbody">
640	681	Write the SWI-Prolog banner message as well as additional messages
641		registered using <a name="idx:version1:763"></a><a class="pred" href="exception.html#version/1">version/1</a>.
	682	registered using <a id="idx:version1:763"></a><a class="pred" href="exception.html#version/1">version/1</a>.
642	683	This is the default <em>initialization goal</em> which can be modified
643	684	using <strong>-g</strong>.</dd>
644		<dt class="pubdef"><a name="version/1"><strong>version</strong>(<var>+Message</var>)</a></dt>
645		<dd class="defbody">
646		Register additional messages to be printed by <a name="idx:version0:764"></a><a class="pred" href="exception.html#version/0">version/0</a>.
	685	<dt class="pubdef"><a id="version/1"><strong>version</strong>(<var>+Message</var>)</a></dt>
	686	<dd class="defbody">
	687	Register additional messages to be printed by <a id="idx:version0:764"></a><a class="pred" href="exception.html#version/0">version/0</a>.
647	688	Each registered message is handed to the message translation DCG and can
648	689	thus be defined using the hook prolog:message//1. If not defined, it is
649	690	simply printed.
650	691	</dd>
651	692	</dl>
652	693
653		<p><h4 id="sec:libprintmsg"><a name="sec:4.11.4.1"><span class="sec-nr">4.11.4.1</span> <span class="sec-title">Printing
	694	<p><h4 id="sec:libprintmsg"><a id="sec:4.11.4.1"><span class="sec-nr">4.11.4.1</span> <span class="sec-title">Printing
654	695	from libraries</span></a></h4>
655	696
656		<a name="sec:libprintmsg"></a>
657
658		<p>Libraries should <em>not</em> use <a name="idx:format3:765"></a><a class="pred" href="format.html#format/3">format/3</a>
	697	<a id="sec:libprintmsg"></a>
	698
	699	<p>Libraries should <em>not</em> use <a id="idx:format3:765"></a><a class="pred" href="format.html#format/3">format/3</a>
659	700	or other output predicates directly. Libraries that print informational
660	701	output directly to the console are hard to use from code that depend on
661		your textual output, such as a CGI script. The predicates in <a class="sec" href="exception.html">section
	702	your textual output, such as a CGI script. The predicates in <a class="sec" href="exception.html#sec:4.11.4">section
662	703	4.11.4</a> define the API for dealing with messages. The idea behind
663	704	this is that a library that wants to provide information about its
664		status, progress, events or problems calls <a name="idx:printmessage2:766"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
	705	status, progress, events or problems calls <a id="idx:printmessage2:766"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
665	706	The first argument is the
666		<em>level</em>. The supported levels are described with <a name="idx:printmessage2:767"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
	707	<em>level</em>. The supported levels are described with <a id="idx:printmessage2:767"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
667	708	Libraries typically use <code>informational</code> and <code>warning</code>,
668		while libraries should use exceptions for errors (see <a name="idx:throw1:768"></a><a class="pred" href="exception.html#throw/1">throw/1</a>, <a name="idx:typeerror2:769"></a><a class="pred" href="error.html#type_error/2">type_error/2</a>,
	709	while libraries should use exceptions for errors (see <a id="idx:throw1:768"></a><a class="pred" href="exception.html#throw/1">throw/1</a>, <a id="idx:typeerror2:769"></a><a class="pred" href="error.html#type_error/2">type_error/2</a>,
669	710	etc.).
670	711
671	712	<p>The second argument is an arbitrary Prolog term that carries the

676	717	into a progress bar).
677	718
678	719	<p>For example, suppose we have a library that must download data from
679		the Internet (e.g., based on <a name="idx:httpopen3:770"></a><span class="pred-ext">http_open/3</span>).
	720	the Internet (e.g., based on <a id="idx:httpopen3:770"></a><span class="pred-ext">http_open/3</span>).
680	721	The library wants to print the progress after each downloaded file. The
681	722	code below is a good skeleton:
682	723

695	736	different languages. This, and the user-hook example below are the
696	737	reason to represent the message as a compound term rather than a string.
697	738	This is similar to using message numbers in non-symbolic languages. The
698		documentation of <a name="idx:printmessagelines3:771"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a>
	739	documentation of <a id="idx:printmessagelines3:771"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a>
699	740	describes the elements that may appear in the output list.
700	741
701	742	<pre class="code">

707	748	[ 'Downloaded ~w; ~D from ~D (~d%)'-[URL, I, Total, Perc] ].
708	749	</pre>
709	750
710		<p>A <em>user</em> of the library may define rules for <a name="idx:messagehook3:772"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>.
	751	<p>A <em>user</em> of the library may define rules for <a id="idx:messagehook3:772"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>.
711	752	The rule below acts on the message content. Other applications can act
712	753	on the message level and, for example, popup a message box for warnings
713	754	and errors.

+75

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193	234	</div>
194		<h2 id="sec:exception3"><a name="sec:B.6"><span class="sec-nr">B.6</span> <span class="sec-title">Hooks
	235	<h2 id="sec:exception3"><a id="sec:B.6"><span class="sec-nr">B.6</span> <span class="sec-title">Hooks
195	236	using the exception predicate</span></a></h2>
196	237
197		<a name="sec:exception3"></a>
198
199		<p>This section describes the predicate <a name="idx:exception3:2211"></a><a class="pred" href="exception3.html#exception/3">exception/3</a>,
	238	<a id="sec:exception3"></a>
	239
	240	<p>This section describes the predicate <a id="idx:exception3:2215"></a><a class="pred" href="exception3.html#exception/3">exception/3</a>,
200	241	which can be defined by the user in the module <code>user</code> as a
201	242	multifile predicate. Unlike the name suggests, this is actually a <em>hook</em>
202	243	predicate that has no relation to Prolog exceptions as defined by the
203	244	ISO predicates
204		<a name="idx:catch3:2212"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
205		and <a name="idx:throw1:2213"></a><a class="pred" href="exception.html#throw/1">throw/1</a>.
206
207		<p>The predicate <a name="idx:exception3:2214"></a><a class="pred" href="exception3.html#exception/3">exception/3</a>
	245	<a id="idx:catch3:2216"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	246	and <a id="idx:throw1:2217"></a><a class="pred" href="exception.html#throw/1">throw/1</a>.
	247
	248	<p>The predicate <a id="idx:exception3:2218"></a><a class="pred" href="exception3.html#exception/3">exception/3</a>
208	249	is called by the kernel on a couple of events, allowing the user to
209	250	`fix' errors just-in-time. The mechanism allows for
210	251	<em>lazy</em> creation of objects such as predicates.
211	252
212	253	<dl class="latex">
213		<dt class="pubdef"><a name="exception/3"><strong>exception</strong>(<var>+Exception,
	254	<dt class="pubdef"><a id="exception/3"><strong>exception</strong>(<var>+Exception,
214	255	+Context, -Action</var>)</a></dt>
215	256	<dd class="defbody">
216	257	Dynamic predicate, normally not defined. Called by the Prolog system on
217	258	run-time exceptions that can be repaired `just-in-time'. The values for <var>Exception</var>
218		are described below. See also <a name="idx:catch3:2215"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
219		and <a name="idx:throw1:2216"></a><a class="pred" href="exception.html#throw/1">throw/1</a>.
	259	are described below. See also <a id="idx:catch3:2219"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	260	and <a id="idx:throw1:2220"></a><a class="pred" href="exception.html#throw/1">throw/1</a>.
220	261
221	262	<p>If this hook predicate succeeds it must instantiate the <var>Action</var>
222	263	argument to the atom <code>fail</code> to make the operation fail

234	275	exception. The hook is intended to implement alternatives to the
235	276	built-in autoloader, such as autoloading code from a database. Do <em>not</em>
236	277	use this hook to suppress existence errors on predicates. See also <a class="flag" href="flags.html#flag:unknown">unknown</a>
237		and <a class="sec" href="autoload.html">section 2.13</a>.</dd>
	278	and <a class="sec" href="autoload.html#sec:2.13">section 2.13</a>.</dd>
238	279	<dt><strong>undefined_global_variable</strong></dt>
239	280	<dd class="defbody">
240	281	<var>Context</var> is instantiated to the name of the missing global
241		variable. The hook must call <a name="idx:nbsetval2:2217"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
242		or <a name="idx:bsetval2:2218"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>
	282	variable. The hook must call <a id="idx:nbsetval2:2221"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
	283	or <a id="idx:bsetval2:2222"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>
243	284	before returning with the action <code>retry</code>.
244	285	</dd>
245	286	</dl>

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193	234	</div>
194		<h2 id="sec:ext-integration"><a name="sec:5.5"><span class="sec-nr">5.5</span> <span class="sec-title">Integration
	235	<h2 id="sec:ext-integration"><a id="sec:5.5"><span class="sec-nr">5.5</span> <span class="sec-title">Integration
195	236	of strings and dicts in the libraries</span></a></h2>
196	237
197		<a name="sec:ext-integration"></a>
	238	<a id="sec:ext-integration"></a>
198	239
199	240	<p>While lacking proper string support and dicts when designed, many
200	241	predicates and libraries use interfaces that must be classified as

207	248	must make a choice. We plan to resolve that using either options that
208	249	specify the desired output or provide an alternative library.
209	250
210		<p><h3 id="sec:ext-dict-options"><a name="sec:5.5.1"><span class="sec-nr">5.5.1</span> <span class="sec-title">Dicts
	251	<p><h3 id="sec:ext-dict-options"><a id="sec:5.5.1"><span class="sec-nr">5.5.1</span> <span class="sec-title">Dicts
211	252	and option processing</span></a></h3>
212	253
213		<a name="sec:ext-dict-options"></a>
	254	<a id="sec:ext-dict-options"></a>
214	255
215	256	<p>System predicates and predicates based on library <code>library(options)</code>
216	257	process dicts as an alternative to traditional option lists.
217	258
218		<p><h3 id="sec:ext-dict-in-core-data"><a name="sec:5.5.2"><span class="sec-nr">5.5.2</span> <span class="sec-title">Dicts
	259	<p><h3 id="sec:ext-dict-in-core-data"><a id="sec:5.5.2"><span class="sec-nr">5.5.2</span> <span class="sec-title">Dicts
219	260	in core data structures</span></a></h3>
220	261
221		<a name="sec:ext-dict-in-core-data"></a>
	262	<a id="sec:ext-dict-in-core-data"></a>
222	263
223	264	<p>Some predicates now produce structured data using compound terms and
224	265	access predicates. We consider migrating these to dicts. Below is a

231	272	<li>Date and time records
232	273	</ul>
233	274
234		<p><h3 id="sec:ext-xml"><a name="sec:5.5.3"><span class="sec-nr">5.5.3</span> <span class="sec-title">Dicts,
	275	<p><h3 id="sec:ext-xml"><a id="sec:5.5.3"><span class="sec-nr">5.5.3</span> <span class="sec-title">Dicts,
235	276	strings and XML</span></a></h3>
236	277
237		<a name="sec:ext-xml"></a>
	278	<a id="sec:ext-xml"></a>
238	279
239	280	<p>The XML representation could benefit significantly from the new
240	281	features. In due time we plan to provide an set of alternative

250	291	<li>CDATA in element content will be represented as strings
251	292	</ul>
252	293
253		<p><h3 id="sec:ext-json"><a name="sec:5.5.4"><span class="sec-nr">5.5.4</span> <span class="sec-title">Dicts,
	294	<p><h3 id="sec:ext-json"><a id="sec:5.5.4"><span class="sec-nr">5.5.4</span> <span class="sec-title">Dicts,
254	295	strings and JSON</span></a></h3>
255	296
256		<a name="sec:ext-json"></a>
	297	<a id="sec:ext-json"></a>
257	298
258	299	<p>The JSON representation could benefit significantly from the new
259	300	features. In due time we plan to provide an set of alternative

274	315	will be represented as atoms.
275	316	</ul>
276	317
277		<p><h3 id="sec:ext-http"><a name="sec:5.5.5"><span class="sec-nr">5.5.5</span> <span class="sec-title">Dicts,
	318	<p><h3 id="sec:ext-http"><a id="sec:5.5.5"><span class="sec-nr">5.5.5</span> <span class="sec-title">Dicts,
278	319	strings and HTTP</span></a></h3>
279	320
280		<a name="sec:ext-http"></a>
	321	<a id="sec:ext-http"></a>
281	322
282	323	<p>The HTTP library and related data structures would profit from
283	324	exploiting dicts. Below is a list of data structures that might be

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193	234	</div>
194		<h2 id="sec:ext-issues"><a name="sec:5.6"><span class="sec-nr">5.6</span> <span class="sec-title">Remaining
	235	<h2 id="sec:ext-issues"><a id="sec:5.6"><span class="sec-nr">5.6</span> <span class="sec-title">Remaining
195	236	issues</span></a></h2>
196	237
197		<a name="sec:ext-issues"></a>
	238	<a id="sec:ext-issues"></a>
198	239
199	240	<p>The changes and extensions described in this chapter resolve a many
200	241	limitations of the Prolog language we have encountered. Still, there are

208	249	representations, a list of <em>character codes</em> (`codes' for short)
209	250	and a list of <em>one-character atoms</em> (`chars' for short). There
210	251	are two sets of predicates, named _code(s) and _char(s) that provide
211		the same functionality (e.g., <a name="idx:atomcodes2:1655"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
212		and <a name="idx:atomchars2:1656"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>)
	252	the same functionality (e.g., <a id="idx:atomcodes2:1659"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
	253	and <a id="idx:atomchars2:1660"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>)
213	254	using their own representation of characters. Codes can be used in
214	255	arithmetic expressions, while chars are more readable. Neither can
215	256	unambiguously be interpreted as a representation for text because codes

229	270	that involve arrays require <em>mutable</em> arrays, while Prolog data
230	271	is immutable by design. Second, standard Prolog has no good syntax
231	272	support for arrays. SWI-Prolog version 7 has `block operators' (see
232		<a class="sec" href="ext-syntax.html">section 5.3.3</a>) which can
233		resolve the syntactic issues. Block operators have been adopted by YAP.
	273	<a class="sec" href="ext-syntax.html#sec:5.3.3">section 5.3.3</a>) which
	274	can resolve the syntactic issues. Block operators have been adopted by
	275	YAP.
234	276
235	277	<p><b>Lambda expressions</b>
236	278
237		<p>Although many alternatives<sup class="fn">151<span class="fn-text">See
	279	<p>Although many alternatives<sup class="fn">152<span class="fn-text">See
238	280	e.g., <a class="url" href="http://www.complang.tuwien.ac.at/ulrich/Prolog-inedit/ISO-Hiord">http://www.complang.tuwien.ac.at/ulrich/Prolog-inedit/ISO-Hiord</a></span></sup>
239	281	have been proposed, we still feel uneasy with them.
240	282

244	286	Prolog for simple iterations over data. ECLiPSe have proposed
245	287	<em>logical loops</em> <cite><a class="cite" href="Bibliography.html#logicalloops:2002">Schimpf,
246	288	2002</a></cite>, while B-Prolog introduced <em>declarative loops</em>
247		and <em>list comprehension</em><sup class="fn">152<span class="fn-text"><a class="url" href="http://www.probp.com/download/loops.pdf">http://www.probp.com/download/loops.pdf</a></span></sup>.
248		The above mentioned lambda expressions, combined with <a name="idx:maplist2:1657"></a><a class="pred" href="apply.html#maplist/2">maplist/2</a>
	289	and <em>list comprehension</em><sup class="fn">153<span class="fn-text"><a class="url" href="http://www.probp.com/download/loops.pdf">http://www.probp.com/download/loops.pdf</a></span></sup>.
	290	The above mentioned lambda expressions, combined with <a id="idx:maplist2:1661"></a><a class="pred" href="apply.html#maplist/2">maplist/2</a>
249	291	can achieve similar results.
250	292	</body></html>⏎

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193	234	</div>
194		<h2 id="sec:ext-lists"><a name="sec:5.1"><span class="sec-nr">5.1</span> <span class="sec-title">Lists
	235	<h2 id="sec:ext-lists"><a id="sec:5.1"><span class="sec-nr">5.1</span> <span class="sec-title">Lists
195	236	are special</span></a></h2>
196	237
197		<a name="sec:ext-lists"></a>
	238	<a id="sec:ext-lists"></a>
198	239
199	240	<p>As of version 7, SWI-Prolog lists can be distinguished
200	241	unambiguously at runtime from <code><code>.</code>/2</code> terms and

215	256	<p>The `cons' operator for creating list cells has changed from the
216	257	pretty atom <code>'.'</code> to the ugly atom <code>'[\|]'</code>, so we
217	258	can use the
218		<code>'.'</code> for other purposes. See <a class="sec" href="dicts.html">section
	259	<code>'.'</code> for other purposes. See <a class="sec" href="dicts.html#sec:5.4.1">section
219	260	5.4.1</a>.
220	261
221	262	<p>This modification has minimal impact on typical Prolog code. It does
222		affect foreign code (see <a class="sec" href="foreign.html">section 11</a>)
223		that uses the normal atom and compound term interface for manipulation
224		lists. In most cases this can be avoided by using the dedicated list
225		functions. For convenience, the macros <code>ATOM_nil</code> and <code>ATOM_dot</code>
226		are provided by
	263	affect foreign code (see <a class="sec" href="foreign.html#sec:11">section
	264	11</a>) that uses the normal atom and compound term interface for
	265	manipulation lists. In most cases this can be avoided by using the
	266	dedicated list functions. For convenience, the macros <code>ATOM_nil</code>
	267	and <code>ATOM_dot</code> are provided by
227	268	<code>SWI-Prolog.h</code>.
228	269
229		<p>Another place that is affected is <a name="idx:writecanonical1:1589"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>.
230		Impact is minimized by using the list syntax for lists. The predicates <a name="idx:readterm2:1590"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	270	<p>Another place that is affected is <a id="idx:writecanonical1:1589"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>.
	271	Impact is minimized by using the list syntax for lists. The predicates <a id="idx:readterm2:1590"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
231	272	and
232		<a name="idx:writeterm2:1591"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	273	<a id="idx:writeterm2:1591"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
233	274	support the option <code>dotlists(true)</code>, which causes
234		<a name="idx:readterm2:1592"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
235		to read <code>.(a,[])</code> as <code>[a]</code> and <a name="idx:writeterm2:1593"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	275	<a id="idx:readterm2:1592"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	276	to read <code>.(a,[])</code> as <code>[a]</code> and <a id="idx:writeterm2:1593"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
236	277	to write <code>[a]</code> as <code>.(a,[])</code>.
237	278
238		<p><h3 id="sec:ext-list-motivation"><a name="sec:5.1.1"><span class="sec-nr">5.1.1</span> <span class="sec-title">Motivating
	279	<p><h3 id="sec:ext-list-motivation"><a id="sec:5.1.1"><span class="sec-nr">5.1.1</span> <span class="sec-title">Motivating
239	280	'<code>[\|]</code>' and <code>[]</code> for lists</span></a></h3>
240	281
241		<a name="sec:ext-list-motivation"></a>
	282	<a id="sec:ext-list-motivation"></a>
242	283
243	284	<p>Representing lists the conventional way using <code><code>.</code>/2</code>
244	285	as cons-cell and '[]' as list terminator both (independently) poses

251	292	distinguished from <code>[a\|B]</code>. Freeing <code><code>.</code>/2</code>
252	293	provides us with a unique term that we can use for functional notation
253	294	on dicts as described in
254		<a class="sec" href="dicts.html">section 5.4.1</a>.
	295	<a class="sec" href="dicts.html#sec:5.4.1">section 5.4.1</a>.
255	296
256	297	<p>
257	298	<li>Using <code>'[]'</code> as list terminator prevents dynamic

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191	232	<a class="nav" href="strings.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:ext-syntax"><a name="sec:5.3"><span class="sec-nr">5.3</span> <span class="sec-title">Syntax
	235	<h2 id="sec:ext-syntax"><a id="sec:5.3"><span class="sec-nr">5.3</span> <span class="sec-title">Syntax
195	236	changes</span></a></h2>
196	237
197		<a name="sec:ext-syntax"></a>
198
199		<p><h3 id="sec:ext-syntax-op"><a name="sec:5.3.1"><span class="sec-nr">5.3.1</span> <span class="sec-title">Operators
	238	<a id="sec:ext-syntax"></a>
	239
	240	<p><h3 id="sec:ext-syntax-op"><a id="sec:5.3.1"><span class="sec-nr">5.3.1</span> <span class="sec-title">Operators
200	241	and quoted atoms</span></a></h3>
201	242
202		<a name="sec:ext-syntax-op"></a>
	243	<a id="sec:ext-syntax-op"></a>
203	244
204	245	<p>As of SWI-Prolog version 7, quoted atoms loose their operator
205	246	property. This means that expressions such as <code>A = 'dynamic'/1</code>

222	263	Y = 1790400.0'J'.
223	264	</pre>
224	265
225		<p><h3 id="sec:ext-compound-zero"><a name="sec:5.3.2"><span class="sec-nr">5.3.2</span> <span class="sec-title">Compound
	266	<p><h3 id="sec:ext-compound-zero"><a id="sec:5.3.2"><span class="sec-nr">5.3.2</span> <span class="sec-title">Compound
226	267	terms with zero arguments</span></a></h3>
227	268
228		<a name="sec:ext-compound-zero"></a>
	269	<a id="sec:ext-compound-zero"></a>
229	270
230	271	<p>As of SWI-Prolog version 7, the system supports compound terms
231	272	that have no arguments. This implies that e.g., <code>name()</code> is
232		valid syntax. This extension aims at functions on dicts (see <a class="sec" href="dicts.html">section
	273	valid syntax. This extension aims at functions on dicts (see <a class="sec" href="dicts.html#sec:5.4">section
233	274	5.4</a>) as well as the implementation of domain specific languages
234		(DSLs). To minimise the consequences, the classic predicates <a name="idx:functor3:1625"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
	275	(DSLs). To minimise the consequences, the classic predicates <a id="idx:functor3:1625"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
235	276	and <a class="pred" href="manipterm.html#=../2">=../2</a> have not been
236		modified. The predicates <a name="idx:compoundnamearity3:1626"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>
	277	modified. The predicates <a id="idx:compoundnamearity3:1626"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>
237	278	and
238		<a name="idx:compoundnamearguments3:1627"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>
	279	<a id="idx:compoundnamearguments3:1627"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>
239	280	have been added. These predicates operate only on compound terms and
240	281	behave consistently for compounds with zero arguments. Code that <em>generalises</em>
241		a term using the sequence below should generally be changed to use <a name="idx:compoundnamearity3:1628"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>.
	282	a term using the sequence below should generally be changed to use <a id="idx:compoundnamearity3:1628"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>.
242	283
243	284	<pre class="code">
244	285	...,

248	289	</pre>
249	290
250	291	<p>Replacement of <a class="pred" href="manipterm.html#=../2">=../2</a>
251		by <a name="idx:compoundnamearguments3:1629"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>
	292	by <a id="idx:compoundnamearguments3:1629"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>
252	293	is typically needed to deal with code that follow the skeleton below.
253	294
254	295	<pre class="code">

281	322
282	323	<p>Note that the <em>cannonical</em> representation of predicate heads
283	324	and functions without arguments is an atom. Thus, <code>clause(go(),
284		Body)</code> returns the clauses for <a name="idx:go0:1630"></a><span class="pred-ext">go/0</span>,
	325	Body)</code> returns the clauses for <a id="idx:go0:1630"></a><span class="pred-ext">go/0</span>,
285	326	but <code>clause(-Head, -Body, +Ref)</code> unifies <var>Head</var> with
286	327	an atom if the clause specified by <var>Ref</var> is part of a predicate
287	328	with zero arguments.
288	329
289		<p><h3 id="sec:ext-blockop"><a name="sec:5.3.3"><span class="sec-nr">5.3.3</span> <span class="sec-title">Block
	330	<p><h3 id="sec:ext-blockop"><a id="sec:5.3.3"><span class="sec-nr">5.3.3</span> <span class="sec-title">Block
290	331	operators</span></a></h3>
291	332
292		<a name="sec:ext-blockop"></a>
	333	<a id="sec:ext-blockop"></a>
293	334
294	335	<p>Introducing curly bracket and array subscripting.<sup class="fn">148<span class="fn-text">Introducing
295	336	block operators was proposed by Jose Morales. It was discussed in the

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193	234	</div>
194		<h1 id="sec:extensions"><a name="sec:5"><span class="sec-nr">5</span> <span class="sec-title">SWI-Prolog
	235	<h1 id="sec:extensions"><a id="sec:5"><span class="sec-nr">5</span> <span class="sec-title">SWI-Prolog
195	236	extensions</span></a></h1>
196	237
197		<a name="sec:extensions"></a>
	238	<a id="sec:extensions"></a>
198	239
199	240	<p>This chapter describes extensions to the Prolog language introduced
200	241	with SWI-Prolog version 7. The changes bring more modern

211	252
212	253	<p>While many programs run unmodified in SWI-Prolog version 7,
213	254	especially those that pass double quoted strings to general purpose list
214		processing predicates require modifications. We provide a tool (<a name="idx:liststrings0:1588"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>)
	255	processing predicates require modifications. We provide a tool (<a id="idx:liststrings0:1588"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>)
215	256	that we used to port a huge code base in half a day.
216	257
217	258	<p>

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194		<h2 id="sec:files"><a name="sec:4.36"><span class="sec-nr">4.36</span> <span class="sec-title">File
	235	<h2 id="sec:files"><a id="sec:4.36"><span class="sec-nr">4.36</span> <span class="sec-title">File
195	236	System Interaction</span></a></h2>
196	237
197		<a name="sec:files"></a>
	238	<a id="sec:files"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="access_file/2"><strong>access_file</strong>(<var>+File,
	241	<dt class="pubdef"><a id="access_file/2"><strong>access_file</strong>(<var>+File,
201	242	+Mode</var>)</a></dt>
202	243	<dd class="defbody">
203	244	True if <var>File</var> exists and can be accessed by this Prolog

220	261	note that checking access never provides a guarantee that a subsequent
221	262	open succeeds without errors due to inherent concurrency in file
222	263	operations. It is generally more robust to try and open the file and
223		handle possible exceptions. See <a name="idx:open4:1493"></a><a class="pred" href="IO.html#open/4">open/4</a>
	264	handle possible exceptions. See <a id="idx:open4:1493"></a><a class="pred" href="IO.html#open/4">open/4</a>
224	265	and
225		<a name="idx:catch3:1494"></a><a class="pred" href="exception.html#catch/3">catch/3</a>.</dd>
226		<dt class="pubdef"><a name="exists_file/1"><strong>exists_file</strong>(<var>+File</var>)</a></dt>
	266	<a id="idx:catch3:1494"></a><a class="pred" href="exception.html#catch/3">catch/3</a>.</dd>
	267	<dt class="pubdef"><a id="exists_file/1"><strong>exists_file</strong>(<var>+File</var>)</a></dt>
227	268	<dd class="defbody">
228	269	True if <var>File</var> exists and is a regular file. This does not
229	270	imply the user has read and/or write permission for the file. This is
230	271	the same as <code>access_file(File, exist)</code>.</dd>
231		<dt class="pubdef"><a name="file_directory_name/2"><strong>file_directory_name</strong>(<var>+File,
	272	<dt class="pubdef"><a id="file_directory_name/2"><strong>file_directory_name</strong>(<var>+File,
232	273	-Directory</var>)</a></dt>
233	274	<dd class="defbody">
234	275	Extracts the directory part of <var>File</var>. The returned <var>Directory</var>

240	281	it is not a valid file name. In this case the final <code><code>/</code></code>
241	282	is removed from <var>File</var>, e.g., <code>'/hello'</code>.
242	283
243		<p>See also <a name="idx:directoryfilepath3:1495"></a><span class="pred-ext">directory_file_path/3</span>
	284	<p>See also <a id="idx:directoryfilepath3:1495"></a><span class="pred-ext">directory_file_path/3</span>
244	285	from <code>library(filesex)</code>. The system ensures that for every
245	286	valid <var>Path</var> using the Prolog (POSIX) directory separators,
246	287	following is true on systems with a sound implementation of
247		<a name="idx:samefile2:1496"></a><a class="pred" href="files.html#same_file/2">same_file/2</a>.<sup class="fn">134<span class="fn-text">On
	288	<a id="idx:samefile2:1496"></a><a class="pred" href="files.html#same_file/2">same_file/2</a>.<sup class="fn">134<span class="fn-text">On
248	289	some systems, <var>Path</var> and <var>Path2</var> refer to the same
249		entry in the file system, but <a name="idx:samefile2:1497"></a><a class="pred" href="files.html#same_file/2">same_file/2</a>
250		may fail.</span></sup> See also <a name="idx:prologtoosfilename2:1498"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>.
	290	entry in the file system, but <a id="idx:samefile2:1497"></a><a class="pred" href="files.html#same_file/2">same_file/2</a>
	291	may fail.</span></sup> See also <a id="idx:prologtoosfilename2:1498"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>.
251	292
252	293	<pre class="code">
253	294	...,

258	299	</pre>
259	300
260	301	</dd>
261		<dt class="pubdef"><a name="file_base_name/2"><strong>file_base_name</strong>(<var>+File,
	302	<dt class="pubdef"><a id="file_base_name/2"><strong>file_base_name</strong>(<var>+File,
262	303	-BaseName</var>)</a></dt>
263	304	<dd class="defbody">
264	305	Extracts the filename part from a path specification. If <var>File</var>
265	306	does not contain any directory separators, <var>File</var> is returned
266	307	in
267		<var>BaseName</var>. See also <a name="idx:filedirectoryname2:1499"></a><a class="pred" href="files.html#file_directory_name/2">file_directory_name/2</a>.
	308	<var>BaseName</var>. See also <a id="idx:filedirectoryname2:1499"></a><a class="pred" href="files.html#file_directory_name/2">file_directory_name/2</a>.
268	309	If the <var>File</var> arguments ends with a <code><code>/</code></code>,
269	310	e.g., <code>'/hello/'</code>, <var>BaseName</var> is unified with the
270	311	empty atom (<code>''</code>).</dd>
271		<dt class="pubdef"><a name="same_file/2"><strong>same_file</strong>(<var>+File1,
	312	<dt class="pubdef"><a id="same_file/2"><strong>same_file</strong>(<var>+File1,
272	313	+File2</var>)</a></dt>
273	314	<dd class="defbody">
274	315	True if both filenames refer to the same physical file. That is, if
275	316	<var>File1</var> and <var>File2</var> are the same string or both names
276	317	exist and point to the same file (due to hard or symbolic links and/or
277	318	relative vs. absolute paths). On systems that provide stat() with
278		meaningful values for <code>st_dev</code> and <code>st_inode</code>, <a name="idx:samefile2:1500"></a><a class="pred" href="files.html#same_file/2">same_file/2</a>
	319	meaningful values for <code>st_dev</code> and <code>st_inode</code>, <a id="idx:samefile2:1500"></a><a class="pred" href="files.html#same_file/2">same_file/2</a>
279	320	is implemented by comparing the device and inode identifiers. On
280	321	Windows,
281		<a name="idx:samefile2:1501"></a><a class="pred" href="files.html#same_file/2">same_file/2</a>
	322	<a id="idx:samefile2:1501"></a><a class="pred" href="files.html#same_file/2">same_file/2</a>
282	323	compares the strings returned by the GetFullPathName() system call.</dd>
283		<dt class="pubdef"><a name="exists_directory/1"><strong>exists_directory</strong>(<var>+Directory</var>)</a></dt>
	324	<dt class="pubdef"><a id="exists_directory/1"><strong>exists_directory</strong>(<var>+Directory</var>)</a></dt>
284	325	<dd class="defbody">
285	326	True if <var>Directory</var> exists and is a directory. This does not
286	327	imply the user has read, search or write permission for the directory.</dd>
287		<dt class="pubdef"><a name="delete_file/1"><strong>delete_file</strong>(<var>+File</var>)</a></dt>
	328	<dt class="pubdef"><a id="delete_file/1"><strong>delete_file</strong>(<var>+File</var>)</a></dt>
288	329	<dd class="defbody">
289	330	Remove <var>File</var> from the file system.</dd>
290		<dt class="pubdef"><a name="rename_file/2"><strong>rename_file</strong>(<var>+File1,
	331	<dt class="pubdef"><a id="rename_file/2"><strong>rename_file</strong>(<var>+File1,
291	332	+File2</var>)</a></dt>
292	333	<dd class="defbody">
293	334	Rename <var>File1</var> as <var>File2</var>. The semantics is compatible

295	336	operating system allows. Notably, if <var>File2</var> exists, the
296	337	operation succeeds (except for possible permission errors) and is <em>atomic</em>
297	338	(meaning there is no window where <var>File2</var> does not exist).</dd>
298		<dt class="pubdef"><a name="size_file/2"><strong>size_file</strong>(<var>+File,
	339	<dt class="pubdef"><a id="size_file/2"><strong>size_file</strong>(<var>+File,
299	340	-Size</var>)</a></dt>
300	341	<dd class="defbody">
301	342	Unify <var>Size</var> with the size of <var>File</var> in bytes.</dd>
302		<dt class="pubdef"><a name="time_file/2"><strong>time_file</strong>(<var>+File,
	343	<dt class="pubdef"><a id="time_file/2"><strong>time_file</strong>(<var>+File,
303	344	-Time</var>)</a></dt>
304	345	<dd class="defbody">
305	346	Unify the last modification time of <var>File</var> with <var>Time</var>.
306	347	<var>Time</var> is a floating point number expressing the seconds
307		elapsed since Jan 1, 1970. See also <a name="idx:converttime28:1502"></a><span class="pred-ext">convert_time/[2,8]</span>
308		and <a name="idx:gettime1:1503"></a><a class="pred" href="system.html#get_time/1">get_time/1</a>.</dd>
309		<dt class="pubdef"><a name="absolute_file_name/2"><strong>absolute_file_name</strong>(<var>+File,
	348	elapsed since Jan 1, 1970. See also <a id="idx:converttime28:1502"></a><span class="pred-ext">convert_time/[2,8]</span>
	349	and <a id="idx:gettime1:1503"></a><a class="pred" href="system.html#get_time/1">get_time/1</a>.</dd>
	350	<dt class="pubdef"><a id="absolute_file_name/2"><strong>absolute_file_name</strong>(<var>+File,
310	351	-Absolute</var>)</a></dt>
311	352	<dd class="defbody">
312	353	Expand a local filename into an absolute path. The absolute path is

314	355	deleted. This predicate ensures that expanding a filename returns the
315	356	same absolute path regardless of how the file is addressed. SWI-Prolog
316	357	uses absolute filenames to register source files independent of the
317		current working directory. See also <a name="idx:absolutefilename3:1504"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
318		and <a name="idx:expandfilename2:1505"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>.</dd>
319		<dt class="pubdef"><a name="absolute_file_name/3"><strong>absolute_file_name</strong>(<var>+Spec,
	358	current working directory. See also <a id="idx:absolutefilename3:1504"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	359	and <a id="idx:expandfilename2:1505"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>.</dd>
	360	<dt class="pubdef"><a id="absolute_file_name/3"><strong>absolute_file_name</strong>(<var>+Spec,
320	361	-Absolute, +Options</var>)</a></dt>
321	362	<dd class="defbody">
322	363	Convert the given file specification into an absolute path. <var>Spec</var>

329	370	<dt><strong>extensions</strong>(<var>ListOfExtensions</var>)</dt>
330	371	<dd class="defbody">
331	372	List of file extensions to try. Default is <code>''</code>. For each
332		extension, <a name="idx:absolutefilename3:1506"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	373	extension, <a id="idx:absolutefilename3:1506"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
333	374	will first add the extension and then verify the conditions imposed by
334	375	the other options. If the condition fails, the next extension on the
335	376	list is tried. Extensions may be specified both as <code>.ext</code> or

338	379	<dd class="defbody">
339	380	Resolve the path relative to the given directory or the directory
340	381	holding the given file. Without this option, paths are resolved relative
341		to the working directory (see <a name="idx:workingdirectory2:1507"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>)
342		or, if <var>Spec</var> is atomic and <a name="idx:absolutefilename23:1508"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/[2,3]</a>
	382	to the working directory (see <a id="idx:workingdirectory2:1507"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>)
	383	or, if <var>Spec</var> is atomic and <a id="idx:absolutefilename23:1508"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/[2,3]</a>
343	384	is executed in a directive, it uses the current source file as
344	385	reference.</dd>
345	386	<dt><strong>access</strong>(<var>Mode</var>)</dt>
346	387	<dd class="defbody">
347	388	Imposes the condition access_file(<var>File</var>, <var>Mode</var>). <var>Mode</var>
348	389	is one of <code>read</code>, <code>write</code>, <code>append</code>,
349		<code>execute</code>, <code>exist</code> or <code>none</code>. See also <a name="idx:accessfile2:1509"></a><a class="pred" href="files.html#access_file/2">access_file/2</a>.</dd>
	390	<code>execute</code>, <code>exist</code> or <code>none</code>. See also <a id="idx:accessfile2:1509"></a><a class="pred" href="files.html#access_file/2">access_file/2</a>.</dd>
350	391	<dt><strong>file_type</strong>(<var>Type</var>)</dt>
351	392	<dd class="defbody">
352	393	Defines extensions. Current mapping: <code>txt</code> implies <code>['']</code>,

356	397	and
357	398	<code>directory</code> implies <code>['']</code>. The file type <code>source</code>
358	399	is an alias for <code>prolog</code> for compatibility with SICStus
359		Prolog. See also <a name="idx:prologfiletype2:1510"></a><a class="pred" href="consulting.html#prolog_file_type/2">prolog_file_type/2</a>.
	400	Prolog. See also <a id="idx:prologfiletype2:1510"></a><a class="pred" href="consulting.html#prolog_file_type/2">prolog_file_type/2</a>.
360	401	This predicate only returns non-directories, unless the option <code>file_type(directory)</code>
361	402	is specified.</dd>
362	403	<dt><strong>file_errors</strong>(<var>fail/error</var>)</dt>

373	414	<dt><strong>expand</strong>(<var>Boolean</var>)</dt>
374	415	<dd class="defbody">
375	416	If <code>true</code> (default is <code>false</code>) and <var>Spec</var>
376		is atomic, call <a name="idx:expandfilename2:1511"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>
377		followed by <a name="idx:member2:1512"></a><a class="pred" href="lists.html#member/2">member/2</a>
	417	is atomic, call <a id="idx:expandfilename2:1511"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>
	418	followed by <a id="idx:member2:1512"></a><a class="pred" href="lists.html#member/2">member/2</a>
378	419	on <var>Spec</var> before proceeding. This is a SWI-Prolog extension
379	420	intended to minimise porting effort after SWI-Prolog stopped expanding
380	421	environment variables and the <code><code>~</code></code> by default.

391	432	argument order was <code>absolute_file_name(+Spec, +Options, -Path)</code>.
392	433	The argument order has been changed for compatibility with ISO and
393	434	SICStus. The Quintus argument order is still accepted.</dd>
394		<dt class="pubdef"><a name="is_absolute_file_name/1"><strong>is_absolute_file_name</strong>(<var>+File</var>)</a></dt>
	435	<dt class="pubdef"><a id="is_absolute_file_name/1"><strong>is_absolute_file_name</strong>(<var>+File</var>)</a></dt>
395	436	<dd class="defbody">
396	437	True if <var>File</var> specifies an absolute path name. On Unix
397	438	systems, this implies the path starts with a `/'. For Microsoft-based
398	439	systems this implies the path starts with <code><<var>letter</var>>:</code>.
399	440	This predicate is intended to provide platform-independent checking for
400		absolute paths. See also <a name="idx:absolutefilename2:1513"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>
401		and <a name="idx:prologtoosfilename2:1514"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>.</dd>
402		<dt class="pubdef"><a name="file_name_extension/3"><strong>file_name_extension</strong>(<var>?Base,
	441	absolute paths. See also <a id="idx:absolutefilename2:1513"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>
	442	and <a id="idx:prologtoosfilename2:1514"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>.</dd>
	443	<dt class="pubdef"><a id="file_name_extension/3"><strong>file_name_extension</strong>(<var>?Base,
403	444	?Extension, ?Name</var>)</a></dt>
404	445	<dd class="defbody">
405	446	This predicate is used to add, remove or test filename extensions. The

408	449	testing for an extension will also be done case-insensitive. <var>Extension</var>
409	450	may be specified with or without a leading dot (<code><code>.</code></code>).
410	451	If an <var>Extension</var> is generated, it will not have a leading dot.</dd>
411		<dt class="pubdef"><a name="directory_files/2"><strong>directory_files</strong>(<var>+Directory,
	452	<dt class="pubdef"><a id="directory_files/2"><strong>directory_files</strong>(<var>+Directory,
412	453	-Entries</var>)</a></dt>
413	454	<dd class="defbody">
414	455	Unify <var>Entries</var> with a list of entries in <var>Directory</var>.

416	457	to <var>Directory</var>. <var>Entries</var> contains all entries,
417	458	including hidden files and, if supplied by the OS, the special entries <code><code>.</code></code>
418	459	and
419		<code>..</code>. See also <a name="idx:expandfilename2:1515"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>.<sup class="fn">136<span class="fn-text">This
	460	<code>..</code>. See also <a id="idx:expandfilename2:1515"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>.<sup class="fn">136<span class="fn-text">This
420	461	predicate should be considered a misnomer because it returns entries
421	462	rather than files. We stick to this name for compatibility with, e.g.,
422	463	SICStus, Ciao and YAP.</span></sup></dd>
423		<dt class="pubdef"><a name="expand_file_name/2"><strong>expand_file_name</strong>(<var>+WildCard,
	464	<dt class="pubdef"><a id="expand_file_name/2"><strong>expand_file_name</strong>(<var>+WildCard,
424	465	-List</var>)</a></dt>
425	466	<dd class="defbody">
426	467	Unify <var>List</var> with a sorted list of files or directories

447	488	set the environment variable <code>HOME</code> to point to the
448	489	SWI-Prolog home directory if neither <code>HOME</code> nor <code>HOMEPATH</code>
449	490	and <code>HOMEDRIVE</code> are defined.</span></sup></dd>
450		<dt class="pubdef"><a name="prolog_to_os_filename/2"><strong>prolog_to_os_filename</strong>(<var>?PrologPath,
	491	<dt class="pubdef"><a id="prolog_to_os_filename/2"><strong>prolog_to_os_filename</strong>(<var>?PrologPath,
451	492	?OsPath</var>)</a></dt>
452	493	<dd class="defbody">
453	494	Convert between the internal Prolog path name conventions and the

455	496	the POSIX standard, which implies that this predicate is equivalent to
456	497	=/2 (unify) on POSIX (e.g., Unix) systems. On Windows systems it changes
457	498	the directory separator from <code><code>\</code></code> into <code><code>/</code></code>.</dd>
458		<dt class="pubdef"><a name="read_link/3"><strong>read_link</strong>(<var>+File,
	499	<dt class="pubdef"><a id="read_link/3"><strong>read_link</strong>(<var>+File,
459	500	-Link, -Target</var>)</a></dt>
460	501	<dd class="defbody">
461	502	If <var>File</var> points to a symbolic link, unify <var>Link</var> with

464	505	<var>Target</var> points to a file, directory or non-existing entry in
465	506	the file system, but never to a link. Fails if <var>File</var> is not a
466	507	link. Fails always on systems that do not support symbolic links.</dd>
467		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="tmp_file/2"><strong>tmp_file</strong>(<var>+Base,
	508	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="tmp_file/2"><strong>tmp_file</strong>(<var>+Base,
468	509	-TmpName</var>)</a></dt>
469	510	<dd class="defbody">
470	511	Create a name for a temporary file. <var>Base</var> is an identifier for

476	517
477	518	<p>Because it is possible to guess the generated filename, attackers may
478	519	create the filesystem entry as a link and possibly create a security
479		issue. New code should use <a name="idx:tmpfilestream3:1516"></a><a class="pred" href="files.html#tmp_file_stream/3">tmp_file_stream/3</a>.</dd>
480		<dt class="pubdef"><a name="tmp_file_stream/3"><strong>tmp_file_stream</strong>(<var>+Encoding,
	520	issue. New code should use <a id="idx:tmpfilestream3:1516"></a><a class="pred" href="files.html#tmp_file_stream/3">tmp_file_stream/3</a>.</dd>
	521	<dt class="pubdef"><a id="tmp_file_stream/3"><strong>tmp_file_stream</strong>(<var>+Encoding,
481	522	-FileName, -Stream</var>)</a></dt>
482	523	<dd class="defbody">
483	524	Create a temporary filename <var>FileName</var> and open it for writing

487	528	supports it, the created file is only accessible to the current user. If
488	529	the OS supports it, the file is created using the open()-flag <code>O_EXCL</code>,
489	530	which guarantees that the file did not exist before this call. This
490		predicate is a safe replacement of <a name="idx:tmpfile2:1517"></a><a class="pred" href="files.html#tmp_file/2">tmp_file/2</a>.
	531	predicate is a safe replacement of <a id="idx:tmpfile2:1517"></a><a class="pred" href="files.html#tmp_file/2">tmp_file/2</a>.
491	532	Note that in those cases where the temporary file is needed to store
492	533	output from an external command, the file must be closed first. E.g.,
493	534	the following downloads a file from a URL to a temporary file and opens

504	545	</pre>
505	546
506	547	<p>Temporary files created using this call are removed if the Prolog
507		process terminates <em>gracefully</em>. Calling <a name="idx:deletefile1:1518"></a><a class="pred" href="files.html#delete_file/1">delete_file/1</a>
	548	process terminates <em>gracefully</em>. Calling <a id="idx:deletefile1:1518"></a><a class="pred" href="files.html#delete_file/1">delete_file/1</a>
508	549	using
509	550	<var>FileName</var> removes the file and removes the entry from the
510	551	administration of files-to-be-deleted.</dd>
511		<dt class="pubdef"><a name="make_directory/1"><strong>make_directory</strong>(<var>+Directory</var>)</a></dt>
	552	<dt class="pubdef"><a id="make_directory/1"><strong>make_directory</strong>(<var>+Directory</var>)</a></dt>
512	553	<dd class="defbody">
513	554	Create a new directory (folder) on the filesystem. Raises an exception
514	555	on failure. On Unix systems, the directory is created with default
515	556	permissions (defined by the process <em>umask</em> setting).</dd>
516		<dt class="pubdef"><a name="delete_directory/1"><strong>delete_directory</strong>(<var>+Directory</var>)</a></dt>
	557	<dt class="pubdef"><a id="delete_directory/1"><strong>delete_directory</strong>(<var>+Directory</var>)</a></dt>
517	558	<dd class="defbody">
518	559	Delete directory (folder) from the filesystem. Raises an exception on
519	560	failure. Please note that in general it will not be possible to delete a
520	561	non-empty directory.</dd>
521		<dt class="pubdef"><a name="working_directory/2"><strong>working_directory</strong>(<var>-Old,
	562	<dt class="pubdef"><a id="working_directory/2"><strong>working_directory</strong>(<var>-Old,
522	563	+New</var>)</a></dt>
523	564	<dd class="defbody">
524	565	Unify <var>Old</var> with an absolute path to the current working
525	566	directory and change working directory to <var>New</var>. Use the
526	567	pattern
527	568	<code>working_directory(CWD, CWD)</code> to get the current directory.
528		See also <a name="idx:absolutefilename2:1519"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>
529		and <a name="idx:chdir1:1520"></a><a class="pred" href="files.html#chdir/1">chdir/1</a>.<sup class="fn">bug<span class="fn-text">Some
	569	See also <a id="idx:absolutefilename2:1519"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>
	570	and <a id="idx:chdir1:1520"></a><a class="pred" href="files.html#chdir/1">chdir/1</a>.<sup class="fn">bug<span class="fn-text">Some
530	571	of the file I/O predicates use local filenames. Changing directory while
531		file-bound streams are open causes wrong results on <a name="idx:telling1:1521"></a><a class="pred" href="IO.html#telling/1">telling/1</a>, <a name="idx:seeing1:1522"></a><a class="pred" href="IO.html#seeing/1">seeing/1</a>
532		and <a name="idx:currentstream3:1523"></a><a class="pred" href="IO.html#current_stream/3">current_stream/3</a>.</span></sup>
	572	file-bound streams are open causes wrong results on <a id="idx:telling1:1521"></a><a class="pred" href="IO.html#telling/1">telling/1</a>, <a id="idx:seeing1:1522"></a><a class="pred" href="IO.html#seeing/1">seeing/1</a>
	573	and <a id="idx:currentstream3:1523"></a><a class="pred" href="IO.html#current_stream/3">current_stream/3</a>.</span></sup>
533	574	Note that the working directory is shared between all threads.</dd>
534		<dt class="pubdef"><a name="chdir/1"><strong>chdir</strong>(<var>+Path</var>)</a></dt>
535		<dd class="defbody">
536		Compatibility predicate. New code should use <a name="idx:workingdirectory2:1524"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>.
	575	<dt class="pubdef"><a id="chdir/1"><strong>chdir</strong>(<var>+Path</var>)</a></dt>
	576	<dd class="defbody">
	577	Compatibility predicate. New code should use <a id="idx:workingdirectory2:1524"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>.
537	578	</dd>
538	579	</dl>
539	580

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 12.4</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:findappfile"><a name="sec:12.4"><span class="sec-nr">12.4</span> <span class="sec-title">Finding
	235	<h2 id="sec:findappfile"><a id="sec:12.4"><span class="sec-nr">12.4</span> <span class="sec-title">Finding
195	236	Application files</span></a></h2>
196	237
197		<a name="sec:findappfile"></a>
	238	<a id="sec:findappfile"></a>
198	239
199	240	<p>If your application uses files that are not part of the saved program
200	241	such as database files, configuration files, etc., the runtime version
201		has to be able to locate these files. The <a name="idx:filesearchpath2:2129"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	242	has to be able to locate these files. The <a id="idx:filesearchpath2:2133"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
202	243	mechanism in combination with the <strong>-p</strong>alias command line
203	244	argument is the preferred way to locate runtime files. The first step is
204	245	to define an alias for the top-level directory of your application. We

227	268	).
228	269	</pre>
229	270
230		<p><h3 id="sec:runtime-file-search-path"><a name="sec:12.4.1"><span class="sec-nr">12.4.1</span> <span class="sec-title">Specifying
	271	<p><h3 id="sec:runtime-file-search-path"><a id="sec:12.4.1"><span class="sec-nr">12.4.1</span> <span class="sec-title">Specifying
231	272	a file search path from the command line</span></a></h3>
232	273
233		<a name="sec:runtime-file-search-path"></a>
	274	<a id="sec:runtime-file-search-path"></a>
234	275
235	276	<p>Suppose the system administrator has installed the SWI-Prolog runtime
236	277	environment in <code>/usr/local/lib/rt-pl-3.2.0</code>. A user wants to

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 11.6</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:findhome"><a name="sec:11.6"><span class="sec-nr">11.6</span> <span class="sec-title">The
	235	<h2 id="sec:findhome"><a id="sec:11.6"><span class="sec-nr">11.6</span> <span class="sec-title">The
195	236	Prolog `home' directory</span></a></h2>
196	237
197		<a name="sec:findhome"></a>
	238	<a id="sec:findhome"></a>
198	239
199	240	<p>Executables embedding SWI-Prolog should be able to find the `home'
200	241	directory of the development environment unless a self-contained saved
201		state has been added to the executable (see <a name="idx:qsaveprogram12:2088"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>
202		and <a class="sec" href="plld.html">section 11.5</a>).
	242	state has been added to the executable (see <a id="idx:qsaveprogram12:2092"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>
	243	and <a class="sec" href="plld.html#sec:11.5">section 11.5</a>).
203	244
204	245	<p>If Prolog starts up, it will try to locate the development
205	246	environment. To do so, it will try the following steps until one

227	268	SWI-Prolog gives up. If a state is attached, the current working
228	269	directory is used.
229	270
230		<p>The <a name="idx:filesearchpath2:2089"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	271	<p>The <a id="idx:filesearchpath2:2093"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
231	272	alias <code>swi</code> is set to point to the home directory located.
232	273
233	274	<p></body></html>⏎

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193	234	</div>
194		<h2 id="sec:flags"><a name="sec:2.11"><span class="sec-nr">2.11</span> <span class="sec-title">Environment
	235	<h2 id="sec:flags"><a id="sec:2.11"><span class="sec-nr">2.11</span> <span class="sec-title">Environment
195	236	Control (Prolog flags)</span></a></h2>
196	237
197		<a name="sec:flags"></a>
198
199		<p>The predicates <a name="idx:currentprologflag2:80"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
200		and <a name="idx:setprologflag2:81"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
	238	<a id="sec:flags"></a>
	239
	240	<p>The predicates <a id="idx:currentprologflag2:80"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
	241	and <a id="idx:setprologflag2:81"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
201	242	allow the user to examine and modify the execution environment. It
202	243	provides access to whether optional features are available on this
203	244	version, operating system, foreign code environment, command line

206	247	Prolog environments.
207	248
208	249	<dl class="latex">
209		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="current_prolog_flag/2"><strong>current_prolog_flag</strong>(<var>?Key,
	250	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="current_prolog_flag/2"><strong>current_prolog_flag</strong>(<var>?Key,
210	251	-Value</var>)</a></dt>
211	252	<dd class="defbody">
212		The predicate <a name="idx:currentprologflag2:82"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
	253	The predicate <a id="idx:currentprologflag2:82"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>
213	254	defines an interface to installation features: options compiled in,
214	255	version, home, etc. With both arguments unbound, it will generate all
215	256	defined Prolog flags. With <var>Key</var> instantiated, it unifies <var>Value</var>

217	258	a Prolog flag.
218	259
219	260	<p>Flags marked <b>rw</b> can be modified by the user using
220		<a name="idx:setprologflag2:83"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>.
	261	<a id="idx:setprologflag2:83"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>.
221	262	Flag values are typed. Flags marked as <code>bool</code> can have the
222	263	values <code>true</code> or <code>false</code>. The predicate
223		<a name="idx:createprologflag3:84"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>
	264	<a id="idx:createprologflag3:84"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>
224	265	may be used to create flags that describe or control behaviour of
225	266	libraries and applications. The library
226	267	<code>library(settings)</code> provides an alternative interface for

246	287	<a class="flag" href="flags.html#flag:generate_debug_info">generate_debug_info</a>
247	288	and <a class="flag" href="flags.html#flag:optimise">optimise</a>.
248	289
249		<p>A new thread (see <a class="sec" href="threads.html">section 9</a>) <em>copies</em>
	290	<p>A new thread (see <a class="sec" href="threads.html#sec:9">section 9</a>) <em>copies</em>
250	291	all flags from the thread that created the new thread (its <em>parent</em>).<sup class="fn">17<span class="fn-text">This
251	292	is implemented using the copy-on-write tecnhnique.</span></sup> As a
252	293	consequence, modifying a flag inside a thread does not affect other
253	294	threads.
254	295
255	296	<dl class="latex">
256		<dt class="pubdef"><a name="flag:access_level"><strong>access_level</strong>(<var>atom</var>, changeable)</a></dt>
	297	<dt class="pubdef"><a id="flag:access_level"><strong>access_level</strong>(<var>atom</var>, changeable)</a></dt>
257	298	<dd class="defbody">
258	299	This flag defines a normal `user' view (<code>user</code>, default) or a
259	300	`system' view. In system view all system code is fully accessible as if

261	302	permitted and some details are kept invisible. We leave the exact
262	303	consequences undefined, but, for example, system code can be traced
263	304	using system access and system predicates can be redefined.</dd>
264		<dt class="pubdef"><a name="flag:address_bits"><strong>address_bits</strong>(<var>integer</var>)</a></dt>
	305	<dt class="pubdef"><a id="flag:address_bits"><strong>address_bits</strong>(<var>integer</var>)</a></dt>
265	306	<dd class="defbody">
266	307	Address size of the hosting machine. Typically 32 or 64. Except for the
267	308	maximum stack limit, this has few implications to the user. See also the
268	309	Prolog flag <a class="flag" href="flags.html#flag:arch">arch</a>.</dd>
269		<dt class="pubdef"><a name="flag:agc_margin"><strong>agc_margin</strong>(<var>integer</var>, changeable)</a></dt>
	310	<dt class="pubdef"><a id="flag:agc_margin"><strong>agc_margin</strong>(<var>integer</var>, changeable)</a></dt>
270	311	<dd class="defbody">
271	312	If this amount of atoms possible garbage atoms exist perform atom
272	313	garbage collection at the first opportunity. Initial value is 10,000.

274	315	See also <a class="func" href="foreigninclude.html#PL_register_atom()">PL_register_atom()</a>.<sup class="fn">18<span class="fn-text">Given
275	316	that SWI-Prolog has no limit on the length of atoms, 10,000 atoms may
276	317	still occupy a lot of memory. Applications using extremely large atoms
277		may wish to call <a name="idx:garbagecollectatoms0:85"></a><a class="pred" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a>
	318	may wish to call <a id="idx:garbagecollectatoms0:85"></a><a class="pred" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a>
278	319	explicitly or lower the margin.</span></sup></dd>
279		<dt class="pubdef"><a name="flag:apple"><strong>apple</strong>(<var>bool</var>)</a></dt>
280		<dd class="defbody">
281		<a name="idx:MacOS:86"></a>If present and <code>true</code>, the
282		operating system is MacOSX. Defined if the C compiler used to compile
283		this version of SWI-Prolog defines
	320	<dt class="pubdef"><a id="flag:apple"><strong>apple</strong>(<var>bool</var>)</a></dt>
	321	<dd class="defbody">
	322	<a id="idx:MacOS:86"></a>If present and <code>true</code>, the operating
	323	system is MacOSX. Defined if the C compiler used to compile this version
	324	of SWI-Prolog defines
284	325	<code>__APPLE__</code>. Note that the <a class="flag" href="flags.html#flag:unix">unix</a>
285	326	is also defined for MacOSX.</dd>
286		<dt class="pubdef"><a name="flag:allow_dot_in_atom"><strong>allow_dot_in_atom</strong>(<var>bool</var>, changeable)</a></dt>
	327	<dt class="pubdef"><a id="flag:allow_dot_in_atom"><strong>allow_dot_in_atom</strong>(<var>bool</var>, changeable)</a></dt>
287	328	<dd class="defbody">
288	329	If <code>true</code> (default <code>false</code>), dots may be embedded
289	330	into atoms that are not quoted and start with a letter. The embedded dot

293	334	that this conflicts with cascading functional notation. For example,
294	335	<code>Post.meta.author</code> is read as <code>.(Post, 'meta.author'</code>
295	336	if this flag is set to <code>true</code>.</dd>
296		<dt class="pubdef"><a name="flag:allow_variable_name_as_functor"><strong>allow_variable_name_as_functor</strong>(<var>bool</var>, changeable)</a></dt>
	337	<dt class="pubdef"><a id="flag:allow_variable_name_as_functor"><strong>allow_variable_name_as_functor</strong>(<var>bool</var>, changeable)</a></dt>
297	338	<dd class="defbody">
298	339	If true (default is false), <code>Functor(arg)</code> is read as if it
299	340	were written <code>'Functor'(arg)</code>. Some applications use the
300		Prolog <a name="idx:read1:87"></a><a class="pred" href="termrw.html#read/1">read/1</a>
	341	Prolog <a id="idx:read1:87"></a><a class="pred" href="termrw.html#read/1">read/1</a>
301	342	predicate for reading an application-defined script language. In these
302	343	cases, it is often difficult to explain to non-Prolog users of the
303	344	application that constants and functions can only start with a lowercase
304	345	letter. Variables can be turned into atoms starting with an uppercase
305		atom by calling <a name="idx:readterm2:88"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	346	atom by calling <a id="idx:readterm2:88"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
306	347	using the option <code>variable_names</code> and binding the variables
307	348	to their name. Using this feature, F(x) can be turned into valid syntax
308	349	for such script languages. Suggested by Robert van Engelen. SWI-Prolog
309	350	specific.</dd>
310		<dt class="pubdef"><a name="flag:argv"><strong>argv</strong>(<var>list</var>, changeable)</a></dt>
	351	<dt class="pubdef"><a id="flag:argv"><strong>argv</strong>(<var>list</var>, changeable)</a></dt>
311	352	<dd class="defbody">
312	353	List is a list of atoms representing the application command line
313	354	arguments. Application command line arguments are those that have

318	359	was defined as <a class="flag" href="flags.html#flag:os_argv">os_argv</a>
319	360	is now. The change was made for compatibility reasons and because the
320	361	current definition is more practical.</span></sup></dd>
321		<dt class="pubdef"><a name="flag:arch"><strong>arch</strong>(<var>atom</var>)</a></dt>
	362	<dt class="pubdef"><a id="flag:arch"><strong>arch</strong>(<var>atom</var>)</a></dt>
322	363	<dd class="defbody">
323	364	Identifier for the hardware and operating system SWI-Prolog is running
324	365	on. Used to select foreign files for the right architecture. See also
325		<a class="sec" href="foreignlink.html">section 11.2.3</a> and <a name="idx:filesearchpath2:89"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.</dd>
326		<dt class="pubdef"><a name="flag:associated_file"><strong>associated_file</strong>(<var>atom</var>)</a></dt>
327		<dd class="defbody">
328		Set if Prolog was started with a prolog file as argument. Used by e.g., <a name="idx:edit0:90"></a><a class="pred" href="edit.html#edit/0">edit/0</a>
	366	<a class="sec" href="foreignlink.html#sec:11.2.3">section 11.2.3</a> and <a id="idx:filesearchpath2:89"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.</dd>
	367	<dt class="pubdef"><a id="flag:associated_file"><strong>associated_file</strong>(<var>atom</var>)</a></dt>
	368	<dd class="defbody">
	369	Set if Prolog was started with a prolog file as argument. Used by e.g., <a id="idx:edit0:90"></a><a class="pred" href="edit.html#edit/0">edit/0</a>
329	370	to edit the initial file.</dd>
330		<dt class="pubdef"><a name="flag:autoload"><strong>autoload</strong>(<var>bool</var>, changeable)</a></dt>
	371	<dt class="pubdef"><a id="flag:autoload"><strong>autoload</strong>(<var>bool</var>, changeable)</a></dt>
331	372	<dd class="defbody">
332	373	If <code>true</code> (default) autoloading of library functions is
333	374	enabled.</dd>
334		<dt class="pubdef"><a name="flag:back_quotes"><strong>back_quotes</strong>(<var>codes,chars,string,symbol_char</var>, changeable)</a></dt>
	375	<dt class="pubdef"><a id="flag:back_quotes"><strong>back_quotes</strong>(<var>codes,chars,string,symbol_char</var>, changeable)</a></dt>
335	376	<dd class="defbody">
336	377	Defines the term-representation for back-quoted material. The default is <code>codes</code>.
337	378	If <strong>--traditional</strong> is given, the default is <code>symbol_char</code>,
338	379	which allows using <code>`</code> in operators composed of symbols.<sup class="fn">20<span class="fn-text">Older
339	380	versions had a boolean flag <code>backquoted_strings</code>, which
340	381	toggled between <code>string</code> and <code>symbol_char</code></span></sup>.
341		See also <a class="sec" href="strings.html">section 5.2</a>.</dd>
342		<dt class="pubdef"><a name="flag:backtrace"><strong>backtrace</strong>(<var>bool</var>, changeable)</a></dt>
	382	See also <a class="sec" href="strings.html#sec:5.2">section 5.2</a>.</dd>
	383	<dt class="pubdef"><a id="flag:backtrace"><strong>backtrace</strong>(<var>bool</var>, changeable)</a></dt>
343	384	<dd class="defbody">
344	385	If <code>true</code> (default), print a backtrace on an uncaught
345	386	exception.</dd>
346		<dt class="pubdef"><a name="flag:backtrace_depth"><strong>backtrace_depth</strong>(<var>integer</var>, changeable)</a></dt>
	387	<dt class="pubdef"><a id="flag:backtrace_depth"><strong>backtrace_depth</strong>(<var>integer</var>, changeable)</a></dt>
347	388	<dd class="defbody">
348	389	If backtraces on errors are enabled, this flag defines the maximum
349	390	number of frames that is printed (default 20).</dd>
350		<dt class="pubdef"><a name="flag:backtrace_goal_depth"><strong>backtrace_goal_depth</strong>(<var>integer</var>, changeable)</a></dt>
	391	<dt class="pubdef"><a id="flag:backtrace_goal_depth"><strong>backtrace_goal_depth</strong>(<var>integer</var>, changeable)</a></dt>
351	392	<dd class="defbody">
352	393	The frame of a backtrace is printed after making a shallow copy of the
353	394	goal. This flag determines the depth to which the goal term is copied.
354	395	Default is `3'.</dd>
355		<dt class="pubdef"><a name="flag:backtrace_show_lines"><strong>backtrace_show_lines</strong>(<var>bool</var>, changeable)</a></dt>
	396	<dt class="pubdef"><a id="flag:backtrace_show_lines"><strong>backtrace_show_lines</strong>(<var>bool</var>, changeable)</a></dt>
356	397	<dd class="defbody">
357	398	If <code>true</code> (default), try to reconstruct the line number at
358	399	which the exception happened.</dd>
359		<dt class="pubdef"><a name="flag:bounded"><strong>bounded</strong>(<var>bool</var>)</a></dt>
	400	<dt class="pubdef"><a id="flag:bounded"><strong>bounded</strong>(<var>bool</var>)</a></dt>
360	401	<dd class="defbody">
361	402	ISO Prolog flag. If <code>true</code>, integer representation is bound
362	403	by

364	405	If <code>false</code> integers can be arbitrarily large and the <a class="flag" href="flags.html#flag:min_integer">min_integer</a>
365	406	and
366	407	<a class="flag" href="flags.html#flag:max_integer">max_integer</a> are
367		not present. See <a class="sec" href="arith.html">section 4.27.2.1</a>.</dd>
368		<dt class="pubdef"><a name="flag:break_level"><strong>break_level</strong>(<var>integer</var>)</a></dt>
	408	not present. See <a class="sec" href="arith.html#sec:4.27.2.1">section
	409	4.27.2.1</a>.</dd>
	410	<dt class="pubdef"><a id="flag:break_level"><strong>break_level</strong>(<var>integer</var>)</a></dt>
369	411	<dd class="defbody">
370	412	Current break-level. The initial top level (started with
371		<strong>-t</strong>) has value 0. See <a name="idx:break0:91"></a><a class="pred" href="toplevel.html#break/0">break/0</a>.
	413	<strong>-t</strong>) has value 0. See <a id="idx:break0:91"></a><a class="pred" href="toplevel.html#break/0">break/0</a>.
372	414	This flag is absent from threads that are not running a top-level loop.</dd>
373		<dt class="pubdef"><a name="flag:c_cc"><strong>c_cc</strong>(<var>atom</var>, changeable)</a></dt>
	415	<dt class="pubdef"><a id="flag:c_cc"><strong>c_cc</strong>(<var>atom</var>, changeable)</a></dt>
374	416	<dd class="defbody">
375	417	Name of the C compiler used to compile SWI-Prolog. Normally either gcc
376		or cc. See <a class="sec" href="plld.html">section 11.5</a>.</dd>
377		<dt class="pubdef"><a name="flag:c_cflags"><strong>c_cflags</strong>(<var>atom</var>, changeable)</a></dt>
378		<dd class="defbody">
379		CFLAGS used to compile SWI-Prolog. See <a class="sec" href="plld.html">section
	418	or cc. See <a class="sec" href="plld.html#sec:11.5">section 11.5</a>.</dd>
	419	<dt class="pubdef"><a id="flag:c_cflags"><strong>c_cflags</strong>(<var>atom</var>, changeable)</a></dt>
	420	<dd class="defbody">
	421	CFLAGS used to compile SWI-Prolog. See <a class="sec" href="plld.html#sec:11.5">section
380	422	11.5</a>.</dd>
381		<dt class="pubdef"><a name="flag:c_ldflags"><strong>c_ldflags</strong>(<var>atom</var>, changeable)</a></dt>
382		<dd class="defbody">
383		LDFLAGS used to link SWI-Prolog. See <a class="sec" href="plld.html">section
	423	<dt class="pubdef"><a id="flag:c_ldflags"><strong>c_ldflags</strong>(<var>atom</var>, changeable)</a></dt>
	424	<dd class="defbody">
	425	LDFLAGS used to link SWI-Prolog. See <a class="sec" href="plld.html#sec:11.5">section
384	426	11.5</a>.</dd>
385		<dt class="pubdef"><a name="flag:c_libs"><strong>c_libs</strong>(<var>atom</var>, changeable)</a></dt>
	427	<dt class="pubdef"><a id="flag:c_libs"><strong>c_libs</strong>(<var>atom</var>, changeable)</a></dt>
386	428	<dd class="defbody">
387	429	Libraries needed to link executables that embed SWI-Prolog. Typically
388	430	<code>-lswipl</code> if the SWI-Prolog kernel is a shared (DLL). If the
389	431	SWI-Prolog kernel is in a static library, this flag also contains the
390	432	dependencies.</dd>
391		<dt class="pubdef"><a name="flag:c_libplso"><strong>c_libplso</strong>(<var>atom</var>, changeable)</a></dt>
	433	<dt class="pubdef"><a id="flag:c_libplso"><strong>c_libplso</strong>(<var>atom</var>, changeable)</a></dt>
392	434	<dd class="defbody">
393	435	Libraries needed to link extensions (shared object, DLL) to SWI-Prolog.
394	436	Typically empty on ELF systems and <code>-lswipl</code> on COFF-based
395		systems. See <a class="sec" href="plld.html">section 11.5</a>.</dd>
396		<dt class="pubdef"><a name="flag:char_conversion"><strong>char_conversion</strong>(<var>bool</var>, changeable)</a></dt>
	437	systems. See <a class="sec" href="plld.html#sec:11.5">section 11.5</a>.</dd>
	438	<dt class="pubdef"><a id="flag:char_conversion"><strong>char_conversion</strong>(<var>bool</var>, changeable)</a></dt>
397	439	<dd class="defbody">
398	440	Determines whether character conversion takes place while reading terms.
399		See also <a name="idx:charconversion2:92"></a><a class="pred" href="charconv.html#char_conversion/2">char_conversion/2</a>.</dd>
400		<dt class="pubdef"><a name="flag:character_escapes"><strong>character_escapes</strong>(<var>bool</var>, changeable)</a></dt>
401		<dd class="defbody">
402		If <code>true</code> (default), <a name="idx:read1:93"></a><a class="pred" href="termrw.html#read/1">read/1</a>
	441	See also <a id="idx:charconversion2:92"></a><a class="pred" href="charconv.html#char_conversion/2">char_conversion/2</a>.</dd>
	442	<dt class="pubdef"><a id="flag:character_escapes"><strong>character_escapes</strong>(<var>bool</var>, changeable)</a></dt>
	443	<dd class="defbody">
	444	If <code>true</code> (default), <a id="idx:read1:93"></a><a class="pred" href="termrw.html#read/1">read/1</a>
403	445	interprets <code>\</code> escape sequences in quoted atoms and strings.
404	446	May be changed. This flag is local to the module in which it is changed.
405		See <a class="sec" href="syntax.html">section 2.16.1.3</a>.</dd>
406		<dt class="pubdef"><a name="flag:colon_sets_calling_context"><strong>colon_sets_calling_context</strong>(<var>bool</var>, changeable)</a></dt>
	447	See <a class="sec" href="syntax.html#sec:2.16.1.3">section 2.16.1.3</a>.</dd>
	448	<dt class="pubdef"><a id="flag:colon_sets_calling_context"><strong>colon_sets_calling_context</strong>(<var>bool</var>, changeable)</a></dt>
407	449	<dd class="defbody">
408	450	Using the construct <<var>module</var>>:<<var>goal</var>>
409	451	sets the <em>calling context</em> for executing <<var>goal</var>>.
410		This flag is defined by ISO/IEC 13211-2 (Prolog modules standard). See <a class="sec" href="modules.html">section
	452	This flag is defined by ISO/IEC 13211-2 (Prolog modules standard). See <a class="sec" href="modules.html#sec:6">section
411	453	6</a>.</dd>
412		<dt class="pubdef"><a name="flag:color_term"><strong>color_term</strong>(<var>bool</var>, changeable)</a></dt>
	454	<dt class="pubdef"><a id="flag:color_term"><strong>color_term</strong>(<var>bool</var>, changeable)</a></dt>
413	455	<dd class="defbody">
414	456	This flag is managed by library <code>library(ansi_term)</code>, which
415	457	is loaded at startup if the two conditions below are both true. Note
416	458	that this implies that setting this flag to <code>false</code> from the
417		system or personal initialization file (see <a class="sec" href="initfile.html">section
418		2.2</a> disables colored output. The predicate <a name="idx:messageproperty2:94"></a><a class="pred" href="exception.html#message_property/2">message_property/2</a>
	459	system or personal initialization file (see <a class="sec" href="initfile.html#sec:2.2">section
	460	2.2</a> disables colored output. The predicate <a id="idx:messageproperty2:94"></a><a class="pred" href="exception.html#message_property/2">message_property/2</a>
419	461	can be used to control the actual color scheme depending in the message
420	462	type passed to
421		<a name="idx:printmessage2:95"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
	463	<a id="idx:printmessage2:95"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
422	464
423	465	<p>
424	466	<ul class="latex">

426	468	<li><code>\+ current_prolog_flag(color_term, false)</code>
427	469	</ul>
428	470	</dd>
429		<dt class="pubdef"><a name="flag:compile_meta_arguments"><strong>compile_meta_arguments</strong>(<var>atom</var>, changeable)</a></dt>
	471	<dt class="pubdef"><a id="flag:compile_meta_arguments"><strong>compile_meta_arguments</strong>(<var>atom</var>, changeable)</a></dt>
430	472	<dd class="defbody">
431	473	Experimental flag that controls compilation of arguments passed to
432		meta-calls marked `0' or `<code><code>^</code></code>' (see <a name="idx:metapredicate1:96"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>).
	474	meta-calls marked `0' or `<code><code>^</code></code>' (see <a id="idx:metapredicate1:96"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>).
433	475	Supported values are:
434	476
435	477	<dl class="latex">

449	491	<dd class="defbody">
450	492	Also compile references to normal user predicates. This harms
451	493	performance (a little), but enhances the power of poor-mens consistency
452		check used by <a name="idx:make0:97"></a><a class="pred" href="consulting.html#make/0">make/0</a>
453		and implemented by <a name="idx:listundefined0:98"></a><a class="pred" href="check.html#list_undefined/0">list_undefined/0</a>.
	494	check used by <a id="idx:make0:97"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	495	and implemented by <a id="idx:listundefined0:98"></a><a class="pred" href="check.html#list_undefined/0">list_undefined/0</a>.
454	496	</dd>
455	497	<dt><strong>always</strong></dt>
456	498	<dd class="defbody">
457	499	Always create an intermediate clause, even for system predicates. This
458	500	prepares for replacing the normal head of the generated predicate with a
459	501	special reference (similar to database references as used by, e.g.,
460		<a name="idx:assert2:99"></a><a class="pred" href="db.html#assert/2">assert/2</a>)
	502	<a id="idx:assert2:99"></a><a class="pred" href="db.html#assert/2">assert/2</a>)
461	503	that provides direct access to the executable code, thus avoiding
462	504	runtime lookup of predicates for meta-calling.
463	505	</dd>
464	506	</dl>
465	507
466	508	</dd>
467		<dt class="pubdef"><a name="flag:compiled_at"><strong>compiled_at</strong>(<var>atom</var>)</a></dt>
	509	<dt class="pubdef"><a id="flag:compiled_at"><strong>compiled_at</strong>(<var>atom</var>)</a></dt>
468	510	<dd class="defbody">
469	511	Describes when the system has been compiled. Only available if the C
470	512	compiler used to compile SWI-Prolog provides the __DATE__ and __TIME__
471	513	macros.</dd>
472		<dt class="pubdef"><a name="flag:console_menu"><strong>console_menu</strong>(<var>bool</var>)</a></dt>
	514	<dt class="pubdef"><a id="flag:console_menu"><strong>console_menu</strong>(<var>bool</var>)</a></dt>
473	515	<dd class="defbody">
474	516	Set to <code>true</code> in <b>swipl-win.exe</b> to indicate that the
475		console supports menus. See also <a class="sec" href="system.html">section
	517	console supports menus. See also <a class="sec" href="system.html#sec:4.35.3">section
476	518	4.35.3</a>.</dd>
477		<dt class="pubdef"><a name="flag:cpu_count"><strong>cpu_count</strong>(<var>integer</var>, changeable)</a></dt>
	519	<dt class="pubdef"><a id="flag:cpu_count"><strong>cpu_count</strong>(<var>integer</var>, changeable)</a></dt>
478	520	<dd class="defbody">
479	521	Number of physical CPUs or cores in the system. The flag is marked
480	522	read-write both to allow pretending the system has more or less
481		processors. See also <a name="idx:threadsetconcurrency2:100"></a><a class="pred" href="threadcreate.html#thread_setconcurrency/2">thread_setconcurrency/2</a>
	523	processors. See also <a id="idx:threadsetconcurrency2:100"></a><a class="pred" href="threadcreate.html#thread_setconcurrency/2">thread_setconcurrency/2</a>
482	524	and the library
483	525	<code>library(thread)</code>. This flag is not available on systems
484	526	where we do not know how to get the number of CPUs. This flag is not
485		included in a saved state (see <a name="idx:qsaveprogram1:101"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/1</a>).</dd>
486		<dt class="pubdef"><a name="flag:dde"><strong>dde</strong>(<var>bool</var>)</a></dt>
	527	included in a saved state (see <a id="idx:qsaveprogram1:101"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/1</a>).</dd>
	528	<dt class="pubdef"><a id="flag:dde"><strong>dde</strong>(<var>bool</var>)</a></dt>
487	529	<dd class="defbody">
488	530	Set to <code>true</code> if this instance of Prolog supports DDE as
489		described in <a class="sec" href="DDE.html">section 4.43</a>.</dd>
490		<dt class="pubdef"><a name="flag:debug"><strong>debug</strong>(<var>bool</var>, changeable)</a></dt>
	531	described in <a class="sec" href="DDE.html#sec:4.43">section 4.43</a>.</dd>
	532	<dt class="pubdef"><a id="flag:debug"><strong>debug</strong>(<var>bool</var>, changeable)</a></dt>
491	533	<dd class="defbody">
492	534	Switch debugging mode on/off. If debug mode is activated the system
493		traps encountered spy points (see <a name="idx:spy1:102"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>)
494		and trace points (see <a name="idx:trace1:103"></a><a class="pred" href="debugger.html#trace/1">trace/1</a>).
	535	traps encountered spy points (see <a id="idx:spy1:102"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>)
	536	and trace points (see <a id="idx:trace1:103"></a><a class="pred" href="debugger.html#trace/1">trace/1</a>).
495	537	In addition, last-call optimisation is disabled and the system is more
496	538	conservative in destroying choice points to simplify debugging.
497	539
498	540	<p>Disabling these optimisations can cause the system to run out of
499	541	memory on programs that behave correctly if debug mode is off.</dd>
500		<dt class="pubdef"><a name="flag:debug_on_error"><strong>debug_on_error</strong>(<var>bool</var>, changeable)</a></dt>
	542	<dt class="pubdef"><a id="flag:debug_on_error"><strong>debug_on_error</strong>(<var>bool</var>, changeable)</a></dt>
501	543	<dd class="defbody">
502	544	If <code>true</code>, start the tracer after an error is detected.
503	545	Otherwise just continue execution. The goal that raised the error will
504	546	normally fail. See also the Prolog flag <a class="flag" href="flags.html#flag:report_error">report_error</a>.
505	547	Default is <code>true</code>.</dd>
506		<dt class="pubdef"><a name="flag:debugger_write_options"><strong>debugger_write_options</strong>(<var>term</var>, changeable)</a></dt>
507		<dd class="defbody">
508		This argument is given as option-list to <a name="idx:writeterm2:104"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	548	<dt class="pubdef"><a id="flag:debugger_write_options"><strong>debugger_write_options</strong>(<var>term</var>, changeable)</a></dt>
	549	<dd class="defbody">
	550	This argument is given as option-list to <a id="idx:writeterm2:104"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
509	551	for printing goals by the debugger. Modified by the `w', `p' and `<N>
510	552	d' commands of the debugger. Default is <code>[quoted(true),
511	553	portray(true), max_depth(10), attributes(portray)]</code>.</dd>
512		<dt class="pubdef"><a name="flag:debugger_show_context"><strong>debugger_show_context</strong>(<var>bool</var>, changeable)</a></dt>
	554	<dt class="pubdef"><a id="flag:debugger_show_context"><strong>debugger_show_context</strong>(<var>bool</var>, changeable)</a></dt>
513	555	<dd class="defbody">
514	556	If <code>true</code>, show the context module while printing a
515	557	stack-frame in the tracer. Normally controlled using the `C' option of
516	558	the tracer.</dd>
517		<dt class="pubdef"><a name="flag:dialect"><strong>dialect</strong>(<var>atom</var>)</a></dt>
	559	<dt class="pubdef"><a id="flag:dialect"><strong>dialect</strong>(<var>atom</var>)</a></dt>
518	560	<dd class="defbody">
519	561	Fixed to <code>swi</code>. The code below is a reliable and portable way
520	562	to detect SWI-Prolog.

525	567	</pre>
526	568
527	569	</dd>
528		<dt class="pubdef"><a name="flag:double_quotes"><strong>double_quotes</strong>(<var>codes,chars,atom,string</var>, changeable)</a></dt>
	570	<dt class="pubdef"><a id="flag:double_quotes"><strong>double_quotes</strong>(<var>codes,chars,atom,string</var>, changeable)</a></dt>
529	571	<dd class="defbody">
530	572	This flag determines how double quoted strings are read by Prolog and is
531	573	---like <a class="flag" href="flags.html#flag:character_escapes">character_escapes</a>
532	574	and <a class="flag" href="flags.html#flag:back_quotes">back_quotes</a>---
533	575	maintained for each module. The default is <code>string</code>, which
534		produces a string as described in <a class="sec" href="strings.html">section
	576	produces a string as described in <a class="sec" href="strings.html#sec:5.2">section
535	577	5.2</a>. If
536	578	<strong>--traditional</strong> is given, the default is <code>codes</code>,
537	579	which produces a list of character codes, integers that represent a
538	580	Unicode code-point. The value <code>chars</code> produces a list of
539	581	one-character atoms and the value <code>atom</code> makes double quotes
540		the same as single quotes, creating a atom. See also <a class="sec" href="extensions.html">section
	582	the same as single quotes, creating a atom. See also <a class="sec" href="extensions.html#sec:5">section
541	583	5</a>.</dd>
542		<dt class="pubdef"><a name="flag:editor"><strong>editor</strong>(<var>atom</var>, changeable)</a></dt>
543		<dd class="defbody">
544		Determines the editor used by <a name="idx:edit1:105"></a><a class="pred" href="edit.html#edit/1">edit/1</a>.
545		See <a class="sec" href="edit.html">section 4.4.1</a> for details on
546		selecting the editor used.</dd>
547		<dt class="pubdef"><a name="flag:emacs_inferior_process"><strong>emacs_inferior_process</strong>(<var>bool</var>)</a></dt>
	584	<dt class="pubdef"><a id="flag:editor"><strong>editor</strong>(<var>atom</var>, changeable)</a></dt>
	585	<dd class="defbody">
	586	Determines the editor used by <a id="idx:edit1:105"></a><a class="pred" href="edit.html#edit/1">edit/1</a>.
	587	See <a class="sec" href="edit.html#sec:4.4.1">section 4.4.1</a> for
	588	details on selecting the editor used.</dd>
	589	<dt class="pubdef"><a id="flag:emacs_inferior_process"><strong>emacs_inferior_process</strong>(<var>bool</var>)</a></dt>
548	590	<dd class="defbody">
549	591	If true, SWI-Prolog is running as an <em>inferior process</em> of
550	592	(GNU/X-)Emacs. SWI-Prolog assumes this is the case if the environment
551	593	variable <code>EMACS</code> is <code>t</code> and <code>INFERIOR</code>
552	594	is <code>yes</code>.</dd>
553		<dt class="pubdef"><a name="flag:encoding"><strong>encoding</strong>(<var>atom</var>, changeable)</a></dt>
	595	<dt class="pubdef"><a id="flag:encoding"><strong>encoding</strong>(<var>atom</var>, changeable)</a></dt>
554	596	<dd class="defbody">
555	597	Default encoding used for opening files in <code>text</code> mode. The
556		initial value is deduced from the environment. See <a class="sec" href="widechars.html">section
	598	initial value is deduced from the environment. See <a class="sec" href="widechars.html#sec:2.19.1">section
557	599	2.19.1</a> for details.</dd>
558		<dt class="pubdef"><a name="flag:executable"><strong>executable</strong>(<var>atom</var>)</a></dt>
559		<dd class="defbody">
560		Pathname of the running executable. Used by <a name="idx:qsaveprogram2:106"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
	600	<dt class="pubdef"><a id="flag:executable"><strong>executable</strong>(<var>atom</var>)</a></dt>
	601	<dd class="defbody">
	602	Pathname of the running executable. Used by <a id="idx:qsaveprogram2:106"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
561	603	as default emulator.</dd>
562		<dt class="pubdef"><a name="flag:exit_status"><strong>exit_status</strong>(<var>integer</var>)</a></dt>
563		<dd class="defbody">
564		Set by <a name="idx:halt1:107"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a>
	604	<dt class="pubdef"><a id="flag:exit_status"><strong>exit_status</strong>(<var>integer</var>)</a></dt>
	605	<dd class="defbody">
	606	Set by <a id="idx:halt1:107"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a>
565	607	to its argument, making the exit status available to hooks registered
566		with <a name="idx:athalt1:108"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>.</dd>
567		<dt class="pubdef"><a name="flag:file_name_case_handling"><strong>file_name_case_handling</strong>(<var>atom</var>, changeable)</a></dt>
	608	with <a id="idx:athalt1:108"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>.</dd>
	609	<dt class="pubdef"><a id="flag:file_name_case_handling"><strong>file_name_case_handling</strong>(<var>atom</var>, changeable)</a></dt>
568	610	<dd class="defbody">
569	611	This flag defines how Prolog handles the case of file names. The flag is
570	612	used for case normalization and to determine whether two names refer to

593	635	</dl>
594	636
595	637	</dd>
596		<dt class="pubdef"><a name="flag:file_name_variables"><strong>file_name_variables</strong>(<var>bool</var>, changeable)</a></dt>
	638	<dt class="pubdef"><a id="flag:file_name_variables"><strong>file_name_variables</strong>(<var>bool</var>, changeable)</a></dt>
597	639	<dd class="defbody">
598	640	If <code>true</code> (default <code>false</code>), expand <code>$<var>varname</var></code>
599	641	and <code><code>~</code></code> in arguments of built-in predicates that
600		accept a file name (<a name="idx:open3:109"></a><a class="pred" href="IO.html#open/3">open/3</a>, <a name="idx:existsfile1:110"></a><a class="pred" href="files.html#exists_file/1">exists_file/1</a>, <a name="idx:accessfile2:111"></a><a class="pred" href="files.html#access_file/2">access_file/2</a>,
	642	accept a file name (<a id="idx:open3:109"></a><a class="pred" href="IO.html#open/3">open/3</a>, <a id="idx:existsfile1:110"></a><a class="pred" href="files.html#exists_file/1">exists_file/1</a>, <a id="idx:accessfile2:111"></a><a class="pred" href="files.html#access_file/2">access_file/2</a>,
601	643	etc.). The predicate
602		<a name="idx:expandfilename2:112"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>
	644	<a id="idx:expandfilename2:112"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>
603	645	can be used to expand environment variables and wildcard patterns. This
604	646	Prolog flag is intended for backward compatibility with older versions
605	647	of SWI-Prolog.</dd>
606		<dt class="pubdef"><a name="flag:file_search_cache_time"><strong>file_search_cache_time</strong>(<var>number</var>, changeable)</a></dt>
607		<dd class="defbody">
608		Time in seconds for which search results from <a name="idx:absolutefilename3:113"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	648	<dt class="pubdef"><a id="flag:file_search_cache_time"><strong>file_search_cache_time</strong>(<var>number</var>, changeable)</a></dt>
	649	<dd class="defbody">
	650	Time in seconds for which search results from <a id="idx:absolutefilename3:113"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
609	651	are cached. Within this time limit, the system will first check that the
610	652	old search result satisfies the conditions. Default is 10 seconds, which
611	653	typically avoids most repetitive searches for (library) files during
612	654	compilation. Setting this value to 0 (zero) disables the cache.</dd>
613		<dt class="pubdef"><a name="flag:gc"><strong>gc</strong>(<var>bool</var>, changeable)</a></dt>
	655	<dt class="pubdef"><a id="flag:gc"><strong>gc</strong>(<var>bool</var>, changeable)</a></dt>
614	656	<dd class="defbody">
615	657	If true (default), the garbage collector is active. If false, neither
616	658	garbage collection, nor stack shifts will take place, even not on
617	659	explicit request. May be changed.</dd>
618		<dt class="pubdef"><a name="flag:rc_thread"><strong>rc_thread</strong>(<var>bool</var>, changeable)</a></dt>
	660	<dt class="pubdef"><a id="flag:rc_thread"><strong>rc_thread</strong>(<var>bool</var>, changeable)</a></dt>
619	661	<dd class="defbody">
620	662	If <code>true</code> (default if threading is enabled), atom and clause
621	663	garbage collection are executed in a seperate thread with the

623	665	sufficient garbage executes the garbage collector. As running these
624	666	global collectors may take relatively using a seperate thread improves
625	667	real time behaviour.</dd>
626		<dt class="pubdef"><a name="flag:generate_debug_info"><strong>generate_debug_info</strong>(<var>bool</var>, changeable)</a></dt>
	668	<dt class="pubdef"><a id="flag:generate_debug_info"><strong>generate_debug_info</strong>(<var>bool</var>, changeable)</a></dt>
627	669	<dd class="defbody">
628	670	If <code>true</code> (default) generate code that can be debugged using
629		<a name="idx:trace0:114"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>, <a name="idx:spy1:115"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>,
	671	<a id="idx:trace0:114"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>, <a id="idx:spy1:115"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>,
630	672	etc. Can be set to <code>false</code> using the
631	673	<strong>-nodebug</strong>. This flag is scoped within a source file.
632	674	Many of the libraries have

635	677	the current implementation this only causes a flag to be set on the
636	678	predicate that causes children to be hidden from the debugger. The name
637	679	anticipates further changes to the compiler.</span></sup></dd>
638		<dt class="pubdef"><a name="flag:gmp_version"><strong>gmp_version</strong>(<var>integer</var>)</a></dt>
	680	<dt class="pubdef"><a id="flag:gmp_version"><strong>gmp_version</strong>(<var>integer</var>)</a></dt>
639	681	<dd class="defbody">
640	682	If Prolog is linked with GMP, this flag gives the major version of the
641		GMP library used. See also <a class="sec" href="foreigninclude.html">section
	683	GMP library used. See also <a class="sec" href="foreigninclude.html#sec:11.4.8">section
642	684	11.4.8</a>.</dd>
643		<dt class="pubdef"><a name="flag:gui"><strong>gui</strong>(<var>bool</var>)</a></dt>
	685	<dt class="pubdef"><a id="flag:gui"><strong>gui</strong>(<var>bool</var>)</a></dt>
644	686	<dd class="defbody">
645	687	Set to <code>true</code> if XPCE is around and can be used for graphics.</dd>
646		<dt class="pubdef"><a name="flag:history"><strong>history</strong>(<var>integer</var>, changeable)</a></dt>
	688	<dt class="pubdef"><a id="flag:history"><strong>history</strong>(<var>integer</var>, changeable)</a></dt>
647	689	<dd class="defbody">
648	690	If <var><var>integer</var>> 0</var>, support Unix <b>csh(1)</b>-like
649		history as described in <a class="sec" href="history.html">section 2.7</a>.
650		Otherwise, only support reusing commands through the command line
651		editor. The default is to set this Prolog flag to 0 if a command line
652		editor is provided (see Prolog flag
	691	history as described in <a class="sec" href="history.html#sec:2.7">section
	692	2.7</a>. Otherwise, only support reusing commands through the command
	693	line editor. The default is to set this Prolog flag to 0 if a command
	694	line editor is provided (see Prolog flag
653	695	<a class="flag" href="flags.html#flag:readline">readline</a>) and 15
654	696	otherwise.</dd>
655		<dt class="pubdef"><a name="flag:home"><strong>home</strong>(<var>atom</var>)</a></dt>
	697	<dt class="pubdef"><a id="flag:home"><strong>home</strong>(<var>atom</var>)</a></dt>
656	698	<dd class="defbody">
657	699	SWI-Prolog's notion of the home directory. SWI-Prolog uses its home
658	700	directory to find its startup file as

660	702	<code><<var>home</var>>/boot64.prc</code> (64-bit machines) and to
661	703	find its library as
662	704	<code><<var>home</var>>/library</code>.</dd>
663		<dt class="pubdef"><a name="flag:hwnd"><strong>hwnd</strong>(<var>integer</var>)</a></dt>
	705	<dt class="pubdef"><a id="flag:hwnd"><strong>hwnd</strong>(<var>integer</var>)</a></dt>
664	706	<dd class="defbody">
665	707	In <b>swipl-win.exe</b>, this refers to the MS-Windows window handle of
666	708	the console window.</dd>
667		<dt class="pubdef"><a name="flag:integer_rounding_function"><strong>integer_rounding_function</strong>(<var>down,toward_zero</var>)</a></dt>
	709	<dt class="pubdef"><a id="flag:integer_rounding_function"><strong>integer_rounding_function</strong>(<var>down,toward_zero</var>)</a></dt>
668	710	<dd class="defbody">
669	711	ISO Prolog flag describing rounding by <code>//</code> and <code>rem</code>
670	712	arithmetic functions. Value depends on the C compiler used.</dd>
671		<dt class="pubdef"><a name="flag:iso"><strong>iso</strong>(<var>bool</var>, changeable)</a></dt>
	713	<dt class="pubdef"><a id="flag:iso"><strong>iso</strong>(<var>bool</var>, changeable)</a></dt>
672	714	<dd class="defbody">
673	715	Include some weird ISO compatibility that is incompatible with normal
674	716	SWI-Prolog behaviour. Currently it has the following effect:
675	717	<ul class="latex">
676	718	<li>The <code><code>/</code>/2</code> (float division) <em>always</em>
677	719	returns a float, even if applied to integers that can be divided.
678		<li>In the standard order of terms (see <a class="sec" href="compare.html">section
	720	<li>In the standard order of terms (see <a class="sec" href="compare.html#sec:4.7.1">section
679	721	4.7.1</a>), all floats are before all integers.
680		<li><a name="idx:atomlength2:116"></a><a class="pred" href="manipatom.html#atom_length/2">atom_length/2</a>
	722	<li><a id="idx:atomlength2:116"></a><a class="pred" href="manipatom.html#atom_length/2">atom_length/2</a>
681	723	yields a type error if the first argument is a number.
682		<li><a name="idx:clause23:117"></a><a class="pred" href="examineprog.html#clause/2">clause/[2,3]</a>
	724	<li><a id="idx:clause23:117"></a><a class="pred" href="examineprog.html#clause/2">clause/[2,3]</a>
683	725	raises a permission error when accessing static predicates.
684		<li><a name="idx:abolish12:118"></a><a class="pred" href="db.html#abolish/1">abolish/[1,2]</a>
	726	<li><a id="idx:abolish12:118"></a><a class="pred" href="db.html#abolish/1">abolish/[1,2]</a>
685	727	raises a permission error when accessing static predicates.
686	728	<li>Syntax is closer to the ISO standard:
687	729	<ul class="latex">

702	744	== -, true.</code> write <code>X == (-), true.</code> Currently, this is
703	745	not entirely enforced.
704	746	<li>Backslash-escaped newlines are interpreted according to the ISO
705		standard. See <a class="sec" href="syntax.html">section 2.16.1.3</a>.
	747	standard. See <a class="sec" href="syntax.html#sec:2.16.1.3">section
	748	2.16.1.3</a>.
706	749	</ul>
707	750	</ul>
708	751	</dd>
709		<dt class="pubdef"><a name="flag:large_files"><strong>large_files</strong>(<var>bool</var>)</a></dt>
	752	<dt class="pubdef"><a id="flag:large_files"><strong>large_files</strong>(<var>bool</var>)</a></dt>
710	753	<dd class="defbody">
711	754	If present and <code>true</code>, SWI-Prolog has been compiled with
712	755	<em>large file support</em> (LFS) and is capable of accessing files
713	756	larger than 2GB on 32-bit hardware. Large file support is default on
714	757	installations built using <b>configure</b> that support it and may be
715	758	switched off using the configure option <code>--disable-largefile</code>.</dd>
716		<dt class="pubdef"><a name="flag:last_call_optimisation"><strong>last_call_optimisation</strong>(<var>bool</var>, changeable)</a></dt>
	759	<dt class="pubdef"><a id="flag:last_call_optimisation"><strong>last_call_optimisation</strong>(<var>bool</var>, changeable)</a></dt>
717	760	<dd class="defbody">
718	761	Determines whether or not last-call optimisation is enabled. Normally
719	762	the value of this flag is the negation of the <a class="flag" href="flags.html#flag:debug">debug</a>
720	763	flag. As programs may run out of stack if last-call optimisation is
721	764	omitted, it is sometimes necessary to enable it during debugging.</dd>
722		<dt class="pubdef"><a name="flag:max_arity"><strong>max_arity</strong>(<var>unbounded</var>)</a></dt>
	765	<dt class="pubdef"><a id="flag:max_arity"><strong>max_arity</strong>(<var>unbounded</var>)</a></dt>
723	766	<dd class="defbody">
724	767	ISO Prolog flag describing there is no maximum arity to compound terms.</dd>
725		<dt class="pubdef"><a name="flag:max_integer"><strong>max_integer</strong>(<var>integer</var>)</a></dt>
	768	<dt class="pubdef"><a id="flag:max_integer"><strong>max_integer</strong>(<var>integer</var>)</a></dt>
726	769	<dd class="defbody">
727	770	Maximum integer value if integers are <em>bounded</em>. See also the
728		flag <a class="flag" href="flags.html#flag:bounded">bounded</a> and <a class="sec" href="arith.html">section
	771	flag <a class="flag" href="flags.html#flag:bounded">bounded</a> and <a class="sec" href="arith.html#sec:4.27.2.1">section
729	772	4.27.2.1</a>.</dd>
730		<dt class="pubdef"><a name="flag:max_tagged_integer"><strong>max_tagged_integer</strong>(<var>integer</var>)</a></dt>
	773	<dt class="pubdef"><a id="flag:max_tagged_integer"><strong>max_tagged_integer</strong>(<var>integer</var>)</a></dt>
731	774	<dd class="defbody">
732	775	Maximum integer value represented as a `tagged' value. Tagged integers
733	776	require one word storage. Larger integers are represented as `indirect
734	777	data' and require significantly more space.</dd>
735		<dt class="pubdef"><a name="flag:min_integer"><strong>min_integer</strong>(<var>integer</var>)</a></dt>
	778	<dt class="pubdef"><a id="flag:min_integer"><strong>min_integer</strong>(<var>integer</var>)</a></dt>
736	779	<dd class="defbody">
737	780	Minimum integer value if integers are <em>bounded</em>. See also the
738		flag <a class="flag" href="flags.html#flag:bounded">bounded</a> and <a class="sec" href="arith.html">section
	781	flag <a class="flag" href="flags.html#flag:bounded">bounded</a> and <a class="sec" href="arith.html#sec:4.27.2.1">section
739	782	4.27.2.1</a>.</dd>
740		<dt class="pubdef"><a name="flag:min_tagged_integer"><strong>min_tagged_integer</strong>(<var>integer</var>)</a></dt>
	783	<dt class="pubdef"><a id="flag:min_tagged_integer"><strong>min_tagged_integer</strong>(<var>integer</var>)</a></dt>
741	784	<dd class="defbody">
742	785	Start of the tagged-integer value range.</dd>
743		<dt class="pubdef"><a name="flag:occurs_check"><strong>occurs_check</strong>(<var>atom</var>, changeable)</a></dt>
	786	<dt class="pubdef"><a id="flag:occurs_check"><strong>occurs_check</strong>(<var>atom</var>, changeable)</a></dt>
744	787	<dd class="defbody">
745	788	This flag controls unification that creates an infinite tree (also
746	789	called <em>cyclic term</em>) and can have three values. Using
747	790	<code>false</code> (default), unification succeeds, creating an infinite
748		tree. Using <code>true</code>, unification behaves as <a name="idx:unifywithoccurscheck2:119"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>,
	791	tree. Using <code>true</code>, unification behaves as <a id="idx:unifywithoccurscheck2:119"></a><a class="pred" href="compare.html#unify_with_occurs_check/2">unify_with_occurs_check/2</a>,
749	792	failing silently. Using <code>error</code>, an attempt to create a
750	793	cyclic term results in an <code>occurs_check</code> exception. The
751	794	latter is intended for debugging unintentional creations of cyclic
752	795	terms. Note that this flag is a global flag modifying fundamental
753	796	behaviour of Prolog. Changing the flag from its default may cause
754	797	libraries to stop functioning properly.</dd>
755		<dt class="pubdef"><a name="flag:open_shared_object"><strong>open_shared_object</strong>(<var>bool</var>)</a></dt>
756		<dd class="defbody">
757		If true, <a name="idx:opensharedobject2:120"></a><a class="pred" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a>
	798	<dt class="pubdef"><a id="flag:open_shared_object"><strong>open_shared_object</strong>(<var>bool</var>)</a></dt>
	799	<dd class="defbody">
	800	If true, <a id="idx:opensharedobject2:120"></a><a class="pred" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a>
758	801	and friends are implemented, providing access to shared libraries (<code>.so</code>
759	802	files) or dynamic link libraries (<code>.DLL</code> files).</dd>
760		<dt class="pubdef"><a name="flag:optimise"><strong>optimise</strong>(<var>bool</var>, changeable)</a></dt>
	803	<dt class="pubdef"><a id="flag:optimise"><strong>optimise</strong>(<var>bool</var>, changeable)</a></dt>
761	804	<dd class="defbody">
762	805	If <code>true</code>, compile in optimised mode. The initial value is
763	806	<code>true</code> if Prolog was started with the <strong>-O</strong>

765	808	flag is scoped to a source file.
766	809
767	810	<p>Currently optimised compilation implies compilation of arithmetic,
768		and deletion of redundant <a name="idx:true0:121"></a><a class="pred" href="control.html#true/0">true/0</a>
769		that may result from <a name="idx:expandgoal2:122"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>.
	811	and deletion of redundant <a id="idx:true0:121"></a><a class="pred" href="control.html#true/0">true/0</a>
	812	that may result from <a id="idx:expandgoal2:122"></a><a class="pred" href="consulting.html#expand_goal/2">expand_goal/2</a>.
770	813
771	814	<p>Later versions might imply various other optimisations such as
772	815	integrating small predicates into their callers, eliminating constant
773	816	expressions and other predictable constructs. Source code optimisation
774	817	is never applied to predicates that are declared dynamic (see
775		<a name="idx:dynamic1:123"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>).</dd>
776		<dt class="pubdef"><a name="flag:os_argv"><strong>os_argv</strong>(<var>list</var>, changeable)</a></dt>
	818	<a id="idx:dynamic1:123"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>).</dd>
	819	<dt class="pubdef"><a id="flag:os_argv"><strong>os_argv</strong>(<var>list</var>, changeable)</a></dt>
777	820	<dd class="defbody">
778	821	List is a list of atoms representing the command line arguments used to
779	822	invoke SWI-Prolog. Please note that <b>all</b> arguments are included in
780	823	the list returned. See <a class="flag" href="flags.html#flag:argv">argv</a>
781	824	to get the application options.</dd>
782		<dt class="pubdef"><a name="flag:pid"><strong>pid</strong>(<var>int</var>)</a></dt>
	825	<dt class="pubdef"><a id="flag:pid"><strong>pid</strong>(<var>int</var>)</a></dt>
783	826	<dd class="defbody">
784	827	Process identifier of the running Prolog process. Existence of this flag
785	828	is implementation-defined.</dd>
786		<dt class="pubdef"><a name="flag:pipe"><strong>pipe</strong>(<var>bool</var>, changeable)</a></dt>
	829	<dt class="pubdef"><a id="flag:pipe"><strong>pipe</strong>(<var>bool</var>, changeable)</a></dt>
787	830	<dd class="defbody">
788	831	If true, <code>open(pipe(command), mode, Stream)</code>, etc. are
789	832	supported. Can be changed to disable the use of pipes in applications
790	833	testing this feature. Not recommended.</dd>
791		<dt class="pubdef"><a name="flag:print_write_options"><strong>print_write_options</strong>(<var>term</var>, changeable)</a></dt>
792		<dd class="defbody">
793		Specifies the options for <a name="idx:writeterm2:124"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
794		used by <a name="idx:print1:125"></a><a class="pred" href="termrw.html#print/1">print/1</a>
795		and <a name="idx:print2:126"></a><a class="pred" href="termrw.html#print/2">print/2</a>.</dd>
796		<dt class="pubdef"><a name="flag:prompt_alternatives_on"><strong>prompt_alternatives_on</strong>(<var>atom</var>, changeable)</a></dt>
797		<dd class="defbody">
798		<a name="idx:promptalternatives:127"></a>Determines prompting for
	834	<dt class="pubdef"><a id="flag:print_write_options"><strong>print_write_options</strong>(<var>term</var>, changeable)</a></dt>
	835	<dd class="defbody">
	836	Specifies the options for <a id="idx:writeterm2:124"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	837	used by <a id="idx:print1:125"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	838	and <a id="idx:print2:126"></a><a class="pred" href="termrw.html#print/2">print/2</a>.</dd>
	839	<dt class="pubdef"><a id="flag:prompt_alternatives_on"><strong>prompt_alternatives_on</strong>(<var>atom</var>, changeable)</a></dt>
	840	<dd class="defbody">
	841	<a id="idx:promptalternatives:127"></a>Determines prompting for
799	842	alternatives in the Prolog top level. Default is
800	843	<code>determinism</code>, which implies the system prompts for
801	844	alternatives if the goal succeeded while leaving choice points. Many
802	845	classical Prolog systems behave as <code>groundness</code>: they prompt
803	846	for alternatives if and only if the query contains variables.</dd>
804		<dt class="pubdef"><a name="flag:protect_static_code"><strong>protect_static_code</strong>(<var>bool</var>, changeable)</a></dt>
805		<dd class="defbody">
806		If <code>true</code> (default <code>false</code>), <a name="idx:clause2:128"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>
	847	<dt class="pubdef"><a id="flag:protect_static_code"><strong>protect_static_code</strong>(<var>bool</var>, changeable)</a></dt>
	848	<dd class="defbody">
	849	If <code>true</code> (default <code>false</code>), <a id="idx:clause2:128"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>
807	850	does not operate on static code, providing some basic protection from
808	851	hackers that wish to list the static code of your Prolog program. Once
809	852	the flag is
810	853	<code>true</code>, it cannot be changed back to <code>false</code>.
811	854	Protection is default in ISO mode (see Prolog flag <a class="flag" href="flags.html#flag:iso">iso</a>).
812		Note that many parts of the development environment require <a name="idx:clause2:129"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>
	855	Note that many parts of the development environment require <a id="idx:clause2:129"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>
813	856	to work on static code, and enabling this flag should thus only be used
814	857	for production code.</dd>
815		<dt class="pubdef"><a name="flag:qcompile"><strong>qcompile</strong>(<var>atom</var>, changeable)</a></dt>
	858	<dt class="pubdef"><a id="flag:qcompile"><strong>qcompile</strong>(<var>atom</var>, changeable)</a></dt>
816	859	<dd class="defbody">
817	860	This option provides the default for the <code>qcompile(+Atom)</code>
818		option of <a name="idx:loadfiles2:130"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.</dd>
819		<dt class="pubdef"><a name="flag:readline"><strong>readline</strong>(<var>atom</var>, changeable)</a></dt>
	861	option of <a id="idx:loadfiles2:130"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.</dd>
	862	<dt class="pubdef"><a id="flag:readline"><strong>readline</strong>(<var>atom</var>, changeable)</a></dt>
820	863	<dd class="defbody">
821	864	Specifies which form of command line editing is provided. Possible
822	865	values are below. The flag may be set from the user's init file (see
823		<a class="sec" href="initgoal.html">section 2.3</a>) to one of <code>false</code>, <code>readline</code>
	866	<a class="sec" href="initgoal.html#sec:2.3">section 2.3</a>) to one of <code>false</code>, <code>readline</code>
824	867	or
825	868	<code>editline</code>. This causes the toplevel not to load a command
826	869	line editor (<code>false</code>) or load the specified one. If loading

847	890	</dl>
848	891
849	892	</dd>
850		<dt class="pubdef"><a name="flag:resource_database"><strong>resource_database</strong>(<var>atom</var>)</a></dt>
	893	<dt class="pubdef"><a id="flag:resource_database"><strong>resource_database</strong>(<var>atom</var>)</a></dt>
851	894	<dd class="defbody">
852	895	Set to the absolute filename of the attached state. Typically this is
853	896	the file <code>boot32.prc</code>, the file specified with <strong>-x</strong>
854		or the running executable. See also <a name="idx:resource3:131"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>.</dd>
855		<dt class="pubdef"><a name="flag:report_error"><strong>report_error</strong>(<var>bool</var>, changeable)</a></dt>
	897	or the running executable. See also <a id="idx:resource3:131"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>.</dd>
	898	<dt class="pubdef"><a id="flag:report_error"><strong>report_error</strong>(<var>bool</var>, changeable)</a></dt>
856	899	<dd class="defbody">
857	900	If <code>true</code>, print error messages; otherwise suppress them. May
858	901	be changed. See also the <a class="flag" href="flags.html#flag:debug_on_error">debug_on_error</a>
859	902	Prolog flag. Default is <code>true</code>, except for the runtime
860	903	version.</dd>
861		<dt class="pubdef"><a name="flag:runtime"><strong>runtime</strong>(<var>bool</var>)</a></dt>
	904	<dt class="pubdef"><a id="flag:runtime"><strong>runtime</strong>(<var>bool</var>)</a></dt>
862	905	<dd class="defbody">
863	906	If present and <code>true</code>, SWI-Prolog is compiled with
864	907	-DO_RUNTIME, disabling various useful development features (currently
865	908	the tracer and profiler).</dd>
866		<dt class="pubdef"><a name="flag:sandboxed_load"><strong>sandboxed_load</strong>(<var>bool</var>, changeable)</a></dt>
867		<dd class="defbody">
868		If <code>true</code> (default <code>false</code>), <a name="idx:loadfiles2:132"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	909	<dt class="pubdef"><a id="flag:sandboxed_load"><strong>sandboxed_load</strong>(<var>bool</var>, changeable)</a></dt>
	910	<dd class="defbody">
	911	If <code>true</code> (default <code>false</code>), <a id="idx:loadfiles2:132"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
869	912	calls hooks to allow library(sandbox) to verify the safety of
870	913	directives.</dd>
871		<dt class="pubdef"><a name="flag:saved_program"><strong>saved_program</strong>(<var>bool</var>)</a></dt>
	914	<dt class="pubdef"><a id="flag:saved_program"><strong>saved_program</strong>(<var>bool</var>)</a></dt>
872	915	<dd class="defbody">
873	916	If present and <code>true</code>, Prolog has been started from a state
874		saved with <a name="idx:qsaveprogram12:133"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>.</dd>
875		<dt class="pubdef"><a name="flag:shared_object_extension"><strong>shared_object_extension</strong>(<var>atom</var>)</a></dt>
	917	saved with <a id="idx:qsaveprogram12:133"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>.</dd>
	918	<dt class="pubdef"><a id="flag:shared_object_extension"><strong>shared_object_extension</strong>(<var>atom</var>)</a></dt>
876	919	<dd class="defbody">
877	920	Extension used by the operating system for shared objects. <code>.so</code>
878	921	for most Unix systems and <code>.dll</code> for Windows. Used for
879	922	locating files using the <code>file_type</code> <code>executable</code>.
880	923	See also
881		<a name="idx:absolutefilename3:134"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.</dd>
882		<dt class="pubdef"><a name="flag:shared_object_search_path"><strong>shared_object_search_path</strong>(<var>atom</var>)</a></dt>
	924	<a id="idx:absolutefilename3:134"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.</dd>
	925	<dt class="pubdef"><a id="flag:shared_object_search_path"><strong>shared_object_search_path</strong>(<var>atom</var>)</a></dt>
883	926	<dd class="defbody">
884	927	Name of the environment variable used by the system to search for shared
885	928	objects.</dd>
886		<dt class="pubdef"><a name="flag:signals"><strong>signals</strong>(<var>bool</var>)</a></dt>
	929	<dt class="pubdef"><a id="flag:signals"><strong>signals</strong>(<var>bool</var>)</a></dt>
887	930	<dd class="defbody">
888	931	Determine whether Prolog is handling signals (software interrupts). This
889	932	flag is <code>false</code> if the hosting OS does not support signal
890	933	handling or the command line option <strong>-nosignals</strong> is
891	934	active. See
892		<a class="sec" href="foreigninclude.html">section 11.4.21.1</a> for
893		details.</dd>
894		<dt class="pubdef"><a name="flag:stream_type_check"><strong>stream_type_check</strong>(<var>atom</var>, changeable)</a></dt>
	935	<a class="sec" href="foreigninclude.html#sec:11.4.21.1">section
	936	11.4.21.1</a> for details.</dd>
	937	<dt class="pubdef"><a id="flag:stream_type_check"><strong>stream_type_check</strong>(<var>atom</var>, changeable)</a></dt>
895	938	<dd class="defbody">
896	939	Defines whether and how strictly the system validates that byte I/O
897	940	should not be applied to text streams and text I/O should not be applied

899	942	(full checking) and <code>loose</code>. Using checking mode <code>loose</code>
900	943	(default), the system accepts byte I/O from text stream that use ISO
901	944	Latin-1 encoding and accepts writing text to binary streams.</dd>
902		<dt class="pubdef"><a name="flag:system_thread_id"><strong>system_thread_id</strong>(<var>int</var>)</a></dt>
903		<dd class="defbody">
904		Available in multithreaded version (see <a class="sec" href="threads.html">section
	945	<dt class="pubdef"><a id="flag:system_thread_id"><strong>system_thread_id</strong>(<var>int</var>)</a></dt>
	946	<dd class="defbody">
	947	Available in multithreaded version (see <a class="sec" href="threads.html#sec:9">section
905	948	9</a>) where the operating system provides system-wide integer thread
906	949	identifiers. The integer is the thread identifier used by the operating
907		system for the calling thread. See also <a name="idx:threadself1:135"></a><a class="pred" href="threadcreate.html#thread_self/1">thread_self/1</a>.</dd>
908		<dt class="pubdef"><a name="flag:table_space"><strong>table_space</strong>(<var>integer</var>, changeable)</a></dt>
	950	system for the calling thread. See also <a id="idx:threadself1:135"></a><a class="pred" href="threadcreate.html#thread_self/1">thread_self/1</a>.</dd>
	951	<dt class="pubdef"><a id="flag:table_space"><strong>table_space</strong>(<var>integer</var>, changeable)</a></dt>
909	952	<dd class="defbody">
910	953	Space reserved for storing answer tables for <em>tabled predicates</em>
911		(see <a name="idx:table1:136"></a><a class="pred" href="tabling.html#table/1">table/1</a>).<sup class="fn">bug<span class="fn-text">Currently
	954	(see <a id="idx:table1:136"></a><a class="pred" href="tabling.html#table/1">table/1</a>).<sup class="fn">bug<span class="fn-text">Currently
912	955	only counts the space occupied by the nodes in the answer tries.</span></sup>
913	956	When exceeded a
914	957	<code>resource_error(table_space)</code> exception is raised.</dd>
915		<dt class="pubdef"><a name="flag:timezone"><strong>timezone</strong>(<var>integer</var>)</a></dt>
	958	<dt class="pubdef"><a id="flag:timezone"><strong>timezone</strong>(<var>integer</var>)</a></dt>
916	959	<dd class="defbody">
917	960	Offset in seconds west of GMT of the current time zone. Set at
918	961	initialization time from the <code>timezone</code> variable associated
919		with the POSIX tzset() function. See also <a name="idx:formattime3:137"></a><a class="pred" href="system.html#format_time/3">format_time/3</a>.</dd>
920		<dt class="pubdef"><a name="flag:toplevel_goal"><strong>toplevel_goal</strong>(<var>term</var>, changeable)</a></dt>
	962	with the POSIX tzset() function. See also <a id="idx:formattime3:137"></a><a class="pred" href="system.html#format_time/3">format_time/3</a>.</dd>
	963	<dt class="pubdef"><a id="flag:toplevel_goal"><strong>toplevel_goal</strong>(<var>term</var>, changeable)</a></dt>
921	964	<dd class="defbody">
922	965	Defines the goal that is executed after running the initialization goals
923		and entry point (see <strong>-g</strong>, <a name="idx:initialization2:138"></a><a class="pred" href="consulting.html#initialization/2">initialization/2</a>
	966	and entry point (see <strong>-g</strong>, <a id="idx:initialization2:138"></a><a class="pred" href="consulting.html#initialization/2">initialization/2</a>
924	967	and
925		<a class="sec" href="compilation.html">section 2.10.2.1</a>. The initial
926		value is <code>default</code>, starting a normal interactive session.
927		This value may be changed using the command line option <strong>-t</strong>.
	968	<a class="sec" href="compilation.html#sec:2.10.2.1">section 2.10.2.1</a>.
	969	The initial value is <code>default</code>, starting a normal interactive
	970	session. This value may be changed using the command line option <strong>-t</strong>.
928	971	The explicit value <code>prolog</code> is equavalent to <code>default</code>.
929	972	If <code>initialization(Goal,main)</code> is used and the toplevel is <code>default</code>,
930	973	the toplevel is set to
931		<code>halt</code> (see <a name="idx:halt0:139"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>).</dd>
932		<dt class="pubdef"><a name="flag:toplevel_mode"><strong>toplevel_mode</strong>(<var>atom</var>, changeable)</a></dt>
	974	<code>halt</code> (see <a id="idx:halt0:139"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>).</dd>
	975	<dt class="pubdef"><a id="flag:toplevel_mode"><strong>toplevel_mode</strong>(<var>atom</var>, changeable)</a></dt>
933	976	<dd class="defbody">
934	977	If <code>backtracking</code> (default), the toplevel backtracks after
935	978	completing a query. If <code>recursive</code>, the toplevel is
936	979	implemented as a recursive loop. This implies that global variables set
937	980	using
938		<a name="idx:bsetval2:140"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>
	981	<a id="idx:bsetval2:140"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>
939	982	are maintained between queries. In <em>recursive</em> mode, answers to
940		toplevel variables (see <a class="sec" href="topvars.html">section 2.8</a>)
941		are kept in backtrackable global variables and thus <b>not copied</b>.
942		In
	983	toplevel variables (see <a class="sec" href="topvars.html#sec:2.8">section
	984	2.8</a>) are kept in backtrackable global variables and thus <b>not
	985	copied</b>. In
943	986	<em>backtracking</em> mode answers to toplevel variables are kept in the
944		recorded database (see <a class="sec" href="db.html">section 4.14.2</a>).
	987	recorded database (see <a class="sec" href="db.html#sec:4.14.2">section
	988	4.14.2</a>).
945	989
946	990	<p>The recursive mode has been added for interactive usage of CHR (see
947		<a class="sec" href="chr.html">section 8</a>),<sup class="fn">22<span class="fn-text">Suggested
	991	<a class="sec" href="chr.html#sec:8">section 8</a>),<sup class="fn">22<span class="fn-text">Suggested
948	992	by Falco Nogatz</span></sup> which maintains the global constraint store
949	993	in backtrackable global variables.</dd>
950		<dt class="pubdef"><a name="flag:toplevel_print_anon"><strong>toplevel_print_anon</strong>(<var>bool</var>, changeable)</a></dt>
	994	<dt class="pubdef"><a id="flag:toplevel_print_anon"><strong>toplevel_print_anon</strong>(<var>bool</var>, changeable)</a></dt>
951	995	<dd class="defbody">
952	996	If <code>true</code>, top-level variables starting with an underscore (<code>_</code>)
953	997	are printed normally. If <code>false</code> they are hidden. This may be
954	998	used to hide bindings in complex queries from the top level.</dd>
955		<dt class="pubdef"><a name="flag:toplevel_print_factorized"><strong>toplevel_print_factorized</strong>(<var>bool</var>, changeable)</a></dt>
	999	<dt class="pubdef"><a id="flag:toplevel_print_factorized"><strong>toplevel_print_factorized</strong>(<var>bool</var>, changeable)</a></dt>
956	1000	<dd class="defbody">
957	1001	If <code>true</code> (default <code>false</code>) show the internal
958	1002	sharing of subterms in the answer substitution. The example below
959	1003	reveals internal sharing of leaf nodes in <em>red-black trees</em> as
960	1004	implemented by the
961		<code>library(rbtrees)</code> predicate rb_new1:
	1005	<code>library(rbtrees)</code> predicate rb_new/1 :
962	1006
963	1007	<pre class="code">
964	1008	?- set_prolog_flag(toplevel_print_factorized, true).

980	1024	</pre>
981	1025
982	1026	</dd>
983		<dt class="pubdef"><a name="flag:answer_write_options"><strong>answer_write_options</strong>(<var>term</var>, changeable)</a></dt>
984		<dd class="defbody">
985		This argument is given as option-list to <a name="idx:writeterm2:141"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	1027	<dt class="pubdef"><a id="flag:answer_write_options"><strong>answer_write_options</strong>(<var>term</var>, changeable)</a></dt>
	1028	<dd class="defbody">
	1029	This argument is given as option-list to <a id="idx:writeterm2:141"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
986	1030	for printing results of queries. Default is <code>[quoted(true),
987	1031	portray(true), max_depth(10), attributes(portray)]</code>.</dd>
988		<dt class="pubdef"><a name="flag:toplevel_prompt"><strong>toplevel_prompt</strong>(<var>atom</var>, changeable)</a></dt>
	1032	<dt class="pubdef"><a id="flag:toplevel_prompt"><strong>toplevel_prompt</strong>(<var>atom</var>, changeable)</a></dt>
989	1033	<dd class="defbody">
990	1034	Define the prompt that is used by the interactive top level. The
991	1035	following <code>~</code> (tilde) sequences are replaced:
992	1036
993		<p><table border="2" frame="hsides" rules="groups" style="margin:auto">
994		<tr valign="top"><td><code><code>~</code></code>m</td><td><em>Type in</em>
995		module if not <code>user</code> (see <a name="idx:module1:142"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>) </td></tr>
996		<tr valign="top"><td><code><code>~</code></code>l</td><td><em>Break
997		level</em> if not 0 (see <a name="idx:break0:143"></a><a class="pred" href="toplevel.html#break/0">break/0</a>) </td></tr>
998		<tr valign="top"><td><code><code>~</code></code>d</td><td><em>Debugging
999		state</em> if not normal execution (see <a name="idx:debug0:144"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>, <a name="idx:trace0:145"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>) </td></tr>
1000		<tr valign="top"><td><code><code>~</code></code>!</td><td><em>History
1001		event</em> if history is enabled (see flag <a class="flag" href="flags.html#flag:history">history</a>) </td></tr>
	1037	<p><table class="latex frame-hsides center">
	1038	<tr><td><code><code>~</code></code>m</td><td><em>Type in</em> module if
	1039	not <code>user</code> (see <a id="idx:module1:142"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>) </td></tr>
	1040	<tr><td><code><code>~</code></code>l</td><td><em>Break level</em> if not
	1041	0 (see <a id="idx:break0:143"></a><a class="pred" href="toplevel.html#break/0">break/0</a>) </td></tr>
	1042	<tr><td><code><code>~</code></code>d</td><td><em>Debugging state</em> if
	1043	not normal execution (see <a id="idx:debug0:144"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>, <a id="idx:trace0:145"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>) </td></tr>
	1044	<tr><td><code><code>~</code></code>!</td><td><em>History event</em> if
	1045	history is enabled (see flag <a class="flag" href="flags.html#flag:history">history</a>) </td></tr>
1002	1046	</table>
1003	1047	</dd>
1004		<dt class="pubdef"><a name="flag:toplevel_var_size"><strong>toplevel_var_size</strong>(<var>int</var>, changeable)</a></dt>
	1048	<dt class="pubdef"><a id="flag:toplevel_var_size"><strong>toplevel_var_size</strong>(<var>int</var>, changeable)</a></dt>
1005	1049	<dd class="defbody">
1006	1050	Maximum size counted in literals of a term returned as a binding for a
1007	1051	variable in a top-level query that is saved for re-use using the
1008		<code><code>$</code></code> variable reference. See <a class="sec" href="topvars.html">section
	1052	<code><code>$</code></code> variable reference. See <a class="sec" href="topvars.html#sec:2.8">section
1009	1053	2.8</a>.</dd>
1010		<dt class="pubdef"><a name="flag:trace_gc"><strong>trace_gc</strong>(<var>bool</var>, changeable)</a></dt>
	1054	<dt class="pubdef"><a id="flag:trace_gc"><strong>trace_gc</strong>(<var>bool</var>, changeable)</a></dt>
1011	1055	<dd class="defbody">
1012	1056	If <code>true</code> (default <code>false</code>), garbage collections
1013	1057	and stack-shifts will be reported on the terminal. May be changed.

1023	1067	</pre>
1024	1068
1025	1069	</dd>
1026		<dt class="pubdef"><a name="flag:traditional"><strong>traditional</strong>(<var>bool</var>)</a></dt>
	1070	<dt class="pubdef"><a id="flag:traditional"><strong>traditional</strong>(<var>bool</var>)</a></dt>
1027	1071	<dd class="defbody">
1028	1072	Available in SWI-Prolog version 7. If <code>true</code>,
1029	1073	`traditional' mode has been selected using <strong>--traditional</strong>.
1030	1074	Notice that some SWI7 features, like the functional notation on dicts,
1031		do not work in this mode. See also <a class="sec" href="extensions.html">section
	1075	do not work in this mode. See also <a class="sec" href="extensions.html#sec:5">section
1032	1076	5</a>.</dd>
1033		<dt class="pubdef"><a name="flag:tty_control"><strong>tty_control</strong>(<var>bool</var>, changeable)</a></dt>
	1077	<dt class="pubdef"><a id="flag:tty_control"><strong>tty_control</strong>(<var>bool</var>, changeable)</a></dt>
1034	1078	<dd class="defbody">
1035	1079	Determines whether the terminal is switched to raw mode for
1036		<a name="idx:getsinglechar1:146"></a><a class="pred" href="chario.html#get_single_char/1">get_single_char/1</a>,
	1080	<a id="idx:getsinglechar1:146"></a><a class="pred" href="chario.html#get_single_char/1">get_single_char/1</a>,
1037	1081	which also reads the user actions for the trace. May be set. If this
1038	1082	flag is <code>false</code> at startup, command line editing is disabled.
1039	1083	See also the <strong>+/-tty</strong> command line option.</dd>
1040		<dt class="pubdef"><a name="flag:unix"><strong>unix</strong>(<var>bool</var>)</a></dt>
1041		<dd class="defbody">
1042		<a name="idx:unix:147"></a>If present and <code>true</code>, the
1043		operating system is some version of Unix. Defined if the C compiler used
1044		to compile this version of SWI-Prolog either defines <code>__unix__</code>
	1084	<dt class="pubdef"><a id="flag:unix"><strong>unix</strong>(<var>bool</var>)</a></dt>
	1085	<dd class="defbody">
	1086	<a id="idx:unix:147"></a>If present and <code>true</code>, the operating
	1087	system is some version of Unix. Defined if the C compiler used to
	1088	compile this version of SWI-Prolog either defines <code>__unix__</code>
1045	1089	or <code>unix</code>. On other systems this flag is not available. See
1046	1090	also <a class="flag" href="flags.html#flag:apple">apple</a> and <a class="flag" href="flags.html#flag:windows">windows</a>.</dd>
1047		<dt class="pubdef"><a name="flag:unknown"><strong>unknown</strong>(<var>fail,warning,error</var>, changeable)</a></dt>
	1091	<dt class="pubdef"><a id="flag:unknown"><strong>unknown</strong>(<var>fail,warning,error</var>, changeable)</a></dt>
1048	1092	<dd class="defbody">
1049	1093	Determines the behaviour if an undefined procedure is encountered. If
1050	1094	<code>fail</code>, the predicate fails silently. If <code>warn</code>, a

1056	1100	which in turn inherit the value <code>error</code> from <code>system</code>.
1057	1101	The user may change the flag for module <code>user</code> to change the
1058	1102	default for all application modules or for a specific module. It is
1059		strongly advised to keep the <code>error</code> default and use <a name="idx:dynamic1:148"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
1060		and/or <a name="idx:multifile1:149"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>
	1103	strongly advised to keep the <code>error</code> default and use <a id="idx:dynamic1:148"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
	1104	and/or <a id="idx:multifile1:149"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>
1061	1105	to specify possible non-existence of a predicate.</dd>
1062		<dt class="pubdef"><a name="flag:unload_foreign_libraries"><strong>unload_foreign_libraries</strong>(<var>bool</var>, changeable)</a></dt>
	1106	<dt class="pubdef"><a id="flag:unload_foreign_libraries"><strong>unload_foreign_libraries</strong>(<var>bool</var>, changeable)</a></dt>
1063	1107	<dd class="defbody">
1064	1108	If <code>true</code> (default <code>false</code>), unload all loaded
1065	1109	foreign libraries. Default is <code>false</code> because modern OSes
1066	1110	reclaim the resources anyway and unloading the foreign code may cause
1067	1111	registered hooks to point to no longer existing data or code.</dd>
1068		<dt class="pubdef"><a name="flag:user_flags"><strong>user_flags</strong>(<var>Atom</var>, changeable)</a></dt>
1069		<dd class="defbody">
1070		Define the behaviour of <a name="idx:setprologflag2:150"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
	1112	<dt class="pubdef"><a id="flag:user_flags"><strong>user_flags</strong>(<var>Atom</var>, changeable)</a></dt>
	1113	<dd class="defbody">
	1114	Define the behaviour of <a id="idx:setprologflag2:150"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
1071	1115	if the flag is not known. Values are <code>silent</code>, <code>warning</code>
1072	1116	and <code>error</code>. The first two create the flag on-the-fly, where <code>warning</code>
1073	1117	prints a message. The value <code>error</code> is consistent with ISO:
1074		it raises an existence error and does not create the flag. See also <a name="idx:createprologflag3:151"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>.
	1118	it raises an existence error and does not create the flag. See also <a id="idx:createprologflag3:151"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>.
1075	1119	The default is <code>silent</code>, but future versions may change that.
1076		Developers are encouraged to use another value and ensure proper use of <a name="idx:createprologflag3:152"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>
	1120	Developers are encouraged to use another value and ensure proper use of <a id="idx:createprologflag3:152"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>
1077	1121	to create flags for their library.</dd>
1078		<dt class="pubdef"><a name="flag:var_prefix"><strong>var_prefix</strong>(<var>bool</var>, changeable)</a></dt>
	1122	<dt class="pubdef"><a id="flag:var_prefix"><strong>var_prefix</strong>(<var>bool</var>, changeable)</a></dt>
1079	1123	<dd class="defbody">
1080	1124	If <code>true</code> (default <code>false</code>), variables must start
1081	1125	with an underscore (<code>_</code>). May be changed. This flag is local
1082		to the module in which it is changed. See <a class="sec" href="syntax.html">section
	1126	to the module in which it is changed. See <a class="sec" href="syntax.html#sec:2.16.1.7">section
1083	1127	2.16.1.7</a>.</dd>
1084		<dt class="pubdef"><a name="flag:verbose"><strong>verbose</strong>(<var>atom</var>, changeable)</a></dt>
1085		<dd class="defbody">
1086		This flag is used by <a name="idx:printmessage2:153"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
	1128	<dt class="pubdef"><a id="flag:verbose"><strong>verbose</strong>(<var>atom</var>, changeable)</a></dt>
	1129	<dd class="defbody">
	1130	This flag is used by <a id="idx:printmessage2:153"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
1087	1131	If its value is <code>silent</code>, messages of type <code>informational</code>
1088	1132	and <code>banner</code> are suppressed. The <strong>-q</strong> switches
1089	1133	the value from the initial
1090	1134	<code>normal</code> to <code>silent</code>.</dd>
1091		<dt class="pubdef"><a name="flag:verbose_autoload"><strong>verbose_autoload</strong>(<var>bool</var>, changeable)</a></dt>
	1135	<dt class="pubdef"><a id="flag:verbose_autoload"><strong>verbose_autoload</strong>(<var>bool</var>, changeable)</a></dt>
1092	1136	<dd class="defbody">
1093	1137	If <code>true</code> the normal consult message will be printed if a
1094	1138	library is autoloaded. By default this message is suppressed. Intended
1095	1139	to be used for debugging purposes.</dd>
1096		<dt class="pubdef"><a name="flag:verbose_load"><strong>verbose_load</strong>(<var>atom</var>, changeable)</a></dt>
	1140	<dt class="pubdef"><a id="flag:verbose_load"><strong>verbose_load</strong>(<var>atom</var>, changeable)</a></dt>
1097	1141	<dd class="defbody">
1098	1142	Determines messages printed for loading (compiling) Prolog files.
1099	1143	Current values are <code>full</code> (print a message at the start and

1102	1146	loading the toplevel file), and <code>silent</code> (no messages are
1103	1147	printed, default). The value of this flag is normally controlled by the
1104	1148	option
1105		<code>silent(Bool)</code> provided by <a name="idx:loadfiles2:154"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.</dd>
1106		<dt class="pubdef"><a name="flag:verbose_file_search"><strong>verbose_file_search</strong>(<var>bool</var>, changeable)</a></dt>
	1149	<code>silent(Bool)</code> provided by <a id="idx:loadfiles2:154"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.</dd>
	1150	<dt class="pubdef"><a id="flag:verbose_file_search"><strong>verbose_file_search</strong>(<var>bool</var>, changeable)</a></dt>
1107	1151	<dd class="defbody">
1108	1152	If <code>true</code> (default <code>false</code>), print messages
1109		indicating the progress of <a name="idx:absolutefilename23:155"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/[2,3]</a>
	1153	indicating the progress of <a id="idx:absolutefilename23:155"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/[2,3]</a>
1110	1154	in locating files. Intended for debugging complicated file-search paths.
1111		See also <a name="idx:filesearchpath2:156"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.</dd>
1112		<dt class="pubdef"><a name="flag:version"><strong>version</strong>(<var>integer</var>)</a></dt>
	1155	See also <a id="idx:filesearchpath2:156"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.</dd>
	1156	<dt class="pubdef"><a id="flag:version"><strong>version</strong>(<var>integer</var>)</a></dt>
1113	1157	<dd class="defbody">
1114	1158	The version identifier is an integer with value:
1115	1159	<blockquote><var>10000 × <var>Major</var> + 100 × <var>Minor</var>
1116	1160	+ <var>Patch</var></var></blockquote>
1117	1161	</dd>
1118		<dt class="pubdef"><a name="flag:version_data"><strong>version_data</strong>(<var>swi(Major, Minor, Patch, Extra)</var>)</a></dt>
	1162	<dt class="pubdef"><a id="flag:version_data"><strong>version_data</strong>(<var>swi(Major, Minor, Patch, Extra)</var>)</a></dt>
1119	1163	<dd class="defbody">
1120	1164	Part of the dialect compatibility layer; see also the Prolog flag
1121		<a class="flag" href="flags.html#flag:dialect">dialect</a> and <a class="sec" href="dialect.html">section
	1165	<a class="flag" href="flags.html#flag:dialect">dialect</a> and <a class="sec" href="dialect.html#sec:C">section
1122	1166	C</a>. <var>Extra</var> provides platform-specific version information
1123	1167	as a list. <var>Extra</var> is used for
1124	1168	<em>tagged versions</em> such as ``7.4.0-rc1'', in which case
1125	1169	<var>Extra</var> contains a term <code>tag(rc1)</code>.</dd>
1126		<dt class="pubdef"><a name="flag:version_git"><strong>version_git</strong>(<var>atom</var>)</a></dt>
	1170	<dt class="pubdef"><a id="flag:version_git"><strong>version_git</strong>(<var>atom</var>)</a></dt>
1127	1171	<dd class="defbody">
1128	1172	Available if created from a git repository. See <b>git-describe</b> for
1129	1173	details.</dd>
1130		<dt class="pubdef"><a name="flag:warn_override_implicit_import"><strong>warn_override_implicit_import</strong>(<var>bool</var>, changeable)</a></dt>
	1174	<dt class="pubdef"><a id="flag:warn_override_implicit_import"><strong>warn_override_implicit_import</strong>(<var>bool</var>, changeable)</a></dt>
1131	1175	<dd class="defbody">
1132	1176	If <code>true</code> (default), a warning is printed if an implicitly
1133	1177	imported predicate is clobbered by a local definition. See
1134		<a name="idx:usemodule1:157"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	1178	<a id="idx:usemodule1:157"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
1135	1179	for details.</dd>
1136		<dt class="pubdef"><a name="flag:win_file_access_check"><strong>win_file_access_check</strong>(<var>atom</var>, changeable)</a></dt>
1137		<dd class="defbody">
1138		Controls the behaviour or <a name="idx:accessfile2:158"></a><a class="pred" href="files.html#access_file/2">access_file/2</a>
	1180	<dt class="pubdef"><a id="flag:win_file_access_check"><strong>win_file_access_check</strong>(<var>atom</var>, changeable)</a></dt>
	1181	<dd class="defbody">
	1182	Controls the behaviour or <a id="idx:accessfile2:158"></a><a class="pred" href="files.html#access_file/2">access_file/2</a>
1139	1183	under Windows. There is no reliable way to check access to files and
1140	1184	directories on Windows. This flag allows for switching between three
1141	1185	alternative approximations.

1161	1205	</dl>
1162	1206
1163	1207	</dd>
1164		<dt class="pubdef"><a name="flag:windows"><strong>windows</strong>(<var>bool</var>)</a></dt>
1165		<dd class="defbody">
1166		<a name="idx:windows:159"></a>If present and <code>true</code>, the
	1208	<dt class="pubdef"><a id="flag:windows"><strong>windows</strong>(<var>bool</var>)</a></dt>
	1209	<dd class="defbody">
	1210	<a id="idx:windows:159"></a>If present and <code>true</code>, the
1167	1211	operating system is an implementation of Microsoft Windows. This flag is
1168	1212	only available on MS-Windows based versions. See also <a class="flag" href="flags.html#flag:unix">unix</a>.</dd>
1169		<dt class="pubdef"><a name="flag:write_attributes"><strong>write_attributes</strong>(<var>atom</var>, changeable)</a></dt>
1170		<dd class="defbody">
1171		Defines how <a name="idx:write1:160"></a><a class="pred" href="termrw.html#write/1">write/1</a>
	1213	<dt class="pubdef"><a id="flag:write_attributes"><strong>write_attributes</strong>(<var>atom</var>, changeable)</a></dt>
	1214	<dd class="defbody">
	1215	Defines how <a id="idx:write1:160"></a><a class="pred" href="termrw.html#write/1">write/1</a>
1172	1216	and friends write attributed variables. The option values are described
1173	1217	with the <code>attributes</code> option of
1174		<a name="idx:writeterm3:161"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>.
	1218	<a id="idx:writeterm3:161"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>.
1175	1219	Default is <code>ignore</code>.</dd>
1176		<dt class="pubdef"><a name="flag:write_help_with_overstrike"><strong>write_help_with_overstrike</strong>(<var>bool</var>)</a></dt>
1177		<dd class="defbody">
1178		Internal flag used by <a name="idx:help1:162"></a><a class="pred" href="help.html#help/1">help/1</a>
	1220	<dt class="pubdef"><a id="flag:write_help_with_overstrike"><strong>write_help_with_overstrike</strong>(<var>bool</var>)</a></dt>
	1221	<dd class="defbody">
	1222	Internal flag used by <a id="idx:help1:162"></a><a class="pred" href="help.html#help/1">help/1</a>
1179	1223	when writing to a terminal. If present and <code>true</code> it prints
1180	1224	bold and underlined text using
1181	1225	<em>overstrike</em>.</dd>
1182		<dt class="pubdef"><a name="flag:xpce"><strong>xpce</strong>(<var>bool</var>)</a></dt>
	1226	<dt class="pubdef"><a id="flag:xpce"><strong>xpce</strong>(<var>bool</var>)</a></dt>
1183	1227	<dd class="defbody">
1184	1228	Available and set to <code>true</code> if the XPCE graphics system is
1185	1229	loaded.</dd>
1186		<dt class="pubdef"><a name="flag:xpce_version"><strong>xpce_version</strong>(<var>atom</var>)</a></dt>
	1230	<dt class="pubdef"><a id="flag:xpce_version"><strong>xpce_version</strong>(<var>atom</var>)</a></dt>
1187	1231	<dd class="defbody">
1188	1232	Available and set to the version of the loaded XPCE system.</dd>
1189		<dt class="pubdef"><a name="flag:xref"><strong>xref</strong>(<var>bool</var>, changeable)</a></dt>
	1233	<dt class="pubdef"><a id="flag:xref"><strong>xref</strong>(<var>bool</var>, changeable)</a></dt>
1190	1234	<dd class="defbody">
1191	1235	If <code>true</code>, source code is being read for <em>analysis</em>
1192	1236	purposes such as cross-referencing. Otherwise (default) it is being read
1193		to be compiled. This flag is used at several places by <a name="idx:termexpansion2:163"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	1237	to be compiled. This flag is used at several places by <a id="idx:termexpansion2:163"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
1194	1238	and
1195		<a name="idx:goalexpansion2:164"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	1239	<a id="idx:goalexpansion2:164"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
1196	1240	hooks, notably if these hooks use side effects. See also the libraries <code>library(prolog_source)</code>
1197	1241	and <code>library(prolog_xref)</code>.
1198	1242	</dd>
1199	1243	</dl>
1200	1244
1201	1245	</dd>
1202		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="set_prolog_flag/2"><strong>set_prolog_flag</strong>(<var>:Key,
	1246	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="set_prolog_flag/2"><strong>set_prolog_flag</strong>(<var>:Key,
1203	1247	+Value</var>)</a></dt>
1204	1248	<dd class="defbody">
1205	1249	Define a new Prolog flag or change its value. <var>Key</var> is an atom.

1224	1268
1225	1269	<p>The behaviour when <var>Key</var> denotes a non-existent key depends
1226	1270	on the Prolog flag <a class="flag" href="flags.html#flag:user_flags">user_flags</a>.
1227		The default is to define them silently. New code is encouraged to use <a name="idx:createprologflag3:165"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>
	1271	The default is to define them silently. New code is encouraged to use <a id="idx:createprologflag3:165"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>
1228	1272	for portability.</dd>
1229		<dt class="pubdef"><span class="pred-tag">[YAP]</span><a name="create_prolog_flag/3"><strong>create_prolog_flag</strong>(<var>+Key,
	1273	<dt class="pubdef"><span class="pred-tag">[YAP]</span><a id="create_prolog_flag/3"><strong>create_prolog_flag</strong>(<var>+Key,
1230	1274	+Value, +Options</var>)</a></dt>
1231	1275	<dd class="defbody">
1232	1276	Create a new Prolog flag. The ISO standard does not foresee creation of

1247	1291	<dt><strong>keep</strong>(<var>+Boolean</var>)</dt>
1248	1292	<dd class="defbody">
1249	1293	If <code>true</code>, do not modify the flag if it already exists.
1250		Otherwise (default), this predicate behaves as <a name="idx:setprologflag2:166"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
	1294	Otherwise (default), this predicate behaves as <a id="idx:setprologflag2:166"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
1251	1295	if the flag already exists.
1252	1296	</dd>
1253	1297	</dl>

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194		<h2 id="sec:forall2"><a name="sec:4.31"><span class="sec-nr">4.31</span> <span class="sec-title">Forall</span></a></h2>
195
196		<a name="sec:forall2"></a>
	235	<h2 id="sec:forall2"><a id="sec:4.31"><span class="sec-nr">4.31</span> <span class="sec-title">Forall</span></a></h2>
	236
	237	<a id="sec:forall2"></a>
197	238
198	239	<dl class="latex">
199		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="forall/2"><strong>forall</strong>(<var>:Cond,
	240	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="forall/2"><strong>forall</strong>(<var>:Cond,
200	241	:Action</var>)</a></dt>
201	242	<dd class="defbody">
202	243	For all alternative bindings of <var>Cond</var>, <var>Action</var> can

209	250	Result =:= Formula).
210	251	</pre>
211	252
212		<p>The predicate <a name="idx:forall2:1375"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
	253	<p>The predicate <a id="idx:forall2:1375"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
213	254	is implemented as <code>\+ ( Cond, \+ Action)</code>, i.e., <i>There is
214	255	no instantiation of <var>Cond</var> for which <var>Action</var> is
215	256	false.</i>. The use of double negation implies that
216		<a name="idx:forall2:1376"></a><a class="pred" href="forall2.html#forall/2">forall/2</a> <em>does
217		not change any variable bindings</em>. It proves a relation. The <a name="idx:forall2:1377"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
	257	<a id="idx:forall2:1376"></a><a class="pred" href="forall2.html#forall/2">forall/2</a> <em>does
	258	not change any variable bindings</em>. It proves a relation. The <a id="idx:forall2:1377"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
218	259	control structure can be used for its side-effects. E.g., the following
219	260	asserts relations in a list into the dynamic database:
220	261

223	264	assertz(child_of(Child, Parent))).
224	265	</pre>
225	266
226		<p>Using <a name="idx:forall2:1378"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
	267	<p>Using <a id="idx:forall2:1378"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
227	268	as <code>forall(Generator, SideEffect)</code> is preferred over the
228	269	classical <em>failure driven loop</em> as shown below because it makes
229	270	it explicit which part of the construct is the generator and which part

241	282	)
242	283	</pre>
243	284
244		<p>If your intent is to create variable bindings, the <a name="idx:forall2:1379"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
245		control structure is inadequate. Possibly you are looking for <a name="idx:maplist2:1380"></a><a class="pred" href="apply.html#maplist/2">maplist/2</a>,
246		<a name="idx:findall3:1381"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
247		or <a name="idx:foreach2:1382"></a><a class="pred" href="aggregate.html#foreach/2">foreach/2</a>.
	285	<p>If your intent is to create variable bindings, the <a id="idx:forall2:1379"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
	286	control structure is inadequate. Possibly you are looking for <a id="idx:maplist2:1380"></a><a class="pred" href="apply.html#maplist/2">maplist/2</a>,
	287	<a id="idx:findall3:1381"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
	288	or <a id="idx:foreach2:1382"></a><a class="pred" href="aggregate.html#foreach/2">foreach/2</a>.
248	289	</dd>
249	290	</dl>
250	291

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193	234	</div>
194		<h1 id="sec:foreign"><a name="sec:11"><span class="sec-nr">11</span> <span class="sec-title">Foreign
	235	<h1 id="sec:foreign"><a id="sec:11"><span class="sec-nr">11</span> <span class="sec-title">Foreign
195	236	Language Interface</span></a></h1>
196	237
197		<a name="sec:foreign"></a>
	238	<a id="sec:foreign"></a>
198	239
199	240	<p>SWI-Prolog offers a powerful interface to C <cite><a class="cite" href="Bibliography.html#Kernighan:78">Kernighan &
200	241	Ritchie, 1978</a></cite>. The main design objectives of the foreign

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193	234	</div>
194		<h2 id="sec:foreigninclude"><a name="sec:11.4"><span class="sec-nr">11.4</span> <span class="sec-title">The
	235	<h2 id="sec:foreigninclude"><a id="sec:11.4"><span class="sec-nr">11.4</span> <span class="sec-title">The
195	236	Foreign Include File</span></a></h2>
196	237
197		<a name="sec:foreigninclude"></a>
198
199		<p><h3 id="sec:foreign-control"><a name="sec:11.4.1"><span class="sec-nr">11.4.1</span> <span class="sec-title">Argument
	238	<a id="sec:foreigninclude"></a>
	239
	240	<p><h3 id="sec:foreign-control"><a id="sec:11.4.1"><span class="sec-nr">11.4.1</span> <span class="sec-title">Argument
200	241	Passing and Control</span></a></h3>
201	242
202		<a name="sec:foreign-control"></a>
	243	<a id="sec:foreign-control"></a>
203	244
204	245	<p>If Prolog encounters a foreign predicate at run time it will call a
205	246	function specified in the predicate definition of the foreign predicate.

210	251	alternatives to return control back to Prolog:
211	252
212	253	<dl class="latex">
213		<dt class="pubdef"><a name="PL_succeed()"><var>(return) foreign_t</var> <strong>PL_succeed</strong>(<var></var>)</a></dt>
	254	<dt class="pubdef"><a id="PL_succeed()"><var>(return) foreign_t</var> <strong>PL_succeed</strong>(<var></var>)</a></dt>
214	255	<dd class="defbody">
215	256	Succeed deterministically. PL_succeed is defined as
216	257	<code>return <code>TRUE</code></code>.
217	258	</dd>
218		<dt class="pubdef"><a name="PL_fail()"><var>(return) foreign_t</var> <strong>PL_fail</strong>(<var></var>)</a></dt>
	259	<dt class="pubdef"><a id="PL_fail()"><var>(return) foreign_t</var> <strong>PL_fail</strong>(<var></var>)</a></dt>
219	260	<dd class="defbody">
220	261	Fail and start Prolog backtracking. PL_fail is defined as <code>return <code>FALSE</code></code>.
221	262	</dd>
222	263	</dl>
223	264
224		<p><h4 id="sec:foreignnondet"><a name="sec:11.4.1.1"><span class="sec-nr">11.4.1.1</span> <span class="sec-title">Non-deterministic
	265	<p><h4 id="sec:foreignnondet"><a id="sec:11.4.1.1"><span class="sec-nr">11.4.1.1</span> <span class="sec-title">Non-deterministic
225	266	Foreign Predicates</span></a></h4>
226	267
227		<a name="sec:foreignnondet"></a>
	268	<a id="sec:foreignnondet"></a>
228	269
229	270	<p>By default foreign predicates are deterministic. Using the
230	271	<code>PL_FA_NONDETERMINISTIC</code> attribute (see <a class="func" href="foreigninclude.html#PL_register_foreign()">PL_register_foreign()</a>)

274	315	<code>PL_foreign_context*()</code> macro.
275	316
276	317	<dl class="latex">
277		<dt class="pubdef"><a name="PL_retry()"><var>(return) foreign_t</var> <strong>PL_retry</strong>(<var>intptr_t
	318	<dt class="pubdef"><a id="PL_retry()"><var>(return) foreign_t</var> <strong>PL_retry</strong>(<var>intptr_t
278	319	value</var>)</a></dt>
279	320	<dd class="defbody">
280	321	The foreign function succeeds while leaving a choice point. On

286	327	or 62 bits (two bits are used for status indication). Defined as <code>return
287	328	_<a class="func" href="foreigninclude.html#PL_retry()">PL_retry(n)</a></code>.
288	329	See also <a class="func" href="foreigninclude.html#PL_succeed()">PL_succeed()</a>.</dd>
289		<dt class="pubdef"><a name="PL_retry_address()"><var>(return) foreign_t</var> <strong>PL_retry_address</strong>(<var>void
	330	<dt class="pubdef"><a id="PL_retry_address()"><var>(return) foreign_t</var> <strong>PL_retry_address</strong>(<var>void
290	331	*</var>)</a></dt>
291	332	<dd class="defbody">
292	333	As <a class="func" href="foreigninclude.html#PL_retry()">PL_retry()</a>,

294	335	Defined as <code>return _<a class="func" href="foreigninclude.html#PL_retry_address()">PL_retry_address(n)</a></code>.
295	336	See also
296	337	<a class="func" href="foreigninclude.html#PL_succeed()">PL_succeed()</a>.</dd>
297		<dt class="pubdef"><a name="PL_foreign_control()"><var>int</var> <strong>PL_foreign_control</strong>(<var>control_t</var>)</a></dt>
	338	<dt class="pubdef"><a id="PL_foreign_control()"><var>int</var> <strong>PL_foreign_control</strong>(<var>control_t</var>)</a></dt>
298	339	<dd class="defbody">
299	340	Extracts the type of call from the control argument. The return values
300	341	are described above. Note that the function should be prepared to handle
301	342	the <code>PL_PRUNED</code> case and should be aware that the other
302	343	arguments are not valid in this case.</dd>
303		<dt class="pubdef"><a name="PL_foreign_context()"><var>intptr_t</var> <strong>PL_foreign_context</strong>(<var>control_t</var>)</a></dt>
	344	<dt class="pubdef"><a id="PL_foreign_context()"><var>intptr_t</var> <strong>PL_foreign_context</strong>(<var>control_t</var>)</a></dt>
304	345	<dd class="defbody">
305	346	Extracts the context from the context argument. If the call type is
306	347	<code>PL_FIRST_CALL</code> the context value is 0L. Otherwise it is the
307	348	value returned by the last <a class="func" href="foreigninclude.html#PL_retry()">PL_retry()</a>
308	349	associated with this goal (both if the call type is <code>PL_REDO</code>
309	350	or <code>PL_PRUNED</code>).</dd>
310		<dt class="pubdef"><a name="PL_foreign_context_address()"><var>void *</var> <strong>PL_foreign_context_address</strong>(<var>control_t</var>)</a></dt>
	351	<dt class="pubdef"><a id="PL_foreign_context_address()"><var>void *</var> <strong>PL_foreign_context_address</strong>(<var>control_t</var>)</a></dt>
311	352	<dd class="defbody">
312	353	Extracts an address as passed in by <a class="func" href="foreigninclude.html#PL_retry_address()">PL_retry_address()</a>.</dd>
313		<dt class="pubdef"><a name="PL_foreign_context_predicate()"><var>predicate_t</var> <strong>PL_foreign_context_predicate</strong>(<var>control_t</var>)</a></dt>
	354	<dt class="pubdef"><a id="PL_foreign_context_predicate()"><var>predicate_t</var> <strong>PL_foreign_context_predicate</strong>(<var>control_t</var>)</a></dt>
314	355	<dd class="defbody">
315	356
316	357	<p>Fetch the Prolog predicate that is executing this function. Note that

361	402
362	403	<div class="caption"><b>Figure 6 : </b>Skeleton for non-deterministic
363	404	foreign functions</div>
364		<a name="fig:nondetermf"></a>
365
366		<p><h3 id="sec:foreign-atoms"><a name="sec:11.4.2"><span class="sec-nr">11.4.2</span> <span class="sec-title">Atoms
	405	<a id="fig:nondetermf"></a>
	406
	407	<p><h3 id="sec:foreign-atoms"><a id="sec:11.4.2"><span class="sec-nr">11.4.2</span> <span class="sec-title">Atoms
367	408	and functors</span></a></h3>
368	409
369		<a name="sec:foreign-atoms"></a>
	410	<a id="sec:foreign-atoms"></a>
370	411
371	412	<p>The following functions provide for communication using atoms and
372	413	functors.
373	414
374	415	<dl class="latex">
375		<dt class="pubdef"><a name="PL_new_atom()"><var>atom_t</var> <strong>PL_new_atom</strong>(<var>const
	416	<dt class="pubdef"><a id="PL_new_atom()"><var>atom_t</var> <strong>PL_new_atom</strong>(<var>const
376	417	char *</var>)</a></dt>
377	418	<dd class="defbody">
378	419	Return an atom handle for the given C-string. This function always
379	420	succeeds. The returned handle is valid as long as the atom is referenced
380		(see <a class="sec" href="foreigninclude.html">section 11.4.2.1</a>).
381		The following atoms are provided as macros, giving access to the empty
382		list symbol and the name of the list constructor. Prior to version 7, <code>ATOM_nil</code>
383		is the same as <code><a class="func" href="foreigninclude.html#PL_new_atom()">PL_new_atom("[]")</a></code>
	421	(see <a class="sec" href="foreigninclude.html#sec:11.4.2.1">section
	422	11.4.2.1</a>). The following atoms are provided as macros, giving access
	423	to the empty list symbol and the name of the list constructor. Prior to
	424	version 7, <code>ATOM_nil</code> is the same as <code><a class="func" href="foreigninclude.html#PL_new_atom()">PL_new_atom("[]")</a></code>
384	425	and <code>ATOM_dot</code> is the same as
385	426	<code><a class="func" href="foreigninclude.html#PL_new_atom()">PL_new_atom(".")</a></code>.
386	427	This is no long the case in SWI-Prolog version 7.
387	428
388	429	<dl class="latex">
389		<dt class="pubdef"><a name="ATOM_nil()"><var>atom_t</var> <strong>ATOM_nil</strong>(<var>ATOM_nil</var>)</a></dt>
	430	<dt class="pubdef"><a id="ATOM_nil()"><var>atom_t</var> <strong>ATOM_nil</strong>(<var>ATOM_nil</var>)</a></dt>
390	431	<dd class="defbody">
391	432	tomic constant that represents the empty list. It is adviced to use <a class="func" href="foreigninclude.html#PL_get_nil()">PL_get_nil()</a>, <a class="func" href="foreigninclude.html#PL_put_nil()">PL_put_nil()</a>
392	433	or <a class="func" href="foreigninclude.html#PL_unify_nil()">PL_unify_nil()</a>
393	434	where applicable.</dd>
394		<dt class="pubdef"><a name="ATOM_dot()"><var>atom_t</var> <strong>ATOM_dot</strong>(<var>ATOM_dot</var>)</a></dt>
	435	<dt class="pubdef"><a id="ATOM_dot()"><var>atom_t</var> <strong>ATOM_dot</strong>(<var>ATOM_dot</var>)</a></dt>
395	436	<dd class="defbody">
396	437	tomic constant that represents the name of the list constructor. The
397	438	list constructor itself is created using

404	445	</dl>
405	446
406	447	</dd>
407		<dt class="pubdef"><a name="PL_new_atom_mbchars()"><var>atom_t</var> <strong>PL_new_atom_mbchars</strong>(<var>int
	448	<dt class="pubdef"><a id="PL_new_atom_mbchars()"><var>atom_t</var> <strong>PL_new_atom_mbchars</strong>(<var>int
408	449	rep, size_t len, const char *s</var>)</a></dt>
409	450	<dd class="defbody">
410	451	This function generalizes <a class="func" href="foreigninclude.html#PL_new_atom()">PL_new_atom()</a>

415	456	If
416	457	<var>len</var> is <code>(size_t)-1</code>, it is computed from <var>s</var>
417	458	using strlen().</dd>
418		<dt class="pubdef"><a name="PL_atom_chars()"><var>const char*</var> <strong>PL_atom_chars</strong>(<var>atom_t
	459	<dt class="pubdef"><a id="PL_atom_chars()"><var>const char*</var> <strong>PL_atom_chars</strong>(<var>atom_t
419	460	atom</var>)</a></dt>
420	461	<dd class="defbody">
421	462	Return a C-string for the text represented by the given atom. The
422	463	returned text will not be changed by Prolog. It is not allowed to modify
423	464	the contents, not even `temporary' as the string may reside in read-only
424	465	memory. The returned string becomes invalid if the atom is garbage
425		collected (see <a class="sec" href="foreigninclude.html">section
	466	collected (see <a class="sec" href="foreigninclude.html#sec:11.4.2.1">section
426	467	11.4.2.1</a>). Foreign functions that require the text from an atom
427	468	passed in a <code>term_t</code> normally use
428	469	<a class="func" href="foreigninclude.html#PL_get_atom_chars()">PL_get_atom_chars()</a>
429	470	or <a class="func" href="foreigninclude.html#PL_get_atom_nchars()">PL_get_atom_nchars()</a>.</dd>
430		<dt class="pubdef"><a name="PL_new_functor()"><var>functor_t</var> <strong>PL_new_functor</strong>(<var>atom_t
	471	<dt class="pubdef"><a id="PL_new_functor()"><var>functor_t</var> <strong>PL_new_functor</strong>(<var>atom_t
431	472	name, int arity</var>)</a></dt>
432	473	<dd class="defbody">
433	474	Returns a <em>functor identifier</em>, a handle for the name/arity pair.
434	475	The returned handle is valid for the entire Prolog session.
435	476	</dd>
436		<dt class="pubdef"><a name="PL_functor_name()"><var>atom_t</var> <strong>PL_functor_name</strong>(<var>functor_t
	477	<dt class="pubdef"><a id="PL_functor_name()"><var>atom_t</var> <strong>PL_functor_name</strong>(<var>functor_t
437	478	f</var>)</a></dt>
438	479	<dd class="defbody">
439	480	Return an atom representing the name of the given functor.
440	481	</dd>
441		<dt class="pubdef"><a name="PL_functor_arity()"><var>size_t</var> <strong>PL_functor_arity</strong>(<var>functor_t
	482	<dt class="pubdef"><a id="PL_functor_arity()"><var>size_t</var> <strong>PL_functor_arity</strong>(<var>functor_t
442	483	f</var>)</a></dt>
443	484	<dd class="defbody">
444	485	Return the arity of the given functor.
445	486	</dd>
446	487	</dl>
447	488
448		<p><h4 id="sec:atomgc"><a name="sec:11.4.2.1"><span class="sec-nr">11.4.2.1</span> <span class="sec-title">Atoms
	489	<p><h4 id="sec:atomgc"><a id="sec:11.4.2.1"><span class="sec-nr">11.4.2.1</span> <span class="sec-title">Atoms
449	490	and atom garbage collection</span></a></h4>
450	491
451		<a name="sec:atomgc"></a>
	492	<a id="sec:atomgc"></a>
452	493
453	494	<p>With the introduction of atom garbage collection in version 3.3.0,
454	495	atoms no longer live as long as the process. Instead, their lifetime is
455	496	guaranteed only as long as they are referenced. In the single-threaded
456	497	version, atom garbage collections are only invoked at the
457		<em>call-port</em>. In the multithreaded version (see <a class="sec" href="threads.html">chapter
	498	<em>call-port</em>. In the multithreaded version (see <a class="sec" href="threads.html#sec:9">chapter
458	499	9</a>), they appear asynchronously, except for the invoking thread.
459	500
460	501	<p>For dealing with atom garbage collection, two additional functions
461	502	are provided:
462	503
463	504	<dl class="latex">
464		<dt class="pubdef"><a name="PL_register_atom()"><var>void</var> <strong>PL_register_atom</strong>(<var>atom_t
	505	<dt class="pubdef"><a id="PL_register_atom()"><var>void</var> <strong>PL_register_atom</strong>(<var>atom_t
465	506	atom</var>)</a></dt>
466	507	<dd class="defbody">
467	508	Increment the reference count of the atom by one. <a class="func" href="foreigninclude.html#PL_new_atom()">PL_new_atom()</a>
468	509	performs this automatically, returning an atom with a reference count of
469		at least one.<sup class="fn">169<span class="fn-text">Otherwise
	510	at least one.<sup class="fn">170<span class="fn-text">Otherwise
470	511	asynchronous atom garbage collection might destroy the atom before it is
471	512	used.</span></sup></dd>
472		<dt class="pubdef"><a name="PL_unregister_atom()"><var>void</var> <strong>PL_unregister_atom</strong>(<var>atom_t
	513	<dt class="pubdef"><a id="PL_unregister_atom()"><var>void</var> <strong>PL_unregister_atom</strong>(<var>atom_t
473	514	atom</var>)</a></dt>
474	515	<dd class="defbody">
475	516	Decrement the reference count of the atom. If the reference count drops

490	531	advised to use the _chars() or _nchars() functions whenever
491	532	applicable.
492	533
493		<p><h3 id="sec:foreign-term-analysis"><a name="sec:11.4.3"><span class="sec-nr">11.4.3</span> <span class="sec-title">Analysing
	534	<p><h3 id="sec:foreign-term-analysis"><a id="sec:11.4.3"><span class="sec-nr">11.4.3</span> <span class="sec-title">Analysing
494	535	Terms via the Foreign Interface</span></a></h3>
495	536
496		<a name="sec:foreign-term-analysis"></a>
	537	<a id="sec:foreign-term-analysis"></a>
497	538
498	539	<p>Each argument of a foreign function (except for the control argument)
499	540	is of type <code>term_t</code>, an opaque handle to a Prolog term. Three
500	541	groups of functions are available for the analysis of terms. The first
501		just validates the type, like the Prolog predicates <a name="idx:var1:2015"></a><a class="pred" href="typetest.html#var/1">var/1</a>, <a name="idx:atom1:2016"></a><a class="pred" href="typetest.html#atom/1">atom/1</a>,
	542	just validates the type, like the Prolog predicates <a id="idx:var1:2019"></a><a class="pred" href="typetest.html#var/1">var/1</a>, <a id="idx:atom1:2020"></a><a class="pred" href="typetest.html#atom/1">atom/1</a>,
502	543	etc., and are called <code>PL_is_*()</code>. The second group attempts
503	544	to translate the argument into a C primitive type. These predicates take
504	545	a <code>term_t</code> and a pointer to the appropriate C type and return <code>TRUE</code>

506	547	<code>FALSE</code> depending on successful or unsuccessful translation.
507	548	If the translation fails, the pointed-to data is never modified.
508	549
509		<p><h4 id="sec:foreign-term-type"><a name="sec:11.4.3.1"><span class="sec-nr">11.4.3.1</span> <span class="sec-title">Testing
	550	<p><h4 id="sec:foreign-term-type"><a id="sec:11.4.3.1"><span class="sec-nr">11.4.3.1</span> <span class="sec-title">Testing
510	551	the type of a term</span></a></h4>
511	552
512		<a name="sec:foreign-term-type"></a>
513
514		<dl class="latex">
515		<dt class="pubdef"><a name="PL_term_type()"><var>int</var> <strong>PL_term_type</strong>(<var>term_t</var>)</a></dt>
	553	<a id="sec:foreign-term-type"></a>
	554
	555	<dl class="latex">
	556	<dt class="pubdef"><a id="PL_term_type()"><var>int</var> <strong>PL_term_type</strong>(<var>term_t</var>)</a></dt>
516	557	<dd class="defbody">
517	558	Obtain the type of a term, which should be a term returned by one of the
518	559	other interface predicates or passed as an argument. The function

541	582	classify <code>PL_NIL</code> and <code>PL_BLOB</code> as <code>PL_ATOM</code>,
542	583	<code>PL_LIST_PAIR</code> as <code>PL_TERM</code> and do not have dicts.
543	584
544		<p><table border="2" frame="box" rules="groups">
545		<tr valign="top"><td><code>PL_VARIABLE</code> </td><td>A variable or
546		attributed variable </td></tr>
547		<tr valign="top"><td><code>PL_ATOM</code> </td><td>A Prolog atom </td></tr>
548		<tr valign="top"><td><code>PL_NIL</code> </td><td>The constant <code>[]</code> </td></tr>
549		<tr valign="top"><td><code>PL_BLOB</code> </td><td>A blob (see <a class="sec" href="foreigninclude.html">section
	585	<p><table class="latex frame-box">
	586	<tr><td><code>PL_VARIABLE</code> </td><td>A variable or attributed
	587	variable </td></tr>
	588	<tr><td><code>PL_ATOM</code> </td><td>A Prolog atom </td></tr>
	589	<tr><td><code>PL_NIL</code> </td><td>The constant <code>[]</code> </td></tr>
	590	<tr><td><code>PL_BLOB</code> </td><td>A blob (see <a class="sec" href="foreigninclude.html#sec:11.4.7.2">section
550	591	11.4.7.2</a>) </td></tr>
551		<tr valign="top"><td><code>PL_STRING</code> </td><td>A string (see <a class="sec" href="strings.html">section
	592	<tr><td><code>PL_STRING</code> </td><td>A string (see <a class="sec" href="strings.html#sec:5.2">section
552	593	5.2</a>) </td></tr>
553		<tr valign="top"><td><code>PL_INTEGER</code> </td><td>A integer </td></tr>
554		<tr valign="top"><td><code>PL_FLOAT</code> </td><td>A floating point
555		number </td></tr>
556		<tr valign="top"><td><code>PL_TERM</code> </td><td>A compound term </td></tr>
557		<tr valign="top"><td><code>PL_LIST_PAIR</code> </td><td>A list cell (<code>[H\|T]</code>) </td></tr>
558		<tr valign="top"><td><code>PL_DICT</code> </td><td>A dict (see <a class="sec" href="dicts.html">section
	594	<tr><td><code>PL_INTEGER</code> </td><td>A integer </td></tr>
	595	<tr><td><code>PL_FLOAT</code> </td><td>A floating point number </td></tr>
	596	<tr><td><code>PL_TERM</code> </td><td>A compound term </td></tr>
	597	<tr><td><code>PL_LIST_PAIR</code> </td><td>A list cell (<code>[H\|T]</code>) </td></tr>
	598	<tr><td><code>PL_DICT</code> </td><td>A dict (see <a class="sec" href="dicts.html#sec:5.4">section
559	599	5.4</a>)) </td></tr>
560	600	</table>
561	601	</dd>

571	611	functions below. All these functions return either <code>TRUE</code> or <code>FALSE</code>.
572	612
573	613	<dl class="latex">
574		<dt class="pubdef"><a name="PL_is_variable()"><var>int</var> <strong>PL_is_variable</strong>(<var>term_t</var>)</a></dt>
	614	<dt class="pubdef"><a id="PL_is_variable()"><var>int</var> <strong>PL_is_variable</strong>(<var>term_t</var>)</a></dt>
575	615	<dd class="defbody">
576	616	Returns non-zero if <var>term</var> is a variable.</dd>
577		<dt class="pubdef"><a name="PL_is_ground()"><var>int</var> <strong>PL_is_ground</strong>(<var>term_t</var>)</a></dt>
578		<dd class="defbody">
579		Returns non-zero if <var>term</var> is a ground term. See also <a name="idx:ground1:2017"></a><a class="pred" href="typetest.html#ground/1">ground/1</a>.
	617	<dt class="pubdef"><a id="PL_is_ground()"><var>int</var> <strong>PL_is_ground</strong>(<var>term_t</var>)</a></dt>
	618	<dd class="defbody">
	619	Returns non-zero if <var>term</var> is a ground term. See also <a id="idx:ground1:2021"></a><a class="pred" href="typetest.html#ground/1">ground/1</a>.
580	620	This function is cycle-safe.</dd>
581		<dt class="pubdef"><a name="PL_is_atom()"><var>int</var> <strong>PL_is_atom</strong>(<var>term_t</var>)</a></dt>
	621	<dt class="pubdef"><a id="PL_is_atom()"><var>int</var> <strong>PL_is_atom</strong>(<var>term_t</var>)</a></dt>
582	622	<dd class="defbody">
583	623	Returns non-zero if <var>term</var> is an atom.</dd>
584		<dt class="pubdef"><a name="PL_is_string()"><var>int</var> <strong>PL_is_string</strong>(<var>term_t</var>)</a></dt>
	624	<dt class="pubdef"><a id="PL_is_string()"><var>int</var> <strong>PL_is_string</strong>(<var>term_t</var>)</a></dt>
585	625	<dd class="defbody">
586	626	Returns non-zero if <var>term</var> is a string.</dd>
587		<dt class="pubdef"><a name="PL_is_integer()"><var>int</var> <strong>PL_is_integer</strong>(<var>term_t</var>)</a></dt>
	627	<dt class="pubdef"><a id="PL_is_integer()"><var>int</var> <strong>PL_is_integer</strong>(<var>term_t</var>)</a></dt>
588	628	<dd class="defbody">
589	629	Returns non-zero if <var>term</var> is an integer.</dd>
590		<dt class="pubdef"><a name="PL_is_float()"><var>int</var> <strong>PL_is_float</strong>(<var>term_t</var>)</a></dt>
	630	<dt class="pubdef"><a id="PL_is_float()"><var>int</var> <strong>PL_is_float</strong>(<var>term_t</var>)</a></dt>
591	631	<dd class="defbody">
592	632	Returns non-zero if <var>term</var> is a float.</dd>
593		<dt class="pubdef"><a name="PL_is_callable()"><var>int</var> <strong>PL_is_callable</strong>(<var>term_t</var>)</a></dt>
594		<dd class="defbody">
595		Returns non-zero if <var>term</var> is a callable term. See <a name="idx:callable1:2018"></a><a class="pred" href="typetest.html#callable/1">callable/1</a>
	633	<dt class="pubdef"><a id="PL_is_callable()"><var>int</var> <strong>PL_is_callable</strong>(<var>term_t</var>)</a></dt>
	634	<dd class="defbody">
	635	Returns non-zero if <var>term</var> is a callable term. See <a id="idx:callable1:2022"></a><a class="pred" href="typetest.html#callable/1">callable/1</a>
596	636	for details.</dd>
597		<dt class="pubdef"><a name="PL_is_compound()"><var>int</var> <strong>PL_is_compound</strong>(<var>term_t</var>)</a></dt>
	637	<dt class="pubdef"><a id="PL_is_compound()"><var>int</var> <strong>PL_is_compound</strong>(<var>term_t</var>)</a></dt>
598	638	<dd class="defbody">
599	639	Returns non-zero if <var>term</var> is a compound term.</dd>
600		<dt class="pubdef"><a name="PL_is_functor()"><var>int</var> <strong>PL_is_functor</strong>(<var>term_t,
	640	<dt class="pubdef"><a id="PL_is_functor()"><var>int</var> <strong>PL_is_functor</strong>(<var>term_t,
601	641	functor_t</var>)</a></dt>
602	642	<dd class="defbody">
603	643	Returns non-zero if <var>term</var> is compound and its functor is <var>functor</var>.
604	644	This test is equivalent to <a class="func" href="foreigninclude.html#PL_get_functor()">PL_get_functor()</a>,
605	645	followed by testing the functor, but easier to write and faster.</dd>
606		<dt class="pubdef"><a name="PL_is_list()"><var>int</var> <strong>PL_is_list</strong>(<var>term_t</var>)</a></dt>
	646	<dt class="pubdef"><a id="PL_is_list()"><var>int</var> <strong>PL_is_list</strong>(<var>term_t</var>)</a></dt>
607	647	<dd class="defbody">
608	648	Returns non-zero if <var>term</var> is a compound term using the list
609	649	constructor or the list terminator. See also <a class="func" href="foreigninclude.html#PL_is_pair()">PL_is_pair()</a>
610	650	and
611	651	<a class="func" href="foreigninclude.html#PL_skip_list()">PL_skip_list()</a>.</dd>
612		<dt class="pubdef"><a name="PL_is_pair()"><var>int</var> <strong>PL_is_pair</strong>(<var>term_t</var>)</a></dt>
	652	<dt class="pubdef"><a id="PL_is_pair()"><var>int</var> <strong>PL_is_pair</strong>(<var>term_t</var>)</a></dt>
613	653	<dd class="defbody">
614	654	Returns non-zero if <var>term</var> is a compound term using the list
615	655	constructor. See also <a class="func" href="foreigninclude.html#PL_is_list()">PL_is_list()</a>
616	656	and <a class="func" href="foreigninclude.html#PL_skip_list()">PL_skip_list()</a>.</dd>
617		<dt class="pubdef"><a name="PL_is_atomic()"><var>int</var> <strong>PL_is_atomic</strong>(<var>term_t</var>)</a></dt>
	657	<dt class="pubdef"><a id="PL_is_atomic()"><var>int</var> <strong>PL_is_atomic</strong>(<var>term_t</var>)</a></dt>
618	658	<dd class="defbody">
619	659	Returns non-zero if <var>term</var> is atomic (not variable or
620	660	compound).</dd>
621		<dt class="pubdef"><a name="PL_is_number()"><var>int</var> <strong>PL_is_number</strong>(<var>term_t</var>)</a></dt>
	661	<dt class="pubdef"><a id="PL_is_number()"><var>int</var> <strong>PL_is_number</strong>(<var>term_t</var>)</a></dt>
622	662	<dd class="defbody">
623	663	Returns non-zero if <var>term</var> is an integer or float.</dd>
624		<dt class="pubdef"><a name="PL_is_acyclic()"><var>int</var> <strong>PL_is_acyclic</strong>(<var>term_t</var>)</a></dt>
	664	<dt class="pubdef"><a id="PL_is_acyclic()"><var>int</var> <strong>PL_is_acyclic</strong>(<var>term_t</var>)</a></dt>
625	665	<dd class="defbody">
626	666	Returns non-zero if <var>term</var> is acyclic (i.e. a finite tree).
627	667	</dd>
628	668	</dl>
629	669
630		<p><h4 id="sec:foreign-extract-from-term"><a name="sec:11.4.3.2"><span class="sec-nr">11.4.3.2</span> <span class="sec-title">Reading
	670	<p><h4 id="sec:foreign-extract-from-term"><a id="sec:11.4.3.2"><span class="sec-nr">11.4.3.2</span> <span class="sec-title">Reading
631	671	data from a term</span></a></h4>
632	672
633		<a name="sec:foreign-extract-from-term"></a>
	673	<a id="sec:foreign-extract-from-term"></a>
634	674
635	675	<p>The functions <code>PL_get_*()</code> read information from a Prolog
636	676	term. Most of them take two arguments. The first is the input term and
637	677	the second is a pointer to the output value or a term reference.
638	678
639	679	<dl class="latex">
640		<dt class="pubdef"><a name="PL_get_atom()"><var>int</var> <strong>PL_get_atom</strong>(<var>term_t
	680	<dt class="pubdef"><a id="PL_get_atom()"><var>int</var> <strong>PL_get_atom</strong>(<var>term_t
641	681	+t, atom_t *a</var>)</a></dt>
642	682	<dd class="defbody">
643	683	If <var>t</var> is an atom, store the unique atom identifier over <var>a</var>.

647	687	advised to manipulate atoms using their handle. As the atom is
648	688	referenced by <var>t</var>, it will live at least as long as <var>t</var>
649	689	does. If longer live-time is required, the atom should be locked using <a class="func" href="foreigninclude.html#PL_register_atom()">PL_register_atom()</a>.</dd>
650		<dt class="pubdef"><a name="PL_get_atom_chars()"><var>int</var> <strong>PL_get_atom_chars</strong>(<var>term_t
	690	<dt class="pubdef"><a id="PL_get_atom_chars()"><var>int</var> <strong>PL_get_atom_chars</strong>(<var>term_t
651	691	+t, char **s</var>)</a></dt>
652	692	<dd class="defbody">
653	693	If <var>t</var> is an atom, store a pointer to a 0-terminated C-string

656	696	the contents of this string. Some built-in atoms may have the string
657	697	allocated in read-only memory, so `temporary manipulation' can cause an
658	698	error.</dd>
659		<dt class="pubdef"><a name="PL_get_string_chars()"><var>int</var> <strong>PL_get_string_chars</strong>(<var>term_t
	699	<dt class="pubdef"><a id="PL_get_string_chars()"><var>int</var> <strong>PL_get_string_chars</strong>(<var>term_t
660	700	+t, char *s, size_t len</var>)</a></dt>
661	701	<dd class="defbody">
662	702	If <var>t</var> is a string object, store a pointer to a 0-terminated

664	704	Note that this pointer is invalidated by backtracking, garbage
665	705	collection and stack-shifts, so generally the only save operations are
666	706	to pass it immediately to a C function that doesn't involve Prolog.</dd>
667		<dt class="pubdef"><a name="PL_get_chars()"><var>int</var> <strong>PL_get_chars</strong>(<var>term_t
	707	<dt class="pubdef"><a id="PL_get_chars()"><var>int</var> <strong>PL_get_chars</strong>(<var>term_t
668	708	+t, char **s, unsigned flags</var>)</a></dt>
669	709	<dd class="defbody">
670	710	Convert the argument term <var>t</var> to a 0-terminated C-string. <em>flags</em>

678	718	using <a class="func" href="foreignnotes.html#PL_free()">PL_free()</a>
679	719	when no longer needed.
680	720
681		<p>With the introduction of wide characters (see <a class="sec" href="widechars.html">section
	721	<p>With the introduction of wide characters (see <a class="sec" href="widechars.html#sec:2.19.1">section
682	722	2.19.1</a>), not all atoms can be converted into a <code>char*</code>.
683	723	This function fails if <var>t</var> is of the wrong type, but also if
684	724	the text cannot be represented. See the <code>REP_*</code> flags below

700	740	<dt><strong>CVT_FLOAT</strong></dt>
701	741	<dd class="defbody">
702	742	Convert if term is a float. The characters returned are the same as
703		<a name="idx:write1:2019"></a><a class="pred" href="termrw.html#write/1">write/1</a>
	743	<a id="idx:write1:2023"></a><a class="pred" href="termrw.html#write/1">write/1</a>
704	744	would write for the floating point number.</dd>
705	745	<dt><strong>CVT_NUMBER</strong></dt>
706	746	<dd class="defbody">

714	754	<dt><strong>CVT_WRITE</strong></dt>
715	755	<dd class="defbody">
716	756	Convert any term that is not converted by any of the other flags using
717		<a name="idx:write1:2020"></a><a class="pred" href="termrw.html#write/1">write/1</a>.
	757	<a id="idx:write1:2024"></a><a class="pred" href="termrw.html#write/1">write/1</a>.
718	758	If no <code>BUF_*</code> is provided, <code>BUF_RING</code> is implied.</dd>
719	759	<dt><strong>CVT_WRITE_CANONICAL</strong></dt>
720	760	<dd class="defbody">
721		As <code>CVT_WRITE</code>, but using <a name="idx:writecanonical2:2021"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>.</dd>
	761	As <code>CVT_WRITE</code>, but using <a id="idx:writecanonical2:2025"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>.</dd>
722	762	<dt><strong>CVT_WRITEQ</strong></dt>
723	763	<dd class="defbody">
724		As <code>CVT_WRITE</code>, but using <a name="idx:writeq2:2022"></a><a class="pred" href="termrw.html#writeq/2">writeq/2</a>.</dd>
	764	As <code>CVT_WRITE</code>, but using <a id="idx:writeq2:2026"></a><a class="pred" href="termrw.html#writeq/2">writeq/2</a>.</dd>
725	765	<dt><strong>CVT_ALL</strong></dt>
726	766	<dd class="defbody">
727	767	Convert if term is any of the above, except for <code>CVT_VARIABLE</code>

757	797	</dl>
758	798
759	799	</dd>
760		<dt class="pubdef"><a name="PL_get_list_chars()"><var>int</var> <strong>PL_get_list_chars</strong>(<var>+term_t
	800	<dt class="pubdef"><a id="PL_get_list_chars()"><var>int</var> <strong>PL_get_list_chars</strong>(<var>+term_t
761	801	l, char **s, unsigned flags</var>)</a></dt>
762	802	<dd class="defbody">
763	803	Same as <code><a class="func" href="foreigninclude.html#PL_get_chars()">PL_get_chars(<var>l</var>, <var>s</var>,
764	804	CVT_LIST\|<var>flags</var>)</a></code>, provided <var>flags</var>
765	805	contains none of the <code>CVT_*</code> flags.
766	806	</dd>
767		<dt class="pubdef"><a name="PL_get_integer()"><var>int</var> <strong>PL_get_integer</strong>(<var>+term_t
	807	<dt class="pubdef"><a id="PL_get_integer()"><var>int</var> <strong>PL_get_integer</strong>(<var>+term_t
768	808	t, int *i</var>)</a></dt>
769	809	<dd class="defbody">
770	810	If <var>t</var> is a Prolog integer, assign its value over <var>i</var>.
771	811	On 32-bit machines, this is the same as <a class="func" href="foreigninclude.html#PL_get_long()">PL_get_long()</a>,
772	812	but avoids a warning from the compiler. See also <a class="func" href="foreigninclude.html#PL_get_long()">PL_get_long()</a>.</dd>
773		<dt class="pubdef"><a name="PL_get_long()"><var>int</var> <strong>PL_get_long</strong>(<var>term_t
	813	<dt class="pubdef"><a id="PL_get_long()"><var>int</var> <strong>PL_get_long</strong>(<var>term_t
774	814	+t, long *i</var>)</a></dt>
775	815	<dd class="defbody">
776	816	If <var>t</var> is a Prolog integer that can be represented as a long,

778	818	cannot be represented by a C long, this function returns <code>FALSE</code>.
779	819	If <var>t</var> is a floating point number that can be represented as a
780	820	long, this function succeeds as well. See also <a class="func" href="foreigninclude.html#PL_get_int64()">PL_get_int64()</a>.</dd>
781		<dt class="pubdef"><a name="PL_get_int64()"><var>int</var> <strong>PL_get_int64</strong>(<var>term_t
	821	<dt class="pubdef"><a id="PL_get_int64()"><var>int</var> <strong>PL_get_int64</strong>(<var>term_t
782	822	+t, int64_t *i</var>)</a></dt>
783	823	<dd class="defbody">
784	824	If <var>t</var> is a Prolog integer or float that can be represented as
785	825	a
786	826	<code>int64_t</code>, assign its value over <var>i</var>.</dd>
787		<dt class="pubdef"><a name="PL_get_intptr()"><var>int</var> <strong>PL_get_intptr</strong>(<var>term_t
	827	<dt class="pubdef"><a id="PL_get_intptr()"><var>int</var> <strong>PL_get_intptr</strong>(<var>term_t
788	828	+t, intptr_t *i</var>)</a></dt>
789	829	<dd class="defbody">
790	830	Get an integer that is at least as wide as a pointer. On most platforms
791	831	this is the same as <a class="func" href="foreigninclude.html#PL_get_long()">PL_get_long()</a>,
792	832	but on Win64 pointers are 8 bytes and longs only 4. Unlike <a class="func" href="foreigninclude.html#PL_get_pointer()">PL_get_pointer()</a>,
793	833	the value is not modified.</dd>
794		<dt class="pubdef"><a name="PL_get_bool()"><var>int</var> <strong>PL_get_bool</strong>(<var>term_t
	834	<dt class="pubdef"><a id="PL_get_bool()"><var>int</var> <strong>PL_get_bool</strong>(<var>term_t
795	835	+t, int *val</var>)</a></dt>
796	836	<dd class="defbody">
797	837	If <var>t</var> has the value <code>true</code> or <code>false</code>,
798	838	set <var>val</var> to the C constant <code>TRUE</code> or <code>FALSE</code>
799	839	and return success, otherwise return failure.
800	840	</dd>
801		<dt class="pubdef"><a name="PL_get_pointer()"><var>int</var> <strong>PL_get_pointer</strong>(<var>term_t
	841	<dt class="pubdef"><a id="PL_get_pointer()"><var>int</var> <strong>PL_get_pointer</strong>(<var>term_t
802	842	+t, void **ptr</var>)</a></dt>
803	843	<dd class="defbody">
804	844	In the current system, pointers are represented by Prolog integers, but

808	848	guarantee pointers in the range of malloc() are handled without
809	849	truncating.
810	850	</dd>
811		<dt class="pubdef"><a name="PL_get_float()"><var>int</var> <strong>PL_get_float</strong>(<var>term_t
	851	<dt class="pubdef"><a id="PL_get_float()"><var>int</var> <strong>PL_get_float</strong>(<var>term_t
812	852	+t, double *f</var>)</a></dt>
813	853	<dd class="defbody">
814	854	If <var>t</var> is a float or integer, its value is assigned over <var>f</var>.
815	855	</dd>
816		<dt class="pubdef"><a name="PL_get_functor()"><var>int</var> <strong>PL_get_functor</strong>(<var>term_t
	856	<dt class="pubdef"><a id="PL_get_functor()"><var>int</var> <strong>PL_get_functor</strong>(<var>term_t
817	857	+t, functor_t *f</var>)</a></dt>
818	858	<dd class="defbody">
819	859	If <var>t</var> is compound or an atom, the Prolog representation of the
820	860	name-arity pair will be assigned over <var>f</var>. See also
821	861	<a class="func" href="foreigninclude.html#PL_get_name_arity()">PL_get_name_arity()</a>
822	862	and <a class="func" href="foreigninclude.html#PL_is_functor()">PL_is_functor()</a>.</dd>
823		<dt class="pubdef"><a name="PL_get_name_arity()"><var>int</var> <strong>PL_get_name_arity</strong>(<var>term_t
	863	<dt class="pubdef"><a id="PL_get_name_arity()"><var>int</var> <strong>PL_get_name_arity</strong>(<var>term_t
824	864	+t, atom_t name, size_t arity</var>)</a></dt>
825	865	<dd class="defbody">
826	866	If <var>t</var> is compound or an atom, the functor name will be

828	868	also
829	869	<a class="func" href="foreigninclude.html#PL_get_functor()">PL_get_functor()</a>
830	870	and <a class="func" href="foreigninclude.html#PL_is_functor()">PL_is_functor()</a>.
831		See <a class="sec" href="foreigntypes.html">section 11.3.2.1</a>.</dd>
832		<dt class="pubdef"><a name="PL_get_compound_name_arity()"><var>int</var> <strong>PL_get_compound_name_arity</strong>(<var>term_t
	871	See <a class="sec" href="foreigntypes.html#sec:11.3.2.1">section
	872	11.3.2.1</a>.</dd>
	873	<dt class="pubdef"><a id="PL_get_compound_name_arity()"><var>int</var> <strong>PL_get_compound_name_arity</strong>(<var>term_t
833	874	+t, atom_t name, size_t arity</var>)</a></dt>
834	875	<dd class="defbody">
835	876	If <var>t</var> is compound term, the functor name will be assigned over
836	877	<var>name</var> and the arity over <var>arity</var>. This is the same as
837	878	<a class="func" href="foreigninclude.html#PL_get_name_arity()">PL_get_name_arity()</a>,
838	879	but this function fails if <var>t</var> is an atom.</dd>
839		<dt class="pubdef"><a name="PL_get_module()"><var>int</var> <strong>PL_get_module</strong>(<var>term_t
	880	<dt class="pubdef"><a id="PL_get_module()"><var>int</var> <strong>PL_get_module</strong>(<var>term_t
840	881	+t, module_t *module</var>)</a></dt>
841	882	<dd class="defbody">
842	883	If <var>t</var> is an atom, the system will look up or create the
843	884	corresponding module and assign an opaque pointer to it over <em>module</em>.
844	885	</dd>
845		<dt class="pubdef"><a name="PL_get_arg()"><var>int</var> <strong>PL_get_arg</strong>(<var>size_t
	886	<dt class="pubdef"><a id="PL_get_arg()"><var>int</var> <strong>PL_get_arg</strong>(<var>size_t
846	887	index, term_t +t, term_t -a</var>)</a></dt>
847	888	<dd class="defbody">
848	889	If <var>t</var> is compound and index is between 1 and arity
849	890	(inclusive), assign <var>a</var> with a term reference to the argument.
850	891	</dd>
851		<dt class="pubdef"><a name="_PL_get_arg()"><var>int</var> <strong>_PL_get_arg</strong>(<var>size_t
	892	<dt class="pubdef"><a id="_PL_get_arg()"><var>int</var> <strong>_PL_get_arg</strong>(<var>size_t
852	893	index, term_t +t, term_t -a</var>)</a></dt>
853	894	<dd class="defbody">
854	895	Same as <a class="func" href="foreigninclude.html#PL_get_arg()">PL_get_arg()</a>,

857	898	</dd>
858	899	</dl>
859	900
860		<p><h4 id="sec:foreign-text-with-length"><a name="sec:11.4.3.3"><span class="sec-nr">11.4.3.3</span> <span class="sec-title">Exchanging
	901	<p><h4 id="sec:foreign-text-with-length"><a id="sec:11.4.3.3"><span class="sec-nr">11.4.3.3</span> <span class="sec-title">Exchanging
861	902	text using length and string</span></a></h4>
862	903
863		<a name="sec:foreign-text-with-length"></a>
	904	<a id="sec:foreign-text-with-length"></a>
864	905
865	906	<p>All internal text representation in SWI-Prolog is represented using
866	907	<code>char *</code> plus length and allow for <em>0-bytes</em> in them.

870	911	*_chars() function.
871	912
872	913	<dl class="latex">
873		<dt class="pubdef"><a name="PL_get_atom_nchars()"><var>int</var> <strong>PL_get_atom_nchars</strong>(<var>term_t
	914	<dt class="pubdef"><a id="PL_get_atom_nchars()"><var>int</var> <strong>PL_get_atom_nchars</strong>(<var>term_t
874	915	t, size_t len, char *s</var>)</a></dt>
875	916	<dd class="defbody">
876	917	See <a class="func" href="foreigninclude.html#PL_get_atom_chars()">PL_get_atom_chars()</a>.
877	918	</dd>
878		<dt class="pubdef"><a name="PL_get_list_nchars()"><var>int</var> <strong>PL_get_list_nchars</strong>(<var>term_t
	919	<dt class="pubdef"><a id="PL_get_list_nchars()"><var>int</var> <strong>PL_get_list_nchars</strong>(<var>term_t
879	920	t, size_t len, char *s</var>)</a></dt>
880	921	<dd class="defbody">
881	922	See <a class="func" href="foreigninclude.html#PL_get_list_chars()">PL_get_list_chars()</a>.
882	923	</dd>
883		<dt class="pubdef"><a name="PL_get_nchars()"><var>int</var> <strong>PL_get_nchars</strong>(<var>term_t
	924	<dt class="pubdef"><a id="PL_get_nchars()"><var>int</var> <strong>PL_get_nchars</strong>(<var>term_t
884	925	t, size_t len, char *s, unsigned int flags</var>)</a></dt>
885	926	<dd class="defbody">
886	927	See <a class="func" href="foreigninclude.html#PL_get_chars()">PL_get_chars()</a>.
887	928	</dd>
888		<dt class="pubdef"><a name="PL_put_atom_nchars()"><var>int</var> <strong>PL_put_atom_nchars</strong>(<var>term_t
	929	<dt class="pubdef"><a id="PL_put_atom_nchars()"><var>int</var> <strong>PL_put_atom_nchars</strong>(<var>term_t
889	930	t, size_t len, const char *s</var>)</a></dt>
890	931	<dd class="defbody">
891	932	See <a class="func" href="foreigninclude.html#PL_put_atom_chars()">PL_put_atom_chars()</a>.
892	933	</dd>
893		<dt class="pubdef"><a name="PL_put_string_nchars()"><var>int</var> <strong>PL_put_string_nchars</strong>(<var>term_t
	934	<dt class="pubdef"><a id="PL_put_string_nchars()"><var>int</var> <strong>PL_put_string_nchars</strong>(<var>term_t
894	935	t, size_t len, const char *s</var>)</a></dt>
895	936	<dd class="defbody">
896	937	See <a class="func" href="foreigninclude.html#PL_put_string_chars()">PL_put_string_chars()</a>.
897	938	</dd>
898		<dt class="pubdef"><a name="PL_put_list_ncodes()"><var>int</var> <strong>PL_put_list_ncodes</strong>(<var>term_t
	939	<dt class="pubdef"><a id="PL_put_list_ncodes()"><var>int</var> <strong>PL_put_list_ncodes</strong>(<var>term_t
899	940	t, size_t len, const char *s</var>)</a></dt>
900	941	<dd class="defbody">
901	942	See <b>PL_put_list_codes()</b>.
902	943	</dd>
903		<dt class="pubdef"><a name="PL_put_list_nchars()"><var>int</var> <strong>PL_put_list_nchars</strong>(<var>term_t
	944	<dt class="pubdef"><a id="PL_put_list_nchars()"><var>int</var> <strong>PL_put_list_nchars</strong>(<var>term_t
904	945	t, size_t len, const char *s</var>)</a></dt>
905	946	<dd class="defbody">
906	947	See <a class="func" href="foreigninclude.html#PL_put_list_chars()">PL_put_list_chars()</a>.
907	948	</dd>
908		<dt class="pubdef"><a name="PL_unify_atom_nchars()"><var>int</var> <strong>PL_unify_atom_nchars</strong>(<var>term_t
	949	<dt class="pubdef"><a id="PL_unify_atom_nchars()"><var>int</var> <strong>PL_unify_atom_nchars</strong>(<var>term_t
909	950	t, size_t len, const char *s</var>)</a></dt>
910	951	<dd class="defbody">
911	952	See <a class="func" href="foreigninclude.html#PL_unify_atom_chars()">PL_unify_atom_chars()</a>.
912	953	</dd>
913		<dt class="pubdef"><a name="PL_unify_string_nchars()"><var>int</var> <strong>PL_unify_string_nchars</strong>(<var>term_t
	954	<dt class="pubdef"><a id="PL_unify_string_nchars()"><var>int</var> <strong>PL_unify_string_nchars</strong>(<var>term_t
914	955	t, size_t len, const char *s</var>)</a></dt>
915	956	<dd class="defbody">
916	957	See <a class="func" href="foreigninclude.html#PL_unify_string_chars()">PL_unify_string_chars()</a>.
917	958	</dd>
918		<dt class="pubdef"><a name="PL_unify_list_ncodes()"><var>int</var> <strong>PL_unify_list_ncodes</strong>(<var>term_t
	959	<dt class="pubdef"><a id="PL_unify_list_ncodes()"><var>int</var> <strong>PL_unify_list_ncodes</strong>(<var>term_t
919	960	t, size_t len, const char *s</var>)</a></dt>
920	961	<dd class="defbody">
921	962	See <b>PL_unify_codes()</b>.
922	963	</dd>
923		<dt class="pubdef"><a name="PL_unify_list_nchars()"><var>int</var> <strong>PL_unify_list_nchars</strong>(<var>term_t
	964	<dt class="pubdef"><a id="PL_unify_list_nchars()"><var>int</var> <strong>PL_unify_list_nchars</strong>(<var>term_t
924	965	t, size_t len, const char *s</var>)</a></dt>
925	966	<dd class="defbody">
926	967	See <a class="func" href="foreigninclude.html#PL_unify_list_chars()">PL_unify_list_chars()</a>.

931	972	inspecting atoms:
932	973
933	974	<dl class="latex">
934		<dt class="pubdef"><a name="PL_new_atom_nchars()"><var>atom_t</var> <strong>PL_new_atom_nchars</strong>(<var>size_t
	975	<dt class="pubdef"><a id="PL_new_atom_nchars()"><var>atom_t</var> <strong>PL_new_atom_nchars</strong>(<var>size_t
935	976	len, const char *s</var>)</a></dt>
936	977	<dd class="defbody">
937	978	Create a new atom as <a class="func" href="foreigninclude.html#PL_new_atom()">PL_new_atom()</a>,
938	979	but using the given length and characters. If <var>len</var> is <code>(size_t)-1</code>,
939	980	it is computed from <var>s</var> using strlen().</dd>
940		<dt class="pubdef"><a name="PL_atom_nchars()"><var>const char *</var> <strong>PL_atom_nchars</strong>(<var>atom_t
	981	<dt class="pubdef"><a id="PL_atom_nchars()"><var>const char *</var> <strong>PL_atom_nchars</strong>(<var>atom_t
941	982	a, size_t *len</var>)</a></dt>
942	983	<dd class="defbody">
943	984	Extract the text and length of an atom.
944	985	</dd>
945	986	</dl>
946	987
947		<p><h4 id="sec:foreign-unicode"><a name="sec:11.4.3.4"><span class="sec-nr">11.4.3.4</span> <span class="sec-title">Wide-character
	988	<p><h4 id="sec:foreign-unicode"><a id="sec:11.4.3.4"><span class="sec-nr">11.4.3.4</span> <span class="sec-title">Wide-character
948	989	versions</span></a></h4>
949	990
950		<a name="sec:foreign-unicode"></a>
	991	<a id="sec:foreign-unicode"></a>
951	992
952	993	<p>Support for exchange of wide-character strings is still under
953	994	consideration. The functions dealing with 8-bit character strings return

960	1001	using the GNU C library (glibc) this represents 32-bit UCS4 characters.
961	1002
962	1003	<dl class="latex">
963		<dt class="pubdef"><a name="PL_new_atom_wchars()"><var>atom_t</var> <strong>PL_new_atom_wchars</strong>(<var>size_t
	1004	<dt class="pubdef"><a id="PL_new_atom_wchars()"><var>atom_t</var> <strong>PL_new_atom_wchars</strong>(<var>size_t
964	1005	len, const pl_wchar_t *s</var>)</a></dt>
965	1006	<dd class="defbody">
966	1007	Create atom from wide-character string as <a class="func" href="foreigninclude.html#PL_new_atom_nchars()">PL_new_atom_nchars()</a>
967	1008	does for ISO-Latin-1 strings. If <var>s</var> only contains ISO-Latin-1
968	1009	characters a normal byte-array atom is created. If <var>len</var> is <code>(size_t)-1</code>,
969	1010	it is computed from <var>s</var> using wcslen().</dd>
970		<dt class="pubdef"><a name="PL_atom_wchars()"><var>pl_wchar_t*</var> <strong>PL_atom_wchars</strong>(<var>atom_t
	1011	<dt class="pubdef"><a id="PL_atom_wchars()"><var>pl_wchar_t*</var> <strong>PL_atom_wchars</strong>(<var>atom_t
971	1012	atom, int *len</var>)</a></dt>
972	1013	<dd class="defbody">
973	1014	Extract characters from a wide-character atom. Succeeds on any atom

975	1016	returned pointer is a pointer into the atom structure. If it is an
976	1017	ISO-Latin-1 character, the returned pointer comes from Prolog's `buffer
977	1018	ring' (see <a class="func" href="foreigninclude.html#PL_get_chars()">PL_get_chars()</a>).</dd>
978		<dt class="pubdef"><a name="PL_get_wchars()"><var>int</var> <strong>PL_get_wchars</strong>(<var>term_t
	1019	<dt class="pubdef"><a id="PL_get_wchars()"><var>int</var> <strong>PL_get_wchars</strong>(<var>term_t
979	1020	t, size_t len, pl_wchar_t *s, unsigned flags</var>)</a></dt>
980	1021	<dd class="defbody">
981	1022	Wide-character version of <a class="func" href="foreigninclude.html#PL_get_chars()">PL_get_chars()</a>.
982	1023	The <var>flags</var> argument is the same as for <a class="func" href="foreigninclude.html#PL_get_chars()">PL_get_chars()</a>.</dd>
983		<dt class="pubdef"><a name="PL_unify_wchars()"><var>int</var> <strong>PL_unify_wchars</strong>(<var>term_t
	1024	<dt class="pubdef"><a id="PL_unify_wchars()"><var>int</var> <strong>PL_unify_wchars</strong>(<var>term_t
984	1025	t, int type, size_t len, const pl_wchar_t *s</var>)</a></dt>
985	1026	<dd class="defbody">
986	1027	Unify <var>t</var> with a textual representation of the C wide-character

988	1029	representation and is one of <code>PL_ATOM</code>, <code>PL_STRING</code>,
989	1030	<code>PL_CODE_LIST</code> or <code>PL_CHAR_LIST</code>.
990	1031	</dd>
991		<dt class="pubdef"><a name="PL_unify_wchars_diff()"><var>int</var> <strong>PL_unify_wchars_diff</strong>(<var>term_t
	1032	<dt class="pubdef"><a id="PL_unify_wchars_diff()"><var>int</var> <strong>PL_unify_wchars_diff</strong>(<var>term_t
992	1033	+t, term_t -tail, int type, size_t len, const pl_wchar_t *s</var>)</a></dt>
993	1034	<dd class="defbody">
994	1035	Difference list version of <a class="func" href="foreigninclude.html#PL_unify_wchars()">PL_unify_wchars()</a>,

1001	1042	</dd>
1002	1043	</dl>
1003	1044
1004		<p><h4 id="sec:foreign-read-list"><a name="sec:11.4.3.5"><span class="sec-nr">11.4.3.5</span> <span class="sec-title">Reading
	1045	<p><h4 id="sec:foreign-read-list"><a id="sec:11.4.3.5"><span class="sec-nr">11.4.3.5</span> <span class="sec-title">Reading
1005	1046	a list</span></a></h4>
1006	1047
1007		<a name="sec:foreign-read-list"></a>
	1048	<a id="sec:foreign-read-list"></a>
1008	1049
1009	1050	<p>The functions from this section are intended to read a Prolog list
1010	1051	from C. Suppose we expect a list of atoms; the following code will print

1030	1071	</pre>
1031	1072
1032	1073	<p>Note that as of version 7, lists have a new representation
1033		unless the option <strong>--traditional</strong> is used. see <a class="sec" href="ext-lists.html">section
	1074	unless the option <strong>--traditional</strong> is used. see <a class="sec" href="ext-lists.html#sec:5.1">section
1034	1075	5.1</a>.
1035	1076
1036	1077	<dl class="latex">
1037		<dt class="pubdef"><a name="PL_get_list()"><var>int</var> <strong>PL_get_list</strong>(<var>term_t
	1078	<dt class="pubdef"><a id="PL_get_list()"><var>int</var> <strong>PL_get_list</strong>(<var>term_t
1038	1079	+l, term_t -h, term_t -t</var>)</a></dt>
1039	1080	<dd class="defbody">
1040	1081	If <var>l</var> is a list and not the empty list, assign a term
1041	1082	reference to the head to <var>h</var> and to the tail to <var>t</var>.</dd>
1042		<dt class="pubdef"><a name="PL_get_head()"><var>int</var> <strong>PL_get_head</strong>(<var>term_t
	1083	<dt class="pubdef"><a id="PL_get_head()"><var>int</var> <strong>PL_get_head</strong>(<var>term_t
1043	1084	+l, term_t -h</var>)</a></dt>
1044	1085	<dd class="defbody">
1045	1086	If <var>l</var> is a list and not the empty list, assign a term
1046	1087	reference to the head to <var>h</var>.</dd>
1047		<dt class="pubdef"><a name="PL_get_tail()"><var>int</var> <strong>PL_get_tail</strong>(<var>term_t
	1088	<dt class="pubdef"><a id="PL_get_tail()"><var>int</var> <strong>PL_get_tail</strong>(<var>term_t
1048	1089	+l, term_t -t</var>)</a></dt>
1049	1090	<dd class="defbody">
1050	1091	If <var>l</var> is a list and not the empty list, assign a term
1051	1092	reference to the tail to <var>t</var>.</dd>
1052		<dt class="pubdef"><a name="PL_get_nil()"><var>int</var> <strong>PL_get_nil</strong>(<var>term_t
	1093	<dt class="pubdef"><a id="PL_get_nil()"><var>int</var> <strong>PL_get_nil</strong>(<var>term_t
1053	1094	+l</var>)</a></dt>
1054	1095	<dd class="defbody">
1055	1096	Succeeds if <var>l</var> represents the list termination constant.</dd>
1056		<dt class="pubdef"><a name="PL_skip_list()"><var>int</var> <strong>PL_skip_list</strong>(<var>term_t
	1097	<dt class="pubdef"><a id="PL_skip_list()"><var>int</var> <strong>PL_skip_list</strong>(<var>term_t
1057	1098	+list, term_t -tail, size_t *len</var>)</a></dt>
1058	1099	<dd class="defbody">
1059	1100	This is a multi-purpose function to deal with lists. It allows for

1063	1104	return value indicates the status of the list:
1064	1105
1065	1106	<dl class="latex">
1066		<dt><a name="PL_LIST"><strong>PL_LIST</strong></a></dt>
	1107	<dt><a id="PL_LIST"><strong>PL_LIST</strong></a></dt>
1067	1108	<dd class="defbody">
1068	1109	The list is a `proper' list: one that ends in the list terminator
1069	1110	constant and <var>tail</var> is filled with the terminator constant.</dd>
1070		<dt><a name="PL_PARTIAL_LIST"><strong>PL_PARTIAL_LIST</strong></a></dt>
	1111	<dt><a id="PL_PARTIAL_LIST"><strong>PL_PARTIAL_LIST</strong></a></dt>
1071	1112	<dd class="defbody">
1072	1113	The list is a `partial' list: one that ends in a variable and
1073	1114	<var>tail</var> is a reference to this variable.</dd>
1074		<dt><a name="PL_CYCLIC_TERM"><strong>PL_CYCLIC_TERM</strong></a></dt>
	1115	<dt><a id="PL_CYCLIC_TERM"><strong>PL_CYCLIC_TERM</strong></a></dt>
1075	1116	<dd class="defbody">
1076	1117	The list is cyclic (e.g. X = [a\|X]). <var>tail</var> points to an
1077	1118	arbitrary cell of the list and <var>len</var> is at most twice the cycle
1078	1119	length of the list.</dd>
1079		<dt><a name="PL_NOT_A_LIST"><strong>PL_NOT_A_LIST</strong></a></dt>
	1120	<dt><a id="PL_NOT_A_LIST"><strong>PL_NOT_A_LIST</strong></a></dt>
1080	1121	<dd class="defbody">
1081	1122	The term <var>list</var> is not a list at all. <var>tail</var> is bound
1082	1123	to the non-list term and <var>len</var> is set to the number of

1088	1129	</dd>
1089	1130	</dl>
1090	1131
1091		<p><h4 id="sec:foreign-write"><a name="sec:11.4.3.6"><span class="sec-nr">11.4.3.6</span> <span class="sec-title">An
	1132	<p><h4 id="sec:foreign-write"><a id="sec:11.4.3.6"><span class="sec-nr">11.4.3.6</span> <span class="sec-title">An
1092	1133	example: defining write/1 in C</span></a></h4>
1093	1134
1094		<a name="sec:foreign-write"></a>
	1135	<a id="sec:foreign-write"></a>
1095	1136
1096	1137	<p><a class="fig" href="foreigninclude.html#fig:pl-display">Figure 7</a>
1097		shows a simplified definition of <a name="idx:write1:2024"></a><a class="pred" href="termrw.html#write/1">write/1</a>
	1138	shows a simplified definition of <a id="idx:write1:2028"></a><a class="pred" href="termrw.html#write/1">write/1</a>
1098	1139	to illustrate the described functions. This simplified version does not
1099		deal with operators. It is called <a name="idx:display1:2025"></a><span class="pred-ext">display/1</span>,
	1140	deal with operators. It is called <a id="idx:display1:2029"></a><span class="pred-ext">display/1</span>,
1100	1141	because it mimics closely the behaviour of this Edinburgh predicate.
1101	1142
1102	1143	<pre class="code">

1140	1181	}
1141	1182	</pre>
1142	1183
1143		<div class="caption"><b>Figure 7 : </b>A Foreign definition of <a name="idx:display1:2026"></a><span class="pred-ext">display/1</span></div>
1144		<a name="fig:pl-display"></a>
1145
1146		<p><h3 id="sec:foreign-term-construct"><a name="sec:11.4.4"><span class="sec-nr">11.4.4</span> <span class="sec-title">Constructing
	1184	<div class="caption"><b>Figure 7 : </b>A Foreign definition of <a id="idx:display1:2030"></a><span class="pred-ext">display/1</span></div>
	1185	<a id="fig:pl-display"></a>
	1186
	1187	<p><h3 id="sec:foreign-term-construct"><a id="sec:11.4.4"><span class="sec-nr">11.4.4</span> <span class="sec-title">Constructing
1147	1188	Terms</span></a></h3>
1148	1189
1149		<a name="sec:foreign-term-construct"></a>
	1190	<a id="sec:foreign-term-construct"></a>
1150	1191
1151	1192	<p>Terms can be constructed using functions from the <code>PL_put_*()</code>
1152	1193	and

1160	1201	<a class="func" href="foreigninclude.html#PL_open_query()">PL_open_query()</a>.
1161	1202
1162	1203	<dl class="latex">
1163		<dt class="pubdef"><a name="PL_put_variable()"><var>void</var> <strong>PL_put_variable</strong>(<var>term_t
	1204	<dt class="pubdef"><a id="PL_put_variable()"><var>void</var> <strong>PL_put_variable</strong>(<var>term_t
1164	1205	-t</var>)</a></dt>
1165	1206	<dd class="defbody">
1166	1207	Put a fresh variable in the term, resetting the term reference to its
1167		initial state.<sup class="fn">170<span class="fn-text">Older versions
	1208	initial state.<sup class="fn">171<span class="fn-text">Older versions
1168	1209	created a variable on the global stack.</span></sup>
1169	1210	</dd>
1170		<dt class="pubdef"><a name="PL_put_atom()"><var>void</var> <strong>PL_put_atom</strong>(<var>term_t
	1211	<dt class="pubdef"><a id="PL_put_atom()"><var>void</var> <strong>PL_put_atom</strong>(<var>term_t
1171	1212	-t, atom_t a</var>)</a></dt>
1172	1213	<dd class="defbody">
1173	1214	Put an atom in the term reference from a handle. See also
1174	1215	<a class="func" href="foreigninclude.html#PL_new_atom()">PL_new_atom()</a>
1175	1216	and <a class="func" href="foreigninclude.html#PL_atom_chars()">PL_atom_chars()</a>.
1176	1217	</dd>
1177		<dt class="pubdef"><a name="PL_put_bool()"><var>void</var> <strong>PL_put_bool</strong>(<var>term_t
	1218	<dt class="pubdef"><a id="PL_put_bool()"><var>void</var> <strong>PL_put_bool</strong>(<var>term_t
1178	1219	-t, int val</var>)</a></dt>
1179	1220	<dd class="defbody">
1180	1221	Put one of the atoms <code>true</code> or <code>false</code> in the term
1181	1222	reference See also <a class="func" href="foreigninclude.html#PL_put_atom()">PL_put_atom()</a>, <a class="func" href="foreigninclude.html#PL_unify_bool()">PL_unify_bool()</a>
1182	1223	and <a class="func" href="foreigninclude.html#PL_get_bool()">PL_get_bool()</a>.
1183	1224	</dd>
1184		<dt class="pubdef"><a name="PL_put_chars()"><var>int</var> <strong>PL_put_chars</strong>(<var>term_t
	1225	<dt class="pubdef"><a id="PL_put_chars()"><var>int</var> <strong>PL_put_chars</strong>(<var>term_t
1185	1226	-t, int flags, size_t len, const char *chars</var>)</a></dt>
1186	1227	<dd class="defbody">
1187	1228	New function to deal with setting a term from a <code>char*</code> with

1198	1239	zero-terminated and the length is computed from <var>chars</var> using
1199	1240	strlen().
1200	1241	</dd>
1201		<dt class="pubdef"><a name="PL_put_atom_chars()"><var>int</var> <strong>PL_put_atom_chars</strong>(<var>term_t
	1242	<dt class="pubdef"><a id="PL_put_atom_chars()"><var>int</var> <strong>PL_put_atom_chars</strong>(<var>term_t
1202	1243	-t, const char *chars</var>)</a></dt>
1203	1244	<dd class="defbody">
1204	1245	Put an atom in the term reference constructed from the zero-terminated
1205	1246	string. The string itself will never be referenced by Prolog after this
1206	1247	function.
1207	1248	</dd>
1208		<dt class="pubdef"><a name="PL_put_string_chars()"><var>int</var> <strong>PL_put_string_chars</strong>(<var>term_t
	1249	<dt class="pubdef"><a id="PL_put_string_chars()"><var>int</var> <strong>PL_put_string_chars</strong>(<var>term_t
1209	1250	-t, const char *chars</var>)</a></dt>
1210	1251	<dd class="defbody">
1211	1252	Put a zero-terminated string in the term reference. The data will be
1212	1253	copied. See also <a class="func" href="foreigninclude.html#PL_put_string_nchars()">PL_put_string_nchars()</a>.
1213	1254	</dd>
1214		<dt class="pubdef"><a name="PL_put_string_nchars()"><var>int</var> <strong>PL_put_string_nchars</strong>(<var>term_t
	1255	<dt class="pubdef"><a id="PL_put_string_nchars()"><var>int</var> <strong>PL_put_string_nchars</strong>(<var>term_t
1215	1256	-t, size_t len, const char *chars</var>)</a></dt>
1216	1257	<dd class="defbody">
1217	1258
1218	1259	<p>Put a string, represented by a length/start pointer pair in the term
1219	1260	reference. The data will be copied. This interface can deal with 0-bytes
1220		in the string. See also <a class="sec" href="foreigninclude.html">section
	1261	in the string. See also <a class="sec" href="foreigninclude.html#sec:11.4.20">section
1221	1262	11.4.20</a>.
1222	1263	</dd>
1223		<dt class="pubdef"><a name="PL_put_list_chars()"><var>int</var> <strong>PL_put_list_chars</strong>(<var>term_t
	1264	<dt class="pubdef"><a id="PL_put_list_chars()"><var>int</var> <strong>PL_put_list_chars</strong>(<var>term_t
1224	1265	-t, const char *chars</var>)</a></dt>
1225	1266	<dd class="defbody">
1226	1267	Put a list of ASCII values in the term reference.
1227	1268	</dd>
1228		<dt class="pubdef"><a name="PL_put_integer()"><var>int</var> <strong>PL_put_integer</strong>(<var>term_t
	1269	<dt class="pubdef"><a id="PL_put_integer()"><var>int</var> <strong>PL_put_integer</strong>(<var>term_t
1229	1270	-t, long i</var>)</a></dt>
1230	1271	<dd class="defbody">
1231	1272	Put a Prolog integer in the term reference.
1232	1273	</dd>
1233		<dt class="pubdef"><a name="PL_put_int64()"><var>int</var> <strong>PL_put_int64</strong>(<var>term_t
	1274	<dt class="pubdef"><a id="PL_put_int64()"><var>int</var> <strong>PL_put_int64</strong>(<var>term_t
1234	1275	-t, int64_t i</var>)</a></dt>
1235	1276	<dd class="defbody">
1236	1277	Put a Prolog integer in the term reference.
1237	1278	</dd>
1238		<dt class="pubdef"><a name="PL_put_pointer()"><var>int</var> <strong>PL_put_pointer</strong>(<var>term_t
	1279	<dt class="pubdef"><a id="PL_put_pointer()"><var>int</var> <strong>PL_put_pointer</strong>(<var>term_t
1239	1280	-t, void *ptr</var>)</a></dt>
1240	1281	<dd class="defbody">
1241	1282	Put a Prolog integer in the term reference. Provided <var>ptr</var> is
1242	1283	in the `malloc()-area', <a class="func" href="foreigninclude.html#PL_get_pointer()">PL_get_pointer()</a>
1243	1284	will get the pointer back.
1244	1285	</dd>
1245		<dt class="pubdef"><a name="PL_put_float()"><var>int</var> <strong>PL_put_float</strong>(<var>term_t
	1286	<dt class="pubdef"><a id="PL_put_float()"><var>int</var> <strong>PL_put_float</strong>(<var>term_t
1246	1287	-t, double f</var>)</a></dt>
1247	1288	<dd class="defbody">
1248	1289	Put a floating-point value in the term reference.</dd>
1249		<dt class="pubdef"><a name="PL_put_functor()"><var>int</var> <strong>PL_put_functor</strong>(<var>term_t
	1290	<dt class="pubdef"><a id="PL_put_functor()"><var>int</var> <strong>PL_put_functor</strong>(<var>term_t
1250	1291	-t, functor_t functor</var>)</a></dt>
1251	1292	<dd class="defbody">
1252	1293	Create a new compound term from <var>functor</var> and bind <var>t</var>
1253	1294	to this term. All arguments of the term will be variables. To create a
1254	1295	term with instantiated arguments, either instantiate the arguments using
1255	1296	the <code>PL_unify_*()</code> functions or use <a class="func" href="foreigninclude.html#PL_cons_functor()">PL_cons_functor()</a>.</dd>
1256		<dt class="pubdef"><a name="PL_put_list()"><var>int</var> <strong>PL_put_list</strong>(<var>term_t
	1297	<dt class="pubdef"><a id="PL_put_list()"><var>int</var> <strong>PL_put_list</strong>(<var>term_t
1257	1298	-l</var>)</a></dt>
1258	1299	<dd class="defbody">
1259	1300	As <a class="func" href="foreigninclude.html#PL_put_functor()">PL_put_functor()</a>,

1261	1302	SWI-Prolog using the option
1262	1303	<strong>--traditional</strong>, this is <code><code>.</code>/2</code>,
1263	1304	while on SWI-Prolog version 7 this is <code><code>[\|]</code>/2</code>.</dd>
1264		<dt class="pubdef"><a name="PL_put_nil()"><var>int</var> <strong>PL_put_nil</strong>(<var>term_t
	1305	<dt class="pubdef"><a id="PL_put_nil()"><var>int</var> <strong>PL_put_nil</strong>(<var>term_t
1265	1306	-l</var>)</a></dt>
1266	1307	<dd class="defbody">
1267	1308	Put the list terminator constant in <var>l</var>. Always returns

1269	1310	SWI-Prolog using the option <strong>--traditional</strong>, this is the
1270	1311	same as
1271	1312	<code><a class="func" href="foreigninclude.html#PL_put_atom_chars()">PL_put_atom_chars("[]")</a></code>.
1272		See <a class="sec" href="ext-lists.html">section 5.1</a>.</dd>
1273		<dt class="pubdef"><a name="PL_put_term()"><var>void</var> <strong>PL_put_term</strong>(<var>term_t
	1313	See <a class="sec" href="ext-lists.html#sec:5.1">section 5.1</a>.</dd>
	1314	<dt class="pubdef"><a id="PL_put_term()"><var>void</var> <strong>PL_put_term</strong>(<var>term_t
1274	1315	-t1, term_t +t2</var>)</a></dt>
1275	1316	<dd class="defbody">
1276	1317	Make <var>t1</var> point to the same term as <var>t2</var>.</dd>
1277		<dt class="pubdef"><a name="PL_cons_functor()"><var>int</var> <strong>PL_cons_functor</strong>(<var>term_t
	1318	<dt class="pubdef"><a id="PL_cons_functor()"><var>int</var> <strong>PL_cons_functor</strong>(<var>term_t
1278	1319	-h, functor_t f, ...</var>)</a></dt>
1279	1320	<dd class="defbody">
1280	1321	Create a term whose arguments are filled from a variable argument list

1301	1342	<p>After this sequence, the term references <var>a1</var> and <var>a2</var>
1302	1343	may be used for other purposes.
1303	1344	</dd>
1304		<dt class="pubdef"><a name="PL_cons_functor_v()"><var>int</var> <strong>PL_cons_functor_v</strong>(<var>term_t
	1345	<dt class="pubdef"><a id="PL_cons_functor_v()"><var>int</var> <strong>PL_cons_functor_v</strong>(<var>term_t
1305	1346	-h, functor_t f, term_t a0</var>)</a></dt>
1306	1347	<dd class="defbody">
1307	1348	Create a compound term like <a class="func" href="foreigninclude.html#PL_cons_functor()">PL_cons_functor()</a>,

1309	1350	The length of this array should match the number of arguments required
1310	1351	by the functor.
1311	1352	</dd>
1312		<dt class="pubdef"><a name="PL_cons_list()"><var>int</var> <strong>PL_cons_list</strong>(<var>term_t
	1353	<dt class="pubdef"><a id="PL_cons_list()"><var>int</var> <strong>PL_cons_list</strong>(<var>term_t
1313	1354	-l, term_t +h, term_t +t</var>)</a></dt>
1314	1355	<dd class="defbody">
1315	1356	Create a list (cons-) cell in <var>l</var> from the head <var>h</var>

1336	1377	</dd>
1337	1378	</dl>
1338	1379
1339		<p><h3 id="sec:foreign-unify"><a name="sec:11.4.5"><span class="sec-nr">11.4.5</span> <span class="sec-title">Unifying
	1380	<p><h3 id="sec:foreign-unify"><a id="sec:11.4.5"><span class="sec-nr">11.4.5</span> <span class="sec-title">Unifying
1340	1381	data</span></a></h3>
1341	1382
1342		<a name="sec:foreign-unify"></a>
	1383	<a id="sec:foreign-unify"></a>
1343	1384
1344	1385	<p>The functions of this section <em>unify</em> terms with other terms
1345	1386	or translated C data structures. Except for <a class="func" href="foreigninclude.html#PL_unify()">PL_unify()</a>,

1387	1428	for details.
1388	1429
1389	1430	<dl class="latex">
1390		<dt class="pubdef"><a name="PL_unify()"><var>int</var> <strong>PL_unify</strong>(<var>term_t
	1431	<dt class="pubdef"><a id="PL_unify()"><var>int</var> <strong>PL_unify</strong>(<var>term_t
1391	1432	?t1, term_t ?t2</var>)</a></dt>
1392	1433	<dd class="defbody">
1393	1434	Unify two Prolog terms and return <code>TRUE</code> on success.

1428	1469	encounter an exception must return <code>FAIL</code> to Prolog as soon
1429	1470	as possible or call <a class="func" href="foreigninclude.html#PL_clear_exception()">PL_clear_exception()</a>
1430	1471	if they wish to ignore the exception.</dd>
1431		<dt class="pubdef"><a name="PL_unify_atom()"><var>int</var> <strong>PL_unify_atom</strong>(<var>term_t
	1472	<dt class="pubdef"><a id="PL_unify_atom()"><var>int</var> <strong>PL_unify_atom</strong>(<var>term_t
1432	1473	?t, atom_t a</var>)</a></dt>
1433	1474	<dd class="defbody">
1434	1475	Unify <var>t</var> with the atom <var>a</var> and return non-zero on
1435	1476	success.</dd>
1436		<dt class="pubdef"><a name="PL_unify_bool()"><var>int</var> <strong>PL_unify_bool</strong>(<var>term_t
	1477	<dt class="pubdef"><a id="PL_unify_bool()"><var>int</var> <strong>PL_unify_bool</strong>(<var>term_t
1437	1478	?t, int a</var>)</a></dt>
1438	1479	<dd class="defbody">
1439	1480	Unify <var>t</var> with either <code>true</code> or <code>false</code>.</dd>
1440		<dt class="pubdef"><a name="PL_unify_chars()"><var>int</var> <strong>PL_unify_chars</strong>(<var>term_t
	1481	<dt class="pubdef"><a id="PL_unify_chars()"><var>int</var> <strong>PL_unify_chars</strong>(<var>term_t
1441	1482	?t, int flags, size_t len, const char *chars</var>)</a></dt>
1442	1483	<dd class="defbody">
1443	1484	New function to deal with unification of <code>char*</code> with various

1461	1502	converted to a <em>difference list</em>. The tail of the difference list
1462	1503	is
1463	1504	<var>t+1</var>.</dd>
1464		<dt class="pubdef"><a name="PL_unify_atom_chars()"><var>int</var> <strong>PL_unify_atom_chars</strong>(<var>term_t
	1505	<dt class="pubdef"><a id="PL_unify_atom_chars()"><var>int</var> <strong>PL_unify_atom_chars</strong>(<var>term_t
1465	1506	?t, const char *chars</var>)</a></dt>
1466	1507	<dd class="defbody">
1467	1508	Unify <var>t</var> with an atom created from <var>chars</var> and return
1468	1509	non-zero on success.</dd>
1469		<dt class="pubdef"><a name="PL_unify_list_chars()"><var>int</var> <strong>PL_unify_list_chars</strong>(<var>term_t
	1510	<dt class="pubdef"><a id="PL_unify_list_chars()"><var>int</var> <strong>PL_unify_list_chars</strong>(<var>term_t
1470	1511	?t, const char *chars</var>)</a></dt>
1471	1512	<dd class="defbody">
1472	1513	Unify <var>t</var> with a list of ASCII characters constructed from
1473	1514	<var>chars</var>.</dd>
1474		<dt class="pubdef"><a name="PL_unify_string_chars()"><var>void</var> <strong>PL_unify_string_chars</strong>(<var>term_t
	1515	<dt class="pubdef"><a id="PL_unify_string_chars()"><var>void</var> <strong>PL_unify_string_chars</strong>(<var>term_t
1475	1516	?t, const char *chars</var>)</a></dt>
1476	1517	<dd class="defbody">
1477	1518	Unify <var>t</var> with a Prolog string object created from the
1478	1519	zero-terminated string <var>chars</var>. The data will be copied. See
1479	1520	also <a class="func" href="foreigninclude.html#PL_unify_string_nchars()">PL_unify_string_nchars()</a>.
1480	1521	</dd>
1481		<dt class="pubdef"><a name="PL_unify_integer()"><var>int</var> <strong>PL_unify_integer</strong>(<var>term_t
	1522	<dt class="pubdef"><a id="PL_unify_integer()"><var>int</var> <strong>PL_unify_integer</strong>(<var>term_t
1482	1523	?t, intptr_t n</var>)</a></dt>
1483	1524	<dd class="defbody">
1484	1525	Unify <var>t</var> with a Prolog integer from <var>n</var>.
1485	1526	</dd>
1486		<dt class="pubdef"><a name="PL_unify_int64()"><var>int</var> <strong>PL_unify_int64</strong>(<var>term_t
	1527	<dt class="pubdef"><a id="PL_unify_int64()"><var>int</var> <strong>PL_unify_int64</strong>(<var>term_t
1487	1528	?t, int64_t n</var>)</a></dt>
1488	1529	<dd class="defbody">
1489	1530	Unify <var>t</var> with a Prolog integer from <var>n</var>.
1490	1531	</dd>
1491		<dt class="pubdef"><a name="PL_unify_uint64()"><var>int</var> <strong>PL_unify_uint64</strong>(<var>term_t
	1532	<dt class="pubdef"><a id="PL_unify_uint64()"><var>int</var> <strong>PL_unify_uint64</strong>(<var>term_t
1492	1533	?t, uint64_t n</var>)</a></dt>
1493	1534	<dd class="defbody">
1494	1535	Unify <var>t</var> with a Prolog integer from <var>n</var>. Note that

1496	1537	<code>int64_t</code>. If unbounded integers are not supported a
1497	1538	<code>representation_error</code> is raised.
1498	1539	</dd>
1499		<dt class="pubdef"><a name="PL_unify_float()"><var>int</var> <strong>PL_unify_float</strong>(<var>term_t
	1540	<dt class="pubdef"><a id="PL_unify_float()"><var>int</var> <strong>PL_unify_float</strong>(<var>term_t
1500	1541	?t, double f</var>)</a></dt>
1501	1542	<dd class="defbody">
1502	1543	Unify <var>t</var> with a Prolog float from <var>f</var>.
1503	1544	</dd>
1504		<dt class="pubdef"><a name="PL_unify_pointer()"><var>int</var> <strong>PL_unify_pointer</strong>(<var>term_t
	1545	<dt class="pubdef"><a id="PL_unify_pointer()"><var>int</var> <strong>PL_unify_pointer</strong>(<var>term_t
1505	1546	?t, void *ptr</var>)</a></dt>
1506	1547	<dd class="defbody">
1507	1548	Unify <var>t</var> with a Prolog integer describing the pointer. See
1508	1549	also
1509	1550	<a class="func" href="foreigninclude.html#PL_put_pointer()">PL_put_pointer()</a>
1510	1551	and <a class="func" href="foreigninclude.html#PL_get_pointer()">PL_get_pointer()</a>.</dd>
1511		<dt class="pubdef"><a name="PL_unify_functor()"><var>int</var> <strong>PL_unify_functor</strong>(<var>term_t
	1552	<dt class="pubdef"><a id="PL_unify_functor()"><var>int</var> <strong>PL_unify_functor</strong>(<var>term_t
1512	1553	?t, functor_t f</var>)</a></dt>
1513	1554	<dd class="defbody">
1514	1555	If <var>t</var> is a compound term with the given functor, just succeed.

1516	1557	that this function does not create a term if the argument is already
1517	1558	instantiated. If <var>f</var> is a functor with arity 0, <var>t</var> is
1518	1559	unified with an atom. See also <a class="func" href="foreigninclude.html#PL_unify_compound()">PL_unify_compound()</a>.</dd>
1519		<dt class="pubdef"><a name="PL_unify_compound()"><var>int</var> <strong>PL_unify_compound</strong>(<var>term_t
	1560	<dt class="pubdef"><a id="PL_unify_compound()"><var>int</var> <strong>PL_unify_compound</strong>(<var>term_t
1520	1561	?t, functor_t f</var>)</a></dt>
1521	1562	<dd class="defbody">
1522	1563	If <var>t</var> is a compound term with the given functor, just succeed.

1525	1566	instantiated. If <var>f</var> is a functor with arity 0, <var>t</var> is
1526	1567	unified with compound without arguments. See also
1527	1568	<a class="func" href="foreigninclude.html#PL_unify_functor()">PL_unify_functor()</a>.</dd>
1528		<dt class="pubdef"><a name="PL_unify_list()"><var>int</var> <strong>PL_unify_list</strong>(<var>term_t
	1569	<dt class="pubdef"><a id="PL_unify_list()"><var>int</var> <strong>PL_unify_list</strong>(<var>term_t
1529	1570	?l, term_t -h, term_t -t</var>)</a></dt>
1530	1571	<dd class="defbody">
1531	1572	Unify <var>l</var> with a list-cell (<code>./2</code>). If successful,

1562	1603	</pre>
1563	1604
1564	1605	</dd>
1565		<dt class="pubdef"><a name="PL_unify_nil()"><var>int</var> <strong>PL_unify_nil</strong>(<var>term_t
	1606	<dt class="pubdef"><a id="PL_unify_nil()"><var>int</var> <strong>PL_unify_nil</strong>(<var>term_t
1566	1607	?l</var>)</a></dt>
1567	1608	<dd class="defbody">
1568	1609	Unify <var>l</var> with the atom <code>[]</code>.
1569	1610	</dd>
1570		<dt class="pubdef"><a name="PL_unify_arg()"><var>int</var> <strong>PL_unify_arg</strong>(<var>int
	1611	<dt class="pubdef"><a id="PL_unify_arg()"><var>int</var> <strong>PL_unify_arg</strong>(<var>int
1571	1612	index, term_t ?t, term_t ?a</var>)</a></dt>
1572	1613	<dd class="defbody">
1573	1614	Unifies the <em>index-th</em> argument (1-based) of <var>t</var> with
1574	1615	<var>a</var>.
1575	1616	</dd>
1576		<dt class="pubdef"><a name="PL_unify_term()"><var>int</var> <strong>PL_unify_term</strong>(<var>term_t
	1617	<dt class="pubdef"><a id="PL_unify_term()"><var>int</var> <strong>PL_unify_term</strong>(<var>term_t
1577	1618	?t, ...</var>)</a></dt>
1578	1619	<dd class="defbody">
1579	1620	Unify <var>t</var> with a (normally) compound term. The remaining

1758	1799	</pre>
1759	1800
1760	1801	</dd>
1761		<dt class="pubdef"><a name="PL_chars_to_term()"><var>int</var> <strong>PL_chars_to_term</strong>(<var>const
	1802	<dt class="pubdef"><a id="PL_chars_to_term()"><var>int</var> <strong>PL_chars_to_term</strong>(<var>const
1762	1803	char *chars, term_t -t</var>)</a></dt>
1763	1804	<dd class="defbody">
1764	1805	Parse the string <var>chars</var> and put the resulting Prolog term into

1766	1807	full-stop (i.e., a dot followed by a blank). Returns <code>FALSE</code>
1767	1808	if a syntax error was encountered and <code>TRUE</code> after successful
1768	1809	completion. In addition to returning <code>FALSE</code>, the
1769		exception-term is returned in <var>t</var> on a syntax error. See also <a name="idx:termtoatom2:2027"></a><a class="pred" href="manipatom.html#term_to_atom/2">term_to_atom/2</a>.
	1810	exception-term is returned in <var>t</var> on a syntax error. See also <a id="idx:termtoatom2:2031"></a><a class="pred" href="manipatom.html#term_to_atom/2">term_to_atom/2</a>.
1770	1811
1771	1812	<p>The following example builds a goal term from a string and calls it.
1772	1813

1791	1832	</pre>
1792	1833
1793	1834	</dd>
1794		<dt class="pubdef"><a name="PL_wchars_to_term()"><var>int</var> <strong>PL_wchars_to_term</strong>(<var>const
	1835	<dt class="pubdef"><a id="PL_wchars_to_term()"><var>int</var> <strong>PL_wchars_to_term</strong>(<var>const
1795	1836	pl_wchar_t *chars, term_t -t</var>)</a></dt>
1796	1837	<dd class="defbody">
1797	1838	Wide character version of <a class="func" href="foreigninclude.html#PL_chars_to_term()">PL_chars_to_term()</a>.</dd>
1798		<dt class="pubdef"><a name="PL_quote()"><var>char *</var> <strong>PL_quote</strong>(<var>int
	1839	<dt class="pubdef"><a id="PL_quote()"><var>char *</var> <strong>PL_quote</strong>(<var>int
1799	1840	chr, const char *string</var>)</a></dt>
1800	1841	<dd class="defbody">
1801	1842	Return a quoted version of <var>string</var>. If <var>chr</var> is

1812	1853	</dd>
1813	1854	</dl>
1814	1855
1815		<p><h3 id="sec:cerror"><a name="sec:11.4.6"><span class="sec-nr">11.4.6</span> <span class="sec-title">Convenient
	1856	<p><h3 id="sec:cerror"><a id="sec:11.4.6"><span class="sec-nr">11.4.6</span> <span class="sec-title">Convenient
1816	1857	functions to generate Prolog exceptions</span></a></h3>
1817	1858
1818		<a name="sec:cerror"></a>
	1859	<a id="sec:cerror"></a>
1819	1860
1820	1861	<p>The typical implementation of a foreign predicate first uses the
1821	1862	PL_get_*() functions to extract C data types from the Prolog terms.

1844	1885	</pre>
1845	1886
1846	1887	<dl class="latex">
1847		<dt class="pubdef"><a name="PL_get_atom_ex()"><var>int</var> <strong>PL_get_atom_ex</strong>(<var>term_t
	1888	<dt class="pubdef"><a id="PL_get_atom_ex()"><var>int</var> <strong>PL_get_atom_ex</strong>(<var>term_t
1848	1889	t, atom_t *a</var>)</a></dt>
1849	1890	<dd class="defbody">
1850	1891	As <a class="func" href="foreigninclude.html#PL_get_atom()">PL_get_atom()</a>,
1851	1892	but raises a type or instantiation error if
1852	1893	<var>t</var> is not an atom.</dd>
1853		<dt class="pubdef"><a name="PL_get_integer_ex()"><var>int</var> <strong>PL_get_integer_ex</strong>(<var>term_t
	1894	<dt class="pubdef"><a id="PL_get_integer_ex()"><var>int</var> <strong>PL_get_integer_ex</strong>(<var>term_t
1854	1895	t, int *i</var>)</a></dt>
1855	1896	<dd class="defbody">
1856	1897	As <a class="func" href="foreigninclude.html#PL_get_integer()">PL_get_integer()</a>,
1857	1898	but raises a type or instantiation error if
1858	1899	<var>t</var> is not an integer, or a representation error if the Prolog
1859	1900	integer does not fit in a C <code>int</code>.</dd>
1860		<dt class="pubdef"><a name="PL_get_long_ex()"><var>int</var> <strong>PL_get_long_ex</strong>(<var>term_t
	1901	<dt class="pubdef"><a id="PL_get_long_ex()"><var>int</var> <strong>PL_get_long_ex</strong>(<var>term_t
1861	1902	t, long *i</var>)</a></dt>
1862	1903	<dd class="defbody">
1863	1904	As <a class="func" href="foreigninclude.html#PL_get_long()">PL_get_long()</a>,
1864	1905	but raises a type or instantiation error if
1865	1906	<var>t</var> is not an atom, or a representation error if the Prolog
1866	1907	integer does not fit in a C <code>long</code>.</dd>
1867		<dt class="pubdef"><a name="PL_get_int64_ex()"><var>int</var> <strong>PL_get_int64_ex</strong>(<var>term_t
	1908	<dt class="pubdef"><a id="PL_get_int64_ex()"><var>int</var> <strong>PL_get_int64_ex</strong>(<var>term_t
1868	1909	t, int64_t *i</var>)</a></dt>
1869	1910	<dd class="defbody">
1870	1911	As <a class="func" href="foreigninclude.html#PL_get_int64()">PL_get_int64()</a>,
1871	1912	but raises a type or instantiation error if
1872	1913	<var>t</var> is not an atom, or a representation error if the Prolog
1873	1914	integer does not fit in a C <code>int64_t</code>.</dd>
1874		<dt class="pubdef"><a name="PL_get_intptr_ex()"><var>int</var> <strong>PL_get_intptr_ex</strong>(<var>term_t
	1915	<dt class="pubdef"><a id="PL_get_intptr_ex()"><var>int</var> <strong>PL_get_intptr_ex</strong>(<var>term_t
1875	1916	t, intptr_t *i</var>)</a></dt>
1876	1917	<dd class="defbody">
1877	1918	As <a class="func" href="foreigninclude.html#PL_get_intptr()">PL_get_intptr()</a>,
1878	1919	but raises a type or instantiation error if
1879	1920	<var>t</var> is not an atom, or a representation error if the Prolog
1880	1921	integer does not fit in a C <code>intptr_t</code>.</dd>
1881		<dt class="pubdef"><a name="PL_get_size_ex()"><var>int</var> <strong>PL_get_size_ex</strong>(<var>term_t
	1922	<dt class="pubdef"><a id="PL_get_size_ex()"><var>int</var> <strong>PL_get_size_ex</strong>(<var>term_t
1882	1923	t, size_t *i</var>)</a></dt>
1883	1924	<dd class="defbody">
1884	1925	As <b>PL_get_size()</b>, but raises a type or instantiation error if
1885	1926	<var>t</var> is not an atom, or a representation error if the Prolog
1886	1927	integer does not fit in a C <code>size_t</code>.</dd>
1887		<dt class="pubdef"><a name="PL_get_bool_ex()"><var>int</var> <strong>PL_get_bool_ex</strong>(<var>term_t
	1928	<dt class="pubdef"><a id="PL_get_bool_ex()"><var>int</var> <strong>PL_get_bool_ex</strong>(<var>term_t
1888	1929	t, int *i</var>)</a></dt>
1889	1930	<dd class="defbody">
1890	1931	As <a class="func" href="foreigninclude.html#PL_get_bool()">PL_get_bool()</a>,
1891	1932	but raises a type or instantiation error if
1892	1933	<var>t</var> is not an boolean.</dd>
1893		<dt class="pubdef"><a name="PL_get_float_ex()"><var>int</var> <strong>PL_get_float_ex</strong>(<var>term_t
	1934	<dt class="pubdef"><a id="PL_get_float_ex()"><var>int</var> <strong>PL_get_float_ex</strong>(<var>term_t
1894	1935	t, double *f</var>)</a></dt>
1895	1936	<dd class="defbody">
1896	1937	As <a class="func" href="foreigninclude.html#PL_get_float()">PL_get_float()</a>,
1897	1938	but raises a type or instantiation error if
1898	1939	<var>t</var> is not a float.</dd>
1899		<dt class="pubdef"><a name="PL_get_char_ex()"><var>int</var> <strong>PL_get_char_ex</strong>(<var>term_t
	1940	<dt class="pubdef"><a id="PL_get_char_ex()"><var>int</var> <strong>PL_get_char_ex</strong>(<var>term_t
1900	1941	t, int *p, int eof</var>)</a></dt>
1901	1942	<dd class="defbody">
1902	1943	Get a character code from <var>t</var>, where <var>t</var> is either an
1903	1944	integer or an atom with length one. If <var>eof</var> is <code>TRUE</code>
1904	1945	and <var>t</var> is -1, <var>p</var> is filled with -1. Raises an
1905	1946	appropriate error if the conversion is not possible.</dd>
1906		<dt class="pubdef"><a name="PL_get_pointer_ex()"><var>int</var> <strong>PL_get_pointer_ex</strong>(<var>term_t
	1947	<dt class="pubdef"><a id="PL_get_pointer_ex()"><var>int</var> <strong>PL_get_pointer_ex</strong>(<var>term_t
1907	1948	t, void **addrp</var>)</a></dt>
1908	1949	<dd class="defbody">
1909	1950	As <a class="func" href="foreigninclude.html#PL_get_pointer()">PL_get_pointer()</a>,
1910	1951	but raises a type or instantiation error if
1911	1952	<var>t</var> is not a pointer.</dd>
1912		<dt class="pubdef"><a name="PL_get_list_ex()"><var>int</var> <strong>PL_get_list_ex</strong>(<var>term_t
	1953	<dt class="pubdef"><a id="PL_get_list_ex()"><var>int</var> <strong>PL_get_list_ex</strong>(<var>term_t
1913	1954	l, term_t h, term_t t</var>)</a></dt>
1914	1955	<dd class="defbody">
1915	1956	As <a class="func" href="foreigninclude.html#PL_get_list()">PL_get_list()</a>,
1916	1957	but raises a type or instantiation error if
1917	1958	<var>t</var> is not a list.</dd>
1918		<dt class="pubdef"><a name="PL_get_nil_ex()"><var>int</var> <strong>PL_get_nil_ex</strong>(<var>term_t
	1959	<dt class="pubdef"><a id="PL_get_nil_ex()"><var>int</var> <strong>PL_get_nil_ex</strong>(<var>term_t
1919	1960	l</var>)</a></dt>
1920	1961	<dd class="defbody">
1921	1962	As <a class="func" href="foreigninclude.html#PL_get_nil()">PL_get_nil()</a>,
1922	1963	but raises a type or instantiation error if
1923	1964	<var>t</var> is not the empty list.</dd>
1924		<dt class="pubdef"><a name="PL_unify_list_ex()"><var>int</var> <strong>PL_unify_list_ex</strong>(<var>term_t
	1965	<dt class="pubdef"><a id="PL_unify_list_ex()"><var>int</var> <strong>PL_unify_list_ex</strong>(<var>term_t
1925	1966	l, term_t h, term_t t</var>)</a></dt>
1926	1967	<dd class="defbody">
1927	1968	As <a class="func" href="foreigninclude.html#PL_unify_list()">PL_unify_list()</a>,
1928	1969	but raises a type error if <var>t</var> is not a variable, list-cell or
1929	1970	the empty list.</dd>
1930		<dt class="pubdef"><a name="PL_unify_nil_ex()"><var>int</var> <strong>PL_unify_nil_ex</strong>(<var>term_t
	1971	<dt class="pubdef"><a id="PL_unify_nil_ex()"><var>int</var> <strong>PL_unify_nil_ex</strong>(<var>term_t
1931	1972	l</var>)</a></dt>
1932	1973	<dd class="defbody">
1933	1974	As <a class="func" href="foreigninclude.html#PL_unify_nil()">PL_unify_nil()</a>,
1934	1975	but raises a type error if <var>t</var> is not a variable, list-cell or
1935	1976	the empty list.</dd>
1936		<dt class="pubdef"><a name="PL_unify_bool_ex()"><var>int</var> <strong>PL_unify_bool_ex</strong>(<var>term_t
	1977	<dt class="pubdef"><a id="PL_unify_bool_ex()"><var>int</var> <strong>PL_unify_bool_ex</strong>(<var>term_t
1937	1978	t, int val</var>)</a></dt>
1938	1979	<dd class="defbody">
1939	1980	As <a class="func" href="foreigninclude.html#PL_unify_bool()">PL_unify_bool()</a>,

1949	1990	context. See also <a class="func" href="foreigninclude.html#PL_raise_exception()">PL_raise_exception()</a>.
1950	1991
1951	1992	<dl class="latex">
1952		<dt class="pubdef"><a name="PL_instantiation_error()"><var>int</var> <strong>PL_instantiation_error</strong>(<var>term_t
	1993	<dt class="pubdef"><a id="PL_instantiation_error()"><var>int</var> <strong>PL_instantiation_error</strong>(<var>term_t
1953	1994	culprit</var>)</a></dt>
1954	1995	<dd class="defbody">
1955	1996	Raise <code>instantiation_error</code>. <var>Culprit</var> is ignored,
1956	1997	but should be bound to the term that is insufficiently instantiated. See
1957		<a name="idx:instantiationerror1:2028"></a><a class="pred" href="error.html#instantiation_error/1">instantiation_error/1</a>.</dd>
1958		<dt class="pubdef"><a name="PL_uninstantiation_error()"><var>int</var> <strong>PL_uninstantiation_error</strong>(<var>term_t
	1998	<a id="idx:instantiationerror1:2032"></a><a class="pred" href="error.html#instantiation_error/1">instantiation_error/1</a>.</dd>
	1999	<dt class="pubdef"><a id="PL_uninstantiation_error()"><var>int</var> <strong>PL_uninstantiation_error</strong>(<var>term_t
1959	2000	culprit</var>)</a></dt>
1960	2001	<dd class="defbody">
1961	2002	Raise <code>uninstantiation_error(culprit)</code>. This should be called
1962	2003	if an argument that must be unbound at entry is bound to <var>culprit</var>.
1963	2004	This error is typically raised for a pure output arguments such as a
1964		newly created stream handle (e.g., the third argument of <a name="idx:open3:2029"></a><a class="pred" href="IO.html#open/3">open/3</a>).</dd>
1965		<dt class="pubdef"><a name="PL_representation_error()"><var>int</var> <strong>PL_representation_error</strong>(<var>const
	2005	newly created stream handle (e.g., the third argument of <a id="idx:open3:2033"></a><a class="pred" href="IO.html#open/3">open/3</a>).</dd>
	2006	<dt class="pubdef"><a id="PL_representation_error()"><var>int</var> <strong>PL_representation_error</strong>(<var>const
1966	2007	char *resource</var>)</a></dt>
1967	2008	<dd class="defbody">
1968		Raise <code>representation_error(resource)</code>. See <a name="idx:representationerror1:2030"></a><a class="pred" href="error.html#representation_error/1">representation_error/1</a>.</dd>
1969		<dt class="pubdef"><a name="PL_type_error()"><var>int</var> <strong>PL_type_error</strong>(<var>const
	2009	Raise <code>representation_error(resource)</code>. See <a id="idx:representationerror1:2034"></a><a class="pred" href="error.html#representation_error/1">representation_error/1</a>.</dd>
	2010	<dt class="pubdef"><a id="PL_type_error()"><var>int</var> <strong>PL_type_error</strong>(<var>const
1970	2011	char *expected, term_t culprit</var>)</a></dt>
1971	2012	<dd class="defbody">
1972		Raise <code>type_error(expected, culprit)</code>. See <a name="idx:typeerror2:2031"></a><a class="pred" href="error.html#type_error/2">type_error/2</a>.</dd>
1973		<dt class="pubdef"><a name="PL_domain_error()"><var>int</var> <strong>PL_domain_error</strong>(<var>const
	2013	Raise <code>type_error(expected, culprit)</code>. See <a id="idx:typeerror2:2035"></a><a class="pred" href="error.html#type_error/2">type_error/2</a>.</dd>
	2014	<dt class="pubdef"><a id="PL_domain_error()"><var>int</var> <strong>PL_domain_error</strong>(<var>const
1974	2015	char *expected, term_t culprit</var>)</a></dt>
1975	2016	<dd class="defbody">
1976		Raise <code>domain_error(expected, culprit)</code>. See <a name="idx:domainerror2:2032"></a><a class="pred" href="error.html#domain_error/2">domain_error/2</a>.</dd>
1977		<dt class="pubdef"><a name="PL_existence_error()"><var>int</var> <strong>PL_existence_error</strong>(<var>const
	2017	Raise <code>domain_error(expected, culprit)</code>. See <a id="idx:domainerror2:2036"></a><a class="pred" href="error.html#domain_error/2">domain_error/2</a>.</dd>
	2018	<dt class="pubdef"><a id="PL_existence_error()"><var>int</var> <strong>PL_existence_error</strong>(<var>const
1978	2019	char *type, term_t culprit</var>)</a></dt>
1979	2020	<dd class="defbody">
1980		Raise <code>existence_error(type, culprit)</code>. See <a name="idx:typeerror2:2033"></a><a class="pred" href="error.html#type_error/2">type_error/2</a>.</dd>
1981		<dt class="pubdef"><a name="PL_permission_error()"><var>int</var> <strong>PL_permission_error</strong>(<var>const
	2021	Raise <code>existence_error(type, culprit)</code>. See <a id="idx:typeerror2:2037"></a><a class="pred" href="error.html#type_error/2">type_error/2</a>.</dd>
	2022	<dt class="pubdef"><a id="PL_permission_error()"><var>int</var> <strong>PL_permission_error</strong>(<var>const
1982	2023	char operation, const char type, term_t culprit</var>)</a></dt>
1983	2024	<dd class="defbody">
1984	2025	Raise <code>permission_error(operation, type, culprit)</code>. See
1985		<a name="idx:permissionerror3:2034"></a><a class="pred" href="error.html#permission_error/3">permission_error/3</a>.
1986		</dd>
1987		<dt class="pubdef"><a name="PL_resource_error()"><var>int</var> <strong>PL_resource_error</strong>(<var>const
	2026	<a id="idx:permissionerror3:2038"></a><a class="pred" href="error.html#permission_error/3">permission_error/3</a>.
	2027	</dd>
	2028	<dt class="pubdef"><a id="PL_resource_error()"><var>int</var> <strong>PL_resource_error</strong>(<var>const
1988	2029	char *resource</var>)</a></dt>
1989	2030	<dd class="defbody">
1990		Raise <code>resource_error(resource)</code>. See <a name="idx:resourceerror1:2035"></a><a class="pred" href="error.html#resource_error/1">resource_error/1</a>.
1991		</dd>
1992		<dt class="pubdef"><a name="PL_syntax_error()"><var>int</var> <strong>PL_syntax_error</strong>(<var>const
	2031	Raise <code>resource_error(resource)</code>. See <a id="idx:resourceerror1:2039"></a><a class="pred" href="error.html#resource_error/1">resource_error/1</a>.
	2032	</dd>
	2033	<dt class="pubdef"><a id="PL_syntax_error()"><var>int</var> <strong>PL_syntax_error</strong>(<var>const
1993	2034	char message, IOSTREAM in</var>)</a></dt>
1994	2035	<dd class="defbody">
1995	2036	Raise <code>syntax_error(message)</code>. If <var>arg</var> is not <code>NULL</code>,

1997	2038	</dd>
1998	2039	</dl>
1999	2040
2000		<p><h3 id="sec:blob"><a name="sec:11.4.7"><span class="sec-nr">11.4.7</span> <span class="sec-title">BLOBS:
	2041	<p><h3 id="sec:blob"><a id="sec:11.4.7"><span class="sec-nr">11.4.7</span> <span class="sec-title">BLOBS:
2001	2042	Using atoms to store arbitrary binary data</span></a></h3>
2002	2043
2003		<a name="sec:blob"></a>
2004
2005		<p><a name="idx:Java:2036"></a><a name="idx:COM:2037"></a>SWI-Prolog
2006		atoms as well as strings can represent arbitrary binary data of
2007		arbitrary length. This facility is attractive for storing foreign data
2008		such as images in an atom. An atom is a unique handle to this data and
2009		the atom garbage collector is able to destroy atoms that are no longer
2010		referenced by the Prolog engine. This property of atoms makes them
2011		attractive as a handle to foreign resources, such as Java atoms,
2012		Microsoft's COM objects, etc., providing safe combined garbage
2013		collection.
	2044	<a id="sec:blob"></a>
	2045
	2046	<p><a id="idx:Java:2040"></a><a id="idx:COM:2041"></a>SWI-Prolog atoms
	2047	as well as strings can represent arbitrary binary data of arbitrary
	2048	length. This facility is attractive for storing foreign data such as
	2049	images in an atom. An atom is a unique handle to this data and the atom
	2050	garbage collector is able to destroy atoms that are no longer referenced
	2051	by the Prolog engine. This property of atoms makes them attractive as a
	2052	handle to foreign resources, such as Java atoms, Microsoft's COM
	2053	objects, etc., providing safe combined garbage collection.
2014	2054
2015	2055	<p>To exploit these features safely and in an organised manner, the
2016	2056	SWI-Prolog foreign interface allows for creating `atoms' with additional

2022	2062	<a class="func" href="foreigninclude.html#compare()">compare()</a>
2023	2063	function. Rank numbers are assigned when the type is registered.
2024	2064
2025		<p><h4 id="sec:blobtype"><a name="sec:11.4.7.1"><span class="sec-nr">11.4.7.1</span> <span class="sec-title">Defining
	2065	<p><h4 id="sec:blobtype"><a id="sec:11.4.7.1"><span class="sec-nr">11.4.7.1</span> <span class="sec-title">Defining
2026	2066	a BLOB type</span></a></h4>
2027	2067
2028		<a name="sec:blobtype"></a>
	2068	<a id="sec:blobtype"></a>
2029	2069
2030	2070	<p>The type <code>PL_blob_t</code> represents a structure with the
2031	2071	layout displayed below. The structure contains additional fields at the

2049	2089	<var>flags</var> is a bitwise <em>or</em> of the following constants:
2050	2090
2051	2091	<dl class="latex">
2052		<dt><a name="PL_BLOB_TEXT"><strong>PL_BLOB_TEXT</strong></a></dt>
	2092	<dt><a id="PL_BLOB_TEXT"><strong>PL_BLOB_TEXT</strong></a></dt>
2053	2093	<dd class="defbody">
2054	2094	If specified the blob is assumed to contain text and is considered a
2055	2095	normal Prolog atom.</dd>
2056		<dt><a name="PL_BLOB_UNIQUE"><strong>PL_BLOB_UNIQUE</strong></a></dt>
	2096	<dt><a id="PL_BLOB_UNIQUE"><strong>PL_BLOB_UNIQUE</strong></a></dt>
2057	2097	<dd class="defbody">
2058	2098	If specified the system ensures that the blob-handle is a unique
2059	2099	reference for a blob with the given type, length and content. If this
2060	2100	flag is not specified, each lookup creates a new blob.</dd>
2061		<dt><a name="PL_BLOB_NOCOPY"><strong>PL_BLOB_NOCOPY</strong></a></dt>
	2101	<dt><a id="PL_BLOB_NOCOPY"><strong>PL_BLOB_NOCOPY</strong></a></dt>
2062	2102	<dd class="defbody">
2063	2103	By default the content of the blob is copied. Using this flag the blob
2064	2104	references the external data directly. The user must ensure the provided

2069	2109	</dl>
2070	2110
2071	2111	<p>The <var>name</var> field represents the type name as available to
2072		Prolog. See also <a name="idx:currentblob2:2038"></a><a class="pred" href="examineprog.html#current_blob/2">current_blob/2</a>.
	2112	Prolog. See also <a id="idx:currentblob2:2042"></a><a class="pred" href="examineprog.html#current_blob/2">current_blob/2</a>.
2073	2113	The other fields are function pointers that must be initialised to
2074	2114	proper functions or <code>NULL</code> to get the default behaviour of
2075	2115	built-in atoms. Below are the defined member functions:
2076	2116
2077	2117	<dl class="latex">
2078		<dt class="pubdef"><a name="acquire()"><var>void</var> <strong>acquire</strong>(<var>atom_t
	2118	<dt class="pubdef"><a id="acquire()"><var>void</var> <strong>acquire</strong>(<var>atom_t
2079	2119	a</var>)</a></dt>
2080	2120	<dd class="defbody">
2081	2121	Called if a new blob of this type is created through <a class="func" href="foreigninclude.html#PL_put_blob()">PL_put_blob()</a>
2082	2122	or <a class="func" href="foreigninclude.html#PL_unify_blob()">PL_unify_blob()</a>.
2083	2123	This callback may be used together with the release hook to deal with
2084	2124	reference-counted external objects.</dd>
2085		<dt class="pubdef"><a name="release()"><var>int</var> <strong>release</strong>(<var>atom_t
	2125	<dt class="pubdef"><a id="release()"><var>int</var> <strong>release</strong>(<var>atom_t
2086	2126	a</var>)</a></dt>
2087	2127	<dd class="defbody">
2088	2128	The blob (atom) <var>a</var> is about to be released. This function can
2089	2129	retrieve the data of the blob using <a class="func" href="foreigninclude.html#PL_blob_data()">PL_blob_data()</a>.
2090	2130	If it returns <code>FALSE</code> the atom garbage collector will <em>not</em>
2091	2131	reclaim the atom.</dd>
2092		<dt class="pubdef"><a name="compare()"><var>int</var> <strong>compare</strong>(<var>atom_t
	2132	<dt class="pubdef"><a id="compare()"><var>int</var> <strong>compare</strong>(<var>atom_t
2093	2133	a, atom_t b</var>)</a></dt>
2094	2134	<dd class="defbody">
2095	2135	Compare the blobs <var>a</var> and <var>b</var>, both of which are of

2097	2137	<var>< 0</var> if <var>a</var> is less than <var>b</var>, <var>= 0</var>
2098	2138	if both are equal, and
2099	2139	<var>> 0</var> otherwise.</dd>
2100		<dt class="pubdef"><a name="write()"><var>int</var> <strong>write</strong>(<var>IOSTREAM
	2140	<dt class="pubdef"><a id="write()"><var>int</var> <strong>write</strong>(<var>IOSTREAM
2101	2141	*s, atom_t a, int flags</var>)</a></dt>
2102	2142	<dd class="defbody">
2103	2143	Write the content of the blob <var>a</var> to the stream <var>s</var>

2107	2147	undocumented <code>SWI-Stream.h</code> is included <em>before</em>
2108	2148	<code>SWI-Prolog.h</code>.
2109	2149
2110		<p>If this function is not provided, <a name="idx:write1:2039"></a><a class="pred" href="termrw.html#write/1">write/1</a>
	2150	<p>If this function is not provided, <a id="idx:write1:2043"></a><a class="pred" href="termrw.html#write/1">write/1</a>
2111	2151	emits the content of the blob for blobs of type <code>PL_BLOB_TEXT</code>
2112	2152	or a string of the format <code><#</code><i>hex data</i><code>></code>
2113	2153	for binary blobs.

2119	2159	released.
2120	2160
2121	2161	<dl class="latex">
2122		<dt class="pubdef"><a name="PL_unregister_blob_type()"><var>int</var> <strong>PL_unregister_blob_type</strong>(<var>PL_blob_t
	2162	<dt class="pubdef"><a id="PL_unregister_blob_type()"><var>int</var> <strong>PL_unregister_blob_type</strong>(<var>PL_blob_t
2123	2163	*type</var>)</a></dt>
2124	2164	<dd class="defbody">
2125	2165	Unlink the blob type from the registered type and transform the type of

2132	2172	</dd>
2133	2173	</dl>
2134	2174
2135		<p><h4 id="sec:blobaccess"><a name="sec:11.4.7.2"><span class="sec-nr">11.4.7.2</span> <span class="sec-title">Accessing
	2175	<p><h4 id="sec:blobaccess"><a id="sec:11.4.7.2"><span class="sec-nr">11.4.7.2</span> <span class="sec-title">Accessing
2136	2176	blobs</span></a></h4>
2137	2177
2138		<a name="sec:blobaccess"></a>
	2178	<a id="sec:blobaccess"></a>
2139	2179
2140	2180	<p>The blob access functions are similar to the atom accessing
2141	2181	functions. Blobs being atoms, the atom functions operate on blobs and

2143	2183	however, it is not advised to rely on this.
2144	2184
2145	2185	<dl class="latex">
2146		<dt class="pubdef"><a name="PL_is_blob()"><var>int</var> <strong>PL_is_blob</strong>(<var>term_t
	2186	<dt class="pubdef"><a id="PL_is_blob()"><var>int</var> <strong>PL_is_blob</strong>(<var>term_t
2147	2187	t, PL_blob_t **type</var>)</a></dt>
2148	2188	<dd class="defbody">
2149	2189	Succeeds if <var>t</var> refers to a blob, in which case <var>type</var>
2150	2190	is filled with the type of the blob.</dd>
2151		<dt class="pubdef"><a name="PL_unify_blob()"><var>int</var> <strong>PL_unify_blob</strong>(<var>term_t
	2191	<dt class="pubdef"><a id="PL_unify_blob()"><var>int</var> <strong>PL_unify_blob</strong>(<var>term_t
2152	2192	t, void blob, size_t len, PL_blob_t type</var>)</a></dt>
2153	2193	<dd class="defbody">
2154	2194	Unify <var>t</var> to a new blob constructed from the given data and
2155	2195	associated to the given type. See also <a class="func" href="foreigninclude.html#PL_unify_atom_nchars()">PL_unify_atom_nchars()</a>.</dd>
2156		<dt class="pubdef"><a name="PL_put_blob()"><var>int</var> <strong>PL_put_blob</strong>(<var>term_t
	2196	<dt class="pubdef"><a id="PL_put_blob()"><var>int</var> <strong>PL_put_blob</strong>(<var>term_t
2157	2197	t, void blob, size_t len, PL_blob_t type</var>)</a></dt>
2158	2198	<dd class="defbody">
2159	2199	Store the described blob in <var>t</var>. The return value indicates

2164	2204	count must be incremented, and it must be decremented on blob
2165	2205	destruction callback. See also
2166	2206	<a class="func" href="foreigninclude.html#PL_put_atom_nchars()">PL_put_atom_nchars()</a>.</dd>
2167		<dt class="pubdef"><a name="PL_get_blob()"><var>int</var> <strong>PL_get_blob</strong>(<var>term_t
	2207	<dt class="pubdef"><a id="PL_get_blob()"><var>int</var> <strong>PL_get_blob</strong>(<var>term_t
2168	2208	t, void *blob, size_t len, PL_blob_t **type</var>)</a></dt>
2169	2209	<dd class="defbody">
2170	2210	If <var>t</var> holds a blob or atom, get the data and type and return
2171	2211	<code>TRUE</code>. Otherwise return <code>FALSE</code>. Each result
2172	2212	pointer may be <code>NULL</code>, in which case the requested
2173	2213	information is ignored.</dd>
2174		<dt class="pubdef"><a name="PL_blob_data()"><var>void *</var> <strong>PL_blob_data</strong>(<var>atom_t
	2214	<dt class="pubdef"><a id="PL_blob_data()"><var>void *</var> <strong>PL_blob_data</strong>(<var>atom_t
2175	2215	a, size_t len, PL_blob_t *type</var>)</a></dt>
2176	2216	<dd class="defbody">
2177	2217	Get the data and type associated to a blob. This function is mainly used
2178		from the callback functions described in <a class="sec" href="foreigninclude.html">section
	2218	from the callback functions described in <a class="sec" href="foreigninclude.html#sec:11.4.7.1">section
2179	2219	11.4.7.1</a>.
2180	2220	</dd>
2181	2221	</dl>
2182	2222
2183		<p><h3 id="sec:gmpforeign"><a name="sec:11.4.8"><span class="sec-nr">11.4.8</span> <span class="sec-title">Exchanging
	2223	<p><h3 id="sec:gmpforeign"><a id="sec:11.4.8"><span class="sec-nr">11.4.8</span> <span class="sec-title">Exchanging
2184	2224	GMP numbers</span></a></h3>
2185	2225
2186		<a name="sec:gmpforeign"></a>
	2226	<a id="sec:gmpforeign"></a>
2187	2227
2188	2228	<p>If SWI-Prolog is linked with the GNU Multiple Precision Arithmetic
2189	2229	Library (GMP, used by default), the foreign interface provides functions

2240	2280	</pre>
2241	2281
2242	2282	<dl class="latex">
2243		<dt class="pubdef"><a name="PL_get_mpz()"><var>int</var> <strong>PL_get_mpz</strong>(<var>term_t
	2283	<dt class="pubdef"><a id="PL_get_mpz()"><var>int</var> <strong>PL_get_mpz</strong>(<var>term_t
2244	2284	t, mpz_t mpz</var>)</a></dt>
2245	2285	<dd class="defbody">
2246	2286	If <var>t</var> represents an integer, <var>mpz</var> is filled with the

2248	2288	is untouched and the function returns <code>FALSE</code>. Note that <var>mpz</var>
2249	2289	must have been initialised before calling this function and must be
2250	2290	cleared using mpz_clear() to reclaim any storage associated with it.</dd>
2251		<dt class="pubdef"><a name="PL_get_mpq()"><var>int</var> <strong>PL_get_mpq</strong>(<var>term_t
	2291	<dt class="pubdef"><a id="PL_get_mpq()"><var>int</var> <strong>PL_get_mpq</strong>(<var>term_t
2252	2292	t, mpq_t mpq</var>)</a></dt>
2253	2293	<dd class="defbody">
2254	2294	If <var>t</var> is an integer or rational number (term <code>rdiv/2</code>),

2257	2297	untouched and the function returns <code>FALSE</code>. Note that <var>mpq</var>
2258	2298	must have been initialised before calling this function and must be
2259	2299	cleared using mpq_clear() to reclaim any storage associated with it.</dd>
2260		<dt class="pubdef"><a name="PL_unify_mpz()"><var>int</var> <strong>PL_unify_mpz</strong>(<var>term_t
	2300	<dt class="pubdef"><a id="PL_unify_mpz()"><var>int</var> <strong>PL_unify_mpz</strong>(<var>term_t
2261	2301	t, mpz_t mpz</var>)</a></dt>
2262	2302	<dd class="defbody">
2263	2303	Unify <var>t</var> with the integer value represented by <var>mpz</var>
2264	2304	and return
2265	2305	<code>TRUE</code> on success. The <var>mpz</var> argument is not
2266	2306	changed.</dd>
2267		<dt class="pubdef"><a name="PL_unify_mpq()"><var>int</var> <strong>PL_unify_mpq</strong>(<var>term_t
	2307	<dt class="pubdef"><a id="PL_unify_mpq()"><var>int</var> <strong>PL_unify_mpq</strong>(<var>term_t
2268	2308	t, mpq_t mpq</var>)</a></dt>
2269	2309	<dd class="defbody">
2270	2310	Unify <var>t</var> with a rational number represented by <var>mpq</var>

2275	2315	</dd>
2276	2316	</dl>
2277	2317
2278		<p><h3 id="sec:calling-prolog-from-c"><a name="sec:11.4.9"><span class="sec-nr">11.4.9</span> <span class="sec-title">Calling
	2318	<p><h3 id="sec:calling-prolog-from-c"><a id="sec:11.4.9"><span class="sec-nr">11.4.9</span> <span class="sec-title">Calling
2279	2319	Prolog from C</span></a></h3>
2280	2320
2281		<a name="sec:calling-prolog-from-c"></a>
	2321	<a id="sec:calling-prolog-from-c"></a>
2282	2322
2283	2323	<p>The Prolog engine can be called from C. There are two interfaces for
2284	2324	this. For the first, a term is created that could be used as an argument
2285		to <a name="idx:call1:2040"></a><a class="pred" href="metacall.html#call/1">call/1</a>,
	2325	to <a id="idx:call1:2044"></a><a class="pred" href="metacall.html#call/1">call/1</a>,
2286	2326	and then <a class="func" href="foreigninclude.html#PL_call()">PL_call()</a>
2287	2327	is used to call Prolog. This system is simple, but does not allow to
2288	2328	inspect the different answers to a non-deterministic goal and is

2294	2334	<a class="func" href="foreigninclude.html#PL_close_query()">PL_close_query()</a>.
2295	2335	This mechanism is more powerful, but also more complicated to use.
2296	2336
2297		<p><h4 id="sec:foreign-predicate-handle"><a name="sec:11.4.9.1"><span class="sec-nr">11.4.9.1</span> <span class="sec-title">Predicate
	2337	<p><h4 id="sec:foreign-predicate-handle"><a id="sec:11.4.9.1"><span class="sec-nr">11.4.9.1</span> <span class="sec-title">Predicate
2298	2338	references</span></a></h4>
2299	2339
2300		<a name="sec:foreign-predicate-handle"></a>
	2340	<a id="sec:foreign-predicate-handle"></a>
2301	2341
2302	2342	<p>This section discusses the functions used to communicate about
2303	2343	predicates. Though a Prolog predicate may be defined or not, redefined,

2305	2345	moved. This handle is known by the type <code>predicate_t</code>.
2306	2346
2307	2347	<dl class="latex">
2308		<dt class="pubdef"><a name="PL_pred()"><var>predicate_t</var> <strong>PL_pred</strong>(<var>functor_t
	2348	<dt class="pubdef"><a id="PL_pred()"><var>predicate_t</var> <strong>PL_pred</strong>(<var>functor_t
2309	2349	f, module_t m</var>)</a></dt>
2310	2350	<dd class="defbody">
2311	2351	Return a handle to a predicate for the specified name/arity in the given
2312	2352	module. This function always succeeds, creating a handle for an
2313	2353	undefined predicate if no handle was available. If the module argument
2314	2354	<var>m</var> is <code>NULL</code>, the current context module is used.</dd>
2315		<dt class="pubdef"><a name="PL_predicate()"><var>predicate_t</var> <strong>PL_predicate</strong>(<var>const
	2355	<dt class="pubdef"><a id="PL_predicate()"><var>predicate_t</var> <strong>PL_predicate</strong>(<var>const
2316	2356	char name, int arity, const char module</var>)</a></dt>
2317	2357	<dd class="defbody">
2318	2358	Same as <a class="func" href="foreigninclude.html#PL_pred()">PL_pred()</a>,
2319	2359	but provides a more convenient interface to the C programmer.</dd>
2320		<dt class="pubdef"><a name="PL_predicate_info()"><var>void</var> <strong>PL_predicate_info</strong>(<var>predicate_t
	2360	<dt class="pubdef"><a id="PL_predicate_info()"><var>void</var> <strong>PL_predicate_info</strong>(<var>predicate_t
2321	2361	p, atom_t n, size_t a, module_t *m</var>)</a></dt>
2322	2362	<dd class="defbody">
2323	2363	Return information on the predicate <var>p</var>. The name is stored

2334	2374	</dd>
2335	2375	</dl>
2336	2376
2337		<p><h4 id="sec:foreign-create-query"><a name="sec:11.4.9.2"><span class="sec-nr">11.4.9.2</span> <span class="sec-title">Initiating
	2377	<p><h4 id="sec:foreign-create-query"><a id="sec:11.4.9.2"><span class="sec-nr">11.4.9.2</span> <span class="sec-title">Initiating
2338	2378	a query from C</span></a></h4>
2339	2379
2340		<a name="sec:foreign-create-query"></a>
	2380	<a id="sec:foreign-create-query"></a>
2341	2381
2342	2382	<p>This section discusses the functions for creating and manipulating
2343	2383	queries from C. Note that a foreign context can have at most one active

2351	2391	back to Prolog.
2352	2392
2353	2393	<dl class="latex">
2354		<dt class="pubdef"><a name="PL_open_query()"><var>qid_t</var> <strong>PL_open_query</strong>(<var>module_t
	2394	<dt class="pubdef"><a id="PL_open_query()"><var>qid_t</var> <strong>PL_open_query</strong>(<var>module_t
2355	2395	ctx, int flags, predicate_t p, term_t +t0</var>)</a></dt>
2356	2396	<dd class="defbody">
2357	2397

2359	2399	module</em> of the goal. When <code>NULL</code>, the context module of
2360	2400	the calling context will be used, or <code>user</code> if there is no
2361	2401	calling context (as may happen in embedded systems). Note that the
2362		context module only matters for <em>meta-predicates</em>. See <a name="idx:metapredicate1:2041"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>,
2363		<a name="idx:contextmodule1:2042"></a><a class="pred" href="ctxmodule.html#context_module/1">context_module/1</a>
2364		and <a name="idx:moduletransparent1:2043"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>.
	2402	context module only matters for <em>meta-predicates</em>. See <a id="idx:metapredicate1:2045"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>,
	2403	<a id="idx:contextmodule1:2046"></a><a class="pred" href="ctxmodule.html#context_module/1">context_module/1</a>
	2404	and <a id="idx:moduletransparent1:2047"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>.
2365	2405	The <var>p</var> argument specifies the predicate, and should be the
2366	2406	result of a call to <a class="func" href="foreigninclude.html#PL_pred()">PL_pred()</a>
2367	2407	or <a class="func" href="foreigninclude.html#PL_predicate()">PL_predicate()</a>.

2379	2419	<dd class="defbody">
2380	2420	Normal operation. The debugger inherits its settings from the
2381	2421	environment. If an exception occurs that is not handled in Prolog, a
2382		message is printed and the tracer is started to debug the error.<sup class="fn">171<span class="fn-text">Do
	2422	message is printed and the tracer is started to debug the error.<sup class="fn">172<span class="fn-text">Do
2383	2423	not pass the integer 0 for normal operation, as this is interpreted as <code>PL_Q_NODEBUG</code>
2384	2424	for backward compatibility reasons.</span></sup>
2385	2425	</dd>
2386	2426	<dt><b><code>PL_Q_NODEBUG</code></b></dt>
2387	2427	<dd class="defbody">
2388	2428	Switch off the debugger while executing the goal. This option is used by
2389		many calls to hook-predicates to avoid tracing the hooks. An example is <a name="idx:print1:2044"></a><a class="pred" href="termrw.html#print/1">print/1</a>
2390		calling <a name="idx:portray1:2045"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	2429	many calls to hook-predicates to avoid tracing the hooks. An example is <a id="idx:print1:2048"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	2430	calling <a id="idx:portray1:2049"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
2391	2431	from foreign code.
2392	2432	</dd>
2393	2433	<dt><b><code>PL_Q_CATCH_EXCEPTION</code></b></dt>

2413	2453	<code>TRUE</code> or <code>FALSE</code> extended status as illustrated
2414	2454	in the following table:
2415	2455
2416		<p><table border="0" frame="void" rules="groups" style="margin:auto">
2417		<tr valign="top"><td><b>Extended</b></td><td><b>Normal</b></td></tr>
2418		<tbody>
2419		<tr valign="top"><td>PL_S_EXCEPTION</td><td>FALSE</td><td>Exception
	2456	<p><table class="latex frame-void center">
	2457	<tr><td><b>Extended</b></td><td><b>Normal</b></td></tr>
	2458	<tr class="hline"><td>PL_S_EXCEPTION</td><td>FALSE</td><td>Exception
2420	2459	available through <a class="func" href="foreigninclude.html#PL_exception()">PL_exception()</a> </td></tr>
2421		<tr valign="top"><td>PL_S_FALSE</td><td>FALSE</td><td>Query failed </td></tr>
2422		<tr valign="top"><td>PL_S_TRUE</td><td>TRUE</td><td>Query succeeded with
	2460	<tr><td>PL_S_FALSE</td><td>FALSE</td><td>Query failed </td></tr>
	2461	<tr><td>PL_S_TRUE</td><td>TRUE</td><td>Query succeeded with choicepoint </td></tr>
	2462	<tr><td>PL_S_LAST</td><td>TRUE</td><td>Query succeeded without
2423	2463	choicepoint </td></tr>
2424		<tr valign="top"><td>PL_S_LAST</td><td>TRUE</td><td>Query succeeded
2425		without choicepoint </td></tr>
2426	2464	</table>
2427	2465	</dd>
2428	2466	</dl>

2454	2492	</pre>
2455	2493
2456	2494	</dd>
2457		<dt class="pubdef"><a name="PL_next_solution()"><var>int</var> <strong>PL_next_solution</strong>(<var>qid_t
	2495	<dt class="pubdef"><a id="PL_next_solution()"><var>int</var> <strong>PL_next_solution</strong>(<var>qid_t
2458	2496	qid</var>)</a></dt>
2459	2497	<dd class="defbody">
2460	2498	Generate the first (next) solution for the given query. The return value

2462	2500	indicate the query could not be proven. This function may be called
2463	2501	repeatedly until it fails to generate all solutions to the query.
2464	2502	</dd>
2465		<dt class="pubdef"><a name="PL_cut_query()"><var>void</var> <strong>PL_cut_query</strong>(<var>qid_t
	2503	<dt class="pubdef"><a id="PL_cut_query()"><var>void</var> <strong>PL_cut_query</strong>(<var>qid_t
2466	2504	qid</var>)</a></dt>
2467	2505	<dd class="defbody">
2468	2506	Discards the query, but does not delete any of the data created by the
2469	2507	query. It just invalidates <var>qid</var>, allowing for a new call to
2470	2508	<a class="func" href="foreigninclude.html#PL_open_query()">PL_open_query()</a>
2471	2509	in this context.</dd>
2472		<dt class="pubdef"><a name="PL_close_query()"><var>void</var> <strong>PL_close_query</strong>(<var>qid_t
	2510	<dt class="pubdef"><a id="PL_close_query()"><var>void</var> <strong>PL_close_query</strong>(<var>qid_t
2473	2511	qid</var>)</a></dt>
2474	2512	<dd class="defbody">
2475	2513	As <a class="func" href="foreigninclude.html#PL_cut_query()">PL_cut_query()</a>,
2476	2514	but all data and bindings created by the query are destroyed.</dd>
2477		<dt class="pubdef"><a name="PL_current_query()"><var>qid_t</var> <strong>PL_current_query</strong>(<var>void</var>)</a></dt>
	2515	<dt class="pubdef"><a id="PL_current_query()"><var>qid_t</var> <strong>PL_current_query</strong>(<var>void</var>)</a></dt>
2478	2516	<dd class="defbody">
2479	2517	Returns the query id of of the current query or <code>0</code> if the
2480	2518	current thread is not executing any queries.</dd>
2481		<dt class="pubdef"><a name="PL_call_predicate()"><var>int</var> <strong>PL_call_predicate</strong>(<var>module_t
	2519	<dt class="pubdef"><a id="PL_call_predicate()"><var>int</var> <strong>PL_call_predicate</strong>(<var>module_t
2482	2520	m, int flags, predicate_t pred, term_t +t0</var>)</a></dt>
2483	2521	<dd class="defbody">
2484	2522	Shorthand for <a class="func" href="foreigninclude.html#PL_open_query()">PL_open_query()</a>, <a class="func" href="foreigninclude.html#PL_next_solution()">PL_next_solution()</a>, <a class="func" href="foreigninclude.html#PL_cut_query()">PL_cut_query()</a>,

2486	2524	<a class="func" href="foreigninclude.html#PL_open_query()">PL_open_query()</a>,
2487	2525	the return value is the same as <a class="func" href="foreigninclude.html#PL_next_solution()">PL_next_solution()</a>.
2488	2526	</dd>
2489		<dt class="pubdef"><a name="PL_call()"><var>int</var> <strong>PL_call</strong>(<var>term_t
	2527	<dt class="pubdef"><a id="PL_call()"><var>int</var> <strong>PL_call</strong>(<var>term_t
2490	2528	t, module_t m</var>)</a></dt>
2491	2529	<dd class="defbody">
2492		Call term <var>t</var> just like the Prolog predicate <a name="idx:once1:2046"></a><a class="pred" href="metacall.html#once/1">once/1</a>. <var>t</var>
	2530	Call term <var>t</var> just like the Prolog predicate <a id="idx:once1:2050"></a><a class="pred" href="metacall.html#once/1">once/1</a>. <var>t</var>
2493	2531	is called in the module <var>m</var>, or in the context module if <var>m</var>
2494	2532	== NULL. Returns <code>TRUE</code> if the call succeeds, <code>FALSE</code>
2495	2533	otherwise.

2499	2537	</dd>
2500	2538	</dl>
2501	2539
2502		<p><h3 id="sec:foreign-discard-term-t"><a name="sec:11.4.10"><span class="sec-nr">11.4.10</span> <span class="sec-title">Discarding
	2540	<p><h3 id="sec:foreign-discard-term-t"><a id="sec:11.4.10"><span class="sec-nr">11.4.10</span> <span class="sec-title">Discarding
2503	2541	Data</span></a></h3>
2504	2542
2505		<a name="sec:foreign-discard-term-t"></a>
	2543	<a id="sec:foreign-discard-term-t"></a>
2506	2544
2507	2545	<p>The Prolog data created and term references needed to set up the call
2508	2546	and/or analyse the result can in most cases be discarded right after the

2512	2550	8</a> for an example.
2513	2551
2514	2552	<dl class="latex">
2515		<dt class="pubdef"><a name="PL_open_foreign_frame()"><var>fid_t</var> <strong>PL_open_foreign_frame</strong>(<var></var>)</a></dt>
	2553	<dt class="pubdef"><a id="PL_open_foreign_frame()"><var>fid_t</var> <strong>PL_open_foreign_frame</strong>(<var></var>)</a></dt>
2516	2554	<dd class="defbody">
2517	2555	Create a foreign frame, holding a mark that allows the system to undo
2518	2556	bindings and destroy data created after it, as well as providing the
2519	2557	environment for creating term references. This function is called by the
2520	2558	kernel before calling a foreign predicate.
2521	2559	</dd>
2522		<dt class="pubdef"><a name="PL_close_foreign_frame()"><var>void</var> <strong>PL_close_foreign_frame</strong>(<var>fid_t
	2560	<dt class="pubdef"><a id="PL_close_foreign_frame()"><var>void</var> <strong>PL_close_foreign_frame</strong>(<var>fid_t
2523	2561	id</var>)</a></dt>
2524	2562	<dd class="defbody">
2525	2563	Discard all term references created after the frame was opened. All
2526	2564	other Prolog data is retained. This function is called by the kernel
2527	2565	whenever a foreign function returns control back to Prolog.
2528	2566	</dd>
2529		<dt class="pubdef"><a name="PL_discard_foreign_frame()"><var>void</var> <strong>PL_discard_foreign_frame</strong>(<var>fid_t
	2567	<dt class="pubdef"><a id="PL_discard_foreign_frame()"><var>void</var> <strong>PL_discard_foreign_frame</strong>(<var>fid_t
2530	2568	id</var>)</a></dt>
2531	2569	<dd class="defbody">
2532	2570	Same as <a class="func" href="foreigninclude.html#PL_close_foreign_frame()">PL_close_foreign_frame()</a>,
2533	2571	but also undo all bindings made since the open and destroy all Prolog
2534	2572	data.
2535	2573	</dd>
2536		<dt class="pubdef"><a name="PL_rewind_foreign_frame()"><var>void</var> <strong>PL_rewind_foreign_frame</strong>(<var>fid_t
	2574	<dt class="pubdef"><a id="PL_rewind_foreign_frame()"><var>void</var> <strong>PL_rewind_foreign_frame</strong>(<var>fid_t
2537	2575	id</var>)</a></dt>
2538	2576	<dd class="defbody">
2539	2577	Undo all bindings and discard all term references created since the

2567	2605	</pre>
2568	2606
2569	2607	<div class="caption"><b>Figure 8 : </b>Calling Prolog</div>
2570		<a name="fig:calling"></a>
2571
2572		<p><h3 id="sec:foreign-modules"><a name="sec:11.4.11"><span class="sec-nr">11.4.11</span> <span class="sec-title">Foreign
	2608	<a id="fig:calling"></a>
	2609
	2610	<p><h3 id="sec:foreign-modules"><a id="sec:11.4.11"><span class="sec-nr">11.4.11</span> <span class="sec-title">Foreign
2573	2611	Code and Modules</span></a></h3>
2574	2612
2575		<a name="sec:foreign-modules"></a>
	2613	<a id="sec:foreign-modules"></a>
2576	2614
2577	2615	<p>Modules are identified via a unique handle. The following functions
2578	2616	are available to query and manipulate modules.
2579	2617
2580	2618	<dl class="latex">
2581		<dt class="pubdef"><a name="PL_context()"><var>module_t</var> <strong>PL_context</strong>(<var></var>)</a></dt>
	2619	<dt class="pubdef"><a id="PL_context()"><var>module_t</var> <strong>PL_context</strong>(<var></var>)</a></dt>
2582	2620	<dd class="defbody">
2583	2621	Return the module identifier of the context module of the currently
2584	2622	active foreign predicate.</dd>
2585		<dt class="pubdef"><a name="PL_strip_module()"><var>int</var> <strong>PL_strip_module</strong>(<var>term_t
	2623	<dt class="pubdef"><a id="PL_strip_module()"><var>int</var> <strong>PL_strip_module</strong>(<var>term_t
2586	2624	+raw, module_t *m, term_t -plain</var>)</a></dt>
2587	2625	<dd class="defbody">
2588	2626	Utility function. If <var>raw</var> is a term, possibly holding the

2608	2646	</pre>
2609	2647
2610	2648	</dd>
2611		<dt class="pubdef"><a name="PL_module_name()"><var>atom_t</var> <strong>PL_module_name</strong>(<var>module_t
	2649	<dt class="pubdef"><a id="PL_module_name()"><var>atom_t</var> <strong>PL_module_name</strong>(<var>module_t
2612	2650	module</var>)</a></dt>
2613	2651	<dd class="defbody">
2614	2652	Return the name of <var>module</var> as an atom.
2615	2653	</dd>
2616		<dt class="pubdef"><a name="PL_new_module()"><var>module_t</var> <strong>PL_new_module</strong>(<var>atom_t
	2654	<dt class="pubdef"><a id="PL_new_module()"><var>module_t</var> <strong>PL_new_module</strong>(<var>atom_t
2617	2655	name</var>)</a></dt>
2618	2656	<dd class="defbody">
2619	2657	Find an existing module or create a new module with the name <var>name</var>.
2620	2658	</dd>
2621	2659	</dl>
2622	2660
2623		<p><h3 id="sec:foreign-exceptions"><a name="sec:11.4.12"><span class="sec-nr">11.4.12</span> <span class="sec-title">Prolog
	2661	<p><h3 id="sec:foreign-exceptions"><a id="sec:11.4.12"><span class="sec-nr">11.4.12</span> <span class="sec-title">Prolog
2624	2662	exceptions in foreign code</span></a></h3>
2625	2663
2626		<a name="sec:foreign-exceptions"></a>
	2664	<a id="sec:foreign-exceptions"></a>
2627	2665
2628	2666	<p>This section discusses <a class="func" href="foreigninclude.html#PL_exception()">PL_exception()</a>, <a class="func" href="foreigninclude.html#PL_throw()">PL_throw()</a>
2629	2667	and

2654	2692	or
2655	2693	<a class="func" href="foreigninclude.html#PL_discard_foreign_frame()">PL_discard_foreign_frame()</a>
2656	2694	afterwards, as this will invalidate the exception term. Below is the
2657		code that calls a Prolog-defined arithmetic function (see <a name="idx:arithmeticfunction1:2047"></a><span class="pred-ext">arithmetic_function/1</span>).
	2695	code that calls a Prolog-defined arithmetic function (see <a id="idx:arithmeticfunction1:2051"></a><span class="pred-ext">arithmetic_function/1</span>).
2658	2696
2659	2697	<p>If <a class="func" href="foreigninclude.html#PL_next_solution()">PL_next_solution()</a>
2660	2698	succeeds, the result is analysed and translated to a number, after which

2704	2742	</pre>
2705	2743
2706	2744	<dl class="latex">
2707		<dt class="pubdef"><a name="PL_raise_exception()"><var>int</var> <strong>PL_raise_exception</strong>(<var>term_t
	2745	<dt class="pubdef"><a id="PL_raise_exception()"><var>int</var> <strong>PL_raise_exception</strong>(<var>term_t
2708	2746	exception</var>)</a></dt>
2709	2747	<dd class="defbody">
2710		Generate an exception (as <a name="idx:throw1:2048"></a><a class="pred" href="exception.html#throw/1">throw/1</a>)
	2748	Generate an exception (as <a id="idx:throw1:2052"></a><a class="pred" href="exception.html#throw/1">throw/1</a>)
2711	2749	and return <code>FALSE</code>. Below is an example returning an
2712	2750	exception from a foreign predicate:
2713	2751

2734	2772	</pre>
2735	2773
2736	2774	</dd>
2737		<dt class="pubdef"><a name="PL_throw()"><var>int</var> <strong>PL_throw</strong>(<var>term_t
	2775	<dt class="pubdef"><a id="PL_throw()"><var>int</var> <strong>PL_throw</strong>(<var>term_t
2738	2776	exception</var>)</a></dt>
2739	2777	<dd class="defbody">
2740	2778	Similar to <a class="func" href="foreigninclude.html#PL_raise_exception()">PL_raise_exception()</a>,
2741	2779	but returns using the C longjmp() function to the innermost <a class="func" href="foreigninclude.html#PL_next_solution()">PL_next_solution()</a>.</dd>
2742		<dt class="pubdef"><a name="PL_exception()"><var>term_t</var> <strong>PL_exception</strong>(<var>qid_t
	2780	<dt class="pubdef"><a id="PL_exception()"><var>term_t</var> <strong>PL_exception</strong>(<var>qid_t
2743	2781	qid</var>)</a></dt>
2744	2782	<dd class="defbody">
2745	2783	If <a class="func" href="foreigninclude.html#PL_next_solution()">PL_next_solution()</a>
2746	2784	fails, this can be due to normal failure of the Prolog call, or because
2747		an exception was raised using <a name="idx:throw1:2049"></a><a class="pred" href="exception.html#throw/1">throw/1</a>.
	2785	an exception was raised using <a id="idx:throw1:2053"></a><a class="pred" href="exception.html#throw/1">throw/1</a>.
2748	2786	This function returns a handle to the exception term if an exception was
2749	2787	raised, or 0 if the Prolog goal simply failed. If there is an exception,
2750	2788	<a class="func" href="foreigninclude.html#PL_exception()">PL_exception()</a>

2755	2793	pending exception in the current query or 0 if no exception is pending.
2756	2794	This can be used to check the error status after a failing call to,
2757	2795	e.g., one of the unification functions.</dd>
2758		<dt class="pubdef"><a name="PL_clear_exception()"><var>void</var> <strong>PL_clear_exception</strong>(<var>void</var>)</a></dt>
	2796	<dt class="pubdef"><a id="PL_clear_exception()"><var>void</var> <strong>PL_clear_exception</strong>(<var>void</var>)</a></dt>
2759	2797	<dd class="defbody">
2760	2798	Tells Prolog that the encountered exception must be ignored. This
2761	2799	function must be called if control remains in C after a previous API
2762		call fails with an exception.<sup class="fn">172<span class="fn-text">This
	2800	call fails with an exception.<sup class="fn">173<span class="fn-text">This
2763	2801	feature is non-portable. Other Prolog systems (e.g., YAP) have no
2764	2802	facilities to ignore raised exceptions, and the design of YAP's
2765	2803	exception handling does not support such a facility.</span></sup>
2766	2804	</dd>
2767	2805	</dl>
2768	2806
2769		<p><h3 id="sec:csignal"><a name="sec:11.4.13"><span class="sec-nr">11.4.13</span> <span class="sec-title">Catching
	2807	<p><h3 id="sec:csignal"><a id="sec:11.4.13"><span class="sec-nr">11.4.13</span> <span class="sec-title">Catching
2770	2808	Signals (Software Interrupts)</span></a></h3>
2771	2809
2772		<a name="sec:csignal"></a>
	2810	<a id="sec:csignal"></a>
2773	2811
2774	2812	<p>SWI-Prolog offers both a C and Prolog interface to deal with software
2775	2813	interrupts (signals). The Prolog mapping is defined in
2776		<a class="sec" href="signal.html">section 4.12</a>. This subsection
2777		deals with handling signals from C.
	2814	<a class="sec" href="signal.html#sec:4.12">section 4.12</a>. This
	2815	subsection deals with handling signals from C.
2778	2816
2779	2817	<p>If a signal is not used by Prolog and the handler does not call
2780	2818	Prolog in any way, the native signal interface routines may be used.

2787	2825	Prolog.
2788	2826
2789	2827	<dl class="latex">
2790		<dt class="pubdef"><a name="PL_sigaction()"><var>int</var> <strong>PL_sigaction</strong>(<var>int
	2828	<dt class="pubdef"><a id="PL_sigaction()"><var>int</var> <strong>PL_sigaction</strong>(<var>int
2791	2829	sig, pl_sigaction_t act, pl_sigaction_t oldact</var>)</a></dt>
2792	2830	<dd class="defbody">
2793	2831	Install or query the status for signal <var>sig</var>. The signal is an

2818	2856	<p>Finally, 0 (zero) may be passsed for <var>sig</var>. In that case the
2819	2857	system allocates a free signal in the <i>Prolog range</i> (32 ... 64).
2820	2858	Such signal handler are activated using <b>PL_thread_raise()</b>.</dd>
2821		<dt class="pubdef"><a name="PL_signal()"><var>void (*)()</var> <strong>PL_signal</strong>(<var>sig,
	2859	<dt class="pubdef"><a id="PL_signal()"><var>void (*)()</var> <strong>PL_signal</strong>(<var>sig,
2822	2860	func</var>)</a></dt>
2823	2861	<dd class="defbody">
2824	2862	This function is equivalent to the BSD-Unix signal() function,

2841	2879	which is checked by <a class="func" href="foreigninclude.html#PL_handle_signals()">PL_handle_signals()</a>
2842	2880	at the call- and redo-port. This behaviour is realised by <em>or</em>-ing <var>sig</var>
2843	2881	with the constant
2844		<code>PL_SIGSYNC</code>.<sup class="fn">173<span class="fn-text">A
	2882	<code>PL_SIGSYNC</code>.<sup class="fn">174<span class="fn-text">A
2845	2883	better default would be to use synchronous handling, but this interface
2846	2884	preserves backward compatibility.</span></sup>
2847	2885

2850	2888	The use of <a class="func" href="foreigninclude.html#PL_throw()">PL_throw()</a>
2851	2889	is not safe. If a synchronous handler raises an exception, the exception
2852	2890	is delayed to the next call to <a class="func" href="foreigninclude.html#PL_handle_signals()">PL_handle_signals()</a>;</dd>
2853		<dt class="pubdef"><a name="PL_raise()"><var>int</var> <strong>PL_raise</strong>(<var>int
	2891	<dt class="pubdef"><a id="PL_raise()"><var>int</var> <strong>PL_raise</strong>(<var>int
2854	2892	sig</var>)</a></dt>
2855	2893	<dd class="defbody">
2856	2894	Register <var>sig</var> for <em>synchronous</em> handling by Prolog.
2857	2895	Synchronous signals are handled at the call-port or if foreign code
2858	2896	calls <a class="func" href="foreigninclude.html#PL_handle_signals()">PL_handle_signals()</a>.
2859		See also <a name="idx:threadsignal2:2050"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>.</dd>
2860		<dt class="pubdef"><a name="PL_handle_signals()"><var>int</var> <strong>PL_handle_signals</strong>(<var>void</var>)</a></dt>
	2897	See also <a id="idx:threadsignal2:2054"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>.</dd>
	2898	<dt class="pubdef"><a id="PL_handle_signals()"><var>int</var> <strong>PL_handle_signals</strong>(<var>void</var>)</a></dt>
2861	2899	<dd class="defbody">
2862	2900	Handle any signals pending from <a class="func" href="foreigninclude.html#PL_raise()">PL_raise()</a>. <a class="func" href="foreigninclude.html#PL_handle_signals()">PL_handle_signals()</a>
2863	2901	is called at each pass through the call- and redo-port at a safe point.

2869	2907	signals handled. If a handler raises an exception, the return value is
2870	2908	-1 and the calling routine should return with <code>FALSE</code> as soon
2871	2909	as possible.</dd>
2872		<dt class="pubdef"><a name="PL_get_signum_ex()"><var>int</var> <strong>PL_get_signum_ex</strong>(<var>term_t
	2910	<dt class="pubdef"><a id="PL_get_signum_ex()"><var>int</var> <strong>PL_get_signum_ex</strong>(<var>term_t
2873	2911	t, int *sig</var>)</a></dt>
2874	2912	<dd class="defbody">
2875	2913	Extract a signal specification from a Prolog term and store as an

2881	2919	</dd>
2882	2920	</dl>
2883	2921
2884		<p><h3 id="sec:foreign-misc"><a name="sec:11.4.14"><span class="sec-nr">11.4.14</span> <span class="sec-title">Miscellaneous</span></a></h3>
2885
2886		<a name="sec:foreign-misc"></a>
2887
2888		<p><h4 id="sec:foreign-compare"><a name="sec:11.4.14.1"><span class="sec-nr">11.4.14.1</span> <span class="sec-title">Term
	2922	<p><h3 id="sec:foreign-misc"><a id="sec:11.4.14"><span class="sec-nr">11.4.14</span> <span class="sec-title">Miscellaneous</span></a></h3>
	2923
	2924	<a id="sec:foreign-misc"></a>
	2925
	2926	<p><h4 id="sec:foreign-compare"><a id="sec:11.4.14.1"><span class="sec-nr">11.4.14.1</span> <span class="sec-title">Term
2889	2927	Comparison</span></a></h4>
2890	2928
2891		<a name="sec:foreign-compare"></a>
2892
2893		<dl class="latex">
2894		<dt class="pubdef"><a name="PL_compare()"><var>int</var> <strong>PL_compare</strong>(<var>term_t
	2929	<a id="sec:foreign-compare"></a>
	2930
	2931	<dl class="latex">
	2932	<dt class="pubdef"><a id="PL_compare()"><var>int</var> <strong>PL_compare</strong>(<var>term_t
2895	2933	t1, term_t t2</var>)</a></dt>
2896	2934	<dd class="defbody">
2897	2935	Compares two terms using the standard order of terms and returns -1, 0
2898		or 1. See also <a name="idx:compare3:2051"></a><a class="pred" href="compare.html#compare/3">compare/3</a>.
2899		</dd>
2900		<dt class="pubdef"><a name="PL_same_compound()"><var>int</var> <strong>PL_same_compound</strong>(<var>term_t
	2936	or 1. See also <a id="idx:compare3:2055"></a><a class="pred" href="compare.html#compare/3">compare/3</a>.
	2937	</dd>
	2938	<dt class="pubdef"><a id="PL_same_compound()"><var>int</var> <strong>PL_same_compound</strong>(<var>term_t
2901	2939	t1, term_t t2</var>)</a></dt>
2902	2940	<dd class="defbody">
2903	2941	Yields <code>TRUE</code> if <var>t1</var> and <var>t2</var> refer to

2905	2943	</dd>
2906	2944	</dl>
2907	2945
2908		<p><h4 id="sec:foreign-recorded"><a name="sec:11.4.14.2"><span class="sec-nr">11.4.14.2</span> <span class="sec-title">Recorded
	2946	<p><h4 id="sec:foreign-recorded"><a id="sec:11.4.14.2"><span class="sec-nr">11.4.14.2</span> <span class="sec-title">Recorded
2909	2947	database</span></a></h4>
2910	2948
2911		<a name="sec:foreign-recorded"></a>
	2949	<a id="sec:foreign-recorded"></a>
2912	2950
2913	2951	<p>In some applications it is useful to store and retrieve Prolog terms
2914	2952	from C code. For example, the XPCE graphical environment does this for

2922	2960
2923	2961	<p>Two groups of functions are provided. The first group (<a class="func" href="foreigninclude.html#PL_record()">PL_record()</a>
2924	2962	and friends) store Prolog terms on the Prolog heap for retrieval during
2925		the same session. These functions are also used by <a name="idx:recorda3:2052"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>
	2963	the same session. These functions are also used by <a id="idx:recorda3:2056"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>
2926	2964	and friends. The recorded database may be used to communicate Prolog
2927	2965	terms between threads.
2928	2966
2929	2967	<dl class="latex">
2930		<dt class="pubdef"><a name="PL_record()"><var>record_t</var> <strong>PL_record</strong>(<var>term_t
	2968	<dt class="pubdef"><a id="PL_record()"><var>record_t</var> <strong>PL_record</strong>(<var>term_t
2931	2969	+t</var>)</a></dt>
2932	2970	<dd class="defbody">
2933		Record the term <var>t</var> into the Prolog database as <a name="idx:recorda3:2053"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>
	2971	Record the term <var>t</var> into the Prolog database as <a id="idx:recorda3:2057"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>
2934	2972	and return an opaque handle to the term. The returned handle remains
2935	2973	valid until <a class="func" href="foreigninclude.html#PL_erase()">PL_erase()</a>
2936	2974	is called on it. <a class="func" href="foreigninclude.html#PL_recorded()">PL_recorded()</a>
2937	2975	is used to copy recorded terms back to the Prolog stack.</dd>
2938		<dt class="pubdef"><a name="PL_duplicate_record()"><var>record_t</var> <strong>PL_duplicate_record</strong>(<var>record_t
	2976	<dt class="pubdef"><a id="PL_duplicate_record()"><var>record_t</var> <strong>PL_duplicate_record</strong>(<var>record_t
2939	2977	record</var>)</a></dt>
2940	2978	<dd class="defbody">
2941	2979	Return a duplicate of <var>record</var>. As records are read-only
2942	2980	objects this function merely increments the records reference count.</dd>
2943		<dt class="pubdef"><a name="PL_recorded()"><var>int</var> <strong>PL_recorded</strong>(<var>record_t
	2981	<dt class="pubdef"><a id="PL_recorded()"><var>int</var> <strong>PL_recorded</strong>(<var>record_t
2944	2982	record, term_t -t</var>)</a></dt>
2945	2983	<dd class="defbody">
2946	2984	Copy a recorded term back to the Prolog stack. The same record may be

2948	2986	on success, and <code>FALSE</code> if there is not enough space on the
2949	2987	stack to accommodate the term. See also <a class="func" href="foreigninclude.html#PL_record()">PL_record()</a>
2950	2988	and <a class="func" href="foreigninclude.html#PL_erase()">PL_erase()</a>.</dd>
2951		<dt class="pubdef"><a name="PL_erase()"><var>void</var> <strong>PL_erase</strong>(<var>record_t
	2989	<dt class="pubdef"><a id="PL_erase()"><var>void</var> <strong>PL_erase</strong>(<var>record_t
2952	2990	record</var>)</a></dt>
2953	2991	<dd class="defbody">
2954	2992	Remove the recorded term from the Prolog database, reclaiming all

2987	3025	</ul>
2988	3026
2989	3027	<dl class="latex">
2990		<dt class="pubdef"><a name="PL_record_external()"><var>char *</var> <strong>PL_record_external</strong>(<var>term_t
	3028	<dt class="pubdef"><a id="PL_record_external()"><var>char *</var> <strong>PL_record_external</strong>(<var>term_t
2991	3029	+t, size_t *len</var>)</a></dt>
2992	3030	<dd class="defbody">
2993		Record the term <var>t</var> into the Prolog database as <a name="idx:recorda3:2054"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>
	3031	Record the term <var>t</var> into the Prolog database as <a id="idx:recorda3:2058"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>
2994	3032	and return an opaque handle to the term. The returned handle remains
2995	3033	valid until <a class="func" href="foreigninclude.html#PL_erase_external()">PL_erase_external()</a>
2996	3034	is called on it.

3003	3041	<p><a class="func" href="foreigninclude.html#PL_recorded_external()">PL_recorded_external()</a>
3004	3042	is used to copy such recorded terms back to the Prolog stack.
3005	3043	</dd>
3006		<dt class="pubdef"><a name="PL_recorded_external()"><var>int</var> <strong>PL_recorded_external</strong>(<var>const
	3044	<dt class="pubdef"><a id="PL_recorded_external()"><var>int</var> <strong>PL_recorded_external</strong>(<var>const
3007	3045	char *record, term_t -t</var>)</a></dt>
3008	3046	<dd class="defbody">
3009	3047	Copy a recorded term back to the Prolog stack. The same record may be

3011	3049	also <a class="func" href="foreigninclude.html#PL_record_external()">PL_record_external()</a>
3012	3050	and <a class="func" href="foreigninclude.html#PL_erase_external()">PL_erase_external()</a>.
3013	3051	</dd>
3014		<dt class="pubdef"><a name="PL_erase_external()"><var>int</var> <strong>PL_erase_external</strong>(<var>char
	3052	<dt class="pubdef"><a id="PL_erase_external()"><var>int</var> <strong>PL_erase_external</strong>(<var>char
3015	3053	*record</var>)</a></dt>
3016	3054	<dd class="defbody">
3017	3055	Remove the recorded term from the Prolog database, reclaiming all

3019	3057	</dd>
3020	3058	</dl>
3021	3059
3022		<p><h4 id="sec:cfilenames"><a name="sec:11.4.14.3"><span class="sec-nr">11.4.14.3</span> <span class="sec-title">Getting
	3060	<p><h4 id="sec:cfilenames"><a id="sec:11.4.14.3"><span class="sec-nr">11.4.14.3</span> <span class="sec-title">Getting
3023	3061	file names</span></a></h4>
3024	3062
3025		<a name="sec:cfilenames"></a>
	3063	<a id="sec:cfilenames"></a>
3026	3064
3027	3065	<p>The function <a class="func" href="foreigninclude.html#PL_get_file_name()">PL_get_file_name()</a>
3028	3066	provides access to Prolog filenames and its file-search mechanism
3029		described with <a name="idx:absolutefilename3:2055"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
	3067	described with <a id="idx:absolutefilename3:2059"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
3030	3068	Its existence is motivated to realise a uniform interface to deal with
3031	3069	file properties, search, naming conventions, etc., from foreign code.
3032	3070
3033	3071	<dl class="latex">
3034		<dt class="pubdef"><a name="PL_get_file_name()"><var>int</var> <strong>PL_get_file_name</strong>(<var>term_t
	3072	<dt class="pubdef"><a id="PL_get_file_name()"><var>int</var> <strong>PL_get_file_name</strong>(<var>term_t
3035	3073	spec, char **name, int flags</var>)</a></dt>
3036	3074	<dd class="defbody">
3037	3075	Translate a Prolog term into a file name. The name is stored in the

3055	3093	</dd>
3056	3094	<dt><b><code>PL_FILE_SEARCH</code></b></dt>
3057	3095	<dd class="defbody">
3058		Invoke <a name="idx:absolutefilename3:2056"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
3059		This implies rules from <a name="idx:filesearchpath2:2057"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	3096	Invoke <a id="idx:absolutefilename3:2060"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
	3097	This implies rules from <a id="idx:filesearchpath2:2061"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
3060	3098	are used.
3061	3099	</dd>
3062	3100	<dt><b><code>PL_FILE_EXIST</code></b></dt>

3082	3120	</dl>
3083	3121
3084	3122	</dd>
3085		<dt class="pubdef"><a name="PL_get_file_nameW()"><var>int</var> <strong>PL_get_file_nameW</strong>(<var>term_t
	3123	<dt class="pubdef"><a id="PL_get_file_nameW()"><var>int</var> <strong>PL_get_file_nameW</strong>(<var>term_t
3086	3124	spec, wchar_t **name, int flags</var>)</a></dt>
3087	3125	<dd class="defbody">
3088	3126	Same as <a class="func" href="foreigninclude.html#PL_get_file_name()">PL_get_file_name()</a>,

3093	3131	</dd>
3094	3132	</dl>
3095	3133
3096		<p><h4 id="sec:cprologflags"><a name="sec:11.4.14.4"><span class="sec-nr">11.4.14.4</span> <span class="sec-title">Dealing
	3134	<p><h4 id="sec:cprologflags"><a id="sec:11.4.14.4"><span class="sec-nr">11.4.14.4</span> <span class="sec-title">Dealing
3097	3135	with Prolog flags from C</span></a></h4>
3098	3136
3099		<a name="sec:cprologflags"></a>
	3137	<a id="sec:cprologflags"></a>
3100	3138
3101	3139	<p>Foreign code can set or create Prolog flags using <a class="func" href="foreigninclude.html#PL_set_prolog_flag()">PL_set_prolog_flag()</a>.
3102		See <a name="idx:setprologflag2:2058"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
3103		and <a name="idx:createprologflag3:2059"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>.<sup class="fn">174<span class="fn-text">The
	3140	See <a id="idx:setprologflag2:2062"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>
	3141	and <a id="idx:createprologflag3:2063"></a><a class="pred" href="flags.html#create_prolog_flag/3">create_prolog_flag/3</a>.<sup class="fn">175<span class="fn-text">The
3104	3142	current C API does not provide for a dedicated mechanism for fetching
3105	3143	the value of Prolog flags. Relatively slow access is provided by calling <a class="func" href="foreigninclude.html#PL_call_predicate()">PL_call_predicate()</a>
3106		using <a name="idx:currentprologflag2:2060"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>.</span></sup>
3107
3108		<dl class="latex">
3109		<dt class="pubdef"><a name="PL_set_prolog_flag()"><var>int</var> <strong>PL_set_prolog_flag</strong>(<var>const
	3144	using <a id="idx:currentprologflag2:2064"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>.</span></sup>
	3145
	3146	<dl class="latex">
	3147	<dt class="pubdef"><a id="PL_set_prolog_flag()"><var>int</var> <strong>PL_set_prolog_flag</strong>(<var>const
3110	3148	char *name, int type, ...</var>)</a></dt>
3111	3149	<dd class="defbody">
3112	3150	Set/create a Prolog flag from C. <var>name</var> is the name of the

3137	3175	</dd>
3138	3176	</dl>
3139	3177
3140		<p><h3 id="sec:foreign-print-warning"><a name="sec:11.4.15"><span class="sec-nr">11.4.15</span> <span class="sec-title">Errors
	3178	<p><h3 id="sec:foreign-print-warning"><a id="sec:11.4.15"><span class="sec-nr">11.4.15</span> <span class="sec-title">Errors
3141	3179	and warnings</span></a></h3>
3142	3180
3143		<a name="sec:foreign-print-warning"></a>
	3181	<a id="sec:foreign-print-warning"></a>
3144	3182
3145	3183	<p><a class="func" href="foreigninclude.html#PL_warning()">PL_warning()</a>
3146	3184	prints a standard Prolog warning message to the standard error (<code>user_error</code>)
3147	3185	stream. Please note that new code should consider using <a class="func" href="foreigninclude.html#PL_raise_exception()">PL_raise_exception()</a>
3148		to raise a Prolog exception. See also <a class="sec" href="exception.html">section
	3186	to raise a Prolog exception. See also <a class="sec" href="exception.html#sec:4.11">section
3149	3187	4.11</a>.
3150	3188
3151	3189	<dl class="latex">
3152		<dt class="pubdef"><a name="PL_warning()"><var>int</var> <strong>PL_warning</strong>(<var>format,
	3190	<dt class="pubdef"><a id="PL_warning()"><var>int</var> <strong>PL_warning</strong>(<var>format,
3153	3191	a1, ...</var>)</a></dt>
3154	3192	<dd class="defbody">
3155	3193	Print an error message starting with `<code>[WARNING: </code>', followed

3159	3197	</dd>
3160	3198	</dl>
3161	3199
3162		<p><h3 id="sec:foreign-control-prolog"><a name="sec:11.4.16"><span class="sec-nr">11.4.16</span> <span class="sec-title">Environment
	3200	<p><h3 id="sec:foreign-control-prolog"><a id="sec:11.4.16"><span class="sec-nr">11.4.16</span> <span class="sec-title">Environment
3163	3201	Control from Foreign Code</span></a></h3>
3164	3202
3165		<a name="sec:foreign-control-prolog"></a>
3166
3167		<dl class="latex">
3168		<dt class="pubdef"><a name="PL_action()"><var>int</var> <strong>PL_action</strong>(<var>int,
	3203	<a id="sec:foreign-control-prolog"></a>
	3204
	3205	<dl class="latex">
	3206	<dt class="pubdef"><a id="PL_action()"><var>int</var> <strong>PL_action</strong>(<var>int,
3169	3207	...</var>)</a></dt>
3170	3208	<dd class="defbody">
3171	3209	Perform some action on the Prolog system. <var>int</var> describes the

3175	3213	<dl class="latex">
3176	3214	<dt><strong>PL_ACTION_TRACE</strong></dt>
3177	3215	<dd class="defbody">
3178		Start Prolog tracer (<a name="idx:trace0:2061"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>).
	3216	Start Prolog tracer (<a id="idx:trace0:2065"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>).
3179	3217	Requires no arguments.</dd>
3180	3218	<dt><strong>PL_ACTION_DEBUG</strong></dt>
3181	3219	<dd class="defbody">
3182		Switch on Prolog debug mode (<a name="idx:debug0:2062"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>).
	3220	Switch on Prolog debug mode (<a id="idx:debug0:2066"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>).
3183	3221	Requires no arguments.</dd>
3184	3222	<dt><strong>PL_ACTION_BACKTRACE</strong></dt>
3185	3223	<dd class="defbody">

3189	3227	<dd class="defbody">
3190	3228	Halt Prolog execution. This action should be called rather than Unix
3191	3229	exit() to give Prolog the opportunity to clean up. This call does not
3192		return. The argument (an <code>int</code>) is the exit code. See <a name="idx:halt1:2063"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a>.</dd>
	3230	return. The argument (an <code>int</code>) is the exit code. See <a id="idx:halt1:2067"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a>.</dd>
3193	3231	<dt><strong>PL_ACTION_ABORT</strong></dt>
3194	3232	<dd class="defbody">
3195		Generate a Prolog abort (<a name="idx:abort0:2064"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>).
	3233	Generate a Prolog abort (<a id="idx:abort0:2068"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>).
3196	3234	This call does not return. Requires no arguments.</dd>
3197	3235	<dt><strong>PL_ACTION_BREAK</strong></dt>
3198	3236	<dd class="defbody">
3199		Create a standard Prolog break environment (<a name="idx:break0:2065"></a><a class="pred" href="toplevel.html#break/0">break/0</a>).
	3237	Create a standard Prolog break environment (<a id="idx:break0:2069"></a><a class="pred" href="toplevel.html#break/0">break/0</a>).
3200	3238	Returns after the user types the end-of-file character. Requires no
3201	3239	arguments.</dd>
3202	3240	<dt><strong>PL_ACTION_GUIAPP</strong></dt>

3219	3257	<dt><strong>PL_ACTION_ATTACH_CONSOLE</strong></dt>
3220	3258	<dd class="defbody">
3221	3259	Attach a console to a thread if it does not have one. See
3222		<a name="idx:attachconsole0:2066"></a><a class="pred" href="thutil.html#attach_console/0">attach_console/0</a>.</dd>
	3260	<a id="idx:attachconsole0:2070"></a><a class="pred" href="thutil.html#attach_console/0">attach_console/0</a>.</dd>
3223	3261	<dt><strong>PL_GMP_SET_ALLOC_FUNCTIONS</strong></dt>
3224	3262	<dd class="defbody">
3225	3263	Takes an integer argument. If <code>TRUE</code>, the GMP allocations are

3234	3272	</dd>
3235	3273	</dl>
3236	3274
3237		<p><h3 id="sec:foreign-query"><a name="sec:11.4.17"><span class="sec-nr">11.4.17</span> <span class="sec-title">Querying
	3275	<p><h3 id="sec:foreign-query"><a id="sec:11.4.17"><span class="sec-nr">11.4.17</span> <span class="sec-title">Querying
3238	3276	Prolog</span></a></h3>
3239	3277
3240		<a name="sec:foreign-query"></a>
3241
3242		<dl class="latex">
3243		<dt class="pubdef"><a name="PL_query()"><var>long</var> <strong>PL_query</strong>(<var>int</var>)</a></dt>
	3278	<a id="sec:foreign-query"></a>
	3279
	3280	<dl class="latex">
	3281	<dt class="pubdef"><a id="PL_query()"><var>long</var> <strong>PL_query</strong>(<var>int</var>)</a></dt>
3244	3282	<dd class="defbody">
3245	3283	Obtain status information on the Prolog system. The actual argument type
3246	3284	depends on the information required. <var>int</var> describes what
3247		information is wanted.<sup class="fn">175<span class="fn-text">Returning
	3285	information is wanted.<sup class="fn">176<span class="fn-text">Returning
3248	3286	pointers and integers as a long is bad style. The signature of this
3249	3287	function should be changed.</span></sup> The options are given in <a class="tab" href="foreigninclude.html#tab:query">table
3250	3288	9</a>.
3251		<blockquote><table border="2" frame="box" rules="groups">
3252		<tr valign="top"><td><code>PL_QUERY_ARGC</code> </td><td>Return an
3253		integer holding the number of arguments given to Prolog from Unix. </td></tr>
3254		<tr valign="top"><td><code>PL_QUERY_ARGV</code> </td><td>Return a <code>char
3255		**</code> holding the argument vector given to Prolog from Unix. </td></tr>
3256		<tr valign="top"><td><code>PL_QUERY_SYMBOLFILE</code> </td><td>Return a <code>char
3257		*</code> holding the current symbol file of the running process. </td></tr>
3258		<tr valign="top"><td><code>PL_MAX_INTEGER</code> </td><td>Return a long,
3259		representing the maximal integer value represented by a Prolog integer. </td></tr>
3260		<tr valign="top"><td><code>PL_MIN_INTEGER</code> </td><td>Return a long,
3261		representing the minimal integer value. </td></tr>
3262		<tr valign="top"><td><code>PL_QUERY_VERSION</code> </td><td>Return a
3263		long, representing the version as
	3289	<blockquote><table class="latex frame-box">
	3290	<tr><td><code>PL_QUERY_ARGC</code> </td><td>Return an integer holding
	3291	the number of arguments given to Prolog from Unix. </td></tr>
	3292	<tr><td><code>PL_QUERY_ARGV</code> </td><td>Return a <code>char **</code>
	3293	holding the argument vector given to Prolog from Unix. </td></tr>
	3294	<tr><td><code>PL_QUERY_SYMBOLFILE</code> </td><td>Return a <code>char *</code>
	3295	holding the current symbol file of the running process. </td></tr>
	3296	<tr><td><code>PL_MAX_INTEGER</code> </td><td>Return a long, representing
	3297	the maximal integer value represented by a Prolog integer. </td></tr>
	3298	<tr><td><code>PL_MIN_INTEGER</code> </td><td>Return a long, representing
	3299	the minimal integer value. </td></tr>
	3300	<tr><td><code>PL_QUERY_VERSION</code> </td><td>Return a long,
	3301	representing the version as
3264	3302	<var>10,000 × M + 100 × m + p</var>, where
3265	3303	<var>M</var> is the major, <var>m</var> the minor version number and <var>p</var>
3266	3304	the patch level. For example,
3267	3305	<code>20717</code> means <code>2.7.17</code>. </td></tr>
3268		<tr valign="top"><td><code>PL_QUERY_ENCODING</code> </td><td>Return the
3269		default stream encoding of Prolog (of type <code>IOENC</code>). </td></tr>
3270		<tr valign="top"><td><code>PL_QUERY_USER_CPU</code> </td><td>Get amount
3271		of user CPU time of the process in milliseconds. </td></tr>
	3306	<tr><td><code>PL_QUERY_ENCODING</code> </td><td>Return the default
	3307	stream encoding of Prolog (of type <code>IOENC</code>). </td></tr>
	3308	<tr><td><code>PL_QUERY_USER_CPU</code> </td><td>Get amount of user CPU
	3309	time of the process in milliseconds. </td></tr>
3272	3310	</table>
3273	3311	</blockquote>
3274	3312	<div class="caption"><b>Table 9 : </b><a class="func" href="foreigninclude.html#PL_query()">PL_query()</a>
3275	3313	options</div>
3276		<a name="tab:query"></a>
3277		</dd>
3278		</dl>
3279
3280		<p><h3 id="sec:foreign-register-predicate"><a name="sec:11.4.18"><span class="sec-nr">11.4.18</span> <span class="sec-title">Registering
	3314	<a id="tab:query"></a>
	3315	</dd>
	3316	</dl>
	3317
	3318	<p><h3 id="sec:foreign-register-predicate"><a id="sec:11.4.18"><span class="sec-nr">11.4.18</span> <span class="sec-title">Registering
3281	3319	Foreign Predicates</span></a></h3>
3282	3320
3283		<a name="sec:foreign-register-predicate"></a>
3284
3285		<dl class="latex">
3286		<dt class="pubdef"><a name="PL_register_foreign_in_module()"><var>int</var> <strong>PL_register_foreign_in_module</strong>(<var>char
	3321	<a id="sec:foreign-register-predicate"></a>
	3322
	3323	<dl class="latex">
	3324	<dt class="pubdef"><a id="PL_register_foreign_in_module()"><var>int</var> <strong>PL_register_foreign_in_module</strong>(<var>char
3287	3325	mod, char name, int arity, foreign_t (*f)(), int flags, ...</var>)</a></dt>
3288	3326	<dd class="defbody">
3289	3327	Register the C function <var>f</var> to implement a Prolog predicate.

3298	3336	form a bitwise <em>or</em>'ed list of options for the installation.
3299	3337	These are:
3300	3338
3301		<p><table border="2" frame="box" rules="groups">
3302		<tr valign="top"><td><code>PL_FA_META</code> </td><td>Provide
3303		meta-predicate info (see below) </td></tr>
3304		<tr valign="top"><td><code>PL_FA_TRANSPARENT</code> </td><td>Predicate
3305		is module transparent (deprecated) </td></tr>
3306		<tr valign="top"><td><code>PL_FA_NONDETERMINISTIC</code> </td><td>Predicate
3307		is non-deterministic. See also <a class="func" href="foreigninclude.html#PL_retry()">PL_retry()</a>. </td></tr>
3308		<tr valign="top"><td><code>PL_FA_NOTRACE</code> </td><td>Predicate
3309		cannot be seen in the tracer </td></tr>
3310		<tr valign="top"><td><code>PL_FA_VARARGS</code> </td><td>Use alternative
3311		calling convention. </td></tr>
	3339	<p><table class="latex frame-box">
	3340	<tr><td><code>PL_FA_META</code> </td><td>Provide meta-predicate info
	3341	(see below) </td></tr>
	3342	<tr><td><code>PL_FA_TRANSPARENT</code> </td><td>Predicate is module
	3343	transparent (deprecated) </td></tr>
	3344	<tr><td><code>PL_FA_NONDETERMINISTIC</code> </td><td>Predicate is
	3345	non-deterministic. See also <a class="func" href="foreigninclude.html#PL_retry()">PL_retry()</a>. </td></tr>
	3346	<tr><td><code>PL_FA_NOTRACE</code> </td><td>Predicate cannot be seen in
	3347	the tracer </td></tr>
	3348	<tr><td><code>PL_FA_VARARGS</code> </td><td>Use alternative calling
	3349	convention. </td></tr>
3312	3350	</table>
3313	3351
3314	3352	<p>If <code>PL_FA_META</code> is provided, <a class="func" href="foreigninclude.html#PL_register_foreign_in_module()">PL_register_foreign_in_module()</a>

3316	3354	This string must be exactly as long as the number of arguments of the
3317	3355	predicate and filled with characters from the set <code>0-9:^-+?</code>.
3318	3356	See
3319		<a name="idx:metapredicate1:2067"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	3357	<a id="idx:metapredicate1:2071"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
3320	3358	for details. <code>PL_FA_TRANSPARENT</code> is implied if at least one
3321	3359	meta-argument is provided (<code>0-9:^</code>). Note that meta-arguments
3322	3360	are <em>not always</em> passed as <<var>module</var>>:<<var>term</var>>.
3323	3361	Always use <a class="func" href="foreigninclude.html#PL_strip_module()">PL_strip_module()</a>
3324		to extract the module and plain term from a meta-argument.<sup class="fn">176<span class="fn-text">It
	3362	to extract the module and plain term from a meta-argument.<sup class="fn">177<span class="fn-text">It
3325	3363	is encouraged to pass an additional <code>NULL</code> pointer for
3326	3364	non-meta-predicates.</span></sup>
3327	3365

3334	3372	is passed the same number of <code>term_t</code> arguments as the arity
3335	3373	of the predicate and, if the predicate is non-deterministic, an extra
3336	3374	argument of type
3337		<code>control_t</code> (see <a class="sec" href="foreigninclude.html">section
	3375	<code>control_t</code> (see <a class="sec" href="foreigninclude.html#sec:11.4.1.1">section
3338	3376	11.4.1.1</a>). If <code>PL_FA_VARARGS</code> is provided, <var>function</var>
3339	3377	is called with three arguments. The first argument is a <code>term_t</code>
3340	3378	handle to the first argument. Further arguments can be reached by adding

3370	3408	</pre>
3371	3409
3372	3410	</dd>
3373		<dt class="pubdef"><a name="PL_register_foreign()"><var>int</var> <strong>PL_register_foreign</strong>(<var>const
	3411	<dt class="pubdef"><a id="PL_register_foreign()"><var>int</var> <strong>PL_register_foreign</strong>(<var>const
3374	3412	char name, int arity, foreign_t (function)(), int flags, ...</var>)</a></dt>
3375	3413	<dd class="defbody">
3376	3414	Same as <a class="func" href="foreigninclude.html#PL_register_foreign_in_module()">PL_register_foreign_in_module()</a>,
3377	3415	passing <code>NULL</code> for the
3378	3416	<var>module</var>.</dd>
3379		<dt class="pubdef"><a name="PL_register_extensions_in_module()"><var>void</var> <strong>PL_register_extensions_in_module</strong>(<var>const
	3417	<dt class="pubdef"><a id="PL_register_extensions_in_module()"><var>void</var> <strong>PL_register_extensions_in_module</strong>(<var>const
3380	3418	char module, PL_extension e</var>)</a></dt>
3381	3419	<dd class="defbody">
3382	3420	Register a series of predicates from an array of definitions of the type

3416	3454	</pre>
3417	3455
3418	3456	</dd>
3419		<dt class="pubdef"><a name="PL_register_extensions()"><var>void</var> <strong>PL_register_extensions</strong>(<var>
	3457	<dt class="pubdef"><a id="PL_register_extensions()"><var>void</var> <strong>PL_register_extensions</strong>(<var>
3420	3458	PL_extension *e</var>)</a></dt>
3421	3459	<dd class="defbody">
3422	3460	Same as <a class="func" href="foreigninclude.html#PL_register_extensions_in_module()">PL_register_extensions_in_module()</a>

3424	3462	</dd>
3425	3463	</dl>
3426	3464
3427		<p><h3 id="sec:foreign-hooks"><a name="sec:11.4.19"><span class="sec-nr">11.4.19</span> <span class="sec-title">Foreign
	3465	<p><h3 id="sec:foreign-hooks"><a id="sec:11.4.19"><span class="sec-nr">11.4.19</span> <span class="sec-title">Foreign
3428	3466	Code Hooks</span></a></h3>
3429	3467
3430		<a name="sec:foreign-hooks"></a>
	3468	<a id="sec:foreign-hooks"></a>
3431	3469
3432	3470	<p>For various specific applications some hooks are provided.
3433	3471
3434	3472	<dl class="latex">
3435		<dt class="pubdef"><a name="PL_dispatch_hook()"><var>PL_dispatch_hook_t</var> <strong>PL_dispatch_hook</strong>(<var>PL_dispatch_hook_t</var>)</a></dt>
	3473	<dt class="pubdef"><a id="PL_dispatch_hook()"><var>PL_dispatch_hook_t</var> <strong>PL_dispatch_hook</strong>(<var>PL_dispatch_hook_t</var>)</a></dt>
3436	3474	<dd class="defbody">
3437	3475	If this hook is not NULL, this function is called when reading from the
3438	3476	terminal. It is supposed to dispatch events when SWI-Prolog is connected

3447	3485	</pre>
3448	3486
3449	3487	</dd>
3450		<dt class="pubdef"><a name="PL_abort_hook()"><var>void</var> <strong>PL_abort_hook</strong>(<var>PL_abort_hook_t</var>)</a></dt>
3451		<dd class="defbody">
3452		Install a hook when <a name="idx:abort0:2068"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
3453		is executed. SWI-Prolog <a name="idx:abort0:2069"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
	3488	<dt class="pubdef"><a id="PL_abort_hook()"><var>void</var> <strong>PL_abort_hook</strong>(<var>PL_abort_hook_t</var>)</a></dt>
	3489	<dd class="defbody">
	3490	Install a hook when <a id="idx:abort0:2072"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
	3491	is executed. SWI-Prolog <a id="idx:abort0:2073"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>
3454	3492	is implemented using C setjmp()/longjmp() construct. The hooks are
3455	3493	executed in the reverse order of their registration after the longjmp()
3456	3494	took place and before the Prolog top level is reinvoked. The type

3461	3499	</pre>
3462	3500
3463	3501	</dd>
3464		<dt class="pubdef"><a name="PL_abort_unhook()"><var>int</var> <strong>PL_abort_unhook</strong>(<var>PL_abort_hook_t</var>)</a></dt>
	3502	<dt class="pubdef"><a id="PL_abort_unhook()"><var>int</var> <strong>PL_abort_unhook</strong>(<var>PL_abort_hook_t</var>)</a></dt>
3465	3503	<dd class="defbody">
3466	3504	Remove a hook installed with <a class="func" href="foreigninclude.html#PL_abort_hook()">PL_abort_hook()</a>.
3467	3505	Returns <code>FALSE</code> if no such hook is found, <code>TRUE</code>
3468	3506	otherwise.</dd>
3469		<dt class="pubdef"><a name="PL_on_halt()"><var>void</var> <strong>PL_on_halt</strong>(<var>int
	3507	<dt class="pubdef"><a id="PL_on_halt()"><var>void</var> <strong>PL_on_halt</strong>(<var>int
3470	3508	(f)(int, void ), void *closure</var>)</a></dt>
3471	3509	<dd class="defbody">
3472	3510	Register the function <var>f</var> to be called if SWI-Prolog is halted.

3474	3512	(0 if this cannot be determined) and the <var>closure</var> argument
3475	3513	passed to the <a class="func" href="foreigninclude.html#PL_on_halt()">PL_on_halt()</a>
3476	3514	call. Handlers <em>must</em> return 0. Other return values are reserved
3477		for future use. See also <a name="idx:athalt1:2070"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>.<sup class="fn">bug<span class="fn-text">Although
	3515	for future use. See also <a id="idx:athalt1:2074"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>.<sup class="fn">bug<span class="fn-text">Although
3478	3516	both <a class="func" href="foreigninclude.html#PL_on_halt()">PL_on_halt()</a>
3479		and <a name="idx:athalt1:2071"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>
3480		are called in FIFO order, <em>all</em> <a name="idx:athalt1:2072"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>
	3517	and <a id="idx:athalt1:2075"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>
	3518	are called in FIFO order, <em>all</em> <a id="idx:athalt1:2076"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>
3481	3519	handlers are called before <em>all</em> <a class="func" href="foreigninclude.html#PL_on_halt()">PL_on_halt()</a>
3482	3520	handlers.</span></sup> These handlers are called <em>before</em> system
3483	3521	cleanup and can therefore access all normal Prolog resources. See also <a class="func" href="foreigninclude.html#PL_exit_hook()">PL_exit_hook()</a>.</dd>
3484		<dt class="pubdef"><a name="PL_exit_hook()"><var>void</var> <strong>PL_exit_hook</strong>(<var>int
	3522	<dt class="pubdef"><a id="PL_exit_hook()"><var>void</var> <strong>PL_exit_hook</strong>(<var>int
3485	3523	(f)(int, void ), void *closure</var>)</a></dt>
3486	3524	<dd class="defbody">
3487	3525	Similar to <a class="func" href="foreigninclude.html#PL_on_halt()">PL_on_halt()</a>,
3488	3526	but the hooks are executed by <a class="func" href="foreigninclude.html#PL_halt()">PL_halt()</a>
3489	3527	instead of <a class="func" href="foreigninclude.html#PL_cleanup()">PL_cleanup()</a>
3490	3528	just before calling exit().</dd>
3491		<dt class="pubdef"><a name="PL_agc_hook()"><var>PL_agc_hook_t</var> <strong>PL_agc_hook</strong>(<var>PL_agc_hook_t
	3529	<dt class="pubdef"><a id="PL_agc_hook()"><var>PL_agc_hook_t</var> <strong>PL_agc_hook</strong>(<var>PL_agc_hook_t
3492	3530	new</var>)</a></dt>
3493	3531	<dd class="defbody">
3494	3532	Register a hook with the atom-garbage collector (see
3495		<a name="idx:garbagecollectatoms0:2073"></a><a class="pred" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a>)
	3533	<a id="idx:garbagecollectatoms0:2077"></a><a class="pred" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a>)
3496	3534	that is called on any atom that is reclaimed. The old hook is returned.
3497	3535	If no hook is currently defined, <code>NULL</code> is returned. The
3498	3536	argument of the called hook is the atom that is to be garbage collected.

3530	3568	<p></dd>
3531	3569	</dl>
3532	3570
3533		<p><h3 id="sec:foreigndata"><a name="sec:11.4.20"><span class="sec-nr">11.4.20</span> <span class="sec-title">Storing
	3571	<p><h3 id="sec:foreigndata"><a id="sec:11.4.20"><span class="sec-nr">11.4.20</span> <span class="sec-title">Storing
3534	3572	foreign data</span></a></h3>
3535	3573
3536		<a name="sec:foreigndata"></a>
	3574	<a id="sec:foreigndata"></a>
3537	3575
3538	3576	<p>When combining foreign code with Prolog, it can be necessary to make
3539	3577	data represented in the foreign language available to Prolog. For

3557	3595	<p>
3558	3596	<li><i>Opaque packed data on the stacks</i><br>
3559	3597	It is possible to represent the raw binary representation of the foreign
3560		object as a Prolog string (see <a class="sec" href="strings.html">section
	3598	object as a Prolog string (see <a class="sec" href="strings.html#sec:5.2">section
3561	3599	5.2</a>). Strings may be created from foreign data using <a class="func" href="foreigninclude.html#PL_put_string_nchars()">PL_put_string_nchars()</a>
3562	3600	and retrieved using
3563	3601	<a class="func" href="foreigninclude.html#PL_get_string_chars()">PL_get_string_chars()</a>.
3564	3602	It is good practice to wrap the string in a compound term with arity 1,
3565	3603	so Prolog can identify the type. The hook
3566		<a name="idx:portray1:2074"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	3604	<a id="idx:portray1:2078"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
3567	3605	rules may be used to streamline printing such terms during development.
3568	3606
3569	3607	<p>
3570	3608	<li><i>Opaque packed data in a blob</i><br>
3571	3609	Similar to the above solution, binary data can be stored in an atom. The
3572		blob interface (<a class="sec" href="foreigninclude.html">section 11.4.7</a>)
3573		provides additional facilities to assign a type and hook-functions that
3574		act on creation and destruction of the underlying atom.
	3610	blob interface (<a class="sec" href="foreigninclude.html#sec:11.4.7">section
	3611	11.4.7</a>) provides additional facilities to assign a type and
	3612	hook-functions that act on creation and destruction of the underlying
	3613	atom.
3575	3614
3576	3615	<p>
3577	3616	<li><i>Natural foreign data, passed as a pointer</i><br>

3613	3652	implements a predicate. If the predicate is deterministic, foreign
3614	3653	automatic variables are suitable. If the predicate is non-deterministic,
3615	3654	the data may be allocated using malloc() and a pointer may be passed.
3616		See <a class="sec" href="foreigninclude.html">section 11.4.1.1</a>.
	3655	See <a class="sec" href="foreigninclude.html#sec:11.4.1.1">section
	3656	11.4.1.1</a>.
3617	3657	</ol>
3618	3658	</ul>
3619	3659
3620		<p><h4 id="sec:foreign-store-data"><a name="sec:11.4.20.1"><span class="sec-nr">11.4.20.1</span> <span class="sec-title">Examples
	3660	<p><h4 id="sec:foreign-store-data"><a id="sec:11.4.20.1"><span class="sec-nr">11.4.20.1</span> <span class="sec-title">Examples
3621	3661	for storing foreign data</span></a></h4>
3622	3662
3623		<a name="sec:foreign-store-data"></a>
	3663	<a id="sec:foreign-store-data"></a>
3624	3664
3625	3665	<p>In this section, we outline some examples, covering typical cases. In
3626	3666	the first example, we will deal with extending Prolog's data

3712	3752	}
3713	3753	</pre>
3714	3754
3715		<p><b>The DDE interface</b> (see <a class="sec" href="DDE.html">section
	3755	<p><b>The DDE interface</b> (see <a class="sec" href="DDE.html#sec:4.43">section
3716	3756	4.43</a>) represents another common usage of the foreign interface:
3717	3757	providing communication to new operating system features. The DDE
3718	3758	interface requires knowledge about active DDE server and client

3738	3778	debugging purposes, wrapping the handle in a compound is a good
3739	3779	suggestion.
3740	3780
3741		<p><h3 id="sec:embedded"><a name="sec:11.4.21"><span class="sec-nr">11.4.21</span> <span class="sec-title">Embedding
	3781	<p><h3 id="sec:embedded"><a id="sec:11.4.21"><span class="sec-nr">11.4.21</span> <span class="sec-title">Embedding
3742	3782	SWI-Prolog in other applications</span></a></h3>
3743	3783
3744		<a name="sec:embedded"></a>
	3784	<a id="sec:embedded"></a>
3745	3785
3746	3786	<p>With embedded Prolog we refer to the situation where the `main'
3747	3787	program is not the Prolog application. Prolog is sometimes embedded in

3772	3812	</pre>
3773	3813
3774	3814	<dl class="latex">
3775		<dt class="pubdef"><a name="PL_initialise()"><var>int</var> <strong>PL_initialise</strong>(<var>int
	3815	<dt class="pubdef"><a id="PL_initialise()"><var>int</var> <strong>PL_initialise</strong>(<var>int
3776	3816	argc, char **argv</var>)</a></dt>
3777	3817	<dd class="defbody">
3778	3818	Initialises the SWI-Prolog heap and stacks, restores the Prolog state,
3779		loads the system and personal initialisation files, runs the <a name="idx:initialization1:2075"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	3819	loads the system and personal initialisation files, runs the <a id="idx:initialization1:2079"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
3780	3820	hooks and finally runs the
3781	3821	<strong>-g</strong> <var>goal</var> hook.
3782	3822

3792	3832	<ul class="latex">
3793	3833	<li>See whether a Prolog saved state is appended to the file. If this is
3794	3834	the case, this state will be loaded instead of the default <code>boot.prc</code>
3795		file from the SWI-Prolog home directory. See also <a name="idx:qsaveprogram12:2076"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>
3796		and <a class="sec" href="plld.html">section 11.5</a>.
	3835	file from the SWI-Prolog home directory. See also <a id="idx:qsaveprogram12:2080"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>
	3836	and <a class="sec" href="plld.html#sec:11.5">section 11.5</a>.
3797	3837	<li>Find the Prolog home directory. This process is described in detail
3798		in <a class="sec" href="findhome.html">section 11.6</a>.
	3838	in <a class="sec" href="findhome.html#sec:11.6">section 11.6</a>.
3799	3839	</ul>
3800	3840
3801	3841	<p><a class="func" href="foreigninclude.html#PL_initialise()">PL_initialise()</a>

3837	3877	<code>"libpl.dll"</code> as <code>argv[0]</code>. If the Prolog state is
3838	3878	attached to a DLL (see the <strong>-dll</strong> option of <b>swipl-ld</b>),
3839	3879	pass the name of this DLL.</dd>
3840		<dt class="pubdef"><a name="PL_is_initialised()"><var>int</var> <strong>PL_is_initialised</strong>(<var>int
	3880	<dt class="pubdef"><a id="PL_is_initialised()"><var>int</var> <strong>PL_is_initialised</strong>(<var>int
3841	3881	argc, char **argv</var>)</a></dt>
3842	3882	<dd class="defbody">
3843	3883	Test whether the Prolog engine is already initialised. Returns

3845	3885	otherwise. If the engine is initialised and <var>argc</var> is not <code>NULL</code>,
3846	3886	the argument count used with <a class="func" href="foreigninclude.html#PL_initialise()">PL_initialise()</a>
3847	3887	is stored in <var>argc</var>. Same for the argument vector <var>argv</var>.</dd>
3848		<dt class="pubdef"><a name="PL_set_resource_db_mem()"><var>int</var> <strong>PL_set_resource_db_mem</strong>(<var>const
	3888	<dt class="pubdef"><a id="PL_set_resource_db_mem()"><var>int</var> <strong>PL_set_resource_db_mem</strong>(<var>const
3849	3889	unsigned char *data, size_t size</var>)</a></dt>
3850	3890	<dd class="defbody">
3851	3891	This function must be called at most once and <em>before</em> calling
3852	3892	<a class="func" href="foreigninclude.html#PL_initialise()">PL_initialise()</a>.
3853	3893	The memory area designated by <var>data</var> and <var>size</var> must
3854	3894	contain the resource data and be in the format as produced by
3855		<a name="idx:qsaveprogram2:2077"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
	3895	<a id="idx:qsaveprogram2:2081"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
3856	3896	The memory area is accessed by <a class="func" href="foreigninclude.html#PL_initialise()">PL_initialise()</a>
3857		as well as calls to <a name="idx:openresource3:2078"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>.<sup class="fn">177<span class="fn-text">This
	3897	as well as calls to <a id="idx:openresource3:2082"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>.<sup class="fn">178<span class="fn-text">This
3858	3898	implies that the data must remain accessible during the lifetime of the
3859		process if <a name="idx:openresource3:2079"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>
	3899	process if <a id="idx:openresource3:2083"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>
3860	3900	is used. Future versions may provide a function to detach the resource
3861		database and cause <a name="idx:openresource3:2080"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>
	3901	database and cause <a id="idx:openresource3:2084"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>
3862	3902	to raise an exception.</span></sup>
3863	3903
3864	3904	<p>For example, we can include the bootstrap data into an embedded

3867	3907
3868	3908	<p>
3869	3909	<ol class="latex">
3870		<li>Create a saved state using <a name="idx:qsaveprogram2:2081"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
	3910	<li>Create a saved state using <a id="idx:qsaveprogram2:2085"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
3871	3911	or
3872	3912
3873	3913	<pre class="code">

3944	3984	<p>As Jose Morales pointed at
3945	3985	<a class="url" href="https://github.com/graphitemaster/incbin">https://github.com/graphitemaster/incbin</a>,
3946	3986	which contains a portability layer on top of the above idea.</dd>
3947		<dt class="pubdef"><a name="PL_toplevel()"><var>int</var> <strong>PL_toplevel</strong>(<var></var>)</a></dt>
	3987	<dt class="pubdef"><a id="PL_toplevel()"><var>int</var> <strong>PL_toplevel</strong>(<var></var>)</a></dt>
3948	3988	<dd class="defbody">
3949	3989	Runs the goal of the <strong>-t</strong> <var>toplevel</var> switch
3950		(default <a name="idx:prolog0:2082"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>)
	3990	(default <a id="idx:prolog0:2086"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>)
3951	3991	and returns 1 if successful, 0 otherwise.</dd>
3952		<dt class="pubdef"><a name="PL_cleanup()"><var>int</var> <strong>PL_cleanup</strong>(<var>int
	3992	<dt class="pubdef"><a id="PL_cleanup()"><var>int</var> <strong>PL_cleanup</strong>(<var>int
3953	3993	status</var>)</a></dt>
3954	3994	<dd class="defbody">
3955	3995	This function performs the reverse of <a class="func" href="foreigninclude.html#PL_initialise()">PL_initialise()</a>.
3956	3996	It runs the
3957	3997	<a class="func" href="foreigninclude.html#PL_on_halt()">PL_on_halt()</a>
3958		and <a name="idx:athalt1:2083"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>
	3998	and <a id="idx:athalt1:2087"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>
3959	3999	handlers, closes all streams (except for the `standard I/O' streams
3960	4000	which are flushed only), deallocates all memory if <var>status</var>
3961	4001	equals `0' and restores all signal handlers. The

3965	4005	<p>The function returns <code>TRUE</code> if successful and <code>FALSE</code>
3966	4006	otherwise. Currently, <code>FALSE</code> is returned when an attempt is
3967	4007	made to call <a class="func" href="foreigninclude.html#PL_cleanup()">PL_cleanup()</a>
3968		recursively or if one of the exit handlers cancels the termination using <a name="idx:cancelhalt1:2084"></a><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a>.
	4008	recursively or if one of the exit handlers cancels the termination using <a id="idx:cancelhalt1:2088"></a><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a>.
3969	4009	Exit handlers may only cancel termination if <var>status</var> is 0.
3970	4010
3971	4011	<p>In theory, this function allows deleting and restarting the Prolog

3977	4017	you want to use Prolog temporarily, consider running it in a separate
3978	4018	process. If you want to be able to reset Prolog, your options are
3979	4019	(again) a separate process, modules or threads.</dd>
3980		<dt class="pubdef"><a name="PL_cleanup_fork()"><var>void</var> <strong>PL_cleanup_fork</strong>(<var></var>)</a></dt>
3981		<dd class="defbody">
3982		Stop intervaltimer that may be running on behalf of <a name="idx:profile1:2085"></a><a class="pred" href="profile.html#profile/1">profile/1</a>.
	4020	<dt class="pubdef"><a id="PL_cleanup_fork()"><var>void</var> <strong>PL_cleanup_fork</strong>(<var></var>)</a></dt>
	4021	<dd class="defbody">
	4022	Stop intervaltimer that may be running on behalf of <a id="idx:profile1:2089"></a><a class="pred" href="profile.html#profile/1">profile/1</a>.
3983	4023	The call is intended to be used in combination with fork():
3984	4024
3985	4025	<pre class="code">

3991	4031
3992	4032	<p>The call behaves the same on Windows, though there is probably no
3993	4033	meaningful application.</dd>
3994		<dt class="pubdef"><a name="PL_halt()"><var>int</var> <strong>PL_halt</strong>(<var>int
	4034	<dt class="pubdef"><a id="PL_halt()"><var>int</var> <strong>PL_halt</strong>(<var>int
3995	4035	status</var>)</a></dt>
3996	4036	<dd class="defbody">
3997	4037	Clean up the Prolog environment using <a class="func" href="foreigninclude.html#PL_cleanup()">PL_cleanup()</a>

4000	4040	</dd>
4001	4041	</dl>
4002	4042
4003		<p><h4 id="sec:sigembedded"><a name="sec:11.4.21.1"><span class="sec-nr">11.4.21.1</span> <span class="sec-title">Threading,
	4043	<p><h4 id="sec:sigembedded"><a id="sec:11.4.21.1"><span class="sec-nr">11.4.21.1</span> <span class="sec-title">Threading,
4004	4044	Signals and embedded Prolog</span></a></h4>
4005	4045
4006		<a name="sec:sigembedded"></a>
	4046	<a id="sec:sigembedded"></a>
4007	4047
4008	4048	<p>This section applies to Unix-based environments that have signals or
4009	4049	multithreading. The Windows version is compiled for multithreading, and

4028	4068	<dd>
4029	4069	has an empty signal handler. This signal is sent to a thread after
4030	4070	sending a thread-signal (see
4031		<a name="idx:threadsignal2:2086"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>).
	4071	<a id="idx:threadsignal2:2090"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>).
4032	4072	It causes blocking system calls to return with <code>EINTR</code>, which
4033	4073	gives them the opportunity to react to thread-signals.
4034	4074

+114

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191	232	<a class="nav" href="foreignoverview.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="foreigntypes.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:foreignlink"><a name="sec:11.2"><span class="sec-nr">11.2</span> <span class="sec-title">Linking
	235	<h2 id="sec:foreignlink"><a id="sec:11.2"><span class="sec-nr">11.2</span> <span class="sec-title">Linking
195	236	Foreign Modules</span></a></h2>
196	237
197		<a name="sec:foreignlink"></a>
	238	<a id="sec:foreignlink"></a>
198	239
199	240	<p>Foreign modules may be linked to Prolog in two ways. Using
200	241	<em>static linking</em>, the extensions, a (short) file defining main()

203	244	executable. Using <em>dynamic linking</em>, the extensions are linked to
204	245	a shared library (<code>.so</code> file on most Unix systems) or dynamic
205	246	link library (<code>.DLL</code> file on Microsoft platforms) and loaded
206		into the running Prolog process.<sup class="fn">167<span class="fn-text">The
	247	into the running Prolog process.<sup class="fn">168<span class="fn-text">The
207	248	system also contains code to load <code>.o</code> files directly for
208	249	some operating systems, notably Unix systems using the BSD <code>a.out</code>
209	250	executable format. As the number of Unix platforms supporting this
210	251	quickly gets smaller and this interface is difficult to port and slow,
211	252	it is no longer described in this manual. The best alternative would be
212		to use the <a name="idx:dld:2007">dld</a> package on machines that do
213		not have shared libraries.</span></sup>
214
215		<p><h3 id="sec:foreign-linking"><a name="sec:11.2.1"><span class="sec-nr">11.2.1</span> <span class="sec-title">What
	253	to use the <a id="idx:dld:2011">dld</a> package on machines that do not
	254	have shared libraries.</span></sup>
	255
	256	<p><h3 id="sec:foreign-linking"><a id="sec:11.2.1"><span class="sec-nr">11.2.1</span> <span class="sec-title">What
216	257	linking is provided?</span></a></h3>
217	258
218		<a name="sec:foreign-linking"></a>
	259	<a id="sec:foreign-linking"></a>
219	260
220	261	<p>The <em>static linking</em> schema can be used on all versions of
221	262	SWI-Prolog. Whether or not dynamic linking is supported can be deduced
222	263	from the Prolog flag <a class="flag" href="flags.html#flag:open_shared_object">open_shared_object</a>
223	264	(see
224		<a name="idx:currentprologflag2:2008"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>).
	265	<a id="idx:currentprologflag2:2012"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>).
225	266	If this Prolog flag yields <code>true</code>,
226		<a name="idx:opensharedobject2:2009"></a><a class="pred" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a>
	267	<a id="idx:opensharedobject2:2013"></a><a class="pred" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a>
227	268	and related predicates are defined. See
228		<a class="sec" href="foreignlink.html">section 11.2.3</a> for a suitable
229		high-level interface to these predicates.
230
231		<p><h3 id="sec:foreign-linking-options"><a name="sec:11.2.2"><span class="sec-nr">11.2.2</span> <span class="sec-title">What
	269	<a class="sec" href="foreignlink.html#sec:11.2.3">section 11.2.3</a> for
	270	a suitable high-level interface to these predicates.
	271
	272	<p><h3 id="sec:foreign-linking-options"><a id="sec:11.2.2"><span class="sec-nr">11.2.2</span> <span class="sec-title">What
232	273	kind of loading should I be using?</span></a></h3>
233	274
234		<a name="sec:foreign-linking-options"></a>
	275	<a id="sec:foreign-linking-options"></a>
235	276
236	277	<p>All described approaches have their advantages and disadvantages.
237	278	Static linking is portable and allows for debugging on all platforms. It
238	279	is relatively cumbersome and the libraries you need to pass to the
239	280	linker may vary from system to system, though the utility program
240		<b>swipl-ld</b> described in <a class="sec" href="plld.html">section
	281	<b>swipl-ld</b> described in <a class="sec" href="plld.html#sec:11.5">section
241	282	11.5</a> often hides these problems from the user.
242	283
243	284	<p>Loading shared objects (DLL files on Windows) provides sharing and
244	285	protection and is generally the best choice. If a saved state is created
245		using <a name="idx:qsaveprogram12:2010"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>,
246		an <a name="idx:initialization1:2011"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	286	using <a id="idx:qsaveprogram12:2014"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>,
	287	an <a id="idx:initialization1:2015"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
247	288	directive may be used to load the appropriate library at startup.
248	289
249	290	<p>Note that the definition of the foreign predicates is the same,
250	291	regardless of the linking type used.
251	292
252		<p><h3 id="sec:shlib"><a name="sec:11.2.3"><span class="sec-nr">11.2.3</span> <span class="sec-title">library(shlib):
	293	<p><h3 id="sec:shlib"><a id="sec:11.2.3"><span class="sec-nr">11.2.3</span> <span class="sec-title">library(shlib):
253	294	Utility library for loading foreign objects (DLLs, shared objects)</span></a></h3>
254	295
255		<p><a name="sec:shlib"></a>
	296	<p><a id="sec:shlib"></a>
256	297
257	298	<p>This section discusses the functionality of the (autoload)
258	299	<code>library(shlib)</code>, providing an interface to manage shared

307	348	and provides the predicate defined in C.
308	349
309	350	<dl class="latex">
310		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="load_foreign_library/1"><strong>load_foreign_library</strong>(<var>:FileSpec</var>)</a></dt>
311		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="load_foreign_library/2"><strong>load_foreign_library</strong>(<var>:FileSpec,
	351	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="load_foreign_library/1"><strong>load_foreign_library</strong>(<var>:FileSpec</var>)</a></dt>
	352	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="load_foreign_library/2"><strong>load_foreign_library</strong>(<var>:FileSpec,
312	353	+Entry:atom</var>)</a></dt>
313	354	<dd class="defbody">
314	355	Load a <i>shared object</i> or <i>DLL</i>. After loading the <var>Entry</var>

325	366	</pre>
326	367
327	368	<table class="arglist">
328		<tr valign="top"><td><var>FileSpec</var> </td><td>is a specification for <a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
	369	<tr><td><var>FileSpec</var> </td><td>is a specification for <a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.
329	370	If searching the file fails, the plain name is passed to the OS to try
330	371	the default method of the OS for locating foreign objects. The default
331	372	definition of <a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>

343	384	</dl>
344	385
345	386	</dd>
346		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="use_foreign_library/1"><strong>use_foreign_library</strong>(<var>+FileSpec</var>)</a></dt>
347		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="use_foreign_library/2"><strong>use_foreign_library</strong>(<var>+FileSpec,
	387	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="use_foreign_library/1"><strong>use_foreign_library</strong>(<var>+FileSpec</var>)</a></dt>
	388	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="use_foreign_library/2"><strong>use_foreign_library</strong>(<var>+FileSpec,
348	389	+Entry:atom</var>)</a></dt>
349	390	<dd class="defbody">
350	391	Load and install a foreign library as <a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>,2

361	402	loads the library
362	403	<i>immediately</i>. I.e. the difference is only relevant if the
363	404	remainder of the file uses functionality of the C-library.</dd>
364		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="unload_foreign_library/1"><strong>unload_foreign_library</strong>(<var>+FileSpec</var>)</a></dt>
365		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="unload_foreign_library/2"><strong>unload_foreign_library</strong>(<var>+FileSpec,
	405	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="unload_foreign_library/1"><strong>unload_foreign_library</strong>(<var>+FileSpec</var>)</a></dt>
	406	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="unload_foreign_library/2"><strong>unload_foreign_library</strong>(<var>+FileSpec,
366	407	+Exit:atom</var>)</a></dt>
367	408	<dd class="defbody">
368	409	Unload a <i>shared object</i> or <i>DLL</i>. After calling the <var>Exit</var>
369	410	function, the shared object is removed from the process. The default
370	411	exit function is composed from =uninstall_=, followed by the file
371	412	base-name.</dd>
372		<dt class="pubdef"><a name="current_foreign_library/2"><strong>current_foreign_library</strong>(<var>?File,
	413	<dt class="pubdef"><a id="current_foreign_library/2"><strong>current_foreign_library</strong>(<var>?File,
373	414	?Public</var>)</a></dt>
374	415	<dd class="defbody">
375	416	Query currently loaded shared libraries.</dd>
376		<dt class="pubdef"><a name="reload_foreign_libraries/0"><strong>reload_foreign_libraries</strong></a></dt>
	417	<dt class="pubdef"><a id="reload_foreign_libraries/0"><strong>reload_foreign_libraries</strong></a></dt>
377	418	<dd class="defbody">
378	419	Reload all foreign libraries loaded (after restore of a state created
379	420	using <a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
380	421	</dd>
381	422	</dl>
382	423
383		<p><h3 id="sec:sharedobj"><a name="sec:11.2.4"><span class="sec-nr">11.2.4</span> <span class="sec-title">Low-level
	424	<p><h3 id="sec:sharedobj"><a id="sec:11.2.4"><span class="sec-nr">11.2.4</span> <span class="sec-title">Low-level
384	425	operations on shared libraries</span></a></h3>
385	426
386		<a name="sec:sharedobj"></a>
	427	<a id="sec:sharedobj"></a>
387	428
388	429	<p>The interface defined in this section allows the user to load shared
389	430	libraries (<code>.so</code> files on most Unix systems, <code>.dll</code>
390	431	files on Windows). This interface is portable to Windows as well as to
391	432	Unix machines providing <strong>dlopen</strong>(2) (Solaris, Linux,
392	433	FreeBSD, Irix and many more) or <strong>shl_open</strong>(2) (HP/UX). It
393		is advised to use the predicates from <a class="sec" href="foreignlink.html">section
	434	is advised to use the predicates from <a class="sec" href="foreignlink.html#sec:11.2.3">section
394	435	11.2.3</a> in your application.
395	436
396	437	<dl class="latex">
397		<dt class="pubdef"><a name="open_shared_object/2"><strong>open_shared_object</strong>(<var>+File,
	438	<dt class="pubdef"><a id="open_shared_object/2"><strong>open_shared_object</strong>(<var>+File,
398	439	-Handle</var>)</a></dt>
399	440	<dd class="defbody">
400	441	<var>File</var> is the name of a shared object file (DLL in MS-Windows).
401	442	This file is attached to the current process, and
402	443	<var>Handle</var> is unified with a handle to the library. Equivalent to
403	444	<code>open_shared_object(File, Handle, [])</code>. See also
404		<a name="idx:opensharedobject3:2012"></a><a class="pred" href="foreignlink.html#open_shared_object/3">open_shared_object/3</a>
405		and <a name="idx:loadforeignlibrary1:2013"></a><a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>.
	445	<a id="idx:opensharedobject3:2016"></a><a class="pred" href="foreignlink.html#open_shared_object/3">open_shared_object/3</a>
	446	and <a id="idx:loadforeignlibrary1:2017"></a><a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>.
406	447
407	448	<p>On errors, an exception <code>shared_object(Action, Message)</code>
408	449	is raised. <var>Message</var> is the return value from dlerror().</dd>
409		<dt class="pubdef"><a name="open_shared_object/3"><strong>open_shared_object</strong>(<var>+File,
	450	<dt class="pubdef"><a id="open_shared_object/3"><strong>open_shared_object</strong>(<var>+File,
410	451	-Handle, +Options</var>)</a></dt>
411	452	<dd class="defbody">
412		As <a name="idx:opensharedobject2:2014"></a><a class="pred" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a>,
	453	As <a id="idx:opensharedobject2:2018"></a><a class="pred" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a>,
413	454	but allows for additional flags to be passed.
414	455	<var>Options</var> is a list of atoms. <code>now</code> implies the
415	456	symbols are resolved immediately rather than lazy (default). <code>global</code>

418	459	not be supported by your operating system. Check the documentation of
419	460	dlopen() or equivalent on your operating system. Unsupported flags are
420	461	silently ignored.</dd>
421		<dt class="pubdef"><a name="close_shared_object/1"><strong>close_shared_object</strong>(<var>+Handle</var>)</a></dt>
	462	<dt class="pubdef"><a id="close_shared_object/1"><strong>close_shared_object</strong>(<var>+Handle</var>)</a></dt>
422	463	<dd class="defbody">
423	464	Detach the shared object identified by <var>Handle</var>.</dd>
424		<dt class="pubdef"><a name="call_shared_object_function/2"><strong>call_shared_object_function</strong>(<var>+Handle,
	465	<dt class="pubdef"><a id="call_shared_object_function/2"><strong>call_shared_object_function</strong>(<var>+Handle,
425	466	+Function</var>)</a></dt>
426	467	<dd class="defbody">
427	468	Call the named function in the loaded shared library. The function is

431	472	</dd>
432	473	</dl>
433	474
434		<p><h3 id="sec:staticl"><a name="sec:11.2.5"><span class="sec-nr">11.2.5</span> <span class="sec-title">Static
	475	<p><h3 id="sec:staticl"><a id="sec:11.2.5"><span class="sec-nr">11.2.5</span> <span class="sec-title">Static
435	476	Linking</span></a></h3>
436	477
437		<a name="sec:staticl"></a>
	478	<a id="sec:staticl"></a>
438	479
439	480	<p>Below is an outline of the file structure required for statically
440	481	linking SWI-Prolog with foreign extensions. <code>.../swipl</code>

442	483	<code><<var>arch</var>></code> refers to the architecture
443	484	identifier that may be obtained using the Prolog flag <a class="flag" href="flags.html#flag:arch">arch</a>.
444	485
445		<p><table border="0" frame="void" rules="groups" style="margin:auto">
446		<tr valign="top"><td><code>.../swipl/runtime/<<var>arch</var>>/libswipl.a</code> </td><td>SWI-Library </td></tr>
447		<tr valign="top"><td><code>.../swipl/include/SWI-Prolog.h</code> </td><td>Include
	486	<p><table class="latex frame-void center">
	487	<tr><td><code>.../swipl/runtime/<<var>arch</var>>/libswipl.a</code> </td><td>SWI-Library </td></tr>
	488	<tr><td><code>.../swipl/include/SWI-Prolog.h</code> </td><td>Include
448	489	file </td></tr>
449		<tr valign="top"><td><code>.../swipl/include/SWI-Stream.h</code> </td><td>Stream
450		I/O include file </td></tr>
451		<tr valign="top"><td><code>.../swipl/include/SWI-Exports</code> </td><td>Export
	490	<tr><td><code>.../swipl/include/SWI-Stream.h</code> </td><td>Stream I/O
	491	include file </td></tr>
	492	<tr><td><code>.../swipl/include/SWI-Exports</code> </td><td>Export
452	493	declarations (AIX only) </td></tr>
453		<tr valign="top"><td><code>.../swipl/include/stub.c</code> </td><td>Extension
454		stub</td></tr>
	494	<tr><td><code>.../swipl/include/stub.c</code> </td><td>Extension stub</td></tr>
455	495	</table>
456	496
457	497	<p>The definition of the foreign predicates is the same as for dynamic

492	532	libraries required by both the extensions and the SWI-Prolog kernel.
493	533	This may be done by hand, or by using the <b>swipl-ld</b> utility
494	534	described in
495		<a class="sec" href="plld.html">section 11.5</a>. If the linking is
496		performed by hand, the command line option <code>-dump-runtime-variables</code>
497		(see <a class="sec" href="cmdline.html">section 2.4</a>) can be used to
498		obtain the required paths, libraries and linking options to link the new
499		executable.
	535	<a class="sec" href="plld.html#sec:11.5">section 11.5</a>. If the
	536	linking is performed by hand, the command line option <code>-dump-runtime-variables</code>
	537	(see <a class="sec" href="cmdline.html#sec:2.4">section 2.4</a>) can be
	538	used to obtain the required paths, libraries and linking options to link
	539	the new executable.
500	540
501	541	<p></body></html>⏎

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 11.8</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 11.8</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="foreignxmp.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="runtime.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:foreignnotes"><a name="sec:11.8"><span class="sec-nr">11.8</span> <span class="sec-title">Notes
	235	<h2 id="sec:foreignnotes"><a id="sec:11.8"><span class="sec-nr">11.8</span> <span class="sec-title">Notes
195	236	on Using Foreign Code</span></a></h2>
196	237
197		<a name="sec:foreignnotes"></a>
198
199		<p><h3 id="sec:foreign-debug"><a name="sec:11.8.1"><span class="sec-nr">11.8.1</span> <span class="sec-title">Foreign
	238	<a id="sec:foreignnotes"></a>
	239
	240	<p><h3 id="sec:foreign-debug"><a id="sec:11.8.1"><span class="sec-nr">11.8.1</span> <span class="sec-title">Foreign
200	241	debugging functions</span></a></h3>
201	242
202		<a name="sec:foreign-debug"></a>
	243	<a id="sec:foreign-debug"></a>
203	244
204	245	<p>The functions in this section are primarily intended for debugging
205	246	foreign extensions or embedded Prolog. Violating the constraints of the

220	261	critical location in your code or the system code.
221	262
222	263	<dl class="latex">
223		<dt class="pubdef"><a name="PL_backtrace()"><var>void</var> <strong>PL_backtrace</strong>(<var>int
	264	<dt class="pubdef"><a id="PL_backtrace()"><var>void</var> <strong>PL_backtrace</strong>(<var>int
224	265	depth, int flags</var>)</a></dt>
225	266	<dd class="defbody">
226	267	Dump a Prolog backtrace to the <code>user_error</code> stream. <var>Depth</var>

243	284	</dl>
244	285
245	286	</dd>
246		<dt class="pubdef"><a name="PL_backtrace_string()"><var>char *</var> <strong>PL_backtrace_string</strong>(<var>int
	287	<dt class="pubdef"><a id="PL_backtrace_string()"><var>char *</var> <strong>PL_backtrace_string</strong>(<var>int
247	288	depth, int flags</var>)</a></dt>
248	289	<dd class="defbody">
249	290	As <a class="func" href="foreignnotes.html#PL_backtrace()">PL_backtrace()</a>,

262	303	that exploits <b>gdb</b> and <a class="func" href="foreignnotes.html#PL_backtrace_string()">PL_backtrace_string()</a>
263	304	to print stack traces in various formats for a SWI-Prolog process, given
264	305	its process id.</dd>
265		<dt class="pubdef"><a name="PL_check_data()"><var>int</var> <strong>PL_check_data</strong>(<var>term_t
	306	<dt class="pubdef"><a id="PL_check_data()"><var>int</var> <strong>PL_check_data</strong>(<var>term_t
266	307	data</var>)</a></dt>
267	308	<dd class="defbody">
268	309	Check the consistency of the term <var>data</var>. Returns <code>TRUE</code>

270	311	<code>FALSE</code> otherwise. The actual implementation only exists if
271	312	the system is compiled with the cflag <code>-DO_DEBUG</code> or
272	313	<code>-DO_MAINTENANCE</code>. This is <em>not</em> the default.</dd>
273		<dt class="pubdef"><a name="PL_check_stacks()"><var>int</var> <strong>PL_check_stacks</strong>(<var></var>)</a></dt>
	314	<dt class="pubdef"><a id="PL_check_stacks()"><var>int</var> <strong>PL_check_stacks</strong>(<var></var>)</a></dt>
274	315	<dd class="defbody">
275	316	Check the consistency of the runtime stacks of the calling thread.
276	317	Returns <code>TRUE</code> this is actually implemented in the current

284	325	<p>The Prolog kernel sources use the macro <b>DEBUG(Topic, Code)</b>.
285	326	These macros are disabled in the production version and must be enabled
286	327	by recompiling the system as described above. Specific topics can be
287		enabled and disabled using the predicates <a name="idx:prologdebug1:2090"></a><a class="pred" href="foreignnotes.html#prolog_debug/1">prolog_debug/1</a>
	328	enabled and disabled using the predicates <a id="idx:prologdebug1:2094"></a><a class="pred" href="foreignnotes.html#prolog_debug/1">prolog_debug/1</a>
288	329	and
289		<a name="idx:prolognodebug1:2091"></a><a class="pred" href="foreignnotes.html#prolog_nodebug/1">prolog_nodebug/1</a>.
	330	<a id="idx:prolognodebug1:2095"></a><a class="pred" href="foreignnotes.html#prolog_nodebug/1">prolog_nodebug/1</a>.
290	331	In addition, they can be activated from the commandline using
291	332	commandline option <code>-d topics</code>, where
292	333	<var>topics</var> is a comma-separated list of debug topics to enable.

298	339	</pre>
299	340
300	341	<dl class="latex">
301		<dt class="pubdef"><a name="prolog_debug/1"><strong>prolog_debug</strong>(<var>+Topic</var>)</a></dt>
302		<dt class="pubdef"><a name="prolog_nodebug/1"><strong>prolog_nodebug</strong>(<var>+Topic</var>)</a></dt>
	342	<dt class="pubdef"><a id="prolog_debug/1"><strong>prolog_debug</strong>(<var>+Topic</var>)</a></dt>
	343	<dt class="pubdef"><a id="prolog_nodebug/1"><strong>prolog_nodebug</strong>(<var>+Topic</var>)</a></dt>
303	344	<dd class="defbody">
304	345	Enable/disable a debug topic. <var>Topic</var> is an atom that
305	346	identifies the desired topic. The available topics are defined in

320	361	</dd>
321	362	</dl>
322	363
323		<p><h3 id="sec:foreign-malloc"><a name="sec:11.8.2"><span class="sec-nr">11.8.2</span> <span class="sec-title">Memory
	364	<p><h3 id="sec:foreign-malloc"><a id="sec:11.8.2"><span class="sec-nr">11.8.2</span> <span class="sec-title">Memory
324	365	Allocation</span></a></h3>
325	366
326		<a name="sec:foreign-malloc"></a>
	367	<a id="sec:foreign-malloc"></a>
327	368
328	369	<p>SWI-Prolog's heap memory allocation is based on the <strong>malloc</strong>(3)
329	370	library routines. SWI-Prolog provides the functions below as a wrapper

340	381	functions on the same memory.
341	382
342	383	<dl class="latex">
343		<dt class="pubdef"><a name="PL_malloc()"><var>void *</var> <strong>PL_malloc</strong>(<var>size_t
	384	<dt class="pubdef"><a id="PL_malloc()"><var>void *</var> <strong>PL_malloc</strong>(<var>size_t
344	385	bytes</var>)</a></dt>
345	386	<dd class="defbody">
346	387	Allocate <var>bytes</var> of memory. On failure SWI-Prolog's fatal-error

348	389	does not return. Memory allocated using these functions must use <a class="func" href="foreignnotes.html#PL_realloc()">PL_realloc()</a>
349	390	and <a class="func" href="foreignnotes.html#PL_free()">PL_free()</a>
350	391	rather than realloc() and free().</dd>
351		<dt class="pubdef"><a name="PL_realloc()"><var>void *</var> <strong>PL_realloc</strong>(<var>void
	392	<dt class="pubdef"><a id="PL_realloc()"><var>void *</var> <strong>PL_realloc</strong>(<var>void
352	393	*mem, size_t size</var>)</a></dt>
353	394	<dd class="defbody">
354	395	Change the size of the allocated chunk, possibly moving it. The

356	397	or
357	398	<a class="func" href="foreignnotes.html#PL_realloc()">PL_realloc()</a>
358	399	call.</dd>
359		<dt class="pubdef"><a name="PL_free()"><var>void</var> <strong>PL_free</strong>(<var>void
	400	<dt class="pubdef"><a id="PL_free()"><var>void</var> <strong>PL_free</strong>(<var>void
360	401	*mem</var>)</a></dt>
361	402	<dd class="defbody">
362	403	Release memory. The <var>mem</var> argument must be obtained from a

366	407	</dd>
367	408	</dl>
368	409
369		<p><h4 id="sec:boehm-gc"><a name="sec:11.8.2.1"><span class="sec-nr">11.8.2.1</span> <span class="sec-title">Boehm-GC
	410	<p><h4 id="sec:boehm-gc"><a id="sec:11.8.2.1"><span class="sec-nr">11.8.2.1</span> <span class="sec-title">Boehm-GC
370	411	support</span></a></h4>
371	412
372		<a name="sec:boehm-gc"></a>
	413	<a id="sec:boehm-gc"></a>
373	414	<blockquote> This section is obsolete. Although the Boehm-GC interfaces
374	415	still exist, it turns out that the scalability is not good enough for
375	416	SWI-Prolog. It is unlikely that SWI-Prolog will ever switch to Boehm-GC.
376	417	</blockquote>
377	418
378		<p><a name="idx:BoehmGC:2092"></a>To accommodate future use of the Boehm
379		garbage collector<sup class="fn">178<span class="fn-text"><a class="url" href="http://www.hpl.hp.com/personal/Hans_Boehm/gc/">http://www.hpl.hp.com/personal/Hans_Boehm/gc/</a></span></sup>
	419	<p><a id="idx:BoehmGC:2096"></a>To accommodate future use of the Boehm
	420	garbage collector<sup class="fn">179<span class="fn-text"><a class="url" href="http://www.hpl.hp.com/personal/Hans_Boehm/gc/">http://www.hpl.hp.com/personal/Hans_Boehm/gc/</a></span></sup>
380	421	for heap memory allocation, the interface provides the functions
381	422	described below. Foreign extensions that wish to use the Boehm-GC
382	423	facilities can use these wrappers. Please note that if SWI-Prolog is not

384	425	to reclaim memory.
385	426
386	427	<dl class="latex">
387		<dt class="pubdef"><a name="PL_malloc_atomic()"><var>void*</var> <strong>PL_malloc_atomic</strong>(<var>size_t
	428	<dt class="pubdef"><a id="PL_malloc_atomic()"><var>void*</var> <strong>PL_malloc_atomic</strong>(<var>size_t
388	429	bytes</var>)</a></dt>
389		<dt class="pubdef"><a name="PL_malloc_uncollectable()"><var>void*</var> <strong>PL_malloc_uncollectable</strong>(<var>size_t
	430	<dt class="pubdef"><a id="PL_malloc_uncollectable()"><var>void*</var> <strong>PL_malloc_uncollectable</strong>(<var>size_t
390	431	bytes</var>)</a></dt>
391		<dt class="pubdef"><a name="PL_malloc_atomic_uncollectable()"><var>void*</var> <strong>PL_malloc_atomic_uncollectable</strong>(<var>size_t
	432	<dt class="pubdef"><a id="PL_malloc_atomic_uncollectable()"><var>void*</var> <strong>PL_malloc_atomic_uncollectable</strong>(<var>size_t
392	433	bytes</var>)</a></dt>
393	434	<dd class="defbody">
394	435	If Boehm-GC is not used, these are all the same as <a class="func" href="foreignnotes.html#PL_malloc()">PL_malloc()</a>.

397	438	pointers, and <em>uncollectable</em> means that the object should never
398	439	be garbage collected.
399	440	</dd>
400		<dt class="pubdef"><a name="PL_malloc_stubborn()"><var>void*</var> <strong>PL_malloc_stubborn</strong>(<var>size_t
	441	<dt class="pubdef"><a id="PL_malloc_stubborn()"><var>void*</var> <strong>PL_malloc_stubborn</strong>(<var>size_t
401	442	bytes</var>)</a></dt>
402		<dt class="pubdef"><a name="PL_end_stubborn_change()"><var>void</var> <strong>PL_end_stubborn_change</strong>(<var>void
	443	<dt class="pubdef"><a id="PL_end_stubborn_change()"><var>void</var> <strong>PL_end_stubborn_change</strong>(<var>void
403	444	*memory</var>)</a></dt>
404	445	<dd class="defbody">
405	446	These functions allow creating objects, promising GC that the content

407	448	</dd>
408	449	</dl>
409	450
410		<p><h3 id="sec:foreign-compat"><a name="sec:11.8.3"><span class="sec-nr">11.8.3</span> <span class="sec-title">Compatibility
	451	<p><h3 id="sec:foreign-compat"><a id="sec:11.8.3"><span class="sec-nr">11.8.3</span> <span class="sec-title">Compatibility
411	452	between Prolog versions</span></a></h3>
412	453
413		<a name="sec:foreign-compat"></a>
	454	<a id="sec:foreign-compat"></a>
414	455
415	456	<p>Great care is taken to ensure binary compatibility of foreign
416	457	extensions between different Prolog versions. Only the much less
417	458	frequently used stream interface has been responsible for binary
418	459	incompatibilities.
419	460
420		<p><a name="idx:PLVERSION:2093"></a>Source code that relies on new
	461	<p><a id="idx:PLVERSION:2097"></a>Source code that relies on new
421	462	features of the foreign interface can use the macro <code>PLVERSION</code>
422	463	to find the version of
423	464	<code>SWI-Prolog.h</code> and <a class="func" href="foreigninclude.html#PL_query()">PL_query()</a>

425	466	<code>PL_QUERY_VERSION</code> to find the version of the attached Prolog
426	467	system. Both follow the same numbering schema explained with <a class="func" href="foreigninclude.html#PL_query()">PL_query()</a>.
427	468
428		<p><h3 id="sec:foreign-debug-and-profile"><a name="sec:11.8.4"><span class="sec-nr">11.8.4</span> <span class="sec-title">Debugging
	469	<p><h3 id="sec:foreign-debug-and-profile"><a id="sec:11.8.4"><span class="sec-nr">11.8.4</span> <span class="sec-title">Debugging
429	470	and profiling foreign code (valgrind)</span></a></h3>
430	471
431		<a name="sec:foreign-debug-and-profile"></a>
432
433		<p><a name="idx:valgrind:2094"></a><a name="idx:profilingforeigncode:2095"></a>This
	472	<a id="sec:foreign-debug-and-profile"></a>
	473
	474	<p><a id="idx:valgrind:2098"></a><a id="idx:profilingforeigncode:2099"></a>This
434	475	section is only relevant for Unix users on platforms supported by
435		http://valgrind.org/valgrind. Valgrind is an excellent binary
436		instrumentation platform. Unlike many other instrumentation platforms,
437		valgrind can deal with code loaded through dlopen().
	476	<a class="url" href="http://valgrind.org/">valgrind</a>. Valgrind is an
	477	excellent binary instrumentation platform. Unlike many other
	478	instrumentation platforms, valgrind can deal with code loaded through
	479	dlopen().
438	480
439	481	<p>The <b>callgrind</b> tool can be used to profile foreign code loaded
440	482	under SWI-Prolog. Compile the foreign library adding <strong>-g</strong>

442	484	variable <code>VALGRIND</code> to <code>yes</code>, SWI-Prolog will <em>not</em>
443	485	release loaded shared objects using dlclose(). This trick is required to
444	486	get source information on the loaded library. Without, valgrind claims
445		that the shared object has no debugging information.<sup class="fn">179<span class="fn-text">Tested
	487	that the shared object has no debugging information.<sup class="fn">180<span class="fn-text">Tested
446	488	using valgrind version 3.2.3 on x64.</span></sup> Here is the complete
447	489	sequence using <b>bash</b> as login shell:
448	490

452	494	% kcachegrind callgrind.out.<pid>
453	495	</pre>
454	496
455		<p><h3 id="sec:foreign-name-conflicts"><a name="sec:11.8.5"><span class="sec-nr">11.8.5</span> <span class="sec-title">Name
	497	<p><h3 id="sec:foreign-name-conflicts"><a id="sec:11.8.5"><span class="sec-nr">11.8.5</span> <span class="sec-title">Name
456	498	Conflicts in C modules</span></a></h3>
457	499
458		<a name="sec:foreign-name-conflicts"></a>
	500	<a id="sec:foreign-name-conflicts"></a>
459	501
460	502	<p>In the current version of the system all public C functions of
461	503	SWI-Prolog are in the symbol table. This can lead to name clashes with

474	516	library loader will only look for symbols in the main executable for
475	517	symbols that are not defined in the library itself.
476	518
477		<p><h3 id="sec:foreign-quintus-sicstus"><a name="sec:11.8.6"><span class="sec-nr">11.8.6</span> <span class="sec-title">Compatibility
	519	<p><h3 id="sec:foreign-quintus-sicstus"><a id="sec:11.8.6"><span class="sec-nr">11.8.6</span> <span class="sec-title">Compatibility
478	520	of the Foreign Interface</span></a></h3>
479	521
480		<a name="sec:foreign-quintus-sicstus"></a>
	522	<a id="sec:foreign-quintus-sicstus"></a>
481	523
482	524	<p>The term reference mechanism was first used by Quintus Prolog version 3.
483	525	SICStus Prolog version 3 is strongly based on the Quintus interface. The

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193	234	</div>
194		<h2 id="sec:foreignoverview"><a name="sec:11.1"><span class="sec-nr">11.1</span> <span class="sec-title">Overview
	235	<h2 id="sec:foreignoverview"><a id="sec:11.1"><span class="sec-nr">11.1</span> <span class="sec-title">Overview
195	236	of the Interface</span></a></h2>
196	237
197		<a name="sec:foreignoverview"></a>
	238	<a id="sec:foreignoverview"></a>
198	239
199	240	<p>A special include file called <code>SWI-Prolog.h</code> should be
200	241	included with each C source file that is to be loaded via the foreign

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193	234	</div>
194		<h2 id="sec:foreignthread"><a name="sec:9.6"><span class="sec-nr">9.6</span> <span class="sec-title">Multithreaded
	235	<h2 id="sec:foreignthread"><a id="sec:9.6"><span class="sec-nr">9.6</span> <span class="sec-title">Multithreaded
195	236	mixed C and Prolog applications</span></a></h2>
196	237
197		<a name="sec:foreignthread"></a>
	238	<a id="sec:foreignthread"></a>
198	239
199	240	<p>All foreign code linked to the multithreading version of SWI-Prolog
200	241	should be thread-safe (<em>reentrant</em>) or guarded in Prolog using
201		<a name="idx:withmutex2:1953"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>
	242	<a id="idx:withmutex2:1957"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>
202	243	from simultaneous access from multiple Prolog threads. If you want to
203	244	write mixed multithreaded C and Prolog applications you should first
204	245	familiarise yourself with writing multithreaded applications in C (C++).

209	250	Without creating an engine, a thread can only use functions that do
210	251	<em>not</em> use the <code>term_t</code> type (for example <a class="func" href="foreigninclude.html#PL_new_atom()">PL_new_atom()</a>).
211	252
212		<p>The system supports two models. <a class="sec" href="foreignthread.html">Section
	253	<p>The system supports two models. <a class="sec" href="foreignthread.html#sec:9.6.1">Section
213	254	9.6.1</a> describes the original one-to-one mapping. In this schema a
214	255	native thread attaches a Prolog thread if it needs to call Prolog and
215		detaches it when finished, as opposed to the model from <a class="sec" href="foreignthread.html">section
	256	detaches it when finished, as opposed to the model from <a class="sec" href="foreignthread.html#sec:9.6.2">section
216	257	9.6.2</a>, where threads temporarily use a Prolog engine.
217	258
218		<p><h3 id="sec:threadoneone"><a name="sec:9.6.1"><span class="sec-nr">9.6.1</span> <span class="sec-title">A
	259	<p><h3 id="sec:threadoneone"><a id="sec:9.6.1"><span class="sec-nr">9.6.1</span> <span class="sec-title">A
219	260	Prolog thread for each native thread (one-to-one)</span></a></h3>
220	261
221		<a name="sec:threadoneone"></a>
	262	<a id="sec:threadoneone"></a>
222	263
223	264	<p>In the one-to-one model, the thread that called <a class="func" href="foreigninclude.html#PL_initialise()">PL_initialise()</a>
224	265	has a Prolog engine attached. If another C thread in the system wishes
225	266	to call Prolog it must first attach an engine using <a class="func" href="foreignthread.html#PL_thread_attach_engine()">PL_thread_attach_engine()</a>
226	267	and call <a class="func" href="foreignthread.html#PL_thread_destroy_engine()">PL_thread_destroy_engine()</a>
227	268	after all Prolog work is finished. This model is especially suitable
228		with long running threads that need to do Prolog work regularly. See <a class="sec" href="foreignthread.html">section
	269	with long running threads that need to do Prolog work regularly. See <a class="sec" href="foreignthread.html#sec:9.6.2">section
229	270	9.6.2</a> for the alternative many-to-many model.
230	271
231	272	<dl class="latex">
232		<dt class="pubdef"><a name="PL_thread_self()"><var>int</var> <strong>PL_thread_self</strong>(<var></var>)</a></dt>
	273	<dt class="pubdef"><a id="PL_thread_self()"><var>int</var> <strong>PL_thread_self</strong>(<var></var>)</a></dt>
233	274	<dd class="defbody">
234	275	Returns the integer Prolog identifier of the engine or -1 if the calling
235	276	thread has no Prolog engine. This function is also provided in the
236	277	single-threaded version of SWI-Prolog, where it returns -2.</dd>
237		<dt class="pubdef"><a name="PL_unify_thread_id()"><var>int</var> <strong>PL_unify_thread_id</strong>(<var>term_t
	278	<dt class="pubdef"><a id="PL_unify_thread_id()"><var>int</var> <strong>PL_unify_thread_id</strong>(<var>term_t
238	279	t, int i</var>)</a></dt>
239	280	<dd class="defbody">
240	281	Unify <var>t</var> with the Prolog thread identifier for thread <var>i</var>.
241	282	Thread identifiers are normally returned from <a class="func" href="foreignthread.html#PL_thread_self()">PL_thread_self()</a>.
242	283	Returns -1 if the thread does not exist or the unification fails.</dd>
243		<dt class="pubdef"><a name="PL_thread_attach_engine()"><var>int</var> <strong>PL_thread_attach_engine</strong>(<var>const
	284	<dt class="pubdef"><a id="PL_thread_attach_engine()"><var>int</var> <strong>PL_thread_attach_engine</strong>(<var>const
244	285	PL_thread_attr_t *attr</var>)</a></dt>
245	286	<dd class="defbody">
246	287	Creates a new Prolog engine in the calling thread. If the calling thread

279	320	(as returned by <a class="func" href="foreignthread.html#PL_thread_self()">PL_thread_self()</a>).
280	321	If an error occurs, -1 is returned. If this Prolog is not compiled for
281	322	multithreading, -2 is returned.</dd>
282		<dt class="pubdef"><a name="PL_thread_destroy_engine()"><var>int</var> <strong>PL_thread_destroy_engine</strong>(<var></var>)</a></dt>
	323	<dt class="pubdef"><a id="PL_thread_destroy_engine()"><var>int</var> <strong>PL_thread_destroy_engine</strong>(<var></var>)</a></dt>
283	324	<dd class="defbody">
284	325	Destroy the Prolog engine in the calling thread. Only takes effect if
285	326	<a class="func" href="foreignthread.html#PL_thread_destroy_engine()">PL_thread_destroy_engine()</a>

292	333	<p>Please note that construction and destruction of engines are
293	334	relatively expensive operations. Only destroy an engine if performance
294	335	is not critical and memory is a critical resource.</dd>
295		<dt class="pubdef"><a name="PL_thread_at_exit()"><var>int</var> <strong>PL_thread_at_exit</strong>(<var>void
	336	<dt class="pubdef"><a id="PL_thread_at_exit()"><var>int</var> <strong>PL_thread_at_exit</strong>(<var>void
296	337	(function)(void ), void *closure, int global</var>)</a></dt>
297	338	<dd class="defbody">
298	339	Register a handle to be called as the Prolog engine is destroyed. The

302	343	<em>for all threads</em>. Globally installed handlers are executed after
303	344	the thread-local handlers. If the handler is installed local for the
304	345	current thread only (<var>global</var> == <code>FALSE</code>) it is
305		stored in the same FIFO queue as used by <a name="idx:threadatexit1:1954"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>.
	346	stored in the same FIFO queue as used by <a id="idx:threadatexit1:1958"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>.
306	347	</dd>
307	348	</dl>
308	349
309		<p><h3 id="sec:threadmanymany"><a name="sec:9.6.2"><span class="sec-nr">9.6.2</span> <span class="sec-title">Pooling
	350	<p><h3 id="sec:threadmanymany"><a id="sec:9.6.2"><span class="sec-nr">9.6.2</span> <span class="sec-title">Pooling
310	351	Prolog engines (many-to-many)</span></a></h3>
311	352
312		<a name="sec:threadmanymany"></a>
	353	<a id="sec:threadmanymany"></a>
313	354
314	355	<p>In this model Prolog engines live as entities that are independent
315	356	from threads. If a thread needs to call Prolog it takes one of the

340	381	</ul>
341	382
342	383	<dl class="latex">
343		<dt class="pubdef"><a name="PL_create_engine()"><var>PL_engine_t</var> <strong>PL_create_engine</strong>(<var>PL_thread_attr_t
	384	<dt class="pubdef"><a id="PL_create_engine()"><var>PL_engine_t</var> <strong>PL_create_engine</strong>(<var>PL_thread_attr_t
344	385	*attributes</var>)</a></dt>
345	386	<dd class="defbody">
346	387	Create a new Prolog engine. <var>attributes</var> is described with

353	394
354	395	<p>In the single-threaded version this call always returns <code>NULL</code>,
355	396	indicating failure.</dd>
356		<dt class="pubdef"><a name="PL_destroy_engine()"><var>int</var> <strong>PL_destroy_engine</strong>(<var>PL_engine_t
	397	<dt class="pubdef"><a id="PL_destroy_engine()"><var>int</var> <strong>PL_destroy_engine</strong>(<var>PL_engine_t
357	398	e</var>)</a></dt>
358	399	<dd class="defbody">
359	400	Destroy the given engine. Destroying an engine is only allowed if the
360	401	engine is not attached to any thread or attached to the calling thread.
361	402	On success this function returns <code>TRUE</code>, on failure the
362	403	return value is <code>FALSE</code>.</dd>
363		<dt class="pubdef"><a name="PL_set_engine()"><var>int</var> <strong>PL_set_engine</strong>(<var>PL_engine_t
	404	<dt class="pubdef"><a id="PL_set_engine()"><var>int</var> <strong>PL_set_engine</strong>(<var>PL_engine_t
364	405	engine, PL_engine_t *old</var>)</a></dt>
365	406	<dd class="defbody">
366	407	Make the calling thread ready to use <var>engine</var>. If <var>old</var>

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191	232	<a class="nav" href="foreignlink.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:foreigntypes"><a name="sec:11.3"><span class="sec-nr">11.3</span> <span class="sec-title">Interface
	235	<h2 id="sec:foreigntypes"><a id="sec:11.3"><span class="sec-nr">11.3</span> <span class="sec-title">Interface
195	236	Data Types</span></a></h2>
196	237
197		<a name="sec:foreigntypes"></a>
198
199		<p><h3 id="sec:type-term-t"><a name="sec:11.3.1"><span class="sec-nr">11.3.1</span> <span class="sec-title">Type <code>term_t</code>:
	238	<a id="sec:foreigntypes"></a>
	239
	240	<p><h3 id="sec:type-term-t"><a id="sec:11.3.1"><span class="sec-nr">11.3.1</span> <span class="sec-title">Type <code>term_t</code>:
200	241	a reference to a Prolog term</span></a></h3>
201	242
202		<a name="sec:type-term-t"></a>
	243	<a id="sec:type-term-t"></a>
203	244
204	245	<p>The principal data type is <code>term_t</code>. Type <code>term_t</code>
205	246	is what Quintus calls <code>QP_term_ref</code>. This name indicates

234	275	<em>write</em> to term references. In this document we use the following
235	276	notation for arguments of type <code>term_t</code>:
236	277	<blockquote>
237		<table border="0" frame="void" rules="groups">
238		<tr valign="top"><td><code>term_t +t</code></td><td>Accessed in
239		read-mode. The `+' indicates the argument is `input'. </td></tr>
240		<tr valign="top"><td><code>term_t -t</code></td><td>Accessed in
241		write-mode. </td></tr>
242		<tr valign="top"><td><code>term_t ?t</code></td><td>Accessed in
243		unify-mode. </td></tr>
	278	<table class="latex frame-void">
	279	<tr><td><code>term_t +t</code></td><td>Accessed in read-mode. The `+'
	280	indicates the argument is `input'. </td></tr>
	281	<tr><td><code>term_t -t</code></td><td>Accessed in write-mode. </td></tr>
	282	<tr><td><code>term_t ?t</code></td><td>Accessed in unify-mode. </td></tr>
244	283	</table>
245	284	</blockquote>
246	285
247	286	<p><b>WARNING</b> Term references that are accessed in `write' (-) mode
248	287	will refer to an invalid term if the term is allocated on the global
249	288	stack and backtracking takes us back to a point before the term was
250		written.<sup class="fn">168<span class="fn-text">This could have been
	289	written.<sup class="fn">169<span class="fn-text">This could have been
251	290	avoided by <em>trailing</em> term references when data is written to
252	291	them. This seriously hurds performance in some scenarios though. If this
253	292	is desired, use <a class="func" href="foreigninclude.html#PL_put_variable()">PL_put_variable()</a>

304	343	<code>term_t</code>, but all copies will always refer to the same term.
305	344
306	345	<dl class="latex">
307		<dt class="pubdef"><a name="PL_new_term_ref()"><var>term_t</var> <strong>PL_new_term_ref</strong>(<var></var>)</a></dt>
	346	<dt class="pubdef"><a id="PL_new_term_ref()"><var>term_t</var> <strong>PL_new_term_ref</strong>(<var></var>)</a></dt>
308	347	<dd class="defbody">
309	348	Return a fresh reference to a term. The reference is allocated on the
310	349	<em>local</em> stack. Allocating a term reference may trigger a

312	351	allocation of the Prolog stacks. The returned reference describes a
313	352	variable.
314	353	</dd>
315		<dt class="pubdef"><a name="PL_new_term_refs()"><var>term_t</var> <strong>PL_new_term_refs</strong>(<var>int
	354	<dt class="pubdef"><a id="PL_new_term_refs()"><var>term_t</var> <strong>PL_new_term_refs</strong>(<var>int
316	355	n</var>)</a></dt>
317	356	<dd class="defbody">
318	357	Return <var>n</var> new term references. The first term reference is

332	371	</pre>
333	372
334	373	</dd>
335		<dt class="pubdef"><a name="PL_copy_term_ref()"><var>term_t</var> <strong>PL_copy_term_ref</strong>(<var>term_t
	374	<dt class="pubdef"><a id="PL_copy_term_ref()"><var>term_t</var> <strong>PL_copy_term_ref</strong>(<var>term_t
336	375	from</var>)</a></dt>
337	376	<dd class="defbody">
338	377	Create a new term reference and make it point initially to the same term
339	378	as <var>from</var>. This function is commonly used to copy a predicate
340	379	argument to a term reference that may be written.
341	380	</dd>
342		<dt class="pubdef"><a name="PL_reset_term_refs()"><var>void</var> <strong>PL_reset_term_refs</strong>(<var>term_t
	381	<dt class="pubdef"><a id="PL_reset_term_refs()"><var>void</var> <strong>PL_reset_term_refs</strong>(<var>term_t
343	382	after</var>)</a></dt>
344	383	<dd class="defbody">
345	384	Destroy all term references that have been created after <var>after</var>,

355	394	</dd>
356	395	</dl>
357	396
358		<p><h4 id="sec:foreign-gc"><a name="sec:11.3.1.1"><span class="sec-nr">11.3.1.1</span> <span class="sec-title">Interaction
	397	<p><h4 id="sec:foreign-gc"><a id="sec:11.3.1.1"><span class="sec-nr">11.3.1.1</span> <span class="sec-title">Interaction
359	398	with the garbage collector and stack-shifter</span></a></h4>
360	399
361		<a name="sec:foreign-gc"></a>
	400	<a id="sec:foreign-gc"></a>
362	401
363	402	<p>Prolog implements two mechanisms for avoiding stack overflow: garbage
364	403	collection and stack expansion. On machines that allow for it, Prolog

370	409	the information necessary to perform its memory management without
371	410	special precautions from the C programmer.
372	411
373		<p><h3 id="sec:foreign-types"><a name="sec:11.3.2"><span class="sec-nr">11.3.2</span> <span class="sec-title">Other
	412	<p><h3 id="sec:foreign-types"><a id="sec:11.3.2"><span class="sec-nr">11.3.2</span> <span class="sec-title">Other
374	413	foreign interface types</span></a></h3>
375	414
376		<a name="sec:foreign-types"></a>
	415	<a id="sec:foreign-types"></a>
377	416
378	417	<dl class="latex">
379	418	<dt><b>atom_t</b></dt>

430	469	<dt><b>install_t</b></dt>
431	470	<dd>
432	471	Type for the install() and uninstall() functions of shared or dynamic
433		link libraries. See <a class="sec" href="foreignlink.html">section
	472	link libraries. See <a class="sec" href="foreignlink.html#sec:11.2.3">section
434	473	11.2.3</a>.
435	474	</dd>
436	475	<dt><b>int64_t</b></dt>

449	488	</dd>
450	489	</dl>
451	490
452		<p><h4 id="sec:pl-arity-as-size"><a name="sec:11.3.2.1"><span class="sec-nr">11.3.2.1</span> <span class="sec-title">PL_ARITY_AS_SIZE</span></a></h4>
453
454		<a name="sec:pl-arity-as-size"></a>
	491	<p><h4 id="sec:pl-arity-as-size"><a id="sec:11.3.2.1"><span class="sec-nr">11.3.2.1</span> <span class="sec-title">PL_ARITY_AS_SIZE</span></a></h4>
	492
	493	<a id="sec:pl-arity-as-size"></a>
455	494
456	495	<p>As of SWI-Prolog 7.3.12, the arity of terms has changed from <code>int</code>
457	496	to <code>size_t</code>. To deal with this transition, all affecting

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193	234	</div>
194		<h2 id="sec:foreignxmp"><a name="sec:11.7"><span class="sec-nr">11.7</span> <span class="sec-title">Example
	235	<h2 id="sec:foreignxmp"><a id="sec:11.7"><span class="sec-nr">11.7</span> <span class="sec-title">Example
195	236	of Using the Foreign Interface</span></a></h2>
196	237
197		<a name="sec:foreignxmp"></a>
	238	<a id="sec:foreignxmp"></a>
198	239
199	240	<p>Below is an example showing all stages of the declaration of a
200	241	foreign predicate that transforms atoms possibly holding uppercase

236	277	</pre>
237	278
238	279	<div class="caption"><b>Figure 10 : </b>Lowercase source file</div>
239		<a name="fig:lowercase-c"></a>
	280	<a id="fig:lowercase-c"></a>
240	281
241	282	<pre class="code">
242	283	% gcc -I/usr/local/lib/swipl-\plversion/include -fpic -c lowercase.c

254	295
255	296	<div class="caption"><b>Figure 11 : </b>Compiling the C source and
256	297	loading the object file</div>
257		<a name="fig:load-foreign"></a>
	298	<a id="fig:load-foreign"></a>
258	299	</body></html>⏎

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193	234	</div>
194		<h2 id="sec:format"><a name="sec:4.32"><span class="sec-nr">4.32</span> <span class="sec-title">Formatted
	235	<h2 id="sec:format"><a id="sec:4.32"><span class="sec-nr">4.32</span> <span class="sec-title">Formatted
195	236	Write</span></a></h2>
196	237
197		<a name="sec:format"></a>
	238	<a id="sec:format"></a>
198	239
199	240	<p>The current version of SWI-Prolog provides two formatted write
200		predicates. The `writef' family (<a name="idx:writef1:1383"></a><a class="pred" href="format.html#writef/1">writef/1</a>, <a name="idx:writef2:1384"></a><a class="pred" href="format.html#writef/2">writef/2</a>, <a name="idx:swritef3:1385"></a><a class="pred" href="format.html#swritef/3">swritef/3</a>),
	241	predicates. The `writef' family (<a id="idx:writef1:1383"></a><a class="pred" href="format.html#writef/1">writef/1</a>, <a id="idx:writef2:1384"></a><a class="pred" href="format.html#writef/2">writef/2</a>, <a id="idx:swritef3:1385"></a><a class="pred" href="format.html#swritef/3">swritef/3</a>),
201	242	is compatible with Edinburgh C-Prolog and should be considered
202		<em>deprecated</em>. The `format' family (<a name="idx:format1:1386"></a><a class="pred" href="format.html#format/1">format/1</a>, <a name="idx:format2:1387"></a><a class="pred" href="format.html#format/2">format/2</a>, <a name="idx:format3:1388"></a><a class="pred" href="format.html#format/3">format/3</a>),
	243	<em>deprecated</em>. The `format' family (<a id="idx:format1:1386"></a><a class="pred" href="format.html#format/1">format/1</a>, <a id="idx:format2:1387"></a><a class="pred" href="format.html#format/2">format/2</a>, <a id="idx:format3:1388"></a><a class="pred" href="format.html#format/3">format/3</a>),
203	244	was defined by Quintus Prolog and currently available in many Prolog
204	245	systems, although the details vary.
205	246
206		<p><h3 id="sec:writef"><a name="sec:4.32.1"><span class="sec-nr">4.32.1</span> <span class="sec-title">Writef</span></a></h3>
207
208		<a name="sec:writef"></a>
	247	<p><h3 id="sec:writef"><a id="sec:4.32.1"><span class="sec-nr">4.32.1</span> <span class="sec-title">Writef</span></a></h3>
	248
	249	<a id="sec:writef"></a>
209	250
210	251	<dl class="latex">
211		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="writef/1"><strong>writef</strong>(<var>+Atom</var>)</a></dt>
212		<dd class="defbody">
213		Equivalent to <code>writef(Atom, []).</code> See <a name="idx:writef2:1389"></a><a class="pred" href="format.html#writef/2">writef/2</a>
	252	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="writef/1"><strong>writef</strong>(<var>+Atom</var>)</a></dt>
	253	<dd class="defbody">
	254	Equivalent to <code>writef(Atom, []).</code> See <a id="idx:writef2:1389"></a><a class="pred" href="format.html#writef/2">writef/2</a>
214	255	for details.
215	256	</dd>
216		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="writef/2"><strong>writef</strong>(<var>+Format,
	257	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="writef/2"><strong>writef</strong>(<var>+Format,
217	258	+Arguments</var>)</a></dt>
218	259	<dd class="defbody">
219	260	Formatted write. <var>Format</var> is an atom whose characters will be

224	265
225	266	<p>Escape sequences to generate a single special character:
226	267
227		<p><table border="2" frame="box" rules="groups" style="margin:auto">
228		<tr valign="top"><td><code>\n</code> </td><td>Output a newline character
229		(see also <a name="idx:nl01:1390"></a><a class="pred" href="chario.html#nl/0">nl/[0,1]</a>) </td></tr>
230		<tr valign="top"><td><code>\l</code> </td><td>Output a line separator
231		(same as <code>\n</code>) </td></tr>
232		<tr valign="top"><td><code>\r</code> </td><td>Output a carriage return
233		character (ASCII 13) </td></tr>
234		<tr valign="top"><td><code>\t</code> </td><td>Output the ASCII character
235		TAB (9) </td></tr>
236		<tr valign="top"><td><code>\\</code> </td><td>The character <code><code>\</code></code>
	268	<p><table class="latex frame-box center">
	269	<tr><td><code>\n</code> </td><td>Output a newline character (see also <a id="idx:nl01:1390"></a><a class="pred" href="chario.html#nl/0">nl/[0,1]</a>) </td></tr>
	270	<tr><td><code>\l</code> </td><td>Output a line separator (same as <code>\n</code>) </td></tr>
	271	<tr><td><code>\r</code> </td><td>Output a carriage return character
	272	(ASCII 13) </td></tr>
	273	<tr><td><code>\t</code> </td><td>Output the ASCII character TAB (9) </td></tr>
	274	<tr><td><code>\\</code> </td><td>The character <code><code>\</code></code>
237	275	is output </td></tr>
238		<tr valign="top"><td><code>\%</code> </td><td>The character <code><code>%</code></code>
	276	<tr><td><code>\%</code> </td><td>The character <code><code>%</code></code>
239	277	is output </td></tr>
240		<tr valign="top"><td><code>\nnn</code> </td><td>where <<var>nnn</var>>
241		is an integer (1-3 digits); the character with code <<var>nnn</var>>
242		is output (NB : <<var>nnn</var>> is read as <strong>decimal</strong>) </td></tr>
	278	<tr><td><code>\nnn</code> </td><td>where <<var>nnn</var>> is an
	279	integer (1-3 digits); the character with code <<var>nnn</var>> is
	280	output (NB : <<var>nnn</var>> is read as <strong>decimal</strong>) </td></tr>
243	281	</table>
244	282
245	283	<p>Note that <code>\l</code>, <code>\nnn</code> and <code>\\</code> are
246	284	interpreted differently when character escapes are in effect. See
247		<a class="sec" href="syntax.html">section 2.16.1.3</a>.
	285	<a class="sec" href="syntax.html#sec:2.16.1.3">section 2.16.1.3</a>.
248	286
249	287	<p>Escape sequences to include arguments from <var>Arguments</var>. Each
250	288	time a
251	289	% escape sequence is found in <var>Format</var> the next argument from <var>Arguments</var>
252	290	is formatted according to the specification.
253	291
254		<p><table border="2" frame="box" rules="groups" style="margin:auto">
255		<tr valign="top"><td><code>%t</code> </td><td><a name="idx:print1:1391"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	292	<p><table class="latex frame-box center">
	293	<tr><td><code>%t</code> </td><td><a id="idx:print1:1391"></a><a class="pred" href="termrw.html#print/1">print/1</a>
256	294	the next item (mnemonic: term) </td></tr>
257		<tr valign="top"><td><code>%w</code> </td><td><a name="idx:write1:1392"></a><a class="pred" href="termrw.html#write/1">write/1</a>
	295	<tr><td><code>%w</code> </td><td><a id="idx:write1:1392"></a><a class="pred" href="termrw.html#write/1">write/1</a>
258	296	the next item </td></tr>
259		<tr valign="top"><td><code>%q</code> </td><td><a name="idx:writeq1:1393"></a><a class="pred" href="termrw.html#writeq/1">writeq/1</a>
	297	<tr><td><code>%q</code> </td><td><a id="idx:writeq1:1393"></a><a class="pred" href="termrw.html#writeq/1">writeq/1</a>
260	298	the next item </td></tr>
261		<tr valign="top"><td><code>%d</code> </td><td>Write the term, ignoring
262		operators. See also
263		<a name="idx:writeterm2:1394"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>.
264		Mnemonic: old Edinburgh <a name="idx:display1:1395"></a><span class="pred-ext">display/1</span> </td></tr>
265		<tr valign="top"><td><code>%p</code> </td><td><a name="idx:print1:1396"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	299	<tr><td><code>%d</code> </td><td>Write the term, ignoring operators. See
	300	also
	301	<a id="idx:writeterm2:1394"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>.
	302	Mnemonic: old Edinburgh <a id="idx:display1:1395"></a><span class="pred-ext">display/1</span> </td></tr>
	303	<tr><td><code>%p</code> </td><td><a id="idx:print1:1396"></a><a class="pred" href="termrw.html#print/1">print/1</a>
266	304	the next item (identical to <code>%t</code>) </td></tr>
267		<tr valign="top"><td><code>%n</code> </td><td>Put the next item as a
268		character (i.e., it is a character code) </td></tr>
269		<tr valign="top"><td><code>%r</code> </td><td>Write the next item N
270		times where N is the second item (an integer) </td></tr>
271		<tr valign="top"><td><code>%s</code> </td><td>Write the next item as a
272		String (so it must be a list of characters) </td></tr>
273		<tr valign="top"><td><code>%f</code> </td><td>Perform a <a name="idx:ttyflush0:1397"></a><a class="pred" href="chario.html#ttyflush/0">ttyflush/0</a>
	305	<tr><td><code>%n</code> </td><td>Put the next item as a character (i.e.,
	306	it is a character code) </td></tr>
	307	<tr><td><code>%r</code> </td><td>Write the next item N times where N is
	308	the second item (an integer) </td></tr>
	309	<tr><td><code>%s</code> </td><td>Write the next item as a String (so it
	310	must be a list of characters) </td></tr>
	311	<tr><td><code>%f</code> </td><td>Perform a <a id="idx:ttyflush0:1397"></a><a class="pred" href="chario.html#ttyflush/0">ttyflush/0</a>
274	312	(no items used) </td></tr>
275		<tr valign="top"><td><code>%Nc</code> </td><td>Write the next item
276		Centered in <var>N</var> columns </td></tr>
277		<tr valign="top"><td><code>%Nl</code> </td><td>Write the next item Left
278		justified in <var>N</var> columns </td></tr>
279		<tr valign="top"><td><code>%Nr</code> </td><td>Write the next item Right
280		justified in <var>N</var> columns.
	313	<tr><td><code>%Nc</code> </td><td>Write the next item Centered in <var>N</var>
	314	columns </td></tr>
	315	<tr><td><code>%Nl</code> </td><td>Write the next item Left justified in <var>N</var>
	316	columns </td></tr>
	317	<tr><td><code>%Nr</code> </td><td>Write the next item Right justified in <var>N</var>
	318	columns.
281	319	<var>N</var> is a decimal number with at least one digit. The item must
282	320	be an atom, integer, float or string. </td></tr>
283	321	</table>
284	322	</dd>
285		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="swritef/3"><strong>swritef</strong>(<var>-String,
	323	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="swritef/3"><strong>swritef</strong>(<var>-String,
286	324	+Format, +Arguments</var>)</a></dt>
287	325	<dd class="defbody">
288		Equivalent to <a name="idx:writef2:1398"></a><a class="pred" href="format.html#writef/2">writef/2</a>,
	326	Equivalent to <a id="idx:writef2:1398"></a><a class="pred" href="format.html#writef/2">writef/2</a>,
289	327	but ``writes'' the result on <var>String</var> instead of the current
290	328	output stream. Example:
291	329

296	334	</pre>
297	335
298	336	</dd>
299		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="swritef/2"><strong>swritef</strong>(<var>-String,
	337	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="swritef/2"><strong>swritef</strong>(<var>-String,
300	338	+Format</var>)</a></dt>
301	339	<dd class="defbody">
302	340	Equivalent to <code>swritef(String, Format, []).</code>
303	341	</dd>
304	342	</dl>
305	343
306		<p><h3 id="sec:format-predicates"><a name="sec:4.32.2"><span class="sec-nr">4.32.2</span> <span class="sec-title">Format</span></a></h3>
307
308		<a name="sec:format-predicates"></a>
	344	<p><h3 id="sec:format-predicates"><a id="sec:4.32.2"><span class="sec-nr">4.32.2</span> <span class="sec-title">Format</span></a></h3>
	345
	346	<a id="sec:format-predicates"></a>
309	347
310	348	<p>The format family of predicates is the most versatile and portable<sup class="fn">126<span class="fn-text">Unfortunately
311	349	not covered by any standard.</span></sup> way to produce textual output.
312	350
313	351	<dl class="latex">
314		<dt class="pubdef"><a name="format/1"><strong>format</strong>(<var>+Format</var>)</a></dt>
	352	<dt class="pubdef"><a id="format/1"><strong>format</strong>(<var>+Format</var>)</a></dt>
315	353	<dd class="defbody">
316	354	Defined as `<code>format(Format) :- format(Format, []).</code>'. See
317		<a name="idx:format2:1399"></a><a class="pred" href="format.html#format/2">format/2</a>
	355	<a id="idx:format2:1399"></a><a class="pred" href="format.html#format/2">format/2</a>
318	356	for details.</dd>
319		<dt class="pubdef"><a name="format/2"><strong>format</strong>(<var>+Format,
	357	<dt class="pubdef"><a id="format/2"><strong>format</strong>(<var>+Format,
320	358	:Arguments</var>)</a></dt>
321	359	<dd class="defbody">
322	360	<var>Format</var> is an atom, list of character codes, or a Prolog

349	387	<p>Numeric conversion (<code>d</code>, <code>D</code>, <code>e</code>, <code>E</code>, <code>f</code>, <code>g</code>
350	388	and <code>G</code>) accept an arithmetic expression as argument. This is
351	389	introduced to handle rational numbers transparently (see
352		<a class="sec" href="arith.html">section 4.27.2.2</a>). The floating
353		point conversions allow for unlimited precision for printing rational
354		numbers in decimal form. E.g., the following will write as many 3's as
355		you want by changing the `50'.
	390	<a class="sec" href="arith.html#sec:4.27.2.2">section 4.27.2.2</a>). The
	391	floating point conversions allow for unlimited precision for printing
	392	rational numbers in decimal form. E.g., the following will write as many
	393	3's as you want by changing the `50'.
356	394
357	395	<pre class="code">
358	396	?- format('~50f', [10 rdiv 3]).

377	415	the actually emitted bytes are defined by the character encoding of the
378	416	output stream and an exception may be raised if the output stream is not
379	417	capable of representing the requested Unicode character. See
380		<a class="sec" href="widechars.html">section 2.19.1</a> for details.
	418	<a class="sec" href="widechars.html#sec:2.19.1">section 2.19.1</a> for
	419	details.
381	420
382	421	<p>
383	422	<li><code>d</code><br>

387	426	integers, such as handling amounts of money).
388	427
389	428	<p>The colon modifier (e.g., <code>~:d</code>) causes the number to be
390		printed according to the locale of the output stream. See <a class="sec" href="locale.html">section
	429	printed according to the locale of the output stream. See <a class="sec" href="locale.html#sec:4.23">section
391	430	4.23</a>.
392	431
393	432	<p>

433	472	<li><code>I</code><br>
434	473	Emit a decimal number using Prolog digit grouping (the underscore,
435	474	<code>_</code>). The argument describes the size of each digit group.
436		The default is 3. See also <a class="sec" href="syntax.html">section
	475	The default is 3. See also <a class="sec" href="syntax.html#sec:2.16.1.5">section
437	476	2.16.1.5</a>. For example:
438	477
439	478	<pre class="code">

443	482
444	483	<p>
445	484	<li><code>k</code><br>
446		Give the next argument to <a name="idx:writecanonical1:1400"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>.
	485	Give the next argument to <a id="idx:writecanonical1:1400"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>.
447	486	<li><code>n</code><br>
448	487	Output a newline character.
449	488	<li><code>N</code><br>
450	489	Only output a newline if the last character output on this stream was
451	490	not a newline. Not properly implemented yet.
452	491	<li><code>p</code><br>
453		Give the next argument to <a name="idx:print1:1401"></a><a class="pred" href="termrw.html#print/1">print/1</a>.
	492	Give the next argument to <a id="idx:print1:1401"></a><a class="pred" href="termrw.html#print/1">print/1</a>.
454	493	<li><code>q</code><br>
455		Give the next argument to <a name="idx:writeq1:1402"></a><a class="pred" href="termrw.html#writeq/1">writeq/1</a>.
	494	Give the next argument to <a id="idx:writeq1:1402"></a><a class="pred" href="termrw.html#writeq/1">writeq/1</a>.
456	495
457	496	<p>
458	497	<li><code>r</code><br>

466	505	<li><code>R</code><br>
467	506	Same as <b>r</b>, but uses uppercase letters for digits above 9.
468	507	<li><code>s</code><br>
469		Output text from a list of character codes or a string (see <a name="idx:string1:1403"></a><a class="pred" href="typetest.html#string/1">string/1</a>
	508	Output text from a list of character codes or a string (see <a id="idx:string1:1403"></a><a class="pred" href="typetest.html#string/1">string/1</a>
470	509	and
471		<a class="sec" href="strings.html">section 5.2</a>) from the next
472		argument.<sup class="fn">128<span class="fn-text">The <b>s</b> modifier
473		also accepts an atom for compatibility. This is deprecated due to the
474		ambiguity of <code>[]</code>.</span></sup>
	510	<a class="sec" href="strings.html#sec:5.2">section 5.2</a>) from the
	511	next argument.<sup class="fn">128<span class="fn-text">The <b>s</b>
	512	modifier also accepts an atom for compatibility. This is deprecated due
	513	to the ambiguity of <code>[]</code>.</span></sup>
475	514	<li><code>@</code><br>
476	515	Interpret the next argument as a goal and execute it. Output written to
477	516	the <code>current_output</code> stream is inserted at this place. Goal
478		is called in the module calling <a name="idx:format3:1404"></a><a class="pred" href="format.html#format/3">format/3</a>.
	517	is called in the module calling <a id="idx:format3:1404"></a><a class="pred" href="format.html#format/3">format/3</a>.
479	518	This option is not present in the original definition by Quintus, but
480	519	supported by some other Prolog systems.
481	520	<li><code>t</code><br>

508	547
509	548	<p>
510	549	<li><code>w</code><br>
511		Give the next argument to <a name="idx:write1:1405"></a><a class="pred" href="termrw.html#write/1">write/1</a>.
	550	Give the next argument to <a id="idx:write1:1405"></a><a class="pred" href="termrw.html#write/1">write/1</a>.
512	551	<li><code>W</code><br>
513		Give the next two arguments to <a name="idx:writeterm2:1406"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>.
	552	Give the next two arguments to <a id="idx:writeterm2:1406"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>.
514	553	For example,
515	554	<code>format('~W', [Term, [numbervars(true)]])</code>. This option is
516	555	SWI-Prolog specific.

536	575	</pre>
537	576
538	577	</dd>
539		<dt class="pubdef"><a name="format/3"><strong>format</strong>(<var>+Output,
	578	<dt class="pubdef"><a id="format/3"><strong>format</strong>(<var>+Output,
540	579	+Format, :Arguments</var>)</a></dt>
541	580	<dd class="defbody">
542		As <a name="idx:format2:1407"></a><a class="pred" href="format.html#format/2">format/2</a>,
	581	As <a id="idx:format2:1407"></a><a class="pred" href="format.html#format/2">format/2</a>,
543	582	but write the output on the given <var>Output</var>. The de-facto
544	583	standard only allows <var>Output</var> to be a stream. The SWI-Prolog
545	584	implementation allows all valid arguments for
546		<a name="idx:withoutputto2:1408"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>.<sup class="fn">129<span class="fn-text">Earlier
	585	<a id="idx:withoutputto2:1408"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>.<sup class="fn">129<span class="fn-text">Earlier
547	586	versions defined sformat/3 . These predicates have been moved to the
548	587	library <code>library(backcomp)</code>.</span></sup> For example:
549	588

555	594	<p></dd>
556	595	</dl>
557	596
558		<p><h3 id="sec:format-hook"><a name="sec:4.32.3"><span class="sec-nr">4.32.3</span> <span class="sec-title">Programming
	597	<p><h3 id="sec:format-hook"><a id="sec:4.32.3"><span class="sec-nr">4.32.3</span> <span class="sec-title">Programming
559	598	Format</span></a></h3>
560	599
561		<a name="sec:format-hook"></a>
	600	<a id="sec:format-hook"></a>
562	601
563	602	<dl class="latex">
564		<dt class="pubdef"><a name="format_predicate/2"><strong>format_predicate</strong>(<var>+Char,
	603	<dt class="pubdef"><a id="format_predicate/2"><strong>format_predicate</strong>(<var>+Char,
565	604	+Head</var>)</a></dt>
566	605	<dd class="defbody">
567	606	If a sequence <code>~c</code> (tilde, followed by some character) is
568		found, the <a name="idx:format3:1409"></a><a class="pred" href="format.html#format/3">format/3</a>
	607	found, the <a id="idx:format3:1409"></a><a class="pred" href="format.html#format/3">format/3</a>
569	608	and friends first check whether the user has defined a predicate to
570	609	handle the format. If not, the built-in formatting rules described above
571	610	are used. <var>Char</var> is either a character code or a one-character

576	615	if no argument is specified. The remaining arguments are filled from the
577	616	argument list. The example below defines <code>~T</code> to print a
578	617	timestamp in ISO8601 format (see
579		<a name="idx:formattime3:1410"></a><a class="pred" href="system.html#format_time/3">format_time/3</a>).
	618	<a id="idx:formattime3:1410"></a><a class="pred" href="system.html#format_time/3">format_time/3</a>).
580	619	The subsequent block illustrates a possible call.
581	620
582	621	<pre class="code">

595	634	</pre>
596	635
597	636	</dd>
598		<dt class="pubdef"><a name="current_format_predicate/2"><strong>current_format_predicate</strong>(<var>?Code,
	637	<dt class="pubdef"><a id="current_format_predicate/2"><strong>current_format_predicate</strong>(<var>?Code,
599	638	?:Head</var>)</a></dt>
600	639	<dd class="defbody">
601	640	True when <code><code>~</code></code><var>Code</var> is handled by the

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section F.3</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section F.3</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:funcsummary"><a name="sec:F.3"><span class="sec-nr">F.3</span> <span class="sec-title">Arithmetic
	235	<h2 id="sec:funcsummary"><a id="sec:F.3"><span class="sec-nr">F.3</span> <span class="sec-title">Arithmetic
195	236	Functions</span></a></h2>
196	237
197		<a name="sec:funcsummary"></a>
	238	<a id="sec:funcsummary"></a>
198	239	<table>
199	240	<tr><td><a class="function" href="arith.html#f-/2">/2</a></td><td>Multiplication</td></tr>
200	241	<tr><td><a class="function" href="arith.html#f-/2">/2</a></td><td>Power

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 2.15</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 2.15</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
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193	234	</div>
194		<h2 id="sec:gc"><a name="sec:2.15"><span class="sec-nr">2.15</span> <span class="sec-title">Garbage
	235	<h2 id="sec:gc"><a id="sec:2.15"><span class="sec-nr">2.15</span> <span class="sec-title">Garbage
195	236	Collection</span></a></h2>
196	237
197		<a name="sec:gc"></a>
	238	<a id="sec:gc"></a>
198	239
199	240	<p>SWI-Prolog provides garbage collection, last-call optimization and
200	241	atom garbage collection. These features are controlled using Prolog
201		flags (see <a name="idx:currentprologflag2:211"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>).
	242	flags (see <a id="idx:currentprologflag2:211"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>).
202	243
203	244	<p></body></html>⏎

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193	234	</div>
194		<h2 id="sec:gemacs"><a name="sec:2.5"><span class="sec-nr">2.5</span> <span class="sec-title">GNU
	235	<h2 id="sec:gemacs"><a id="sec:2.5"><span class="sec-nr">2.5</span> <span class="sec-title">GNU
195	236	Emacs Interface</span></a></h2>
196	237
197		<a name="sec:gemacs"></a>
198
199		<p><a name="idx:GNUEmacs:46"></a><a name="idx:Emacs:47"></a>Unfortunately
	238	<a id="sec:gemacs"></a>
	239
	240	<p><a id="idx:GNUEmacs:46"></a><a id="idx:Emacs:47"></a>Unfortunately
200	241	the default Prolog mode of GNU Emacs is not very good. There are
201	242	several alternatives though:
202	243

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193	234	</div>
194		<h2 id="sec:gensym"><a name="sec:A.13"><span class="sec-nr">A.13</span> <span class="sec-title">library(gensym):
	235	<h2 id="sec:gensym"><a id="sec:A.13"><span class="sec-nr">A.13</span> <span class="sec-title">library(gensym):
195	236	Generate unique identifiers</span></a></h2>
196	237
197		<a name="sec:gensym"></a>
	238	<a id="sec:gensym"></a>
198	239
199	240	<p>Gensym (<b>Gen</b>erate <b>Sym</b>bols) is an old library for
200	241	generating unique symbols (atoms). Such symbols are generated from a

207	248	over all threads.
208	249
209	250	<dl class="latex">
210		<dt class="pubdef"><a name="gensym/2"><strong>gensym</strong>(<var>+Base,
	251	<dt class="pubdef"><a id="gensym/2"><strong>gensym</strong>(<var>+Base,
211	252	-Unique</var>)</a></dt>
212	253	<dd class="defbody">
213	254	Generate a unique atom from base <var>Base</var> and unify it with <var>Unique</var>.
214	255	<var>Base</var> should be an atom. The first call will return <<var>base</var>>1
215	256	, the next <<var>base</var>>2 , etc. Note that this is no
216	257	guarantee that the atom is unique in the system.</dd>
217		<dt class="pubdef"><a name="reset_gensym/1"><strong>reset_gensym</strong>(<var>+Base</var>)</a></dt>
	258	<dt class="pubdef"><a id="reset_gensym/1"><strong>reset_gensym</strong>(<var>+Base</var>)</a></dt>
218	259	<dd class="defbody">
219	260	Restart generation of identifiers from <var>Base</var> at <<var>Base</var>>1.
220	261	Used to make sure a program produces the same results on subsequent
221	262	runs. Use with care.</dd>
222		<dt class="pubdef"><a name="reset_gensym/0"><strong>reset_gensym</strong></a></dt>
	263	<dt class="pubdef"><a id="reset_gensym/0"><strong>reset_gensym</strong></a></dt>
223	264	<dd class="defbody">
224	265	Reset gensym for all registered keys. This predicate is available for
225	266	compatibility only. New code is strongly advised to avoid the use of

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193	234	</div>
194		<h1 id="sec:glossary"><a name="sec:D"><span class="sec-nr">D</span> <span class="sec-title">Glossary
	235	<h1 id="sec:glossary"><a id="sec:D"><span class="sec-nr">D</span> <span class="sec-title">Glossary
195	236	of Terms</span></a></h1>
196	237
197		<a name="sec:glossary"></a>
	238	<a id="sec:glossary"></a>
198	239
199	240	<dl class="latex">
200		<dt><a name="gloss:anonymou"><strong>anonymous [variable]</strong></a></dt>
201		<dd class="defbody">
202		<a name="idx:anonymousvariable:2266"></a><a name="idx:variableanonymous:2267"></a>The
	241	<dt><a id="gloss:anonymou"><strong>anonymous [variable]</strong></a></dt>
	242	<dd class="defbody">
	243	<a id="idx:anonymousvariable:2270"></a><a id="idx:variableanonymous:2271"></a>The
203	244	variable <code>_</code> is called the <a class="gloss" href="glossary.html#gloss:anonymou">anonymous</a>
204	245	variable. Multiple occurrences of <code>_</code> in a single <a class="gloss" href="glossary.html#gloss:term">term</a>
205	246	are not <a class="gloss" href="glossary.html#gloss:shared">shared</a>.</dd>
206		<dt><a name="gloss:argument"><strong>arguments</strong></a></dt>
	247	<dt><a id="gloss:argument"><strong>arguments</strong></a></dt>
207	248	<dd class="defbody">
208	249	Arguments are <a class="gloss" href="glossary.html#gloss:term">terms</a>
209	250	that appear in a <a class="gloss" href="glossary.html#gloss:compound">compound</a> <a class="gloss" href="glossary.html#gloss:term">term</a>. <var>A1</var>
210	251	and <var>a2</var> are the first and second argument of the term
211	252	<code>myterm(A1, a2)</code>.</dd>
212		<dt><a name="gloss:arity"><strong>arity</strong></a></dt>
213		<dd class="defbody">
214		<a name="idx:arity:2268"></a>Argument count (= number of arguments) of a <a class="gloss" href="glossary.html#gloss:compound">compound</a> <a class="gloss" href="glossary.html#gloss:term">term</a>.</dd>
215		<dt><a name="gloss:assert"><strong>assert</strong></a></dt>
216		<dd class="defbody">
217		<a name="idx:assert:2269"></a>Add a <a class="gloss" href="glossary.html#gloss:clause">clause</a>
	253	<dt><a id="gloss:arity"><strong>arity</strong></a></dt>
	254	<dd class="defbody">
	255	<a id="idx:arity:2272"></a>Argument count (= number of arguments) of a <a class="gloss" href="glossary.html#gloss:compound">compound</a> <a class="gloss" href="glossary.html#gloss:term">term</a>.</dd>
	256	<dt><a id="gloss:assert"><strong>assert</strong></a></dt>
	257	<dd class="defbody">
	258	<a id="idx:assert:2273"></a>Add a <a class="gloss" href="glossary.html#gloss:clause">clause</a>
218	259	to a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>.
219	260	Clauses can be added at either end of the clause-list of a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>.
220		See <a name="idx:asserta1:2270"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
221		and <a name="idx:assertz1:2271"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>.</dd>
222		<dt><a name="gloss:atom"><strong>atom</strong></a></dt>
223		<dd class="defbody">
224		<a name="idx:atom:2272"></a>Textual constant. Used as name for <a class="gloss" href="glossary.html#gloss:compound">compound</a>
	261	See <a id="idx:asserta1:2274"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
	262	and <a id="idx:assertz1:2275"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>.</dd>
	263	<dt><a id="gloss:atom"><strong>atom</strong></a></dt>
	264	<dd class="defbody">
	265	<a id="idx:atom:2276"></a>Textual constant. Used as name for <a class="gloss" href="glossary.html#gloss:compound">compound</a>
225	266	terms, to represent constants or text.</dd>
226		<dt><a name="gloss:backtracking"><strong>backtracking</strong></a></dt>
227		<dd class="defbody">
228		<a name="idx:backtracking:2273"></a>Search process used by Prolog. If a
	267	<dt><a id="gloss:backtracking"><strong>backtracking</strong></a></dt>
	268	<dd class="defbody">
	269	<a id="idx:backtracking:2277"></a>Search process used by Prolog. If a
229	270	predicate offers multiple
230	271	<a class="gloss" href="glossary.html#gloss:clause">clauses</a> to solve
231	272	a <a class="gloss" href="glossary.html#gloss:goal">goal</a>, they are

236	277	the <a class="gloss" href="glossary.html#gloss:variable">variables</a>),
237	278	causing Prolog to reject the previously chosen <a class="gloss" href="glossary.html#gloss:clause">clause</a>
238	279	and try the next one.</dd>
239		<dt><a name="gloss:binding"><strong>binding [of a variable]</strong></a></dt>
240		<dd class="defbody">
241		<a name="idx:binding:2274"></a>Current value of the <a class="gloss" href="glossary.html#gloss:variable">variable</a>.
	280	<dt><a id="gloss:binding"><strong>binding [of a variable]</strong></a></dt>
	281	<dd class="defbody">
	282	<a id="idx:binding:2278"></a>Current value of the <a class="gloss" href="glossary.html#gloss:variable">variable</a>.
242	283	See also <a class="gloss" href="glossary.html#gloss:backtracking">backtracking</a>
243	284	and
244	285	<a class="gloss" href="glossary.html#gloss:query">query</a>.</dd>
245		<dt><a name="gloss:built-in"><strong>built-in [predicate]</strong></a></dt>
246		<dd class="defbody">
247		<a name="idx:builtinpredicate:2275"></a>Predicate that is part of the
	286	<dt><a id="gloss:built-in"><strong>built-in [predicate]</strong></a></dt>
	287	<dd class="defbody">
	288	<a id="idx:builtinpredicate:2279"></a>Predicate that is part of the
248	289	Prolog system. Built-in predicates cannot be redefined by the user,
249	290	unless this is overruled using
250		<a name="idx:redefinesystempredicate1:2276"></a><a class="pred" href="db.html#redefine_system_predicate/1">redefine_system_predicate/1</a>.</dd>
251		<dt><a name="gloss:body"><strong>body</strong></a></dt>
252		<dd class="defbody">
253		<a name="idx:body:2277"></a>Part of a <a class="gloss" href="glossary.html#gloss:clause">clause</a>
	291	<a id="idx:redefinesystempredicate1:2280"></a><a class="pred" href="db.html#redefine_system_predicate/1">redefine_system_predicate/1</a>.</dd>
	292	<dt><a id="gloss:body"><strong>body</strong></a></dt>
	293	<dd class="defbody">
	294	<a id="idx:body:2281"></a>Part of a <a class="gloss" href="glossary.html#gloss:clause">clause</a>
254	295	behind the <a class="gloss" href="glossary.html#gloss:neck">neck</a>
255	296	operator (<code><code>:-</code></code>).</dd>
256		<dt><a name="gloss:choice-point"><strong>choice point</strong></a></dt>
257		<dd class="defbody">
258		<a name="idx:choicepoint:2278"></a>A <a class="gloss" href="glossary.html#gloss:choice-point">choice point</a>
	297	<dt><a id="gloss:choice-point"><strong>choice point</strong></a></dt>
	298	<dd class="defbody">
	299	<a id="idx:choicepoint:2282"></a>A <a class="gloss" href="glossary.html#gloss:choice-point">choice point</a>
259	300	represents a choice in the search for a <a class="gloss" href="glossary.html#gloss:solution">solution</a>.
260	301	Choice points are created if multiple clauses match a <a class="gloss" href="glossary.html#gloss:query">query</a>
261	302	or using disjunction (<a class="pred" href="control.html#;/2">;/2</a>).

264	305	is restored and search continues with the next alternative (i.e., next
265	306	clause or second branch of
266	307	<a class="pred" href="control.html#;/2">;/2</a>).</dd>
267		<dt><a name="gloss:clause"><strong>clause</strong></a></dt>
268		<dd class="defbody">
269		<a name="idx:clause:2279"></a>`Sentence' of a Prolog program. A <a class="gloss" href="glossary.html#gloss:clause">clause</a>
	308	<dt><a id="gloss:clause"><strong>clause</strong></a></dt>
	309	<dd class="defbody">
	310	<a id="idx:clause:2283"></a>`Sentence' of a Prolog program. A <a class="gloss" href="glossary.html#gloss:clause">clause</a>
270	311	consists of a <a class="gloss" href="glossary.html#gloss:head">head</a>
271	312	and
272	313	<a class="gloss" href="glossary.html#gloss:body">body</a> separated by

281	322
282	323	<p>Expressed as ``X is a parent if X is a father of someone''. See also
283	324	<a class="gloss" href="glossary.html#gloss:variable">variable</a> and <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>.</dd>
284		<dt><a name="gloss:compile"><strong>compile</strong></a></dt>
	325	<dt><a id="gloss:compile"><strong>compile</strong></a></dt>
285	326	<dd class="defbody">
286	327	Process where a Prolog <a class="gloss" href="glossary.html#gloss:program">program</a>
287	328	is translated to a sequence of instructions. See also <a class="gloss" href="glossary.html#gloss:interpreted">interpreted</a>.
288	329	SWI-Prolog always compiles your program before executing it.</dd>
289		<dt><a name="gloss:compound"><strong>compound [term]</strong></a></dt>
290		<dd class="defbody">
291		<a name="idx:compound:2280"></a>Also called <a class="gloss" href="glossary.html#gloss:structure">structure</a>.
	330	<dt><a id="gloss:compound"><strong>compound [term]</strong></a></dt>
	331	<dd class="defbody">
	332	<a id="idx:compound:2284"></a>Also called <a class="gloss" href="glossary.html#gloss:structure">structure</a>.
292	333	It consists of a name followed by <var>N</var>
293	334	<a class="gloss" href="glossary.html#gloss:argument">arguments</a>, each
294	335	of which are <a class="gloss" href="glossary.html#gloss:term">terms</a>. <var>N</var>
295	336	is called the
296	337	<a class="gloss" href="glossary.html#gloss:arity">arity</a> of the term.</dd>
297		<dt><a name="gloss:context-module"><strong>context module</strong></a></dt>
298		<dd class="defbody">
299		<a name="idx:contextmodule:2281"></a><a name="idx:modulecontex:2282"></a>If
	338	<dt><a id="gloss:context-module"><strong>context module</strong></a></dt>
	339	<dd class="defbody">
	340	<a id="idx:contextmodule:2285"></a><a id="idx:modulecontex:2286"></a>If
300	341	a <a class="gloss" href="glossary.html#gloss:term">term</a> is referring
301	342	to a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
302	343	in a <a class="gloss" href="glossary.html#gloss:module">module</a>, the

307	348	is <a class="gloss" href="glossary.html#gloss:module-transparent">module transparent</a>,
308	349	in which case the <a class="gloss" href="glossary.html#gloss:context-module">context module</a>
309	350	is inherited from the parent
310		<a class="gloss" href="glossary.html#gloss:goal">goal</a>. See also <a name="idx:moduletransparent1:2283"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>
	351	<a class="gloss" href="glossary.html#gloss:goal">goal</a>. See also <a id="idx:moduletransparent1:2287"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>
311	352	and <a class="gloss" href="glossary.html#gloss:meta-predicate">meta-predicate</a>.</dd>
312		<dt><a name="gloss:dcg"><strong>dcg</strong></a></dt>
313		<dd class="defbody">
314		<a name="idx:dcg:2284"></a>Abbreviation for <b>Definite Clause Grammar</b>.</dd>
315		<dt><a name="gloss:det"><strong>det [determinism]</strong></a></dt>
316		<dd class="defbody">
317		<a name="idx:det:2285"></a>Short for <a class="gloss" href="glossary.html#gloss:deterministic">deterministic</a>.</dd>
318		<dt><a name="gloss:determinism"><strong>determinism</strong></a></dt>
319		<dd class="defbody">
320		<a name="idx:determinism:2286"></a>How many solutions a <a class="gloss" href="glossary.html#gloss:goal">goal</a>
	353	<dt><a id="gloss:dcg"><strong>dcg</strong></a></dt>
	354	<dd class="defbody">
	355	<a id="idx:dcg:2288"></a>Abbreviation for <b>Definite Clause Grammar</b>.</dd>
	356	<dt><a id="gloss:det"><strong>det [determinism]</strong></a></dt>
	357	<dd class="defbody">
	358	<a id="idx:det:2289"></a>Short for <a class="gloss" href="glossary.html#gloss:deterministic">deterministic</a>.</dd>
	359	<dt><a id="gloss:determinism"><strong>determinism</strong></a></dt>
	360	<dd class="defbody">
	361	<a id="idx:determinism:2290"></a>How many solutions a <a class="gloss" href="glossary.html#gloss:goal">goal</a>
321	362	can provide. Values are `nondet' (zero to infinite), `multi' (one to
322	363	infinite), `det' (exactly one) and `semidet' (zero or one).</dd>
323		<dt><a name="gloss:deterministic"><strong>deterministic</strong></a></dt>
324		<dd class="defbody">
325		<a name="idx:deterministic:2287"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
	364	<dt><a id="gloss:deterministic"><strong>deterministic</strong></a></dt>
	365	<dd class="defbody">
	366	<a id="idx:deterministic:2291"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
326	367	is <a class="gloss" href="glossary.html#gloss:deterministic">deterministic</a>
327	368	if it succeeds exactly one time without leaving a <a class="gloss" href="glossary.html#gloss:choice-point">choice point</a>.</dd>
328		<dt><a name="gloss:dynamic"><strong>dynamic [predicate]</strong></a></dt>
329		<dd class="defbody">
330		<a name="idx:dynamicpredicate:2288"></a><a name="idx:predicatedynamic:2289"></a>A <a class="gloss" href="glossary.html#gloss:dynamic">dynamic</a>
	369	<dt><a id="gloss:dynamic"><strong>dynamic [predicate]</strong></a></dt>
	370	<dd class="defbody">
	371	<a id="idx:dynamicpredicate:2292"></a><a id="idx:predicatedynamic:2293"></a>A <a class="gloss" href="glossary.html#gloss:dynamic">dynamic</a>
331	372	predicate is a predicate to which <a class="gloss" href="glossary.html#gloss:clause">clauses</a>
332	373	may be
333	374	<a class="gloss" href="glossary.html#gloss:assert">assert</a>ed and from
334	375	which <a class="gloss" href="glossary.html#gloss:clause">clauses</a> may
335	376	be <a class="gloss" href="glossary.html#gloss:retract">retract</a>ed
336	377	while the program is running. See also <a class="gloss" href="glossary.html#gloss:update-view">update view</a>.</dd>
337		<dt><a name="gloss:exported"><strong>exported [predicate]</strong></a></dt>
338		<dd class="defbody">
339		<a name="idx:exportedpredicate:2290"></a><a name="idx:predicateexported:2291"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
	378	<dt><a id="gloss:exported"><strong>exported [predicate]</strong></a></dt>
	379	<dd class="defbody">
	380	<a id="idx:exportedpredicate:2294"></a><a id="idx:predicateexported:2295"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
340	381	is said to be <a class="gloss" href="glossary.html#gloss:exported">exported</a>
341	382	from a <a class="gloss" href="glossary.html#gloss:module">module</a> if
342	383	it appears in the <a class="gloss" href="glossary.html#gloss:public-list">public list</a>.
343	384	This implies that the predicate can be <a class="gloss" href="glossary.html#gloss:imported">imported</a>
344		into another module to make it visible there. See also <a name="idx:usemodule12:2292"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.</dd>
345		<dt><a name="gloss:fact"><strong>fact</strong></a></dt>
346		<dd class="defbody">
347		<a name="idx:fact:2293"></a><a class="gloss" href="glossary.html#gloss:clause">Clause</a>
	385	into another module to make it visible there. See also <a id="idx:usemodule12:2296"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>.</dd>
	386	<dt><a id="gloss:fact"><strong>fact</strong></a></dt>
	387	<dd class="defbody">
	388	<a id="idx:fact:2297"></a><a class="gloss" href="glossary.html#gloss:clause">Clause</a>
348	389	without a <a class="gloss" href="glossary.html#gloss:body">body</a>.
349	390	This is called a fact because, interpreted as logic, there is no
350	391	condition to be satisfied. The example below states <code>john</code> is

355	396	</pre>
356	397
357	398	</dd>
358		<dt><a name="gloss:fail"><strong>fail</strong></a></dt>
	399	<dt><a id="gloss:fail"><strong>fail</strong></a></dt>
359	400	<dd class="defbody">
360	401	A <a class="gloss" href="glossary.html#gloss:goal">goal</a> is said to
361	402	haved failed if it could not be <a class="gloss" href="glossary.html#gloss:prove">proven</a>.</dd>
362		<dt><a name="gloss:float"><strong>float</strong></a></dt>
	403	<dt><a id="gloss:float"><strong>float</strong></a></dt>
363	404	<dd class="defbody">
364	405	Computer's crippled representation of a real number. Represented as
365	406	`IEEE double'.</dd>
366		<dt><a name="gloss:foreign"><strong>foreign</strong></a></dt>
	407	<dt><a id="gloss:foreign"><strong>foreign</strong></a></dt>
367	408	<dd class="defbody">
368	409	Computer code expressed in languages other than Prolog. SWI-Prolog can
369	410	only cooperate directly with the C and C++ computer languages.</dd>
370		<dt><a name="gloss:functor"><strong>functor</strong></a></dt>
371		<dd class="defbody">
372		<a name="idx:functor:2294"></a>Combination of name and <a class="gloss" href="glossary.html#gloss:arity">arity</a>
	411	<dt><a id="gloss:functor"><strong>functor</strong></a></dt>
	412	<dd class="defbody">
	413	<a id="idx:functor:2298"></a>Combination of name and <a class="gloss" href="glossary.html#gloss:arity">arity</a>
373	414	of a <a class="gloss" href="glossary.html#gloss:compound">compound</a>
374	415	term. The term
375	416	<code>foo(a, b, c)</code> is said to be a term belonging to the functor
376	417	foo/3 . foo/0 is used to refer to the <a class="gloss" href="glossary.html#gloss:atom">atom</a>
377	418	<code>foo</code>.</dd>
378		<dt><a name="gloss:goal"><strong>goal</strong></a></dt>
379		<dd class="defbody">
380		<a name="idx:goal:2295"></a><a name="idx:query:2296"></a>Question stated
381		to the Prolog engine. A <a class="gloss" href="glossary.html#gloss:goal">goal</a>
	419	<dt><a id="gloss:goal"><strong>goal</strong></a></dt>
	420	<dd class="defbody">
	421	<a id="idx:goal:2299"></a><a id="idx:query:2300"></a>Question stated to
	422	the Prolog engine. A <a class="gloss" href="glossary.html#gloss:goal">goal</a>
382	423	is either an <a class="gloss" href="glossary.html#gloss:atom">atom</a>
383	424	or a <a class="gloss" href="glossary.html#gloss:compound">compound</a>
384	425	term. A <a class="gloss" href="glossary.html#gloss:goal">goal</a> either

388	429	terms have a <a class="gloss" href="glossary.html#gloss:binding">binding</a>,
389	430	or it <a class="gloss" href="glossary.html#gloss:fail">fails</a> if
390	431	Prolog fails to prove it.</dd>
391		<dt><a name="gloss:hashing"><strong>hashing</strong></a></dt>
392		<dd class="defbody">
393		<a name="idx:hashing:2297"></a><a class="gloss" href="glossary.html#gloss:indexing">Indexing</a>
	432	<dt><a id="gloss:hashing"><strong>hashing</strong></a></dt>
	433	<dd class="defbody">
	434	<a id="idx:hashing:2301"></a><a class="gloss" href="glossary.html#gloss:indexing">Indexing</a>
394	435	technique used for quick lookup.</dd>
395		<dt><a name="gloss:head"><strong>head</strong></a></dt>
396		<dd class="defbody">
397		<a name="idx:head:2298"></a>Part of a <a class="gloss" href="glossary.html#gloss:clause">clause</a>
	436	<dt><a id="gloss:head"><strong>head</strong></a></dt>
	437	<dd class="defbody">
	438	<a id="idx:head:2302"></a>Part of a <a class="gloss" href="glossary.html#gloss:clause">clause</a>
398	439	before the <a class="gloss" href="glossary.html#gloss:neck">neck</a>
399	440	operator (<code><code>:-</code></code>). This is an <a class="gloss" href="glossary.html#gloss:atom">atom</a>
400	441	or <a class="gloss" href="glossary.html#gloss:compound">compound</a>
401	442	term.</dd>
402		<dt><a name="gloss:imported"><strong>imported [predicate]</strong></a></dt>
403		<dd class="defbody">
404		<a name="idx:importedpredicate:2299"></a><a name="idx:predicateimported:2300"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
	443	<dt><a id="gloss:imported"><strong>imported [predicate]</strong></a></dt>
	444	<dd class="defbody">
	445	<a id="idx:importedpredicate:2303"></a><a id="idx:predicateimported:2304"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
405	446	is said to be <a class="gloss" href="glossary.html#gloss:imported">imported</a>
406	447	into a <a class="gloss" href="glossary.html#gloss:module">module</a> if
407	448	it is defined in another <a class="gloss" href="glossary.html#gloss:module">module</a>
408	449	and made available in this <a class="gloss" href="glossary.html#gloss:module">module</a>.
409		See also <a class="sec" href="modules.html">chapter 6</a>.</dd>
410		<dt><a name="gloss:indexing"><strong>indexing</strong></a></dt>
411		<dd class="defbody">
412		<a name="idx:indexing:2301"></a>Indexing is a technique used to quickly
	450	See also <a class="sec" href="modules.html#sec:6">chapter 6</a>.</dd>
	451	<dt><a id="gloss:indexing"><strong>indexing</strong></a></dt>
	452	<dd class="defbody">
	453	<a id="idx:indexing:2305"></a>Indexing is a technique used to quickly
413	454	select candidate <a class="gloss" href="glossary.html#gloss:clause">clauses</a>
414	455	of a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
415	456	for a specific <a class="gloss" href="glossary.html#gloss:goal">goal</a>.

422	463	is used to quickly select all <a class="gloss" href="glossary.html#gloss:clause">clauses</a>
423	464	where the first argument may <a class="gloss" href="glossary.html#gloss:unify">unify</a>
424	465	with the first argument of the <a class="gloss" href="glossary.html#gloss:goal">goal</a>.
425		SWI-Prolog supports just-in-time and multi-argument indexing. See <a class="sec" href="jitindex.html">section
	466	SWI-Prolog supports just-in-time and multi-argument indexing. See <a class="sec" href="jitindex.html#sec:2.18">section
426	467	2.18</a>.</dd>
427		<dt><a name="gloss:integer"><strong>integer</strong></a></dt>
428		<dd class="defbody">
429		<a name="idx:integer:2302"></a>Whole number. On all implementations of
	468	<dt><a id="gloss:integer"><strong>integer</strong></a></dt>
	469	<dd class="defbody">
	470	<a id="idx:integer:2306"></a>Whole number. On all implementations of
430	471	SWI-Prolog integers are at least 64-bit signed values. When linked to
431		the GNU GMP library, integer arithmetic is unbounded. See also <a name="idx:currentprologflag2:2303"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>,
	472	the GNU GMP library, integer arithmetic is unbounded. See also <a id="idx:currentprologflag2:2307"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>,
432	473	flags <a class="flag" href="flags.html#flag:bounded">bounded</a>, <a class="flag" href="flags.html#flag:max_integer">max_integer</a>
433	474	and <a class="flag" href="flags.html#flag:min_integer">min_integer</a>.</dd>
434		<dt><a name="gloss:interpreted"><strong>interpreted</strong></a></dt>
435		<dd class="defbody">
436		<a name="idx:interpreted:2304"></a>As opposed to <a class="gloss" href="glossary.html#gloss:compile">compiled</a>,
	475	<dt><a id="gloss:interpreted"><strong>interpreted</strong></a></dt>
	476	<dd class="defbody">
	477	<a id="idx:interpreted:2308"></a>As opposed to <a class="gloss" href="glossary.html#gloss:compile">compiled</a>,
437	478	interpreted means the Prolog system attempts to prove a <a class="gloss" href="glossary.html#gloss:goal">goal</a>
438	479	by directly reading the <a class="gloss" href="glossary.html#gloss:clause">clauses</a>
439	480	rather than executing instructions from an (abstract) instruction set
440	481	that is not or only indirectly related to Prolog.</dd>
441		<dt><a name="gloss:instantiation"><strong>instantiation [of an argument]</strong></a></dt>
442		<dd class="defbody">
443		<a name="idx:instantiation:2305"></a>To what extend a term is bound to a
	482	<dt><a id="gloss:instantiation"><strong>instantiation [of an argument]</strong></a></dt>
	483	<dd class="defbody">
	484	<a id="idx:instantiation:2309"></a>To what extend a term is bound to a
444	485	value. Typical levels are `unbound' (a <a class="gloss" href="glossary.html#gloss:variable">variable</a>),
445	486	`ground' (term without variables) or `partially bound' (term with
446	487	embedded variables).</dd>
447		<dt><a name="gloss:meta-predicate"><strong>meta-predicate</strong></a></dt>
448		<dd class="defbody">
449		<a name="idx:metapredicate:2306"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
	488	<dt><a id="gloss:meta-predicate"><strong>meta-predicate</strong></a></dt>
	489	<dd class="defbody">
	490	<a id="idx:metapredicate:2310"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
450	491	that reasons about other <a class="gloss" href="glossary.html#gloss:predicate">predicates</a>,
451	492	either by calling them, (re)defining them or querying <a class="gloss" href="glossary.html#gloss:property">properties</a>.</dd>
452		<dt><a name="gloss:mode"><strong>mode [declaration]</strong></a></dt>
453		<dd class="defbody">
454		<a name="idx:mode:2307"></a>Declaration of an argument <a class="gloss" href="glossary.html#gloss:instantiation">instantiation</a>
	493	<dt><a id="gloss:mode"><strong>mode [declaration]</strong></a></dt>
	494	<dd class="defbody">
	495	<a id="idx:mode:2311"></a>Declaration of an argument <a class="gloss" href="glossary.html#gloss:instantiation">instantiation</a>
455	496	pattern for a
456	497	<a class="gloss" href="glossary.html#gloss:predicate">predicate</a>,
457	498	often accompanied with a <a class="gloss" href="glossary.html#gloss:determinism">determinism</a>.</dd>
458		<dt><a name="gloss:module"><strong>module</strong></a></dt>
459		<dd class="defbody">
460		<a name="idx:module:2308"></a>Collection of predicates. Each module
	499	<dt><a id="gloss:module"><strong>module</strong></a></dt>
	500	<dd class="defbody">
	501	<a id="idx:module:2312"></a>Collection of predicates. Each module
461	502	defines a name-space for predicates. <a class="gloss" href="glossary.html#gloss:built-in">built-in</a>
462	503	predicates are accessible from all modules. Predicates can be published
463	504	(<a class="gloss" href="glossary.html#gloss:exported">exported</a>) and <a class="gloss" href="glossary.html#gloss:imported">imported</a>
464	505	to make their definition available to other modules.</dd>
465		<dt><a name="gloss:module-transparent"><strong>module transparent [predicate]</strong></a></dt>
466		<dd class="defbody">
467		<a name="idx:moduletransparent:2309"></a><a name="idx:transparent:2310"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
	506	<dt><a id="gloss:module-transparent"><strong>module transparent [predicate]</strong></a></dt>
	507	<dd class="defbody">
	508	<a id="idx:moduletransparent:2313"></a><a id="idx:transparent:2314"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
468	509	that does not change the <a class="gloss" href="glossary.html#gloss:context-module">context module</a>.
469	510	Sometimes also called a <a class="gloss" href="glossary.html#gloss:meta-predicate">meta-predicate</a>.</dd>
470		<dt><a name="gloss:multi"><strong>multi [determinism]</strong></a></dt>
471		<dd class="defbody">
472		<a name="idx:multi:2311"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
	511	<dt><a id="gloss:multi"><strong>multi [determinism]</strong></a></dt>
	512	<dd class="defbody">
	513	<a id="idx:multi:2315"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
473	514	is said to have <a class="gloss" href="glossary.html#gloss:determinism">determinism</a>
474	515	multi if it generates at
475	516	<em>least</em> one answer.</dd>
476		<dt><a name="gloss:multifile"><strong>multifile [predicate]</strong></a></dt>
	517	<dt><a id="gloss:multifile"><strong>multifile [predicate]</strong></a></dt>
477	518	<dd class="defbody">
478	519	Predicate for which the definition is distributed over multiple source
479		files. See <a name="idx:multifile1:2312"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.</dd>
480		<dt><a name="gloss:neck"><strong>neck</strong></a></dt>
481		<dd class="defbody">
482		<a name="idx:neck:2313"></a>Operator (<code><code>:-</code></code>)
	520	files. See <a id="idx:multifile1:2316"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.</dd>
	521	<dt><a id="gloss:neck"><strong>neck</strong></a></dt>
	522	<dd class="defbody">
	523	<a id="idx:neck:2317"></a>Operator (<code><code>:-</code></code>)
483	524	separating <a class="gloss" href="glossary.html#gloss:head">head</a>
484	525	from <a class="gloss" href="glossary.html#gloss:body">body</a> in a <a class="gloss" href="glossary.html#gloss:clause">clause</a>.</dd>
485		<dt><a name="gloss:nondet"><strong>nondet</strong></a></dt>
486		<dd class="defbody">
487		<a name="idx:nondet:2314"></a>Short for <a class="gloss" href="glossary.html#gloss:non-deterministic">non deterministic</a>.</dd>
488		<dt><a name="gloss:non-deterministic"><strong>non deterministic</strong></a></dt>
489		<dd class="defbody">
490		<a name="idx:nondeterministic:2315"></a>A <a class="gloss" href="glossary.html#gloss:non-deterministic">non deterministic</a>
	526	<dt><a id="gloss:nondet"><strong>nondet</strong></a></dt>
	527	<dd class="defbody">
	528	<a id="idx:nondet:2318"></a>Short for <a class="gloss" href="glossary.html#gloss:non-deterministic">non deterministic</a>.</dd>
	529	<dt><a id="gloss:non-deterministic"><strong>non deterministic</strong></a></dt>
	530	<dd class="defbody">
	531	<a id="idx:nondeterministic:2319"></a>A <a class="gloss" href="glossary.html#gloss:non-deterministic">non deterministic</a>
491	532	predicate is a predicate that mail fail or succeed any number of times.</dd>
492		<dt><a name="gloss:operator"><strong>operator</strong></a></dt>
493		<dd class="defbody">
494		<a name="idx:operator:2316"></a>Symbol (<a class="gloss" href="glossary.html#gloss:atom">atom</a>)
	533	<dt><a id="gloss:operator"><strong>operator</strong></a></dt>
	534	<dd class="defbody">
	535	<a id="idx:operator:2320"></a>Symbol (<a class="gloss" href="glossary.html#gloss:atom">atom</a>)
495	536	that may be placed before its <a class="gloss" href="glossary.html#gloss:operand">operand</a>
496	537	(prefix), after its <a class="gloss" href="glossary.html#gloss:operand">operand</a>
497	538	(postfix) or between its two <a class="gloss" href="glossary.html#gloss:operand">operands</a>

499	540
500	541	<p>In Prolog, the expression <code>a+b</code> is exactly the same as the
501	542	canonical term <code>+(a,b)</code>.</dd>
502		<dt><a name="gloss:operand"><strong>operand</strong></a></dt>
503		<dd class="defbody">
504		<a name="idx:operand:2317"></a><a class="gloss" href="glossary.html#gloss:argument">Argument</a>
	543	<dt><a id="gloss:operand"><strong>operand</strong></a></dt>
	544	<dd class="defbody">
	545	<a id="idx:operand:2321"></a><a class="gloss" href="glossary.html#gloss:argument">Argument</a>
505	546	of an <a class="gloss" href="glossary.html#gloss:operator">operator</a>.</dd>
506		<dt><a name="gloss:precedence"><strong>precedence</strong></a></dt>
507		<dd class="defbody">
508		<a name="idx:precedence:2318"></a>The <a class="gloss" href="glossary.html#gloss:priority">priority</a>
	547	<dt><a id="gloss:precedence"><strong>precedence</strong></a></dt>
	548	<dd class="defbody">
	549	<a id="idx:precedence:2322"></a>The <a class="gloss" href="glossary.html#gloss:priority">priority</a>
509	550	of an <a class="gloss" href="glossary.html#gloss:operator">operator</a>.
510	551	Operator precedence is used to interpret <code>a+bc</code> as <code>+(a, (b,c))</code>.</dd>
511		<dt><a name="gloss:predicate"><strong>predicate</strong></a></dt>
512		<dd class="defbody">
513		<a name="idx:predicate:2319"></a>Collection of <a class="gloss" href="glossary.html#gloss:clause">clauses</a>
	552	<dt><a id="gloss:predicate"><strong>predicate</strong></a></dt>
	553	<dd class="defbody">
	554	<a id="idx:predicate:2323"></a>Collection of <a class="gloss" href="glossary.html#gloss:clause">clauses</a>
514	555	with the same <a class="gloss" href="glossary.html#gloss:functor">functor</a>
515	556	(name/<a class="gloss" href="glossary.html#gloss:arity">arity</a>). If a <a class="gloss" href="glossary.html#gloss:goal">goal</a>
516	557	is proved, the system looks for a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>

518	559	to select candidate <a class="gloss" href="glossary.html#gloss:clause">clauses</a>
519	560	and then tries these <a class="gloss" href="glossary.html#gloss:clause">clauses</a>
520	561	one-by-one. See also <a class="gloss" href="glossary.html#gloss:backtracking">backtracking</a>.</dd>
521		<dt><a name="gloss:predicate-indicator"><strong>predicate indicator</strong></a></dt>
522		<dd class="defbody">
523		<a name="idx:predicateindicator:2320"></a>Term of the form Name/Arity
	562	<dt><a id="gloss:predicate-indicator"><strong>predicate indicator</strong></a></dt>
	563	<dd class="defbody">
	564	<a id="idx:predicateindicator:2324"></a>Term of the form Name/Arity
524	565	(traditional) or Name//Arity (ISO DCG proposal), where Name is an atom
525	566	and Arity a non-negative integer. It acts as an <em>indicator</em> (or
526	567	reference) to a predicate or
527	568	<a class="gloss" href="glossary.html#gloss:dcg">DCG</a> rule.</dd>
528		<dt><a name="gloss:priority"><strong>priority</strong></a></dt>
529		<dd class="defbody">
530		<a name="idx:priority:2321"></a>In the context of <a class="gloss" href="glossary.html#gloss:operator">operators</a>
	569	<dt><a id="gloss:priority"><strong>priority</strong></a></dt>
	570	<dd class="defbody">
	571	<a id="idx:priority:2325"></a>In the context of <a class="gloss" href="glossary.html#gloss:operator">operators</a>
531	572	a synonym for <a class="gloss" href="glossary.html#gloss:precedence">precedence</a>.</dd>
532		<dt><a name="gloss:program"><strong>program</strong></a></dt>
533		<dd class="defbody">
534		<a name="idx:program:2322"></a>Collection of <a class="gloss" href="glossary.html#gloss:predicate">predicates</a>.</dd>
535		<dt><a name="gloss:property"><strong>property</strong></a></dt>
536		<dd class="defbody">
537		<a name="idx:property:2323"></a>Attribute of an object. SWI-Prolog
538		defines various <em>*_property</em> predicates to query the status of
	573	<dt><a id="gloss:program"><strong>program</strong></a></dt>
	574	<dd class="defbody">
	575	<a id="idx:program:2326"></a>Collection of <a class="gloss" href="glossary.html#gloss:predicate">predicates</a>.</dd>
	576	<dt><a id="gloss:property"><strong>property</strong></a></dt>
	577	<dd class="defbody">
	578	<a id="idx:property:2327"></a>Attribute of an object. SWI-Prolog defines
	579	various <em>*_property</em> predicates to query the status of
539	580	predicates, clauses. etc.</dd>
540		<dt><a name="gloss:prove"><strong>prove</strong></a></dt>
541		<dd class="defbody">
542		<a name="idx:prove:2324"></a>Process where Prolog attempts to prove a <a class="gloss" href="glossary.html#gloss:query">query</a>
	581	<dt><a id="gloss:prove"><strong>prove</strong></a></dt>
	582	<dd class="defbody">
	583	<a id="idx:prove:2328"></a>Process where Prolog attempts to prove a <a class="gloss" href="glossary.html#gloss:query">query</a>
543	584	using the available
544	585	<a class="gloss" href="glossary.html#gloss:predicate">predicates</a>.</dd>
545		<dt><a name="gloss:public-list"><strong>public list</strong></a></dt>
546		<dd class="defbody">
547		<a name="idx:publiclist:2325"></a>List of <a class="gloss" href="glossary.html#gloss:predicate">predicates</a>
	586	<dt><a id="gloss:public-list"><strong>public list</strong></a></dt>
	587	<dd class="defbody">
	588	<a id="idx:publiclist:2329"></a>List of <a class="gloss" href="glossary.html#gloss:predicate">predicates</a>
548	589	exported from a <a class="gloss" href="glossary.html#gloss:module">module</a>.</dd>
549		<dt><a name="gloss:query"><strong>query</strong></a></dt>
	590	<dt><a id="gloss:query"><strong>query</strong></a></dt>
550	591	<dd class="defbody">
551	592	See <a class="gloss" href="glossary.html#gloss:goal">goal</a>.</dd>
552		<dt><a name="gloss:retract"><strong>retract</strong></a></dt>
553		<dd class="defbody">
554		<a name="idx:retract:2326"></a>Remove a <a class="gloss" href="glossary.html#gloss:clause">clause</a>
	593	<dt><a id="gloss:retract"><strong>retract</strong></a></dt>
	594	<dd class="defbody">
	595	<a id="idx:retract:2330"></a>Remove a <a class="gloss" href="glossary.html#gloss:clause">clause</a>
555	596	from a <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>.
556	597	See also <a class="gloss" href="glossary.html#gloss:dynamic">dynamic</a>,
557	598	<a class="gloss" href="glossary.html#gloss:update-view">update view</a>
558	599	and <a class="gloss" href="glossary.html#gloss:assert">assert</a>.</dd>
559		<dt><a name="gloss:semidet"><strong>semidet</strong></a></dt>
560		<dd class="defbody">
561		<a name="idx:semidet:2327"></a>Shorthand for </dd>
562		<dt><a name="gloss:semi-deterministic"><strong>semi deterministic</strong></a></dt>
	600	<dt><a id="gloss:semidet"><strong>semidet</strong></a></dt>
	601	<dd class="defbody">
	602	<a id="idx:semidet:2331"></a>Shorthand for </dd>
	603	<dt><a id="gloss:semi-deterministic"><strong>semi deterministic</strong></a></dt>
563	604	<dd class="defbody">
564	605	.</dd>
565		<dt><a name="gloss:semi-deterministic"><strong>semi deterministic</strong></a></dt>
566		<dd class="defbody">
567		<a name="idx:semideterministic:2328"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
	606	<dt><a id="gloss:semi-deterministic"><strong>semi deterministic</strong></a></dt>
	607	<dd class="defbody">
	608	<a id="idx:semideterministic:2332"></a>A <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
568	609	that is <a class="gloss" href="glossary.html#gloss:semi-deterministic">semi deterministic</a>
569	610	either fails or succeeds exactly once without a <a class="gloss" href="glossary.html#gloss:choice-point">choice point</a>.
570	611	See also
571	612	<a class="gloss" href="glossary.html#gloss:deterministic">deterministic</a>.</dd>
572		<dt><a name="gloss:shared"><strong>shared</strong></a></dt>
573		<dd class="defbody">
574		<a name="idx:shared:2329"></a>Two <a class="gloss" href="glossary.html#gloss:variable">variables</a>
	613	<dt><a id="gloss:shared"><strong>shared</strong></a></dt>
	614	<dd class="defbody">
	615	<a id="idx:shared:2333"></a>Two <a class="gloss" href="glossary.html#gloss:variable">variables</a>
575	616	are called <a class="gloss" href="glossary.html#gloss:shared">shared</a>
576	617	after they are <a class="gloss" href="glossary.html#gloss:unify">unified</a>.
577	618	This implies if either of them is <a class="gloss" href="glossary.html#gloss:binding">bound</a>,

583	624	</pre>
584	625
585	626	</dd>
586		<dt><a name="gloss:singleton"><strong>singleton [variable]</strong></a></dt>
587		<dd class="defbody">
588		<a name="idx:singleton:2330"></a><a class="gloss" href="glossary.html#gloss:variable">Variable</a>
	627	<dt><a id="gloss:singleton"><strong>singleton [variable]</strong></a></dt>
	628	<dd class="defbody">
	629	<a id="idx:singleton:2334"></a><a class="gloss" href="glossary.html#gloss:variable">Variable</a>
589	630	appearing only one time in a <a class="gloss" href="glossary.html#gloss:clause">clause</a>.
590	631	SWI-Prolog normally warns for this to avoid you making spelling
591	632	mistakes. If a variable appears on purpose only once in a clause, write
592	633	it as <code>_</code> (see <a class="gloss" href="glossary.html#gloss:anonymou">anonymous</a>).
593		Rules for naming a variable and avoiding a warning are given in <a class="sec" href="syntax.html">section
	634	Rules for naming a variable and avoiding a warning are given in <a class="sec" href="syntax.html#sec:2.16.1.9">section
594	635	2.16.1.9</a>.</dd>
595		<dt><a name="gloss:solution"><strong>solution</strong></a></dt>
596		<dd class="defbody">
597		<a name="idx:solution:2331"></a><a class="gloss" href="glossary.html#gloss:binding">Bindings</a>
	636	<dt><a id="gloss:solution"><strong>solution</strong></a></dt>
	637	<dd class="defbody">
	638	<a id="idx:solution:2335"></a><a class="gloss" href="glossary.html#gloss:binding">Bindings</a>
598	639	resulting from a successfully <a class="gloss" href="glossary.html#gloss:prove">prove</a>n <a class="gloss" href="glossary.html#gloss:goal">goal</a>.</dd>
599		<dt><a name="gloss:structure"><strong>structure</strong></a></dt>
600		<dd class="defbody">
601		<a name="idx:structure:2332"></a>Synonym for <a class="gloss" href="glossary.html#gloss:compound">compound</a>
	640	<dt><a id="gloss:structure"><strong>structure</strong></a></dt>
	641	<dd class="defbody">
	642	<a id="idx:structure:2336"></a>Synonym for <a class="gloss" href="glossary.html#gloss:compound">compound</a>
602	643	term.</dd>
603		<dt><a name="gloss:string"><strong>string</strong></a></dt>
604		<dd class="defbody">
605		Used for the following representations of text: a packed array (see <a class="sec" href="strings.html">section
	644	<dt><a id="gloss:string"><strong>string</strong></a></dt>
	645	<dd class="defbody">
	646	Used for the following representations of text: a packed array (see <a class="sec" href="strings.html#sec:5.2">section
606	647	5.2</a>, SWI-Prolog specific), a list of character codes or a list of
607	648	one-character <a class="gloss" href="glossary.html#gloss:atom">atoms</a>.</dd>
608		<dt><a name="gloss:succeed"><strong>succeed</strong></a></dt>
609		<dd class="defbody">
610		<a name="idx:succeed:2333"></a>A <a class="gloss" href="glossary.html#gloss:goal">goal</a>
	649	<dt><a id="gloss:succeed"><strong>succeed</strong></a></dt>
	650	<dd class="defbody">
	651	<a id="idx:succeed:2337"></a>A <a class="gloss" href="glossary.html#gloss:goal">goal</a>
611	652	is said to have <a class="gloss" href="glossary.html#gloss:succeed">succeeded</a>
612	653	if it has been <a class="gloss" href="glossary.html#gloss:prove">proven</a>.</dd>
613		<dt><a name="gloss:term"><strong>term</strong></a></dt>
614		<dd class="defbody">
615		<a name="idx:term:2334"></a>Value in Prolog. A <a class="gloss" href="glossary.html#gloss:term">term</a>
	654	<dt><a id="gloss:term"><strong>term</strong></a></dt>
	655	<dd class="defbody">
	656	<a id="idx:term:2338"></a>Value in Prolog. A <a class="gloss" href="glossary.html#gloss:term">term</a>
616	657	is either a <a class="gloss" href="glossary.html#gloss:variable">variable</a>, <a class="gloss" href="glossary.html#gloss:atom">atom</a>, <a class="gloss" href="glossary.html#gloss:integer">integer</a>,
617	658	<a class="gloss" href="glossary.html#gloss:float">float</a> or <a class="gloss" href="glossary.html#gloss:compound">compound</a>
618	659	term. In addition, SWI-Prolog also defines the type <a class="gloss" href="glossary.html#gloss:string">string</a>.</dd>
619		<dt><a name="gloss:transparent"><strong>transparent</strong></a></dt>
	660	<dt><a id="gloss:transparent"><strong>transparent</strong></a></dt>
620	661	<dd class="defbody">
621	662	See <a class="gloss" href="glossary.html#gloss:module-transparent">module transparent</a>.</dd>
622		<dt><a name="gloss:unify"><strong>unify</strong></a></dt>
623		<dd class="defbody">
624		<a name="idx:unify:2335"></a>Prolog process to make two terms equal by
	663	<dt><a id="gloss:unify"><strong>unify</strong></a></dt>
	664	<dd class="defbody">
	665	<a id="idx:unify:2339"></a>Prolog process to make two terms equal by
625	666	assigning variables in one term to values at the corresponding location
626	667	of the other term. For example:
627	668

633	674
634	675	<p>Unlike assignment (which does not exist in Prolog), unification is
635	676	not directed.</dd>
636		<dt><a name="gloss:update-view"><strong>update view</strong></a></dt>
637		<dd class="defbody">
638		<a name="idx:updateview:2336"></a><a name="idx:viewupdate:2337"></a>How
	677	<dt><a id="gloss:update-view"><strong>update view</strong></a></dt>
	678	<dd class="defbody">
	679	<a id="idx:updateview:2340"></a><a id="idx:viewupdate:2341"></a>How
639	680	Prolog behaves when a <a class="gloss" href="glossary.html#gloss:dynamic">dynamic</a> <a class="gloss" href="glossary.html#gloss:predicate">predicate</a>
640	681	is changed while it is running. There are two models. In most older
641	682	Prolog systems the change becomes immediately visible to the <a class="gloss" href="glossary.html#gloss:goal">goal</a>,
642	683	in modern systems including SWI-Prolog, the running <a class="gloss" href="glossary.html#gloss:goal">goal</a>
643	684	is not affected. Only new <a class="gloss" href="glossary.html#gloss:goal">goals</a>
644	685	`see' the new definition.</dd>
645		<dt><a name="gloss:variable"><strong>variable</strong></a></dt>
646		<dd class="defbody">
647		<a name="idx:variable:2338"></a>A Prolog variable is a value that `is
648		not yet bound'. After <a class="gloss" href="glossary.html#gloss:binding">binding</a>
	686	<dt><a id="gloss:variable"><strong>variable</strong></a></dt>
	687	<dd class="defbody">
	688	<a id="idx:variable:2342"></a>A Prolog variable is a value that `is not
	689	yet bound'. After <a class="gloss" href="glossary.html#gloss:binding">binding</a>
649	690	a variable, it cannot be modified. <a class="gloss" href="glossary.html#gloss:backtracking">Backtracking</a>
650	691	to a point in the execution before the variable was bound will turn it
651	692	back into a variable:

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193	234	</div>
194		<h2 id="sec:guidelines"><a name="sec:8.7"><span class="sec-nr">8.7</span> <span class="sec-title">Programming
	235	<h2 id="sec:guidelines"><a id="sec:8.7"><span class="sec-nr">8.7</span> <span class="sec-title">Programming
195	236	Tips and Tricks</span></a></h2>
196	237
197		<a name="sec:guidelines"></a> In this section we cover several
198		guidelines on how to use CHR to write constraint solvers and how to do
199		so efficiently.
	238	<a id="sec:guidelines"></a> In this section we cover several guidelines
	239	on how to use CHR to write constraint solvers and how to do so
	240	efficiently.
200	241
201	242	<p>
202	243	<ul class="latex">

231	272	into Prolog code. When you disable optimizations the CHR compiler will
232	273	be a lot quicker, but you may lose performance. Alternatively, you can
233	274	just use SWI-Prolog's
234		<a name="idx:qcompile1:1826"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>
	275	<a id="idx:qcompile1:1830"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>
235	276	to generate a <code>.qlf</code> file once from your
236	277	<code>.pl</code> file. This <code>.qlf</code> contains the generated
237	278	code of the CHR compiler (be it in a binary format). When you consult

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193	234	</div>
194		<h2 id="sec:guitracer"><a name="sec:3.5"><span class="sec-nr">3.5</span> <span class="sec-title">The
	235	<h2 id="sec:guitracer"><a id="sec:3.5"><span class="sec-nr">3.5</span> <span class="sec-title">The
195	236	Graphical Debugger</span></a></h2>
196	237
197		<a name="sec:guitracer"></a>
	238	<a id="sec:guitracer"></a>
198	239
199	240	<p>SWI-Prolog offers two debuggers. One is the traditional text
200	241	console-based 4-port Prolog tracer and the other is a window-based
201	242	source level debugger. The window-based debugger requires XPCE
202		installed. It operates based on the <a name="idx:prologtraceinterception4:314"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>
203		hook and other low-level functionality described in <a class="sec" href="hack.html">chapter
	243	installed. It operates based on the <a id="idx:prologtraceinterception4:314"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>
	244	hook and other low-level functionality described in <a class="sec" href="hack.html#sec:B">chapter
204	245	B</a>.
205	246
206	247	<p>Window-based tracing provides a much better overview due to the

211	252	the graphical debugger just presents a (much better) overview of the
212	253	current state.
213	254
214		<p><h3 id="sec:start-guitracer"><a name="sec:3.5.1"><span class="sec-nr">3.5.1</span> <span class="sec-title">Invoking
	255	<p><h3 id="sec:start-guitracer"><a id="sec:3.5.1"><span class="sec-nr">3.5.1</span> <span class="sec-title">Invoking
215	256	the window-based debugger</span></a></h3>
216	257
217		<a name="sec:start-guitracer"></a>
	258	<a id="sec:start-guitracer"></a>
218	259
219	260	<p>Whether the text-based or window-based debugger is used is controlled
220		using the predicates <a name="idx:guitracer0:315"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>
221		and <a name="idx:noguitracer0:316"></a><a class="pred" href="guitracer.html#noguitracer/0">noguitracer/0</a>.
222		Entering debug mode is controlled using the normal predicates for this: <a name="idx:trace0:317"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	261	using the predicates <a id="idx:guitracer0:315"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>
	262	and <a id="idx:noguitracer0:316"></a><a class="pred" href="guitracer.html#noguitracer/0">noguitracer/0</a>.
	263	Entering debug mode is controlled using the normal predicates for this: <a id="idx:trace0:317"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
223	264	and
224		<a name="idx:spy1:318"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>.
	265	<a id="idx:spy1:318"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>.
225	266	In addition, PceEmacs prolog mode provides the command
226	267	<strong>Prolog/Break at</strong> (<code>Control-c b</code>) to insert a
227	268	break-point at a specific location in the source code.

231	272	used from a background thread.
232	273
233	274	<dl class="latex">
234		<dt class="pubdef"><a name="guitracer/0"><strong>guitracer</strong></a></dt>
	275	<dt class="pubdef"><a id="guitracer/0"><strong>guitracer</strong></a></dt>
235	276	<dd class="defbody">
236	277	This predicate installs the above-mentioned hooks that redirect tracing
237	278	to the window-based environment. No window appears. The debugger window
238		appears as actual tracing is started through <a name="idx:trace0:319"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>,
239		by hitting a spy point defined by <a name="idx:spy1:320"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
	279	appears as actual tracing is started through <a id="idx:trace0:319"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>,
	280	by hitting a spy point defined by <a id="idx:spy1:320"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
240	281	or a break point defined using the PceEmacs command <strong>Prolog/Break
241	282	at</strong> (<code>Control-c b</code>).</dd>
242		<dt class="pubdef"><a name="noguitracer/0"><strong>noguitracer</strong></a></dt>
243		<dd class="defbody">
244		Disable the hooks installed by <a name="idx:guitracer0:321"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>,
	283	<dt class="pubdef"><a id="noguitracer/0"><strong>noguitracer</strong></a></dt>
	284	<dd class="defbody">
	285	Disable the hooks installed by <a id="idx:guitracer0:321"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>,
245	286	reverting to normal text console-based tracing.</dd>
246		<dt class="pubdef"><a name="gtrace/0"><strong>gtrace</strong></a></dt>
	287	<dt class="pubdef"><a id="gtrace/0"><strong>gtrace</strong></a></dt>
247	288	<dd class="defbody">
248	289	Utility defined as <code>guitracer,trace</code>.</dd>
249		<dt class="pubdef"><a name="gdebug/0"><strong>gdebug</strong></a></dt>
	290	<dt class="pubdef"><a id="gdebug/0"><strong>gdebug</strong></a></dt>
250	291	<dd class="defbody">
251	292	Utility defined as <code>guitracer,debug</code>.</dd>
252		<dt class="pubdef"><a name="gspy/1"><strong>gspy</strong>(<var>+Predicate</var>)</a></dt>
	293	<dt class="pubdef"><a id="gspy/1"><strong>gspy</strong>(<var>+Predicate</var>)</a></dt>
253	294	<dd class="defbody">
254	295	Utility defined as <code>guitracer,spy(Predicate)</code>.
255	296	</dd>

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186	227	<body style="background:white">

191	232	<a class="nav" href="format.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="tty.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:gvar"><a name="sec:4.33"><span class="sec-nr">4.33</span> <span class="sec-title">Global
	235	<h2 id="sec:gvar"><a id="sec:4.33"><span class="sec-nr">4.33</span> <span class="sec-title">Global
195	236	variables</span></a></h2>
196	237
197		<a name="sec:gvar"></a>
	238	<a id="sec:gvar"></a>
198	239
199	240	<p>Global variables are associations between names (atoms) and terms.
200		They differ in various ways from storing information using <a name="idx:assert1:1411"></a><a class="pred" href="db.html#assert/1">assert/1</a>
201		or <a name="idx:recorda3:1412"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>.
	241	They differ in various ways from storing information using <a id="idx:assert1:1411"></a><a class="pred" href="db.html#assert/1">assert/1</a>
	242	or <a id="idx:recorda3:1412"></a><a class="pred" href="db.html#recorda/3">recorda/3</a>.
202	243
203	244	<p>
204	245	<ul class="latex">

208	249	the CHR global constraint store.
209	250
210	251	<p>
211		<li>They support both global assignment using <a name="idx:nbsetval2:1413"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
212		and backtrackable assignment using <a name="idx:bsetval2:1414"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>.
	252	<li>They support both global assignment using <a id="idx:nbsetval2:1413"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
	253	and backtrackable assignment using <a id="idx:bsetval2:1414"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>.
213	254
214	255	<p>
215	256	<li>Only one value (which can be an arbitrary complex Prolog term) can

224	265	module scoping in future versions.
225	266	</ul>
226	267
227		<p>Both <a name="idx:bsetval2:1415"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>
228		and <a name="idx:nbsetval2:1416"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
	268	<p>Both <a id="idx:bsetval2:1415"></a><a class="pred" href="gvar.html#b_setval/2">b_setval/2</a>
	269	and <a id="idx:nbsetval2:1416"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
229	270	implicitly create a variable if the referenced name does not already
230	271	refer to a variable.
231	272
232	273	<p>Global variables may be initialised from directives to make them
233	274	available during the program lifetime, but some considerations are
234	275	necessary for saved states and threads. Saved states do not store global
235		variables, which implies they have to be declared with <a name="idx:initialization1:1417"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	276	variables, which implies they have to be declared with <a id="idx:initialization1:1417"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
236	277	to recreate them after loading the saved state. Each thread has its own
237	278	set of global variables, starting with an empty set. Using
238		<a name="idx:threadinitialization1:1418"></a><a class="pred" href="threadcreate.html#thread_initialization/1">thread_initialization/1</a>
	279	<a id="idx:threadinitialization1:1418"></a><a class="pred" href="threadcreate.html#thread_initialization/1">thread_initialization/1</a>
239	280	to define a global variable it will be defined, restored after reloading
240	281	a saved state and created in all threads that are created <em>after</em>
241	282	the registration. Finally, global variables can be initialised using the
242	283	exception hook
243		<a name="idx:exception3:1419"></a><a class="pred" href="exception3.html#exception/3">exception/3</a>.
244		The latter technique is used by CHR (see <a class="sec" href="chr.html">chapter
	284	<a id="idx:exception3:1419"></a><a class="pred" href="exception3.html#exception/3">exception/3</a>.
	285	The latter technique is used by CHR (see <a class="sec" href="chr.html#sec:8">chapter
245	286	8</a>).
246	287
247	288	<dl class="latex">
248		<dt class="pubdef"><a name="b_setval/2"><strong>b_setval</strong>(<var>+Name,
	289	<dt class="pubdef"><a id="b_setval/2"><strong>b_setval</strong>(<var>+Name,
249	290	+Value</var>)</a></dt>
250	291	<dd class="defbody">
251	292	Associate the term <var>Value</var> with the atom <var>Name</var> or

254	295	value
255	296	<code>[]</code> is created (the empty list). On backtracking the
256	297	assignment is reversed.</dd>
257		<dt class="pubdef"><a name="b_getval/2"><strong>b_getval</strong>(<var>+Name,
	298	<dt class="pubdef"><a id="b_getval/2"><strong>b_getval</strong>(<var>+Name,
258	299	-Value</var>)</a></dt>
259	300	<dd class="defbody">
260	301	Get the value associated with the global variable <var>Name</var> and
261	302	unify it with <var>Value</var>. Note that this unification may further
262	303	instantiate the value of the global variable. If this is undesirable the
263		normal precautions (double negation or <a name="idx:copyterm2:1420"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>)
	304	normal precautions (double negation or <a id="idx:copyterm2:1420"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>)
264	305	must be taken. The
265		<a name="idx:bgetval2:1421"></a><a class="pred" href="gvar.html#b_getval/2">b_getval/2</a>
	306	<a id="idx:bgetval2:1421"></a><a class="pred" href="gvar.html#b_getval/2">b_getval/2</a>
266	307	predicate generates errors if <var>Name</var> is not an atom or the
267	308	requested variable does not exist.
268	309	</dd>
269	310	</dl>
270	311
271	312	<dl class="latex">
272		<dt class="pubdef"><a name="nb_setval/2"><strong>nb_setval</strong>(<var>+Name,
	313	<dt class="pubdef"><a id="nb_setval/2"><strong>nb_setval</strong>(<var>+Name,
273	314	+Value</var>)</a></dt>
274	315	<dd class="defbody">
275		Associates a copy of <var>Value</var> created with <a name="idx:duplicateterm2:1422"></a><a class="pred" href="manipterm.html#duplicate_term/2">duplicate_term/2</a>
	316	Associates a copy of <var>Value</var> created with <a id="idx:duplicateterm2:1422"></a><a class="pred" href="manipterm.html#duplicate_term/2">duplicate_term/2</a>
276	317	with the atom <var>Name</var>. Note that this can be used to set an
277	318	initial value other than <code>[]</code> prior to backtrackable
278	319	assignment.</dd>
279		<dt class="pubdef"><a name="nb_getval/2"><strong>nb_getval</strong>(<var>+Name,
	320	<dt class="pubdef"><a id="nb_getval/2"><strong>nb_getval</strong>(<var>+Name,
280	321	-Value</var>)</a></dt>
281	322	<dd class="defbody">
282		The <a name="idx:nbgetval2:1423"></a><a class="pred" href="gvar.html#nb_getval/2">nb_getval/2</a>
283		predicate is a synonym for <a name="idx:bgetval2:1424"></a><a class="pred" href="gvar.html#b_getval/2">b_getval/2</a>,
	323	The <a id="idx:nbgetval2:1423"></a><a class="pred" href="gvar.html#nb_getval/2">nb_getval/2</a>
	324	predicate is a synonym for <a id="idx:bgetval2:1424"></a><a class="pred" href="gvar.html#b_getval/2">b_getval/2</a>,
284	325	introduced for compatibility and symmetry. As most scenarios will use a
285	326	particular global variable using either non-backtrackable or
286		backtrackable assignment, using <a name="idx:nbgetval2:1425"></a><a class="pred" href="gvar.html#nb_getval/2">nb_getval/2</a>
	327	backtrackable assignment, using <a id="idx:nbgetval2:1425"></a><a class="pred" href="gvar.html#nb_getval/2">nb_getval/2</a>
287	328	can be used to document that the variable is non-backtrackable. Raises <code>existence_error(variable,
288		Name)</code> if the variable does not exist. Alternatively, <a name="idx:nbcurrent2:1426"></a><a class="pred" href="gvar.html#nb_current/2">nb_current/2</a>
	329	Name)</code> if the variable does not exist. Alternatively, <a id="idx:nbcurrent2:1426"></a><a class="pred" href="gvar.html#nb_current/2">nb_current/2</a>
289	330	can used to query a global variable. This version <em>fails</em> if the
290	331	variable does not exist rather than raising an exception.</dd>
291		<dt class="pubdef"><a name="nb_linkval/2"><strong>nb_linkval</strong>(<var>+Name,
	332	<dt class="pubdef"><a id="nb_linkval/2"><strong>nb_linkval</strong>(<var>+Name,
292	333	+Value</var>)</a></dt>
293	334	<dd class="defbody">
294	335	Associates the term <var>Value</var> with the atom <var>Name</var>
295		without copying it. This is a fast special-purpose variation of <a name="idx:nbsetval2:1427"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
	336	without copying it. This is a fast special-purpose variation of <a id="idx:nbsetval2:1427"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
296	337	intended for expert users only because the semantics on backtracking to
297	338	a point before creating the link are poorly defined for compound terms.
298	339	The principal term is always left untouched, but backtracking behaviour

313	354	</pre>
314	355
315	356	</dd>
316		<dt class="pubdef"><a name="nb_current/2"><strong>nb_current</strong>(<var>?Name,
	357	<dt class="pubdef"><a id="nb_current/2"><strong>nb_current</strong>(<var>?Name,
317	358	?Value</var>)</a></dt>
318	359	<dd class="defbody">
319	360	Enumerate all defined variables with their value. The order of
320		enumeration is undefined. Note that <a name="idx:nbcurrent2:1428"></a><a class="pred" href="gvar.html#nb_current/2">nb_current/2</a>
321		can be used as an alternative for <a name="idx:nbgetval2:1429"></a><a class="pred" href="gvar.html#nb_getval/2">nb_getval/2</a>
	361	enumeration is undefined. Note that <a id="idx:nbcurrent2:1428"></a><a class="pred" href="gvar.html#nb_current/2">nb_current/2</a>
	362	can be used as an alternative for <a id="idx:nbgetval2:1429"></a><a class="pred" href="gvar.html#nb_getval/2">nb_getval/2</a>
322	363	to request the value of a variable and fail silently if the variable
323	364	does not exists.</dd>
324		<dt class="pubdef"><a name="nb_delete/1"><strong>nb_delete</strong>(<var>+Name</var>)</a></dt>
	365	<dt class="pubdef"><a id="nb_delete/1"><strong>nb_delete</strong>(<var>+Name</var>)</a></dt>
325	366	<dd class="defbody">
326	367	Delete the named global variable. Succeeds also if the named variable
327	368	does not exist.
328	369	</dd>
329	370	</dl>
330	371
331		<p><h3 id="sec:gvars-compat"><a name="sec:4.33.1"><span class="sec-nr">4.33.1</span> <span class="sec-title">Compatibility
	372	<p><h3 id="sec:gvars-compat"><a id="sec:4.33.1"><span class="sec-nr">4.33.1</span> <span class="sec-title">Compatibility
332	373	of SWI-Prolog Global Variables</span></a></h3>
333	374
334		<a name="sec:gvars-compat"></a>
	375	<a id="sec:gvars-compat"></a>
335	376
336	377	<p>Global variables have been introduced by various Prolog
337	378	implementations recently. The implementation of them in SWI-Prolog is
338	379	based on hProlog by Bart Demoen. In discussion with Bart it was decided
339		that the semantics of hProlog <a name="idx:nbsetval2:1430"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>,
340		which is equivalent to <a name="idx:nblinkval2:1431"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>,
	380	that the semantics of hProlog <a id="idx:nbsetval2:1430"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>,
	381	which is equivalent to <a id="idx:nblinkval2:1431"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>,
341	382	is not acceptable for normal Prolog users as the behaviour is influenced
342		by how built-in predicates that construct terms (<a name="idx:read1:1432"></a><a class="pred" href="termrw.html#read/1">read/1</a>,
	383	by how built-in predicates that construct terms (<a id="idx:read1:1432"></a><a class="pred" href="termrw.html#read/1">read/1</a>,
343	384	=../2, etc.) are implemented.
344	385
345	386	<p>GNU-Prolog provides a rich set of global variables, including arrays.
346		Arrays can be implemented easily in SWI-Prolog using <a name="idx:functor3:1433"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
	387	Arrays can be implemented easily in SWI-Prolog using <a id="idx:functor3:1433"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
347	388	and
348		<a name="idx:setarg3:1434"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	389	<a id="idx:setarg3:1434"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
349	390	due to the unrestricted arity of compound terms.
350	391
351	392	<p></body></html>⏎

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193	234	</div>
194		<h1 id="sec:hack"><a name="sec:B"><span class="sec-nr">B</span> <span class="sec-title">Hackers
	235	<h1 id="sec:hack"><a id="sec:B"><span class="sec-nr">B</span> <span class="sec-title">Hackers
195	236	corner</span></a></h1>
196	237
197		<a name="sec:hack"></a>
	238	<a id="sec:hack"></a>
198	239
199	240	<p>This appendix describes a number of predicates which enable the
200	241	Prolog user to inspect the Prolog environment and manipulate (or even

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194		<h2 id="sec:help"><a name="sec:2.6"><span class="sec-nr">2.6</span> <span class="sec-title">Online
	235	<h2 id="sec:help"><a id="sec:2.6"><span class="sec-nr">2.6</span> <span class="sec-title">Online
195	236	Help</span></a></h2>
196	237
197		<a name="sec:help"></a>
	238	<a id="sec:help"></a>
198	239
199	240	<p>SWI-Prolog provides an online help system that covers this manual. If
200	241	the XPCE graphics system is available, online help opens a graphical

208	249	and following the instructions in the <code>README</code> file.
209	250
210	251	<dl class="latex">
211		<dt class="pubdef"><a name="help/0"><strong>help</strong></a></dt>
212		<dd class="defbody">
213		Equivalent to <code>help(<a name="idx:help1:48"></a><a class="pred" href="help.html#help/1">help/1</a>)</code>.</dd>
214		<dt class="pubdef"><a name="help/1"><strong>help</strong>(<var>+What</var>)</a></dt>
	252	<dt class="pubdef"><a id="help/0"><strong>help</strong></a></dt>
	253	<dd class="defbody">
	254	Equivalent to <code>help(<a id="idx:help1:48"></a><a class="pred" href="help.html#help/1">help/1</a>)</code>.</dd>
	255	<dt class="pubdef"><a id="help/1"><strong>help</strong>(<var>+What</var>)</a></dt>
215	256	<dd class="defbody">
216	257	Show specified part of the manual. <var>What</var> is one of:
217		<div style="text-align:center"><table border="0" frame="void" rules="groups">
218		<tr valign="top"><td><<var>Name</var>>/<<var>Arity</var>> </td><td>Give
	258	<table class="latex frame-void center">
	259	<tr><td><<var>Name</var>>/<<var>Arity</var>> </td><td>Give
219	260	help on specified predicate </td></tr>
220		<tr valign="top"><td><<var>Name</var>> </td><td>Give help on named
221		predicate with any arity or C interface function with that name </td></tr>
222		<tr valign="top"><td><<var>Section</var>> </td><td>Display
223		specified section. Section numbers are dash-separated numbers: <code>2-3</code>
224		refers to section 2.3 of the manual. Section numbers are obtained using <a name="idx:apropos1:49"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>.</td></tr>
	261	<tr><td><<var>Name</var>> </td><td>Give help on named predicate
	262	with any arity or C interface function with that name </td></tr>
	263	<tr><td><<var>Section</var>> </td><td>Display specified section.
	264	Section numbers are dash-separated numbers: <code>2-3</code> refers to
	265	section 2.3 of the manual. Section numbers are obtained using <a id="idx:apropos1:49"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>.</td></tr>
225	266	</table>
226		</div>
227	267
228	268	<p>Examples:
229		<div style="text-align:center"><table border="0" frame="void" rules="groups">
230		<tr valign="top"><td><code>?- help(assert).</code> </td><td>Give help on
231		predicate assert </td></tr>
232		<tr valign="top"><td><code>?- help(3-4).</code> </td><td>Display section
233		3.4 of the manual </td></tr>
234		<tr valign="top"><td><code>?- help('PL_retry').</code></td><td>Give help
235		on interface function <a class="func" href="foreigninclude.html#PL_retry()">PL_retry()</a> </td></tr>
	269	<table class="latex frame-void center">
	270	<tr><td><code>?- help(assert).</code> </td><td>Give help on predicate
	271	assert </td></tr>
	272	<tr><td><code>?- help(3-4).</code> </td><td>Display section 3.4 of the
	273	manual </td></tr>
	274	<tr><td><code>?- help('PL_retry').</code></td><td>Give help on interface
	275	function <a class="func" href="foreigninclude.html#PL_retry()">PL_retry()</a> </td></tr>
236	276	</table>
237		</div>
238
239		<p>See also <a name="idx:apropos1:50"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>
	277
	278	<p>See also <a id="idx:apropos1:50"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>
240	279	and the SWI-Prolog home page at
241	280	<a class="url" href="http://www.swi-prolog.org">http://www.swi-prolog.org</a>,
242	281	which provides a FAQ, an HTML version of the manual for online browsing,
243	282	and HTML and PDF versions for downloading.</dd>
244		<dt class="pubdef"><a name="apropos/1"><strong>apropos</strong>(<var>+Pattern</var>)</a></dt>
	283	<dt class="pubdef"><a id="apropos/1"><strong>apropos</strong>(<var>+Pattern</var>)</a></dt>
245	284	<dd class="defbody">
246	285	Display all predicates, functions and sections that have <em>Pattern</em>
247	286	in their name or summary description. Lowercase letters in
248	287	<var>Pattern</var> also match a corresponding uppercase letter. Example:
249		<div style="text-align:center"><table border="0" frame="void" rules="groups">
250		<tr valign="top"><td><code>?- apropos(file).</code> </td><td>Display
251		predicates, functions and sections that have `file' (or `File', etc.) in
252		their summary description. </td></tr>
	288	<table class="latex frame-void center">
	289	<tr><td><code>?- apropos(file).</code> </td><td>Display predicates,
	290	functions and sections that have `file' (or `File', etc.) in their
	291	summary description. </td></tr>
253	292	</table>
254		</div>
255	293	</dd>
256		<dt class="pubdef"><a name="explain/1"><strong>explain</strong>(<var>+ToExplain</var>)</a></dt>
	294	<dt class="pubdef"><a id="explain/1"><strong>explain</strong>(<var>+ToExplain</var>)</a></dt>
257	295	<dd class="defbody">
258	296	Give an explanation on the given `object'. The argument may be any
259	297	Prolog data object. If the argument is an atom, a term of the form
260	298	<var>Name/Arity</var> or a term of the form <em>Module:Name/Arity</em>,
261		<a name="idx:explain1:51"></a><a class="pred" href="help.html#explain/1">explain/1</a>
262		describes the predicate as well as possible references to it. See also <a name="idx:gxref0:52"></a><a class="pred" href="xref.html#gxref/0">gxref/0</a>.</dd>
263		<dt class="pubdef"><a name="explain/2"><strong>explain</strong>(<var>+ToExplain,
	299	<a id="idx:explain1:51"></a><a class="pred" href="help.html#explain/1">explain/1</a>
	300	describes the predicate as well as possible references to it. See also <a id="idx:gxref0:52"></a><a class="pred" href="xref.html#gxref/0">gxref/0</a>.</dd>
	301	<dt class="pubdef"><a id="explain/2"><strong>explain</strong>(<var>+ToExplain,
264	302	-Explanation</var>)</a></dt>
265	303	<dd class="defbody">
266	304	Unify <var>Explanation</var> with an explanation for <var>ToExplain</var>.

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193	234	</div>
194		<h2 id="sec:history"><a name="sec:2.7"><span class="sec-nr">2.7</span> <span class="sec-title">Command
	235	<h2 id="sec:history"><a id="sec:2.7"><span class="sec-nr">2.7</span> <span class="sec-title">Command
195	236	line history</span></a></h2>
196	237
197		<a name="sec:history"></a>
	238	<a id="sec:history"></a>
198	239
199	240	<p>SWI-Prolog offers a query substitution mechanism similar to what is
200	241	seen in Unix shells. The availability of this feature is controlled by
201		<a name="idx:setprologflag2:53"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>,
	242	<a id="idx:setprologflag2:53"></a><a class="pred" href="flags.html#set_prolog_flag/2">set_prolog_flag/2</a>,
202	243	using the <a class="flag" href="flags.html#flag:history">history</a>
203	244	Prolog flag. By default, history is available if no interactive command
204	245	line editor is available. To enable history, remembering the last 50
205		commands, put the following into your startup file (see <a class="sec" href="initfile.html">section
	246	commands, put the following into your startup file (see <a class="sec" href="initfile.html#sec:2.2">section
206	247	2.2</a>):
207	248
208	249	<pre class="code">

215	256	1</a>. History expansion is not done if these sequences appear in quoted
216	257	atoms or strings.
217	258
218		<p><table border="2" frame="box" rules="groups" style="margin:auto">
219		<tr valign="top"><td><code>!!.</code> </td><td>Repeat last query </td></tr>
220		<tr valign="top"><td><code>!nr.</code> </td><td>Repeat query numbered <<var>nr</var>> </td></tr>
221		<tr valign="top"><td><code>!str.</code> </td><td>Repeat last query
222		starting with <<var>str</var>> </td></tr>
223		<tr valign="top"><td><code>h.</code> </td><td>Show history of commands </td></tr>
224		<tr valign="top"><td><code>!h.</code> </td><td>Show this list </td></tr>
	259	<p><table class="latex frame-box center">
	260	<tr><td><code>!!.</code> </td><td>Repeat last query </td></tr>
	261	<tr><td><code>!nr.</code> </td><td>Repeat query numbered <<var>nr</var>> </td></tr>
	262	<tr><td><code>!str.</code> </td><td>Repeat last query starting with <<var>str</var>> </td></tr>
	263	<tr><td><code>h.</code> </td><td>Show history of commands </td></tr>
	264	<tr><td><code>!h.</code> </td><td>Show this list </td></tr>
225	265	</table>
226	266	<div class="caption"><b>Table 1 : </b>History commands</div>
227		<a name="tab:history"></a>
	267	<a id="tab:history"></a>
228	268
229	269	<p></body></html>⏎

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193	234	</div>
194		<h2 id="sec:hooks"><a name="sec:2.12"><span class="sec-nr">2.12</span> <span class="sec-title">An
	235	<h2 id="sec:hooks"><a id="sec:2.12"><span class="sec-nr">2.12</span> <span class="sec-title">An
195	236	overview of hook predicates</span></a></h2>
196	237
197		<a name="sec:hooks"></a>
198
199		<p><a name="idx:hooks:167"></a>SWI-Prolog provides a large number of
	238	<a id="sec:hooks"></a>
	239
	240	<p><a id="idx:hooks:167"></a>SWI-Prolog provides a large number of
200	241	hooks, mainly to control handling messages, debugging, startup,
201	242	shut-down, macro-expansion, etc. Below is a summary of all defined hooks
202	243	with an indication of their portability.

204	245	<p>
205	246	<ul class="latex">
206	247	<li><i>portray/1</i><br>
207		Hook into <a name="idx:writeterm3:168"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>
	248	Hook into <a id="idx:writeterm3:168"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>
208	249	to alter the way terms are printed (ISO).
209	250	<li><i>message_hook/3</i><br>
210		Hook into <a name="idx:printmessage2:169"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	251	Hook into <a id="idx:printmessage2:169"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
211	252	to alter the way system messages are printed (Quintus/SICStus).
212	253	<li><i>message_property/2</i><br>
213		Hook into <a name="idx:printmessage2:170"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	254	Hook into <a id="idx:printmessage2:170"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
214	255	that defines prefix, output stream, color, etc.
215	256	<li><i>library_directory/1</i><br>
216		Hook into <a name="idx:absolutefilename3:171"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	257	Hook into <a id="idx:absolutefilename3:171"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
217	258	to define new library directories (most Prolog systems).
218	259	<li><i>file_search_path/2</i><br>
219		Hook into <a name="idx:absolutefilename3:172"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	260	Hook into <a id="idx:absolutefilename3:172"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
220	261	to define new search paths (Quintus/SICStus).
221	262	<li><i>term_expansion/2</i><br>
222		Hook into <a name="idx:loadfiles2:173"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	263	Hook into <a id="idx:loadfiles2:173"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
223	264	to modify read terms before they are compiled (macro-processing) (most
224	265	Prolog systems).
225	266	<li><i>goal_expansion/2</i><br>
226		Same as <a name="idx:termexpansion2:174"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	267	Same as <a id="idx:termexpansion2:174"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
227	268	for individual goals (SICStus).
228	269	<li><i>prolog_load_file/2</i><br>
229		Hook into <a name="idx:loadfiles2:175"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	270	Hook into <a id="idx:loadfiles2:175"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
230	271	to load other data formats for Prolog sources from `non-file' resources.
231		The <a name="idx:loadfiles2:176"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
232		predicate is the ancestor of <a name="idx:consult1:177"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>, <a name="idx:usemodule1:178"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>,
	272	The <a id="idx:loadfiles2:176"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	273	predicate is the ancestor of <a id="idx:consult1:177"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>, <a id="idx:usemodule1:178"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>,
233	274	etc.
234	275	<li><i>qpredrefprolog_editlocate3</i><br>
235		Hook into <a name="idx:edit1:179"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	276	Hook into <a id="idx:edit1:179"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
236	277	to locate objects (SWI).
237	278	<li><i>qpredrefprolog_editedit_source1</i><br>
238		Hook into <a name="idx:edit1:180"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	279	Hook into <a id="idx:edit1:180"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
239	280	to call an internal editor (SWI).
240	281	<li><i>prolog_edit:edit_command/2</i><br>
241		Hook into <a name="idx:edit1:181"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	282	Hook into <a id="idx:edit1:181"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
242	283	to define the external editor to use (SWI).
243	284	<li><i>prolog_list_goal/1</i><br>
244	285	Hook into the tracer to list the code associated to a particular goal

246	287	<li><i>prolog_trace_interception/4</i><br>
247	288	Hook into the tracer to handle trace events (SWI).
248	289	<li><i>qpredrefprologdebug_control_hook1</i><br>
249		Hook in <a name="idx:spy1:182"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>, <a name="idx:nospy1:183"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>, <a name="idx:nospyall0:184"></a><a class="pred" href="debugger.html#nospyall/0">nospyall/0</a>
250		and <a name="idx:debugging0:185"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a>
	290	Hook in <a id="idx:spy1:182"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>, <a id="idx:nospy1:183"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>, <a id="idx:nospyall0:184"></a><a class="pred" href="debugger.html#nospyall/0">nospyall/0</a>
	291	and <a id="idx:debugging0:185"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a>
251	292	to extend these control predicates to higher-level libraries.
252	293	<li><i>qpredrefprologhelp_hook1</i><br>
253		Hook in <a name="idx:help0:186"></a><a class="pred" href="help.html#help/0">help/0</a>, <a name="idx:help1:187"></a><a class="pred" href="help.html#help/1">help/1</a>
254		and <a name="idx:apropos1:188"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>
	294	Hook in <a id="idx:help0:186"></a><a class="pred" href="help.html#help/0">help/0</a>, <a id="idx:help1:187"></a><a class="pred" href="help.html#help/1">help/1</a>
	295	and <a id="idx:apropos1:188"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>
255	296	to extend the help system.
256	297	<li><i>resource/3</i><br>
257	298	Define a new resource (not really a hook, but similar) (SWI).

260	301	(SWI).
261	302	<li><i>attr_unify_hook/2</i><br>
262	303	Unification hook for attributed variables. Can be defined in any module.
263		See <a class="sec" href="attvar.html">section 7.1</a> for details.
	304	See <a class="sec" href="attvar.html#sec:7.1">section 7.1</a> for
	305	details.
264	306	</ul>
265	307
266	308	<p></body></html>⏎

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 3.8</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:idepreds"><a name="sec:3.8"><span class="sec-nr">3.8</span> <span class="sec-title">Accessing
	235	<h2 id="sec:idepreds"><a id="sec:3.8"><span class="sec-nr">3.8</span> <span class="sec-title">Accessing
195	236	the IDE from your program</span></a></h2>
196	237
197		<a name="sec:idepreds"></a>
	238	<a id="sec:idepreds"></a>
198	239
199	240	<p>Over the years a collection of IDE components have been developed,
200	241	each with its own interface. In addition, some of these components
201	242	require each other, and loading IDE components must be on demand to
202		avoid the IDE being part of a saved state (see <a name="idx:qsaveprogram2:325"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>).
	243	avoid the IDE being part of a saved state (see <a id="idx:qsaveprogram2:325"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>).
203	244	For this reason, access to the IDE is concentrated on a single interface
204		called <a name="idx:prologide1:326"></a><a class="pred" href="idepreds.html#prolog_ide/1">prolog_ide/1</a>:
	245	called <a id="idx:prologide1:326"></a><a class="pred" href="idepreds.html#prolog_ide/1">prolog_ide/1</a>:
205	246
206	247	<dl class="latex">
207		<dt class="pubdef"><a name="prolog_ide/1"><strong>prolog_ide</strong>(<var>+Action</var>)</a></dt>
	248	<dt class="pubdef"><a id="prolog_ide/1"><strong>prolog_ide</strong>(<var>+Action</var>)</a></dt>
208	249	<dd class="defbody">
209	250	This predicate ensures the IDE-enabling XPCE component is loaded,
210		creates the XPCE class and sends <var>Action</var> to its one and only
211		instance <code>@prolog_ide</code>. <var>Action</var> is one of the
212		following:
	251	creates the XPCE class <i>prolog_ide</i> and sends <var>Action</var> to
	252	its one and only instance <code>@prolog_ide</code>. <var>Action</var> is
	253	one of the following:
213	254
214	255	<dl class="latex">
215	256	<dt><strong>open_navigator</strong>(<var>+Directory</var>)</dt>
216	257	<dd class="defbody">
217		Open the Prolog Navigator (see <a class="sec" href="navigator.html">section
	258	Open the Prolog Navigator (see <a class="sec" href="navigator.html#sec:3.6">section
218	259	3.6</a>) in the given
219	260	<var>Directory</var>.</dd>
220	261	<dt><strong>open_debug_status</strong></dt>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 3.9</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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193	234	</div>
194		<h2 id="sec:idesummary"><a name="sec:3.9"><span class="sec-nr">3.9</span> <span class="sec-title">Summary
	235	<h2 id="sec:idesummary"><a id="sec:3.9"><span class="sec-nr">3.9</span> <span class="sec-title">Summary
195	236	of the IDE</span></a></h2>
196	237
197		<a name="sec:idesummary"></a>
	238	<a id="sec:idesummary"></a>
198	239
199	240	<p>The SWI-Prolog development environment consists of a number of
200	241	interrelated but not (yet) integrated tools. Here is a list of the most

210	251	alternatives on the command <code>Alt-?</code>.
211	252
212	253	<p>
213		<li><i>Use <a name="idx:edit1:327"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	254	<li><i>Use <a id="idx:edit1:327"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
214	255	for finding locations</i><br>
215		The command <a name="idx:edit1:328"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	256	The command <a id="idx:edit1:328"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
216	257	takes the name of a file, module, predicate or other entity registered
217	258	through extensions and starts the user's preferred editor at the right
218	259	location.

225	266
226	267	<p>
227	268	<li><i>Update Prolog after editing</i><br>
228		Using <a name="idx:make0:329"></a><a class="pred" href="consulting.html#make/0">make/0</a>,
	269	Using <a id="idx:make0:329"></a><a class="pred" href="consulting.html#make/0">make/0</a>,
229	270	all files you have edited are re-loaded.
230	271
231	272	<p>

235	276
236	277	<p>
237	278	<li><i>Using the graphical debugger</i><br>
238		The predicates <a name="idx:guitracer0:330"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>
239		and <a name="idx:noguitracer0:331"></a><a class="pred" href="guitracer.html#noguitracer/0">noguitracer/0</a>
	279	The predicates <a id="idx:guitracer0:330"></a><a class="pred" href="guitracer.html#guitracer/0">guitracer/0</a>
	280	and <a id="idx:noguitracer0:331"></a><a class="pred" href="guitracer.html#noguitracer/0">noguitracer/0</a>
240	281	switch between traditional text-based and window-based debugging. The
241		tracer is activated using the <a name="idx:trace0:332"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>, <a name="idx:spy1:333"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
	282	tracer is activated using the <a id="idx:trace0:332"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>, <a id="idx:spy1:333"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
242	283	or menu items from PceEmacs or the Prolog Navigator.
243	284
244	285	<p>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 1.5</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
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191	232	<a class="nav" href="sponsor.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:implhistory"><a name="sec:1.5"><span class="sec-nr">1.5</span> <span class="sec-title">Implementation
	235	<h2 id="sec:implhistory"><a id="sec:1.5"><span class="sec-nr">1.5</span> <span class="sec-title">Implementation
195	236	history</span></a></h2>
196	237
197		<a name="sec:implhistory"></a>
	238	<a id="sec:implhistory"></a>
198	239
199	240	<p>SWI-Prolog started back in 1986 with the requirement for a Prolog
200	241	that could handle recursive interaction with the C-language: Prolog

229	270	of compiled code. The extensions include specialised instructions for
230	271	unification, predicate invocation, some frequently used built-in
231	272	predicates, arithmetic, and control (<a class="pred" href="control.html#;/2">;/2</a>, <a class="pred" href="control.html#\|/2">\|/2</a>),
232		if-then (<a class="pred" href="control.html#send_arrow/2">->/2</a>)
233		and negation-by-failure (<a class="pred" href="control.html#\+/1">\+/1</a>).
	273	if-then (<a class="pred" href="control.html#->/2">->/2</a>) and
	274	negation-by-failure (<a class="pred" href="control.html#\+/1">\+/1</a>).
234	275
235	276	<p></body></html>⏎

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194		<h2 id="sec:import"><a name="sec:6.3"><span class="sec-nr">6.3</span> <span class="sec-title">Importing
	235	<h2 id="sec:import"><a id="sec:6.3"><span class="sec-nr">6.3</span> <span class="sec-title">Importing
195	236	Predicates into a Module</span></a></h2>
196	237
197		<a name="sec:import"></a>
	238	<a id="sec:import"></a>
198	239
199	240	<p>Predicates can be added to a module by <em>importing</em> them from
200	241	another module. Importing adds predicates to the namespace of a module.

203	244	module in which it has been defined.
204	245
205	246	<p>Importing the predicates from another module is achieved using the
206		directives <a name="idx:usemodule1:1666"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
207		or <a name="idx:usemodule2:1667"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>.
	247	directives <a id="idx:usemodule1:1670"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	248	or <a id="idx:usemodule2:1671"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>.
208	249	Note that both directives take
209	250	<var>filename(s)</var> as arguments. That is, modules are imported based
210	251	on their filename rather than their module name.
211	252
212	253	<dl class="latex">
213		<dt class="pubdef"><a name="use_module/1"><strong>use_module</strong>(<var>+Files</var>)</a></dt>
	254	<dt class="pubdef"><a id="use_module/1"><strong>use_module</strong>(<var>+Files</var>)</a></dt>
214	255	<dd class="defbody">
215		Load the file(s) specified with <var>Files</var> just like <a name="idx:ensureloaded1:1668"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>.
	256	Load the file(s) specified with <var>Files</var> just like <a id="idx:ensureloaded1:1672"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>.
216	257	The files must all be module files. All exported predicates from the
217	258	loaded files are imported into the module from which this predicate is
218		called. This predicate is equivalent to <a name="idx:ensureloaded1:1669"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>,
	259	called. This predicate is equivalent to <a id="idx:ensureloaded1:1673"></a><a class="pred" href="consulting.html#ensure_loaded/1">ensure_loaded/1</a>,
219	260	except that it raises an error if <var>Files</var> are not module files.
220	261
221	262	<p>The imported predicates act as <em>weak symbols</em> in the module

223	264	predicate overrides (clobbers) the imported definition. If the flag
224	265	<a class="flag" href="flags.html#flag:warn_override_implicit_import">warn_override_implicit_import</a>
225	266	is <code>true</code> (default), a warning is printed. Below is an
226		example of a module that uses library(lists), but redefines <a name="idx:flatten2:1670"></a><a class="pred" href="lists.html#flatten/2">flatten/2</a>,
	267	example of a module that uses library(lists), but redefines <a id="idx:flatten2:1674"></a><a class="pred" href="lists.html#flatten/2">flatten/2</a>,
227	268	giving it a totally different meaning:
228	269
229	270	<pre class="code">

242	283	overrides weak import from lists
243	284	</pre>
244	285
245		<p>This warning can be avoided by (1) using <a name="idx:usemodule2:1671"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
	286	<p>This warning can be avoided by (1) using <a id="idx:usemodule2:1675"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
246	287	to only import the predicates from the <code>lists</code> library that
247	288	are actually used in the `shapes' module, (2) using the <code>except([flatten/2])</code>
248		option of <a name="idx:usemodule2:1672"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>,
	289	option of <a id="idx:usemodule2:1676"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>,
249	290	(3) use
250		<code>:- abolish(<a name="idx:flatten2:1673"></a><a class="pred" href="lists.html#flatten/2">flatten/2</a>).</code>
	291	<code>:- abolish(<a id="idx:flatten2:1677"></a><a class="pred" href="lists.html#flatten/2">flatten/2</a>).</code>
251	292	before the local definition or (4) setting
252	293	<a class="flag" href="flags.html#flag:warn_override_implicit_import">warn_override_implicit_import</a>
253	294	to <code>false</code>. Globally disabling this warning is only

255	296	design choices or the program is ported from a system that silently
256	297	overrides imported predicates.
257	298
258		<p>Note that it is always an error to import two modules with <a name="idx:usemodule1:1674"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	299	<p>Note that it is always an error to import two modules with <a id="idx:usemodule1:1678"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
259	300	that export the same predicate. Such conflicts must be resolved with
260		<a name="idx:usemodule2:1675"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
	301	<a id="idx:usemodule2:1679"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
261	302	as described above.</dd>
262		<dt class="pubdef"><a name="use_module/2"><strong>use_module</strong>(<var>+File,
	303	<dt class="pubdef"><a id="use_module/2"><strong>use_module</strong>(<var>+File,
263	304	+ImportList</var>)</a></dt>
264	305	<dd class="defbody">
265	306	Load <var>File</var>, which must be a module file, and import the

268	309	imported from the loaded module. <var>ImportList</var> also allows for
269	310	renaming or import-everything-except. See also the <code>import</code>
270	311	option of
271		<a name="idx:loadfiles2:1676"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
272		The first example below loads <a name="idx:member2:1677"></a><a class="pred" href="lists.html#member/2">member/2</a>
273		from the <code>lists</code> library and <a name="idx:append2:1678"></a><a class="pred" href="lists.html#append/2">append/2</a>
	312	<a id="idx:loadfiles2:1680"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
	313	The first example below loads <a id="idx:member2:1681"></a><a class="pred" href="lists.html#member/2">member/2</a>
	314	from the <code>lists</code> library and <a id="idx:append2:1682"></a><a class="pred" href="lists.html#append/2">append/2</a>
274	315	under the name <code>list_concat</code>, which is how this predicate is
275	316	named in YAP. The second example loads all exports from library <code>option</code>
276		except for <a name="idx:metaoptions3:1679"></a><a class="pred" href="option.html#meta_options/3">meta_options/3</a>.
	317	except for <a id="idx:metaoptions3:1683"></a><a class="pred" href="option.html#meta_options/3">meta_options/3</a>.
277	318	These renaming facilities are generally used to deal with portability
278		issues with as few changes as possible to the actual code. See also <a class="sec" href="dialect.html">section
	319	issues with as few changes as possible to the actual code. See also <a class="sec" href="dialect.html#sec:C">section
279	320	C</a> and
280		<a class="sec" href="reexport.html">section 6.7</a>.
	321	<a class="sec" href="reexport.html#sec:6.7">section 6.7</a>.
281	322
282	323	<pre class="code">
283	324	:- use_module(library(lists), [ member/2,

291	332
292	333	<p>In most cases a module is imported because some of its predicates are
293	334	being used. However, sometimes a module is imported for other reasons,
294		e.g., for its declarations. In such cases it is best practice to use <a name="idx:usemodule2:1680"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
	335	e.g., for its declarations. In such cases it is best practice to use <a id="idx:usemodule2:1684"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
295	336	with empty ImportList. This distinguishes an imported module that is
296	337	used, although not for its predicates, from a module that is needlessly
297	338	imported.
298	339
299		<p>The <a name="idx:module2:1681"></a><a class="pred" href="defmodule.html#module/2">module/2</a>, <a name="idx:usemodule1:1682"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
300		and <a name="idx:usemodule2:1683"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
	340	<p>The <a id="idx:module2:1685"></a><a class="pred" href="defmodule.html#module/2">module/2</a>, <a id="idx:usemodule1:1686"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	341	and <a id="idx:usemodule2:1687"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
301	342	directives are sufficient to partition a simple Prolog program into
302		modules. The SWI-Prolog graphical cross-referencing tool <a name="idx:gxref0:1684"></a><a class="pred" href="xref.html#gxref/0">gxref/0</a>
	343	modules. The SWI-Prolog graphical cross-referencing tool <a id="idx:gxref0:1688"></a><a class="pred" href="xref.html#gxref/0">gxref/0</a>
303	344	can be used to analyse the dependencies between non-module files and
304	345	propose module declarations for each file.
305	346

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3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 6.9</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 6.9</title><link rel="home" href="index.html">
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130
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141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
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191	232	<a class="nav" href="moduleop.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="resmodules.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:importmodule"><a name="sec:6.9"><span class="sec-nr">6.9</span> <span class="sec-title">Dynamic
	235	<h2 id="sec:importmodule"><a id="sec:6.9"><span class="sec-nr">6.9</span> <span class="sec-title">Dynamic
195	236	importing using import modules</span></a></h2>
196	237
197		<a name="sec:importmodule"></a>
	238	<a id="sec:importmodule"></a>
198	239
199	240	<p>Until now we discussed the public module interface that is, at least
200	241	to some extent, portable between Prolog implementations with a module

210	251	and
211	252	<code>system</code> for all system library modules. Module <code>user</code>
212	253	imports from <code>system</code> where all built-in predicates reside.
213		These special modules are described in more detail in <a class="sec" href="resmodules.html">section
	254	These special modules are described in more detail in <a class="sec" href="resmodules.html#sec:6.10">section
214	255	6.10</a>.
215	256
216	257	<p>The list of import modules can be manipulated and queried using the
217		following predicates, as well as using <a name="idx:setmodule1:1718"></a><a class="pred" href="manipmodule.html#set_module/1">set_module/1</a>.
	258	following predicates, as well as using <a id="idx:setmodule1:1722"></a><a class="pred" href="manipmodule.html#set_module/1">set_module/1</a>.
218	259
219	260	<dl class="latex">
220		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="import_module/2"><strong>import_module</strong>(<var>+Module,
	261	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="import_module/2"><strong>import_module</strong>(<var>+Module,
221	262	-Import</var>)</a></dt>
222	263	<dd class="defbody">
223	264	True if <var>Module</var> inherits directly from <var>Import</var>. All
224	265	normal modules only import from <code>user</code>, which imports from
225		<code>system</code>. The predicates <a name="idx:addimportmodule3:1719"></a><a class="pred" href="importmodule.html#add_import_module/3">add_import_module/3</a>
	266	<code>system</code>. The predicates <a id="idx:addimportmodule3:1723"></a><a class="pred" href="importmodule.html#add_import_module/3">add_import_module/3</a>
226	267	and
227		<a name="idx:deleteimportmodule2:1720"></a><a class="pred" href="importmodule.html#delete_import_module/2">delete_import_module/2</a>
228		can be used to manipulate the import list. See also <a name="idx:defaultmodule2:1721"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>.</dd>
229		<dt class="pubdef"><span class="pred-tag">[multi]</span><a name="default_module/2"><strong>default_module</strong>(<var>+Module,
	268	<a id="idx:deleteimportmodule2:1724"></a><a class="pred" href="importmodule.html#delete_import_module/2">delete_import_module/2</a>
	269	can be used to manipulate the import list. See also <a id="idx:defaultmodule2:1725"></a><a class="pred" href="importmodule.html#default_module/2">default_module/2</a>.</dd>
	270	<dt class="pubdef"><span class="pred-tag">[multi]</span><a id="default_module/2"><strong>default_module</strong>(<var>+Module,
230	271	-Default</var>)</a></dt>
231	272	<dd class="defbody">
232	273	True if predicates and operators in <var>Default</var> are visible in
233	274	<var>Module</var>. Modules are returned in the same search order used
234	275	for predicates and operators. That is, <var>Default</var> is first
235	276	unified with <var>Module</var>, followed by the depth-first transitive
236		closure of <a name="idx:importmodule2:1722"></a><a class="pred" href="importmodule.html#import_module/2">import_module/2</a>.</dd>
237		<dt class="pubdef"><a name="add_import_module/3"><strong>add_import_module</strong>(<var>+Module,
	277	closure of <a id="idx:importmodule2:1726"></a><a class="pred" href="importmodule.html#import_module/2">import_module/2</a>.</dd>
	278	<dt class="pubdef"><a id="add_import_module/3"><strong>add_import_module</strong>(<var>+Module,
238	279	+Import, +StartOrEnd</var>)</a></dt>
239	280	<dd class="defbody">
240	281	If <var>Import</var> is not already an import module for <var>Module</var>,
241	282	add it to this list at the <code>start</code> or <code>end</code>
242	283	depending on
243		<var>StartOrEnd</var>. See also <a name="idx:importmodule2:1723"></a><a class="pred" href="importmodule.html#import_module/2">import_module/2</a>
244		and <a name="idx:deleteimportmodule2:1724"></a><a class="pred" href="importmodule.html#delete_import_module/2">delete_import_module/2</a>.</dd>
245		<dt class="pubdef"><a name="delete_import_module/2"><strong>delete_import_module</strong>(<var>+Module,
	284	<var>StartOrEnd</var>. See also <a id="idx:importmodule2:1727"></a><a class="pred" href="importmodule.html#import_module/2">import_module/2</a>
	285	and <a id="idx:deleteimportmodule2:1728"></a><a class="pred" href="importmodule.html#delete_import_module/2">delete_import_module/2</a>.</dd>
	286	<dt class="pubdef"><a id="delete_import_module/2"><strong>delete_import_module</strong>(<var>+Module,
246	287	+Import</var>)</a></dt>
247	288	<dd class="defbody">
248	289	Delete <var>Import</var> from the list of import modules for <var>Module</var>.

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25	29
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187	228	<a class="nav" href="summary.html"><img src="info.gif" alt="Summary"></a>
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189	230	</div>
190		<div class="title">SWI-Prolog 7.6.2 Reference Manual</div>
191		<div class="author">mailto:J.Wielemaker@vu.nlJan Wielemaker <br>
	231	<div class="title">SWI-Prolog 7.7.4 Reference Manual</div>
	232	<div class="author"><a class="url" href="mailto:J.Wielemaker@vu.nl">Jan
	233	Wielemaker</a> <br>
192	234	Department of Computer Science <br>
193	235	VU University Amsterdam <br>
194	236	De Boelelaan 1081a, 1081 HV  Amsterdam

230	272	sources. From the same source we generate the plain-text version and
231	273	index used by the online help system (located in the file <code>MANUAL</code>
232	274	in the library directory) as well as the PDF version. Sources, binaries
233		and documentation can be downloaded from the http://www.swi-prolog.org/Download.htmlSWI-Prolog
234		download page .
	275	and documentation can be downloaded from the <a class="url" href="http://www.swi-prolog.org/Download.html">SWI-Prolog
	276	download page</a>.
235	277
236	278	<p>The SWI-Prolog project <b>home page</b> is
237		http://www.swi-prolog.orghttp://www.swi-prolog.org
	279	<a class="url" href="http://www.swi-prolog.org">http://www.swi-prolog.org</a>
	280
	281	<p><img src="by-sa.png">
238	282
239	283	<p>This work is licensed under the Creative Commons
240	284	Attribution-ShareAlike 3.0 Unported License. To view a copy of this

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3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 2.2</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 2.2</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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191	232	<a class="nav" href="quickstart.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="initgoal.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:initfile"><a name="sec:2.2"><span class="sec-nr">2.2</span> <span class="sec-title">The
	235	<h2 id="sec:initfile"><a id="sec:2.2"><span class="sec-nr">2.2</span> <span class="sec-title">The
195	236	user's initialisation file</span></a></h2>
196	237
197		<a name="sec:initfile"></a>
198
199		<p><a name="idx:startupfile:18"></a><a name="idx:userprofilefile:19"></a><a name="idx:profilefile:20"></a>After
	238	<a id="sec:initfile"></a>
	239
	240	<p><a id="idx:startupfile:18"></a><a id="idx:userprofilefile:19"></a><a id="idx:profilefile:20"></a>After
200	241	the system initialisation, the system consults (see
201		<a name="idx:consult1:21"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>)
	242	<a id="idx:consult1:21"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>)
202	243	the user's startup file. The basename of this file follows conventions
203	244	of the operating system. On MS-Windows, it is the file
204	245	<code>swipl.ini</code> and on Unix systems <code>.swiplrc</code>. The
205		file is searched using the <a name="idx:filesearchpath2:22"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	246	file is searched using the <a id="idx:filesearchpath2:22"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
206	247	clauses for
207	248	<code>user_profile</code>.<sup class="fn">9<span class="fn-text">Older
208	249	versions first searched in the current working directory. This feature

211	252	The table below shows the default value for this search path. The phrase <<var>appdata</var>>
212	253	refers to the Windows CSIDL name for the folder. The actual name depends
213	254	on the Windows language. English versions typically use <code>ApplicationData</code>.
214		See also <a name="idx:winfolder2:23"></a><a class="pred" href="system.html#win_folder/2">win_folder/2</a>
215
216		<p><table border="2" frame="box" rules="groups" style="margin:auto">
217		<tr valign="top"><td></td><td><b>Unix</b></td><td><b>Windows </b></td></tr>
218		<tbody>
219		<tr valign="top"><td><b>home</b></td><td><code><code>~</code></code> </td><td><<var>appdata</var>>/SWI-Prolog </td></tr>
	255	See also <a id="idx:winfolder2:23"></a><a class="pred" href="system.html#win_folder/2">win_folder/2</a>
	256
	257	<p><table class="latex frame-box center">
	258	<tr><td></td><td><b>Unix</b></td><td><b>Windows </b></td></tr>
	259	<tr class="hline"><td><b>home</b></td><td><code><code>~</code></code> </td><td><<var>appdata</var>>/SWI-Prolog </td></tr>
220	260	</table>
221	261
222	262	<p>After the first startup file is found it is loaded and Prolog stops

235	275	system skeleton.
236	276
237	277	<p>See also the <strong>-s</strong> (script) and <strong>-F</strong>
238		(system-wide initialisation) in <a class="sec" href="cmdline.html">section
239		2.4</a> and <a class="sec" href="initgoal.html">section 2.3</a>.
	278	(system-wide initialisation) in <a class="sec" href="cmdline.html#sec:2.4">section
	279	2.4</a> and <a class="sec" href="initgoal.html#sec:2.3">section 2.3</a>.
240	280
241	281	<p></body></html>⏎

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 2.3</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="initfile.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="cmdline.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:initgoal"><a name="sec:2.3"><span class="sec-nr">2.3</span> <span class="sec-title">Initialisation
	235	<h2 id="sec:initgoal"><a id="sec:2.3"><span class="sec-nr">2.3</span> <span class="sec-title">Initialisation
195	236	files and goals</span></a></h2>
196	237
197		<a name="sec:initgoal"></a>
198
199		<p>Using command line arguments (see <a class="sec" href="cmdline.html">section
	238	<a id="sec:initgoal"></a>
	239
	240	<p>Using command line arguments (see <a class="sec" href="cmdline.html#sec:2.4">section
200	241	2.4</a>), SWI-Prolog can be forced to load files and execute queries for
201	242	initialisation purposes or non-interactive operation. The most commonly
202	243	used options are

238	279	:- halt. % and exit
239	280	</pre>
240	281
241		<p><a class="sec" href="compilation.html">Section 2.10.2.1</a> discusses
242		further scripting options, and
243		<a class="sec" href="runtime.html">chapter 12</a> discusses the
	282	<p><a class="sec" href="compilation.html#sec:2.10.2.1">Section 2.10.2.1</a>
	283	discusses further scripting options, and
	284	<a class="sec" href="runtime.html#sec:12">chapter 12</a> discusses the
244	285	generation of runtime executables. Runtime executables are a means to
245	286	deliver executables that do not require the Prolog system.
246	287

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section B.7</title><link rel="home" href="index.html">
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130
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191	232	<a class="nav" href="exception3.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="loadfilehook.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:intlibs"><a name="sec:B.7"><span class="sec-nr">B.7</span> <span class="sec-title">Hooks
	235	<h2 id="sec:intlibs"><a id="sec:B.7"><span class="sec-nr">B.7</span> <span class="sec-title">Hooks
195	236	for integrating libraries</span></a></h2>
196	237
197		<a name="sec:intlibs"></a>
	238	<a id="sec:intlibs"></a>
198	239
199	240	<p>Some libraries realise an entirely new programming paradigm on top of
200	241	Prolog. An example is XPCE which adds an object system to Prolog as well
201	242	as an extensive set of graphical primitives. SWI-Prolog provides several
202	243	hooks to improve the integration of such libraries. See also
203		<a class="sec" href="listing.html">section 4.5</a> for editing hooks and <a class="sec" href="exception.html">section
204		4.11.4</a> for hooking into the message system.
	244	<a class="sec" href="listing.html#sec:4.5">section 4.5</a> for editing
	245	hooks and <a class="sec" href="exception.html#sec:4.11.4">section 4.11.4</a>
	246	for hooking into the message system.
205	247
206	248	<dl class="latex">
207		<dt class="pubdef"><a name="prolog_list_goal/1"><strong>prolog_list_goal</strong>(<var>:Goal</var>)</a></dt>
	249	<dt class="pubdef"><a id="prolog_list_goal/1"><strong>prolog_list_goal</strong>(<var>:Goal</var>)</a></dt>
208	250	<dd class="defbody">
209	251	Hook, normally not defined. This hook is called by the 'L' command of
210	252	the tracer in the module <code>user</code> to list the currently called
211	253	predicate. This hook may be defined to list only relevant clauses of the
212	254	indicated <var>Goal</var> and/or show the actual source code in an
213		editor. See also <a name="idx:portray1:2219"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
214		and <a name="idx:multifile1:2220"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.</dd>
215		<dt class="pubdef"><a name="prolog:debug_control_hook/1"><strong>prolog:debug_control_hook</strong>(<var>:Action</var>)</a></dt>
	255	editor. See also <a id="idx:portray1:2223"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	256	and <a id="idx:multifile1:2224"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>.</dd>
	257	<dt class="pubdef"><a id="prolog:debug_control_hook/1"><strong>prolog:debug_control_hook</strong>(<var>:Action</var>)</a></dt>
216	258	<dd class="defbody">
217	259	Hook for the debugger control predicates that allows the creator of more
218	260	high-level programming languages to use the common front-end predicates

222	264	<dl class="latex">
223	265	<dt><strong>spy</strong>(<var>Spec</var>)</dt>
224	266	<dd class="defbody">
225		Hook in <a name="idx:spy1:2221"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>.
226		If the hook succeeds <a name="idx:spy1:2222"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
	267	Hook in <a id="idx:spy1:2225"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>.
	268	If the hook succeeds <a id="idx:spy1:2226"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
227	269	takes no further action.
228	270	</dd>
229	271	<dt><strong>nospy</strong>(<var>Spec</var>)</dt>
230	272	<dd class="defbody">
231		Hook in <a name="idx:nospy1:2223"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>.
232		If the hook succeeds <a name="idx:nospy1:2224"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>
233		takes no further action. If <a name="idx:spy1:2225"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
	273	Hook in <a id="idx:nospy1:2227"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>.
	274	If the hook succeeds <a id="idx:nospy1:2228"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>
	275	takes no further action. If <a id="idx:spy1:2229"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
234	276	is hooked, it is advised to place a complementary hook for
235		<a name="idx:nospy1:2226"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>.
	277	<a id="idx:nospy1:2230"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>.
236	278	</dd>
237	279	<dt><strong>nospyall</strong></dt>
238	280	<dd class="defbody">
239		Hook in <a name="idx:nospyall0:2227"></a><a class="pred" href="debugger.html#nospyall/0">nospyall/0</a>.
	281	Hook in <a id="idx:nospyall0:2231"></a><a class="pred" href="debugger.html#nospyall/0">nospyall/0</a>.
240	282	Should remove all spy points. This hook is called in a failure-driven
241	283	loop.
242	284	</dd>
243	285	<dt><strong>debugging</strong></dt>
244	286	<dd class="defbody">
245		Hook in <a name="idx:debugging0:2228"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a>.
	287	Hook in <a id="idx:debugging0:2232"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a>.
246	288	It can be used in two ways. It can report the status of the additional
247	289	debug points controlled by the above hooks and fail to let the system
248		report the others, or it succeeds, overruling the entire behaviour of <a name="idx:debugging0:2229"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a>.
	290	report the others, or it succeeds, overruling the entire behaviour of <a id="idx:debugging0:2233"></a><a class="pred" href="debugger.html#debugging/0">debugging/0</a>.
249	291	</dd>
250	292	</dl>
251	293
252	294	</dd>
253		<dt class="pubdef"><a name="prolog:help_hook/1"><strong>prolog:help_hook</strong>(<var>+Action</var>)</a></dt>
254		<dd class="defbody">
255		Hook into <a name="idx:help0:2230"></a><a class="pred" href="help.html#help/0">help/0</a>
256		and <a name="idx:help1:2231"></a><a class="pred" href="help.html#help/1">help/1</a>.
	295	<dt class="pubdef"><a id="prolog:help_hook/1"><strong>prolog:help_hook</strong>(<var>+Action</var>)</a></dt>
	296	<dd class="defbody">
	297	Hook into <a id="idx:help0:2234"></a><a class="pred" href="help.html#help/0">help/0</a>
	298	and <a id="idx:help1:2235"></a><a class="pred" href="help.html#help/1">help/1</a>.
257	299	If the hook succeeds, the built-in actions are not executed. For
258	300	example, <code>?- help(picture).</code> is caught by the XPCE help hook
259	301	to give help on the class <em>picture</em>. Defined actions are:

261	303	<dl class="latex">
262	304	<dt><strong>help</strong></dt>
263	305	<dd class="defbody">
264		User entered plain <a name="idx:help0:2232"></a><a class="pred" href="help.html#help/0">help/0</a>
	306	User entered plain <a id="idx:help0:2236"></a><a class="pred" href="help.html#help/0">help/0</a>
265	307	to give default help. The default performs
266		<code>help(<a name="idx:help1:2233"></a><a class="pred" href="help.html#help/1">help/1</a>)</code>,
	308	<code>help(<a id="idx:help1:2237"></a><a class="pred" href="help.html#help/1">help/1</a>)</code>,
267	309	giving help on help.
268	310	</dd>
269	311	<dt><strong>help</strong>(<var>What</var>)</dt>
270	312	<dd class="defbody">
271		Hook in <a name="idx:help1:2234"></a><a class="pred" href="help.html#help/1">help/1</a>
	313	Hook in <a id="idx:help1:2238"></a><a class="pred" href="help.html#help/1">help/1</a>
272	314	on the topic <var>What</var>.
273	315	</dd>
274	316	<dt><strong>apropos</strong>(<var>What</var>)</dt>
275	317	<dd class="defbody">
276		Hook in <a name="idx:apropos1:2235"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>
	318	Hook in <a id="idx:apropos1:2239"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>
277	319	on the topic <var>What</var>.
278	320	</dd>
279	321	</dl>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual</title><link rel="home" href="index.html">
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193	234	</div>
194		<h1 id="sec:intro"><a name="sec:1"><span class="sec-nr">1</span> <span class="sec-title">Introduction</span></a></h1>
195
196		<a name="sec:intro"></a>
	235	<h1 id="sec:intro"><a id="sec:1"><span class="sec-nr">1</span> <span class="sec-title">Introduction</span></a></h1>
	236
	237	<a id="sec:intro"></a>
197	238
198	239	<p>This document is a <em>reference manual</em>. That means that it
199	240	documents the system, but it does not explain the basics of the Prolog

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.14</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:iostream"><a name="sec:A.14"><span class="sec-nr">A.14</span> <span class="sec-title">library(iostream):
	235	<h2 id="sec:iostream"><a id="sec:A.14"><span class="sec-nr">A.14</span> <span class="sec-title">library(iostream):
195	236	Utilities to deal with streams</span></a></h2>
196	237
197		<p><a name="sec:iostream"></a>
	238	<p><a id="sec:iostream"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">See also</dt>

229	270	<a class="pred" href="iostream.html#open_any/5">open_any/5</a>.
230	271
231	272	<dl class="latex">
232		<dt class="pubdef"><a name="open_any/5"><strong>open_any</strong>(<var>+Specification,
	273	<dt class="pubdef"><a id="open_any/5"><strong>open_any</strong>(<var>+Specification,
233	274	+Mode, -Stream, -Close, +Options</var>)</a></dt>
234	275	<dd class="defbody">
235	276	Establish a stream from <var>Specification</var> that should be closed

299	340	</dl>
300	341
301	342	</dd>
302		<dt class="pubdef"><a name="close_any/1"><strong>close_any</strong>(<var>+Goal</var>)</a></dt>
	343	<dt class="pubdef"><a id="close_any/1"><strong>close_any</strong>(<var>+Goal</var>)</a></dt>
303	344	<dd class="defbody">
304	345	Execute the <var>Close</var> closure returned by <a class="pred" href="iostream.html#open_any/5">open_any/5</a>.
305	346	The closure can also be called directly. Using <a class="pred" href="iostream.html#close_any/1">close_any/1</a>
306	347	can be considered better style and enhances tractability of the source
307	348	code.</dd>
308		<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a name="open_hook/6"><strong>open_hook</strong>(<var>+Spec,
	349	<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="open_hook/6"><strong>open_hook</strong>(<var>+Spec,
309	350	+Mode, -Stream, -Close, +Options0, -Options</var>)</a></dt>
310	351	<dd class="defbody">
311	352	Open <var>Spec</var> in <var>Mode</var>, producing <var>Stream</var>.
312	353	<table class="arglist">
313		<tr valign="top"><td><var>Close</var> </td><td>is unified to a goal that
314		must be called to undo the side-effects of the action, e.g., typically
315		the term <code>close(Stream)</code> </td></tr>
316		<tr valign="top"><td><var>Options0</var> </td><td>are the options passed
317		to <a class="pred" href="iostream.html#open_any/5">open_any/5</a> </td></tr>
318		<tr valign="top"><td><var>Options</var> </td><td>are passed to the post
319		processing filters that may be installed by <a class="pred" href="iostream.html#open_any/5">open_any/5</a>. </td></tr>
	354	<tr><td><var>Close</var> </td><td>is unified to a goal that must be
	355	called to undo the side-effects of the action, e.g., typically the term <code>close(Stream)</code> </td></tr>
	356	<tr><td><var>Options0</var> </td><td>are the options passed to <a class="pred" href="iostream.html#open_any/5">open_any/5</a> </td></tr>
	357	<tr><td><var>Options</var> </td><td>are passed to the post processing
	358	filters that may be installed by <a class="pred" href="iostream.html#open_any/5">open_any/5</a>. </td></tr>
320	359	</table>
321	360	</dd>
322	361	</dl>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 2.18</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:jitindex"><a name="sec:2.18"><span class="sec-nr">2.18</span> <span class="sec-title">Just-in-time
	235	<h2 id="sec:jitindex"><a id="sec:2.18"><span class="sec-nr">2.18</span> <span class="sec-title">Just-in-time
195	236	clause indexing</span></a></h2>
196	237
197		<a name="sec:jitindex"></a>
198
199		<p><a name="idx:jitindex:255"></a>SWI-Prolog provides `just-in-time'
	238	<a id="sec:jitindex"></a>
	239
	240	<p><a id="idx:jitindex:255"></a>SWI-Prolog provides `just-in-time'
200	241	indexing over multiple arguments.<sup class="fn">31<span class="fn-text">JIT
201	242	indexing was added in version 5.11.29 (Oct. 2011).</span></sup>
202	243	`Just-in-time' means that clause indexes are not built by the compiler
203		(or <a name="idx:asserta1:256"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
	244	(or <a id="idx:asserta1:256"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
204	245	for dynamic predicates), but on the first call to such a predicate where
205	246	an index might help (i.e., a call where at least one argument is
206	247	instantiated). This section describes the rules used by the indexing

258	299	approach will recreate a suitable index on the next call. Indexes of
259	300	running predicates cannot be deleted. They are added to a `removed index
260	301	list' associated to the predicate. Outdated indexes of predicates are
261		reclaimed by <a name="idx:garbagecollectclauses0:257"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>.
	302	reclaimed by <a id="idx:garbagecollectclauses0:257"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>.
262	303	The clause garbage collector is scheduled automatically, based on time
263		and space based heuristics. See <a name="idx:garbagecollectclauses0:258"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>
	304	and space based heuristics. See <a id="idx:garbagecollectclauses0:258"></a><a class="pred" href="consulting.html#garbage_collect_clauses/0">garbage_collect_clauses/0</a>
264	305	for details.
265	306	</ul>
266	307
267		<p>The library <code>library(prolog_jiti)</code> provides <a name="idx:jitilist0:259"></a><span class="pred-ext">jiti_list/0</span>,1
	308	<p>The library <code>library(prolog_jiti)</code> provides <a id="idx:jitilist0:259"></a><span class="pred-ext">jiti_list/0</span>,1
268	309	to list the characteristics of all or some of the created hash tables.
269	310
270		<p><h3 id="sec:indexfut"><a name="sec:2.18.1"><span class="sec-nr">2.18.1</span> <span class="sec-title">Future
	311	<p><h3 id="sec:indexfut"><a id="sec:2.18.1"><span class="sec-nr">2.18.1</span> <span class="sec-title">Future
271	312	directions</span></a></h3>
272	313
273		<a name="sec:indexfut"></a>
	314	<a id="sec:indexfut"></a>
274	315
275	316	<p>
276	317	<ul class="latex">

286	327	lookup is too costly.
287	328	</ul>
288	329
289		<p><h3 id="sec:indexport"><a name="sec:2.18.2"><span class="sec-nr">2.18.2</span> <span class="sec-title">Indexing
	330	<p><h3 id="sec:indexport"><a id="sec:2.18.2"><span class="sec-nr">2.18.2</span> <span class="sec-title">Indexing
290	331	and portability</span></a></h3>
291	332
292		<a name="sec:indexport"></a>
	333	<a id="sec:indexport"></a>
293	334
294	335	<p>The base-line functionality of Prolog implementations provides
295	336	indexing on constants and functor (name/arity) on the first argument.
296	337	This must be your assumption if wide portability of your program is
297		important. This can typically be achieved by exploiting <a name="idx:termhash2:260"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>
298		or <a name="idx:termhash4:261"></a><a class="pred" href="db.html#term_hash/4">term_hash/4</a>
	338	important. This can typically be achieved by exploiting <a id="idx:termhash2:260"></a><a class="pred" href="db.html#term_hash/2">term_hash/2</a>
	339	or <a id="idx:termhash4:261"></a><a class="pred" href="db.html#term_hash/4">term_hash/4</a>
299	340	and/or maintaining multiple copies of a predicate with reordered
300	341	arguments and wrappers that update all implementations (assert/retract)
301	342	and selects the appropriate implementation (query).

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193	234	</div>
194		<h1 id="sec:libpl"><a name="sec:A"><span class="sec-nr">A</span> <span class="sec-title">The
	235	<h1 id="sec:libpl"><a id="sec:A"><span class="sec-nr">A</span> <span class="sec-title">The
195	236	SWI-Prolog library</span></a></h1>
196	237
197		<a name="sec:libpl"></a>
	238	<a id="sec:libpl"></a>
198	239
199	240	<p>This chapter documents the SWI-Prolog library. As SWI-Prolog provides
200	241	auto-loading, there is little difference between library predicates and

209	250
210	251	<p>
211	252	<li>If autoloading is disabled explicitly or because trapping unknown
212		predicates is disabled (see <a name="idx:unknown2:2130"></a><a class="pred" href="debugger.html#unknown/2">unknown/2</a>
	253	predicates is disabled (see <a id="idx:unknown2:2134"></a><a class="pred" href="debugger.html#unknown/2">unknown/2</a>
213	254	and
214		<a name="idx:currentprologflag2:2131"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>),
	255	<a id="idx:currentprologflag2:2135"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>),
215	256	library predicates must be loaded explicitly.
216	257
217	258	<p>

+196

-150

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section F.2</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section F.2</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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130
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191	232	<a class="nav" href="predsummary.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="funcsummary.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:library"><a name="sec:F.2"><span class="sec-nr">F.2</span> <span class="sec-title">Library
	235	<h2 id="sec:library"><a id="sec:F.2"><span class="sec-nr">F.2</span> <span class="sec-title">Library
195	236	predicates</span></a></h2>
196	237
197		<a name="sec:library"></a>
198
199		<p><h3 id="sec:summary-lib-aggregate"><a name="sec:F.2.1"><span class="sec-nr">F.2.1</span> <span class="sec-title">library(aggregate)</span></a></h3>
200
201		<a name="sec:summary-lib-aggregate"></a>
	238	<a id="sec:library"></a>
	239
	240	<p><h3 id="sec:summary-lib-aggregate"><a id="sec:F.2.1"><span class="sec-nr">F.2.1</span> <span class="sec-title">library(aggregate)</span></a></h3>
	241
	242	<a id="sec:summary-lib-aggregate"></a>
202	243	<table>
203	244	<tr><td><a class="pred" href="aggregate.html#aggregate/3">aggregate/3</a></td><td>Aggregate
204	245	bindings in Goal according to Template.</td></tr>

214	255	free variables in bagof/setof template.</td></tr>
215	256	</table>
216	257
217		<p><h3 id="sec:summary-lib-apply"><a name="sec:F.2.2"><span class="sec-nr">F.2.2</span> <span class="sec-title">library(apply)</span></a></h3>
218
219		<a name="sec:summary-lib-apply"></a>
	258	<p><h3 id="sec:summary-lib-apply"><a id="sec:F.2.2"><span class="sec-nr">F.2.2</span> <span class="sec-title">library(apply)</span></a></h3>
	259
	260	<a id="sec:summary-lib-apply"></a>
220	261	<table>
221	262	<tr><td><a class="pred" href="apply.html#convlist/3">convlist/3</a></td><td>Similar
222	263	to maplist/3, but elements for which call(Goal, ElemIn, _) fails are

255	296	scan of list.</td></tr>
256	297	</table>
257	298
258		<p><h3 id="sec:summary-lib-assoc"><a name="sec:F.2.3"><span class="sec-nr">F.2.3</span> <span class="sec-title">library(assoc)</span></a></h3>
259
260		<a name="sec:summary-lib-assoc"></a>
	299	<p><h3 id="sec:summary-lib-assoc"><a id="sec:F.2.3"><span class="sec-nr">F.2.3</span> <span class="sec-title">library(assoc)</span></a></h3>
	300
	301	<a id="sec:summary-lib-assoc"></a>
261	302	<table>
262	303	<tr><td><a class="pred" href="assoc.html#assoc_to_list/2">assoc_to_list/2</a></td><td>Translate
263	304	assoc into a pairs list</td></tr>

289	330	association to an assoc</td></tr>
290	331	</table>
291	332
292		<p><h3 id="sec:summary-lib-broadcast"><a name="sec:F.2.4"><span class="sec-nr">F.2.4</span> <span class="sec-title">library(broadcast)</span></a></h3>
293
294		<a name="sec:summary-lib-broadcast"></a>
	333	<p><h3 id="sec:summary-lib-broadcast"><a id="sec:F.2.4"><span class="sec-nr">F.2.4</span> <span class="sec-title">library(broadcast)</span></a></h3>
	334
	335	<a id="sec:summary-lib-broadcast"></a>
295	336	<table>
296	337	<tr><td><a class="pred" href="broadcast.html#broadcast/1">broadcast/1</a></td><td>Send
297	338	event notification</td></tr>

311	352	is listening to event notifications?</td></tr>
312	353	</table>
313	354
314		<p><h3 id="sec:summary-lib-charsio"><a name="sec:F.2.5"><span class="sec-nr">F.2.5</span> <span class="sec-title">library(charsio)</span></a></h3>
315
316		<a name="sec:summary-lib-charsio"></a>
	355	<p><h3 id="sec:summary-lib-charsio"><a id="sec:F.2.5"><span class="sec-nr">F.2.5</span> <span class="sec-title">library(charsio)</span></a></h3>
	356
	357	<a id="sec:summary-lib-charsio"></a>
317	358	<table>
318	359	<tr><td><a class="pred" href="charsio.html#atom_to_chars/2">atom_to_chars/2</a></td><td>Convert
319	360	Atom into a list of character codes.</td></tr>

345	386	a term to a code list.</td></tr>
346	387	</table>
347	388
348		<p><h3 id="sec:summary-lib-check"><a name="sec:F.2.6"><span class="sec-nr">F.2.6</span> <span class="sec-title">library(check)</span></a></h3>
349
350		<a name="sec:summary-lib-check"></a>
	389	<p><h3 id="sec:summary-lib-check"><a id="sec:F.2.6"><span class="sec-nr">F.2.6</span> <span class="sec-title">library(check)</span></a></h3>
	390
	391	<a id="sec:summary-lib-check"></a>
351	392	<table>
352	393	<tr><td><a class="pred" href="check.html#check/0">check/0</a></td><td>Run
353	394	all consistency checks defined by checker/2.</td></tr>

381	422	hook that qualifies Goal as valid for list_strings/0.</td></tr>
382	423	</table>
383	424
384		<p><h3 id="sec:summary-lib-clpb"><a name="sec:F.2.7"><span class="sec-nr">F.2.7</span> <span class="sec-title">library(clpb)</span></a></h3>
385
386		<a name="sec:summary-lib-clpb"></a>
	425	<p><h3 id="sec:summary-lib-clpb"><a id="sec:F.2.7"><span class="sec-nr">F.2.7</span> <span class="sec-title">library(clpb)</span></a></h3>
	426
	427	<a id="sec:summary-lib-clpb"></a>
387	428	<table>
388	429	<tr><td><a class="pred" href="clpb.html#labeling/1">labeling/1</a></td><td>Enumerate
389	430	concrete solutions.</td></tr>

399	440	weighted optima over admissible assignments.</td></tr>
400	441	</table>
401	442
402		<p><h3 id="sec:summary-lib-clpfd"><a name="sec:F.2.8"><span class="sec-nr">F.2.8</span> <span class="sec-title">library(clpfd)</span></a></h3>
403
404		<a name="sec:summary-lib-clpfd"></a>
	443	<p><h3 id="sec:summary-lib-clpfd"><a id="sec:F.2.8"><span class="sec-nr">F.2.8</span> <span class="sec-title">library(clpfd)</span></a></h3>
	444
	445	<a id="sec:summary-lib-clpfd"></a>
405	446	<table>
406	447	<tr><td><a class="pred" href="clpfd.html##/\/2">#/\/2</a></td><td>P and
407	448	Q hold.</td></tr>

490	531	to compare/3, with finite domain variables A and B.</td></tr>
491	532	</table>
492	533
493		<p><h3 id="sec:summary-lib-clpqr"><a name="sec:F.2.9"><span class="sec-nr">F.2.9</span> <span class="sec-title">library(clpqr)</span></a></h3>
494
495		<a name="sec:summary-lib-clpqr"></a>
	534	<p><h3 id="sec:summary-lib-clpqr"><a id="sec:F.2.9"><span class="sec-nr">F.2.9</span> <span class="sec-title">library(clpqr)</span></a></h3>
	535
	536	<a id="sec:summary-lib-clpqr"></a>
496	537	<table>
497	538	<tr><td><a class="pred" href="clpqr.html#entailed/1">entailed/1</a></td><td>Check
498	539	if constraint is entailed</td></tr>

514	555	constraints on variables</td></tr>
515	556	</table>
516	557
517		<p><h3 id="sec:summary-lib-csv"><a name="sec:F.2.10"><span class="sec-nr">F.2.10</span> <span class="sec-title">library(csv)</span></a></h3>
518
519		<a name="sec:summary-lib-csv"></a>
	558	<p><h3 id="sec:summary-lib-csv"><a id="sec:F.2.10"><span class="sec-nr">F.2.10</span> <span class="sec-title">library(csv)</span></a></h3>
	559
	560	<a id="sec:summary-lib-csv"></a>
520	561	<table>
521	562	<tr><td><a class="pred" href="csv.html#csv_options/2">csv_options/2</a></td><td>Compiled
522	563	is the compiled representation of the CSV processing options as they may

535	576	a list of Prolog terms to a CSV file.</td></tr>
536	577	<tr><td><a class="pred" href="csv.html#csv_write_stream/3">csv_write_stream/3</a></td><td>Write
537	578	the rows in Data to Stream.</td></tr>
538		csv1Prolog DCG to `read/write' CSV data.
539		csv2Prolog DCG to `read/write' CSV data.
540		</table>
541
542		<p><h3 id="sec:summary-lib-debug"><a name="sec:F.2.11"><span class="sec-nr">F.2.11</span> <span class="sec-title">library(debug)</span></a></h3>
543
544		<a name="sec:summary-lib-debug"></a>
	579	<tr><td><a class="pred" href="csv.html#csv//1">csv//1</a></td><td>Prolog
	580	DCG to `read/write' CSV data.</td></tr>
	581	<tr><td><a class="pred" href="csv.html#csv//2">csv//2</a></td><td>Prolog
	582	DCG to `read/write' CSV data.</td></tr>
	583	</table>
	584
	585	<p><h3 id="sec:summary-lib-debug"><a id="sec:F.2.11"><span class="sec-nr">F.2.11</span> <span class="sec-title">library(debug)</span></a></h3>
	586
	587	<a id="sec:summary-lib-debug"></a>
545	588	<table>
546	589	<tr><td><a class="pred" href="debug.html#assertion/1">assertion/1</a></td><td>Acts
547	590	similar to C assert() macro.</td></tr>

565	608	a topic from being printed.</td></tr>
566	609	</table>
567	610
568		<p><h3 id="sec:summary-lib-error"><a name="sec:F.2.12"><span class="sec-nr">F.2.12</span> <span class="sec-title">library(error)</span></a></h3>
569
570		<a name="sec:summary-lib-error"></a>
	611	<p><h3 id="sec:summary-lib-error"><a id="sec:F.2.12"><span class="sec-nr">F.2.12</span> <span class="sec-title">library(error)</span></a></h3>
	612
	613	<a id="sec:summary-lib-error"></a>
571	614	<table>
572	615	<tr><td><a class="pred" href="error.html#current_type/3">current_type/3</a></td><td>True
573	616	when Type is a currently defined type and Var satisfies Type of the body

601	644	argument is over-instantiated.</td></tr>
602	645	</table>
603	646
604		<p><h3 id="sec:summary-lib-iostream"><a name="sec:F.2.13"><span class="sec-nr">F.2.13</span> <span class="sec-title">library(iostream)</span></a></h3>
605
606		<a name="sec:summary-lib-iostream"></a>
607		<h3 id="sec:summary-lib-summaries.d-iostream-tex"><a name="sec:F.2.14"><span class="sec-nr">F.2.14</span> <span class="sec-title">library(summaries.d/iostream/tex)</span></a></h3>
608
609		<a name="sec:summary-lib-summaries.d-iostream-tex"></a>
610
611		<p><h3 id="sec:summary-lib-lists"><a name="sec:F.2.15"><span class="sec-nr">F.2.15</span> <span class="sec-title">library(lists)</span></a></h3>
612
613		<a name="sec:summary-lib-lists"></a>
	647	<p><h3 id="sec:summary-lib-iostream"><a id="sec:F.2.13"><span class="sec-nr">F.2.13</span> <span class="sec-title">library(iostream)</span></a></h3>
	648
	649	<a id="sec:summary-lib-iostream"></a>
	650	<h3 id="sec:summary-lib-summaries.d-iostream-tex"><a id="sec:F.2.14"><span class="sec-nr">F.2.14</span> <span class="sec-title">library(summaries.d/iostream/tex)</span></a></h3>
	651
	652	<a id="sec:summary-lib-summaries.d-iostream-tex"></a>
	653
	654	<p><h3 id="sec:summary-lib-lists"><a id="sec:F.2.15"><span class="sec-nr">F.2.15</span> <span class="sec-title">library(lists)</span></a></h3>
	655
	656	<a id="sec:summary-lib-lists"></a>
614	657	<table>
615	658	<tr><td><a class="pred" href="lists.html#append/2">append/2</a></td><td>Concatenate
616	659	a list of lists.</td></tr>

678	721	if Set3 unifies with the union of the lists Set1 and Set2.</td></tr>
679	722	</table>
680	723
681		<p><h3 id="sec:summary-lib-main"><a name="sec:F.2.16"><span class="sec-nr">F.2.16</span> <span class="sec-title">library(main)</span></a></h3>
682
683		<a name="sec:summary-lib-main"></a>
	724	<p><h3 id="sec:summary-lib-main"><a id="sec:F.2.16"><span class="sec-nr">F.2.16</span> <span class="sec-title">library(main)</span></a></h3>
	725
	726	<a id="sec:summary-lib-main"></a>
684	727	<table>
685	728	<tr><td><a class="pred" href="main.html#argv_options/3">argv_options/3</a></td><td>Generic
686	729	transformation of long commandline arguments to options.</td></tr>

688	731	main/1 using the passed command-line arguments.</td></tr>
689	732	</table>
690	733
691		<p><h3 id="sec:summary-lib-option"><a name="sec:F.2.17"><span class="sec-nr">F.2.17</span> <span class="sec-title">library(option)</span></a></h3>
692
693		<a name="sec:summary-lib-option"></a>
	734	<p><h3 id="sec:summary-lib-option"><a id="sec:F.2.17"><span class="sec-nr">F.2.17</span> <span class="sec-title">library(option)</span></a></h3>
	735
	736	<a id="sec:summary-lib-option"></a>
694	737	<table>
695	738	<tr><td><a class="pred" href="option.html#dict_options/2">dict_options/2</a></td><td>Convert
696	739	between an option list and a dictionary.</td></tr>

708	751	and remove Option with default value.</td></tr>
709	752	</table>
710	753
711		<p><h3 id="sec:summary-lib-optparse"><a name="sec:F.2.18"><span class="sec-nr">F.2.18</span> <span class="sec-title">library(optparse)</span></a></h3>
712
713		<a name="sec:summary-lib-optparse"></a>
	754	<p><h3 id="sec:summary-lib-optparse"><a id="sec:F.2.18"><span class="sec-nr">F.2.18</span> <span class="sec-title">library(optparse)</span></a></h3>
	755
	756	<a id="sec:summary-lib-optparse"></a>
714	757	<table>
715	758	<tr><td><a class="pred" href="optparse.html#opt_arguments/3">opt_arguments/3</a></td><td>Extract
716	759	commandline options according to a specification.</td></tr>

724	767	to parse option text Codes to an object of type Type.</td></tr>
725	768	</table>
726	769
727		<p><h3 id="sec:summary-lib-ordsets"><a name="sec:F.2.19"><span class="sec-nr">F.2.19</span> <span class="sec-title">library(ordsets)</span></a></h3>
728
729		<a name="sec:summary-lib-ordsets"></a>
	770	<p><h3 id="sec:summary-lib-ordsets"><a id="sec:F.2.19"><span class="sec-nr">F.2.19</span> <span class="sec-title">library(ordsets)</span></a></h3>
	771
	772	<a id="sec:summary-lib-ordsets"></a>
730	773	<table>
731	774	<tr><td><a class="pred" href="ordsets.html#is_ordset/1">is_ordset/1</a></td><td>True
732	775	if Term is an ordered set.</td></tr>

770	813	iff ord_union(Set1, Set2, Union) and ord_subtract(Set2, Set1, New).</td></tr>
771	814	</table>
772	815
773		<p><h3 id="sec:summary-lib-persistency"><a name="sec:F.2.20"><span class="sec-nr">F.2.20</span> <span class="sec-title">library(persistency)</span></a></h3>
774
775		<a name="sec:summary-lib-persistency"></a>
	816	<p><h3 id="sec:summary-lib-persistency"><a id="sec:F.2.20"><span class="sec-nr">F.2.20</span> <span class="sec-title">library(persistency)</span></a></h3>
	817
	818	<a id="sec:summary-lib-persistency"></a>
776	819	<table>
777	820	<tr><td><a class="pred" href="persistency.html#current_persistent_predicate/1">current_persistent_predicate/1</a></td><td>True
778	821	if PI is a predicate that provides access to the persistent database DB.</td></tr>

791	834	dynamic database terms.</td></tr>
792	835	</table>
793	836
794		<p><h3 id="sec:summary-lib-predicate_options"><a name="sec:F.2.21"><span class="sec-nr">F.2.21</span> <span class="sec-title">library(predicate_options)</span></a></h3>
795
796		<a name="sec:summary-lib-predicate_options"></a>
	837	<p><h3 id="sec:summary-lib-predicate_options"><a id="sec:F.2.21"><span class="sec-nr">F.2.21</span> <span class="sec-title">library(predicate_options)</span></a></h3>
	838
	839	<a id="sec:summary-lib-predicate_options"></a>
797	840	<table>
798	841	<tr><td><a class="pred" href="predicate_options.html#assert_predicate_options/4">assert_predicate_options/4</a></td><td>As
799	842	predicate_options(:PI, +Arg, +Options).</td></tr>

819	862	all dynamically (derived) predicate options.</td></tr>
820	863	</table>
821	864
822		<p><h3 id="sec:summary-lib-prologpack"><a name="sec:F.2.22"><span class="sec-nr">F.2.22</span> <span class="sec-title">library(prologpack)</span></a></h3>
823
824		<a name="sec:summary-lib-prologpack"></a>
	865	<p><h3 id="sec:summary-lib-prologpack"><a id="sec:F.2.22"><span class="sec-nr">F.2.22</span> <span class="sec-title">library(prologpack)</span></a></h3>
	866
	867	<a id="sec:summary-lib-prologpack"></a>
825	868	<table>
826	869	<tr><td><a class="pred" href="prologpack.html#environment/2">environment/2</a></td><td>Hook
827	870	to define the environment for building packs.</td></tr>

851	894	if File is a unique id for the referenced pack and version.</td></tr>
852	895	</table>
853	896
854		<p><h3 id="sec:summary-lib-prologxref"><a name="sec:F.2.23"><span class="sec-nr">F.2.23</span> <span class="sec-title">library(prologxref)</span></a></h3>
855
856		<a name="sec:summary-lib-prologxref"></a>
	897	<p><h3 id="sec:summary-lib-prologxref"><a id="sec:F.2.23"><span class="sec-nr">F.2.23</span> <span class="sec-title">library(prologxref)</span></a></h3>
	898
	899	<a id="sec:summary-lib-prologxref"></a>
857	900	<table>
858	901	<tr><td><a class="pred" href="prolog_xref.html#prolog:called_by/2">prolog:called_by/2</a></td><td><i>(hook)</i>
859	902	Extend cross-referencer</td></tr>

875	918	analysis of source</td></tr>
876	919	</table>
877	920
878		<p><h3 id="sec:summary-lib-pairs"><a name="sec:F.2.24"><span class="sec-nr">F.2.24</span> <span class="sec-title">library(pairs)</span></a></h3>
879
880		<a name="sec:summary-lib-pairs"></a>
	921	<p><h3 id="sec:summary-lib-pairs"><a id="sec:F.2.24"><span class="sec-nr">F.2.24</span> <span class="sec-title">library(pairs)</span></a></h3>
	922
	923	<a id="sec:summary-lib-pairs"></a>
881	924	<table>
882	925	<tr><td><a class="pred" href="pairs.html#group_pairs_by_key/2">group_pairs_by_key/2</a></td><td>Group
883	926	values with equivalent (==/2) consecutive keys.</td></tr>

893	936	Key-Value to Value-Key.</td></tr>
894	937	</table>
895	938
896		<p><h3 id="sec:summary-lib-pio"><a name="sec:F.2.25"><span class="sec-nr">F.2.25</span> <span class="sec-title">library(pio)</span></a></h3>
897
898		<a name="sec:summary-lib-pio"></a>
899		<h4 id="sec:summary-lib-pure-input"><a name="sec:F.2.25.1"><span class="sec-nr">F.2.25.1</span> <span class="sec-title">library(pure_input)</span></a></h4>
900
901		<a name="sec:summary-lib-pure-input"></a>
	939	<p><h3 id="sec:summary-lib-pio"><a id="sec:F.2.25"><span class="sec-nr">F.2.25</span> <span class="sec-title">library(pio)</span></a></h3>
	940
	941	<a id="sec:summary-lib-pio"></a>
	942	<h4 id="sec:summary-lib-pure-input"><a id="sec:F.2.25.1"><span class="sec-nr">F.2.25.1</span> <span class="sec-title">library(pure_input)</span></a></h4>
	943
	944	<a id="sec:summary-lib-pure-input"></a>
902	945	<table>
903	946	<tr><td><a class="pred" href="pio.html#phrase_from_file/2">phrase_from_file/2</a></td><td>Process
904	947	the content of File using the DCG rule Grammar.</td></tr>

908	951	Grammer against the character codes on Stream.</td></tr>
909	952	<tr><td><a class="pred" href="pio.html#stream_to_lazy_list/2">stream_to_lazy_list/2</a></td><td>Create
910	953	a lazy list representing the character codes in Stream.</td></tr>
911		lazy_list_character_count1True when CharCount is the current character
912		count in the Lazy list.
913		lazy_list_location1Determine current (error) location in a lazy list.
914		syntax_error1Throw the syntax error Error at the current location of the
915		input.
916		</table>
917
918		<p><h3 id="sec:summary-lib-random"><a name="sec:F.2.26"><span class="sec-nr">F.2.26</span> <span class="sec-title">library(random)</span></a></h3>
919
920		<a name="sec:summary-lib-random"></a>
	954	<tr><td><a class="pred" href="pio.html#lazy_list_character_count//1">lazy_list_character_count//1</a></td><td>True
	955	when CharCount is the current character count in the Lazy list.</td></tr>
	956	<tr><td><a class="pred" href="pio.html#lazy_list_location//1">lazy_list_location//1</a></td><td>Determine
	957	current (error) location in a lazy list.</td></tr>
	958	<tr><td><a class="pred" href="pio.html#syntax_error//1">syntax_error//1</a></td><td>Throw
	959	the syntax error Error at the current location of the input.</td></tr>
	960	</table>
	961
	962	<p><h3 id="sec:summary-lib-random"><a id="sec:F.2.26"><span class="sec-nr">F.2.26</span> <span class="sec-title">library(random)</span></a></h3>
	963
	964	<a id="sec:summary-lib-random"></a>
921	965	<table>
922	966	<tr><td><a class="pred" href="random.html#getrand/1">getrand/1</a></td><td>Query/set
923	967	the state of the random generator.</td></tr>

949	993	the state of the random generator.</td></tr>
950	994	</table>
951	995
952		<p><h3 id="sec:summary-lib-readutil"><a name="sec:F.2.27"><span class="sec-nr">F.2.27</span> <span class="sec-title">library(readutil)</span></a></h3>
953
954		<a name="sec:summary-lib-readutil"></a>
	996	<p><h3 id="sec:summary-lib-readutil"><a id="sec:F.2.27"><span class="sec-nr">F.2.27</span> <span class="sec-title">library(readutil)</span></a></h3>
	997
	998	<a id="sec:summary-lib-readutil"></a>
955	999	<table>
956	1000	<tr><td><a class="pred" href="readutil.html#read_line_to_codes/2">read_line_to_codes/2</a></td><td>Read
957	1001	line from a stream</td></tr>

967	1011	contents of file to Prolog terms</td></tr>
968	1012	</table>
969	1013
970		<p><h3 id="sec:summary-lib-record"><a name="sec:F.2.28"><span class="sec-nr">F.2.28</span> <span class="sec-title">library(record)</span></a></h3>
971
972		<a name="sec:summary-lib-record"></a>
	1014	<p><h3 id="sec:summary-lib-record"><a id="sec:F.2.28"><span class="sec-nr">F.2.28</span> <span class="sec-title">library(record)</span></a></h3>
	1015
	1016	<a id="sec:summary-lib-record"></a>
973	1017	<table>
974	1018	<tr><td><a class="pred" href="record.html#record/1">record/1</a></td><td>Define
975	1019	named fields in a term</td></tr>
976	1020	</table>
977	1021
978		<p><h3 id="sec:summary-lib-registry"><a name="sec:F.2.29"><span class="sec-nr">F.2.29</span> <span class="sec-title">library(registry)</span></a></h3>
979
980		<a name="sec:summary-lib-registry"></a>
	1022	<p><h3 id="sec:summary-lib-registry"><a id="sec:F.2.29"><span class="sec-nr">F.2.29</span> <span class="sec-title">library(registry)</span></a></h3>
	1023
	1024	<a id="sec:summary-lib-registry"></a>
981	1025
982	1026	<p>This library is only available on Windows systems.
983	1027	<table>

999	1043	Prolog</td></tr>
1000	1044	</table>
1001	1045
1002		<p><h3 id="sec:summary-lib-simplex"><a name="sec:F.2.30"><span class="sec-nr">F.2.30</span> <span class="sec-title">library(simplex)</span></a></h3>
1003
1004		<a name="sec:summary-lib-simplex"></a>
	1046	<p><h3 id="sec:summary-lib-simplex"><a id="sec:F.2.30"><span class="sec-nr">F.2.30</span> <span class="sec-title">library(simplex)</span></a></h3>
	1047
	1048	<a id="sec:summary-lib-simplex"></a>
1005	1049	<table>
1006	1050	<tr><td><a class="pred" href="simplex.html#assignment/2">assignment/2</a></td><td>Solve
1007	1051	assignment problem</td></tr>

1027	1071	value of variable in solved state</td></tr>
1028	1072	</table>
1029	1073
1030		<p><h3 id="sec:summary-lib-ugraphs"><a name="sec:F.2.31"><span class="sec-nr">F.2.31</span> <span class="sec-title">library(ugraphs)</span></a></h3>
1031
1032		<a name="sec:summary-lib-ugraphs"></a>
	1074	<p><h3 id="sec:summary-lib-ugraphs"><a id="sec:F.2.31"><span class="sec-nr">F.2.31</span> <span class="sec-title">library(ugraphs)</span></a></h3>
	1075
	1076	<a id="sec:summary-lib-ugraphs"></a>
1033	1077	<table>
1034	1078	<tr><td><a class="pred" href="ugraphs.html#vertices_edges_to_ugraph/3">vertices_edges_to_ugraph/3</a></td><td>Create
1035	1079	unweighted graph</td></tr>

1066	1110	of two graphs</td></tr>
1067	1111	</table>
1068	1112
1069		<p><h3 id="sec:summary-lib-url"><a name="sec:F.2.32"><span class="sec-nr">F.2.32</span> <span class="sec-title">library(url)</span></a></h3>
1070
1071		<a name="sec:summary-lib-url"></a>
	1113	<p><h3 id="sec:summary-lib-url"><a id="sec:F.2.32"><span class="sec-nr">F.2.32</span> <span class="sec-title">library(url)</span></a></h3>
	1114
	1115	<a id="sec:summary-lib-url"></a>
1072	1116	<table>
1073	1117	<tr><td><a class="pred" href="url.html#file_name_to_url/2">file_name_to_url/2</a></td><td>Translate
1074	1118	between a filename and a file:<code>//</code> URL.</td></tr>

1092	1136	to/from application/x-www-form-encoded.</td></tr>
1093	1137	</table>
1094	1138
1095		<p><h3 id="sec:summary-lib-www_browser"><a name="sec:F.2.33"><span class="sec-nr">F.2.33</span> <span class="sec-title">library(www_browser)</span></a></h3>
1096
1097		<a name="sec:summary-lib-www_browser"></a>
	1139	<p><h3 id="sec:summary-lib-www_browser"><a id="sec:F.2.33"><span class="sec-nr">F.2.33</span> <span class="sec-title">library(www_browser)</span></a></h3>
	1140
	1141	<a id="sec:summary-lib-www_browser"></a>
1098	1142	<table>
1099	1143	<tr><td><a class="pred" href="www_browser.html#www_open_url/1">www_open_url/1</a></td><td>Open
1100	1144	a web-page in a browser</td></tr>
1101	1145	</table>
1102	1146
1103		<p><h3 id="sec:summary-lib-solution_sequences"><a name="sec:F.2.34"><span class="sec-nr">F.2.34</span> <span class="sec-title">library(solution_sequences)</span></a></h3>
1104
1105		<a name="sec:summary-lib-solution_sequences"></a>
1106		<table>
	1147	<p><h3 id="sec:summary-lib-solution_sequences"><a id="sec:F.2.34"><span class="sec-nr">F.2.34</span> <span class="sec-title">library(solution_sequences)</span></a></h3>
	1148
	1149	<a id="sec:summary-lib-solution_sequences"></a>
	1150	<table>
	1151	<tr><td><a class="pred" href="solutionsequences.html#call_nth/2">call_nth/2</a></td><td>True
	1152	when Goal succeeded for the Nth time.</td></tr>
1107	1153	<tr><td><a class="pred" href="solutionsequences.html#distinct/1">distinct/1</a></td><td>True
1108	1154	if Goal is true and no previous solution of Goal bound Witness to the
1109	1155	same value.</td></tr>

1126	1172	a limited amount of memory.</td></tr>
1127	1173	</table>
1128	1174
1129		<p><h3 id="sec:summary-lib-thread_pool"><a name="sec:F.2.35"><span class="sec-nr">F.2.35</span> <span class="sec-title">library(thread_pool)</span></a></h3>
1130
1131		<a name="sec:summary-lib-thread_pool"></a>
	1175	<p><h3 id="sec:summary-lib-thread_pool"><a id="sec:F.2.35"><span class="sec-nr">F.2.35</span> <span class="sec-title">library(thread_pool)</span></a></h3>
	1176
	1177	<a id="sec:summary-lib-thread_pool"></a>
1132	1178	<table>
1133	1179	<tr><td><a class="pred" href="threadpool.html#create_pool/1">create_pool/1</a></td><td>Hook
1134	1180	to create a thread pool lazily.</td></tr>

1144	1190	if Property is a property of thread pool Name.</td></tr>
1145	1191	</table>
1146	1192
1147		<p><h3 id="sec:summary-lib-varnumbers"><a name="sec:F.2.36"><span class="sec-nr">F.2.36</span> <span class="sec-title">library(varnumbers)</span></a></h3>
1148
1149		<a name="sec:summary-lib-varnumbers"></a>
	1193	<p><h3 id="sec:summary-lib-varnumbers"><a id="sec:F.2.36"><span class="sec-nr">F.2.36</span> <span class="sec-title">library(varnumbers)</span></a></h3>
	1194
	1195	<a id="sec:summary-lib-varnumbers"></a>
1150	1196	<table>
1151	1197	<tr><td><a class="pred" href="varnumbers.html#max_var_number/3">max_var_number/3</a></td><td>True
1152	1198	when Max is the max of Start and the highest numbered $VAR(N) term.</td></tr>

1163	1209	the `X` terms with the variable it is mapped to.</td></tr>
1164	1210	</table>
1165	1211
1166		<p><h3 id="sec:summary-lib-yall"><a name="sec:F.2.37"><span class="sec-nr">F.2.37</span> <span class="sec-title">library(yall)</span></a></h3>
1167
1168		<a name="sec:summary-lib-yall"></a>
	1212	<p><h3 id="sec:summary-lib-yall"><a id="sec:F.2.37"><span class="sec-nr">F.2.37</span> <span class="sec-title">library(yall)</span></a></h3>
	1213
	1214	<a id="sec:summary-lib-yall"></a>
1169	1215	<table>
1170	1216	<tr><td><a class="pred" href="yall.html#//2">//2</a></td><td>Shorthand
1171	1217	for `Free/[]<code>>></code>Lambda`.</td></tr>

+69

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	4	<title>SWI-Prolog 7.7.4 Reference Manual</title><link rel="home" href="index.html">
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193	234	</div>
194		<h1 id="sec:license"><a name="sec:E"><span class="sec-nr">E</span> <span class="sec-title">SWI-Prolog
	235	<h1 id="sec:license"><a id="sec:E"><span class="sec-nr">E</span> <span class="sec-title">SWI-Prolog
195	236	License Conditions and Tools</span></a></h1>
196	237
197		<a name="sec:license"></a>
198
199		<p>As of version 7.4.0<sup class="fn">188<span class="fn-text">Actually
	238	<a id="sec:license"></a>
	239
	240	<p>As of version 7.4.0<sup class="fn">189<span class="fn-text">Actually
200	241	pre-release 7.3.33</span></sup>, the SWI-Prolog source code is
201	242	distributed under the
202		https://opensource.org/licenses/BSD-2-ClauseSimplified BSD license:
	243	<a class="url" href="https://opensource.org/licenses/BSD-2-Clause">Simplified
	244	BSD</a> license:
203	245
204	246	<pre class="code">
205	247	Redistribution and use in source and binary forms, with or without

233	275	linked to libraries that are more restrictive and in addition your code
234	276	may have loaded extension packages that have more restrictive
235	277	conditions. In particular, the core is by default linked to
236		https://gmplib.org/libgmp, distributed under the Lesser GNU Public
237		license.
	278	<a class="url" href="https://gmplib.org/">libgmp</a>, distributed under
	279	the Lesser GNU Public license.
238	280
239	281	<p>The above implies you need to configure and recompile the system
240	282	without these components. For this we provide options to the <b>configure</b>

+90

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193	234	</div>
194		<h2 id="sec:limits"><a name="sec:2.20"><span class="sec-nr">2.20</span> <span class="sec-title">System
	235	<h2 id="sec:limits"><a id="sec:2.20"><span class="sec-nr">2.20</span> <span class="sec-title">System
195	236	limits</span></a></h2>
196	237
197		<a name="sec:limits"></a>
198
199		<p><h3 id="sec:memlimit"><a name="sec:2.20.1"><span class="sec-nr">2.20.1</span> <span class="sec-title">Limits
	238	<a id="sec:limits"></a>
	239
	240	<p><h3 id="sec:memlimit"><a id="sec:2.20.1"><span class="sec-nr">2.20.1</span> <span class="sec-title">Limits
200	241	on memory areas</span></a></h3>
201	242
202		<a name="sec:memlimit"></a>
	243	<a id="sec:memlimit"></a>
203	244
204	245	<p>SWI-Prolog has a number of memory areas which are only enlarged to a
205	246	certain limit. The internal data representation limits the local, global

213	254	data.
214	255
215	256	<p>The limits can be changed from the command line as well as at runtime
216		using <a name="idx:setprologstack2:278"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>.
	257	using <a id="idx:setprologstack2:278"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>.
217	258	The table below shows these areas. The first column gives the option
218	259	name to modify the size of the area. The option character is immediately
219	260	followed by a number and optionally by a

221	262	indicator, the value is interpreted in Kbytes (1024 bytes); with <code>m</code>,
222	263	the value is interpreted in Mbytes (<var>1024 × 1024</var> bytes).
223	264
224		<p>The PrologScript facility described in <a class="sec" href="compilation.html">section
	265	<p>The PrologScript facility described in <a class="sec" href="compilation.html#sec:2.10.2.1">section
225	266	2.10.2.1</a> provides a mechanism for specifying options with the load
226	267	file. On Windows the default stack sizes are controlled using the
227		Windows <a name="idx:registry:279">registry</a> on the key <code>HKEY_CURRENT_USER\Software\SWI\Prolog</code>
	268	Windows <a id="idx:registry:279">registry</a> on the key <code>HKEY_CURRENT_USER\Software\SWI\Prolog</code>
228	269	using the names <code>localSize</code>, <code>globalSize</code> and <code>trailSize</code>.
229	270	The value is a <code>DWORD</code> expressing the default stack size in
230	271	Kbytes. A GUI for modifying these values is provided using the XPCE
231		package. To use this, start the XPCE manual tools using manpce0, after
	272	package. To use this, start the XPCE manual tools using manpce/0 , after
232	273	which you find <i>Preferences</i> in the <i>File</i> menu.
233	274
234	275	<p>Considering portability, applications that need to modify the default
235		limits are advised to do so using <a name="idx:setprologstack2:280"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>.
236
237		<p><table border="2" frame="box" rules="groups" style="margin:auto">
238		<tr valign="top"><td align=center>Option</td><td align=center>Default</td><td>Area
	276	limits are advised to do so using <a id="idx:setprologstack2:280"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>.
	277
	278	<p><table class="latex frame-box center">
	279	<tr><td align=center>Option</td><td align=center>Default</td><td>Area
239	280	name</td><td>Description </td></tr>
240		<tbody>
241		<tr valign="top"><td align=center><strong>-L</strong> </td><td align=center>128M</td><td><b>local
	281	<tr class="hline"><td align=center><strong>-L</strong> </td><td align=center>128M</td><td><b>local
242	282	stack</b></td><td>The local stack is used to store the execution
243	283	environments of procedure invocations. The space for an environment is
244	284	reclaimed when it fails, exits without leaving choice points, the
245	285	alternatives are cut off with the !/0 predicate or no choice points have
246	286	been created since the invocation and the last subclause is started
247	287	(last call optimisation). </td></tr>
248		<tr valign="top"><td align=center><strong>-G</strong> </td><td align=center>128M</td><td><b>global
	288	<tr><td align=center><strong>-G</strong> </td><td align=center>128M</td><td><b>global
249	289	stack</b></td><td>The global stack is used to store terms created during
250	290	Prolog's execution. Terms on this stack will be reclaimed by
251	291	backtracking to a point before the term was created or by garbage
252	292	collection (provided the term is no longer referenced). </td></tr>
253		<tr valign="top"><td align=center><strong>-T</strong> </td><td align=center>128M</td><td><b>trail
	293	<tr><td align=center><strong>-T</strong> </td><td align=center>128M</td><td><b>trail
254	294	stack</b></td><td>The trail stack is used to store assignments during
255	295	execution. Entries on this stack remain alive until backtracking before
256	296	the point of creation or the garbage collector determines they are no
257	297	longer needed. </td></tr>
258	298	</table>
259	299	<div class="caption"><b>Table 2 : </b>Memory areas</div>
260		<a name="tab:areas"></a>
261
262		<p><h4 id="sec:heap"><a name="sec:2.20.1.1"><span class="sec-nr">2.20.1.1</span> <span class="sec-title">The
	300	<a id="tab:areas"></a>
	301
	302	<p><h4 id="sec:heap"><a id="sec:2.20.1.1"><span class="sec-nr">2.20.1.1</span> <span class="sec-title">The
263	303	heap</span></a></h4>
264	304
265		<a name="sec:heap"></a>
266
267		<p><a name="idx:stackmemorymanagement:281"></a><a name="idx:memorylayout:282"></a>With
	305	<a id="sec:heap"></a>
	306
	307	<p><a id="idx:stackmemorymanagement:281"></a><a id="idx:memorylayout:282"></a>With
268	308	the heap, we refer to the memory area used by malloc() and friends.
269	309	SWI-Prolog uses the area to store atoms, functors, predicates and their
270	310	clauses, records and other dynamic data. No limits are imposed on the
271	311	addresses returned by malloc() and friends.
272	312
273		<p><h3 id="sec:morelimits"><a name="sec:2.20.2"><span class="sec-nr">2.20.2</span> <span class="sec-title">Other
	313	<p><h3 id="sec:morelimits"><a id="sec:2.20.2"><span class="sec-nr">2.20.2</span> <span class="sec-title">Other
274	314	Limits</span></a></h3>
275	315
276		<a name="sec:morelimits"></a>
	316	<a id="sec:morelimits"></a>
277	317
278	318	<dl class="latex">
279	319	<dt><b>Clauses</b></dt>

285	325	<dd>
286	326	SWI-Prolog has no limits on the length of atoms and strings. The number
287	327	of atoms is limited to 16777216 (16M) on 32-bit machines. On 64-bit
288		machines this is virtually unlimited. See also <a class="sec" href="foreigninclude.html">section
	328	machines this is virtually unlimited. See also <a class="sec" href="foreigninclude.html#sec:11.4.2.1">section
289	329	11.4.2.1</a>.</dd>
290	330	<dt><b>Memory areas</b></dt>
291	331	<dd>

300	340	managed stack and perform optimization for processing the last argument
301	341	of a term. This implies they can process deeply nested terms at constant
302	342	and low usage of the C stack, and the system raises a resource error if
303		no more stack can be allocated. Currently only <a name="idx:read1:283"></a><a class="pred" href="termrw.html#read/1">read/1</a>
304		and <a name="idx:write1:284"></a><a class="pred" href="termrw.html#write/1">write/1</a>
	343	no more stack can be allocated. Currently only <a id="idx:read1:283"></a><a class="pred" href="termrw.html#read/1">read/1</a>
	344	and <a id="idx:write1:284"></a><a class="pred" href="termrw.html#write/1">write/1</a>
305	345	(and all variations thereof) still use the C stack and may cause the
306	346	system to crash in an uncontrolled way (i.e., not mapped to a Prolog
307	347	exception that can be caught).</dd>

324	364	</dd>
325	365	</dl>
326	366
327		<p><h3 id="sec:resnames"><a name="sec:2.20.3"><span class="sec-nr">2.20.3</span> <span class="sec-title">Reserved
	367	<p><h3 id="sec:resnames"><a id="sec:2.20.3"><span class="sec-nr">2.20.3</span> <span class="sec-title">Reserved
328	368	Names</span></a></h3>
329	369
330		<a name="sec:resnames"></a>
	370	<a id="sec:resnames"></a>
331	371
332	372	<p>The boot compiler (see <strong>-b</strong> option) does not support
333	373	the module system. As large parts of the system are written in Prolog

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193	234	</div>
194		<h2 id="sec:listing"><a name="sec:4.5"><span class="sec-nr">4.5</span> <span class="sec-title">List
	235	<h2 id="sec:listing"><a id="sec:4.5"><span class="sec-nr">4.5</span> <span class="sec-title">List
195	236	the program, predicates or clauses</span></a></h2>
196	237
197		<a name="sec:listing"></a>
	238	<a id="sec:listing"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="listing/1"><strong>listing</strong>(<var>:Pred</var>)</a></dt>
	241	<dt class="pubdef"><a id="listing/1"><strong>listing</strong>(<var>:Pred</var>)</a></dt>
201	242	<dd class="defbody">
202	243	List predicates specified by <var>Pred</var>. <var>Pred</var> may be a
203	244	predicate name (atom), which lists all predicates with this name,

209	250
210	251	<p>A listing is produced by enumerating the clauses of the predicate
211	252	using
212		<a name="idx:clause2:595"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>
213		and printing each clause using <a name="idx:portrayclause1:596"></a><a class="pred" href="listing.html#portray_clause/1">portray_clause/1</a>.
	253	<a id="idx:clause2:595"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>
	254	and printing each clause using <a id="idx:portrayclause1:596"></a><a class="pred" href="listing.html#portray_clause/1">portray_clause/1</a>.
214	255	This implies that the variable names are generated (<var>A</var>, <var>B</var>,
215		... ) and the layout is defined by rules in <a name="idx:portrayclause1:597"></a><a class="pred" href="listing.html#portray_clause/1">portray_clause/1</a>.</dd>
216		<dt class="pubdef"><a name="listing/0"><strong>listing</strong></a></dt>
217		<dd class="defbody">
218		List all predicates from the calling module using <a name="idx:listing1:598"></a><a class="pred" href="listing.html#listing/1">listing/1</a>.
	256	... ) and the layout is defined by rules in <a id="idx:portrayclause1:597"></a><a class="pred" href="listing.html#portray_clause/1">portray_clause/1</a>.</dd>
	257	<dt class="pubdef"><a id="listing/0"><strong>listing</strong></a></dt>
	258	<dd class="defbody">
	259	List all predicates from the calling module using <a id="idx:listing1:598"></a><a class="pred" href="listing.html#listing/1">listing/1</a>.
219	260	For example,
220	261	<code>?- listing.</code> lists clauses in the default <code>user</code>
221	262	module and <code>?- lists:listing.</code> lists the clauses in the
222	263	module
223	264	<code>lists</code>.</dd>
224		<dt class="pubdef"><a name="portray_clause/1"><strong>portray_clause</strong>(<var>+Clause</var>)</a></dt>
	265	<dt class="pubdef"><a id="portray_clause/1"><strong>portray_clause</strong>(<var>+Clause</var>)</a></dt>
225	266	<dd class="defbody">
226	267	Pretty print a clause. A clause should be specified as a term `<code><<var>Head</var>>
227	268	:- <<var>Body</var>></code>'. Facts are represented as `<code><<var>Head</var>>
228	269	:- true</code>' or simply <code><<var>Head</var>></code>.
229	270	Variables in the clause are written as <var>A</var>, <var>B</var>, ... .
230		Singleton variables are written as <code>_</code>. See also <a name="idx:portrayclause2:599"></a><a class="pred" href="listing.html#portray_clause/2">portray_clause/2</a>.</dd>
231		<dt class="pubdef"><a name="portray_clause/2"><strong>portray_clause</strong>(<var>+Stream,
	271	Singleton variables are written as <code>_</code>. See also <a id="idx:portrayclause2:599"></a><a class="pred" href="listing.html#portray_clause/2">portray_clause/2</a>.</dd>
	272	<dt class="pubdef"><a id="portray_clause/2"><strong>portray_clause</strong>(<var>+Stream,
232	273	+Clause</var>)</a></dt>
233	274	<dd class="defbody">
234		Pretty print a clause to <var>Stream</var>. See <a name="idx:portrayclause1:600"></a><a class="pred" href="listing.html#portray_clause/1">portray_clause/1</a>
	275	Pretty print a clause to <var>Stream</var>. See <a id="idx:portrayclause1:600"></a><a class="pred" href="listing.html#portray_clause/1">portray_clause/1</a>
235	276	for details.
236	277	</dd>
237	278	</dl>

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193	234	</div>
194		<h2 id="sec:lists"><a name="sec:A.15"><span class="sec-nr">A.15</span> <span class="sec-title">library(lists):
	235	<h2 id="sec:lists"><a id="sec:A.15"><span class="sec-nr">A.15</span> <span class="sec-title">library(lists):
195	236	List Manipulation</span></a></h2>
196	237
197		<p><a name="sec:lists"></a>
	238	<p><a id="sec:lists"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">Compatibility</dt>

215	256	their specification by Quintus and SICStus.
216	257
217	258	<dl class="latex">
218		<dt class="pubdef"><a name="member/2"><strong>member</strong>(<var>?Elem,
	259	<dt class="pubdef"><a id="member/2"><strong>member</strong>(<var>?Elem,
219	260	?List</var>)</a></dt>
220	261	<dd class="defbody">
221	262	True if <var>Elem</var> is a member of <var>List</var>. The SWI-Prolog

235	276	</dl>
236	277
237	278	</dd>
238		<dt class="pubdef"><a name="append/3"><strong>append</strong>(<var>?List1,
	279	<dt class="pubdef"><a id="append/3"><strong>append</strong>(<var>?List1,
239	280	?List2, ?List1AndList2</var>)</a></dt>
240	281	<dd class="defbody">
241	282	<var>List1AndList2</var> is the concatenation of <var>List1</var> and <var>List2</var></dd>
242		<dt class="pubdef"><a name="append/2"><strong>append</strong>(<var>+ListOfLists,
	283	<dt class="pubdef"><a id="append/2"><strong>append</strong>(<var>+ListOfLists,
243	284	?List</var>)</a></dt>
244	285	<dd class="defbody">
245	286	Concatenate a list of lists. Is true if <var>ListOfLists</var> is a list
246	287	of lists, and <var>List</var> is the concatenation of these lists.
247	288	<table class="arglist">
248		<tr valign="top"><td><var>ListOfLists</var> </td><td>must be a list of <i>possibly</i>
	289	<tr><td><var>ListOfLists</var> </td><td>must be a list of <i>possibly</i>
249	290	partial lists </td></tr>
250	291	</table>
251	292	</dd>
252		<dt class="pubdef"><a name="prefix/2"><strong>prefix</strong>(<var>?Part,
	293	<dt class="pubdef"><a id="prefix/2"><strong>prefix</strong>(<var>?Part,
253	294	?Whole</var>)</a></dt>
254	295	<dd class="defbody">
255	296	True iff <var>Part</var> is a leading substring of <var>Whole</var>.
256	297	This is the same as <code>append(Part, _, Whole)</code>.</dd>
257		<dt class="pubdef"><a name="select/3"><strong>select</strong>(<var>?Elem,
	298	<dt class="pubdef"><a id="select/3"><strong>select</strong>(<var>?Elem,
258	299	?List1, ?List2</var>)</a></dt>
259	300	<dd class="defbody">
260	301	Is true when <var>List1</var>, with <var>Elem</var> removed, results in <var>List2</var>.</dd>
261		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="selectchk/3"><strong>selectchk</strong>(<var>+Elem,
	302	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="selectchk/3"><strong>selectchk</strong>(<var>+Elem,
262	303	+List, -Rest</var>)</a></dt>
263	304	<dd class="defbody">
264	305	Semi-deterministic removal of first element in <var>List</var> that
265	306	unifies with <var>Elem</var>.</dd>
266		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="select/4"><strong>select</strong>(<var>?X,
	307	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="select/4"><strong>select</strong>(<var>?X,
267	308	?XList, ?Y, ?YList</var>)</a></dt>
268	309	<dd class="defbody">
269	310	Select from two lists at the same positon. True if <var>XList</var> is

289	330	</dl>
290	331
291	332	</dd>
292		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="selectchk/4"><strong>selectchk</strong>(<var>?X,
	333	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="selectchk/4"><strong>selectchk</strong>(<var>?X,
293	334	?XList, ?Y, ?YList</var>)</a></dt>
294	335	<dd class="defbody">
295	336	Semi-deterministic version of <a class="pred" href="lists.html#select/4">select/4</a>.</dd>
296		<dt class="pubdef"><a name="nextto/3"><strong>nextto</strong>(<var>?X,
297		?Y, ?List</var>)</a></dt>
	337	<dt class="pubdef"><a id="nextto/3"><strong>nextto</strong>(<var>?X, ?Y,
	338	?List</var>)</a></dt>
298	339	<dd class="defbody">
299	340	True if <var>Y</var> directly follows <var>X</var> in <var>List</var>.</dd>
300		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="delete/3"><strong>delete</strong>(<var>+List1,
	341	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="delete/3"><strong>delete</strong>(<var>+List1,
301	342	@Elem, -List2</var>)</a></dt>
302	343	<dd class="defbody">
303	344	Delete matching elements from a list. True when <var>List2</var> is a

321	362	</dl>
322	363
323	364	</dd>
324		<dt class="pubdef"><a name="nth0/3"><strong>nth0</strong>(<var>?Index,
	365	<dt class="pubdef"><a id="nth0/3"><strong>nth0</strong>(<var>?Index,
325	366	?List, ?Elem</var>)</a></dt>
326	367	<dd class="defbody">
327	368	True when <var>Elem</var> is the <var>Index</var>'th element of <var>List</var>.

340	381	</dl>
341	382
342	383	</dd>
343		<dt class="pubdef"><a name="nth1/3"><strong>nth1</strong>(<var>?Index,
	384	<dt class="pubdef"><a id="nth1/3"><strong>nth1</strong>(<var>?Index,
344	385	?List, ?Elem</var>)</a></dt>
345	386	<dd class="defbody">
346	387	Is true when <var>Elem</var> is the <var>Index</var>'th element of <var>List</var>.

354	395	</dl>
355	396
356	397	</dd>
357		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="nth0/4"><strong>nth0</strong>(<var>?N,
	398	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="nth0/4"><strong>nth0</strong>(<var>?N,
358	399	?List, ?Elem, ?Rest</var>)</a></dt>
359	400	<dd class="defbody">
360	401	Select/insert element at index. True when <var>Elem</var> is the <var>N</var>'th

377	418	</pre>
378	419
379	420	</dd>
380		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="nth1/4"><strong>nth1</strong>(<var>?N,
	421	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="nth1/4"><strong>nth1</strong>(<var>?N,
381	422	?List, ?Elem, ?Rest</var>)</a></dt>
382	423	<dd class="defbody">
383	424	As <a class="pred" href="lists.html#nth0/4">nth0/4</a>, but counting
384	425	starts at 1.</dd>
385		<dt class="pubdef"><a name="last/2"><strong>last</strong>(<var>?List,
	426	<dt class="pubdef"><a id="last/2"><strong>last</strong>(<var>?List,
386	427	?Last</var>)</a></dt>
387	428	<dd class="defbody">
388	429	Succeeds when <var>Last</var> is the last element of <var>List</var>.

400	441	</dl>
401	442
402	443	</dd>
403		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="proper_length/2"><strong>proper_length</strong>(<var>@List,
	444	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="proper_length/2"><strong>proper_length</strong>(<var>@List,
404	445	-Length</var>)</a></dt>
405	446	<dd class="defbody">
406	447	True when <var>Length</var> is the number of elements in the proper list

413	454	</pre>
414	455
415	456	</dd>
416		<dt class="pubdef"><a name="same_length/2"><strong>same_length</strong>(<var>?List1,
	457	<dt class="pubdef"><a id="same_length/2"><strong>same_length</strong>(<var>?List1,
417	458	?List2</var>)</a></dt>
418	459	<dd class="defbody">
419	460	Is true when <var>List1</var> and <var>List2</var> are lists with the

429	470	</dl>
430	471
431	472	</dd>
432		<dt class="pubdef"><a name="reverse/2"><strong>reverse</strong>(<var>?List1,
	473	<dt class="pubdef"><a id="reverse/2"><strong>reverse</strong>(<var>?List1,
433	474	?List2</var>)</a></dt>
434	475	<dd class="defbody">
435	476	Is true when the elements of <var>List2</var> are in reverse order
436	477	compared to
437	478	<var>List1</var>.</dd>
438		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="permutation/2"><strong>permutation</strong>(<var>?Xs,
	479	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="permutation/2"><strong>permutation</strong>(<var>?Xs,
439	480	?Ys</var>)</a></dt>
440	481	<dd class="defbody">
441	482	True when <var>Xs</var> is a permutation of <var>Ys</var>. This can

480	521	</dl>
481	522
482	523	</dd>
483		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="flatten/2"><strong>flatten</strong>(<var>+NestedList,
	524	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="flatten/2"><strong>flatten</strong>(<var>+NestedList,
484	525	-FlatList</var>)</a></dt>
485	526	<dd class="defbody">
486	527	Is true if <var>FlatList</var> is a non-nested version of <var>NestedList</var>.

502	543	</dl>
503	544
504	545	</dd>
505		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="max_member/2"><strong>max_member</strong>(<var>-Max,
	546	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="max_member/2"><strong>max_member</strong>(<var>-Max,
506	547	+List</var>)</a></dt>
507	548	<dd class="defbody">
508	549	True when <var>Max</var> is the largest member in the standard order of

518	559	</dl>
519	560
520	561	</dd>
521		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="min_member/2"><strong>min_member</strong>(<var>-Min,
	562	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="min_member/2"><strong>min_member</strong>(<var>-Min,
522	563	+List</var>)</a></dt>
523	564	<dd class="defbody">
524	565	True when <var>Min</var> is the smallest member in the standard order of

534	575	</dl>
535	576
536	577	</dd>
537		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="sum_list/2"><strong>sum_list</strong>(<var>+List,
	578	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="sum_list/2"><strong>sum_list</strong>(<var>+List,
538	579	-Sum</var>)</a></dt>
539	580	<dd class="defbody">
540	581	<var>Sum</var> is the result of adding all numbers in <var>List</var>.</dd>
541		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="max_list/2"><strong>max_list</strong>(<var>+List:list(number),
	582	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="max_list/2"><strong>max_list</strong>(<var>+List:list(number),
542	583	-Max:number</var>)</a></dt>
543	584	<dd class="defbody">
544	585	True if <var>Max</var> is the largest number in <var>List</var>. Fails

552	593	</dl>
553	594
554	595	</dd>
555		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="min_list/2"><strong>min_list</strong>(<var>+List:list(number),
	596	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="min_list/2"><strong>min_list</strong>(<var>+List:list(number),
556	597	-Min:number</var>)</a></dt>
557	598	<dd class="defbody">
558	599	True if <var>Min</var> is the smallest number in <var>List</var>. Fails

566	607	</dl>
567	608
568	609	</dd>
569		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="numlist/3"><strong>numlist</strong>(<var>+Low,
	610	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="numlist/3"><strong>numlist</strong>(<var>+Low,
570	611	+High, -List</var>)</a></dt>
571	612	<dd class="defbody">
572	613	<var>List</var> is a list [<var>Low</var>, <var>Low</var>+1, ... <var>High</var>].

581	622	</dl>
582	623
583	624	</dd>
584		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="is_set/1"><strong>is_set</strong>(<var>@Set</var>)</a></dt>
	625	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="is_set/1"><strong>is_set</strong>(<var>@Set</var>)</a></dt>
585	626	<dd class="defbody">
586	627	True if <var>Set</var> is a proper list without duplicates. Equivalence
587	628	is based on <a class="pred" href="compare.html#==/2">==/2</a>. The

589	630	which implies that the complexity is N*<code>log(N)</code> and the
590	631	predicate may cause a resource-error. There are no other error
591	632	conditions.</dd>
592		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_to_set/2"><strong>list_to_set</strong>(<var>+List,
	633	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_to_set/2"><strong>list_to_set</strong>(<var>+List,
593	634	?Set</var>)</a></dt>
594	635	<dd class="defbody">
595	636	True when <var>Set</var> has the same elements as <var>List</var> in the

619	660	</dl>
620	661
621	662	</dd>
622		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="intersection/3"><strong>intersection</strong>(<var>+Set1,
	663	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="intersection/3"><strong>intersection</strong>(<var>+Set1,
623	664	+Set2, -Set3</var>)</a></dt>
624	665	<dd class="defbody">
625	666	True if <var>Set3</var> unifies with the intersection of <var>Set1</var>

635	676	</dl>
636	677
637	678	</dd>
638		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="union/3"><strong>union</strong>(<var>+Set1,
	679	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="union/3"><strong>union</strong>(<var>+Set1,
639	680	+Set2, -Set3</var>)</a></dt>
640	681	<dd class="defbody">
641	682	True if <var>Set3</var> unifies with the union of the lists <var>Set1</var>

651	692	</dl>
652	693
653	694	</dd>
654		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="subset/2"><strong>subset</strong>(<var>+SubSet,
	695	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="subset/2"><strong>subset</strong>(<var>+SubSet,
655	696	+Set</var>)</a></dt>
656	697	<dd class="defbody">
657	698	True if all elements of <var>SubSet</var> belong to <var>Set</var> as

669	710	</dl>
670	711
671	712	</dd>
672		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="subtract/3"><strong>subtract</strong>(<var>+Set,
	713	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="subtract/3"><strong>subtract</strong>(<var>+Set,
673	714	+Delete, -Result</var>)</a></dt>
674	715	<dd class="defbody">
675	716	<var>Delete</var> all elements in <var>Delete</var> from <var>Set</var>.

+74

-33

man/Manual/loadfilehook.html less more

1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section B.8</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section B.8</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

17	17	{ margin-bottom: 1em;
18	18	}
19	19
20		dt.pubdef
21		{ background-color: #c5e1ff;
22		}
23
24		dt.multidef
25		{ background-color: #c8ffc7;
26		}
	20	dt.pubdef, dt.multidef
	21	{ color: #fff;
	22	padding: 2px 10px 0px 10px;
	23	margin-bottom: 5px;
	24	font-size: 18px;
	25	vertical-align: middle;
	26	overflow: hidden;
	27	}
	28
	29	dt.pubdef { background-color: #0c3d6e; }
	30	dt.multidef { background-color: #ef9439; }
27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
	124	color: #fff;
121	125	}
122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
135		{ display: block !important;
136		position: absolute; top: auto; left: auto; width: 80%;
137		color: #000; background: white;
138		border: 2px solid;
139		padding: 5px; margin: 10px; z-index: 100;
140		font-size: smaller;
	134	.fn {
	135	color: red;
	136	font-size: 70%;
	137	}
	138
	139	.fn-text, .fnp {
	140	position: absolute;
	141	top: auto;
	142	left: 10%;
	143	border: 1px solid #000;
	144	box-shadow: 5px 5px 5px #888;
	145	display: none;
	146	background: #fff;
	147	color: #000;
	148	margin-top: 25px;
	149	padding: 8px 12px;
	150	font-size: larger;
	151	}
	152
	153	sup:hover span.fn-text
	154	{ display: block;
141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
	200
	201	table.center
	202	{ margin: auto;
	203	}
	204
	205	table.latex
	206	{ border-collapse:collapse;
	207	}
	208
	209	table.latex tr
	210	{ vertical-align: text-top;
	211	}
	212
	213	table.latex td,th
	214	{ padding: 2px 1em;
	215	}
	216
	217	table.latex tr.hline td,th
	218	{ border-top: 1px solid black;
	219	}
	220
	221	table.frame-box
	222	{ border: 2px solid black;
	223	}
	224
184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="intlibs.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="dialect.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:loadfilehook"><a name="sec:B.8"><span class="sec-nr">B.8</span> <span class="sec-title">Hooks
	235	<h2 id="sec:loadfilehook"><a id="sec:B.8"><span class="sec-nr">B.8</span> <span class="sec-title">Hooks
195	236	for loading files</span></a></h2>
196	237
197		<a name="sec:loadfilehook"></a>
198
199		<p>All loading of source files is achieved by <a name="idx:loadfiles2:2236"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
	238	<a id="sec:loadfilehook"></a>
	239
	240	<p>All loading of source files is achieved by <a id="idx:loadfiles2:2240"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>.
200	241	The hook
201		<a name="idx:prologloadfile2:2237"></a><a class="pred" href="loadfilehook.html#prolog_load_file/2">prolog_load_file/2</a>
	242	<a id="idx:prologloadfile2:2241"></a><a class="pred" href="loadfilehook.html#prolog_load_file/2">prolog_load_file/2</a>
202	243	can be used to load Prolog code from non-files or even load entirely
203	244	different information, such as foreign files.
204	245
205	246	<dl class="latex">
206		<dt class="pubdef"><a name="prolog_load_file/2"><strong>prolog_load_file</strong>(<var>+Spec,
	247	<dt class="pubdef"><a id="prolog_load_file/2"><strong>prolog_load_file</strong>(<var>+Spec,
207	248	+Options</var>)</a></dt>
208	249	<dd class="defbody">
209		Load a single object. If this call succeeds, <a name="idx:loadfiles2:2238"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	250	Load a single object. If this call succeeds, <a id="idx:loadfiles2:2242"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
210	251	assumes the action has been taken care of. This hook is only called if <var>Options</var>
211	252	does not contain the <code>stream(Input)</code> option. The hook must be
212	253	defined in the module <code>user</code>.

216	257	server. It can also be used to load source in unusual forms, such as
217	258	loading compressed files without decompressing them first. There is
218	259	currently no example of that.</dd>
219		<dt class="pubdef"><a name="prolog:comment_hook/3"><strong>prolog:comment_hook</strong>(<var>+Comments,
	260	<dt class="pubdef"><a id="prolog:comment_hook/3"><strong>prolog:comment_hook</strong>(<var>+Comments,
220	261	+Pos, +Term</var>)</a></dt>
221	262	<dd class="defbody">
222	263	This hook allows for processing comments encountered by the compiler. If
223		this hook is defined, the compiler calls <a name="idx:readterm2:2239"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	264	this hook is defined, the compiler calls <a id="idx:readterm2:2243"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
224	265	with the option
225	266	<code>comments(Comments)</code>. If the list of comments returned by
226		<a name="idx:readterm2:2240"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	267	<a id="idx:readterm2:2244"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
227	268	is not empty it calls this comment hook with the following arguments.
228	269
229	270	<p>
230	271	<ul class="latex">
231	272	<li><var>Comments</var> is the non-empty list of comments. Each comment
232	273	is a pair <var>Position</var>-<var>String</var>, where
233		<var>String</var> is a string object (see <a class="sec" href="strings.html">section
	274	<var>String</var> is a string object (see <a class="sec" href="strings.html#sec:5.2">section
234	275	5.2</a>) that contains the comment <em>including</em> delimiters.
235	276	Consecutive line comments are returned as a single comment.
236	277	<li><var>Pos</var> is a stream-position term that describes the starting

239	280	</ul>
240	281
241	282	<p>This hook is exploited by the documentation system. See
242		<a name="idx:streampositiondata3:2241"></a><a class="pred" href="IO.html#stream_position_data/3">stream_position_data/3</a>.
243		See also <a name="idx:readterm3:2242"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.
	283	<a id="idx:streampositiondata3:2245"></a><a class="pred" href="IO.html#stream_position_data/3">stream_position_data/3</a>.
	284	See also <a id="idx:readterm3:2246"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.
244	285	</dd>
245	286	</dl>
246	287

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191	232	<a class="nav" href="manipatom.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:locale"><a name="sec:4.23"><span class="sec-nr">4.23</span> <span class="sec-title">Localization
	235	<h2 id="sec:locale"><a id="sec:4.23"><span class="sec-nr">4.23</span> <span class="sec-title">Localization
195	236	(locale) support</span></a></h2>
196	237
197		<a name="sec:locale"></a>
	238	<a id="sec:locale"></a>
198	239
199	240	<p>SWI-Prolog provides (currently limited) support for localized
200	241	applications.
201	242
202	243	<p>
203	244	<ul class="latex">
204		<li>The predicates <a name="idx:chartype2:1280"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>
205		and <a name="idx:codetype2:1281"></a><a class="pred" href="chartype.html#code_type/2">code_type/2</a>
	245	<li>The predicates <a id="idx:chartype2:1280"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>
	246	and <a id="idx:codetype2:1281"></a><a class="pred" href="chartype.html#code_type/2">code_type/2</a>
206	247	query character classes depending on the locale.
207		<li>The predicates <a name="idx:collationkey2:1282"></a><a class="pred" href="chartype.html#collation_key/2">collation_key/2</a>
208		and <a name="idx:localesort2:1283"></a><a class="pred" href="chartype.html#locale_sort/2">locale_sort/2</a>
	248	<li>The predicates <a id="idx:collationkey2:1282"></a><a class="pred" href="chartype.html#collation_key/2">collation_key/2</a>
	249	and <a id="idx:localesort2:1283"></a><a class="pred" href="chartype.html#locale_sort/2">locale_sort/2</a>
209	250	can be used for locale dependent sorting of atoms.
210		<li>The predicate <a name="idx:formattime3:1284"></a><a class="pred" href="system.html#format_time/3">format_time/3</a>
	251	<li>The predicate <a id="idx:formattime3:1284"></a><a class="pred" href="system.html#format_time/3">format_time/3</a>
211	252	can be used to format time and date representations, where some of the
212	253	specifiers are locale dependent.
213		<li>The predicate <a name="idx:format2:1285"></a><a class="pred" href="format.html#format/2">format/2</a>
	254	<li>The predicate <a id="idx:format2:1285"></a><a class="pred" href="format.html#format/2">format/2</a>
214	255	provides locale-specific formating of numbers. This functionality is
215	256	based on a more fine-grained localization model that is the subject of
216	257	this section.

218	259
219	260	<p>A locale is a (optionally named) read-only object that provides
220	261	information to locale specific functions.<sup class="fn">105<span class="fn-text">The
221		locale interface described in this section and its effect on <a name="idx:format2:1286"></a><a class="pred" href="format.html#format/2">format/2</a>
	262	locale interface described in this section and its effect on <a id="idx:format2:1286"></a><a class="pred" href="format.html#format/2">format/2</a>
222	263	and reading integers from digit groups was discussed on the SWI-Prolog
223	264	mailinglist. Most input in this discussion is from Ulrich Neumerkel and
224	265	Richard O'Keefe. The predicates in this section were designed by Jan

226	267	named
227	268	<code>default</code> from the system locale. This locale is used as the
228	269	initial locale for the three standard streams as well as the
229		<code>main</code> thread. Locale sensitive output predicates such as <a name="idx:format3:1287"></a><a class="pred" href="format.html#format/3">format/3</a>
	270	<code>main</code> thread. Locale sensitive output predicates such as <a id="idx:format3:1287"></a><a class="pred" href="format.html#format/3">format/3</a>
230	271	get their locale from the stream to which they deliver their output. New
231	272	streams get their locale from the thread that created the stream.
232	273	Threads get their locale from the thread that created them.
233	274
234	275	<dl class="latex">
235		<dt class="pubdef"><a name="locale_create/3"><strong>locale_create</strong>(<var>-Locale,
	276	<dt class="pubdef"><a id="locale_create/3"><strong>locale_create</strong>(<var>-Locale,
236	277	+Default, +Options</var>)</a></dt>
237	278	<dd class="defbody">
238	279	Create a new locale object. <var>Default</var> is either an existing

273	314	[ decimal_point('.'), thousands_sep(','), grouping([repeat(3)]) ]
274	315	</pre>
275	316
276		<p>Named locales exists until they are destroyed using <a name="idx:localedestroy1:1288"></a><a class="pred" href="locale.html#locale_destroy/1">locale_destroy/1</a>
	317	<p>Named locales exists until they are destroyed using <a id="idx:localedestroy1:1288"></a><a class="pred" href="locale.html#locale_destroy/1">locale_destroy/1</a>
277	318	and they are no longer referenced. Unnamed locales are subject to (atom)
278	319	garbage collection.</dd>
279		<dt class="pubdef"><a name="locale_destroy/1"><strong>locale_destroy</strong>(<var>+Locale</var>)</a></dt>
	320	<dt class="pubdef"><a id="locale_destroy/1"><strong>locale_destroy</strong>(<var>+Locale</var>)</a></dt>
280	321	<dd class="defbody">
281	322	Destroy a locale. If the locale is named, this removes the name
282	323	association from the locale, after which the locale is left to be
283	324	reclaimed by garbage collection.</dd>
284		<dt class="pubdef"><a name="locale_property/2"><strong>locale_property</strong>(<var>?Locale,
	325	<dt class="pubdef"><a id="locale_property/2"><strong>locale_property</strong>(<var>?Locale,
285	326	?Property</var>)</a></dt>
286	327	<dd class="defbody">
287	328	True when <var>Locale</var> has <var>Property</var>. Properties are the
288		same as the <var>Options</var> described with <a name="idx:localecreate3:1289"></a><a class="pred" href="locale.html#locale_create/3">locale_create/3</a>.</dd>
289		<dt class="pubdef"><a name="set_locale/1"><strong>set_locale</strong>(<var>+Locale</var>)</a></dt>
	329	same as the <var>Options</var> described with <a id="idx:localecreate3:1289"></a><a class="pred" href="locale.html#locale_create/3">locale_create/3</a>.</dd>
	330	<dt class="pubdef"><a id="set_locale/1"><strong>set_locale</strong>(<var>+Locale</var>)</a></dt>
290	331	<dd class="defbody">
291	332	Set the default locale for the current thread, as well as the locale for
292	333	the standard streams (<code>user_input</code>, <code>user_output</code>,
293	334	<code>user_error</code>, <code>current_output</code> and <code>current_input</code>.
294	335	This locale is used for new streams, unless overruled using the
295		<code>locale(Locale)</code> option of <a name="idx:open4:1290"></a><a class="pred" href="IO.html#open/4">open/4</a>
296		or <a name="idx:setstream2:1291"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.</dd>
297		<dt class="pubdef"><a name="current_locale/1"><strong>current_locale</strong>(<var>-Locale</var>)</a></dt>
	336	<code>locale(Locale)</code> option of <a id="idx:open4:1290"></a><a class="pred" href="IO.html#open/4">open/4</a>
	337	or <a id="idx:setstream2:1291"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.</dd>
	338	<dt class="pubdef"><a id="current_locale/1"><strong>current_locale</strong>(<var>-Locale</var>)</a></dt>
298	339	<dd class="defbody">
299	340	True when <var>Locale</var> is the locale of the calling thread.
300	341	</dd>

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193	234	</div>
194		<h2 id="sec:main"><a name="sec:A.16"><span class="sec-nr">A.16</span> <span class="sec-title">library(main):
	235	<h2 id="sec:main"><a id="sec:A.16"><span class="sec-nr">A.16</span> <span class="sec-title">library(main):
195	236	Provide entry point for scripts</span></a></h2>
196	237
197		<p><a name="sec:main"></a>
	238	<p><a id="sec:main"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">See also</dt>

229	270	</pre>
230	271
231	272	<dl class="latex">
232		<dt class="pubdef"><a name="main/0"><strong>main</strong></a></dt>
	273	<dt class="pubdef"><a id="main/0"><strong>main</strong></a></dt>
233	274	<dd class="defbody">
234	275	Call <span class="pred-ext">main/1</span> using the passed command-line
235	276	arguments. Before calling
236	277	<span class="pred-ext">main/1</span> this predicate installs a signal
237	278	handler for <code>SIGINT</code> (Control-C) that terminates the process
238	279	with status 1.</dd>
239		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="argv_options/3"><strong>argv_options</strong>(<var>+Argv,
	280	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="argv_options/3"><strong>argv_options</strong>(<var>+Argv,
240	281	-RestArgv, -Options</var>)</a></dt>
241	282	<dd class="defbody">
242	283	Generic transformation of long commandline arguments to options. Each

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193	234	</div>
194		<h2 id="sec:manipatom"><a name="sec:4.22"><span class="sec-nr">4.22</span> <span class="sec-title">Analysing
	235	<h2 id="sec:manipatom"><a id="sec:4.22"><span class="sec-nr">4.22</span> <span class="sec-title">Analysing
195	236	and Constructing Atoms</span></a></h2>
196	237
197		<a name="sec:manipatom"></a>
	238	<a id="sec:manipatom"></a>
198	239
199	240	<p>These predicates convert between Prolog constants and lists of
200		character codes. The predicates <a name="idx:atomcodes2:1240"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>, <a name="idx:numbercodes2:1241"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
201		and <a name="idx:name2:1242"></a><a class="pred" href="manipatom.html#name/2">name/2</a>
	241	character codes. The predicates <a id="idx:atomcodes2:1240"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>, <a id="idx:numbercodes2:1241"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
	242	and <a id="idx:name2:1242"></a><a class="pred" href="manipatom.html#name/2">name/2</a>
202	243	behave the same when converting from a constant to a list of character
203		codes. When converting the other way around, <a name="idx:atomcodes2:1243"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
204		will generate an atom, <a name="idx:numbercodes2:1244"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
205		will generate a number or exception and <a name="idx:name2:1245"></a><a class="pred" href="manipatom.html#name/2">name/2</a>
	244	codes. When converting the other way around, <a id="idx:atomcodes2:1243"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
	245	will generate an atom, <a id="idx:numbercodes2:1244"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
	246	will generate a number or exception and <a id="idx:name2:1245"></a><a class="pred" href="manipatom.html#name/2">name/2</a>
206	247	will return a number if possible and an atom otherwise.
207	248
208		<p>The ISO standard defines <a name="idx:atomchars2:1246"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
	249	<p>The ISO standard defines <a id="idx:atomchars2:1246"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
209	250	to describe the `broken-up' atom as a list of one-character atoms
210		instead of a list of codes. Up to version 3.2.x, SWI-Prolog's <a name="idx:atomchars2:1247"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
	251	instead of a list of codes. Up to version 3.2.x, SWI-Prolog's <a id="idx:atomchars2:1247"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
211	252	behaved like atom_codes, compatible with Quintus and SICStus Prolog. As
212	253	of 3.3.x, SWI-Prolog
213		<a name="idx:atomcodes2:1248"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
214		and <a name="idx:atomchars2:1249"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
	254	<a id="idx:atomcodes2:1248"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
	255	and <a id="idx:atomchars2:1249"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
215	256	are compliant to the ISO standard.
216	257
217	258	<p>To ease the pain of all variations in the Prolog community, all

220	261	`atom-side' accepts all atomic types (atom, number and string).
221	262
222	263	<dl class="latex">
223		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="atom_codes/2"><strong>atom_codes</strong>(<var>?Atom,
	264	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="atom_codes/2"><strong>atom_codes</strong>(<var>?Atom,
224	265	?String</var>)</a></dt>
225	266	<dd class="defbody">
226	267	Convert between an atom and a list of character codes. If

228	269	character codes and the result is unified with <var>String</var>. If <var>Atom</var>
229	270	is unbound and <var>String</var> is a list of character codes,
230	271	<var>Atom</var> will be unified with an atom constructed from this list.</dd>
231		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="atom_chars/2"><strong>atom_chars</strong>(<var>?Atom,
	272	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="atom_chars/2"><strong>atom_chars</strong>(<var>?Atom,
232	273	?CharList</var>)</a></dt>
233	274	<dd class="defbody">
234		As <a name="idx:atomcodes2:1250"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>,
	275	As <a id="idx:atomcodes2:1250"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>,
235	276	but <var>CharList</var> is a list of one-character atoms rather than a
236	277	list of character codes.<sup class="fn">100<span class="fn-text">Up to
237		version 3.2.x, <a name="idx:atomchars2:1251"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
238		behaved as the current <a name="idx:atomcodes2:1252"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>.
	278	version 3.2.x, <a id="idx:atomchars2:1251"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>
	279	behaved as the current <a id="idx:atomcodes2:1252"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>.
239	280	The current definition is compliant with the ISO standard.</span></sup>
240	281
241	282	<pre class="code">

245	286	</pre>
246	287
247	288	</dd>
248		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="char_code/2"><strong>char_code</strong>(<var>?Atom,
	289	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="char_code/2"><strong>char_code</strong>(<var>?Atom,
249	290	?Code</var>)</a></dt>
250	291	<dd class="defbody">
251	292	Convert between character and character code for a single character.<sup class="fn">101<span class="fn-text">This
252	293	is also called atom_char/2 in older versions of SWI-Prolog as well as
253	294	some other Prolog implementations. The atom_char/2 predicate is
254	295	available from the library <code>backcomp.pl</code></span></sup></dd>
255		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="number_chars/2"><strong>number_chars</strong>(<var>?Number,
	296	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="number_chars/2"><strong>number_chars</strong>(<var>?Number,
256	297	?CharList</var>)</a></dt>
257	298	<dd class="defbody">
258		Similar to <a name="idx:atomchars2:1253"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>,
	299	Similar to <a id="idx:atomchars2:1253"></a><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a>,
259	300	but converts between a number and its representation as a list of
260	301	one-character atoms. If <var>CharList</var> is a
261	302	<em>proper list</em>, i.e., not unbound or a <em>partial list</em>,

273	314	implementations--believe this is incorrect. We also beleive it would
274	315	have been better not to allow for white space, or to allow for both
275	316	leading and trailing white space. Prolog syntax-based conversion can
276		also be achieved using <a name="idx:format3:1254"></a><a class="pred" href="format.html#format/3">format/3</a>
277		and <a name="idx:readfromchars2:1255"></a><a class="pred" href="charsio.html#read_from_chars/2">read_from_chars/2</a>.</span></sup>
	317	also be achieved using <a id="idx:format3:1254"></a><a class="pred" href="format.html#format/3">format/3</a>
	318	and <a id="idx:readfromchars2:1255"></a><a class="pred" href="charsio.html#read_from_chars/2">read_from_chars/2</a>.</span></sup>
278	319	A <code>syntax_error</code> exception is raised if <var>CharList</var>
279	320	does not represent a valid Prolog number.</dd>
280		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="number_codes/2"><strong>number_codes</strong>(<var>?Number,
	321	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="number_codes/2"><strong>number_codes</strong>(<var>?Number,
281	322	?CodeList</var>)</a></dt>
282	323	<dd class="defbody">
283		As <a name="idx:numberchars2:1256"></a><a class="pred" href="manipatom.html#number_chars/2">number_chars/2</a>,
	324	As <a id="idx:numberchars2:1256"></a><a class="pred" href="manipatom.html#number_chars/2">number_chars/2</a>,
284	325	but converts to a list of character codes rather than one-character
285	326	atoms. In the mode (-,+), both predicates behave identically to improve
286	327	handling of non-ISO source.</dd>
287		<dt class="pubdef"><a name="atom_number/2"><strong>atom_number</strong>(<var>?Atom,
	328	<dt class="pubdef"><a id="atom_number/2"><strong>atom_number</strong>(<var>?Atom,
288	329	?Number</var>)</a></dt>
289	330	<dd class="defbody">
290		Realises the popular combination of <a name="idx:atomcodes2:1257"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
291		and <a name="idx:numbercodes2:1258"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
	331	Realises the popular combination of <a id="idx:atomcodes2:1257"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>
	332	and <a id="idx:numbercodes2:1258"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
292	333	to convert between atom and number (integer or float) in one predicate,
293		avoiding the intermediate list. Unlike the ISO <a name="idx:numbercodes2:1259"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
294		predicates, <a name="idx:atomnumber2:1260"></a><a class="pred" href="manipatom.html#atom_number/2">atom_number/2</a>
	334	avoiding the intermediate list. Unlike the ISO <a id="idx:numbercodes2:1259"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
	335	predicates, <a id="idx:atomnumber2:1260"></a><a class="pred" href="manipatom.html#atom_number/2">atom_number/2</a>
295	336	fails silently in mode (+,-) if <var>Atom</var> does not represent a
296	337	number.<sup class="fn">103<span class="fn-text">Versions prior to 6.1.7
297		raised a syntax error, compliant to <a name="idx:numbercodes2:1261"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a></span></sup>
298		See also <a name="idx:atomiclistconcat2:1262"></a><a class="pred" href="manipatom.html#atomic_list_concat/2">atomic_list_concat/2</a>
	338	raised a syntax error, compliant to <a id="idx:numbercodes2:1261"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a></span></sup>
	339	See also <a id="idx:atomiclistconcat2:1262"></a><a class="pred" href="manipatom.html#atomic_list_concat/2">atomic_list_concat/2</a>
299	340	for assembling an atom from atoms and numbers.</dd>
300		<dt class="pubdef"><a name="name/2"><strong>name</strong>(<var>?Atomic,
	341	<dt class="pubdef"><a id="name/2"><strong>name</strong>(<var>?Atomic,
301	342	?CodeList</var>)</a></dt>
302	343	<dd class="defbody">
303	344	<var>CodeList</var> is a list of character codes representing the same

317	358	considered <em>deprecated</em> although, given its long tradition, it is
318	359	unlikely to be removed from the system. It still has some value for
319	360	converting input to, depending on the syntax, a number or atom. New code
320		should consider the ISO predicates <a name="idx:atomcodes2:1263"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>, <a name="idx:numbercodes2:1264"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
321		or the SWI-Prolog predicate <a name="idx:atomnumber2:1265"></a><a class="pred" href="manipatom.html#atom_number/2">atom_number/2</a>.</dd>
322		<dt class="pubdef"><a name="term_to_atom/2"><strong>term_to_atom</strong>(<var>?Term,
	361	should consider the ISO predicates <a id="idx:atomcodes2:1263"></a><a class="pred" href="manipatom.html#atom_codes/2">atom_codes/2</a>, <a id="idx:numbercodes2:1264"></a><a class="pred" href="manipatom.html#number_codes/2">number_codes/2</a>
	362	or the SWI-Prolog predicate <a id="idx:atomnumber2:1265"></a><a class="pred" href="manipatom.html#atom_number/2">atom_number/2</a>.</dd>
	363	<dt class="pubdef"><a id="term_to_atom/2"><strong>term_to_atom</strong>(<var>?Term,
323	364	?Atom</var>)</a></dt>
324	365	<dd class="defbody">
325	366	True if <var>Atom</var> describes a term that unifies with <var>Term</var>.

328	369	result unified with <var>Term</var>. If <var>Atom</var> has no valid
329	370	syntax, a
330	371	<code>syntax_error</code> exception is raised. Otherwise <var>Term</var>
331		is ``written'' on <var>Atom</var> using <a name="idx:writeterm2:1266"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	372	is ``written'' on <var>Atom</var> using <a id="idx:writeterm2:1266"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
332	373	with the option
333		<code>quoted(true)</code>. See also <a name="idx:format3:1267"></a><a class="pred" href="format.html#format/3">format/3</a>, <a name="idx:withoutputto2:1268"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
	374	<code>quoted(true)</code>. See also <a id="idx:format3:1267"></a><a class="pred" href="format.html#format/3">format/3</a>, <a id="idx:withoutputto2:1268"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
334	375	and
335		<a name="idx:termstring2:1269"></a><a class="pred" href="strings.html#term_string/2">term_string/2</a>.</dd>
336		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="atom_to_term/3"><strong>atom_to_term</strong>(<var>+Atom,
	376	<a id="idx:termstring2:1269"></a><a class="pred" href="strings.html#term_string/2">term_string/2</a>.</dd>
	377	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="atom_to_term/3"><strong>atom_to_term</strong>(<var>+Atom,
337	378	-Term, -Bindings</var>)</a></dt>
338	379	<dd class="defbody">
339		Use <var>Atom</var> as input to <a name="idx:readterm2:1270"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	380	Use <var>Atom</var> as input to <a id="idx:readterm2:1270"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
340	381	using the option
341	382	<code>variable_names</code> and return the read term in <var>Term</var>
342	383	and the variable bindings in <var>Bindings</var>. <var>Bindings</var> is
343	384	a list of
344	385	<var><var>Name</var> = <var>Var</var></var> couples, thus providing
345		access to the actual variable names. See also <a name="idx:readterm2:1271"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.
	386	access to the actual variable names. See also <a id="idx:readterm2:1271"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.
346	387	If <var>Atom</var> has no valid syntax, a <code>syntax_error</code>
347	388	exception is raised. New code should use
348		<a name="idx:readtermfromatom3:1272"></a><a class="pred" href="termrw.html#read_term_from_atom/3">read_term_from_atom/3</a>.</dd>
349		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="atom_concat/3"><strong>atom_concat</strong>(<var>?Atom1,
	389	<a id="idx:readtermfromatom3:1272"></a><a class="pred" href="termrw.html#read_term_from_atom/3">read_term_from_atom/3</a>.</dd>
	390	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="atom_concat/3"><strong>atom_concat</strong>(<var>?Atom1,
350	391	?Atom2, ?Atom3</var>)</a></dt>
351	392	<dd class="defbody">
352	393	<var>Atom3</var> forms the concatenation of <var>Atom1</var> and <var>Atom2</var>.
353	394	At least two of the arguments must be instantiated to atoms. This
354	395	predicate also allows for the mode (-,-,+), non-deterministically
355		splitting the 3rd argument into two parts (as <a name="idx:append3:1273"></a><a class="pred" href="lists.html#append/3">append/3</a>
	396	splitting the 3rd argument into two parts (as <a id="idx:append3:1273"></a><a class="pred" href="lists.html#append/3">append/3</a>
356	397	does for lists). SWI-Prolog allows for atomic arguments. Portable code
357		must use <a name="idx:atomicconcat3:1274"></a><a class="pred" href="manipatom.html#atomic_concat/3">atomic_concat/3</a>
	398	must use <a id="idx:atomicconcat3:1274"></a><a class="pred" href="manipatom.html#atomic_concat/3">atomic_concat/3</a>
358	399	if non-atom arguments are involved.</dd>
359		<dt class="pubdef"><a name="atomic_concat/3"><strong>atomic_concat</strong>(<var>+Atomic1,
	400	<dt class="pubdef"><a id="atomic_concat/3"><strong>atomic_concat</strong>(<var>+Atomic1,
360	401	+Atomic2, -Atom</var>)</a></dt>
361	402	<dd class="defbody">
362	403	<var>Atom</var> represents the text after converting <var>Atomic1</var>

369	410	</pre>
370	411
371	412	</dd>
372		<dt class="pubdef"><span class="pred-tag">[commons]</span><a name="atomic_list_concat/2"><strong>atomic_list_concat</strong>(<var>+List,
	413	<dt class="pubdef"><span class="pred-tag">[commons]</span><a id="atomic_list_concat/2"><strong>atomic_list_concat</strong>(<var>+List,
373	414	-Atom</var>)</a></dt>
374	415	<dd class="defbody">
375	416	<var>List</var> is a list of strings, atoms, integers or floating point
376	417	numbers. Succeeds if <var>Atom</var> can be unified with the
377	418	concatenated elements of <var>List</var>. Equivalent to <code>atomic_list_concat(List,
378	419	'', Atom)</code>.</dd>
379		<dt class="pubdef"><span class="pred-tag">[commons]</span><a name="atomic_list_concat/3"><strong>atomic_list_concat</strong>(<var>+List,
	420	<dt class="pubdef"><span class="pred-tag">[commons]</span><a id="atomic_list_concat/3"><strong>atomic_list_concat</strong>(<var>+List,
380	421	+Separator, -Atom</var>)</a></dt>
381	422	<dd class="defbody">
382		Creates an atom just like <a name="idx:atomiclistconcat2:1275"></a><a class="pred" href="manipatom.html#atomic_list_concat/2">atomic_list_concat/2</a>,
	423	Creates an atom just like <a id="idx:atomiclistconcat2:1275"></a><a class="pred" href="manipatom.html#atomic_list_concat/2">atomic_list_concat/2</a>,
383	424	but inserts <var>Separator</var> between each pair of inputs. For
384	425	example:
385	426

392	433	<p>The SWI-Prolog version of this predicate can also be used to split
393	434	atoms by instantiating <var>Separator</var> and <var>Atom</var> as shown
394	435	below. We kept this functionality to simplify porting old SWI-Prolog
395		code where this predicate was called <a name="idx:concatatom3:1276"></a><span class="pred-ext">concat_atom/3</span>.
	436	code where this predicate was called <a id="idx:concatatom3:1276"></a><span class="pred-ext">concat_atom/3</span>.
396	437	When used in mode (-,+,+),
397		<var>Separator</var> must be a non-empty atom. See also <a name="idx:splitstring4:1277"></a><a class="pred" href="strings.html#split_string/4">split_string/4</a>.
	438	<var>Separator</var> must be a non-empty atom. See also <a id="idx:splitstring4:1277"></a><a class="pred" href="strings.html#split_string/4">split_string/4</a>.
398	439
399	440	<pre class="code">
400	441	?- atomic_list_concat(L, -, 'gnu-gnat').

403	444	</pre>
404	445
405	446	</dd>
406		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="atom_length/2"><strong>atom_length</strong>(<var>+Atom,
	447	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="atom_length/2"><strong>atom_length</strong>(<var>+Atom,
407	448	-Length</var>)</a></dt>
408	449	<dd class="defbody">
409	450	True if <var>Atom</var> is an atom of <var>Length</var> characters. The
410	451	SWI-Prolog version accepts all atomic types, as well as code-lists and
411	452	character-lists. New code should avoid this feature and use
412		<a name="idx:writelength3:1278"></a><a class="pred" href="termrw.html#write_length/3">write_length/3</a>
	453	<a id="idx:writelength3:1278"></a><a class="pred" href="termrw.html#write_length/3">write_length/3</a>
413	454	to get the number of characters that would be written if the argument
414		was handed to <a name="idx:writeterm3:1279"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>.</dd>
415		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="atom_prefix/2"><strong>atom_prefix</strong>(<var>+Atom,
	455	was handed to <a id="idx:writeterm3:1279"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>.</dd>
	456	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="atom_prefix/2"><strong>atom_prefix</strong>(<var>+Atom,
416	457	+Prefix</var>)</a></dt>
417	458	<dd class="defbody">
418	459	True if <var>Atom</var> starts with the characters from <var>Prefix</var>.
419	460	Its behaviour is equivalent to
420	461	<code>?- sub_atom(<var>Atom</var>, 0, _, _, <var>Prefix</var>)</code>.
421	462	Deprecated.</dd>
422		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="sub_atom/5"><strong>sub_atom</strong>(<var>+Atom,
	463	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="sub_atom/5"><strong>sub_atom</strong>(<var>+Atom,
423	464	?Before, ?Len, ?After, ?Sub</var>)</a></dt>
424	465	<dd class="defbody">
425	466	ISO predicate for breaking atoms. It maintains the following relation:

437	478	<p>The implementation minimises non-determinism and creation of atoms.
438	479	This is a flexible predicate that can do search, prefix- and
439	480	suffix-matching, etc.</dd>
440		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="sub_atom_icasechk/3"><strong>sub_atom_icasechk</strong>(<var>+Haystack,
	481	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="sub_atom_icasechk/3"><strong>sub_atom_icasechk</strong>(<var>+Haystack,
441	482	?Start, +Needle</var>)</a></dt>
442	483	<dd class="defbody">
443	484	True when <var>Needle</var> is a sub atom of <var>Haystack</var>

+73

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193	234	</div>
194		<h2 id="sec:manipmodule"><a name="sec:6.14"><span class="sec-nr">6.14</span> <span class="sec-title">Module
	235	<h2 id="sec:manipmodule"><a id="sec:6.14"><span class="sec-nr">6.14</span> <span class="sec-title">Module
195	236	properties</span></a></h2>
196	237
197		<a name="sec:manipmodule"></a>
	238	<a id="sec:manipmodule"></a>
198	239
199	240	<p>The following predicates can be used to query the module system for
200	241	reflexive programming:
201	242
202	243	<dl class="latex">
203		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_module/1"><strong>current_module</strong>(<var>?Module</var>)</a></dt>
	244	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_module/1"><strong>current_module</strong>(<var>?Module</var>)</a></dt>
204	245	<dd class="defbody">
205	246	True if <var>Module</var> is a currently defined module. This predicate
206	247	enumerates all modules, whether loaded from a file or created
207	248	dynamically. Note that modules cannot be destroyed in the current
208	249	version of SWI-Prolog.</dd>
209		<dt class="pubdef"><a name="module_property/2"><strong>module_property</strong>(<var>?Module,
	250	<dt class="pubdef"><a id="module_property/2"><strong>module_property</strong>(<var>?Module,
210	251	?Property</var>)</a></dt>
211	252	<dd class="defbody">
212	253	True if <var>Property</var> is a property of <var>Module</var>. Defined

260	301	indicators are in canonical form (i.e., always using name/arity and
261	302	never the DCG form name//arity). Future versions may also use the DCG
262	303	form and include public operators. See also
263		<a name="idx:predicateproperty2:1746"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.
	304	<a id="idx:predicateproperty2:1750"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.
264	305	</dd>
265	306	<dt><strong>exported_operators</strong>(<var>-ListOfOperators</var>)</dt>
266	307	<dd class="defbody">

276	317	<dt><strong>program_space</strong>(<var>-Bytes</var>)</dt>
277	318	<dd class="defbody">
278	319	If present, this number limits the <code>program_size</code>. See
279		<a name="idx:setmodule1:1747"></a><a class="pred" href="manipmodule.html#set_module/1">set_module/1</a>.
	320	<a id="idx:setmodule1:1751"></a><a class="pred" href="manipmodule.html#set_module/1">set_module/1</a>.
280	321	</dd>
281	322	<dt><strong>last_modified_generation</strong>(<var>-Generation</var>)</dt>
282	323	<dd class="defbody">
283	324	Integer expression the last database generation where a clause was added
284		or removed from a predicate that is implemented in this module. See also <a name="idx:predicateproperty2:1748"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.
	325	or removed from a predicate that is implemented in this module. See also <a id="idx:predicateproperty2:1752"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>.
285	326	</dd>
286	327	</dl>
287	328
288	329	</dd>
289		<dt class="pubdef"><a name="set_module/1"><strong>set_module</strong>(<var>:Property</var>)</a></dt>
	330	<dt class="pubdef"><a id="set_module/1"><strong>set_module</strong>(<var>:Property</var>)</a></dt>
290	331	<dd class="defbody">
291	332	Modify properties of the module. Currently, the following properties may
292	333	be modified:

297	338	Set the default import module of the current module to <var>Module</var>.
298	339	Typically, <var>Module</var> is one of <code>user</code> or <code>system</code>.
299	340	See
300		<a class="sec" href="importmodule.html">section 6.9</a>.
	341	<a class="sec" href="importmodule.html#sec:6.9">section 6.9</a>.
301	342	</dd>
302	343	<dt><strong>class</strong>(<var>+Class</var>)</dt>
303	344	<dd class="defbody">
304		Set the class of the module. See <a name="idx:moduleproperty2:1749"></a><a class="pred" href="manipmodule.html#module_property/2">module_property/2</a>.
	345	Set the class of the module. See <a id="idx:moduleproperty2:1753"></a><a class="pred" href="manipmodule.html#module_property/2">module_property/2</a>.
305	346	</dd>
306	347	<dt><strong>program_space</strong>(<var>+Bytes</var>)</dt>
307	348	<dd class="defbody">

309	350	module. Raises a permission error if the current usage is above the
310	351	requested limit. Setting the limit to 0 (zero) removes the limit. An
311	352	attempt to assert clauses that causes the limit to be exceeded causes a
312		<code>resource_error(program_space)</code> exception. See <a name="idx:assertz1:1750"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
	353	<code>resource_error(program_space)</code> exception. See <a id="idx:assertz1:1754"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
313	354	and
314		<a name="idx:moduleproperty2:1751"></a><a class="pred" href="manipmodule.html#module_property/2">module_property/2</a>.
	355	<a id="idx:moduleproperty2:1755"></a><a class="pred" href="manipmodule.html#module_property/2">module_property/2</a>.
315	356	</dd>
316	357	</dl>
317	358

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193	234	</div>
194		<h2 id="sec:manipstack"><a name="sec:B.1"><span class="sec-nr">B.1</span> <span class="sec-title">Examining
	235	<h2 id="sec:manipstack"><a id="sec:B.1"><span class="sec-nr">B.1</span> <span class="sec-title">Examining
195	236	the Environment Stack</span></a></h2>
196	237
197		<a name="sec:manipstack"></a>
	238	<a id="sec:manipstack"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="prolog_current_frame/1"><strong>prolog_current_frame</strong>(<var>-Frame</var>)</a></dt>
	241	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="prolog_current_frame/1"><strong>prolog_current_frame</strong>(<var>-Frame</var>)</a></dt>
201	242	<dd class="defbody">
202	243	Unify <var>Frame</var> with an integer providing a reference to the
203	244	parent of the current local stack frame. A pointer to the current local
204	245	frame cannot be provided as the predicate succeeds deterministically and
205	246	therefore its frame is destroyed immediately after succeeding.</dd>
206		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="prolog_current_choice/1"><strong>prolog_current_choice</strong>(<var>-Choice</var>)</a></dt>
	247	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="prolog_current_choice/1"><strong>prolog_current_choice</strong>(<var>-Choice</var>)</a></dt>
207	248	<dd class="defbody">
208	249	Unify <var>Choice</var> with an integer provided a reference to the last
209	250	choice point. Fails if the current environment has no choice points. See
210		also <a name="idx:prologchoiceattribute3:2177"></a><a class="pred" href="manipstack.html#prolog_choice_attribute/3">prolog_choice_attribute/3</a>.</dd>
211		<dt class="pubdef"><a name="prolog_frame_attribute/3"><strong>prolog_frame_attribute</strong>(<var>+Frame,
	251	also <a id="idx:prologchoiceattribute3:2181"></a><a class="pred" href="manipstack.html#prolog_choice_attribute/3">prolog_choice_attribute/3</a>.</dd>
	252	<dt class="pubdef"><a id="prolog_frame_attribute/3"><strong>prolog_frame_attribute</strong>(<var>+Frame,
212	253	+Key, :Value</var>)</a></dt>
213	254	<dd class="defbody">
214	255	Obtain information about the local stack frame <var>Frame</var>. <var>Frame</var>
215		is a frame reference as obtained through <a name="idx:prologcurrentframe1:2178"></a><a class="pred" href="manipstack.html#prolog_current_frame/1">prolog_current_frame/1</a>,
216		<a name="idx:prologtraceinterception4:2179"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>
	256	is a frame reference as obtained through <a id="idx:prologcurrentframe1:2182"></a><a class="pred" href="manipstack.html#prolog_current_frame/1">prolog_current_frame/1</a>,
	257	<a id="idx:prologtraceinterception4:2183"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>
217	258	or this predicate. The key values are described below.
218	259
219	260	<dl class="latex">

233	274	context, the goal is represented as <code><<var>module</var>>:<<var>goal</var>></code>.
234	275	Do not instantiate variables in this goal unless you <b>know</b> what
235	276	you are doing! Note that the returned term may contain references to the
236		frame and should be discarded before the frame terminates.<sup class="fn">185<span class="fn-text">The
	277	frame and should be discarded before the frame terminates.<sup class="fn">186<span class="fn-text">The
237	278	returned term is actually an illegal Prolog term that may hold
238	279	references from the global to the local stack to preserve the variable
239	280	names.</span></sup></dd>

255	296	<dd class="defbody">
256	297	<var>Value</var> is unified with a reference to the currently running
257	298	clause. Fails if the current goal is associated with a foreign (C)
258		defined predicate. See also <a name="idx:nthclause3:2180"></a><a class="pred" href="examineprog.html#nth_clause/3">nth_clause/3</a>
259		and <a name="idx:clauseproperty2:2181"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>.</dd>
	299	defined predicate. See also <a id="idx:nthclause3:2184"></a><a class="pred" href="examineprog.html#nth_clause/3">nth_clause/3</a>
	300	and <a id="idx:clauseproperty2:2185"></a><a class="pred" href="examineprog.html#clause_property/2">clause_property/2</a>.</dd>
260	301	<dt><strong>level</strong></dt>
261	302	<dd class="defbody">
262	303	<var>Value</var> is unified with the recursion level of <var>Frame</var>.

300	341	</dl>
301	342
302	343	</dd>
303		<dt class="pubdef"><a name="prolog_choice_attribute/3"><strong>prolog_choice_attribute</strong>(<var>+ChoicePoint,
	344	<dt class="pubdef"><a id="prolog_choice_attribute/3"><strong>prolog_choice_attribute</strong>(<var>+ChoicePoint,
304	345	+Key, -Value</var>)</a></dt>
305	346	<dd class="defbody">
306	347	Extract attributes of a choice point. <var>ChoicePoint</var> is a
307		reference to a choice point as passed to <a name="idx:prologtraceinterception4:2182"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>
308		on the 3rd argument or obtained using <a name="idx:prologcurrentchoice1:2183"></a><a class="pred" href="manipstack.html#prolog_current_choice/1">prolog_current_choice/1</a>. <var>Key</var>
	348	reference to a choice point as passed to <a id="idx:prologtraceinterception4:2186"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>
	349	on the 3rd argument or obtained using <a id="idx:prologcurrentchoice1:2187"></a><a class="pred" href="manipstack.html#prolog_current_choice/1">prolog_current_choice/1</a>. <var>Key</var>
309	350	specifies the requested information:
310	351
311	352	<dl class="latex">

322	363	Requests the type. Defined values are <code>clause</code> (the goal has
323	364	alternative clauses), <code>foreign</code> (non-deterministic foreign
324	365	predicate), <code>jump</code> (clause internal choice point), <code>top</code>
325		(first dummy choice point), <code>catch</code> (<a name="idx:catch3:2184"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	366	(first dummy choice point), <code>catch</code> (<a id="idx:catch3:2188"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
326	367	to allow for undo),
327	368	<code>debug</code> (help the debugger), or <code>none</code> (has been
328	369	deleted).

331	372
332	373	<p>This predicate is used for the graphical debugger to show the choice
333	374	point stack.</dd>
334		<dt class="pubdef"><a name="deterministic/1"><strong>deterministic</strong>(<var>-Boolean</var>)</a></dt>
	375	<dt class="pubdef"><a id="deterministic/1"><strong>deterministic</strong>(<var>-Boolean</var>)</a></dt>
335	376	<dd class="defbody">
336	377	Unifies its argument with <code>true</code> if no choice point exists
337	378	that is more recent than the entry of the clause in which it appears.
338	379	There are few realistic situations for using this predicate. It is used
339	380	by the
340		<a name="idx:prolog0:2185"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>
	381	<a id="idx:prolog0:2189"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>
341	382	top level to check whether Prolog should prompt the user for
342	383	alternatives. Similar results can be achieved in a more portable fashion
343		using <a name="idx:callcleanup2:2186"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>.
	384	using <a id="idx:callcleanup2:2190"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>.
344	385	</dd>
345	386	</dl>
346	387

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193	234	</div>
194		<h2 id="sec:manipterm"><a name="sec:4.21"><span class="sec-nr">4.21</span> <span class="sec-title">Analysing
	235	<h2 id="sec:manipterm"><a id="sec:4.21"><span class="sec-nr">4.21</span> <span class="sec-title">Analysing
195	236	and Constructing Terms</span></a></h2>
196	237
197		<a name="sec:manipterm"></a>
	238	<a id="sec:manipterm"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="functor/3"><strong>functor</strong>(<var>?Term,
	241	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="functor/3"><strong>functor</strong>(<var>?Term,
201	242	?Name, ?Arity</var>)</a></dt>
202	243	<dd class="defbody">
203	244	True when <var>Term</var> is a term with functor <var>Name</var>/<var>Arity</var>.

211	252
212	253	<p>SWI-Prolog also supports terms with arity 0, as in <code>a()</code>
213	254	(see
214		<a class="sec" href="extensions.html">section 5</a>. Such terms must be
215		processed using
216		<a name="idx:compoundnamearity3:1190"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>.
217		The predicate <a name="idx:functor3:1191"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
	255	<a class="sec" href="extensions.html#sec:5">section 5</a>. Such terms
	256	must be processed using
	257	<a id="idx:compoundnamearity3:1190"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>.
	258	The predicate <a id="idx:functor3:1191"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
218	259	and <a class="pred" href="manipterm.html#=../2">=../2</a> raise a <code>domain_error</code>
219	260	when faced with these terms. Without this precaution, the inconsistency
220	261	demonstrated below could happen silently.<sup class="fn">96<span class="fn-text">Raising

228	269	</pre>
229	270
230	271	</dd>
231		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="arg/3"><strong>arg</strong>(<var>?Arg,
	272	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="arg/3"><strong>arg</strong>(<var>?Arg,
232	273	+Term, ?Value</var>)</a></dt>
233	274	<dd class="defbody">
234	275	<var>Term</var> should be instantiated to a term, <var>Arg</var> to an

240	281	is unified with the argument number. Backtracking yields alternative
241	282	solutions.<sup class="fn">97<span class="fn-text">The instantiation
242	283	pattern (-, +, ?) is an extension to `standard' Prolog. Some systems
243		provide genarg/3 that covers this pattern.</span></sup> The predicate <a name="idx:arg3:1192"></a><a class="pred" href="manipterm.html#arg/3">arg/3</a>
	284	provide genarg/3 that covers this pattern.</span></sup> The predicate <a id="idx:arg3:1192"></a><a class="pred" href="manipterm.html#arg/3">arg/3</a>
244	285	fails silently if <var><var>Arg</var> = 0</var> or
245	286	<var><var>Arg</var> > <em>arity</em></var> and raises the exception
246	287	<code>domain_error(not_less_than_zero, <var>Arg</var>)</code> if <var><var>Arg</var>
247	288	< 0</var>.</dd>
248		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="=../2"><var>?Term</var> <strong>=..</strong> <var>?List</var></a></dt>
	289	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="=../2"><var>?Term</var> <strong>=..</strong> <var>?List</var></a></dt>
249	290	<dd class="defbody">
250	291	<var>List</var> is a list whose head is the functor of <var>Term</var>
251	292	and the remaining arguments are the arguments of the term. Either side

262	303
263	304	<p>SWI-Prolog also supports terms with arity 0, as in <code>a()</code>
264	305	(see
265		<a class="sec" href="extensions.html">section 5</a>. Such terms must be
266		processed using
267		<a name="idx:compoundnamearguments3:1193"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>.
268		This predicate raises a domain error as shown below. See also <a name="idx:functor3:1194"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>.
	306	<a class="sec" href="extensions.html#sec:5">section 5</a>. Such terms
	307	must be processed using
	308	<a id="idx:compoundnamearguments3:1193"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>.
	309	This predicate raises a domain error as shown below. See also <a id="idx:functor3:1194"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>.
269	310
270	311	<pre class="code">
271	312	?- a() =.. L.

273	314	</pre>
274	315
275	316	</dd>
276		<dt class="pubdef"><a name="compound_name_arity/3"><strong>compound_name_arity</strong>(<var>?Compound,
	317	<dt class="pubdef"><a id="compound_name_arity/3"><strong>compound_name_arity</strong>(<var>?Compound,
277	318	?Name, ?Arity</var>)</a></dt>
278	319	<dd class="defbody">
279		Rationalized version of <a name="idx:functor3:1195"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
	320	Rationalized version of <a id="idx:functor3:1195"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
280	321	that only works for compound terms and can examine and create compound
281	322	terms with zero arguments (e.g,
282		<code>name()</code>. See also <a name="idx:compoundnamearguments3:1196"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>.</dd>
283		<dt class="pubdef"><a name="compound_name_arguments/3"><strong>compound_name_arguments</strong>(<var>?Compound,
	323	<code>name()</code>. See also <a id="idx:compoundnamearguments3:1196"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>.</dd>
	324	<dt class="pubdef"><a id="compound_name_arguments/3"><strong>compound_name_arguments</strong>(<var>?Compound,
284	325	?Name, ?Arguments</var>)</a></dt>
285	326	<dd class="defbody">
286	327	Rationalized version of <a class="pred" href="manipterm.html#=../2">=../2</a>
287	328	that can compose and decompose compound terms with zero arguments. See
288		also <a name="idx:compoundnamearity3:1197"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>.</dd>
289		<dt class="pubdef"><a name="numbervars/3"><strong>numbervars</strong>(<var>+Term,
	329	also <a id="idx:compoundnamearity3:1197"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>.</dd>
	330	<dt class="pubdef"><a id="numbervars/3"><strong>numbervars</strong>(<var>+Term,
290	331	+Start, -End</var>)</a></dt>
291	332	<dd class="defbody">
292	333	Unify the free variables in <var>Term</var> with a term <code>$VAR(N)</code>,

313	354	End = 2.
314	355	</pre>
315	356
316		<p>See also the <code>numbervars</code> option to <a name="idx:writeterm3:1198"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>
317		and <a name="idx:numbervars4:1199"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>.</dd>
318		<dt class="pubdef"><a name="numbervars/4"><strong>numbervars</strong>(<var>+Term,
	357	<p>See also the <code>numbervars</code> option to <a id="idx:writeterm3:1198"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>
	358	and <a id="idx:numbervars4:1199"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>.</dd>
	359	<dt class="pubdef"><a id="numbervars/4"><strong>numbervars</strong>(<var>+Term,
319	360	+Start, -End, +Options</var>)</a></dt>
320	361	<dd class="defbody">
321		As <a name="idx:numbervars3:1200"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>,
	362	As <a id="idx:numbervars3:1200"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>,
322	363	providing the following options:
323	364
324	365	<dl class="latex">

328	369	<dt><strong>attvar</strong>(<var>+Action</var>)</dt>
329	370	<dd class="defbody">
330	371	What to do if an attributed variable is encountered. Options are
331		<code>skip</code>, which causes <a name="idx:numbervars3:1201"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>
	372	<code>skip</code>, which causes <a id="idx:numbervars3:1201"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>
332	373	to ignore the attributed variable, <code>bind</code> which causes it to
333	374	treat it as a normal variable and assign the next <code>'$VAR'</code>(N)
334	375	term to it, or (default)

337	378	Richard O'Keefe, Bart Demoen and Tom Schrijvers.</span></sup></dd>
338	379	<dt><strong>singletons</strong>(<var>+Bool</var>)</dt>
339	380	<dd class="defbody">
340		If <code>true</code> (default <code>false</code>), <a name="idx:numbervars4:1202"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>
	381	If <code>true</code> (default <code>false</code>), <a id="idx:numbervars4:1202"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>
341	382	does singleton detection. Singleton variables are unified with <code>'$VAR'('_')</code>,
342		causing them to be printed as <code>_</code> by <a name="idx:writeterm2:1203"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
343		using the numbervars option. This option is exploited by <a name="idx:portrayclause2:1204"></a><a class="pred" href="listing.html#portray_clause/2">portray_clause/2</a>
344		and <a name="idx:writecanonical2:1205"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>.<sup class="fn">bug<span class="fn-text">Currently
	383	causing them to be printed as <code>_</code> by <a id="idx:writeterm2:1203"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	384	using the numbervars option. This option is exploited by <a id="idx:portrayclause2:1204"></a><a class="pred" href="listing.html#portray_clause/2">portray_clause/2</a>
	385	and <a id="idx:writecanonical2:1205"></a><a class="pred" href="termrw.html#write_canonical/2">write_canonical/2</a>.<sup class="fn">bug<span class="fn-text">Currently
345	386	this option is ignored for cyclic terms.</span></sup>
346	387	</dd>
347	388	</dl>
348	389
349	390	</dd>
350		<dt class="pubdef"><a name="var_number/2"><strong>var_number</strong>(<var>@Term,
	391	<dt class="pubdef"><a id="var_number/2"><strong>var_number</strong>(<var>@Term,
351	392	-VarNumber</var>)</a></dt>
352	393	<dd class="defbody">
353		True if <var>Term</var> is numbered by <a name="idx:numbervars3:1206"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>
	394	True if <var>Term</var> is numbered by <a id="idx:numbervars3:1206"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>
354	395	and <var>VarNumber</var> is the number given to this variable. This
355	396	predicate avoids the need for unification with <code>'$VAR'(X)</code>
356	397	and opens the path for replacing this valid Prolog term by an internal
357	398	representation that has no textual equivalent.</dd>
358		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="term_variables/2"><strong>term_variables</strong>(<var>+Term,
	399	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="term_variables/2"><strong>term_variables</strong>(<var>+Term,
359	400	-List</var>)</a></dt>
360	401	<dd class="defbody">
361	402	Unify <var>List</var> with a list of variables, each sharing with a
362	403	unique variable of <var>Term</var>.<sup class="fn">99<span class="fn-text">This
363		predicate used to be called free_variables/2 . The name <a name="idx:termvariables2:1207"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>
	404	predicate used to be called free_variables/2 . The name <a id="idx:termvariables2:1207"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>
364	405	is more widely used. The old predicate is still available from the
365	406	library <code>library(backcomp)</code>.</span></sup> The variables in <var>List</var>
366	407	are ordered in order of appearance traversing <var>Term</var>
367	408	depth-first and left-to-right. See also
368		<a name="idx:termvariables3:1208"></a><a class="pred" href="manipterm.html#term_variables/3">term_variables/3</a>
369		and <a name="idx:nonground2:1209"></a><a class="pred" href="manipterm.html#nonground/2">nonground/2</a>.
	409	<a id="idx:termvariables3:1208"></a><a class="pred" href="manipterm.html#term_variables/3">term_variables/3</a>
	410	and <a id="idx:nonground2:1209"></a><a class="pred" href="manipterm.html#nonground/2">nonground/2</a>.
370	411	For example:
371	412
372	413	<pre class="code">

375	416	</pre>
376	417
377	418	</dd>
378		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="nonground/2"><strong>nonground</strong>(<var>+Term,
	419	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="nonground/2"><strong>nonground</strong>(<var>+Term,
379	420	-Var</var>)</a></dt>
380	421	<dd class="defbody">
381	422	True when <var>Var</var> is a variable in <var>Term</var>. Fails if <var>Term</var>
382		is <em>ground</em> (see <a name="idx:ground1:1210"></a><a class="pred" href="typetest.html#ground/1">ground/1</a>).
	423	is <em>ground</em> (see <a id="idx:ground1:1210"></a><a class="pred" href="typetest.html#ground/1">ground/1</a>).
383	424	This predicate is intended for coroutining to trigger a wakeup if <var>Term</var>
384		becomes ground, e.g., using <a name="idx:when2:1211"></a><a class="pred" href="coroutining.html#when/2">when/2</a>.
	425	becomes ground, e.g., using <a id="idx:when2:1211"></a><a class="pred" href="coroutining.html#when/2">when/2</a>.
385	426	The current implemention always returns the first variable in
386	427	depth-first left-right search. Ideally it should return a random member
387		of the set of variables (see <a name="idx:termvariables2:1212"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>)
	428	of the set of variables (see <a id="idx:termvariables2:1212"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>)
388	429	to realise logarithmetic complexity for the ground trigger. Compatible
389	430	with ECLiPSe and hProlog.</dd>
390		<dt class="pubdef"><a name="term_variables/3"><strong>term_variables</strong>(<var>+Term,
	431	<dt class="pubdef"><a id="term_variables/3"><strong>term_variables</strong>(<var>+Term,
391	432	-List, ?Tail</var>)</a></dt>
392	433	<dd class="defbody">
393		Difference list version of <a name="idx:termvariables2:1213"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>.
	434	Difference list version of <a id="idx:termvariables2:1213"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>.
394	435	That is, <var>Tail</var> is the tail of the variable list <var>List</var>.</dd>
395		<dt class="pubdef"><a name="term_singletons/2"><strong>term_singletons</strong>(<var>+Term,
	436	<dt class="pubdef"><a id="term_singletons/2"><strong>term_singletons</strong>(<var>+Term,
396	437	-List</var>)</a></dt>
397	438	<dd class="defbody">
398	439	Unify <var>List</var> with a list of variables, each sharing with a

401	442	is raised.</span></sup> Note that, if a variable appears in a shared
402	443	subterm, it is <em>not</em> considered singleton. Thus,
403	444	<var>A</var> is <em>not</em> a singleton in the example below. See also
404		the <code>singleton</code> option of <a name="idx:numbervars4:1214"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>.
	445	the <code>singleton</code> option of <a id="idx:numbervars4:1214"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>.
405	446
406	447	<pre class="code">
407	448

410	451	</pre>
411	452
412	453	</dd>
413		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="copy_term/2"><strong>copy_term</strong>(<var>+In,
	454	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="copy_term/2"><strong>copy_term</strong>(<var>+In,
414	455	-Out</var>)</a></dt>
415	456	<dd class="defbody">
416	457	Create a version of <var>In</var> with renamed (fresh) variables and
417		unify it to <var>Out</var>. Attributed variables (see <a class="sec" href="attvar.html">section
418		7.1</a>) have their attributes copied. The implementation of <a name="idx:copyterm2:1215"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>
	458	unify it to <var>Out</var>. Attributed variables (see <a class="sec" href="attvar.html#sec:7.1">section
	459	7.1</a>) have their attributes copied. The implementation of <a id="idx:copyterm2:1215"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>
419	460	can deal with infinite trees (cyclic terms). As pure Prolog cannot
420	461	distinguish a ground term from another ground term with exactly the same
421	462	structure, ground sub-terms are <em>shared</em> between <var>In</var>
422		and <var>Out</var>. Sharing ground terms does affect <a name="idx:setarg3:1216"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>.
	463	and <var>Out</var>. Sharing ground terms does affect <a id="idx:setarg3:1216"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>.
423	464	SWI-Prolog provides
424		<a name="idx:duplicateterm2:1217"></a><a class="pred" href="manipterm.html#duplicate_term/2">duplicate_term/2</a>
	465	<a id="idx:duplicateterm2:1217"></a><a class="pred" href="manipterm.html#duplicate_term/2">duplicate_term/2</a>
425	466	to create a true copy of a term.
426	467	</dd>
427	468	</dl>
428	469
429		<p><h3 id="sec:setarg"><a name="sec:4.21.1"><span class="sec-nr">4.21.1</span> <span class="sec-title">Non-logical
	470	<p><h3 id="sec:setarg"><a id="sec:4.21.1"><span class="sec-nr">4.21.1</span> <span class="sec-title">Non-logical
430	471	operations on terms</span></a></h3>
431	472
432		<a name="sec:setarg"></a>
	473	<a id="sec:setarg"></a>
433	474
434	475	<p>Prolog is not able to <em>modify</em> instantiated parts of a term.
435	476	Lacking that capability makes the language much safer, but unfortunately
436	477	there are problems that suffer severely in terms of time and/or memory
437	478	usage. Always try hard to avoid the use of these primitives, but they
438		can be a good alternative to using dynamic predicates. See also <a class="sec" href="gvar.html">section
	479	can be a good alternative to using dynamic predicates. See also <a class="sec" href="gvar.html#sec:4.33">section
439	480	4.33</a>, discussing the use of global variables.
440	481
441	482	<dl class="latex">
442		<dt class="pubdef"><a name="setarg/3"><strong>setarg</strong>(<var>+Arg,
	483	<dt class="pubdef"><a id="setarg/3"><strong>setarg</strong>(<var>+Arg,
443	484	+Term, +Value</var>)</a></dt>
444	485	<dd class="defbody">
445	486	Extra-logical predicate. Assigns the <var>Arg</var>-th argument of the
446	487	compound term <var>Term</var> with the given <var>Value</var>. The
447	488	assignment is undone if backtracking brings the state back into a
448		position before the <a name="idx:setarg3:1218"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
449		call. See also <a name="idx:nbsetarg3:1219"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
	489	position before the <a id="idx:setarg3:1218"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	490	call. See also <a id="idx:nbsetarg3:1219"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
450	491
451	492	<p>This predicate may be used for destructive assignment to terms, using
452	493	them as an extra-logical storage bin. Always try hard to avoid the use
453		of <a name="idx:setarg3:1220"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	494	of <a id="idx:setarg3:1220"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
454	495	as it is not supported by many Prolog systems and one has to be very
455	496	careful about unexpected copying as well as unexpected noncopying of
456	497	terms. A good practice to improve somewhat on this situation is to make
457		sure that terms whose arguments are subject to <a name="idx:setarg3:1221"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	498	sure that terms whose arguments are subject to <a id="idx:setarg3:1221"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
458	499	have one unused and unshared variable in addition to the used arguments.
459		This variable avoids unwanted sharing in, e.g., <a name="idx:copyterm2:1222"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>,
	500	This variable avoids unwanted sharing in, e.g., <a id="idx:copyterm2:1222"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>,
460	501	and causes the term to be considered as non-ground. An alternative is to
461		use <a name="idx:putattr3:1223"></a><a class="pred" href="attvar.html#put_attr/3">put_attr/3</a>
462		to attach information to attributed variables (see <a class="sec" href="attvar.html">section
	502	use <a id="idx:putattr3:1223"></a><a class="pred" href="attvar.html#put_attr/3">put_attr/3</a>
	503	to attach information to attributed variables (see <a class="sec" href="attvar.html#sec:7.1">section
463	504	7.1</a>).</dd>
464		<dt class="pubdef"><a name="nb_setarg/3"><strong>nb_setarg</strong>(<var>+Arg,
	505	<dt class="pubdef"><a id="nb_setarg/3"><strong>nb_setarg</strong>(<var>+Arg,
465	506	+Term, +Value</var>)</a></dt>
466	507	<dd class="defbody">
467	508	Assigns the <var>Arg</var>-th argument of the compound term <var>Term</var>
468		with the given <var>Value</var> as <a name="idx:setarg3:1224"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>,
	509	with the given <var>Value</var> as <a id="idx:setarg3:1224"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>,
469	510	but on backtracking the assignment is <em>not</em> reversed. If <var>Value</var>
470		is not atomic, it is duplicated using <a name="idx:duplicateterm2:1225"></a><a class="pred" href="manipterm.html#duplicate_term/2">duplicate_term/2</a>.
	511	is not atomic, it is duplicated using <a id="idx:duplicateterm2:1225"></a><a class="pred" href="manipterm.html#duplicate_term/2">duplicate_term/2</a>.
471	512	This predicate uses the same technique as
472		<a name="idx:nbsetval2:1226"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>.
473		We therefore refer to the description of <a name="idx:nbsetval2:1227"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
	513	<a id="idx:nbsetval2:1226"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>.
	514	We therefore refer to the description of <a id="idx:nbsetval2:1227"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>
474	515	for details on non-backtrackable assignment of terms. This predicate is
475	516	compatible with GNU-Prolog <code>setarg(A,T,V,false)</code>, removing
476		the type restriction on <var>Value</var>. See also <a name="idx:nblinkarg3:1228"></a><a class="pred" href="manipterm.html#nb_linkarg/3">nb_linkarg/3</a>.
	517	the type restriction on <var>Value</var>. See also <a id="idx:nblinkarg3:1228"></a><a class="pred" href="manipterm.html#nb_linkarg/3">nb_linkarg/3</a>.
477	518	Below is an example for counting the number of solutions of a goal. Note
478	519	that this implementation is thread-safe, reentrant and capable of
479	520	handling exceptions. Realising these features with a traditional
480		implementation based on assert/retract or <a name="idx:flag3:1229"></a><a class="pred" href="db.html#flag/3">flag/3</a>
	521	implementation based on assert/retract or <a id="idx:flag3:1229"></a><a class="pred" href="db.html#flag/3">flag/3</a>
481	522	is much more complicated.
482	523
483	524	<pre class="code">

496	537	</pre>
497	538
498	539	</dd>
499		<dt class="pubdef"><a name="nb_linkarg/3"><strong>nb_linkarg</strong>(<var>+Arg,
	540	<dt class="pubdef"><a id="nb_linkarg/3"><strong>nb_linkarg</strong>(<var>+Arg,
500	541	+Term, +Value</var>)</a></dt>
501	542	<dd class="defbody">
502		As <a name="idx:nbsetarg3:1230"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>,
503		but like <a name="idx:nblinkval2:1231"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>
	543	As <a id="idx:nbsetarg3:1230"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>,
	544	but like <a id="idx:nblinkval2:1231"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>
504	545	it does <em>not</em> duplicate
505		<var>Value</var>. Use with extreme care and consult the documentation of <a name="idx:nblinkval2:1232"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>
	546	<var>Value</var>. Use with extreme care and consult the documentation of <a id="idx:nblinkval2:1232"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>
506	547	before use.</dd>
507		<dt class="pubdef"><a name="duplicate_term/2"><strong>duplicate_term</strong>(<var>+In,
	548	<dt class="pubdef"><a id="duplicate_term/2"><strong>duplicate_term</strong>(<var>+In,
508	549	-Out</var>)</a></dt>
509	550	<dd class="defbody">
510		Version of <a name="idx:copyterm2:1233"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>
	551	Version of <a id="idx:copyterm2:1233"></a><a class="pred" href="manipterm.html#copy_term/2">copy_term/2</a>
511	552	that also copies ground terms and therefore ensures that destructive
512		modification using <a name="idx:setarg3:1234"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
513		does not affect the copy. See also <a name="idx:nbsetval2:1235"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>, <a name="idx:nblinkval2:1236"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>, <a name="idx:nbsetarg3:1237"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>
514		and <a name="idx:nblinkarg3:1238"></a><a class="pred" href="manipterm.html#nb_linkarg/3">nb_linkarg/3</a>.</dd>
515		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="same_term/2"><strong>same_term</strong>(<var>@T1,
	553	modification using <a id="idx:setarg3:1234"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	554	does not affect the copy. See also <a id="idx:nbsetval2:1235"></a><a class="pred" href="gvar.html#nb_setval/2">nb_setval/2</a>, <a id="idx:nblinkval2:1236"></a><a class="pred" href="gvar.html#nb_linkval/2">nb_linkval/2</a>, <a id="idx:nbsetarg3:1237"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>
	555	and <a id="idx:nblinkarg3:1238"></a><a class="pred" href="manipterm.html#nb_linkarg/3">nb_linkarg/3</a>.</dd>
	556	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="same_term/2"><strong>same_term</strong>(<var>@T1,
516	557	@T2</var>)</a></dt>
517	558	<dd class="defbody">
518	559	True if <var>T1</var> and <var>T2</var> are equivalent and will remain
519		equivalent, even if <a name="idx:setarg3:1239"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	560	equivalent, even if <a id="idx:setarg3:1239"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
520	561	is used on either of them. This means
521	562	<var>T1</var> and <var>T2</var> are the same variable, equivalent atomic
522	563	data or a compound term allocated at the same address.

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193	234	</div>
194		<h2 id="sec:memory"><a name="sec:4.42"><span class="sec-nr">4.42</span> <span class="sec-title">Memory
	235	<h2 id="sec:memory"><a id="sec:4.42"><span class="sec-nr">4.42</span> <span class="sec-title">Memory
195	236	Management</span></a></h2>
196	237
197		<a name="sec:memory"></a>
	238	<a id="sec:memory"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="garbage_collect/0"><strong>garbage_collect</strong></a></dt>
	241	<dt class="pubdef"><a id="garbage_collect/0"><strong>garbage_collect</strong></a></dt>
201	242	<dd class="defbody">
202	243	Invoke the global and trail stack garbage collector. Normally the
203	244	garbage collector is invoked automatically if necessary. Explicit
204	245	invocation might be useful to reduce the need for garbage collections in
205	246	time-critical segments of the code. After the garbage collection
206		<a name="idx:trimstacks0:1575"></a><a class="pred" href="memory.html#trim_stacks/0">trim_stacks/0</a>
	247	<a id="idx:trimstacks0:1575"></a><a class="pred" href="memory.html#trim_stacks/0">trim_stacks/0</a>
207	248	is invoked to release the collected memory resources.</dd>
208		<dt class="pubdef"><a name="garbage_collect_atoms/0"><strong>garbage_collect_atoms</strong></a></dt>
	249	<dt class="pubdef"><a id="garbage_collect_atoms/0"><strong>garbage_collect_atoms</strong></a></dt>
209	250	<dd class="defbody">
210	251	Reclaim unused atoms. Normally invoked after <a class="flag" href="flags.html#flag:agc_margin">agc_margin</a>
211	252	(a Prolog flag) atoms have been created. On multithreaded versions the
212	253	actual collection is delayed until there are no threads performing
213		normal garbage collection. In this case <a name="idx:garbagecollectatoms0:1576"></a><a class="pred" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a>
	254	normal garbage collection. In this case <a id="idx:garbagecollectatoms0:1576"></a><a class="pred" href="memory.html#garbage_collect_atoms/0">garbage_collect_atoms/0</a>
214	255	returns immediately. Note that there is no guarantee it will <em>ever</em>
215	256	happen, as there may always be threads performing garbage collection.</dd>
216		<dt class="pubdef"><a name="trim_stacks/0"><strong>trim_stacks</strong></a></dt>
	257	<dt class="pubdef"><a id="trim_stacks/0"><strong>trim_stacks</strong></a></dt>
217	258	<dd class="defbody">
218	259	Release stack memory resources that are not in use at this moment,
219	260	returning them to the operating system. It can be used to release memory

231	272
232	273	<p>The Prolog top-level loop is written this way, reclaiming memory
233	274	resources after every user query.</dd>
234		<dt class="pubdef"><a name="set_prolog_stack/2"><strong>set_prolog_stack</strong>(<var>+Stack,
	275	<dt class="pubdef"><a id="set_prolog_stack/2"><strong>set_prolog_stack</strong>(<var>+Stack,
235	276	+KeyValue</var>)</a></dt>
236	277	<dd class="defbody">
237	278	Set a parameter for one of the Prolog runtime stacks. <var>Stack</var>

244	285	?- set_prolog_stack(global, limit(210*9)).
245	286	</pre>
246	287
247		<p>Current settings can be retrieved with <a name="idx:prologstackproperty2:1577"></a><a class="pred" href="memory.html#prolog_stack_property/2">prolog_stack_property/2</a>.
	288	<p>Current settings can be retrieved with <a id="idx:prologstackproperty2:1577"></a><a class="pred" href="memory.html#prolog_stack_property/2">prolog_stack_property/2</a>.
248	289
249	290	<dl class="latex">
250	291	<dt><strong>limit</strong>(<var>+Bytes</var>)</dt>

261	302	amount is reported and specified in `cells'. A cell is 4 bytes in the
262	303	32-bit version and 8 bytes on the 64-bit version. See
263	304	<a class="flag" href="flags.html#flag:address_bits">address_bits</a>.
264		See also <a name="idx:trimstacks0:1578"></a><a class="pred" href="memory.html#trim_stacks/0">trim_stacks/0</a>
265		and <a name="idx:debug0:1579"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.</dd>
	305	See also <a id="idx:trimstacks0:1578"></a><a class="pred" href="memory.html#trim_stacks/0">trim_stacks/0</a>
	306	and <a id="idx:debug0:1579"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.</dd>
266	307	<dt><strong>spare</strong>(<var>+Cells</var>)</dt>
267	308	<dd class="defbody">
268	309	All stacks trigger overflow before actually reaching the limit, so the
269	310	resulting error can be handled gracefully. The spare stack is used for
270		<a name="idx:printmessage2:1580"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	311	<a id="idx:printmessage2:1580"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
271	312	from the garbage collector and for handling exceptions. The default
272	313	suffices, unless the user redefines related hooks. Do
273	314	<b>not</b> specify large values for this because it reduces the amount
274	315	of memory available for your real task.
275	316
276		<p>Related hooks are <a name="idx:messagehook3:1581"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
	317	<p>Related hooks are <a id="idx:messagehook3:1581"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a>
277	318	(redefining GC messages),
278		<a name="idx:prologtraceinterception4:1582"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>
279		and <a name="idx:prologexceptionhook4:1583"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>.
	319	<a id="idx:prologtraceinterception4:1582"></a><a class="pred" href="tracehook.html#prolog_trace_interception/4">prolog_trace_interception/4</a>
	320	and <a id="idx:prologexceptionhook4:1583"></a><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a>.
280	321	</dd>
281	322	</dl>
282	323
283	324	</dd>
284		<dt class="pubdef"><a name="prolog_stack_property/2"><strong>prolog_stack_property</strong>(<var>?Stack,
	325	<dt class="pubdef"><a id="prolog_stack_property/2"><strong>prolog_stack_property</strong>(<var>?Stack,
285	326	?KeyValue</var>)</a></dt>
286	327	<dd class="defbody">
287	328	True if <var>KeyValue</var> is a current property of <var>Stack</var>.
288	329	See
289		<a name="idx:setprologstack2:1584"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>
	330	<a id="idx:setprologstack2:1584"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>
290	331	for defined properties.
291	332	</dd>
292	333	</dl>

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194		<h2 id="sec:metacall"><a name="sec:4.9"><span class="sec-nr">4.9</span> <span class="sec-title">Meta-Call
	235	<h2 id="sec:metacall"><a id="sec:4.9"><span class="sec-nr">4.9</span> <span class="sec-title">Meta-Call
195	236	Predicates</span></a></h2>
196	237
197		<a name="sec:metacall"></a>
	238	<a id="sec:metacall"></a>
198	239
199	240	<p>Meta-call predicates are used to call terms constructed at run time.
200	241	The basic meta-call mechanism offered by SWI-Prolog is to use variables

204	245	normal calls this search is done at compile time.
205	246
206	247	<dl class="latex">
207		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="call/1"><strong>call</strong>(<var>:Goal</var>)</a></dt>
	248	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="call/1"><strong>call</strong>(<var>:Goal</var>)</a></dt>
208	249	<dd class="defbody">
209	250	Invoke <var>Goal</var> as a goal. Note that clauses may have variables
210		as subclauses, which is identical to <a name="idx:call1:649"></a><a class="pred" href="metacall.html#call/1">call/1</a>.</dd>
211		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="call/2"><strong>call</strong>(<var>:Goal,
	251	as subclauses, which is identical to <a id="idx:call1:649"></a><a class="pred" href="metacall.html#call/1">call/1</a>.</dd>
	252	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="call/2"><strong>call</strong>(<var>:Goal,
212	253	+ExtraArg1, ...</var>)</a></dt>
213	254	<dd class="defbody">
214	255	Append <var>ExtraArg1, ExtraArg2, ...</var> to the argument list of

217	258	3.
218	259
219	260	<p>The call/[2..] construct is handled by the compiler. The predicates
220		<a name="idx:call28:650"></a><a class="pred" href="metacall.html#call/2">call/[2-8]</a>
	261	<a id="idx:call28:650"></a><a class="pred" href="metacall.html#call/2">call/[2-8]</a>
221	262	are defined as real (meta-)predicates and are available to inspection
222		through <a name="idx:currentpredicate1:651"></a><a class="pred" href="examineprog.html#current_predicate/1">current_predicate/1</a>, <a name="idx:predicateproperty2:652"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>,
	263	through <a id="idx:currentpredicate1:651"></a><a class="pred" href="examineprog.html#current_predicate/1">current_predicate/1</a>, <a id="idx:predicateproperty2:652"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>,
223	264	etc.<sup class="fn">64<span class="fn-text">Arities 2..8 are demanded by
224	265	ISO/IEC 13211-1:1995/Cor.2:2012.</span></sup> Higher arities are handled
225	266	by the compiler and runtime system, but the predicates are not

228	269	Full logical behaviour, generating all these pseudo predicates, is
229	270	probably undesirable and will become impossible if <em>max_arity</em> is
230	271	removed.</span></sup></dd>
231		<dt class="pubdef"><a name="apply/2"><strong>apply</strong>(<var>:Goal,
	272	<dt class="pubdef"><a id="apply/2"><strong>apply</strong>(<var>:Goal,
232	273	+List</var>)</a></dt>
233	274	<dd class="defbody">
234	275	Append the members of <var>List</var> to the arguments of <var>Goal</var>

237	278	<code>plus(1, 2, X)</code>. New code should use call/[2..] if the length
238	279	of
239	280	<var>List</var> is fixed.</dd>
240		<dt class="pubdef"><a name="not/1"><strong>not</strong>(<var>:Goal</var>)</a></dt>
	281	<dt class="pubdef"><a id="not/1"><strong>not</strong>(<var>:Goal</var>)</a></dt>
241	282	<dd class="defbody">
242	283	True if <var>Goal</var> cannot be proven. Retained for compatibility
243	284	only. New code should use <a class="pred" href="control.html#\+/1">\+/1</a>.</dd>
244		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="once/1"><strong>once</strong>(<var>:Goal</var>)</a></dt>
	285	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="once/1"><strong>once</strong>(<var>:Goal</var>)</a></dt>
245	286	<dd class="defbody">
246	287	Make a possibly <em>nondet</em> goal <em>semidet</em>, i.e., succeed at
247	288	most once. Defined as:

251	292	call(Goal), !.
252	293	</pre>
253	294
254		<p><a name="idx:once1:653"></a><a class="pred" href="metacall.html#once/1">once/1</a>
255		can in many cases be replaced with <a class="pred" href="control.html#send_arrow/2">->/2</a>.
	295	<p><a id="idx:once1:653"></a><a class="pred" href="metacall.html#once/1">once/1</a>
	296	can in many cases be replaced with <a class="pred" href="control.html#->/2">->/2</a>.
256	297	The only difference is how the cut behaves (see !/0). The following two
257	298	clauses below are identical. Be careful about the interaction with
258	299	<a class="pred" href="control.html#;/2">;/2</a>. The <code>library(apply_macros)</code>
259		library defines an inline expansion of <a name="idx:once1:654"></a><a class="pred" href="metacall.html#once/1">once/1</a>,
	300	library defines an inline expansion of <a id="idx:once1:654"></a><a class="pred" href="metacall.html#once/1">once/1</a>,
260	301	mapping it to <code>(Goal\send{true};fail)</code>. Using the full
261	302	if-then-else constructs prevents its semantics from being changed when
262	303	embedded in a <a class="pred" href="control.html#;/2">;/2</a>

268	309	</pre>
269	310
270	311	</dd>
271		<dt class="pubdef"><a name="ignore/1"><strong>ignore</strong>(<var>:Goal</var>)</a></dt>
272		<dd class="defbody">
273		Calls <var>Goal</var> as <a name="idx:once1:655"></a><a class="pred" href="metacall.html#once/1">once/1</a>,
	312	<dt class="pubdef"><a id="ignore/1"><strong>ignore</strong>(<var>:Goal</var>)</a></dt>
	313	<dd class="defbody">
	314	Calls <var>Goal</var> as <a id="idx:once1:655"></a><a class="pred" href="metacall.html#once/1">once/1</a>,
274	315	but succeeds, regardless of whether
275	316	<var>Goal</var> succeeded or not. Defined as:
276	317

281	322	</pre>
282	323
283	324	</dd>
284		<dt class="pubdef"><a name="call_with_depth_limit/3"><strong>call_with_depth_limit</strong>(<var>:Goal,
	325	<dt class="pubdef"><a id="call_with_depth_limit/3"><strong>call_with_depth_limit</strong>(<var>:Goal,
285	326	+Limit, -Result</var>)</a></dt>
286	327	<dd class="defbody">
287	328	If <var>Goal</var> can be proven without recursion deeper than <var>Limit</var>
288		levels, <a name="idx:callwithdepthlimit3:656"></a><a class="pred" href="metacall.html#call_with_depth_limit/3">call_with_depth_limit/3</a>
	329	levels, <a id="idx:callwithdepthlimit3:656"></a><a class="pred" href="metacall.html#call_with_depth_limit/3">call_with_depth_limit/3</a>
289	330	succeeds, binding <var>Result</var> to the deepest recursion level used
290	331	during the proof. Otherwise, <var>Result</var> is unified with <code>depth_limit_exceeded</code>
291	332	if the limit was exceeded during the proof, or the entire predicate

293	334
294	335	<p>The depth limit is guarded by the internal machinery. This may differ
295	336	from the depth computed based on a theoretical model. For example,
296		<a name="idx:true0:657"></a><a class="pred" href="control.html#true/0">true/0</a>
	337	<a id="idx:true0:657"></a><a class="pred" href="control.html#true/0">true/0</a>
297	338	is translated into an inline virtual machine instruction. Also,
298		<a name="idx:repeat0:658"></a><a class="pred" href="control.html#repeat/0">repeat/0</a>
	339	<a id="idx:repeat0:658"></a><a class="pred" href="control.html#repeat/0">repeat/0</a>
299	340	is not implemented as below, but as a non-deterministic foreign
300	341	predicate.
301	342

305	346	repeat.
306	347	</pre>
307	348
308		<p>As a result, <a name="idx:callwithdepthlimit3:659"></a><a class="pred" href="metacall.html#call_with_depth_limit/3">call_with_depth_limit/3</a>
	349	<p>As a result, <a id="idx:callwithdepthlimit3:659"></a><a class="pred" href="metacall.html#call_with_depth_limit/3">call_with_depth_limit/3</a>
309	350	may still loop infinitely on programs that should theoretically finish
310	351	in finite time. This problem can be cured by using Prolog equivalents to
311	352	such built-in predicates.
312	353
313	354	<p>This predicate may be used for theorem provers to realise techniques
314		like <em>iterative deepening</em>. See also <a name="idx:callwithinferencelimit3:660"></a><a class="pred" href="metacall.html#call_with_inference_limit/3">call_with_inference_limit/3</a>.
	355	like <em>iterative deepening</em>. See also <a id="idx:callwithinferencelimit3:660"></a><a class="pred" href="metacall.html#call_with_inference_limit/3">call_with_inference_limit/3</a>.
315	356	It was implemented after discussion with Steve Moyle
316	357	<a class="url" href="mailto:smoyle@ermine.ox.ac.uk">smoyle@ermine.ox.ac.uk</a>.</dd>
317		<dt class="pubdef"><a name="call_with_inference_limit/3"><strong>call_with_inference_limit</strong>(<var>:Goal,
	358	<dt class="pubdef"><a id="call_with_inference_limit/3"><strong>call_with_inference_limit</strong>(<var>:Goal,
318	359	+Limit, -Result</var>)</a></dt>
319	360	<dd class="defbody">
320	361	Equivalent to <code>call(Goal)</code>, but limits the number of

331	372	<var>Result</var> is unified with the atom
332	373	<code>inference_limit_exceeded</code>.
333	374	<i>Otherwise</i>,
334		<li>If <var>Goal</var> fails, <a name="idx:callwithinferencelimit3:661"></a><a class="pred" href="metacall.html#call_with_inference_limit/3">call_with_inference_limit/3</a>
	375	<li>If <var>Goal</var> fails, <a id="idx:callwithinferencelimit3:661"></a><a class="pred" href="metacall.html#call_with_inference_limit/3">call_with_inference_limit/3</a>
335	376	fails.
336	377	<li>If <var>Goal</var> succeeds <em>without a choice point</em>,
337	378	<var>Result</var> is unified with <code><code>!</code></code>.
338	379	<li>If <var>Goal</var> succeeds <em>with a choice point</em>,
339	380	<var>Result</var> is unified with <code>true</code>.
340		<li>If <var>Goal</var> throws an exception, <a name="idx:callwithinferencelimit3:662"></a><a class="pred" href="metacall.html#call_with_inference_limit/3">call_with_inference_limit/3</a>
	381	<li>If <var>Goal</var> throws an exception, <a id="idx:callwithinferencelimit3:662"></a><a class="pred" href="metacall.html#call_with_inference_limit/3">call_with_inference_limit/3</a>
341	382	re-throws the exception.
342	383	</ul>
343	384

346	387	instructions for which inferences are not counted. The execution of
347	388	predicates defined in other languages (e.g., C, C++) count as a single
348	389	inference. This includes potentially expensive built-in predicates such
349		as <a name="idx:sort2:663"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>.
	390	as <a id="idx:sort2:663"></a><a class="pred" href="builtinlist.html#sort/2">sort/2</a>.
350	391
351	392	<p>Calls to this predicate may be nested. An inner call that sets the
352	393	limit below the current is honoured. An inner call that would terminate
353	394	after the current limit does not change the effective limit. See also
354		<a name="idx:callwithdepthlimit3:664"></a><a class="pred" href="metacall.html#call_with_depth_limit/3">call_with_depth_limit/3</a>
355		and <a name="idx:callwithtimelimit2:665"></a><span class="pred-ext">call_with_time_limit/2</span>.</dd>
356		<dt class="pubdef"><a name="setup_call_cleanup/3"><strong>setup_call_cleanup</strong>(<var>:Setup,
	395	<a id="idx:callwithdepthlimit3:664"></a><a class="pred" href="metacall.html#call_with_depth_limit/3">call_with_depth_limit/3</a>
	396	and <a id="idx:callwithtimelimit2:665"></a><span class="pred-ext">call_with_time_limit/2</span>.</dd>
	397	<dt class="pubdef"><a id="setup_call_cleanup/3"><strong>setup_call_cleanup</strong>(<var>:Setup,
357	398	:Goal, :Cleanup</var>)</a></dt>
358	399	<dd class="defbody">
359	400	Calls <code>(once(Setup), Goal)</code>. If <var>Setup</var> succeeds, <var>Cleanup</var>
360	401	will be called exactly once after <var>Goal</var> is finished: either on
361	402	failure, deterministic success, commit, or an exception. The execution
362	403	of <var>Setup</var> is protected from asynchronous interrupts like
363		<a name="idx:callwithtimelimit2:666"></a><span class="pred-ext">call_with_time_limit/2</span>
364		(package clib) or <a name="idx:threadsignal2:667"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>.
	404	<a id="idx:callwithtimelimit2:666"></a><span class="pred-ext">call_with_time_limit/2</span>
	405	(package clib) or <a id="idx:threadsignal2:667"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>.
365	406	In most uses,
366	407	<var>Setup</var> will perform temporary side-effects required by <var>Goal</var>
367	408	that are finally undone by <var>Cleanup</var>.
368	409
369	410	<p>Success or failure of <var>Cleanup</var> is ignored, and choice
370		points it created are destroyed (as <a name="idx:once1:668"></a><a class="pred" href="metacall.html#once/1">once/1</a>).
	411	points it created are destroyed (as <a id="idx:once1:668"></a><a class="pred" href="metacall.html#once/1">once/1</a>).
371	412	If <var>Cleanup</var> throws an exception, this is executed as normal
372	413	while it was not triggered as the result of an exception the exception
373	414	is propagated as normal. If <var>Cleanup</var> was triggered by an
374	415	exception the rules are described in
375		<a class="sec" href="exception.html">section 4.11.1</a>
	416	<a class="sec" href="exception.html#sec:4.11.1">section 4.11.1</a>
376	417
377	418	<p>Typically, this predicate is used to cleanup permanent data storage
378	419	required to execute <var>Goal</var>, close file descriptors, etc. The

396	437
397	438	<p>Note that it is impossible to implement this predicate in Prolog. The
398	439	closest approximation would be to read all terms into a list, close the
399		file and call <a name="idx:member2:669"></a><a class="pred" href="lists.html#member/2">member/2</a>.
400		Without <a name="idx:setupcallcleanup3:670"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
401		there is no way to gain control if the choice point left by <a name="idx:repeat0:671"></a><a class="pred" href="control.html#repeat/0">repeat/0</a>
	440	file and call <a id="idx:member2:669"></a><a class="pred" href="lists.html#member/2">member/2</a>.
	441	Without <a id="idx:setupcallcleanup3:670"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
	442	there is no way to gain control if the choice point left by <a id="idx:repeat0:671"></a><a class="pred" href="control.html#repeat/0">repeat/0</a>
402	443	is removed by a cut or an exception.
403	444
404		<p><a name="idx:setupcallcleanup3:672"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
	445	<p><a id="idx:setupcallcleanup3:672"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
405	446	can also be used to test determinism of a goal, providing a portable
406		alternative to <a name="idx:deterministic1:673"></a><a class="pred" href="manipstack.html#deterministic/1">deterministic/1</a>:
	447	alternative to <a id="idx:deterministic1:673"></a><a class="pred" href="manipstack.html#deterministic/1">deterministic/1</a>:
407	448
408	449	<pre class="code">
409	450	?- setup_call_cleanup(true,(X=1;X=2), Det=yes).

415	456	</pre>
416	457
417	458	<p>This predicate is under consideration for inclusion into the ISO
418		standard. For compatibility with other Prolog implementations see <a name="idx:callcleanup2:674"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>.</dd>
419		<dt class="pubdef"><a name="setup_call_catcher_cleanup/4"><strong>setup_call_catcher_cleanup</strong>(<var>:Setup,
	459	standard. For compatibility with other Prolog implementations see <a id="idx:callcleanup2:674"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>.</dd>
	460	<dt class="pubdef"><a id="setup_call_catcher_cleanup/4"><strong>setup_call_catcher_cleanup</strong>(<var>:Setup,
420	461	:Goal, +Catcher, :Cleanup</var>)</a></dt>
421	462	<dd class="defbody">
422	463	Similar to <code>setup_call_cleanup(Setup, Goal, Cleanup)</code> with

458	499	</dl>
459	500
460	501	</dd>
461		<dt class="pubdef"><a name="call_cleanup/2"><strong>call_cleanup</strong>(<var>:Goal,
	502	<dt class="pubdef"><a id="call_cleanup/2"><strong>call_cleanup</strong>(<var>:Goal,
462	503	:Cleanup</var>)</a></dt>
463	504	<dd class="defbody">
464	505	Same as <code>setup_call_cleanup(true, Goal, Cleanup)</code>. This is
465	506	provided for compatibility with a number of other Prolog implementations
466		only. Do not use <a name="idx:callcleanup2:675"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>
	507	only. Do not use <a id="idx:callcleanup2:675"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>
467	508	if you perform side-effects prior to calling that will be undone by <var>Cleanup</var>.
468	509	Instead, use
469		<a name="idx:setupcallcleanup3:676"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
	510	<a id="idx:setupcallcleanup3:676"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
470	511	with an appropriate first argument to perform those side-effects.</dd>
471		<dt class="pubdef"><a name="call_cleanup/3"><strong>call_cleanup</strong>(<var>:Goal,
	512	<dt class="pubdef"><a id="call_cleanup/3"><strong>call_cleanup</strong>(<var>:Goal,
472	513	+Catcher, :Cleanup</var>)</a></dt>
473	514	<dd class="defbody">
474	515	Same as <code>setup_call_catcher_cleanup(true, Goal, Catcher, Cleanup)</code>.
475		The same warning as for <a name="idx:callcleanup2:677"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>
	516	The same warning as for <a id="idx:callcleanup2:677"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>
476	517	applies.
477	518	</dd>
478	519	</dl>

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193	234	</div>
194		<h2 id="sec:metapred"><a name="sec:6.4"><span class="sec-nr">6.4</span> <span class="sec-title">Defining
	235	<h2 id="sec:metapred"><a id="sec:6.4"><span class="sec-nr">6.4</span> <span class="sec-title">Defining
195	236	a meta-predicate</span></a></h2>
196	237
197		<a name="sec:metapred"></a>
	238	<a id="sec:metapred"></a>
198	239
199	240	<p>A meta-predicate is a predicate that calls other predicates
200	241	dynamically, modifies a predicate, or reasons about properties of a
201	242	predicate. Such predicates use either a compound term or a <em>predicate
202	243	indicator</em> to describe the predicate they address, e.g., <code>assert(name(jan))</code>
203		or <code>abolish(<a name="idx:name1:1685"></a><span class="pred-ext">name/1</span>)</code>.
	244	or <code>abolish(<a id="idx:name1:1689"></a><span class="pred-ext">name/1</span>)</code>.
204	245	With modules, this simple schema no longer works as each module defines
205	246	its own mapping from name+arity to predicate. This is resolved by
206	247	wrapping the original description in a term <<var>module</var>>:<<var>term</var>>,
207	248	e.g., <code>assert(person:name(jan))</code> or
208	249	<code>abolish(person:name/1)</code>.
209	250
210		<p>Of course, when calling <a name="idx:assert1:1686"></a><a class="pred" href="db.html#assert/1">assert/1</a>
	251	<p>Of course, when calling <a id="idx:assert1:1690"></a><a class="pred" href="db.html#assert/1">assert/1</a>
211	252	from inside a module, we expect to assert to a predicate local to this
212	253	module. In other words, we do not wish to provide this <code><code>:</code>/2</code>
213		wrapper by hand. The <a name="idx:metapredicate1:1687"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	254	wrapper by hand. The <a id="idx:metapredicate1:1691"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
214	255	directive tells the compiler that certain arguments are terms that will
215	256	be used to look up a predicate and thus need to be wrapped (qualified)
216	257	with <<var>module</var>>:<<var>term</var>>, unless they are
217	258	already wrapped.
218	259
219		<p>In the example below, we use this to define <a name="idx:maplist3:1688"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
	260	<p>In the example below, we use this to define <a id="idx:maplist3:1692"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
220	261	inside a module. The argument `2' in the meta_predicate declaration
221	262	means that the argument is module-sensitive and refers to a predicate
222	263	with an arity that is two more than the term that is passed in. The

225	266	and <code><code>?</code></code>, which denote
226	267	<em>modes</em>. The values 0..9 are used by the
227	268	<em>cross-referencer</em> and syntax highlighting. Note that the helper
228		predicate <a name="idx:maplist3:1689"></a><span class="pred-ext">maplist_/3</span>
229		does not need to be declared as a meta-predicate because the <a name="idx:maplist3:1690"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
	269	predicate <a id="idx:maplist3:1693"></a><span class="pred-ext">maplist_/3</span>
	270	does not need to be declared as a meta-predicate because the <a id="idx:maplist3:1694"></a><a class="pred" href="apply.html#maplist/3">maplist/3</a>
230	271	wrapper already ensures that
231	272	<var>Goal</var> is qualified as <<var>module</var>>:<var>Goal</var>.
232	273	See the description of
233		<a name="idx:metapredicate1:1691"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	274	<a id="idx:metapredicate1:1695"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
234	275	for details.
235	276
236	277	<pre class="code">

252	293	</pre>
253	294
254	295	<dl class="latex">
255		<dt class="pubdef"><a name="meta_predicate/1"><strong>meta_predicate</strong> <var>+Head,
	296	<dt class="pubdef"><a id="meta_predicate/1"><strong>meta_predicate</strong> <var>+Head,
256	297	...</var></a></dt>
257	298	<dd class="defbody">
258	299	Define the predicates referenced by the comma-separated list <var>Head</var>

287	328	<dd class="defbody">
288	329	The argument is not module-sensitive and the mode is unspecified. The
289	330	specification <code><code>*</code></code> is equivalent to <code><code>?</code></code>.
290		It is accepted for compatibility reasons. The predicate <a name="idx:predicateproperty2:1692"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
	331	It is accepted for compatibility reasons. The predicate <a id="idx:predicateproperty2:1696"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>
291	332	reports arguments declared using <code><code>*</code></code> with <code><code>?</code></code>.
292	333	</dd>
293	334	<dt><strong><code>+</code></strong></dt>

298	339	<dd class="defbody">
299	340	This extension is used to denote the possibly <code>^</code>-annotated
300	341	goal of
301		<a name="idx:setof3:1693"></a><a class="pred" href="allsolutions.html#setof/3">setof/3</a>, <a name="idx:bagof3:1694"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>, <a name="idx:aggregate3:1695"></a><a class="pred" href="aggregate.html#aggregate/3">aggregate/3</a>
302		and <a name="idx:aggregate4:1696"></a><a class="pred" href="aggregate.html#aggregate/4">aggregate/4</a>.
	342	<a id="idx:setof3:1697"></a><a class="pred" href="allsolutions.html#setof/3">setof/3</a>, <a id="idx:bagof3:1698"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>, <a id="idx:aggregate3:1699"></a><a class="pred" href="aggregate.html#aggregate/3">aggregate/3</a>
	343	and <a id="idx:aggregate4:1700"></a><a class="pred" href="aggregate.html#aggregate/4">aggregate/4</a>.
303	344	It is processed similar to `0', but leaving the <code><code>^</code></code>/2
304	345	intact.
305	346	</dd>
306	347	<dt><strong><code>//</code></strong></dt>
307	348	<dd class="defbody">
308		The argument is a DCG body. See <a name="idx:phrase3:1697"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>.
	349	The argument is a DCG body. See <a id="idx:phrase3:1701"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>.
309	350	</dd>
310	351	</dl>
311	352

342	383	Module=42, Term = test
343	384	</pre>
344	385
345		<p>The <a name="idx:metapredicate1:1698"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	386	<p>The <a id="idx:metapredicate1:1702"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
346	387	declaration is the portable mechanism for defining meta-predicates and
347	388	replaces the old SWI-Prolog specific mechanism provided by the
348		deprecated predicates <a name="idx:moduletransparent1:1699"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>,
349		<a name="idx:contextmodule1:1700"></a><a class="pred" href="ctxmodule.html#context_module/1">context_module/1</a>
350		and <a name="idx:stripmodule3:1701"></a><a class="pred" href="ctxmodule.html#strip_module/3">strip_module/3</a>.
351		See also <a class="sec" href="modulecompat.html">section 6.15</a>.
	389	deprecated predicates <a id="idx:moduletransparent1:1703"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>,
	390	<a id="idx:contextmodule1:1704"></a><a class="pred" href="ctxmodule.html#context_module/1">context_module/1</a>
	391	and <a id="idx:stripmodule3:1705"></a><a class="pred" href="ctxmodule.html#strip_module/3">strip_module/3</a>.
	392	See also <a class="sec" href="modulecompat.html#sec:6.15">section 6.15</a>.
352	393	</dd>
353	394	</dl>
354	395

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193	234	</div>
194		<h2 id="sec:miscarith"><a name="sec:4.28"><span class="sec-nr">4.28</span> <span class="sec-title">Misc
	235	<h2 id="sec:miscarith"><a id="sec:4.28"><span class="sec-nr">4.28</span> <span class="sec-title">Misc
195	236	arithmetic support predicates</span></a></h2>
196	237
197		<a name="sec:miscarith"></a>
	238	<a id="sec:miscarith"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="set_random/1"><strong>set_random</strong>(<var>+Option</var>)</a></dt>
	241	<dt class="pubdef"><a id="set_random/1"><strong>set_random</strong>(<var>+Option</var>)</a></dt>
201	242	<dd class="defbody">
202	243	Controls the random number generator accessible through the
203	244	<em>functions</em> <a class="function" href="arith.html#f-random/1">random/1</a>

224	265	</dd>
225	266	<dt><strong>state</strong>(<var>+State</var>)</dt>
226	267	<dd class="defbody">
227		Set the generator to a state fetched using the state property of <a name="idx:randomproperty1:1340"></a><a class="pred" href="miscarith.html#random_property/1">random_property/1</a>.
	268	Set the generator to a state fetched using the state property of <a id="idx:randomproperty1:1340"></a><a class="pred" href="miscarith.html#random_property/1">random_property/1</a>.
228	269	Using other values may lead to undefined behaviour.<sup class="fn">117<span class="fn-text">The
229	270	limitations of the underlying (GMP) library are unknown, which makes it
230	271	impossible to validate the <var>State</var>.</span></sup>

232	273	</dl>
233	274
234	275	</dd>
235		<dt class="pubdef"><a name="random_property/1"><strong>random_property</strong>(<var>?Option</var>)</a></dt>
	276	<dt class="pubdef"><a id="random_property/1"><strong>random_property</strong>(<var>?Option</var>)</a></dt>
236	277	<dd class="defbody">
237	278	True when <var>Option</var> is a current property of the random
238	279	generator. Currently, this predicate provides access to the state. This

244	285	Describes the current state of the random generator. State is a normal
245	286	Prolog term that can be asserted or written to a file. Applications
246	287	should make no other assumptions about its representation. The only
247		meaningful operation is to use as argument to <a name="idx:setrandom1:1341"></a><a class="pred" href="miscarith.html#set_random/1">set_random/1</a>
	288	meaningful operation is to use as argument to <a id="idx:setrandom1:1341"></a><a class="pred" href="miscarith.html#set_random/1">set_random/1</a>
248	289	using the
249	290	<code>state(State)</code> option.<sup class="fn">bug<span class="fn-text">GMP
250	291	provides no portable mechanism to fetch and restore the state. The

255	296	</dl>
256	297
257	298	</dd>
258		<dt class="pubdef"><a name="current_arithmetic_function/1"><strong>current_arithmetic_function</strong>(<var>?Head</var>)</a></dt>
	299	<dt class="pubdef"><a id="current_arithmetic_function/1"><strong>current_arithmetic_function</strong>(<var>?Head</var>)</a></dt>
259	300	<dd class="defbody">
260	301	True when <var>Head</var> is an evaluable function. For example:
261	302

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193	234	</div>
194		<h2 id="sec:miscpreds"><a name="sec:4.44"><span class="sec-nr">4.44</span> <span class="sec-title">Miscellaneous</span></a></h2>
195
196		<a name="sec:miscpreds"></a>
	235	<h2 id="sec:miscpreds"><a id="sec:4.44"><span class="sec-nr">4.44</span> <span class="sec-title">Miscellaneous</span></a></h2>
	236
	237	<a id="sec:miscpreds"></a>
197	238
198	239	<dl class="latex">
199		<dt class="pubdef"><a name="dwim_match/2"><strong>dwim_match</strong>(<var>+Atom1,
	240	<dt class="pubdef"><a id="dwim_match/2"><strong>dwim_match</strong>(<var>+Atom1,
200	241	+Atom2</var>)</a></dt>
201	242	<dd class="defbody">
202	243	True if <var>Atom1</var> matches <var>Atom2</var> in the `Do What I

213	254	fileExists)
214	255	</ul>
215	256	</dd>
216		<dt class="pubdef"><a name="dwim_match/3"><strong>dwim_match</strong>(<var>+Atom1,
	257	<dt class="pubdef"><a id="dwim_match/3"><strong>dwim_match</strong>(<var>+Atom1,
217	258	+Atom2, -Difference</var>)</a></dt>
218	259	<dd class="defbody">
219		Equivalent to <a name="idx:dwimmatch2:1586"></a><a class="pred" href="miscpreds.html#dwim_match/2">dwim_match/2</a>,
	260	Equivalent to <a id="idx:dwimmatch2:1586"></a><a class="pred" href="miscpreds.html#dwim_match/2">dwim_match/2</a>,
220	261	but unifies <var>Difference</var> with an atom identifying the
221	262	difference between <var>Atom1</var> and <var>Atom2</var>. The return
222	263	values are (in the same order as above): <code>equal</code>,
223	264	<code>mismatched_char</code>, <code>inserted_char</code>, <code>transposed_char</code>,
224	265	<code>separated</code> and <code>transposed_word</code>.
225	266	</dd>
226		<dt class="pubdef"><a name="wildcard_match/2"><strong>wildcard_match</strong>(<var>+Pattern,
	267	<dt class="pubdef"><a id="wildcard_match/2"><strong>wildcard_match</strong>(<var>+Pattern,
227	268	+String</var>)</a></dt>
228	269	<dd class="defbody">
229	270	True if <var>String</var> matches the wildcard pattern <var>Pattern</var>.
230	271	<var>Pattern</var> is very similar to the Unix <code>csh</code> pattern
231	272	matcher. The patterns are given below:
232		<div style="text-align:center"><table border="0" frame="void" rules="groups">
233		<tr valign="top"><td><code><code>?</code></code> </td><td>Matches one
234		arbitrary character. </td></tr>
235		<tr valign="top"><td><code><code>*</code></code> </td><td>Matches any
236		number of arbitrary characters. </td></tr>
237		<tr valign="top"><td><code>[ ... ]</code> </td><td>Matches one of the
238		characters specified between the brackets. </td></tr>
239		<tr valign="top"><td></td><td><code><<var>char1</var>>-<<var>char2</var>></code>
	273
	274	<p><table class="latex frame-void center">
	275	<tr><td><code><code>?</code></code> </td><td>Matches one arbitrary
	276	character. </td></tr>
	277	<tr><td><code><code>*</code></code> </td><td>Matches any number of
	278	arbitrary characters. </td></tr>
	279	<tr><td><code>[ ... ]</code> </td><td>Matches one of the characters
	280	specified between the brackets. </td></tr>
	281	<tr><td></td><td><code><<var>char1</var>>-<<var>char2</var>></code>
240	282	indicates a range. </td></tr>
241		<tr valign="top"><td><code>{...}</code> </td><td>Matches any of the
242		patterns of the comma-separated list between the braces.</td></tr>
	283	<tr><td><code>{...}</code> </td><td>Matches any of the patterns of the
	284	comma-separated list between the braces.</td></tr>
243	285	</table>
244		</div>
245	286
246	287	<p>Example:
247	288

251	292	</pre>
252	293
253	294	</dd>
254		<dt class="pubdef"><a name="sleep/1"><strong>sleep</strong>(<var>+Time</var>)</a></dt>
	295	<dt class="pubdef"><a id="sleep/1"><strong>sleep</strong>(<var>+Time</var>)</a></dt>
255	296	<dd class="defbody">
256	297	Suspend execution <var>Time</var> seconds. <var>Time</var> is either a
257	298	floating point number or an integer. Granularity is dependent on the

259	300	immediately. On most non-realtime operating systems we can only ensure
260	301	execution is suspended for <b>at least</b> <var>Time</var> seconds.
261	302
262		<p>On Unix systems the <a name="idx:sleep1:1587"></a><a class="pred" href="miscpreds.html#sleep/1">sleep/1</a>
	303	<p>On Unix systems the <a id="idx:sleep1:1587"></a><a class="pred" href="miscpreds.html#sleep/1">sleep/1</a>
263	304	predicate is realised ---in order of preference--- by nanosleep(),
264	305	usleep(), select() if the time is below 1 minute, or sleep(). On Windows
265	306	systems Sleep() is used.

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192	233	<a class="nav" href="clp.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:modulecompat"><a name="sec:6.15"><span class="sec-nr">6.15</span> <span class="sec-title">Compatibility
	235	<h2 id="sec:modulecompat"><a id="sec:6.15"><span class="sec-nr">6.15</span> <span class="sec-title">Compatibility
195	236	of the Module System</span></a></h2>
196	237
197		<a name="sec:modulecompat"></a>
	238	<a id="sec:modulecompat"></a>
198	239
199	240	<p>The SWI-Prolog module system is largely derived from the Quintus
200	241	Prolog module system, which is also adopted by SICStus, Ciao and YAP.
201	242	Originally, the mechanism for defining meta-predicates in SWI-Prolog was
202		based on the <a name="idx:moduletransparent1:1752"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>
203		directive and <a name="idx:stripmodule3:1753"></a><a class="pred" href="ctxmodule.html#strip_module/3">strip_module/3</a>.
204		Since 5.7.4 it supports the de-facto standard <a name="idx:metapredicate1:1754"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	243	based on the <a id="idx:moduletransparent1:1756"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>
	244	directive and <a id="idx:stripmodule3:1757"></a><a class="pred" href="ctxmodule.html#strip_module/3">strip_module/3</a>.
	245	Since 5.7.4 it supports the de-facto standard <a id="idx:metapredicate1:1758"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
205	246	directive for implementing meta-predicates, providing much better
206	247	compatibility.
207	248
208		<p>The support for the <a name="idx:metapredicate1:1755"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
	249	<p>The support for the <a id="idx:metapredicate1:1759"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>
209	250	mechanism, however, is considerably different. On most systems, the <em>caller</em>
210	251	of a meta-predicate is compiled differently to provide the required <<var>module</var>>:<<var>term</var>>
211	252	qualification. This implies that the meta-declaration must be available

217	258	<ul class="latex">
218	259	<li>Modules that provide meta-predicates for a module to be compiled
219	260	must be loaded explicitly by that module.
220		<li>The meta-predicate directives of exported predicates must follow the <a name="idx:module2:1756"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
	261	<li>The meta-predicate directives of exported predicates must follow the <a id="idx:module2:1760"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
221	262	directive immediately.
222	263	<li>After changing a meta-declaration, all modules that <em>call</em>
223	264	the modified predicates need to be recompiled.

239	280	user-defined module is the <code>user</code> module. In turn, the
240	281	<code>user</code> module imports from the module <code>system</code>
241	282	that provides all built-in predicates. The auto-import hierarchy can be
242		changed using <a name="idx:addimportmodule3:1757"></a><a class="pred" href="importmodule.html#add_import_module/3">add_import_module/3</a>
243		and <a name="idx:deleteimportmodule2:1758"></a><a class="pred" href="importmodule.html#delete_import_module/2">delete_import_module/2</a>.
	283	changed using <a id="idx:addimportmodule3:1761"></a><a class="pred" href="importmodule.html#add_import_module/3">add_import_module/3</a>
	284	and <a id="idx:deleteimportmodule2:1762"></a><a class="pred" href="importmodule.html#delete_import_module/2">delete_import_module/2</a>.
244	285
245	286	<p>This mechanism can be used to realise a simple object-oriented system
246	287	or a hierarchical module system.

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 6.8</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 6.8</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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193	234	</div>
194		<h2 id="sec:moduleop"><a name="sec:6.8"><span class="sec-nr">6.8</span> <span class="sec-title">Operators
	235	<h2 id="sec:moduleop"><a id="sec:6.8"><span class="sec-nr">6.8</span> <span class="sec-title">Operators
195	236	and modules</span></a></h2>
196	237
197		<a name="sec:moduleop"></a>
198
199		<p>Operators (<a class="sec" href="operators.html">section 4.25</a>) are
200		local to modules, where the initial table behaves as if it is copied
	238	<a id="sec:moduleop"></a>
	239
	240	<p>Operators (<a class="sec" href="operators.html#sec:4.25">section 4.25</a>)
	241	are local to modules, where the initial table behaves as if it is copied
201	242	from the module <code>user</code> (see
202		<a class="sec" href="resmodules.html">section 6.10</a>). A specific
203		operator can be disabled inside a module using <code>:- op(0, Type,
204		Name)</code>. Inheritance from the public table can be restored using <code>:-
205		op(-1, Type, Name)</code>.
206
207		<p>In addition to using the <a name="idx:op3:1716"></a><a class="pred" href="operators.html#op/3">op/3</a>
208		directive, operators can be declared in the <a name="idx:module2:1717"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
	243	<a class="sec" href="resmodules.html#sec:6.10">section 6.10</a>). A
	244	specific operator can be disabled inside a module using <code>:- op(0,
	245	Type, Name)</code>. Inheritance from the public table can be restored
	246	using <code>:- op(-1, Type, Name)</code>.
	247
	248	<p>In addition to using the <a id="idx:op3:1720"></a><a class="pred" href="operators.html#op/3">op/3</a>
	249	directive, operators can be declared in the <a id="idx:module2:1721"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
209	250	directive as shown below. Such operator declarations are visible inside
210	251	the module, and importing such a module makes the operators visible in
211	252	the target module. Exporting operators is typically used by modules that
212	253	implement sub-languages such as chr (see
213		<a class="sec" href="chr.html">chapter 8</a>). The example below is
214		copied from the library
	254	<a class="sec" href="chr.html#sec:8">chapter 8</a>). The example below
	255	is copied from the library
215	256	<code>library(clpfd)</code>.
216	257
217	258	<pre class="code">

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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	27	}
	28
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118	122	font-size: 80%;
119	123	font-style: italic;
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122	126
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130
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138		border: 2px solid;
139		padding: 5px; margin: 10px; z-index: 100;
140		font-size: smaller;
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	135	color: red;
	136	font-size: 70%;
	137	}
	138
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142	156
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193	234	</div>
194		<h1 id="sec:modules"><a name="sec:6"><span class="sec-nr">6</span> <span class="sec-title">Modules</span></a></h1>
195
196		<a name="sec:modules"></a>
	235	<h1 id="sec:modules"><a id="sec:6"><span class="sec-nr">6</span> <span class="sec-title">Modules</span></a></h1>
	236
	237	<a id="sec:modules"></a>
197	238
198	239	<p>A Prolog module is a collection of predicates which defines a public
199	240	interface by means of a set of provided predicates and operators. Prolog

209	250
210	251	<p>This chapter motivates and describes the SWI-Prolog module system.
211	252	Novices can start using the module system after reading
212		<a class="sec" href="defmodule.html">section 6.2</a> and <a class="sec" href="import.html">section
	253	<a class="sec" href="defmodule.html#sec:6.2">section 6.2</a> and <a class="sec" href="import.html#sec:6.3">section
213	254	6.3</a>. The primitives defined in these sections suffice for basic
214	255	usage until one needs to export predicates that call or manage other
215		predicates dynamically (e.g., use <a name="idx:call1:1658"></a><a class="pred" href="metacall.html#call/1">call/1</a>,
216		<a name="idx:assert1:1659"></a><a class="pred" href="db.html#assert/1">assert/1</a>,
	256	predicates dynamically (e.g., use <a id="idx:call1:1662"></a><a class="pred" href="metacall.html#call/1">call/1</a>,
	257	<a id="idx:assert1:1663"></a><a class="pred" href="db.html#assert/1">assert/1</a>,
217	258	etc.). Such predicates are called <em>meta predicates</em> and are
218		discussed in <a class="sec" href="metapred.html">section 6.4</a>. <a class="sec" href="overrule.html">Section
219		6.5</a> to <a class="sec" href="moduleop.html">section 6.8</a> describe
220		more advanced issues. Starting with <a class="sec" href="importmodule.html">section
	259	discussed in <a class="sec" href="metapred.html#sec:6.4">section 6.4</a>. <a class="sec" href="overrule.html#sec:6.5">Section
	260	6.5</a> to <a class="sec" href="moduleop.html#sec:6.8">section 6.8</a>
	261	describe more advanced issues. Starting with <a class="sec" href="importmodule.html#sec:6.9">section
221	262	6.9</a>, we discuss more low-level aspects of the SWI-Prolog module
222	263	system that are used to implement the visible module system, and can be
223	264	used to build other code reuse mechanisms.

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2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 9.7</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 9.7</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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18	18	}
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	28
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27	31
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29	33	{ margin-bottom: 1em;

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119	123	font-style: italic;
120		color: #202020;
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122	126
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127	131	}
128	132
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130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
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135		{ display: block !important;
136		position: absolute; top: auto; left: auto; width: 80%;
137		color: #000; background: white;
138		border: 2px solid;
139		padding: 5px; margin: 10px; z-index: 100;
140		font-size: smaller;
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	135	color: red;
	136	font-size: 70%;
	137	}
	138
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	210	{ vertical-align: text-top;
	211	}
	212
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	214	{ padding: 2px 1em;
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	216
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193	234	</div>
194		<h2 id="sec:mt-xpce"><a name="sec:9.7"><span class="sec-nr">9.7</span> <span class="sec-title">Multithreading
	235	<h2 id="sec:mt-xpce"><a id="sec:9.7"><span class="sec-nr">9.7</span> <span class="sec-title">Multithreading
195	236	and the XPCE graphics system</span></a></h2>
196	237
197		<a name="sec:mt-xpce"></a>
198		<a name="sec:xpcethread"></a>
	238	<a id="sec:mt-xpce"></a>
	239	<a id="sec:xpcethread"></a>
199	240
200	241	<p>GUI applications written in XPCE can benefit from Prolog threads if
201	242	they need to do expensive computations that would otherwise block the

210	251	<p>Traditionally, XPCE runs in the foreground (<code>main</code>)
211	252	thread. We are working towards a situation where XPCE can run
212	253	comfortably in a separate thread. A separate XPCE thread can be created
213		using <a name="idx:pcedispatch1:1955"></a><a class="pred" href="mt-xpce.html#pce_dispatch/1">pce_dispatch/1</a>.
	254	using <a id="idx:pcedispatch1:1959"></a><a class="pred" href="mt-xpce.html#pce_dispatch/1">pce_dispatch/1</a>.
214	255	It is also possible to create this thread as the <code>library(1)</code>pce)
215	256	is loaded by setting the <b>xpce_threaded</b> to <code>true</code>.
216	257

218	259	two predicates to communicate with XPCE.
219	260
220	261	<dl class="latex">
221		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="in_pce_thread/1"><strong>in_pce_thread</strong>(<var>:Goal</var>)</a></dt>
	262	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="in_pce_thread/1"><strong>in_pce_thread</strong>(<var>:Goal</var>)</a></dt>
222	263	<dd class="defbody">
223	264	Assuming XPCE is running in the foreground thread, this call gives
224	265	background threads the opportunity to make calls to the XPCE thread. A
225		call to <a name="idx:inpcethread1:1956"></a><a class="pred" href="mt-xpce.html#in_pce_thread/1">in_pce_thread/1</a>
	266	call to <a id="idx:inpcethread1:1960"></a><a class="pred" href="mt-xpce.html#in_pce_thread/1">in_pce_thread/1</a>
226	267	succeeds immediately, copying <var>Goal</var> to the XPCE thread. <var>Goal</var>
227	268	is added to the XPCE event queue and executed synchronous to normal user
228	269	events like typing and clicking.</dd>
229		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="in_pce_thread_sync/1"><strong>in_pce_thread_sync</strong>(<var>:Goal</var>)</a></dt>
	270	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="in_pce_thread_sync/1"><strong>in_pce_thread_sync</strong>(<var>:Goal</var>)</a></dt>
230	271	<dd class="defbody">
231		Same as <a name="idx:inpcethread1:1957"></a><a class="pred" href="mt-xpce.html#in_pce_thread/1">in_pce_thread/1</a>,
	272	Same as <a id="idx:inpcethread1:1961"></a><a class="pred" href="mt-xpce.html#in_pce_thread/1">in_pce_thread/1</a>,
232	273	but wait for <var>Goal</var> to be completed. Success depends on the
233	274	success of executing <var>Goal</var>. Variable bindings inside <var>Goal</var>
234	275	are visible to the caller, but it should be noted that the values are
235	276	being <em>copied</em>. If <var>Goal</var> throws an exception, this
236		exception is re-thrown by <a name="idx:inpcethread1:1958"></a><a class="pred" href="mt-xpce.html#in_pce_thread/1">in_pce_thread/1</a>.
237		If the calling thread is the `pce thread', <a name="idx:inpcethreadsync1:1959"></a><a class="pred" href="mt-xpce.html#in_pce_thread_sync/1">in_pce_thread_sync/1</a>
238		executes a direct meta-call. See also <a name="idx:pcethread1:1960"></a><span class="pred-ext">pce_thread/1</span>.
239
240		<p>Note that <a name="idx:inpcethreadsync1:1961"></a><a class="pred" href="mt-xpce.html#in_pce_thread_sync/1">in_pce_thread_sync/1</a>
	277	exception is re-thrown by <a id="idx:inpcethread1:1962"></a><a class="pred" href="mt-xpce.html#in_pce_thread/1">in_pce_thread/1</a>.
	278	If the calling thread is the `pce thread', <a id="idx:inpcethreadsync1:1963"></a><a class="pred" href="mt-xpce.html#in_pce_thread_sync/1">in_pce_thread_sync/1</a>
	279	executes a direct meta-call. See also <a id="idx:pcethread1:1964"></a><span class="pred-ext">pce_thread/1</span>.
	280
	281	<p>Note that <a id="idx:inpcethreadsync1:1965"></a><a class="pred" href="mt-xpce.html#in_pce_thread_sync/1">in_pce_thread_sync/1</a>
241	282	is expensive because it requires copying and thread communication. For
242	283	example, <code>in_pce_thread_synctrue</code> runs at approximately
243	284	50,000 calls per second (AMD Phenom 9600B, Ubuntu 11.04).</dd>
244		<dt class="pubdef"><a name="pce_dispatch/1"><strong>pce_dispatch</strong>(<var>+Options</var>)</a></dt>
	285	<dt class="pubdef"><a id="pce_dispatch/1"><strong>pce_dispatch</strong>(<var>+Options</var>)</a></dt>
245	286	<dd class="defbody">
246	287	Create a Prolog thread with the alias name <code>pce</code> for XPCE
247	288	event handling. In the X11 version this call creates a thread that
248	289	executes the X11 event-dispatch loop. In MS-Windows it creates a thread
249	290	that executes a windows event-dispatch loop. The XPCE event-handling
250	291	thread has the alias <code>pce</code>. <var>Options</var> specifies the
251		thread attributes as <a name="idx:threadcreate3:1962"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>.
	292	thread attributes as <a id="idx:threadcreate3:1966"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>.
252	293	</dd>
253	294	</dl>
254	295

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 6.6</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:mtoplevel"><a name="sec:6.6"><span class="sec-nr">6.6</span> <span class="sec-title">Interacting
	235	<h2 id="sec:mtoplevel"><a id="sec:6.6"><span class="sec-nr">6.6</span> <span class="sec-title">Interacting
195	236	with modules from the top level</span></a></h2>
196	237
197		<a name="sec:mtoplevel"></a>
	238	<a id="sec:mtoplevel"></a>
198	239
199	240	<p>Debugging often requires interaction with predicates that reside in
200	241	modules: running them, setting spy points on them, etc. This can be
201	242	achieved using the <<var>module</var>>:<<var>term</var>>
202	243	construct explicitly as described above. In SWI-Prolog, you may also
203		wish to omit the module qualification. Setting a spy point (<a name="idx:spy1:1705"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>)
	244	wish to omit the module qualification. Setting a spy point (<a id="idx:spy1:1709"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>)
204	245	on a plain predicate sets a spy point on any predicate with that name in
205		any module. Editing (<a name="idx:edit1:1706"></a><a class="pred" href="edit.html#edit/1">edit/1</a>)
	246	any module. Editing (<a id="idx:edit1:1710"></a><a class="pred" href="edit.html#edit/1">edit/1</a>)
206	247	or calling an unqualified predicate invokes the DWIM (Do What I Mean)
207	248	mechanism, which generally suggests the correct qualified query.
208	249
209		<p>Mainly for compatibility, we provide <a name="idx:module1:1707"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>
	250	<p>Mainly for compatibility, we provide <a id="idx:module1:1711"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>
210	251	to switch the module with which the interactive top level interacts:
211	252
212	253	<dl class="latex">
213		<dt class="pubdef"><a name="module/1"><strong>module</strong>(<var>+Module</var>)</a></dt>
	254	<dt class="pubdef"><a id="module/1"><strong>module</strong>(<var>+Module</var>)</a></dt>
214	255	<dd class="defbody">
215	256	The call <code>module(<var>Module</var>)</code> may be used to switch
216		the default working module for the interactive top level (see <a name="idx:prolog0:1708"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>).
	257	the default working module for the interactive top level (see <a id="idx:prolog0:1712"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>).
217	258	This may be used when debugging a module. The example below lists the
218		clauses of <a name="idx:fileoflabel2:1709"></a><span class="pred-ext">file_of_label/2</span>
	259	clauses of <a id="idx:fileoflabel2:1713"></a><span class="pred-ext">file_of_label/2</span>
219	260	in the module <code>tex</code>.
220	261
221	262	<pre class="code">

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193	234	</div>
194		<h2 id="sec:navigator"><a name="sec:3.6"><span class="sec-nr">3.6</span> <span class="sec-title">The
	235	<h2 id="sec:navigator"><a id="sec:3.6"><span class="sec-nr">3.6</span> <span class="sec-title">The
195	236	Prolog Navigator</span></a></h2>
196	237
197		<a name="sec:navigator"></a>
	238	<a id="sec:navigator"></a>
198	239
199	240	<p>Another tool is the <em>Prolog Navigator</em>. This tool can be
200	241	started from PceEmacs using the command <strong>Browse/Prolog navigator</strong>,
201	242	from the GUI debugger or using the programmatic IDE interface described
202	243	in
203		<a class="sec" href="idepreds.html">section 3.8</a>.
	244	<a class="sec" href="idepreds.html#sec:3.8">section 3.8</a>.
204	245
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193	234	</div>
194		<h2 id="sec:nb_set"><a name="sec:A.17"><span class="sec-nr">A.17</span> <span class="sec-title">library(nb_set):
	235	<h2 id="sec:nb_set"><a id="sec:A.17"><span class="sec-nr">A.17</span> <span class="sec-title">library(nb_set):
195	236	Non-backtrackable set</span></a></h2>
196	237
197		<a name="sec:nb_set"></a>
	238	<a id="sec:nb_set"></a>
198	239
199	240	<p>The library <code>library(nb_set)</code> defines <em>non-backtrackable
200	241	sets</em>, implemented as binary trees. The sets are represented as
201		compound terms and manipulated using <a name="idx:nbsetarg3:2145"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
	242	compound terms and manipulated using <a id="idx:nbsetarg3:2149"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
202	243	Non-backtrackable manipulation of datastructures is not supported by a
203	244	large number of Prolog implementations, but it has several advantages
204	245	over using the database. It produces less garbage, is thread-safe,

221	262	</pre>
222	263
223	264	<dl class="latex">
224		<dt class="pubdef"><a name="empty_nb_set/1"><strong>empty_nb_set</strong>(<var>?Set</var>)</a></dt>
	265	<dt class="pubdef"><a id="empty_nb_set/1"><strong>empty_nb_set</strong>(<var>?Set</var>)</a></dt>
225	266	<dd class="defbody">
226	267	True if <var>Set</var> is a non-backtrackable empty set.</dd>
227		<dt class="pubdef"><a name="add_nb_set/2"><strong>add_nb_set</strong>(<var>+Key,
	268	<dt class="pubdef"><a id="add_nb_set/2"><strong>add_nb_set</strong>(<var>+Key,
228	269	!Set</var>)</a></dt>
229	270	<dd class="defbody">
230	271	Add <var>Key</var> to <var>Set</var>. If <var>Key</var> is already a
231	272	member of
232		<var>Set</var>, <a name="idx:addnbset3:2146"></a><a class="pred" href="nb_set.html#add_nb_set/3">add_nb_set/3</a>
	273	<var>Set</var>, <a id="idx:addnbset3:2150"></a><a class="pred" href="nb_set.html#add_nb_set/3">add_nb_set/3</a>
233	274	succeeds without modifying <var>Set</var>.</dd>
234		<dt class="pubdef"><a name="add_nb_set/3"><strong>add_nb_set</strong>(<var>+Key,
	275	<dt class="pubdef"><a id="add_nb_set/3"><strong>add_nb_set</strong>(<var>+Key,
235	276	!Set, ?New</var>)</a></dt>
236	277	<dd class="defbody">
237	278	If <var>Key</var> is not in <var>Set</var> and <var>New</var> is unified

240	281	is in <var>Set</var>, <var>New</var> is unified to <code>false</code>.
241	282	It can be used for many purposes:
242	283
243		<p><table border="0" frame="void" rules="groups" style="margin:auto">
244		<tr valign="top"><td><code>add_nb_set(+, +, false)</code></td><td>Test
245		membership </td></tr>
246		<tr valign="top"><td><code>add_nb_set(+, +, true)</code></td><td>Succeed
247		only if new member </td></tr>
248		<tr valign="top"><td><code>add_nb_set(+, +, Var)</code></td><td>Succeed,
249		binding <var>Var</var> </td></tr>
	284	<p><table class="latex frame-void center">
	285	<tr><td><code>add_nb_set(+, +, false)</code></td><td>Test membership </td></tr>
	286	<tr><td><code>add_nb_set(+, +, true)</code></td><td>Succeed only if new
	287	member </td></tr>
	288	<tr><td><code>add_nb_set(+, +, Var)</code></td><td>Succeed, binding <var>Var</var> </td></tr>
250	289	</table>
251	290	</dd>
252		<dt class="pubdef"><a name="gen_nb_set/2"><strong>gen_nb_set</strong>(<var>+Set,
	291	<dt class="pubdef"><a id="gen_nb_set/2"><strong>gen_nb_set</strong>(<var>+Set,
253	292	-Key</var>)</a></dt>
254	293	<dd class="defbody">
255	294	Generate all members of <var>Set</var> on backtracking in the standard
256		order of terms. To test membership, use <a name="idx:addnbset3:2147"></a><a class="pred" href="nb_set.html#add_nb_set/3">add_nb_set/3</a>.</dd>
257		<dt class="pubdef"><a name="size_nb_set/2"><strong>size_nb_set</strong>(<var>+Set,
	295	order of terms. To test membership, use <a id="idx:addnbset3:2151"></a><a class="pred" href="nb_set.html#add_nb_set/3">add_nb_set/3</a>.</dd>
	296	<dt class="pubdef"><a id="size_nb_set/2"><strong>size_nb_set</strong>(<var>+Set,
258	297	-Size</var>)</a></dt>
259	298	<dd class="defbody">
260	299	Unify <var>Size</var> with the number of elements in <var>Set</var>.</dd>
261		<dt class="pubdef"><a name="nb_set_to_list/2"><strong>nb_set_to_list</strong>(<var>+Set,
	300	<dt class="pubdef"><a id="nb_set_to_list/2"><strong>nb_set_to_list</strong>(<var>+Set,
262	301	-List</var>)</a></dt>
263	302	<dd class="defbody">
264	303	Unify <var>List</var> with a list of all elements in <var>Set</var> in

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193	234	</div>
194		<h2 id="sec:operators"><a name="sec:4.25"><span class="sec-nr">4.25</span> <span class="sec-title">Operators</span></a></h2>
195
196		<a name="sec:operators"></a>
	235	<h2 id="sec:operators"><a id="sec:4.25"><span class="sec-nr">4.25</span> <span class="sec-title">Operators</span></a></h2>
	236
	237	<a id="sec:operators"></a>
197	238
198	239	<p>Operators are defined to improve the readability of source code. For
199	240	example, without operators, to write <code>23+45</code> one would have

201	242	have been predefined. All operators, except for the comma (,) can be
202	243	redefined by the user.
203	244
204		<p><a name="idx:operatorandmodules:1314"></a>Some care has to be taken
	245	<p><a id="idx:operatorandmodules:1314"></a>Some care has to be taken
205	246	before defining new operators. Defining too many operators might make
206	247	your source `natural' looking, but at the same time make it hard to
207	248	understand the limits of your syntax. To ease the pain, as of SWI-Prolog

209	250	Operators can be exported from modules using a term
210	251	<code>op(Precedence, Type, Name)</code> in the export list as specified
211	252	by
212		<a name="idx:module2:1315"></a><a class="pred" href="defmodule.html#module/2">module/2</a>.
	253	<a id="idx:module2:1315"></a><a class="pred" href="defmodule.html#module/2">module/2</a>.
213	254	Many modern Prolog systems have module specific operators.
214	255	Unfortunately, there is no established interface for exporting and
215	256	importing operators. SWI-Prolog's convention has been addopted by YAP.

230	271	<p>In SWI-Prolog, a <em>quoted atom</em> never acts as an operator. Note
231	272	that the portable way to stop an atom acting as an operator is to
232	273	enclose it in parentheses like this: (myop). See also
233		<a class="sec" href="ext-syntax.html">section 5.3.1</a>.
	274	<a class="sec" href="ext-syntax.html#sec:5.3.1">section 5.3.1</a>.
234	275
235	276	<dl class="latex">
236		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="op/3"><strong>op</strong>(<var>+Precedence,
	277	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="op/3"><strong>op</strong>(<var>+Precedence,
237	278	+Type, :Name</var>)</a></dt>
238	279	<dd class="defbody">
239	280	Declare <var>Name</var> to be an operator of type <var>Type</var> with

274	315	</ul>
275	316
276	317	<p>In SWI-Prolog, operators are <em>local</em> to a module (see also
277		<a class="sec" href="moduleop.html">section 6.8</a>). Keeping operators
278		in modules and using controlled import/export of operators as described
279		with the <a name="idx:module2:1316"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
	318	<a class="sec" href="moduleop.html#sec:6.8">section 6.8</a>). Keeping
	319	operators in modules and using controlled import/export of operators as
	320	described with the <a id="idx:module2:1316"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
280	321	directive keep the issues manageable. The module <code>system</code>
281	322	provides the operators from <a class="tab" href="operators.html#tab:operators">table
282	323	5</a> and these operators cannot be modified. Files that are loaded from

285	326	library and development system modules independent of operator changes
286	327	to the <code>user</code> module.
287	328
288		<p><table border="2" frame="box" rules="groups" style="margin:auto">
289		<tr valign="top"><td align=right>1200</td><td ALIGN=char CHAR=f>xfx</td><td><strong><code>--></code></strong>, <strong><code>:-</code></strong> </td></tr>
290		<tr valign="top"><td align=right>1200</td><td ALIGN=char CHAR=f>fx</td><td><strong><code>:-</code></strong>, <strong><code>?-</code></strong> </td></tr>
291		<tr valign="top"><td align=right>1150</td><td ALIGN=char CHAR=f>fx</td><td><strong>dynamic</strong>, <strong>discontiguous</strong>, <strong>initialization</strong>,
	329	<p><table class="latex frame-box center">
	330	<tr><td align=right>1200</td><td>xfx</td><td><strong><code>--></code></strong>, <strong><code>:-</code></strong> </td></tr>
	331	<tr><td align=right>1200</td><td>fx</td><td><strong><code>:-</code></strong>, <strong><code>?-</code></strong> </td></tr>
	332	<tr><td align=right>1150</td><td>fx</td><td><strong>dynamic</strong>, <strong>discontiguous</strong>, <strong>initialization</strong>,
292	333	<strong>meta_predicate</strong>,
293	334	<strong>module_transparent</strong>, <strong>multifile</strong>, <strong>public</strong>,
294	335	<strong>thread_local</strong>, <strong>thread_initialization</strong>, <strong>volatile</strong> </td></tr>
295		<tr valign="top"><td align=right>1100</td><td ALIGN=char CHAR=f>xfy</td><td><strong><code>;</code></strong>, <strong><code>\|</code></strong> </td></tr>
296		<tr valign="top"><td align=right>1050</td><td ALIGN=char CHAR=f>xfy</td><td><strong><code>-></code></strong>, <strong><code>*-></code></strong> </td></tr>
297		<tr valign="top"><td align=right>1000</td><td ALIGN=char CHAR=f>xfy</td><td><strong><code>,</code></strong> </td></tr>
298		<tr valign="top"><td align=right>990</td><td ALIGN=char CHAR=f>xfx</td><td><strong>:=</strong> </td></tr>
299		<tr valign="top"><td align=right>900</td><td ALIGN=char CHAR=f>fy</td><td><strong><code>\+</code></strong> </td></tr>
300		<tr valign="top"><td align=right>700</td><td ALIGN=char CHAR=f>xfx</td><td><strong><code><</code></strong>, <strong><code>=</code></strong>, <strong><code>=..</code></strong>, <strong><code>=@=</code></strong>, <strong><code>\=@=</code></strong>,
	336	<tr><td align=right>1100</td><td>xfy</td><td><strong><code>;</code></strong>, <strong><code>\|</code></strong> </td></tr>
	337	<tr><td align=right>1050</td><td>xfy</td><td><strong><code>-></code></strong>, <strong><code>*-></code></strong> </td></tr>
	338	<tr><td align=right>1000</td><td>xfy</td><td><strong><code>,</code></strong> </td></tr>
	339	<tr><td align=right>990</td><td>xfx</td><td><strong>:=</strong> </td></tr>
	340	<tr><td align=right>900</td><td>fy</td><td><strong><code>\+</code></strong> </td></tr>
	341	<tr><td align=right>700</td><td>xfx</td><td><strong><code><</code></strong>, <strong><code>=</code></strong>, <strong><code>=..</code></strong>, <strong><code>=@=</code></strong>, <strong><code>\=@=</code></strong>,
301	342	<strong><code>=:=</code></strong>, <strong><code>=<</code></strong>, <strong><code>==</code></strong>,
302	343	<strong><code>=\=</code></strong>, <strong><code>></code></strong>, <strong><code>>=</code></strong>, <strong><code>@<</code></strong>, <strong><code>@=<</code></strong>, <strong><code>@></code></strong>,
303	344	<strong><code>@>=</code></strong>, <strong><code>\=</code></strong>, <strong><code>\==</code></strong>, <strong>as</strong>, <strong>is</strong>,
304	345	<strong><code>>:<</code></strong>, <strong><code>:<</code></strong>
305	346	</td></tr>
306		<tr valign="top"><td align=right>600</td><td ALIGN=char CHAR=f>xfy</td><td><strong><code>:</code></strong> </td></tr>
307		<tr valign="top"><td align=right>500</td><td ALIGN=char CHAR=f>yfx</td><td><strong><code>+</code></strong>, <strong><code>-</code></strong>, <strong><code>/\</code></strong>, <strong><code>\/</code></strong>, <strong>xor</strong> </td></tr>
308		<tr valign="top"><td align=right>500</td><td ALIGN=char CHAR=f>fx</td><td><strong><code>?</code></strong> </td></tr>
309		<tr valign="top"><td align=right>400</td><td ALIGN=char CHAR=f>yfx</td><td><strong><code>*</code></strong>, <strong><code>/</code></strong>, <strong><code>//</code></strong>, <strong>div</strong>, <strong>rdiv</strong>,
	347	<tr><td align=right>600</td><td>xfy</td><td><strong><code>:</code></strong> </td></tr>
	348	<tr><td align=right>500</td><td>yfx</td><td><strong><code>+</code></strong>, <strong><code>-</code></strong>, <strong><code>/\</code></strong>, <strong><code>\/</code></strong>, <strong>xor</strong> </td></tr>
	349	<tr><td align=right>500</td><td>fx</td><td><strong><code>?</code></strong> </td></tr>
	350	<tr><td align=right>400</td><td>yfx</td><td><strong><code>*</code></strong>, <strong><code>/</code></strong>, <strong><code>//</code></strong>, <strong>div</strong>, <strong>rdiv</strong>,
310	351	<strong><code><<</code></strong>, <strong><code>>></code></strong>, <strong>mod</strong>, <strong>rem</strong> </td></tr>
311		<tr valign="top"><td align=right>200</td><td ALIGN=char CHAR=f>xfx</td><td><strong><code>**</code></strong> </td></tr>
312		<tr valign="top"><td align=right>200</td><td ALIGN=char CHAR=f>xfy</td><td><strong><code>^</code></strong> </td></tr>
313		<tr valign="top"><td align=right>200</td><td ALIGN=char CHAR=f>fy</td><td><strong><code>+</code></strong>, <strong><code>-</code></strong>, <strong><code>\</code></strong> </td></tr>
314		<tr valign="top"><td align=right>100</td><td ALIGN=char CHAR=f>yfx</td><td><strong><code>.</code></strong> </td></tr>
315		<tr valign="top"><td align=right>1</td><td ALIGN=char CHAR=f>fx</td><td><strong><code>$</code></strong> </td></tr>
	352	<tr><td align=right>200</td><td>xfx</td><td><strong><code>**</code></strong> </td></tr>
	353	<tr><td align=right>200</td><td>xfy</td><td><strong><code>^</code></strong> </td></tr>
	354	<tr><td align=right>200</td><td>fy</td><td><strong><code>+</code></strong>, <strong><code>-</code></strong>, <strong><code>\</code></strong> </td></tr>
	355	<tr><td align=right>100</td><td>yfx</td><td><strong><code>.</code></strong> </td></tr>
	356	<tr><td align=right>1</td><td>fx</td><td><strong><code>$</code></strong> </td></tr>
316	357	</table>
317	358	<div class="caption"><b>Table 5 : </b>System operators</div>
318		<a name="tab:operators"></a>
	359	<a id="tab:operators"></a>
319	360	</dd>
320		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="current_op/3"><strong>current_op</strong>(<var>?Precedence,
	361	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="current_op/3"><strong>current_op</strong>(<var>?Precedence,
321	362	?Type, ?:Name</var>)</a></dt>
322	363	<dd class="defbody">
323	364	True if <var>Name</var> is currently defined as an operator of type <var>Type</var>
324		with precedence <var>Precedence</var>. See also <a name="idx:op3:1317"></a><a class="pred" href="operators.html#op/3">op/3</a>.
	365	with precedence <var>Precedence</var>. See also <a id="idx:op3:1317"></a><a class="pred" href="operators.html#op/3">op/3</a>.
325	366	</dd>
326	367	</dl>
327	368

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194		<h2 id="sec:opsummary"><a name="sec:F.4"><span class="sec-nr">F.4</span> <span class="sec-title">Operators</span></a></h2>
195
196		<a name="sec:opsummary"></a>
	235	<h2 id="sec:opsummary"><a id="sec:F.4"><span class="sec-nr">F.4</span> <span class="sec-title">Operators</span></a></h2>
	236
	237	<a id="sec:opsummary"></a>
197	238	<table>
198	239	<tr><td>1</td><td>fx</td><td>$</td><td>Bind top-level variable</td></tr>
199	240	<tr><td>200</td><td>xfy</td><td>^</td><td>Existential qualification</td></tr>

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	153	sup:hover span.fn-text
	154	{ display: block;
141	155	}
142	156
143	157	/* Lists */

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182	196	margin-top: 1ex;
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	198
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185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="www_browser.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="optparse.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:option"><a name="sec:A.19"><span class="sec-nr">A.19</span> <span class="sec-title">library(option):
	235	<h2 id="sec:option"><a id="sec:A.19"><span class="sec-nr">A.19</span> <span class="sec-title">library(option):
195	236	Option list processing</span></a></h2>
196	237
197		<p><a name="sec:option"></a>
	238	<p><a id="sec:option"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="mtag">See also</dt>

263	304	</ul>
264	305
265	306	<dl class="latex">
266		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="option/3"><strong>option</strong>(<var>?Option,
	307	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="option/3"><strong>option</strong>(<var>?Option,
267	308	+OptionList, +Default</var>)</a></dt>
268	309	<dd class="defbody">
269	310	Get an <var>Option</var> from <var>OptionList</var>. <var>OptionList</var>
270	311	can use the Name=Value as well as the Name(Value) convention.
271	312	<table class="arglist">
272		<tr valign="top"><td><var>Option</var> </td><td>Term of the form
273		Name(?Value). </td></tr>
	313	<tr><td><var>Option</var> </td><td>Term of the form Name(?Value). </td></tr>
274	314	</table>
275	315	</dd>
276		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="option/2"><strong>option</strong>(<var>?Option,
	316	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="option/2"><strong>option</strong>(<var>?Option,
277	317	+OptionList</var>)</a></dt>
278	318	<dd class="defbody">
279	319	Get an <var>Option</var> from <var>OptionList</var>. <var>OptionList</var>
280	320	can use the Name=Value as well as the Name(Value) convention. Fails
281	321	silently if the option does not appear in <var>OptionList</var>.
282	322	<table class="arglist">
283		<tr valign="top"><td><var>Option</var> </td><td>Term of the form
284		Name(?Value). </td></tr>
	323	<tr><td><var>Option</var> </td><td>Term of the form Name(?Value). </td></tr>
285	324	</table>
286	325	</dd>
287		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="select_option/3"><strong>select_option</strong>(<var>?Option,
	326	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="select_option/3"><strong>select_option</strong>(<var>?Option,
288	327	+Options, -RestOptions</var>)</a></dt>
289	328	<dd class="defbody">
290	329	Get and remove <var>Option</var> from an option list. As <a class="pred" href="option.html#option/2">option/2</a>,
291	330	removing the matching option from <var>Options</var> and unifying the
292	331	remaining options with <var>RestOptions</var>.</dd>
293		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="select_option/4"><strong>select_option</strong>(<var>?Option,
	332	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="select_option/4"><strong>select_option</strong>(<var>?Option,
294	333	+Options, -RestOptions, +Default</var>)</a></dt>
295	334	<dd class="defbody">
296	335	Get and remove <var>Option</var> with default value. As <a class="pred" href="option.html#select_option/3">select_option/3</a>,
297	336	but if <var>Option</var> is not in <var>Options</var>, its value is
298	337	unified with
299	338	<var>Default</var> and <var>RestOptions</var> with <var>Options</var>.</dd>
300		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="merge_options/3"><strong>merge_options</strong>(<var>+New,
	339	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="merge_options/3"><strong>merge_options</strong>(<var>+New,
301	340	+Old, -Merged</var>)</a></dt>
302	341	<dd class="defbody">
303	342	Merge two option lists. <var>Merged</var> is a sorted list of options

307	346	<p>Multi-values options (e.g., <code>proxy(Host, Port)</code>) are
308	347	allowed, where both option-name and arity define the identity of the
309	348	option.</dd>
310		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="meta_options/3"><strong>meta_options</strong>(<var>+IsMeta,
	349	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="meta_options/3"><strong>meta_options</strong>(<var>+IsMeta,
311	350	:Options0, -Options</var>)</a></dt>
312	351	<dd class="defbody">
313	352	Perform meta-expansion on options that are module-sensitive. Whether an

333	372	</dl>
334	373
335	374	</dd>
336		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="dict_options/2"><strong>dict_options</strong>(<var>?Dict,
	375	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="dict_options/2"><strong>dict_options</strong>(<var>?Dict,
337	376	?Options</var>)</a></dt>
338	377	<dd class="defbody">
339	378	Convert between an option list and a dictionary. One of the arguments

+70

-29

man/Manual/optparse.html less more

1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.20</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.20</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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130
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191	232	<a class="nav" href="option.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="ordsets.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:optparse"><a name="sec:A.20"><span class="sec-nr">A.20</span> <span class="sec-title">library(optparse):
	235	<h2 id="sec:optparse"><a id="sec:A.20"><span class="sec-nr">A.20</span> <span class="sec-title">library(optparse):
195	236	command line parsing</span></a></h2>
196	237
197		<p><a name="sec:optparse"></a>
	238	<p><a id="sec:optparse"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">author</dt>

480	521	<p>This representation may be preferable with the empty-flag
481	522	configuration parameter style above (perhaps with asserting <span class="pred-ext">appl_config/2</span>).
482	523
483		<p><h3 id="sec:optparse-notes"><a name="sec:A.20.1"><span class="sec-nr">A.20.1</span> <span class="sec-title">Notes
	524	<p><h3 id="sec:optparse-notes"><a id="sec:A.20.1"><span class="sec-nr">A.20.1</span> <span class="sec-title">Notes
484	525	and tips</span></a></h3>
485	526
486		<p><a name="sec:optparse-notes"></a>
	527	<p><a id="sec:optparse-notes"></a>
487	528
488	529	<p>
489	530	<ul class="latex">

520	561	</ul>
521	562
522	563	<dl class="latex">
523		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="opt_arguments/3"><strong>opt_arguments</strong>(<var>+OptsSpec,
	564	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="opt_arguments/3"><strong>opt_arguments</strong>(<var>+OptsSpec,
524	565	-Opts, -PositionalArgs</var>)</a></dt>
525	566	<dd class="defbody">
526	567	Extract commandline options according to a specification. Convenience

539	580	they may go anywhere (although it is good practice to put them last).
540	581	Any leading arguments for the runtime (up to and including '--') are
541	582	discarded.</dd>
542		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="opt_parse/4"><strong>opt_parse</strong>(<var>+OptsSpec,
	583	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="opt_parse/4"><strong>opt_parse</strong>(<var>+OptsSpec,
543	584	+ApplArgs, -Opts, -PositionalArgs</var>)</a></dt>
544	585	<dd class="defbody">
545	586	Equivalent to <code>opt_parse(OptsSpec, ApplArgs, Opts, PositionalArgs, [])</code>.</dd>
546		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="opt_parse/5"><strong>opt_parse</strong>(<var>+OptsSpec,
	587	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="opt_parse/5"><strong>opt_parse</strong>(<var>+OptsSpec,
547	588	+ApplArgs, -Opts, -PositionalArgs, +ParseOptions</var>)</a></dt>
548	589	<dd class="defbody">
549	590	Parse the arguments Args (as list of atoms) according to <var>OptsSpec</var>.

589	630	</dl>
590	631
591	632	</dd>
592		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="opt_help/2"><strong>opt_help</strong>(<var>+OptsSpec,
	633	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="opt_help/2"><strong>opt_help</strong>(<var>+OptsSpec,
593	634	-Help:atom</var>)</a></dt>
594	635	<dd class="defbody">
595	636	True when <var>Help</var> is a help string synthesized from <var>OptsSpec</var>.</dd>
596		<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a name="parse_type/3"><strong>parse_type</strong>(<var>+Type,
	637	<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="parse_type/3"><strong>parse_type</strong>(<var>+Type,
597	638	+Codes:list(code), -Result</var>)</a></dt>
598	639	<dd class="defbody">
599	640	Hook to parse option text <var>Codes</var> to an object of type <var>Type</var>.

+83

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.21</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.21</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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191	232	<a class="nav" href="optparse.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="pairs.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:ordsets"><a name="sec:A.21"><span class="sec-nr">A.21</span> <span class="sec-title">library(ordsets):
	235	<h2 id="sec:ordsets"><a id="sec:A.21"><span class="sec-nr">A.21</span> <span class="sec-title">library(ordsets):
195	236	Ordered set manipulation</span></a></h2>
196	237
197		<p><a name="sec:ordsets"></a>
	238	<p><a id="sec:ordsets"></a>
198	239
199	240	<p>Ordered sets are lists with unique elements sorted to the standard
200	241	order of terms (see <a class="pred" href="builtinlist.html#sort/2">sort/2</a>).

225	266	as an ordset because the order it relies on may have been changed.
226	267
227	268	<dl class="latex">
228		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="is_ordset/1"><strong>is_ordset</strong>(<var>@Term</var>)</a></dt>
	269	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="is_ordset/1"><strong>is_ordset</strong>(<var>@Term</var>)</a></dt>
229	270	<dd class="defbody">
230	271	True if <var>Term</var> is an ordered set. All predicates in this
231	272	library expect ordered sets as input arguments. Failing to fullfil this

233	274	created by predicates from this library, <a class="pred" href="builtinlist.html#sort/2">sort/2</a>
234	275	or
235	276	<a class="pred" href="allsolutions.html#setof/3">setof/3</a>.</dd>
236		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="ord_empty/1"><strong>ord_empty</strong>(<var>?List</var>)</a></dt>
	277	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="ord_empty/1"><strong>ord_empty</strong>(<var>?List</var>)</a></dt>
237	278	<dd class="defbody">
238	279	True when <var>List</var> is the empty ordered set. Simply unifies list
239	280	with the empty list. Not part of Quintus.</dd>
240		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="ord_seteq/2"><strong>ord_seteq</strong>(<var>+Set1,
	281	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="ord_seteq/2"><strong>ord_seteq</strong>(<var>+Set1,
241	282	+Set2</var>)</a></dt>
242	283	<dd class="defbody">
243	284	True if <var>Set1</var> and <var>Set2</var> have the same elements. As

251	292	</dl>
252	293
253	294	</dd>
254		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="list_to_ord_set/2"><strong>list_to_ord_set</strong>(<var>+List,
	295	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="list_to_ord_set/2"><strong>list_to_ord_set</strong>(<var>+List,
255	296	-OrdSet</var>)</a></dt>
256	297	<dd class="defbody">
257	298	Transform a list into an ordered set. This is the same as sorting the
258	299	list.</dd>
259		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="ord_intersect/2"><strong>ord_intersect</strong>(<var>+Set1,
	300	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="ord_intersect/2"><strong>ord_intersect</strong>(<var>+Set1,
260	301	+Set2</var>)</a></dt>
261	302	<dd class="defbody">
262	303	True if both ordered sets have a non-empty intersection.</dd>
263		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="ord_disjoint/2"><strong>ord_disjoint</strong>(<var>+Set1,
	304	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="ord_disjoint/2"><strong>ord_disjoint</strong>(<var>+Set1,
264	305	+Set2</var>)</a></dt>
265	306	<dd class="defbody">
266	307	True if <var>Set1</var> and <var>Set2</var> have no common elements.
267	308	This is the negation of <a class="pred" href="ordsets.html#ord_intersect/2">ord_intersect/2</a>.</dd>
268		<dt class="pubdef"><a name="ord_intersect/3"><strong>ord_intersect</strong>(<var>+Set1,
	309	<dt class="pubdef"><a id="ord_intersect/3"><strong>ord_intersect</strong>(<var>+Set1,
269	310	+Set2, -Intersection</var>)</a></dt>
270	311	<dd class="defbody">
271	312	<var>Intersection</var> holds the common elements of <var>Set1</var> and <var>Set2</var>.

278	319	</dl>
279	320
280	321	</dd>
281		<dt class="pubdef"><a name="ord_intersection/2"><strong>ord_intersection</strong>(<var>+PowerSet,
	322	<dt class="pubdef"><a id="ord_intersection/2"><strong>ord_intersection</strong>(<var>+PowerSet,
282	323	-Intersection</var>)</a></dt>
283	324	<dd class="defbody">
284	325	<var>Intersection</var> of a powerset. True when <var>Intersection</var>

292	333	</dl>
293	334
294	335	</dd>
295		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_intersection/3"><strong>ord_intersection</strong>(<var>+Set1,
	336	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_intersection/3"><strong>ord_intersection</strong>(<var>+Set1,
296	337	+Set2, -Intersection</var>)</a></dt>
297	338	<dd class="defbody">
298	339	<var>Intersection</var> holds the common elements of <var>Set1</var> and <var>Set2</var>.
299	340	Uses
300	341	<a class="pred" href="ordsets.html#ord_disjoint/2">ord_disjoint/2</a> if <var>Intersection</var>
301	342	is bound to <code>[]</code> on entry.</dd>
302		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_intersection/4"><strong>ord_intersection</strong>(<var>+Set1,
	343	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_intersection/4"><strong>ord_intersection</strong>(<var>+Set1,
303	344	+Set2, ?Intersection, ?Difference</var>)</a></dt>
304	345	<dd class="defbody">
305	346	<var>Intersection</var> and difference between two ordered sets.

316	357	</dl>
317	358
318	359	</dd>
319		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_add_element/3"><strong>ord_add_element</strong>(<var>+Set1,
	360	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_add_element/3"><strong>ord_add_element</strong>(<var>+Set1,
320	361	+Element, ?Set2</var>)</a></dt>
321	362	<dd class="defbody">
322	363	Insert an element into the set. This is the same as
323	364	<code>ord_union(Set1, [Element], Set2)</code>.</dd>
324		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_del_element/3"><strong>ord_del_element</strong>(<var>+Set,
	365	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_del_element/3"><strong>ord_del_element</strong>(<var>+Set,
325	366	+Element, -NewSet</var>)</a></dt>
326	367	<dd class="defbody">
327	368	Delete an element from an ordered set. This is the same as
328	369	<code>ord_subtract(Set, [Element], NewSet)</code>.</dd>
329		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="ord_selectchk/3"><strong>ord_selectchk</strong>(<var>+Item,
	370	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="ord_selectchk/3"><strong>ord_selectchk</strong>(<var>+Item,
330	371	?Set1, ?Set2</var>)</a></dt>
331	372	<dd class="defbody">
332	373	Selectchk/3, specialised for ordered sets. Is true when

346	387	</dl>
347	388
348	389	</dd>
349		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="ord_memberchk/2"><strong>ord_memberchk</strong>(<var>+Element,
	390	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="ord_memberchk/2"><strong>ord_memberchk</strong>(<var>+Element,
350	391	+OrdSet</var>)</a></dt>
351	392	<dd class="defbody">
352	393	True if <var>Element</var> is a member of <var>OrdSet</var>, compared

370	411	</dl>
371	412
372	413	</dd>
373		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="ord_subset/2"><strong>ord_subset</strong>(<var>+Sub,
	414	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="ord_subset/2"><strong>ord_subset</strong>(<var>+Sub,
374	415	+Super</var>)</a></dt>
375	416	<dd class="defbody">
376	417	Is true if all elements of <var>Sub</var> are in <var>Super</var></dd>
377		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_subtract/3"><strong>ord_subtract</strong>(<var>+InOSet,
	418	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_subtract/3"><strong>ord_subtract</strong>(<var>+InOSet,
378	419	+NotInOSet, -Diff</var>)</a></dt>
379	420	<dd class="defbody">
380	421	<var>Diff</var> is the set holding all elements of <var>InOSet</var>
381	422	that are not in
382	423	<var>NotInOSet</var>.</dd>
383		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_union/2"><strong>ord_union</strong>(<var>+SetOfSets,
	424	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_union/2"><strong>ord_union</strong>(<var>+SetOfSets,
384	425	-Union</var>)</a></dt>
385	426	<dd class="defbody">
386	427	True if <var>Union</var> is the union of all elements in the superset

395	436	</dl>
396	437
397	438	</dd>
398		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_union/3"><strong>ord_union</strong>(<var>+Set1,
	439	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_union/3"><strong>ord_union</strong>(<var>+Set1,
399	440	+Set2, ?Union</var>)</a></dt>
400	441	<dd class="defbody">
401	442	<var>Union</var> is the union of <var>Set1</var> and <var>Set2</var></dd>
402		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_union/4"><strong>ord_union</strong>(<var>+Set1,
	443	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_union/4"><strong>ord_union</strong>(<var>+Set1,
403	444	+Set2, -Union, -New</var>)</a></dt>
404	445	<dd class="defbody">
405	446	True iff <code>ord_union(Set1, Set2, Union)</code> and
406	447	<code>ord_subtract(Set2, Set1, New)</code>.</dd>
407		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="ord_symdiff/3"><strong>ord_symdiff</strong>(<var>+Set1,
	448	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="ord_symdiff/3"><strong>ord_symdiff</strong>(<var>+Set1,
408	449	+Set2, ?Difference</var>)</a></dt>
409	450	<dd class="defbody">
410	451	Is true when <var>Difference</var> is the symmetric difference of <var>Set1</var>

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193	234	</div>
194		<h2 id="sec:otherlicenses"><a name="sec:E.3"><span class="sec-nr">E.3</span> <span class="sec-title">License
	235	<h2 id="sec:otherlicenses"><a id="sec:E.3"><span class="sec-nr">E.3</span> <span class="sec-title">License
195	236	conditions inherited from used code</span></a></h2>
196	237
197		<a name="sec:otherlicenses"></a>
198
199		<p><h3 id="sec:cryptlicense"><a name="sec:E.3.1"><span class="sec-nr">E.3.1</span> <span class="sec-title">Cryptographic
	238	<a id="sec:otherlicenses"></a>
	239
	240	<p><h3 id="sec:cryptlicense"><a id="sec:E.3.1"><span class="sec-nr">E.3.1</span> <span class="sec-title">Cryptographic
200	241	routines</span></a></h3>
201	242
202		<a name="sec:cryptlicense"></a>
203
204		<p>Cryptographic routines are used in <a name="idx:variantsha12:2344"></a><a class="pred" href="db.html#variant_sha1/2">variant_sha1/2</a>
	243	<a id="sec:cryptlicense"></a>
	244
	245	<p>Cryptographic routines are used in <a id="idx:variantsha12:2348"></a><a class="pred" href="db.html#variant_sha1/2">variant_sha1/2</a>
205	246	and <code>library(crypt)</code>. These routines are provided under the
206	247	following conditions:
207	248

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193	234	</div>
194		<h2 id="sec:overrule"><a name="sec:6.5"><span class="sec-nr">6.5</span> <span class="sec-title">Overruling
	235	<h2 id="sec:overrule"><a id="sec:6.5"><span class="sec-nr">6.5</span> <span class="sec-title">Overruling
195	236	Module Boundaries</span></a></h2>
196	237
197		<a name="sec:overrule"></a>
	238	<a id="sec:overrule"></a>
198	239
199	240	<p>The module system described so far is sufficient to distribute
200	241	programs over multiple modules. There are, however, cases in which we

206	247	cannot be achieved using importing because importing a predicate with
207	248	the same name and arity from two modules results in a name conflict.
208	249	Asserting in a different module can be used to create models dynamically
209		in a new module. See <a class="sec" href="dynamic-modules.html">section
	250	in a new module. See <a class="sec" href="dynamic-modules.html#sec:6.12">section
210	251	6.12</a>.
211	252
212	253	<p>Direct addressing of modules is achieved using a <code><code>:</code>/2</code>
213	254	explicitly in a program and relies on the module qualification mechanism
214		described in <a class="sec" href="metapred.html">section 6.4</a>. Here
215		are a few examples:
	255	described in <a class="sec" href="metapred.html#sec:6.4">section 6.4</a>.
	256	Here are a few examples:
216	257
217	258	<pre class="code">
218	259	?- assert(world:done). % asserts done/0 into module world

222	263
223	264	<p>Note that the second example is the same due to the Prolog flag
224	265	<a class="flag" href="flags.html#flag:colon_sets_calling_context">colon_sets_calling_context</a>.
225		The system predicate <a name="idx:asserta1:1702"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
	266	The system predicate <a id="idx:asserta1:1706"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
226	267	is called in the module <code>world</code>, which is possible because
227	268	system predicates are <em>visible</em> in all modules. At the same time,
228	269	the

230	271	arguments are qualified with the calling context, the resulting call is
231	272	the same as the first example.
232	273
233		<p><h3 id="sec:set-calling-context"><a name="sec:6.5.1"><span class="sec-nr">6.5.1</span> <span class="sec-title">Explicit
	274	<p><h3 id="sec:set-calling-context"><a id="sec:6.5.1"><span class="sec-nr">6.5.1</span> <span class="sec-title">Explicit
234	275	manipulation of the calling context</span></a></h3>
235	276
236		<a name="sec:set-calling-context"></a>
	277	<a id="sec:set-calling-context"></a>
237	278
238	279	<p>Quintus' derived module systems have no means to separate the lookup
239	280	module (for finding predicates) from the calling context (for qualifying

243	284	currently mainly to support compatibility layers.
244	285
245	286	<dl class="latex">
246		<dt class="pubdef"><a name="@/2"><strong>@</strong>(<var>:Goal, +Module</var>)</a></dt>
	287	<dt class="pubdef"><a id="@/2"><strong>@</strong>(<var>:Goal, +Module</var>)</a></dt>
247	288	<dd class="defbody">
248	289	Execute <var>Goal</var>, setting the calling context to <var>Module</var>.
249	290	Setting the calling context affects meta-predicates, for which meta
250	291	arguments are qualified with <var>Module</var> and transparent
251	292	predicates (see
252		<a name="idx:moduletransparent1:1703"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>).
	293	<a id="idx:moduletransparent1:1707"></a><a class="pred" href="ctxmodule.html#module_transparent/1">module_transparent/1</a>).
253	294	It has no implications for other predicates.
254	295
255	296	<p>For example, the code <code>asserta(done)@world</code> is the same as
256	297	<code>asserta(world:done)</code>. Unlike in <code>world:asserta(done)</code>,
257		<a name="idx:asserta1:1704"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
	298	<a id="idx:asserta1:1708"></a><a class="pred" href="db.html#asserta/1">asserta/1</a>
258	299	is resolved in the current module rather than the module
259	300	<code>world</code>. This makes no difference for system predicates, but
260	301	usually does make a difference for user predicates.

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194		<h1 id="sec:overview"><a name="sec:2"><span class="sec-nr">2</span> <span class="sec-title">Overview</span></a></h1>
195
196		<a name="sec:overview"></a>
	235	<h1 id="sec:overview"><a id="sec:2"><span class="sec-nr">2</span> <span class="sec-title">Overview</span></a></h1>
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197	238
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193	234	</div>
194		<h2 id="sec:packs"><a name="sec:2.14"><span class="sec-nr">2.14</span> <span class="sec-title">Packs:
	235	<h2 id="sec:packs"><a id="sec:2.14"><span class="sec-nr">2.14</span> <span class="sec-title">Packs:
195	236	community add-ons</span></a></h2>
196	237
197		<a name="sec:packs"></a>
	238	<a id="sec:packs"></a>
198	239
199	240	<p>SWI-Prolog has a mechanism for easy incorporation of community
200		extensions. See the http://www.swi-prolog.org/pack/listpack landing page
201		for details and available packs. This section documents the built-in
202		predicates to attach packs. Predicates for creating, registering and
203		installing packs are provided by the library
	241	extensions. See the <a class="url" href="http://www.swi-prolog.org/pack/list">pack
	242	landing page</a> for details and available packs. This section documents
	243	the built-in predicates to attach packs. Predicates for creating,
	244	registering and installing packs are provided by the library
204	245	<code>library(prolog_pack)</code>.
205	246
206	247	<dl class="latex">
207		<dt class="pubdef"><a name="attach_packs/0"><strong>attach_packs</strong></a></dt>
	248	<dt class="pubdef"><a id="attach_packs/0"><strong>attach_packs</strong></a></dt>
208	249	<dd class="defbody">
209	250	Attaches all packs in subdirectories of directories that are accessible
210		through the <em>file search path</em> (see <a name="idx:absolutefilename3:208"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>)
	251	through the <em>file search path</em> (see <a id="idx:absolutefilename3:208"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>)
211	252	<code>pack</code>. The default for this search path is:
212	253
213	254	<pre class="code">

215	256	user:file_search_path(pack, swi(pack)).
216	257	</pre>
217	258
218		<p>The predicate <a name="idx:attachpacks0:209"></a><a class="pred" href="packs.html#attach_packs/0">attach_packs/0</a>
	259	<p>The predicate <a id="idx:attachpacks0:209"></a><a class="pred" href="packs.html#attach_packs/0">attach_packs/0</a>
219	260	is called on startup of SWI-Prolog.</dd>
220		<dt class="pubdef"><a name="attach_packs/1"><strong>attach_packs</strong>(<var>+Directory</var>)</a></dt>
	261	<dt class="pubdef"><a id="attach_packs/1"><strong>attach_packs</strong>(<var>+Directory</var>)</a></dt>
221	262	<dd class="defbody">
222	263	Attach all packs in subdirectories of <var>Directory</var>. Same as
223	264	<code>attach_packs(Directory,[])</code>.
224	265	</dd>
225		<dt class="pubdef"><a name="attach_packs/2"><strong>attach_packs</strong>(<var>+Directory,
	266	<dt class="pubdef"><a id="attach_packs/2"><strong>attach_packs</strong>(<var>+Directory,
226	267	+Options</var>)</a></dt>
227	268	<dd class="defbody">
228	269	Attach all packs in subdirectories of <var>Directory</var>. Options is

244	285	</dd>
245	286	</dl>
246	287
247		<p>The predicate <a name="idx:attachpacks2:210"></a><a class="pred" href="packs.html#attach_packs/2">attach_packs/2</a>
	288	<p>The predicate <a id="idx:attachpacks2:210"></a><a class="pred" href="packs.html#attach_packs/2">attach_packs/2</a>
248	289	can be used to attach packages that are bundled with an application.
249	290	</dd>
250	291	</dl>

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193	234	</div>
194		<h2 id="sec:pairs"><a name="sec:A.22"><span class="sec-nr">A.22</span> <span class="sec-title">library(pairs):
	235	<h2 id="sec:pairs"><a id="sec:A.22"><span class="sec-nr">A.22</span> <span class="sec-title">library(pairs):
195	236	Operations on key-value lists</span></a></h2>
196	237
197		<p><a name="sec:pairs"></a>
	238	<p><a id="sec:pairs"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">author</dt>

218	259	O'Keefe.
219	260
220	261	<dl class="latex">
221		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pairs_keys_values/3"><strong>pairs_keys_values</strong>(<var>?Pairs,
	262	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pairs_keys_values/3"><strong>pairs_keys_values</strong>(<var>?Pairs,
222	263	?Keys, ?Values</var>)</a></dt>
223	264	<dd class="defbody">
224	265	True if <var>Keys</var> holds the keys of <var>Pairs</var> and <var>Values</var>

236	277	</dl>
237	278
238	279	</dd>
239		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pairs_values/2"><strong>pairs_values</strong>(<var>+Pairs,
	280	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pairs_values/2"><strong>pairs_values</strong>(<var>+Pairs,
240	281	-Values</var>)</a></dt>
241	282	<dd class="defbody">
242	283	Remove the keys from a list of Key-Value pairs. Same as
243	284	<code>pairs_keys_values(Pairs, _, Values)</code></dd>
244		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pairs_keys/2"><strong>pairs_keys</strong>(<var>+Pairs,
	285	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pairs_keys/2"><strong>pairs_keys</strong>(<var>+Pairs,
245	286	-Keys</var>)</a></dt>
246	287	<dd class="defbody">
247	288	Remove the values from a list of Key-Value pairs. Same as
248	289	<code>pairs_keys_values(Pairs, Keys, _)</code></dd>
249		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="group_pairs_by_key/2"><strong>group_pairs_by_key</strong>(<var>+Pairs,
	290	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="group_pairs_by_key/2"><strong>group_pairs_by_key</strong>(<var>+Pairs,
250	291	-Joined:list(Key-Values)</var>)</a></dt>
251	292	<dd class="defbody">
252	293	Group values with equivalent (<a class="pred" href="compare.html#==/2">==/2</a>)

273	314	is 1) ensures that the order of the values in the original list of pairs
274	315	is maintained.
275	316	<table class="arglist">
276		<tr valign="top"><td><var>Pairs</var> </td><td><var>Key</var>-Value list </td></tr>
277		<tr valign="top"><td><var>Joined</var> </td><td>List of <var>Key</var>-Group,
278		where Group is the list of <var>Values</var> associated with equivalent
	317	<tr><td><var>Pairs</var> </td><td><var>Key</var>-Value list </td></tr>
	318	<tr><td><var>Joined</var> </td><td>List of <var>Key</var>-Group, where
	319	Group is the list of <var>Values</var> associated with equivalent
279	320	consecutive Keys in the same order as they appear in <var>Pairs</var>. </td></tr>
280	321	</table>
281	322	</dd>
282		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="transpose_pairs/2"><strong>transpose_pairs</strong>(<var>+Pairs,
	323	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="transpose_pairs/2"><strong>transpose_pairs</strong>(<var>+Pairs,
283	324	-Transposed</var>)</a></dt>
284	325	<dd class="defbody">
285	326	Swap Key-Value to Value-Key. The resulting list is sorted using
286	327	<a class="pred" href="builtinlist.html#keysort/2">keysort/2</a> on the
287	328	new key.</dd>
288		<dt class="pubdef"><a name="map_list_to_pairs/3"><strong>map_list_to_pairs</strong>(<var>:Function,
	329	<dt class="pubdef"><a id="map_list_to_pairs/3"><strong>map_list_to_pairs</strong>(<var>:Function,
289	330	+List, -Keyed</var>)</a></dt>
290	331	<dd class="defbody">
291	332	Create a Key-Value list by mapping each element of <var>List</var>. For

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193	234	</div>
194		<h2 id="sec:pceemacs"><a name="sec:3.4"><span class="sec-nr">3.4</span> <span class="sec-title">Using
	235	<h2 id="sec:pceemacs"><a id="sec:3.4"><span class="sec-nr">3.4</span> <span class="sec-title">Using
195	236	the PceEmacs built-in editor</span></a></h2>
196	237
197		<a name="sec:pceemacs"></a>
198
199		<p><h3 id="sec:runpceemacs"><a name="sec:3.4.1"><span class="sec-nr">3.4.1</span> <span class="sec-title">Activating
	238	<a id="sec:pceemacs"></a>
	239
	240	<p><h3 id="sec:runpceemacs"><a id="sec:3.4.1"><span class="sec-nr">3.4.1</span> <span class="sec-title">Activating
200	241	PceEmacs</span></a></h3>
201	242
202		<a name="sec:runpceemacs"></a>
203
204		<p>Initially <a name="idx:edit1:309"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	243	<a id="sec:runpceemacs"></a>
	244
	245	<p>Initially <a id="idx:edit1:309"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
205	246	uses the editor specified in the <code>EDITOR</code> environment
206	247	variable. There are two ways to force it to use the built-in editor. One
207	248	is to set the Prolog flag <a class="flag" href="flags.html#flag:editor">editor</a>
208	249	to
209	250	<code>pce_emacs</code> and the other is by starting the editor
210		explicitly using the emacs[0,1] predicates.
211
212		<p><h3 id="sec:emacsbluff"><a name="sec:3.4.2"><span class="sec-nr">3.4.2</span> <span class="sec-title">Bluffing
	251	explicitly using the emacs/[0,1] predicates.
	252
	253	<p><h3 id="sec:emacsbluff"><a id="sec:3.4.2"><span class="sec-nr">3.4.2</span> <span class="sec-title">Bluffing
213	254	through PceEmacs</span></a></h3>
214	255
215		<a name="sec:emacsbluff"></a>
	256	<a id="sec:emacsbluff"></a>
216	257
217	258	<p>PceEmacs closely mimics Richard Stallman's GNU-Emacs commands, adding
218	259	features from modern window-based editors to make it more acceptable for

222	263	important GNU-Emacs commands.</span></sup>
223	264
224	265	<p>At the basis, PceEmacs maps keyboard sequences to methods defined on
225		the extended object. Some frequently used commands are, with their
226		key-binding, presented in the menu bar above each editor window. A
227		complete overview of the bindings for the current <em>mode</em> is
228		provided through <strong>Help/Show key bindings</strong> (<code>Control-h
	266	the extended <i>editor</i> object. Some frequently used commands are,
	267	with their key-binding, presented in the menu bar above each editor
	268	window. A complete overview of the bindings for the current <em>mode</em>
	269	is provided through <strong>Help/Show key bindings</strong> (<code>Control-h
229	270	Control-b</code>).
230	271
231		<p><h4 id="sec:pceemacsmodes"><a name="sec:3.4.2.1"><span class="sec-nr">3.4.2.1</span> <span class="sec-title">Edit
	272	<p><h4 id="sec:pceemacsmodes"><a id="sec:3.4.2.1"><span class="sec-nr">3.4.2.1</span> <span class="sec-title">Edit
232	273	modes</span></a></h4>
233	274
234		<a name="sec:pceemacsmodes"></a>
	275	<a id="sec:pceemacsmodes"></a>
235	276
236	277	<p>Modes are the heart of (Pce)Emacs. Modes define dedicated editing
237	278	support for a particular kind of (source) text. For our purpose we want

261	302	Prolog mode explicitly.
262	303	</ul>
263	304
264		<p><h4 id="sec:pceemacscommands"><a name="sec:3.4.2.2"><span class="sec-nr">3.4.2.2</span> <span class="sec-title">Frequently
	305	<p><h4 id="sec:pceemacscommands"><a id="sec:3.4.2.2"><span class="sec-nr">3.4.2.2</span> <span class="sec-title">Frequently
265	306	used editor commands</span></a></h4>
266	307
267		<a name="sec:pceemacscommands"></a>
	308	<a id="sec:pceemacscommands"></a>
268	309
269	310	<p>Below we list a few important commands and how to activate them.
270	311

366	407	</ul>
367	408
368	409	<p>These are the most commonly used commands. In
369		<a class="sec" href="pceemacs.html">section 3.4.3</a> we discuss
370		specific support for dealing with Prolog source code.
371
372		<p><h3 id="sec:emacsprologmode"><a name="sec:3.4.3"><span class="sec-nr">3.4.3</span> <span class="sec-title">Prolog
	410	<a class="sec" href="pceemacs.html#sec:3.4.3">section 3.4.3</a> we
	411	discuss specific support for dealing with Prolog source code.
	412
	413	<p><h3 id="sec:emacsprologmode"><a id="sec:3.4.3"><span class="sec-nr">3.4.3</span> <span class="sec-title">Prolog
373	414	Mode</span></a></h3>
374	415
375		<a name="sec:emacsprologmode"></a>
376
377		<p>In the previous section (<a class="sec" href="pceemacs.html">section
	416	<a id="sec:emacsprologmode"></a>
	417
	418	<p>In the previous section (<a class="sec" href="pceemacs.html#sec:3.4.2">section
378	419	3.4.2</a>) we explained the basics of PceEmacs. Here we continue with
379	420	Prolog-specific functionality. Possibly the most interesting is <em>Syntax
380	421	highlighting</em>. Unlike most editors where this is based on simple

425	466	Other colours follow intuitive conventions. See <a class="tab" href="pceemacs.html#tab:plcolour">table
426	467	3</a>.
427	468
428		<p><table border="2" frame="box" rules="groups" style="margin:auto">
429		<tr valign="top"><td colspan=2 align=center>Clauses</tr>
430		<tbody>
431		<tr valign="top"><td>Blue bold</td><td>Head of an exported predicate </td></tr>
432		<tr valign="top"><td>Red bold</td><td>Head of a predicate that is not
433		called </td></tr>
434		<tr valign="top"><td>Black bold</td><td>Head of remaining predicates </td></tr>
435		<tbody>
436		<tr valign="top"><td colspan=2 align=center>Calls in the clause body</tr>
437		<tbody>
438		<tr valign="top"><td>Blue</td><td>Call to built-in or imported predicate </td></tr>
439		<tr valign="top"><td>Red</td><td>Call to undefined predicate </td></tr>
440		<tr valign="top"><td>Purple</td><td>Call to dynamic predicate </td></tr>
441		<tbody>
442		<tr valign="top"><td colspan=2 align=center>Other entities</tr>
443		<tbody>
444		<tr valign="top"><td>Dark green</td><td>Comment </td></tr>
445		<tr valign="top"><td>Dark blue</td><td>Quoted atom or string </td></tr>
446		<tr valign="top"><td>Brown</td><td>Variable </td></tr>
	469	<p><table class="latex frame-box center">
	470	<tr><td colspan=2 align=center>Clauses</tr>
	471	<tr class="hline"><td>Blue bold</td><td>Head of an exported predicate </td></tr>
	472	<tr><td>Red bold</td><td>Head of a predicate that is not called </td></tr>
	473	<tr><td>Black bold</td><td>Head of remaining predicates </td></tr>
	474	<tr class="hline"><td colspan=2 align=center>Calls in the clause body</tr>
	475	<tr class="hline"><td>Blue</td><td>Call to built-in or imported
	476	predicate </td></tr>
	477	<tr><td>Red</td><td>Call to undefined predicate </td></tr>
	478	<tr><td>Purple</td><td>Call to dynamic predicate </td></tr>
	479	<tr class="hline"><td colspan=2 align=center>Other entities</tr>
	480	<tr class="hline"><td>Dark green</td><td>Comment </td></tr>
	481	<tr><td>Dark blue</td><td>Quoted atom or string </td></tr>
	482	<tr><td>Brown</td><td>Variable </td></tr>
447	483	</table>
448		<a name="tab:plcolour"></a>
	484	<a id="tab:plcolour"></a>
449	485	<div class="caption"><b>Table 3 : </b>Colour conventions</div>
450	486
451	487	<p><b>Layout support</b>

498	534	calls (indented 1 tab), if-then-else, disjunction and argument lists
499	535	broken across multiple lines as illustrated above.
500	536
501		<p><h4 id="sec:pceemacshelp"><a name="sec:3.4.3.1"><span class="sec-nr">3.4.3.1</span> <span class="sec-title">Finding
	537	<p><h4 id="sec:pceemacshelp"><a id="sec:3.4.3.1"><span class="sec-nr">3.4.3.1</span> <span class="sec-title">Finding
502	538	your way around</span></a></h4>
503	539
504		<a name="sec:pceemacshelp"></a>
	540	<a id="sec:pceemacshelp"></a>
505	541
506	542	<p>The command <code>Alt-.</code> extracts name and arity from the caret
507	543	location and jumps (after conformation or edit) to the definition of the
508	544	predicate. It does so based on the source-location database of loaded
509		predicates also used by <a name="idx:edit1:310"></a><a class="pred" href="edit.html#edit/1">edit/1</a>.
	545	predicates also used by <a id="idx:edit1:310"></a><a class="pred" href="edit.html#edit/1">edit/1</a>.
510	546	This makes locating predicates reliable if all sources are loaded and
511		up-to-date (see <a name="idx:make0:311"></a><a class="pred" href="consulting.html#make/0">make/0</a>).
512
513		<p>In addition, references to files in <a name="idx:usemodule12:312"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>, <a name="idx:consult1:313"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
	547	up-to-date (see <a id="idx:make0:311"></a><a class="pred" href="consulting.html#make/0">make/0</a>).
	548
	549	<p>In addition, references to files in <a id="idx:usemodule12:312"></a><a class="pred" href="import.html#use_module/1">use_module/[1,2]</a>, <a id="idx:consult1:313"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
514	550	etc. are red if the file cannot be found and underlined blue if the file
515	551	can be loaded. A popup allows for opening the referenced file.
516	552

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.23</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.23</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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130
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133		sup.fn span {display: none;}
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141	155	}
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	198
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	204
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	207	}
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186	227	<body style="background:white">

191	232	<a class="nav" href="pairs.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="pio.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:persistency"><a name="sec:A.23"><span class="sec-nr">A.23</span> <span class="sec-title">library(persistency):
	235	<h2 id="sec:persistency"><a id="sec:A.23"><span class="sec-nr">A.23</span> <span class="sec-title">library(persistency):
195	236	Provide persistent dynamic predicates</span></a></h2>
196	237
197		<p><a name="sec:persistency"></a>
	238	<p><a id="sec:persistency"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="mtag">To be done</dt>

263	304	</pre>
264	305
265	306	<dl class="latex">
266		<dt class="pubdef"><a name="persistent/1"><strong>persistent</strong> <var>+Spec</var></a></dt>
	307	<dt class="pubdef"><a id="persistent/1"><strong>persistent</strong> <var>+Spec</var></a></dt>
267	308	<dd class="defbody">
268	309	Declare dynamic database terms. Declarations appear in a directive and
269	310	have the following format:

283	324	</pre>
284	325
285	326	<p>Types are defined by <code>library(error)</code>.</dd>
286		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_persistent_predicate/1"><strong>current_persistent_predicate</strong>(<var>:PI</var>)</a></dt>
	327	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_persistent_predicate/1"><strong>current_persistent_predicate</strong>(<var>:PI</var>)</a></dt>
287	328	<dd class="defbody">
288	329	True if <var>PI</var> is a predicate that provides access to the
289	330	persistent database DB.</dd>
290		<dt class="pubdef"><a name="db_attach/2"><strong>db_attach</strong>(<var>:File,
	331	<dt class="pubdef"><a id="db_attach/2"><strong>db_attach</strong>(<var>:File,
291	332	+Options</var>)</a></dt>
292	333	<dd class="defbody">
293	334	Use <var>File</var> as persistent database for the calling module. The

305	346
306	347	<p>If <var>File</var> is already attached this operation may change the <code>sync</code>
307	348	behaviour.</dd>
308		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="db_attached/1"><strong>db_attached</strong>(<var>:File</var>)</a></dt>
	349	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="db_attached/1"><strong>db_attached</strong>(<var>:File</var>)</a></dt>
309	350	<dd class="defbody">
310	351	True if the context module attached to the persistent database <var>File</var>.</dd>
311		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="db_detach/0"><strong>db_detach</strong></a></dt>
	352	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="db_detach/0"><strong>db_detach</strong></a></dt>
312	353	<dd class="defbody">
313	354	Detach persistency from the calling module and delete all persistent
314	355	clauses from the Prolog database. Note that the file is not affected.
315	356	After this operation another file may be attached, providing it
316	357	satisfies the same persistency declaration.</dd>
317		<dt class="pubdef"><a name="db_sync/1"><strong>db_sync</strong>(<var>:What</var>)</a></dt>
	358	<dt class="pubdef"><a id="db_sync/1"><strong>db_sync</strong>(<var>:What</var>)</a></dt>
318	359	<dd class="defbody">
319	360	Synchronise database with the associated file. <var>What</var> is one
320	361	of:

358	399	<p>With unbound <var>What</var>, <a class="pred" href="persistency.html#db_sync/1">db_sync/1</a>
359	400	reloads the database if it was modified on disk, gc it if it is dirty
360	401	and close it if it is opened.</dd>
361		<dt class="pubdef"><a name="db_sync_all/1"><strong>db_sync_all</strong>(<var>+What</var>)</a></dt>
	402	<dt class="pubdef"><a id="db_sync_all/1"><strong>db_sync_all</strong>(<var>+What</var>)</a></dt>
362	403	<dd class="defbody">
363	404	Sync all registered databases.
364	405	</dd>

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2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.24</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.24</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

17	17	{ margin-bottom: 1em;
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	28
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27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
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122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
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141	155	}
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191	232	<a class="nav" href="persistency.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="predicate_options.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:pio"><a name="sec:A.24"><span class="sec-nr">A.24</span> <span class="sec-title">library(pio):
	235	<h2 id="sec:pio"><a id="sec:A.24"><span class="sec-nr">A.24</span> <span class="sec-title">library(pio):
195	236	Pure I/O</span></a></h2>
196	237
197		<a name="sec:pio"></a>
198		<a name="sec:lib:pio"></a>
	238	<a id="sec:pio"></a>
	239	<a id="sec:lib:pio"></a>
199	240
200	241	<p>This library provides pure list-based I/O processing for Prolog,
201	242	where the communication to the actual I/O device is performed
202	243	transparently through coroutining. This module itself is just an
203	244	interface to the actual implementation modules.
204	245
205		<p><h3 id="sec:pureinput"><a name="sec:A.24.1"><span class="sec-nr">A.24.1</span> <span class="sec-title">library(pure_input):
	246	<p><h3 id="sec:pureinput"><a id="sec:A.24.1"><span class="sec-nr">A.24.1</span> <span class="sec-title">library(pure_input):
206	247	Pure Input from files and streams</span></a></h3>
207	248
208		<p><a name="sec:pureinput"></a>
	249	<p><a id="sec:pureinput"></a>
209	250
210	251	<dl class="tags">
211	252	<dt class="tag">To be done</dt>

232	273	attribute handling to realise pure input on any (buffered) stream.
233	274
234	275	<dl class="latex">
235		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="phrase_from_file/2"><strong>phrase_from_file</strong>(<var>:Grammar,
	276	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="phrase_from_file/2"><strong>phrase_from_file</strong>(<var>:Grammar,
236	277	+File</var>)</a></dt>
237	278	<dd class="defbody">
238	279	Process the content of <var>File</var> using the DCG rule <var>Grammar</var>.

242	283	on demand due to unification of the attributed tail variable. Below is
243	284	an example that counts the number of times a string appears in a file.
244	285	The library dcg/basics provides
245		<span class="pred-ext">string/3</span> matching an arbitrary string and <span class="pred-ext">remainder/3</span>
	286	<span class="pred-ext">string//1</span> matching an arbitrary string and <span class="pred-ext">remainder//1</span>
246	287	which matches the remainder of the input without parsing.
247	288
248	289	<pre class="code">

268	309	</pre>
269	310
270	311	</dd>
271		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="phrase_from_file/3"><strong>phrase_from_file</strong>(<var>:Grammar,
	312	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="phrase_from_file/3"><strong>phrase_from_file</strong>(<var>:Grammar,
272	313	+File, +Options</var>)</a></dt>
273	314	<dd class="defbody">
274	315	As <a class="pred" href="pio.html#phrase_from_file/2">phrase_from_file/2</a>,
275	316	providing additional <var>Options</var>. <var>Options</var> are passed
276	317	to <a class="pred" href="IO.html#open/4">open/4</a>.</dd>
277		<dt class="pubdef"><a name="phrase_from_stream/2"><strong>phrase_from_stream</strong>(<var>:Grammar,
	318	<dt class="pubdef"><a id="phrase_from_stream/2"><strong>phrase_from_stream</strong>(<var>:Grammar,
278	319	+Stream</var>)</a></dt>
279	320	<dd class="defbody">
280	321	Run Grammer against the character codes on <var>Stream</var>. <var>Stream</var>
281	322	must be buffered.</dd>
282		<dt class="pubdef"><a name="syntax_error/1"><strong>syntax_error</strong>(<var>+Error</var>)</a><code>//</code></dt>
	323	<dt class="pubdef"><a id="syntax_error//1"><strong>syntax_error</strong>(<var>+Error</var>)</a><code>//</code></dt>
283	324	<dd class="defbody">
284	325	Throw the syntax error <var>Error</var> at the current location of the
285	326	input. This predicate is designed to be called from the handler of <a class="pred" href="pio.html#phrase_from_file/3">phrase_from_file/3</a>.

292	333	</dl>
293	334
294	335	</dd>
295		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="lazy_list_location/1"><strong>lazy_list_location</strong>(<var>-Location</var>)</a><code>//</code></dt>
	336	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="lazy_list_location//1"><strong>lazy_list_location</strong>(<var>-Location</var>)</a><code>//</code></dt>
296	337	<dd class="defbody">
297	338	Determine current (error) location in a lazy list. True when
298	339	<var>Location</var> is an (error) location term that represents the
299	340	current location in the DCG list.
300	341	<table class="arglist">
301		<tr valign="top"><td><var>Location</var> </td><td>is a term <code>file(Name, Line, LinePos, CharNo)</code>
	342	<tr><td><var>Location</var> </td><td>is a term <code>file(Name, Line, LinePos, CharNo)</code>
302	343	or
303	344	<code>stream(Stream, Line, LinePos, CharNo)</code> if no file is
304	345	associated to the stream RestLazyList. Finally, if the Lazy list is

309	350	<dl class="tags">
310	351	<dt class="tag">See also</dt>
311	352	<dd>
312		<span class="pred-ext">lazy_list_character_count/3</span> only provides
313		the character count.
314		</dd>
315		</dl>
316
317		</dd>
318		<dt class="pubdef"><a name="lazy_list_character_count/1"><strong>lazy_list_character_count</strong>(<var>-CharCount</var>)</a><code>//</code></dt>
	353	<a class="pred" href="pio.html#lazy_list_character_count//1">lazy_list_character_count//1</a>
	354	only provides the character count.
	355	</dd>
	356	</dl>
	357
	358	</dd>
	359	<dt class="pubdef"><a id="lazy_list_character_count//1"><strong>lazy_list_character_count</strong>(<var>-CharCount</var>)</a><code>//</code></dt>
319	360	<dd class="defbody">
320	361	True when <var>CharCount</var> is the current character count in the
321	362	Lazy list. The character count is computed by finding the distance to

330	371	<dl class="tags">
331	372	<dt class="tag">See also</dt>
332	373	<dd>
333		<span class="pred-ext">lazy_list_location/3</span> provides full details
334		of the location for error reporting.
335		</dd>
336		</dl>
337
338		</dd>
339		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="stream_to_lazy_list/2"><strong>stream_to_lazy_list</strong>(<var>+Stream,
	374	<a class="pred" href="pio.html#lazy_list_location//1">lazy_list_location//1</a>
	375	provides full details of the location for error reporting.
	376	</dd>
	377	</dl>
	378
	379	</dd>
	380	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="stream_to_lazy_list/2"><strong>stream_to_lazy_list</strong>(<var>+Stream,
340	381	-List</var>)</a></dt>
341	382	<dd class="defbody">
342	383	Create a lazy list representing the character codes in <var>Stream</var>.

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 11.5</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:plld"><a name="sec:11.5"><span class="sec-nr">11.5</span> <span class="sec-title">Linking
	235	<h2 id="sec:plld"><a id="sec:11.5"><span class="sec-nr">11.5</span> <span class="sec-title">Linking
195	236	embedded applications using swipl-ld</span></a></h2>
196	237
197		<a name="sec:plld"></a>
	238	<a id="sec:plld"></a>
198	239
199	240	<p>The utility program <b>swipl-ld</b> (Win32: swipl-ld.exe) may be used
200	241	to link a combination of C files and Prolog files into a stand-alone

267	308	<dt><strong>-shared</strong> <var></var></dt>
268	309	<dd class="defbody">
269	310	Link C, C++ or object files into a shared object (DLL) that can be
270		loaded by the <a name="idx:loadforeignlibrary1:2087"></a><a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>
	311	loaded by the <a id="idx:loadforeignlibrary1:2091"></a><a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>
271	312	predicate. If used with
272	313	<strong>-c</strong> it sets the proper options to compile a C or C++
273	314	file ready for linking into a shared object.</dd>

354	395	</dd>
355	396	</dl>
356	397
357		<p><h3 id="sec:foreign-example"><a name="sec:11.5.1"><span class="sec-nr">11.5.1</span> <span class="sec-title">A
	398	<p><h3 id="sec:foreign-example"><a id="sec:11.5.1"><span class="sec-nr">11.5.1</span> <span class="sec-title">A
358	399	simple example</span></a></h3>
359	400
360		<a name="sec:foreign-example"></a>
	401	<a id="sec:foreign-example"></a>
361	402
362	403	<p>The following is a very simple example going through all the steps
363	404	outlined above. It provides an arithmetic expression evaluator. We will

427	468	</pre>
428	469
429	470	<div class="caption"><b>Figure 9 : </b>C source for the calc application</div>
430		<a name="fig:calc"></a>
	471	<a id="fig:calc"></a>
431	472
432	473	<p>The application is now created using the following command line:
433	474

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193	234	</div>
194		<h2 id="sec:portabilitystrategies"><a name="sec:C.1"><span class="sec-nr">C.1</span> <span class="sec-title">Some
	235	<h2 id="sec:portabilitystrategies"><a id="sec:C.1"><span class="sec-nr">C.1</span> <span class="sec-title">Some
195	236	considerations for writing portable code</span></a></h2>
196	237
197		<a name="sec:portabilitystrategies"></a>
	238	<a id="sec:portabilitystrategies"></a>
198	239
199	240	<p>The traditional way to write portable code is to define custom
200	241	predicates for all potentially non-portable code and define these

210	251	the defined semantics are those of dialect <var>X</var>. Emulating all
211	252	extreme cases and full error handling compatibility may be tedious and
212	253	result in a much slower implementation that needed. Take for example
213		<a name="idx:callcleanup2:2256"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>.
	254	<a id="idx:callcleanup2:2260"></a><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a>.
214	255	The SICStus definition is fundamentally different from the SWI
215	256	definition, but 99% of the applications just want to make calls like
216	257	below to guarantee <var>StreamIn</var> is closed, even if process/1

238	279	keeping compatibility with the original dialect(s). This problem is well
239	280	known from the C/Unix world and we advise anyone to study the philosophy
240	281	of
241		http://www.gnu.org/software/autoconf/GNU autoconf , from which we will
242		illustrate some highlights below.
	282	<a class="url" href="http://www.gnu.org/software/autoconf/">GNU autoconf</a>,
	283	from which we will illustrate some highlights below.
243	284	</ul>
244	285
245	286	<p>The GNU autoconf suite, known to most people as <b>configure</b>, was

248	289	dialects today. Writing a portable C program can only be achieved using
249	290	cpp, the C preprocessor. The C preprocessor performs two tasks: macro
250	291	expansion and conditional compilation. Prolog realises macro expansion
251		through <a name="idx:termexpansion2:2257"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
252		and <a name="idx:goalexpansion2:2258"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>.
	292	through <a id="idx:termexpansion2:2261"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	293	and <a id="idx:goalexpansion2:2262"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>.
253	294	Conditional compilation is achieved using <code>:- if(Condition)</code>
254	295	as explained in
255		<a class="sec" href="consulting.html">section 4.3.1.2</a>. The situation
256		appears similar.
	296	<a class="sec" href="consulting.html#sec:4.3.1.2">section 4.3.1.2</a>.
	297	The situation appears similar.
257	298
258	299	<p>The important lesson learned from GNU autoconf is that the <em>last</em>
259	300	resort for conditional compilation to achieve portability is to switch

271	312
272	313	<p>We must learn from the distinction to test for features instead of
273	314	platform (dialect), as this makes the platform-specific code robust for
274		future changes of the dialect. Suppose we need <a name="idx:compare3:2259"></a><a class="pred" href="compare.html#compare/3">compare/3</a>
275		as defined in this manual. The <a name="idx:compare3:2260"></a><a class="pred" href="compare.html#compare/3">compare/3</a>
	315	future changes of the dialect. Suppose we need <a id="idx:compare3:2263"></a><a class="pred" href="compare.html#compare/3">compare/3</a>
	316	as defined in this manual. The <a id="idx:compare3:2264"></a><a class="pred" href="compare.html#compare/3">compare/3</a>
276	317	predicate is not part of the ISO standard, but many systems support it
277	318	and it is not unlikely it will become ISO standard or the intended
278	319	dialect will start supporting it. GNU autoconf strongly advises to test

293	334	dialect and, possibly at least as important, will provide compatibility
294	335	with dialects you didn't even consider porting to right now.
295	336
296		<p>In a more challenging case, the target Prolog has <a name="idx:compare3:2261"></a><a class="pred" href="compare.html#compare/3">compare/3</a>,
	337	<p>In a more challenging case, the target Prolog has <a id="idx:compare3:2265"></a><a class="pred" href="compare.html#compare/3">compare/3</a>,
297	338	but the semantics are different. What to do? One option is to write a
298		<a name="idx:mycompare3:2262"></a><span class="pred-ext">my_compare/3</span>
	339	<a id="idx:mycompare3:2266"></a><span class="pred-ext">my_compare/3</span>
299	340	and change all occurrences in the code. Alternatively you can rename
300		calls using <a name="idx:goalexpansion2:2263"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
	341	calls using <a id="idx:goalexpansion2:2267"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>
301	342	like below. This construct will not only deal with Prolog dialects
302		lacking <a name="idx:compare3:2264"></a><a class="pred" href="compare.html#compare/3">compare/3</a>
	343	lacking <a id="idx:compare3:2268"></a><a class="pred" href="compare.html#compare/3">compare/3</a>
303	344	as well as those that only implement it for numeric comparison or have
304	345	changed the argument order. Of course, writing rock-solid code would
305	346	require a complete test-suite, but this example will probably cover all
306	347	Prolog dialects that allow for conditional compilation, have core ISO
307		facilities and provide <a name="idx:goalexpansion2:2265"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>,
	348	facilities and provide <a id="idx:goalexpansion2:2269"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a>,
308	349	the things we claim a Prolog dialect should have to start writing
309	350	portable code for it.
310	351

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193	234	</div>
194		<h2 id="sec:practical"><a name="sec:8.3"><span class="sec-nr">8.3</span> <span class="sec-title">CHR
	235	<h2 id="sec:practical"><a id="sec:8.3"><span class="sec-nr">8.3</span> <span class="sec-title">CHR
195	236	in SWI-Prolog Programs</span></a></h2>
196	237
197		<a name="sec:practical"></a>
198		<h3 id="sec:chr-embedding"><a name="sec:8.3.1"><span class="sec-nr">8.3.1</span> <span class="sec-title">Embedding
	238	<a id="sec:practical"></a>
	239	<h3 id="sec:chr-embedding"><a id="sec:8.3.1"><span class="sec-nr">8.3.1</span> <span class="sec-title">Embedding
199	240	in Prolog Programs</span></a></h3>
200	241
201		<a name="sec:chr-embedding"></a>
	242	<a id="sec:chr-embedding"></a>
202	243
203	244	<p>The CHR constraints defined in a <code>.pl</code> file are associated
204	245	with a module. The default module is <code>user</code>. One should never
205	246	load different <code>.pl</code> files with the same CHR module name.
206	247
207		<p><h3 id="sec:chr-declarations"><a name="sec:8.3.2"><span class="sec-nr">8.3.2</span> <span class="sec-title">Constraint
	248	<p><h3 id="sec:chr-declarations"><a id="sec:8.3.2"><span class="sec-nr">8.3.2</span> <span class="sec-title">Constraint
208	249	declaration</span></a></h3>
209	250
210		<a name="sec:chr-declarations"></a>
	251	<a id="sec:chr-declarations"></a>
211	252
212	253	<dl class="latex">
213		<dt class="pubdef"><a name="chr_constraint/1">:- <strong>chr_constraint</strong>(<var>+Specifier</var>)</a></dt>
	254	<dt class="pubdef"><a id="chr_constraint/1">:- <strong>chr_constraint</strong>(<var>+Specifier</var>)</a></dt>
214	255	<dd class="defbody">
215	256	Every constraint used in CHR rules has to be declared with a
216		<a name="idx:chrconstraint1:1811"></a><a class="pred" href="practical.html#chr_constraint/1">chr_constraint/1</a>
	257	<a id="idx:chrconstraint1:1815"></a><a class="pred" href="practical.html#chr_constraint/1">chr_constraint/1</a>
217	258	declaration by the <em>constraint specifier</em>. For convenience
218	259	multiple constraints may be declared at once with the same
219	260	<a class="pred" href="practical.html#chr_constraint/1">chr_constraint/1</a>

311	352	</dl>
312	353
313	354	<dl class="latex">
314		<dt class="pubdef"><a name="chr_type/1">:- <strong>chr_type</strong>(<var>+TypeDeclaration</var>)</a></dt>
	355	<dt class="pubdef"><a id="chr_type/1">:- <strong>chr_type</strong>(<var>+TypeDeclaration</var>)</a></dt>
315	356	<dd class="defbody">
316	357	User-defined types are algebraic data types, similar to those in Haskell
317	358	or the discriminated unions in Mercury. An algebraic data type is
318		defined using <a name="idx:chrtype1:1812"></a><a class="pred" href="practical.html#chr_type/1">chr_type/1</a>:
	359	defined using <a id="idx:chrtype1:1816"></a><a class="pred" href="practical.html#chr_type/1">chr_type/1</a>:
319	360
320	361	<pre class="code">
321	362	:- chr_type type ---> body.

449	490	runtime overhead.
450	491	</ol>
451	492
452		<p><h3 id="sec:chr-compilation"><a name="sec:8.3.3"><span class="sec-nr">8.3.3</span> <span class="sec-title">Compilation</span></a></h3>
453
454		<a name="sec:chr-compilation"></a> The SWI-Prolog CHR compiler exploits <a name="idx:termexpansion2:1813"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
	493	<p><h3 id="sec:chr-compilation"><a id="sec:8.3.3"><span class="sec-nr">8.3.3</span> <span class="sec-title">Compilation</span></a></h3>
	494
	495	<a id="sec:chr-compilation"></a> The SWI-Prolog CHR compiler exploits <a id="idx:termexpansion2:1817"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>
455	496	rules to translate the constraint handling rules to plain Prolog. These
456	497	rules are loaded from the library <code>library(chr)</code>. They are
457	498	activated if the compiled file has the <code>.chr</code> extension or

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193	234	</div>
194		<h2 id="sec:preddesc"><a name="sec:4.1"><span class="sec-nr">4.1</span> <span class="sec-title">Notation
	235	<h2 id="sec:preddesc"><a id="sec:4.1"><span class="sec-nr">4.1</span> <span class="sec-title">Notation
195	236	of Predicate Descriptions</span></a></h2>
196	237
197		<a name="sec:preddesc"></a>
	238	<a id="sec:preddesc"></a>
198	239
199	240	<p>We have tried to keep the predicate descriptions clear and concise.
200	241	First, the predicate name is printed in bold face, followed by the

206	247	(-,+) are described as (?,?). The <code>@</code>-mode is often replaced
207	248	by <code><code>+</code></code>.</span></sup>
208	249
209		<p><table border="2" frame="hsides" rules="groups" style="margin:auto">
210		<tr valign="top"><td>++</td><td>Argument must be ground, i.e., the
211		argument may not contain a variable anywhere. </td></tr>
212		<tr valign="top"><td>+</td><td>Argument must be fully instantiated to a
213		term that satisfies the type. This is not necessarily <em>ground</em>,
214		e.g., the term
	250	<p><table class="latex frame-hsides center">
	251	<tr><td>++</td><td>Argument must be ground, i.e., the argument may not
	252	contain a variable anywhere. </td></tr>
	253	<tr><td>+</td><td>Argument must be fully instantiated to a term that
	254	satisfies the type. This is not necessarily <em>ground</em>, e.g., the
	255	term
215	256	<code>[_]</code> is a <em>list</em>, although its only member is
216	257	unbound. </td></tr>
217		<tr valign="top"><td>-</td><td>Argument is an <em>output</em> argument.
218		Unless specified otherwise, output arguments need not to be unbound. For
	258	<tr><td>-</td><td>Argument is an <em>output</em> argument. Unless
	259	specified otherwise, output arguments need not to be unbound. For
219	260	example, the goal <code>findall(X, Goal, [T])</code> is good style and
220	261	equivalent to <code>findall(X, Goal, Xs), Xs = [T]</code><sup class="fn">44<span class="fn-text">The
221	262	ISO standard dictates that <code>findall(X, Goal, 1)</code> raises a <code>type_error</code>

223	264	the standard here.</span></sup> Note that the
224	265	<em>determinism</em> specification, e.g., ``det'' only applies if this
225	266	argument is unbound. </td></tr>
226		<tr valign="top"><td>--</td><td>Argument must be unbound. Typically used
227		by predicates that create `something' and return a handle to the created
228		object, such as <a name="idx:open3:334"></a><a class="pred" href="IO.html#open/3">open/3</a>
	267	<tr><td>--</td><td>Argument must be unbound. Typically used by
	268	predicates that create `something' and return a handle to the created
	269	object, such as <a id="idx:open3:334"></a><a class="pred" href="IO.html#open/3">open/3</a>
229	270	which creates a <em>stream</em>. </td></tr>
230		<tr valign="top"><td>?</td><td>Argument must be bound to a <em>partial
231		term</em> of the indicated type. Note that a variable is a partial term
232		for any type. Think of the argument as either <em>input</em> or <em>output</em>
233		or
	271	<tr><td>?</td><td>Argument must be bound to a <em>partial term</em> of
	272	the indicated type. Note that a variable is a partial term for any type.
	273	Think of the argument as either <em>input</em> or <em>output</em> or
234	274	<em>both</em> input and output. For example, in
235	275	<code>stream_property(S, reposition(Bool))</code>, the <code>reposition</code>
236	276	part of the term is input and the uninstantiated <var>Bool</var> is
237	277	output. </td></tr>
238		<tr valign="top"><td>:</td><td>Argument is a meta-argument. Implies <code><code>+</code></code>.
239		See <a class="sec" href="modules.html">chapter 6</a> for more
	278	<tr><td>:</td><td>Argument is a meta-argument. Implies <code><code>+</code></code>.
	279	See <a class="sec" href="modules.html#sec:6">chapter 6</a> for more
240	280	information on module handling. </td></tr>
241		<tr valign="top"><td>@</td><td>Argument is not further instantiated.
242		Typically used for type tests.</td></tr>
243		<tr valign="top"><td>!</td><td>Argument contains a mutable structure
244		that may be modified using
245		<a name="idx:setarg3:335"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
246		or <a name="idx:nbsetarg3:336"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>. </td></tr>
	281	<tr><td>@</td><td>Argument is not further instantiated. Typically used
	282	for type tests.</td></tr>
	283	<tr><td>!</td><td>Argument contains a mutable structure that may be
	284	modified using
	285	<a id="idx:setarg3:335"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>
	286	or <a id="idx:nbsetarg3:336"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>. </td></tr>
247	287	</table>
248	288
249		<p><a name="idx:predicateindicator:337"></a>Referring to a predicate in
	289	<p><a id="idx:predicateindicator:337"></a>Referring to a predicate in
250	290	running text is done using a
251	291	<em>predicate indicator</em>. The canonical and most generic form of a
252	292	predicate indicator is a term <<var>module</var>>:<<var>name</var>>/<<var>arity</var>>.
253	293	If the module is irrelevant (built-in predicate) or can be inferred from
254	294	the context it is often omitted. Compliant to the ISO standard draft on
255	295	DCG (see
256		<a class="sec" href="DCG.html">section 4.13</a>), SWI-Prolog also allows
257		for [<<var>module</var>>]:<<var>name</var>>//<<var>arity</var>>
	296	<a class="sec" href="DCG.html#sec:4.13">section 4.13</a>), SWI-Prolog
	297	also allows for [<<var>module</var>>]:<<var>name</var>>//<<var>arity</var>>
258	298	to refer to a grammar rule. For all non-negative arity, <<var>name</var>>//<<var>arity</var>>
259	299	is the same as <<var>name</var>>/<<var>arity</var>>+2,
260	300	regardless of whether or not the referenced predicate is defined or can
261	301	be used as a grammar rule. The //-notation can be used in all places
262	302	that traditionally allow for a predicate indicator, e.g., the module
263		declaration, <a name="idx:spy1:338"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>,
264		and <a name="idx:dynamic1:339"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>.
	303	declaration, <a id="idx:spy1:338"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>,
	304	and <a id="idx:dynamic1:339"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>.
265	305
266	306	<p></body></html>⏎

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194		<h2 id="sec:predicate_options"><a name="sec:A.25"><span class="sec-nr">A.25</span> <span class="sec-title">library(predicate_options):
	235	<h2 id="sec:predicate_options"><a id="sec:A.25"><span class="sec-nr">A.25</span> <span class="sec-title">library(predicate_options):
195	236	Declare option-processing of predicates</span></a></h2>
196	237
197		<a name="sec:predicate_options"></a>
	238	<a id="sec:predicate_options"></a>
198	239
199	240	<p><i>Discussions with Jeff Schultz helped shaping this library</i>
200	241
201		<p><h3 id="sec:predopts-pro-cons"><a name="sec:A.25.1"><span class="sec-nr">A.25.1</span> <span class="sec-title">The
	242	<p><h3 id="sec:predopts-pro-cons"><a id="sec:A.25.1"><span class="sec-nr">A.25.1</span> <span class="sec-title">The
202	243	strength and weakness of predicate options</span></a></h3>
203	244
204		<p><a name="sec:predopts-pro-cons"></a>
	245	<p><a id="sec:predopts-pro-cons"></a>
205	246
206	247	<p>Many ISO predicates accept options, e.g., <a class="pred" href="IO.html#open/4">open/4</a>, <a class="pred" href="termrw.html#write_term/3">write_term/3</a>.
207	248	Options offer an attractive alternative to proliferation into many

258	299	Unfortunately, the consequences of a partial emulation cannot be
259	300	assessed by tools.
260	301
261		<p><h3 id="sec:predopts-environment"><a name="sec:A.25.2"><span class="sec-nr">A.25.2</span> <span class="sec-title">Options
	302	<p><h3 id="sec:predopts-environment"><a id="sec:A.25.2"><span class="sec-nr">A.25.2</span> <span class="sec-title">Options
262	303	as arguments or environment?</span></a></h3>
263	304
264		<p><a name="sec:predopts-environment"></a>
	305	<p><a id="sec:predopts-environment"></a>
265	306
266	307	<p>We distinguish two views on options. One is to see them as additional
267	308	parameters that require strict existence, type and domain-checking and

294	335	mistyped options are silently ignored. The option infrastructure
295	336	described in this section tries to remedy these problems.
296	337
297		<p><h3 id="sec:predopts-improving"><a name="sec:A.25.3"><span class="sec-nr">A.25.3</span> <span class="sec-title">Improving
	338	<p><h3 id="sec:predopts-improving"><a id="sec:A.25.3"><span class="sec-nr">A.25.3</span> <span class="sec-title">Improving
298	339	on the current situation</span></a></h3>
299	340
300		<p><a name="sec:predopts-improving"></a>
	341	<p><a id="sec:predopts-improving"></a>
301	342
302	343	<p>Whether we see options as arguments or locally scoped environment
303	344	variables, the most obvious way to improve on the current situation is

306	347	options can be used by the compiler and development environment as well
307	348	as by the runtime system to warn or throw errors.
308	349
309		<p><h4 id="sec:predopts-as-types"><a name="sec:A.25.3.1"><span class="sec-nr">A.25.3.1</span> <span class="sec-title">Options
	350	<p><h4 id="sec:predopts-as-types"><a id="sec:A.25.3.1"><span class="sec-nr">A.25.3.1</span> <span class="sec-title">Options
310	351	as types</span></a></h4>
311	352
312		<p><a name="sec:predopts-as-types"></a>
	353	<p><a id="sec:predopts-as-types"></a>
313	354
314	355	<p>An obvious approach to deal with options is to define the different
315	356	possible option values as a type and type the argument that processes

337	378	code.
338	379	</ul>
339	380
340		<p><h4 id="sec:predopts-reflextion"><a name="sec:A.25.3.2"><span class="sec-nr">A.25.3.2</span> <span class="sec-title">Reflective
	381	<p><h4 id="sec:predopts-reflextion"><a id="sec:A.25.3.2"><span class="sec-nr">A.25.3.2</span> <span class="sec-title">Reflective
341	382	access to options</span></a></h4>
342	383
343		<p><a name="sec:predopts-reflextion"></a>
	384	<p><a id="sec:predopts-reflextion"></a>
344	385
345	386	<p>From the above, we conclude that we require reflective access to find
346	387	out whether an option is supported and valid for a particular predicate.

349	390	values. Predicate options are declared using <a class="pred" href="predicate_options.html#predicate_options/3">predicate_options/3</a>:
350	391
351	392	<dl class="latex">
352		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="predicate_options/3"><strong>predicate_options</strong>(<var>:PI,
	393	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="predicate_options/3"><strong>predicate_options</strong>(<var>:PI,
353	394	+Arg, +Options</var>)</a></dt>
354	395	<dd class="defbody">
355	396	Declare that the predicate <var>PI</var> processes options on <var>Arg</var>. <var>Options</var>

386	427	processed by <a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>.
387	428	Option processing can be specified at runtime using <span class="pred-ext">assert_predicate_options/3</span>,
388	429	which is intended to support program analysis.</dd>
389		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="assert_predicate_options/4"><strong>assert_predicate_options</strong>(<var>:PI,
	430	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="assert_predicate_options/4"><strong>assert_predicate_options</strong>(<var>:PI,
390	431	+Arg, +Options, ?New</var>)</a></dt>
391	432	<dd class="defbody">
392	433	As predicate_options(:<var>PI</var>, +<var>Arg</var>, +<var>Options</var>). <var>New</var>

400	441	checking for supported options.
401	442
402	443	<dl class="latex">
403		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_predicate_option/3"><strong>current_predicate_option</strong>(<var>:PI,
	444	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_predicate_option/3"><strong>current_predicate_option</strong>(<var>:PI,
404	445	?Arg, ?Option</var>)</a></dt>
405	446	<dd class="defbody">
406	447	True when <var>Arg</var> of <var>PI</var> processes <var>Option</var>.

416	457	predicate
417	458	<a class="pred" href="predicate_options.html#current_predicate_options/3">current_predicate_options/3</a>
418	459	can be used to access the full capabilities of a predicate.</dd>
419		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="check_predicate_option/3"><strong>check_predicate_option</strong>(<var>:PI,
	460	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="check_predicate_option/3"><strong>check_predicate_option</strong>(<var>:PI,
420	461	+Arg, +Option</var>)</a></dt>
421	462	<dd class="defbody">
422	463	Verify predicate options at runtime. Similar to

441	482	colouring option names and values.
442	483
443	484	<dl class="latex">
444		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_option_arg/2"><strong>current_option_arg</strong>(<var>:PI,
	485	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_option_arg/2"><strong>current_option_arg</strong>(<var>:PI,
445	486	?Arg</var>)</a></dt>
446	487	<dd class="defbody">
447	488	True when <var>Arg</var> of <var>PI</var> processes predicate options.
448	489	Which options are processed can be accessed using <a class="pred" href="predicate_options.html#current_predicate_option/3">current_predicate_option/3</a>.</dd>
449		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_predicate_options/3"><strong>current_predicate_options</strong>(<var>:PI,
	490	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_predicate_options/3"><strong>current_predicate_options</strong>(<var>:PI,
450	491	?Arg, ?Options</var>)</a></dt>
451	492	<dd class="defbody">
452	493	True when <var>Options</var> is the current active option declaration

462	503	<a class="pred" href="predicate_options.html#check_predicate_options/0">check_predicate_options/0</a>:
463	504
464	505	<dl class="latex">
465		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="check_predicate_options/0"><strong>check_predicate_options</strong></a></dt>
	506	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="check_predicate_options/0"><strong>check_predicate_options</strong></a></dt>
466	507	<dd class="defbody">
467	508	Analyse loaded program for erroneous options. This predicate decompiles
468	509	the current program and searches for calls to predicates that process

488	529	the module system.
489	530
490	531	<dl class="latex">
491		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="derive_predicate_options/0"><strong>derive_predicate_options</strong></a></dt>
	532	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="derive_predicate_options/0"><strong>derive_predicate_options</strong></a></dt>
492	533	<dd class="defbody">
493	534	Derive new predicate option declarations. This predicate analyses the
494	535	loaded program to find clauses that process options using one of the

505	546	</dl>
506	547
507	548	</dd>
508		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="retractall_predicate_options/0"><strong>retractall_predicate_options</strong></a></dt>
	549	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="retractall_predicate_options/0"><strong>retractall_predicate_options</strong></a></dt>
509	550	<dd class="defbody">
510	551	Remove all dynamically (derived) predicate options.</dd>
511		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="derived_predicate_options/3"><strong>derived_predicate_options</strong>(<var>:PI,
	552	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="derived_predicate_options/3"><strong>derived_predicate_options</strong>(<var>:PI,
512	553	?Arg, ?Options</var>)</a></dt>
513	554	<dd class="defbody">
514	555	Derive option arguments using static analysis. True when <var>Options</var>
515	556	is the current <i>derived</i> active option declaration for <var>PI</var>
516	557	on
517	558	<var>Arg</var>.</dd>
518		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="derived_predicate_options/1"><strong>derived_predicate_options</strong>(<var>+Module</var>)</a></dt>
	559	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="derived_predicate_options/1"><strong>derived_predicate_options</strong>(<var>+Module</var>)</a></dt>
519	560	<dd class="defbody">
520	561	Derive predicate option declarations for a module. The derived options
521	562	are printed to the <code>current_output</code> stream.

+91

-50

man/Manual/predsummary.html less more

1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section F.1</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section F.1</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

17	17	{ margin-bottom: 1em;
18	18	}
19	19
20		dt.pubdef
21		{ background-color: #c5e1ff;
22		}
23
24		dt.multidef
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26		}
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27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
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121	125	}
122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
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132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
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	147	color: #000;
	148	margin-top: 25px;
	149	padding: 8px 12px;
	150	font-size: larger;
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	152
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141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
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185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="summary.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="library.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:predsummary"><a name="sec:F.1"><span class="sec-nr">F.1</span> <span class="sec-title">Predicates</span></a></h2>
195
196		<a name="sec:predsummary"></a>
197
198		<p>The predicate summary is used by the Prolog predicate <a name="idx:apropos1:2345"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>
	235	<h2 id="sec:predsummary"><a id="sec:F.1"><span class="sec-nr">F.1</span> <span class="sec-title">Predicates</span></a></h2>
	236
	237	<a id="sec:predsummary"></a>
	238
	239	<p>The predicate summary is used by the Prolog predicate <a id="idx:apropos1:2349"></a><a class="pred" href="help.html#apropos/1">apropos/1</a>
199	240	to suggest predicates from a keyword.
200	241	<table>
201	242	<tr><td><a class="pred" href="overrule.html#@/2">@/2</a></td><td>Call

204	245	(discard choicepoints)</td></tr>
205	246	<tr><td><a class="pred" href="control.html#,/2">,/2</a></td><td>Conjunction
206	247	of goals</td></tr>
207		<tr><td><span class="pred-ext">->/2</span></td><td>If-then-else</td></tr>
	248	<tr><td><a class="pred" href="control.html#->/2">->/2</a></td><td>If-then-else</td></tr>
208	249	<tr><td><a class="pred" href="control.html#->/2">->/2</a></td><td>Soft-cut</td></tr>
209	250	<tr><td><span class="pred-ext">./2</span></td><td>Consult. Also
210	251	functional notation</td></tr>

245	286	<tr><td><a class="pred" href="compare.html#@>=/2">@>=/2</a></td><td>Standard
246	287	order larger or equal</td></tr>
247	288	<tr><td><a class="pred" href="control.html#\+/1">\+/1</a></td><td>Negation
248		by failure. Same as <a name="idx:not1:2346"></a><a class="pred" href="metacall.html#not/1">not/1</a></td></tr>
	289	by failure. Same as <a id="idx:not1:2350"></a><a class="pred" href="metacall.html#not/1">not/1</a></td></tr>
249	290	<tr><td><a class="pred" href="compare.html#\=/2">\=/2</a></td><td>True
250	291	if arguments cannot be unified</td></tr>
251	292	<tr><td><a class="pred" href="compare.html#\==/2">\==/2</a></td><td>True

253	294	<tr><td><a class="pred" href="compare.html#\=@=/2">\=@=/2</a></td><td>Not
254	295	structural identical</td></tr>
255	296	<tr><td><span class="pred-ext">^/2</span></td><td>Existential
256		quantification (<a name="idx:bagof3:2347"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>, <a name="idx:setof3:2348"></a><a class="pred" href="allsolutions.html#setof/3">setof/3</a>)</td></tr>
	297	quantification (<a id="idx:bagof3:2351"></a><a class="pred" href="allsolutions.html#bagof/3">bagof/3</a>, <a id="idx:setof3:2352"></a><a class="pred" href="allsolutions.html#setof/3">setof/3</a>)</td></tr>
257	298	<tr><td><a class="pred" href="control.html#\|/2">\|/2</a></td><td>Disjunction
258	299	in DCGs. Same as <a class="pred" href="control.html#;/2">;/2</a></td></tr>
259	300	<tr><td><span class="pred-ext">/1</span></td><td>DCG escape; constraints</td></tr>

326	367	<tr><td><a class="pred" href="chario.html#at_end_of_stream/1">at_end_of_stream/1</a></td><td>Test
327	368	for end of file on stream</td></tr>
328	369	<tr><td><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a></td><td>Register
329		goal to run at <a name="idx:halt1:2349"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a></td></tr>
	370	goal to run at <a id="idx:halt1:2353"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a></td></tr>
330	371	<tr><td><a class="pred" href="typetest.html#atom/1">atom/1</a></td><td>Type
331	372	check for an atom</td></tr>
332	373	<tr><td><a class="pred" href="manipatom.html#atom_chars/2">atom_chars/2</a></td><td>Convert

387	428	a goal with a cleaup-handler</td></tr>
388	429	<tr><td><a class="pred" href="metacall.html#call_cleanup/2">call_cleanup/2</a></td><td>Guard
389	430	a goal with a cleaup-handler</td></tr>
390		<tr><td><a class="pred" href="DCG.html#call_dcg/3">call_dcg/3</a></td><td>As <a name="idx:phrase3:2350"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>
	431	<tr><td><a class="pred" href="DCG.html#call_dcg/3">call_dcg/3</a></td><td>As <a id="idx:phrase3:2354"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>
391	432	without type checking</td></tr>
392	433	<tr><td><a class="pred" href="coroutining.html#call_residue_vars/2">call_residue_vars/2</a></td><td>Find
393	434	residual attributed variables</td></tr>

399	440	goal in limited inferences</td></tr>
400	441	<tr><td><a class="pred" href="typetest.html#callable/1">callable/1</a></td><td>Test
401	442	for atom or compound term</td></tr>
402		<tr><td><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a></td><td>Cancel <a name="idx:halt0:2351"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>
403		from an <a name="idx:athalt1:2352"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>
	443	<tr><td><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a></td><td>Cancel <a id="idx:halt0:2355"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>
	444	from an <a id="idx:athalt1:2356"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>
404	445	hook</td></tr>
405	446	<tr><td><a class="pred" href="exception.html#catch/3">catch/3</a></td><td>Call
406	447	goal, watching for exceptions</td></tr>

449	490	<tr><td><a class="pred" href="compare.html#compare/3">compare/3</a></td><td>Compare,
450	491	using a predicate to determine the order</td></tr>
451	492	<tr><td><a class="pred" href="consulting.html#compile_aux_clauses/1">compile_aux_clauses/1</a></td><td>Compile
452		predicates for <a name="idx:goalexpansion2:2353"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a></td></tr>
	493	predicates for <a id="idx:goalexpansion2:2357"></a><a class="pred" href="consulting.html#goal_expansion/2">goal_expansion/2</a></td></tr>
453	494	<tr><td><a class="pred" href="dynamic.html#compile_predicates/1">compile_predicates/1</a></td><td>Compile
454	495	dynamic code to static</td></tr>
455	496	<tr><td><a class="pred" href="consulting.html#compiling/0">compiling/0</a></td><td>Is

557	598	<tr><td><a class="pred" href="debug.html#debug/3">debug/3</a></td><td>Print
558	599	debugging message on topic</td></tr>
559	600	<tr><td><span class="pred-ext">debug_control_hook/1</span></td><td><i>(hook)</i>
560		Extend <a name="idx:spy1:2354"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>,
	601	Extend <a id="idx:spy1:2358"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>,
561	602	etc.</td></tr>
562	603	<tr><td><a class="pred" href="debugger.html#debugging/0">debugging/0</a></td><td>Show
563	604	debugger status</td></tr>

696	737	<tr><td><a class="pred" href="allsolutions.html#findall/3">findall/3</a></td><td>Find
697	738	all solutions to a goal</td></tr>
698	739	<tr><td><a class="pred" href="allsolutions.html#findall/4">findall/4</a></td><td>Difference
699		list version of <a name="idx:findall3:2355"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a></td></tr>
	740	list version of <a id="idx:findall3:2359"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a></td></tr>
700	741	<tr><td><a class="pred" href="allsolutions.html#findnsols/4">findnsols/4</a></td><td>Find
701	742	first <var>N</var> solutions</td></tr>
702	743	<tr><td><a class="pred" href="allsolutions.html#findnsols/5">findnsols/5</a></td><td>Difference
703		list version of <a name="idx:findnsols4:2356"></a><a class="pred" href="allsolutions.html#findnsols/4">findnsols/4</a></td></tr>
	744	list version of <a id="idx:findnsols4:2360"></a><a class="pred" href="allsolutions.html#findnsols/4">findnsols/4</a></td></tr>
704	745	<tr><td><a class="pred" href="chario.html#fill_buffer/1">fill_buffer/1</a></td><td>Fill
705	746	the input buffer of a stream</td></tr>
706	747	<tr><td><a class="pred" href="db.html#flag/3">flag/3</a></td><td>Simple

723	764	strftime() like date/time formatter</td></tr>
724	765	<tr><td><a class="pred" href="system.html#format_time/4">format_time/4</a></td><td>date/time
725	766	formatter with explicit locale</td></tr>
726		<tr><td><a class="pred" href="format.html#format_predicate/2">format_predicate/2</a></td><td>Program <a name="idx:format12:2357"></a><a class="pred" href="format.html#format/1">format/[1,2]</a></td></tr>
	767	<tr><td><a class="pred" href="format.html#format_predicate/2">format_predicate/2</a></td><td>Program <a id="idx:format12:2361"></a><a class="pred" href="format.html#format/1">format/[1,2]</a></td></tr>
727	768	<tr><td><a class="pred" href="attvar.html#term_attvars/2">term_attvars/2</a></td><td>Find
728	769	attributed variables in a term</td></tr>
729	770	<tr><td><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a></td><td>Find

938	979	between dict and list of pairs</td></tr>
939	980	<tr><td><a class="pred" href="assoc.html#max_assoc/3">max_assoc/3</a></td><td>Highest
940	981	key in association tree</td></tr>
941		<tr><td><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a></td><td>Deterministic <a name="idx:member2:2358"></a><a class="pred" href="lists.html#member/2">member/2</a></td></tr>
942		<tr><td><a class="pred" href="exception.html#message_hook/3">message_hook/3</a></td><td>Intercept <a name="idx:printmessage2:2359"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a></td></tr>
	982	<tr><td><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a></td><td>Deterministic <a id="idx:member2:2362"></a><a class="pred" href="lists.html#member/2">member/2</a></td></tr>
	983	<tr><td><a class="pred" href="exception.html#message_hook/3">message_hook/3</a></td><td>Intercept <a id="idx:printmessage2:2363"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a></td></tr>
943	984	<tr><td><span class="pred-ext">message_line_element/2</span></td><td><i>(hook)</i>
944		Intercept <a name="idx:printmessagelines3:2360"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a></td></tr>
	985	Intercept <a id="idx:printmessagelines3:2364"></a><a class="pred" href="exception.html#print_message_lines/3">print_message_lines/3</a></td></tr>
945	986	<tr><td><a class="pred" href="exception.html#message_property/2">message_property/2</a></td><td><i>(hook)</i>
946	987	Define display of a message</td></tr>
947	988	<tr><td><a class="pred" href="threadcom.html#message_queue_create/1">message_queue_create/1</a></td><td>Create

1115	1156	<tr><td><a class="pred" href="arith.html#plus/3">plus/3</a></td><td>Logical
1116	1157	integer addition</td></tr>
1117	1158	<tr><td><a class="pred" href="termrw.html#portray/1">portray/1</a></td><td><i>(hook)</i>
1118		Modify behaviour of <a name="idx:print1:2361"></a><a class="pred" href="termrw.html#print/1">print/1</a></td></tr>
	1159	Modify behaviour of <a id="idx:print1:2365"></a><a class="pred" href="termrw.html#print/1">print/1</a></td></tr>
1119	1160	<tr><td><a class="pred" href="listing.html#portray_clause/1">portray_clause/1</a></td><td>Pretty
1120	1161	print a clause</td></tr>
1121	1162	<tr><td><a class="pred" href="listing.html#portray_clause/2">portray_clause/2</a></td><td>Pretty

1151	1192	<tr><td><a class="pred" href="ancestral-cut.html#prolog_cut_to/1">prolog_cut_to/1</a></td><td>Realise
1152	1193	global cuts</td></tr>
1153	1194	<tr><td><a class="pred" href="edit.html#prolog_edit:locate/2">prolog_edit:locate/2</a></td><td>Locate
1154		targets for <a name="idx:edit1:2362"></a><a class="pred" href="edit.html#edit/1">edit/1</a></td></tr>
	1195	targets for <a id="idx:edit1:2366"></a><a class="pred" href="edit.html#edit/1">edit/1</a></td></tr>
1155	1196	<tr><td><a class="pred" href="edit.html#prolog_edit:locate/3">prolog_edit:locate/3</a></td><td>Locate
1156		targets for <a name="idx:edit1:2363"></a><a class="pred" href="edit.html#edit/1">edit/1</a></td></tr>
	1197	targets for <a id="idx:edit1:2367"></a><a class="pred" href="edit.html#edit/1">edit/1</a></td></tr>
1157	1198	<tr><td><a class="pred" href="edit.html#prolog_edit:edit_source/1">prolog_edit:edit_source/1</a></td><td>Call
1158		editor for <a name="idx:edit1:2364"></a><a class="pred" href="edit.html#edit/1">edit/1</a></td></tr>
	1199	editor for <a id="idx:edit1:2368"></a><a class="pred" href="edit.html#edit/1">edit/1</a></td></tr>
1159	1200	<tr><td><a class="pred" href="edit.html#prolog_edit:edit_command/2">prolog_edit:edit_command/2</a></td><td>Specify
1160	1201	editor activation</td></tr>
1161		<tr><td><a class="pred" href="edit.html#prolog_edit:load/0">prolog_edit:load/0</a></td><td>Load <a name="idx:edit1:2365"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	1202	<tr><td><a class="pred" href="edit.html#prolog_edit:load/0">prolog_edit:load/0</a></td><td>Load <a id="idx:edit1:2369"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
1162	1203	extensions</td></tr>
1163	1204	<tr><td><a class="pred" href="excepthook.html#prolog_exception_hook/4">prolog_exception_hook/4</a></td><td>Rewrite
1164	1205	exceptions</td></tr>

1173	1214	<tr><td><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a></td><td>Context
1174	1215	information for directives</td></tr>
1175	1216	<tr><td><a class="pred" href="loadfilehook.html#prolog_load_file/2">prolog_load_file/2</a></td><td><i>(hook)</i>
1176		Program <a name="idx:loadfiles2:2366"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a></td></tr>
	1217	Program <a id="idx:loadfiles2:2370"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a></td></tr>
1177	1218	<tr><td><a class="pred" href="tracehook.html#prolog_skip_level/2">prolog_skip_level/2</a></td><td>Indicate
1178	1219	deepest recursion to trace</td></tr>
1179	1220	<tr><td><a class="pred" href="tracehook.html#prolog_skip_frame/1">prolog_skip_frame/1</a></td><td>Perform

1189	1230	<tr><td><a class="pred" href="termrw.html#prompt1/1">prompt1/1</a></td><td>Change
1190	1231	prompt for 1 line</td></tr>
1191	1232	<tr><td><a class="pred" href="termrw.html#prompt/2">prompt/2</a></td><td>Change
1192		the prompt used by <a name="idx:read1:2367"></a><a class="pred" href="termrw.html#read/1">read/1</a></td></tr>
	1233	the prompt used by <a id="idx:read1:2371"></a><a class="pred" href="termrw.html#read/1">read/1</a></td></tr>
1193	1234	<tr><td><a class="pred" href="protocol.html#protocol/1">protocol/1</a></td><td>Make
1194	1235	a log of the user interaction</td></tr>
1195	1236	<tr><td><a class="pred" href="protocol.html#protocola/1">protocola/1</a></td><td>Append

1365	1406	<tr><td><a class="pred" href="system.html#shell/2">shell/2</a></td><td>Execute
1366	1407	OS command</td></tr>
1367	1408	<tr><td><a class="pred" href="delcont.html#shift/1">shift/1</a></td><td>Shift
1368		control to the closest <a name="idx:reset3:2368"></a><a class="pred" href="delcont.html#reset/3">reset/3</a></td></tr>
	1409	control to the closest <a id="idx:reset3:2372"></a><a class="pred" href="delcont.html#reset/3">reset/3</a></td></tr>
1369	1410	<tr><td><a class="pred" href="profile.html#show_profile/1">show_profile/1</a></td><td>Show
1370	1411	results of the profiler</td></tr>
1371	1412	<tr><td><a class="pred" href="files.html#size_file/2">size_file/2</a></td><td>Get

1497	1538	<tr><td><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a></td><td>Declare
1498	1539	thread-specific clauses for a predicate</td></tr>
1499	1540	<tr><td><a class="pred" href="exception.html#thread_message_hook/3">thread_message_hook/3</a></td><td>Thread
1500		local <a name="idx:messagehook3:2369"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a></td></tr>
	1541	local <a id="idx:messagehook3:2373"></a><a class="pred" href="exception.html#message_hook/3">message_hook/3</a></td></tr>
1501	1542	<tr><td><a class="pred" href="threadcom.html#thread_peek_message/1">thread_peek_message/1</a></td><td>Test
1502	1543	for message</td></tr>
1503	1544	<tr><td><a class="pred" href="threadcom.html#thread_peek_message/2">thread_peek_message/2</a></td><td>Test

1519	1560	<tr><td><a class="pred" href="thutil.html#threads/0">threads/0</a></td><td>List
1520	1561	running threads</td></tr>
1521	1562	<tr><td><a class="pred" href="exception.html#throw/1">throw/1</a></td><td>Raise
1522		an exception (see <a name="idx:catch3:2370"></a><a class="pred" href="exception.html#catch/3">catch/3</a>)</td></tr>
	1563	an exception (see <a id="idx:catch3:2374"></a><a class="pred" href="exception.html#catch/3">catch/3</a>)</td></tr>
1523	1564	<tr><td><a class="pred" href="statistics.html#time/1">time/1</a></td><td>Determine
1524	1565	time needed to execute goal</td></tr>
1525	1566	<tr><td><a class="pred" href="files.html#time_file/2">time_file/2</a></td><td>Get

+89

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 4.41</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.41</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="statistics.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:profile"><a name="sec:4.41"><span class="sec-nr">4.41</span> <span class="sec-title">Execution
	235	<h2 id="sec:profile"><a id="sec:4.41"><span class="sec-nr">4.41</span> <span class="sec-title">Execution
195	236	profiling</span></a></h2>
196	237
197		<a name="sec:profile"></a>
	238	<a id="sec:profile"></a>
198	239
199	240	<p>This section describes the hierarchical execution profiler. This
200	241	profiler is based on ideas from <b>gprof</b> described in

209	250	<code>library(swi/pce_profile)</code> to provide an interactive
210	251	graphical frontend for the results.
211	252
212		<p><h3 id="sec:profiling-predicates"><a name="sec:4.41.1"><span class="sec-nr">4.41.1</span> <span class="sec-title">Profiling
	253	<p><h3 id="sec:profiling-predicates"><a id="sec:4.41.1"><span class="sec-nr">4.41.1</span> <span class="sec-title">Profiling
213	254	predicates</span></a></h3>
214	255
215		<a name="sec:profiling-predicates"></a>
	256	<a id="sec:profiling-predicates"></a>
216	257
217	258	<p>The following predicates are defined to interact with the profiler.
218	259
219	260	<dl class="latex">
220		<dt class="pubdef"><a name="profile/1"><strong>profile</strong>(<var>:Goal</var>)</a></dt>
221		<dd class="defbody">
222		Execute <var>Goal</var> just like <a name="idx:once1:1566"></a><a class="pred" href="metacall.html#once/1">once/1</a>,
	261	<dt class="pubdef"><a id="profile/1"><strong>profile</strong>(<var>:Goal</var>)</a></dt>
	262	<dd class="defbody">
	263	Execute <var>Goal</var> just like <a id="idx:once1:1566"></a><a class="pred" href="metacall.html#once/1">once/1</a>,
223	264	collecting profiling statistics, and call <code>show_profile([])</code>.
224	265	With XPCE installed this opens a graphical interface to examine the
225	266	collected profiling data.</dd>
226		<dt class="pubdef"><a name="profile/3"><strong>profile</strong>(<var>:Goal,
	267	<dt class="pubdef"><a id="profile/3"><strong>profile</strong>(<var>:Goal,
227	268	+Options</var>)</a></dt>
228	269	<dd class="defbody">
229		Execute <var>Goal</var> just like <a name="idx:once1:1567"></a><a class="pred" href="metacall.html#once/1">once/1</a>.
230		Collect profiling statistics according to <var>Options</var> and call <a name="idx:showprofile1:1568"></a><a class="pred" href="profile.html#show_profile/1">show_profile/1</a>
	270	Execute <var>Goal</var> just like <a id="idx:once1:1567"></a><a class="pred" href="metacall.html#once/1">once/1</a>.
	271	Collect profiling statistics according to <var>Options</var> and call <a id="idx:showprofile1:1568"></a><a class="pred" href="profile.html#show_profile/1">show_profile/1</a>
231	272	with <var>Options</var>. The default collects CPU profiling and opens a
232	273	graphical interface when provided, printing the `plain' time usage of
233	274	the top 25 predicates as a ballback. Options are described below.
234		Remaining options are passed to <a name="idx:showprofile1:1569"></a><a class="pred" href="profile.html#show_profile/1">show_profile/1</a>.
	275	Remaining options are passed to <a id="idx:showprofile1:1569"></a><a class="pred" href="profile.html#show_profile/1">show_profile/1</a>.
235	276
236	277	<dl class="latex">
237	278	<dt><strong>time</strong>(<var>+Which</var>)</dt>

244	285	</dl>
245	286
246	287	</dd>
247		<dt class="pubdef"><a name="show_profile/1"><strong>show_profile</strong>(<var>+Options</var>)</a></dt>
	288	<dt class="pubdef"><a id="show_profile/1"><strong>show_profile</strong>(<var>+Options</var>)</a></dt>
248	289	<dd class="defbody">
249	290	This predicate first calls prolog:show_profile_hook/1. If XPCE is
250	291	loaded, this hook is used to activate a GUI interface to visualise the

264	305	</dl>
265	306
266	307	</dd>
267		<dt class="pubdef"><a name="profiler/2"><strong>profiler</strong>(<var>-Old,
	308	<dt class="pubdef"><a id="profiler/2"><strong>profiler</strong>(<var>-Old,
268	309	+New</var>)</a></dt>
269	310	<dd class="defbody">
270	311	Query or change the status of the profiler. The status is one of

286	327
287	328	<p>The value <code>true</code> is accepted as a synonym for <code>cputime</code>
288	329	for compatibility reasons.</dd>
289		<dt class="pubdef"><a name="reset_profiler/0"><strong>reset_profiler</strong></a></dt>
	330	<dt class="pubdef"><a id="reset_profiler/0"><strong>reset_profiler</strong></a></dt>
290	331	<dd class="defbody">
291	332	Switches the profiler to <code>false</code> and clears all collected
292	333	statistics.</dd>
293		<dt class="pubdef"><a name="noprofile/1"><strong>noprofile</strong>(<var>+Name/+Arity,
	334	<dt class="pubdef"><a id="noprofile/1"><strong>noprofile</strong>(<var>+Name/+Arity,
294	335	...</var>)</a></dt>
295	336	<dd class="defbody">
296	337	Declares the predicate <var>Name</var>/<var>Arity</var> to be invisible
297	338	to the profiler. The time spent in the named predicate is added to the
298	339	caller, and the callees are linked directly to the caller. This is
299		particularly useful for simple meta-predicates such as <a name="idx:call1:1570"></a><a class="pred" href="metacall.html#call/1">call/1</a>, <a name="idx:ignore1:1571"></a><a class="pred" href="metacall.html#ignore/1">ignore/1</a>, <a name="idx:catch3:1572"></a><a class="pred" href="exception.html#catch/3">catch/3</a>,
	340	particularly useful for simple meta-predicates such as <a id="idx:call1:1570"></a><a class="pred" href="metacall.html#call/1">call/1</a>, <a id="idx:ignore1:1571"></a><a class="pred" href="metacall.html#ignore/1">ignore/1</a>, <a id="idx:catch3:1572"></a><a class="pred" href="exception.html#catch/3">catch/3</a>,
300	341	etc.
301	342	</dd>
302	343	</dl>
303	344
304		<p><h3 id="sec:pceprofile"><a name="sec:4.41.2"><span class="sec-nr">4.41.2</span> <span class="sec-title">Visualizing
	345	<p><h3 id="sec:pceprofile"><a id="sec:4.41.2"><span class="sec-nr">4.41.2</span> <span class="sec-title">Visualizing
305	346	profiling data</span></a></h3>
306	347
307		<a name="sec:pceprofile"></a>
308
309		<p>Browsing the annotated call-tree as described in <a class="sec" href="profile.html">section
	348	<a id="sec:pceprofile"></a>
	349
	350	<p>Browsing the annotated call-tree as described in <a class="sec" href="profile.html#sec:4.41.3">section
310	351	4.41.3</a> itself is not very attractive. Therefore, the results are
311	352	combined per predicate, collecting all <em>callers</em> and <em>callees</em>
312	353	as well as the propagation of time and activations in both directions.

329	370	detail window to the given caller or callee, showing the documentation
330	371	(if it is a built-in) and/or jumping to the source.
331	372
332		<p><a name="fig:profnode"></a><div style="text-align:center"><img src="profnode.gif"></div>
	373	<p><a id="fig:profnode"></a><div style="text-align:center"><img src="profnode.gif"></div>
333	374	<div class="caption"><b>Figure 5 : </b> Execution profiler showing the
334	375	activity of the predicate chat:inv_map_list/5.</div>
335	376

365	406	the call-tree are not added to the call-tree.
366	407	</ul>
367	408
368		<p><h3 id="sec:profilegather"><a name="sec:4.41.3"><span class="sec-nr">4.41.3</span> <span class="sec-title">Information
	409	<p><h3 id="sec:profilegather"><a id="sec:4.41.3"><span class="sec-nr">4.41.3</span> <span class="sec-title">Information
369	410	gathering</span></a></h3>
370	411
371		<a name="sec:profilegather"></a>
	412	<a id="sec:profilegather"></a>
372	413
373	414	<p>While the program executes under the profiler, the system builds a
374	415	<em>dynamic</em> call-tree. It does this using three hooks from the

386	427	to recursion. For this reason the system performs detection of
387	428	recursion. In the simplest case, recursive procedures increment the
388	429	`recursive' count on the current node. Mutual recursion, however, is not
389		easily detected. For example, <a name="idx:call1:1573"></a><a class="pred" href="metacall.html#call/1">call/1</a>
390		can call a predicate that uses <a name="idx:call1:1574"></a><a class="pred" href="metacall.html#call/1">call/1</a>
	430	easily detected. For example, <a id="idx:call1:1573"></a><a class="pred" href="metacall.html#call/1">call/1</a>
	431	can call a predicate that uses <a id="idx:call1:1574"></a><a class="pred" href="metacall.html#call/1">call/1</a>
391	432	itself. This can be viewed as a recursive invocation, but this is
392	433	generally not desirable. Recursion is currently assumed if the same
393	434	predicate <em>with the same parent</em> appears higher in the

399	440	<code>SIGPROF</code>, it `ticks' the current node of the call-tree each
400	441	time the timer fires. On Windows, a MM-timer in a separate thread checks
401	442	100 times per second how much time is spent in the profiled thread and
402		adds this to the current node. See <a class="sec" href="profile.html">section
	443	adds this to the current node. See <a class="sec" href="profile.html#sec:4.41.3.1">section
403	444	4.41.3.1</a> for details.
404	445
405		<p><h4 id="sec:winprofile"><a name="sec:4.41.3.1"><span class="sec-nr">4.41.3.1</span> <span class="sec-title">Profiling
	446	<p><h4 id="sec:winprofile"><a id="sec:4.41.3.1"><span class="sec-nr">4.41.3.1</span> <span class="sec-title">Profiling
406	447	in the Windows Implementation</span></a></h4>
407	448
408		<a name="sec:winprofile"></a>
	449	<a id="sec:winprofile"></a>
409	450
410	451	<p>Profiling in the Windows version is similar, but as profiling is a
411	452	statistical process it is good to be aware of the implementation<sup class="fn">140<span class="fn-text">We

+104

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 3.1</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:projectfiles"><a name="sec:3.1"><span class="sec-nr">3.1</span> <span class="sec-title">The
	235	<h2 id="sec:projectfiles"><a id="sec:3.1"><span class="sec-nr">3.1</span> <span class="sec-title">The
195	236	project source files</span></a></h2>
196	237
197		<a name="sec:projectfiles"></a>
	238	<a id="sec:projectfiles"></a>
198	239
199	240	<p>Organisation of source files depends largely on the size of your
200	241	project. If you are doing exercises for a Prolog course you'll normally

203	244	all together. Even bigger projects will be organised in sub-projects,
204	245	each using its own directory.
205	246
206		<p><h3 id="sec:filelocs"><a name="sec:3.1.1"><span class="sec-nr">3.1.1</span> <span class="sec-title">File
	247	<p><h3 id="sec:filelocs"><a id="sec:3.1.1"><span class="sec-nr">3.1.1</span> <span class="sec-title">File
207	248	Names and Locations</span></a></h3>
208	249
209		<a name="sec:filelocs"></a>
210
211		<p><h4 id="sec:fileext"><a name="sec:3.1.1.1"><span class="sec-nr">3.1.1.1</span> <span class="sec-title">File
	250	<a id="sec:filelocs"></a>
	251
	252	<p><h4 id="sec:fileext"><a id="sec:3.1.1.1"><span class="sec-nr">3.1.1.1</span> <span class="sec-title">File
212	253	Name Extensions</span></a></h4>
213	254
214		<a name="sec:fileext"></a>
215
216		<p><a name="idx:pl:292"></a><a name="idx:pro:293"></a>The first
	255	<a id="sec:fileext"></a>
	256
	257	<p><a id="idx:pl:292"></a><a id="idx:pro:293"></a>The first
217	258	consideration is what extension to use for the source files. Tradition
218	259	calls for <code>.pl</code>, but conflicts with Perl force the use of
219	260	another extension on systems where extensions have global meaning, such

240	281	</dd>
241	282	</dl>
242	283
243		<p><h4 id="sec:projectdirs"><a name="sec:3.1.1.2"><span class="sec-nr">3.1.1.2</span> <span class="sec-title">Project
	284	<p><h4 id="sec:projectdirs"><a id="sec:3.1.1.2"><span class="sec-nr">3.1.1.2</span> <span class="sec-title">Project
244	285	Directories</span></a></h4>
245	286
246		<a name="sec:projectdirs"></a>
247
248		<p><a name="idx:Sdiv:294"></a><a name="idx:chrSneg:295"></a>Large
249		projects are generally composed of sub-projects, each using its own
250		directory or directory structure. If nobody else will ever touch your
251		files and you use only one computer, there is little to worry about, but
252		this is rarely the case with a large project.
	287	<a id="sec:projectdirs"></a>
	288
	289	<p><a id="idx:Sdiv:294"></a><a id="idx:chrSneg:295"></a>Large projects
	290	are generally composed of sub-projects, each using its own directory or
	291	directory structure. If nobody else will ever touch your files and you
	292	use only one computer, there is little to worry about, but this is
	293	rarely the case with a large project.
253	294
254	295	<p>To improve portability, SWI-Prolog uses the POSIX notation for
255	296	filenames, which uses the forward slash (<code><code>/</code></code>) to
256	297	separate directories. Just before reaching the file system, SWI-Prolog
257	298	uses
258		<a name="idx:prologtoosfilename2:296"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>
	299	<a id="idx:prologtoosfilename2:296"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>
259	300	to convert the filename to the conventions used by the hosting operating
260	301	system. It is <em>strongly</em> advised to write paths using the <code><code>/</code></code>,
261	302	especially on systems using the

263	304	violates the portability rules and requires you to <em>double</em> the <code><code>\</code></code>
264	305	due to the Prolog quoted-atom escape rules.
265	306
266		<p>Portable code should use <a name="idx:prologtoosfilename2:297"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>
	307	<p>Portable code should use <a id="idx:prologtoosfilename2:297"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>
267	308	to convert computed paths into system paths when constructing commands
268		for <a name="idx:shell1:298"></a><a class="pred" href="system.html#shell/1">shell/1</a>
	309	for <a id="idx:shell1:298"></a><a class="pred" href="system.html#shell/1">shell/1</a>
269	310	and friends.
270	311
271		<p><h4 id="sec:projectpaths"><a name="sec:3.1.1.3"><span class="sec-nr">3.1.1.3</span> <span class="sec-title">Sub-projects
	312	<p><h4 id="sec:projectpaths"><a id="sec:3.1.1.3"><span class="sec-nr">3.1.1.3</span> <span class="sec-title">Sub-projects
272	313	using search paths</span></a></h4>
273	314
274		<a name="sec:projectpaths"></a>
	315	<a id="sec:projectpaths"></a>
275	316
276	317	<p>Thanks to Quintus, Prolog adapted an extensible mechanism for
277		searching files using <a name="idx:filesearchpath2:299"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
	318	searching files using <a id="idx:filesearchpath2:299"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
278	319	This mechanism allows for comfortable and readable specifications.
279	320
280	321	<p>Suppose you have extensive library packages on graph algorithms, set

285	326	<p>Next, there are three options. One is to add the sub-projects to the
286	327	directory hierarchy of the current project. Another is to use a
287	328	completely dislocated directory. Third, the sub-project can be added to
288		the SWI-Prolog hierarchy. Using local installation, a typical <a name="idx:filesearchpath2:300"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	329	the SWI-Prolog hierarchy. Using local installation, a typical <a id="idx:filesearchpath2:300"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
289	330	is:
290	331
291	332	<pre class="code">

301	342	installation, use an absolute path.
302	343
303	344	<p>Extensive sub-projects with a small well-defined API should define a
304		load file with calls to <a name="idx:usemodule1:301"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	345	load file with calls to <a id="idx:usemodule1:301"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
305	346	to import the various library components and export the API.
306	347
307		<p><h3 id="sec:project-special-files"><a name="sec:3.1.2"><span class="sec-nr">3.1.2</span> <span class="sec-title">Project
	348	<p><h3 id="sec:project-special-files"><a id="sec:3.1.2"><span class="sec-nr">3.1.2</span> <span class="sec-title">Project
308	349	Special Files</span></a></h3>
309	350
310		<a name="sec:project-special-files"></a>
	351	<a id="sec:project-special-files"></a>
311	352
312	353	<p>There are a number of tasks you typically carry out on your project,
313	354	such as loading it, creating a saved state, debugging it, etc. Good
314	355	practice on large projects is to define small files that hold the
315	356	commands to execute such a task, name this file after the task and give
316	357	it a file extension that makes starting easy (see
317		<a class="sec" href="projectfiles.html">section 3.1.1.1</a>). The task <em>load</em>
318		is generally central to these tasks. Here is a tentative list:
	358	<a class="sec" href="projectfiles.html#sec:3.1.1.1">section 3.1.1.1</a>).
	359	The task <em>load</em> is generally central to these tasks. Here is a
	360	tentative list:
319	361
320	362	<p>
321	363	<ul class="latex">

334	376	<p>
335	377	<li><i><code>save.pl</code></i><br>
336	378	Use this file to create a saved state of the application by loading
337		<code>load.pl</code> and calling <a name="idx:qsaveprogram2:302"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
	379	<code>load.pl</code> and calling <a id="idx:qsaveprogram2:302"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>
338	380	to generate a saved state with the proper options.
339	381
340	382	<p>
341	383	<li><i><code>debug.pl</code></i><br>
342	384	Loads the program for debugging. In addition to loading <code>load.pl</code>
343		this file defines rules for <a name="idx:portray1:303"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	385	this file defines rules for <a id="idx:portray1:303"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
344	386	to modify printing rules for complex terms and customisation rules for
345	387	the debugger and editing environment. It may start some of these tools.
346	388	</ul>
347	389
348		<p><h3 id="sec:intsrcfile"><a name="sec:3.1.3"><span class="sec-nr">3.1.3</span> <span class="sec-title">International
	390	<p><h3 id="sec:intsrcfile"><a id="sec:3.1.3"><span class="sec-nr">3.1.3</span> <span class="sec-title">International
349	391	source files</span></a></h3>
350	392
351		<a name="sec:intsrcfile"></a>
352
353		<p>As discussed in <a class="sec" href="widechars.html">section 2.19</a>,
354		SWI-Prolog supports international character handling. Its internal
355		encoding is UNICODE. I/O streams convert to/from this internal format.
356		This section discusses the options for source files not in US-ASCII.
	393	<a id="sec:intsrcfile"></a>
	394
	395	<p>As discussed in <a class="sec" href="widechars.html#sec:2.19">section
	396	2.19</a>, SWI-Prolog supports international character handling. Its
	397	internal encoding is UNICODE. I/O streams convert to/from this internal
	398	format. This section discusses the options for source files not in
	399	US-ASCII.
357	400
358	401	<p>SWI-Prolog can read files in any of the encodings described in
359		<a class="sec" href="widechars.html">section 2.19</a>. Two encodings are
360		of particular interest. The
	402	<a class="sec" href="widechars.html#sec:2.19">section 2.19</a>. Two
	403	encodings are of particular interest. The
361	404	<code>text</code> encoding deals with the current <em>locale</em>, the
362	405	default used by this computer for representing text files. The encodings
363	406	<code>utf8</code>, <code>unicode_le</code> and <code>unicode_be</code>

394	437	<li><i>Using UTF-8 files</i><br>
395	438	The best way to specify source files with many NON-ASCII characters is
396	439	definitely the use of UTF-8 encoding. Prolog can be notified of this
397		encoding in two ways, using a UTF-8 <em>BOM</em> (see <a class="sec" href="widechars.html">section
	440	encoding in two ways, using a UTF-8 <em>BOM</em> (see <a class="sec" href="widechars.html#sec:2.19.1.1">section
398	441	2.19.1.1</a>) or using the directive <code>:- encoding(utf8).</code>
399	442	Many of today's text editors, including PceEmacs, are capable of editing
400	443	UTF-8 files. Projects that were started using local conventions can be

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193	234	</div>
194		<h2 id="sec:prolog_xref"><a name="sec:A.27"><span class="sec-nr">A.27</span> <span class="sec-title">library(prolog_xref):
	235	<h2 id="sec:prolog_xref"><a id="sec:A.27"><span class="sec-nr">A.27</span> <span class="sec-title">library(prolog_xref):
195	236	Cross-reference data collection library</span></a></h2>
196	237
197		<a name="sec:prolog_xref"></a>
198		<a name="sec:lib:prologxref"></a>
	238	<a id="sec:prolog_xref"></a>
	239	<a id="sec:lib:prologxref"></a>
199	240
200	241	<p>This library collects information on defined and used objects in
201	242	Prolog source files. Typically these are predicates, but we expect the

214	255	consider this interface rock-solid.</b>
215	256
216	257	<p>The library is exploited by two graphical tools in the SWI-Prolog
217		environment: the XPCE front-end started by <a name="idx:gxref0:2151"></a><a class="pred" href="xref.html#gxref/0">gxref/0</a>
	258	environment: the XPCE front-end started by <a id="idx:gxref0:2155"></a><a class="pred" href="xref.html#gxref/0">gxref/0</a>
218	259	and described in
219		<a class="sec" href="xref.html">section 3.7</a>, and PceEmacs (<a class="sec" href="pceemacs.html">section
	260	<a class="sec" href="xref.html#sec:3.7">section 3.7</a>, and PceEmacs (<a class="sec" href="pceemacs.html#sec:3.4">section
220	261	3.4</a>), which exploits this library for its syntax colouring.
221	262
222	263	<p>For all predicates described below, <var>Source</var> is the source
223	264	that is processed. This is normally a filename in any notation
224		acceptable to the file loading predicates (see <a name="idx:loadfiles2:2152"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>).
225		Using the hooks defined in <a class="sec" href="prolog_xref.html">section
	265	acceptable to the file loading predicates (see <a id="idx:loadfiles2:2156"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>).
	266	Using the hooks defined in <a class="sec" href="prolog_xref.html#sec:A.27.1">section
226	267	A.27.1</a> it can be anything else that can be translated into a Prolog
227	268	stream holding Prolog source text. <var>Callable</var> is a callable
228		term (see <a name="idx:callable1:2153"></a><a class="pred" href="typetest.html#callable/1">callable/1</a>).
	269	term (see <a id="idx:callable1:2157"></a><a class="pred" href="typetest.html#callable/1">callable/1</a>).
229	270	Callables do not carry a module qualifier unless the referred predicate
230	271	is not in the module defined
231	272	<var>Source</var>.
232	273
233	274	<dl class="latex">
234		<dt class="pubdef"><a name="xref_source/1"><strong>xref_source</strong>(<var>+Source</var>)</a></dt>
	275	<dt class="pubdef"><a id="xref_source/1"><strong>xref_source</strong>(<var>+Source</var>)</a></dt>
235	276	<dd class="defbody">
236	277	Gather information on <var>Source</var>. If <var>Source</var> has
237	278	already been processed and is still up-to-date according to the file
238	279	timestamp, no action is taken. This predicate must be called on a file
239	280	before information can be gathered.</dd>
240		<dt class="pubdef"><a name="xref_current_source/1"><strong>xref_current_source</strong>(<var>?Source</var>)</a></dt>
	281	<dt class="pubdef"><a id="xref_current_source/1"><strong>xref_current_source</strong>(<var>?Source</var>)</a></dt>
241	282	<dd class="defbody">
242	283	<var>Source</var> has been processed.</dd>
243		<dt class="pubdef"><a name="xref_clean/1"><strong>xref_clean</strong>(<var>+Source</var>)</a></dt>
	284	<dt class="pubdef"><a id="xref_clean/1"><strong>xref_clean</strong>(<var>+Source</var>)</a></dt>
244	285	<dd class="defbody">
245	286	Remove the information gathered for <var>Source</var></dd>
246		<dt class="pubdef"><a name="xref_defined/3"><strong>xref_defined</strong>(<var>?Source,
	287	<dt class="pubdef"><a id="xref_defined/3"><strong>xref_defined</strong>(<var>?Source,
247	288	?Callable, -How</var>)</a></dt>
248	289	<dd class="defbody">
249	290	<var>Callable</var> is defined in <var>Source</var>. <var>How</var> is
250	291	one of
251		<table border="0" frame="void" rules="groups" style="margin:auto">
252		<tr valign="top"><td><code>dynamic(Line)</code> </td><td>Declared
253		dynamic at <var>Line</var> </td></tr>
254		<tr valign="top"><td><code>thread_local(Line)</code> </td><td>Declared
255		thread local at <var>Line</var> </td></tr>
256		<tr valign="top"><td><code>multifile(Line)</code> </td><td>Declared
257		multifile at <var>Line</var> </td></tr>
258		<tr valign="top"><td><code>local(Line)</code> </td><td>First clause at <var>Line</var> </td></tr>
259		<tr valign="top"><td><code>foreign(Line)</code> </td><td>Foreign library
260		loaded at <var>Line</var> </td></tr>
261		<tr valign="top"><td><code>constraint(Line)</code> </td><td>CHR
262		Constraint at <var>Line</var> </td></tr>
263		<tr valign="top"><td><code>imported(File)</code> </td><td>Imported from <var>File</var> </td></tr>
	292	<table class="latex frame-void center">
	293	<tr><td><code>dynamic(Line)</code> </td><td>Declared dynamic at <var>Line</var> </td></tr>
	294	<tr><td><code>thread_local(Line)</code> </td><td>Declared thread local
	295	at <var>Line</var> </td></tr>
	296	<tr><td><code>multifile(Line)</code> </td><td>Declared multifile at <var>Line</var> </td></tr>
	297	<tr><td><code>local(Line)</code> </td><td>First clause at <var>Line</var> </td></tr>
	298	<tr><td><code>foreign(Line)</code> </td><td>Foreign library loaded at <var>Line</var> </td></tr>
	299	<tr><td><code>constraint(Line)</code> </td><td>CHR Constraint at <var>Line</var> </td></tr>
	300	<tr><td><code>imported(File)</code> </td><td>Imported from <var>File</var> </td></tr>
264	301	</table>
265	302	</dd>
266		<dt class="pubdef"><a name="xref_called/3"><strong>xref_called</strong>(<var>?Source,
	303	<dt class="pubdef"><a id="xref_called/3"><strong>xref_called</strong>(<var>?Source,
267	304	?Callable, ?By</var>)</a></dt>
268	305	<dd class="defbody">
269	306	<var>Callable</var> is called in <var>Source</var> by <var>By</var>.</dd>
270		<dt class="pubdef"><a name="xref_exported/2"><strong>xref_exported</strong>(<var>?Source,
	307	<dt class="pubdef"><a id="xref_exported/2"><strong>xref_exported</strong>(<var>?Source,
271	308	?Callable</var>)</a></dt>
272	309	<dd class="defbody">
273	310	<var>Callable</var> is public (exported from the module).</dd>
274		<dt class="pubdef"><a name="xref_module/2"><strong>xref_module</strong>(<var>?Source,
	311	<dt class="pubdef"><a id="xref_module/2"><strong>xref_module</strong>(<var>?Source,
275	312	?Module</var>)</a></dt>
276	313	<dd class="defbody">
277	314	<var>Source</var> is a module file defining the given module.</dd>
278		<dt class="pubdef"><a name="xref_built_in/1"><strong>xref_built_in</strong>(<var>?Callable</var>)</a></dt>
	315	<dt class="pubdef"><a id="xref_built_in/1"><strong>xref_built_in</strong>(<var>?Callable</var>)</a></dt>
279	316	<dd class="defbody">
280	317	True if <var>Callable</var> is a built-in predicate. Currently this is
281	318	assumed for all predicates defined in the <code>system</code> module and

284	321	</dd>
285	322	</dl>
286	323
287		<p><h3 id="sec:xrefhooks"><a name="sec:A.27.1"><span class="sec-nr">A.27.1</span> <span class="sec-title">Extending
	324	<p><h3 id="sec:xrefhooks"><a id="sec:A.27.1"><span class="sec-nr">A.27.1</span> <span class="sec-title">Extending
288	325	the library</span></a></h3>
289	326
290		<a name="sec:xrefhooks"></a>
	327	<a id="sec:xrefhooks"></a>
291	328
292	329	<p>The library provides hooks for extending the rules it uses for
293	330	finding predicates called by some programming construct.
294	331
295	332	<dl class="latex">
296		<dt class="pubdef"><a name="prolog:called_by/2"><strong>prolog:called_by</strong>(<var>+Goal,
	333	<dt class="pubdef"><a id="prolog:called_by/2"><strong>prolog:called_by</strong>(<var>+Goal,
297	334	-Called</var>)</a></dt>
298	335	<dd class="defbody">
299	336	<var>Goal</var> is a non-var subgoal appearing in the called object

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	153	sup:hover span.fn-text
	154	{ display: block;
141	155	}
142	156
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184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="predicate_options.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="prolog_xref.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:prologpack"><a name="sec:A.26"><span class="sec-nr">A.26</span> <span class="sec-title">library(prolog_pack):
	235	<h2 id="sec:prologpack"><a id="sec:A.26"><span class="sec-nr">A.26</span> <span class="sec-title">library(prolog_pack):
195	236	A package manager for Prolog</span></a></h2>
196	237
197		<p><a name="sec:prologpack"></a>
	238	<p><a id="sec:prologpack"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">See also</dt>

216	257	that makes installed packages available as libaries.
217	258
218	259	<dl class="latex">
219		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_list_installed/0"><strong>pack_list_installed</strong></a></dt>
	260	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_list_installed/0"><strong>pack_list_installed</strong></a></dt>
220	261	<dd class="defbody">
221	262	List currently installed packages. Unlike <a class="pred" href="prologpack.html#pack_list/1">pack_list/1</a>,
222	263	only locally installed packages are displayed and no connection is made

231	272	</dl>
232	273
233	274	</dd>
234		<dt class="pubdef"><a name="pack_info/1"><strong>pack_info</strong>(<var>+Pack</var>)</a></dt>
	275	<dt class="pubdef"><a id="pack_info/1"><strong>pack_info</strong>(<var>+Pack</var>)</a></dt>
235	276	<dd class="defbody">
236	277	Print more detailed information about <var>Pack</var>.</dd>
237		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_search/1"><strong>pack_search</strong>(<var>+Query</var>)</a></dt>
238		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_list/1"><strong>pack_list</strong>(<var>+Query</var>)</a></dt>
	278	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_search/1"><strong>pack_search</strong>(<var>+Query</var>)</a></dt>
	279	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_list/1"><strong>pack_list</strong>(<var>+Query</var>)</a></dt>
239	280	<dd class="defbody">
240	281	<var>Query</var> package server and installed packages and display
241	282	results.

278	319	</dl>
279	320
280	321	</dd>
281		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_install/1"><strong>pack_install</strong>(<var>+Spec:atom</var>)</a></dt>
	322	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_install/1"><strong>pack_install</strong>(<var>+Spec:atom</var>)</a></dt>
282	323	<dd class="defbody">
283	324	Install a package. <var>Spec</var> is one of
284	325

295	336
296	337	<p>After resolving the type of package, <a class="pred" href="prologpack.html#pack_install/2">pack_install/2</a>
297	338	is used to do the actual installation.</dd>
298		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_install/2"><strong>pack_install</strong>(<var>+Name,
	339	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_install/2"><strong>pack_install</strong>(<var>+Name,
299	340	+Options</var>)</a></dt>
300	341	<dd class="defbody">
301	342	Install package <var>Name</var>. Processes the options below. Default

337	378	particular
338	379	<i>trusted</i> URL instead of the plain pack name for unattented
339	380	operation.</dd>
340		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_url_file/2"><strong>pack_url_file</strong>(<var>+URL,
	381	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_url_file/2"><strong>pack_url_file</strong>(<var>+URL,
341	382	-File</var>)</a></dt>
342	383	<dd class="defbody">
343	384	True if <var>File</var> is a unique id for the referenced pack and
344	385	version. Normally, that is simply the base name, but GitHub archives
345	386	destroy this picture. Needed by the pack manager.</dd>
346		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_rebuild/1"><strong>pack_rebuild</strong>(<var>+Pack</var>)</a></dt>
	387	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_rebuild/1"><strong>pack_rebuild</strong>(<var>+Pack</var>)</a></dt>
347	388	<dd class="defbody">
348	389	Rebuilt possible foreign components of <var>Pack</var>.</dd>
349		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_rebuild/0"><strong>pack_rebuild</strong></a></dt>
	390	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_rebuild/0"><strong>pack_rebuild</strong></a></dt>
350	391	<dd class="defbody">
351	392	Rebuild foreign components of all packages.</dd>
352		<dt class="multidef"><span class="pred-tag">[nondet,multifile]</span><a name="environment/2"><strong>environment</strong>(<var>-Name,
	393	<dt class="multidef"><span class="pred-tag">[nondet,multifile]</span><a id="environment/2"><strong>environment</strong>(<var>-Name,
353	394	-Value</var>)</a></dt>
354	395	<dd class="defbody">
355	396	Hook to define the environment for building packs. This Multifile hook

364	405	</pre>
365	406
366	407	<table class="arglist">
367		<tr valign="top"><td><var>Name</var> </td><td>is an atom denoting a
368		valid variable name </td></tr>
369		<tr valign="top"><td><var>Value</var> </td><td>is either an atom or
370		number representing the value of the variable. </td></tr>
	408	<tr><td><var>Name</var> </td><td>is an atom denoting a valid variable
	409	name </td></tr>
	410	<tr><td><var>Value</var> </td><td>is either an atom or number
	411	representing the value of the variable. </td></tr>
371	412	</table>
372	413	</dd>
373		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="pack_upgrade/1"><strong>pack_upgrade</strong>(<var>+Pack</var>)</a></dt>
	414	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="pack_upgrade/1"><strong>pack_upgrade</strong>(<var>+Pack</var>)</a></dt>
374	415	<dd class="defbody">
375	416	Try to upgrade the package <var>Pack</var>.
376	417

382	423	</dl>
383	424
384	425	</dd>
385		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="pack_remove/1"><strong>pack_remove</strong>(<var>+Name</var>)</a></dt>
	426	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="pack_remove/1"><strong>pack_remove</strong>(<var>+Name</var>)</a></dt>
386	427	<dd class="defbody">
387	428	Remove the indicated package.</dd>
388		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="pack_property/2"><strong>pack_property</strong>(<var>?Pack,
	429	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="pack_property/2"><strong>pack_property</strong>(<var>?Pack,
389	430	?Property</var>)</a></dt>
390	431	<dd class="defbody">
391	432	True when <var>Property</var> is a property of an installed <var>Pack</var>.

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 4.38</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 4.38</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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141	155	}
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143	157	/* Lists */

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186	227	<body style="background:white">

191	232	<a class="nav" href="toplevel.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="debugger.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:protocol"><a name="sec:4.38"><span class="sec-nr">4.38</span> <span class="sec-title">Creating
	235	<h2 id="sec:protocol"><a id="sec:4.38"><span class="sec-nr">4.38</span> <span class="sec-title">Creating
195	236	a Protocol of the User Interaction</span></a></h2>
196	237
197		<a name="sec:protocol"></a>
	238	<a id="sec:protocol"></a>
198	239
199	240	<p>SWI-Prolog offers the possibility to log the interaction with the
200	241	user on a file.<sup class="fn">138<span class="fn-text">A similar

203	244	written to the protocol file.
204	245
205	246	<dl class="latex">
206		<dt class="pubdef"><a name="protocol/1"><strong>protocol</strong>(<var>+File</var>)</a></dt>
	247	<dt class="pubdef"><a id="protocol/1"><strong>protocol</strong>(<var>+File</var>)</a></dt>
207	248	<dd class="defbody">
208	249	Start protocolling on file <var>File</var>. If there is already a
209	250	protocol file open, then close it first. If <var>File</var> exists it is
210	251	truncated.
211	252	</dd>
212		<dt class="pubdef"><a name="protocola/1"><strong>protocola</strong>(<var>+File</var>)</a></dt>
213		<dd class="defbody">
214		Equivalent to <a name="idx:protocol1:1538"></a><a class="pred" href="protocol.html#protocol/1">protocol/1</a>,
	253	<dt class="pubdef"><a id="protocola/1"><strong>protocola</strong>(<var>+File</var>)</a></dt>
	254	<dd class="defbody">
	255	Equivalent to <a id="idx:protocol1:1538"></a><a class="pred" href="protocol.html#protocol/1">protocol/1</a>,
215	256	but does not truncate the <var>File</var> if it exists.
216	257	</dd>
217		<dt class="pubdef"><a name="noprotocol/0"><strong>noprotocol</strong></a></dt>
	258	<dt class="pubdef"><a id="noprotocol/0"><strong>noprotocol</strong></a></dt>
218	259	<dd class="defbody">
219	260	Stop making a protocol of the user interaction. Pending output is
220	261	flushed on the file.
221	262	</dd>
222		<dt class="pubdef"><a name="protocolling/1"><strong>protocolling</strong>(<var>-File</var>)</a></dt>
223		<dd class="defbody">
224		True if a protocol was started with <a name="idx:protocol1:1539"></a><a class="pred" href="protocol.html#protocol/1">protocol/1</a>
225		or <a name="idx:protocola1:1540"></a><a class="pred" href="protocol.html#protocola/1">protocola/1</a>
	263	<dt class="pubdef"><a id="protocolling/1"><strong>protocolling</strong>(<var>-File</var>)</a></dt>
	264	<dd class="defbody">
	265	True if a protocol was started with <a id="idx:protocol1:1539"></a><a class="pred" href="protocol.html#protocol/1">protocol/1</a>
	266	or <a id="idx:protocola1:1540"></a><a class="pred" href="protocol.html#protocola/1">protocola/1</a>
226	267	and unifies <var>File</var> with the current protocol output file.
227	268	</dd>
228	269	</dl>

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2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 12.2</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 12.2</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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	154	{ display: block;
141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
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191	232	<a class="nav" href="qsavelimits.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="useresource.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:qsaveforeign"><a name="sec:12.2"><span class="sec-nr">12.2</span> <span class="sec-title">Runtimes
	235	<h2 id="sec:qsaveforeign"><a id="sec:12.2"><span class="sec-nr">12.2</span> <span class="sec-title">Runtimes
195	236	and Foreign Code</span></a></h2>
196	237
197		<a name="sec:qsaveforeign"></a>
198
199		<p><a name="sec:qforeign"></a> Some applications may need to use the
	238	<a id="sec:qsaveforeign"></a>
	239
	240	<p><a id="sec:qforeign"></a> Some applications may need to use the
200	241	foreign language interface. Object code is by definition
201	242	machine-dependent and thus cannot be part of the saved program file.
202	243

223	264	have a source file <code>myextension.c</code> defining the installation
224	265	function install().
225	266
226		<p>If this file is compiled into a shared library, <a name="idx:loadforeignlibrary1:2116"></a><a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>
	267	<p>If this file is compiled into a shared library, <a id="idx:loadforeignlibrary1:2120"></a><a class="pred" href="foreignlink.html#load_foreign_library/1">load_foreign_library/1</a>
227	268	will load this library and call the installation function to initialise
228	269	the foreign code. If it is loaded as a static extension, define
229	270	install() as the predicate install/0 :

257	298	:- initialization load_foreign_extensions.
258	299	</pre>
259	300
260		<p>The path alias <code>foreign</code> is defined by <a name="idx:filesearchpath2:2117"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
	301	<p>The path alias <code>foreign</code> is defined by <a id="idx:filesearchpath2:2121"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
261	302	By default it searches the directories <code><<var>home</var>>/lib/<<var>arch</var>></code>
262	303	and
263	304	<code><<var>home</var>>/lib</code>. The application can specify
264	305	additional rules for
265		<a name="idx:filesearchpath2:2118"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
	306	<a id="idx:filesearchpath2:2122"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>.
266	307
267	308	<p></body></html>⏎

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193	234	</div>
194		<h2 id="sec:qsavelimits"><a name="sec:12.1"><span class="sec-nr">12.1</span> <span class="sec-title">Limitations
	235	<h2 id="sec:qsavelimits"><a id="sec:12.1"><span class="sec-nr">12.1</span> <span class="sec-title">Limitations
195	236	of qsave_program</span></a></h2>
196	237
197		<a name="sec:qsavelimits"></a>
	238	<a id="sec:qsavelimits"></a>
198	239
199	240	<p>There are three areas that require special attention when using
200		<a name="idx:qsaveprogram12:2112"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>.
	241	<a id="idx:qsaveprogram12:2116"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>.
201	242
202	243	<p>
203	244	<ul class="latex">
204	245	<li>If the program is an embedded Prolog application or uses the foreign
205	246	language interface, care has to be taken to restore the appropriate
206		foreign context. See <a class="sec" href="qsaveforeign.html">section
	247	foreign context. See <a class="sec" href="qsaveforeign.html#sec:12.2">section
207	248	12.2</a> for details.
208	249
209	250	<p>
210	251	<li>If the program uses directives (<code>:- goal.</code> lines) that
211	252	perform other actions than setting predicate attributes (dynamic,
212	253	volatile, etc.) or loading files (consult, etc.), the directive may need
213		to be prefixed with <a name="idx:initialization1:2113"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>.
	254	to be prefixed with <a id="idx:initialization1:2117"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>.
214	255
215	256	<p>
216		<li>Database references as returned by <a name="idx:clause3:2114"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>, <a name="idx:recorded3:2115"></a><a class="pred" href="db.html#recorded/3">recorded/3</a>,
	257	<li>Database references as returned by <a id="idx:clause3:2118"></a><a class="pred" href="examineprog.html#clause/3">clause/3</a>, <a id="idx:recorded3:2119"></a><a class="pred" href="db.html#recorded/3">recorded/3</a>,
217	258	etc., are not preserved and may thus not be part of the database when
218	259	saved.
219	260	</ul>

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193	234	</div>
194		<h2 id="sec:quasiquotations"><a name="sec:A.28"><span class="sec-nr">A.28</span> <span class="sec-title">library(quasi_quotations):
	235	<h2 id="sec:quasiquotations"><a id="sec:A.28"><span class="sec-nr">A.28</span> <span class="sec-title">library(quasi_quotations):
195	236	Define Quasi Quotation syntax</span></a></h2>
196	237
197		<p><a name="sec:quasiquotations"></a>
	238	<p><a id="sec:quasiquotations"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">author</dt>

204	245	</dd>
205	246	<dt class="tag">See also</dt>
206	247	<dd>
207		http://www.cs.tufts.edu/comp/150FP/archive/geoff-mainland/quasiquoting.pdfWhy
208		it's nice to be quoted: quasiquoting for haskell
	248	<a class="url" href="http://www.cs.tufts.edu/comp/150FP/archive/geoff-mainland/quasiquoting.pdf">Why
	249	it's nice to be quoted: quasiquoting for haskell</a>
209	250	</dd>
210	251	</dl>
211	252
212	253	<p>Inspired by
213		http://www.haskell.org/haskellwiki/QuasiquotationHaskell, SWI-Prolog
214		support <i>quasi quotation</i>. Quasi quotation allows for embedding
215		(long) strings using the syntax of an external language (e.g., HTML,
216		SQL) in Prolog text and syntax-aware embedding of Prolog variables in
217		this syntax. At the same time, quasi quotation provides an alternative
218		to represent long strings and atoms in Prolog.
	254	<a class="url" href="http://www.haskell.org/haskellwiki/Quasiquotation">Haskell</a>,
	255	SWI-Prolog support <i>quasi quotation</i>. Quasi quotation allows for
	256	embedding (long) strings using the syntax of an external language (e.g.,
	257	HTML, SQL) in Prolog text and syntax-aware embedding of Prolog variables
	258	in this syntax. At the same time, quasi quotation provides an
	259	alternative to represent long strings and atoms in Prolog.
219	260
220	261	<p>The basic form of a quasi quotation is defined below. Here, <var>Syntax</var>
221	262	is an arbitrary Prolog term that must parse into a <i>callable</i> (atom

284	325	the, suprisingly simple, quasi quotation parser for HTML.
285	326
286	327	<dl class="latex">
287		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="with_quasi_quotation_input/3"><strong>with_quasi_quotation_input</strong>(<var>+Content,
	328	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="with_quasi_quotation_input/3"><strong>with_quasi_quotation_input</strong>(<var>+Content,
288	329	-Stream, :Goal</var>)</a></dt>
289	330	<dd class="defbody">
290	331	Process the quasi-quoted <var>Content</var> using <var>Stream</var>

300	341	<li>It will be closed after <var>Goal</var> completes.
301	342	</ul>
302	343	<table class="arglist">
303		<tr valign="top"><td><var>Goal</var> </td><td>is executed as <code>once(Goal)</code>. <var>Goal</var>
	344	<tr><td><var>Goal</var> </td><td>is executed as <code>once(Goal)</code>. <var>Goal</var>
304	345	must succeed. Failure or exceptions from <var>Goal</var> are interpreted
305	346	as syntax errors. </td></tr>
306	347	</table>

314	355	</dl>
315	356
316	357	</dd>
317		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="phrase_from_quasi_quotation/2"><strong>phrase_from_quasi_quotation</strong>(<var>:Grammar,
	358	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="phrase_from_quasi_quotation/2"><strong>phrase_from_quasi_quotation</strong>(<var>:Grammar,
318	359	+Content</var>)</a></dt>
319	360	<dd class="defbody">
320	361	Process the quasi quotation using the DCG <var>Grammar</var>. Failure of

329	370	</dl>
330	371
331	372	</dd>
332		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="quasi_quotation_syntax/1"><strong>quasi_quotation_syntax</strong>(<var>:SyntaxName</var>)</a></dt>
	373	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="quasi_quotation_syntax/1"><strong>quasi_quotation_syntax</strong>(<var>:SyntaxName</var>)</a></dt>
333	374	<dd class="defbody">
334	375	Declare the predicate <var>SyntaxName</var>/4 to implement the the quasi
335	376	quote syntax <var>SyntaxName</var>. Normally used as a directive.</dd>
336		<dt class="pubdef"><a name="quasi_quotation_syntax_error/1"><strong>quasi_quotation_syntax_error</strong>(<var>+Error</var>)</a></dt>
	377	<dt class="pubdef"><a id="quasi_quotation_syntax_error/1"><strong>quasi_quotation_syntax_error</strong>(<var>+Error</var>)</a></dt>
337	378	<dd class="defbody">
338	379	Report <code>syntax_error(Error)</code> using the current location in
339	380	the quasi quoted input parser.

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193	234	</div>
194		<h2 id="sec:quickstart"><a name="sec:2.1"><span class="sec-nr">2.1</span> <span class="sec-title">Getting
	235	<h2 id="sec:quickstart"><a id="sec:2.1"><span class="sec-nr">2.1</span> <span class="sec-title">Getting
195	236	started quickly</span></a></h2>
196	237
197		<a name="sec:quickstart"></a>
198
199		<p><h3 id="sec:startpl"><a name="sec:2.1.1"><span class="sec-nr">2.1.1</span> <span class="sec-title">Starting
	238	<a id="sec:quickstart"></a>
	239
	240	<p><h3 id="sec:startpl"><a id="sec:2.1.1"><span class="sec-nr">2.1.1</span> <span class="sec-title">Starting
200	241	SWI-Prolog</span></a></h3>
201	242
202		<a name="sec:startpl"></a>
203
204		<p><h4 id="sec:startunix"><a name="sec:2.1.1.1"><span class="sec-nr">2.1.1.1</span> <span class="sec-title">Starting
	243	<a id="sec:startpl"></a>
	244
	245	<p><h4 id="sec:startunix"><a id="sec:2.1.1.1"><span class="sec-nr">2.1.1.1</span> <span class="sec-title">Starting
205	246	SWI-Prolog on Unix</span></a></h4>
206	247
207		<a name="sec:startunix"></a>
	248	<a id="sec:startunix"></a>
208	249
209	250	<p>By default, SWI-Prolog is installed as `swipl'. The command line
210	251	arguments of SWI-Prolog itself and its utility programs are documented

220	261	</pre>
221	262
222	263	<p>After starting Prolog, one normally loads a program into it using
223		<a name="idx:consult1:6"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
	264	<a id="idx:consult1:6"></a><a class="pred" href="consulting.html#consult/1">consult/1</a>,
224	265	which may be abbreviated by putting the name of the program file between
225	266	square brackets. The following goal loads the file
226		https://raw.githubusercontent.com/SWI-Prolog/swipl-devel/master/demo/likes.pllikes.pl
	267	<a class="url" href="https://raw.githubusercontent.com/SWI-Prolog/swipl-devel/master/demo/likes.pl">likes.pl</a>
227	268	containing clauses for the predicates likes/2 :
228	269
229	270	<pre class="code">

245	286	</pre>
246	287
247	288	<p>After this point, Unix and Windows users unite, so if you are using
248		Unix please continue at <a class="sec" href="quickstart.html">section
	289	Unix please continue at <a class="sec" href="quickstart.html#sec:2.1.3">section
249	290	2.1.3</a>.
250	291
251		<p><h4 id="sec:startwin"><a name="sec:2.1.1.2"><span class="sec-nr">2.1.1.2</span> <span class="sec-title">Starting
	292	<p><h4 id="sec:startwin"><a id="sec:2.1.1.2"><span class="sec-nr">2.1.1.2</span> <span class="sec-title">Starting
252	293	SWI-Prolog on Windows</span></a></h4>
253	294
254		<a name="sec:startwin"></a>
	295	<a id="sec:startwin"></a>
255	296
256	297	<p>After SWI-Prolog has been installed on a Windows system, the
257	298	following important new things are available to the user:

272	313	</ul>
273	314
274	315	<p>The normal way to start the <code>likes.pl</code> file mentioned in
275		<a class="sec" href="quickstart.html">section 2.1.1.1</a> is by simply
276		double-clicking this file in the Windows explorer.
277
278		<p><h3 id="sec:consultuser"><a name="sec:2.1.2"><span class="sec-nr">2.1.2</span> <span class="sec-title">Adding
	316	<a class="sec" href="quickstart.html#sec:2.1.1.1">section 2.1.1.1</a> is
	317	by simply double-clicking this file in the Windows explorer.
	318
	319	<p><h3 id="sec:consultuser"><a id="sec:2.1.2"><span class="sec-nr">2.1.2</span> <span class="sec-title">Adding
279	320	rules from the console</span></a></h3>
280	321
281		<a name="sec:consultuser"></a>
	322	<a id="sec:consultuser"></a>
282	323
283	324	<p>Although we strongly advice to put your program in a file, optionally
284		edit it and use <a name="idx:make0:7"></a><a class="pred" href="consulting.html#make/0">make/0</a>
285		to reload it (see <a class="sec" href="quickstart.html">section 2.1.4</a>),
286		it is possible to manage facts and rules from the terminal. The most
287		conveniant way to add a few clauses is by consulting the pseudo file
	325	edit it and use <a id="idx:make0:7"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	326	to reload it (see <a class="sec" href="quickstart.html#sec:2.1.4">section
	327	2.1.4</a>), it is possible to manage facts and rules from the terminal.
	328	The most conveniant way to add a few clauses is by consulting the pseudo
	329	file
288	330	<code>user</code>. The input is ended using the system end-of-file
289	331	character.
290	332

299	341	true.
300	342	</pre>
301	343
302		<p>The predicates <a name="idx:assertz1:8"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
303		and <a name="idx:retract1:9"></a><a class="pred" href="db.html#retract/1">retract/1</a>
	344	<p>The predicates <a id="idx:assertz1:8"></a><a class="pred" href="db.html#assertz/1">assertz/1</a>
	345	and <a id="idx:retract1:9"></a><a class="pred" href="db.html#retract/1">retract/1</a>
304	346	are alternatives to add and remove rules and facts.
305	347
306		<p><h3 id="sec:execquery"><a name="sec:2.1.3"><span class="sec-nr">2.1.3</span> <span class="sec-title">Executing
	348	<p><h3 id="sec:execquery"><a id="sec:2.1.3"><span class="sec-nr">2.1.3</span> <span class="sec-title">Executing
307	349	a query</span></a></h3>
308	350
309		<a name="sec:execquery"></a>
	351	<a id="sec:execquery"></a>
310	352
311	353	<p>After loading a program, one can ask Prolog queries about the
312	354	program. The query below asks Prolog what food `sam' likes. The system

339	381	differs in several ways from traditional Prolog top level. The current
340	382	top level was designed in cooperation with Ulrich Neumerkel.</span></sup>
341	383
342		<p><h3 id="sec:viewprogram"><a name="sec:2.1.4"><span class="sec-nr">2.1.4</span> <span class="sec-title">Examining
	384	<p><h3 id="sec:viewprogram"><a id="sec:2.1.4"><span class="sec-nr">2.1.4</span> <span class="sec-title">Examining
343	385	and modifying your program</span></a></h3>
344	386
345		<a name="sec:viewprogram"></a>
346
347		<p>If properly configured, the predicate <a name="idx:edit1:10"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
	387	<a id="sec:viewprogram"></a>
	388
	389	<p>If properly configured, the predicate <a id="idx:edit1:10"></a><a class="pred" href="edit.html#edit/1">edit/1</a>
348	390	starts the built-in or user configured editor on the argument. The
349	391	argument can be anything that can be linked to a location: a file name,
350	392	predicate name, module name, etc. If the argument resolves to only one

353	395
354	396	<p>If a graphical user interface is available, the editor normally
355	397	creates a new window and the system prompts for the next command. The
356		user may edit the source file, save it and run <a name="idx:make0:11"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	398	user may edit the source file, save it and run <a id="idx:make0:11"></a><a class="pred" href="consulting.html#make/0">make/0</a>
357	399	to update any modified source file. If the editor cannot be opened in a
358		window it the same console and leaving the editor runs <a name="idx:make0:12"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	400	window it the same console and leaving the editor runs <a id="idx:make0:12"></a><a class="pred" href="consulting.html#make/0">make/0</a>
359	401	to reload any source files that have been modified.
360	402
361	403	<pre class="code">

369	411	...
370	412	</pre>
371	413
372		<p>The program can also be <em>decompiled</em> using <a name="idx:listing1:13"></a><a class="pred" href="listing.html#listing/1">listing/1</a>
373		as below. The argument is <a name="idx:listing1:14"></a><a class="pred" href="listing.html#listing/1">listing/1</a>
	414	<p>The program can also be <em>decompiled</em> using <a id="idx:listing1:13"></a><a class="pred" href="listing.html#listing/1">listing/1</a>
	415	as below. The argument is <a id="idx:listing1:14"></a><a class="pred" href="listing.html#listing/1">listing/1</a>
374	416	is just a predicate name, a predicate
375	417	<em>indicator</em> of the form <var>Name/Arity</var>, e.g., <code>?-
376		listing(<a name="idx:mild1:15"></a><span class="pred-ext">mild/1</span>).</code>
	418	listing(<a id="idx:mild1:15"></a><span class="pred-ext">mild/1</span>).</code>
377	419	or a <em>head</em>, e.g., <code>?- listing(likes(sam, _).</code>,
378		listing all <em>matching</em> clauses. The predicate <a name="idx:listing0:16"></a><a class="pred" href="listing.html#listing/0">listing/0</a>,
	420	listing all <em>matching</em> clauses. The predicate <a id="idx:listing0:16"></a><a class="pred" href="listing.html#listing/0">listing/0</a>,
379	421	i.e., without arguments lists the entire program.<sup class="fn">8<span class="fn-text">This
380	422	lists several <em>hook</em> predicates that are defined by default and
381	423	is typically not very informative.</span></sup>

389	431	true.
390	432	</pre>
391	433
392		<p><h3 id="sec:halt"><a name="sec:2.1.5"><span class="sec-nr">2.1.5</span> <span class="sec-title">Stopping
	434	<p><h3 id="sec:halt"><a id="sec:2.1.5"><span class="sec-nr">2.1.5</span> <span class="sec-title">Stopping
393	435	Prolog</span></a></h3>
394	436
395		<a name="sec:halt"></a>
	437	<a id="sec:halt"></a>
396	438
397	439	<p>The interactive toplevel can be stopped in two ways: enter the system
398	440	end-of-file character (typically <i>Control-D</i>) or by executing the
399		<a name="idx:halt0:17"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>
	441	<a id="idx:halt0:17"></a><a class="pred" href="toplevel.html#halt/0">halt/0</a>
400	442	predicate:
401	443
402	444	<pre class="code">

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193	234	</div>
194		<h2 id="sec:random"><a name="sec:A.29"><span class="sec-nr">A.29</span> <span class="sec-title">library(random):
	235	<h2 id="sec:random"><a id="sec:A.29"><span class="sec-nr">A.29</span> <span class="sec-title">library(random):
195	236	Random numbers</span></a></h2>
196	237
197		<p><a name="sec:random"></a>
	238	<p><a id="sec:random"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">author</dt>

214	255	are based on the GMP library.
215	256
216	257	<dl class="latex">
217		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="random/1"><strong>random</strong>(<var>-R:float</var>)</a></dt>
	258	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random/1"><strong>random</strong>(<var>-R:float</var>)</a></dt>
218	259	<dd class="defbody">
219	260	Binds <var>R</var> to a new random float in the <i>open</i> interval
220	261	(0.0,1.0).

231	272	</dl>
232	273
233	274	</dd>
234		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="random_between/3"><strong>random_between</strong>(<var>+L:int,
	275	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="random_between/3"><strong>random_between</strong>(<var>+L:int,
235	276	+U:int, -R:int</var>)</a></dt>
236	277	<dd class="defbody">
237	278	Binds <var>R</var> to a random integer in [<var>L</var>,<var>U</var>]
238	279	(i.e., including both <var>L</var> and
239	280	<var>U</var>). Fails silently if <var>U</var><var><</var><var>L</var>.</dd>
240		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="random/3"><strong>random</strong>(<var>+L:int,
	281	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random/3"><strong>random</strong>(<var>+L:int,
241	282	+U:int, -R:int</var>)</a></dt>
242		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="random/3"><strong>random</strong>(<var>+L:float,
	283	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random/3"><strong>random</strong>(<var>+L:float,
243	284	+U:float, -R:float</var>)</a></dt>
244	285	<dd class="defbody">
245	286	Generate a random integer or float in a range. If <var>L</var> and <var>U</var>

259	300	</dl>
260	301
261	302	</dd>
262		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="setrand/1"><strong>setrand</strong>(<var>+State</var>)</a></dt>
263		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="getrand/1"><strong>getrand</strong>(<var>-State</var>)</a></dt>
	303	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="setrand/1"><strong>setrand</strong>(<var>+State</var>)</a></dt>
	304	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="getrand/1"><strong>getrand</strong>(<var>-State</var>)</a></dt>
264	305	<dd class="defbody">
265	306	Query/set the state of the random generator. This is intended for
266	307	restarting the generator at a known state only. The predicate <a class="pred" href="random.html#setrand/1">setrand/1</a>

290	331	</dl>
291	332
292	333	</dd>
293		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="maybe/0"><strong>maybe</strong></a></dt>
	334	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="maybe/0"><strong>maybe</strong></a></dt>
294	335	<dd class="defbody">
295	336	Succeed/fail with equal probability (variant of <a class="pred" href="random.html#maybe/1">maybe/1</a>).</dd>
296		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="maybe/1"><strong>maybe</strong>(<var>+P</var>)</a></dt>
	337	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="maybe/1"><strong>maybe</strong>(<var>+P</var>)</a></dt>
297	338	<dd class="defbody">
298	339	Succeed with probability <var>P</var>, fail with probability 1-<var>P</var></dd>
299		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="maybe/2"><strong>maybe</strong>(<var>+K,
	340	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="maybe/2"><strong>maybe</strong>(<var>+K,
300	341	+N</var>)</a></dt>
301	342	<dd class="defbody">
302	343	Succeed with probability <var>K</var>/<var>N</var> (variant of <a class="pred" href="random.html#maybe/1">maybe/1</a>)</dd>
303		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="random_perm2/4"><strong>random_perm2</strong>(<var>?A,
	344	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="random_perm2/4"><strong>random_perm2</strong>(<var>?A,
304	345	?B, ?X, ?Y</var>)</a></dt>
305	346	<dd class="defbody">
306	347	Does <var>X</var>=<var>A</var>,<var>Y</var>=<var>B</var> or <var>X</var>=<var>B</var>,<var>Y</var>=<var>A</var>
307	348	with equal probability.</dd>
308		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="random_member/2"><strong>random_member</strong>(<var>-X,
	349	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="random_member/2"><strong>random_member</strong>(<var>-X,
309	350	+List:list</var>)</a></dt>
310	351	<dd class="defbody">
311	352	<var>X</var> is a random member of <var>List</var>. Equivalent to

321	362	</dl>
322	363
323	364	</dd>
324		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="random_select/3"><strong>random_select</strong>(<var>-X,
	365	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="random_select/3"><strong>random_select</strong>(<var>-X,
325	366	+List, -Rest</var>)</a></dt>
326		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="random_select/3"><strong>random_select</strong>(<var>+X,
	367	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random_select/3"><strong>random_select</strong>(<var>+X,
327	368	-List, +Rest</var>)</a></dt>
328	369	<dd class="defbody">
329	370	Randomly select or insert an element. Either <var>List</var> or <var>Rest</var>

337	378	</dl>
338	379
339	380	</dd>
340		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="randset/3"><strong>randset</strong>(<var>+K:int,
	381	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="randset/3"><strong>randset</strong>(<var>+K:int,
341	382	+N:int, -S:list(int)</var>)</a></dt>
342	383	<dd class="defbody">
343	384	<var>S</var> is a sorted list of <var>K</var> unique random integers in

364	405	</dl>
365	406
366	407	</dd>
367		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="randseq/3"><strong>randseq</strong>(<var>+K:int,
	408	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="randseq/3"><strong>randseq</strong>(<var>+K:int,
368	409	+N:int, -List:list(int)</var>)</a></dt>
369	410	<dd class="defbody">
370	411	S is a list of <var>K</var> unique random integers in the range 1..<var>N</var>.

384	425	</dl>
385	426
386	427	</dd>
387		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="random_permutation/2"><strong>random_permutation</strong>(<var>+List,
	428	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random_permutation/2"><strong>random_permutation</strong>(<var>+List,
388	429	-Permutation</var>)</a></dt>
389		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="random_permutation/2"><strong>random_permutation</strong>(<var>-List,
	430	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="random_permutation/2"><strong>random_permutation</strong>(<var>-List,
390	431	+Permutation</var>)</a></dt>
391	432	<dd class="defbody">
392	433	<var>Permutation</var> is a random permutation of <var>List</var>. This

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193	234	</div>
194		<h2 id="sec:readutil"><a name="sec:A.30"><span class="sec-nr">A.30</span> <span class="sec-title">library(readutil):
	235	<h2 id="sec:readutil"><a id="sec:A.30"><span class="sec-nr">A.30</span> <span class="sec-title">library(readutil):
195	236	Reading lines, streams and files</span></a></h2>
196	237
197		<a name="sec:readutil"></a>
	238	<a id="sec:readutil"></a>
198	239
199	240	<p>This library contains primitives to read lines, files, multiple
200	241	terms, etc. The package <code>clib</code> provides a shared object (DLL)

205	246	shared object if performance of these predicates is critical.
206	247
207	248	<dl class="latex">
208		<dt class="pubdef"><a name="read_line_to_codes/2"><strong>read_line_to_codes</strong>(<var>+Stream,
	249	<dt class="pubdef"><a id="read_line_to_codes/2"><strong>read_line_to_codes</strong>(<var>+Stream,
209	250	-Codes</var>)</a></dt>
210	251	<dd class="defbody">
211	252	Read the next line of input from <var>Stream</var> and unify the result
212	253	with
213	254	<var>Codes</var> <em>after</em> the line has been read. A line is ended
214		by a newline character or end-of-file. Unlike <a name="idx:readlinetocodes3:2154"></a><a class="pred" href="readutil.html#read_line_to_codes/3">read_line_to_codes/3</a>,
	255	by a newline character or end-of-file. Unlike <a id="idx:readlinetocodes3:2158"></a><a class="pred" href="readutil.html#read_line_to_codes/3">read_line_to_codes/3</a>,
215	256	this predicate removes a trailing newline character.
216	257
217	258	<p>On end-of-file the atom <code>end_of_file</code> is returned. See
218	259	also
219		<a name="idx:atendofstream01:2155"></a><a class="pred" href="chario.html#at_end_of_stream/0">at_end_of_stream/[0,1]</a>.</dd>
220		<dt class="pubdef"><a name="read_line_to_codes/3"><strong>read_line_to_codes</strong>(<var>+Stream,
	260	<a id="idx:atendofstream01:2159"></a><a class="pred" href="chario.html#at_end_of_stream/0">at_end_of_stream/[0,1]</a>.</dd>
	261	<dt class="pubdef"><a id="read_line_to_codes/3"><strong>read_line_to_codes</strong>(<var>+Stream,
221	262	-Codes, ?Tail</var>)</a></dt>
222	263	<dd class="defbody">
223	264	Difference-list version to read an input line to a list of character
224		codes. Reading stops at the newline or end-of-file character, but unlike <a name="idx:readlinetocodes2:2156"></a><a class="pred" href="readutil.html#read_line_to_codes/2">read_line_to_codes/2</a>,
	265	codes. Reading stops at the newline or end-of-file character, but unlike <a id="idx:readlinetocodes2:2160"></a><a class="pred" href="readutil.html#read_line_to_codes/2">read_line_to_codes/2</a>,
225	266	the newline is retained in the output. This predicate is especially
226	267	useful for reading a block of lines up to some delimiter. The following
227	268	example reads an HTTP header ended by a blank line:

240	281	</pre>
241	282
242	283	</dd>
243		<dt class="pubdef"><a name="read_stream_to_codes/2"><strong>read_stream_to_codes</strong>(<var>+Stream,
	284	<dt class="pubdef"><a id="read_stream_to_codes/2"><strong>read_stream_to_codes</strong>(<var>+Stream,
244	285	-Codes</var>)</a></dt>
245	286	<dd class="defbody">
246	287	Read all input until end-of-file and unify the result to <var>Codes</var>.</dd>
247		<dt class="pubdef"><a name="read_stream_to_codes/3"><strong>read_stream_to_codes</strong>(<var>+Stream,
	288	<dt class="pubdef"><a id="read_stream_to_codes/3"><strong>read_stream_to_codes</strong>(<var>+Stream,
248	289	-Codes, ?Tail</var>)</a></dt>
249	290	<dd class="defbody">
250		Difference-list version of <a name="idx:readstreamtocodes2:2157"></a><a class="pred" href="readutil.html#read_stream_to_codes/2">read_stream_to_codes/2</a>.</dd>
251		<dt class="pubdef"><a name="read_file_to_codes/3"><strong>read_file_to_codes</strong>(<var>+Spec,
	291	Difference-list version of <a id="idx:readstreamtocodes2:2161"></a><a class="pred" href="readutil.html#read_stream_to_codes/2">read_stream_to_codes/2</a>.</dd>
	292	<dt class="pubdef"><a id="read_file_to_codes/3"><strong>read_file_to_codes</strong>(<var>+Spec,
252	293	-Codes, +Options</var>)</a></dt>
253	294	<dd class="defbody">
254	295	Read a file to a list of character codes. <var>Spec</var> is a file
255		specification for <a name="idx:absolutefilename3:2158"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>. <var>Codes</var>
	296	specification for <a id="idx:absolutefilename3:2162"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>. <var>Codes</var>
256	297	is the resulting code list. <var>Options</var> is a list of options for
257		<a name="idx:absolutefilename3:2159"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
258		and <a name="idx:open4:2160"></a><a class="pred" href="IO.html#open/4">open/4</a>.
	298	<a id="idx:absolutefilename3:2163"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	299	and <a id="idx:open4:2164"></a><a class="pred" href="IO.html#open/4">open/4</a>.
259	300	In addition, the option
260	301	<code>tail(Tail)</code> is defined, forming a difference-list.</dd>
261		<dt class="pubdef"><a name="read_file_to_terms/3"><strong>read_file_to_terms</strong>(<var>+Spec,
	302	<dt class="pubdef"><a id="read_file_to_terms/3"><strong>read_file_to_terms</strong>(<var>+Spec,
262	303	-Terms, +Options</var>)</a></dt>
263	304	<dd class="defbody">
264		Read a file to a list of Prolog terms (see <a name="idx:read1:2161"></a><a class="pred" href="termrw.html#read/1">read/1</a>). <var>Spec</var>
265		is a file specification for <a name="idx:absolutefilename3:2162"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>. <var>Terms</var>
	305	Read a file to a list of Prolog terms (see <a id="idx:read1:2165"></a><a class="pred" href="termrw.html#read/1">read/1</a>). <var>Spec</var>
	306	is a file specification for <a id="idx:absolutefilename3:2166"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>. <var>Terms</var>
266	307	is the resulting list of Prolog terms. <var>Options</var> is a list of
267	308	options for
268		<a name="idx:absolutefilename3:2163"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
269		and <a name="idx:open4:2164"></a><a class="pred" href="IO.html#open/4">open/4</a>.
	309	<a id="idx:absolutefilename3:2167"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>
	310	and <a id="idx:open4:2168"></a><a class="pred" href="IO.html#open/4">open/4</a>.
270	311	In addition, the option
271	312	<code>tail(Tail)</code> is defined, forming a difference-list.
272	313	</dd>

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.31</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:record"><a name="sec:A.31"><span class="sec-nr">A.31</span> <span class="sec-title">library(record):
	235	<h2 id="sec:record"><a id="sec:A.31"><span class="sec-nr">A.31</span> <span class="sec-title">library(record):
195	236	Access named fields in a term</span></a></h2>
196	237
197		<a name="sec:record"></a>
198		<a name="sec:lib:record"></a>
	238	<a id="sec:record"></a>
	239	<a id="sec:lib:record"></a>
199	240
200	241	<p>The library <code>library(record)</code> provides named access to
201	242	fields in a record represented as a compound term such as <code>point(X,

210	251	predicates, an optimizing compiler can easily inline them for optimal
211	252	preformance.
212	253
213		<p>A record is defined using the directive <a name="idx:record1:2165"></a><a class="pred" href="record.html#record/1">record/1</a>.
	254	<p>A record is defined using the directive <a id="idx:record1:2169"></a><a class="pred" href="record.html#record/1">record/1</a>.
214	255	We introduce the library with a short example:
215	256
216	257	<pre class="code">

233	274
234	275	<p>In this definition, <<var>name</var>> is an atom defining the
235	276	name of the argument,
236		<<var>type</var>> is an optional type specification as defined by <a name="idx:mustbe2:2166"></a><a class="pred" href="error.html#must_be/2">must_be/2</a>
	277	<<var>type</var>> is an optional type specification as defined by <a id="idx:mustbe2:2170"></a><a class="pred" href="error.html#must_be/2">must_be/2</a>
237	278	from library <code>library(error)</code>, and <<var>default</var>>
238	279	is the default initial value. The
239	280	<<var>type</var>> defaults to <code>any</code>. If no default

269	310	<p>
270	311	<li><i><<var>constructor</var>>_<<var>name</var>>(Record,
271	312	Value)</i><br>
272		Unify <var>Value</var> with argument in <var>Record</var> named <<var>name</var>>.<sup class="fn">182<span class="fn-text">Note
	313	Unify <var>Value</var> with argument in <var>Record</var> named <<var>name</var>>.<sup class="fn">183<span class="fn-text">Note
273	314	this is not called `get_' as it performs unification and can perfectly
274	315	well instantiate the argument.</span></sup>
275	316

289	330	!Record)</i><br>
290	331	Destructively replace the argument <<var>name</var>> in <var>Record</var>
291	332	by
292		<var>Value</var> based on <a name="idx:setarg3:2167"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>.
	333	<var>Value</var> based on <a id="idx:setarg3:2171"></a><a class="pred" href="manipterm.html#setarg/3">setarg/3</a>.
293	334	Use with care.
294	335
295	336	<p>
296	337	<li><i>nb_set_<<var>name</var>>_of_<<var>constructor</var>>(+Value,
297	338	!Record)</i><br>
298		As above, but using non-backtrackable assignment based on <a name="idx:nbsetarg3:2168"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
	339	As above, but using non-backtrackable assignment based on <a id="idx:nbsetarg3:2172"></a><a class="pred" href="manipterm.html#nb_setarg/3">nb_setarg/3</a>.
299	340	Use with <em>extreme</em> care.
300	341
301	342	<p>

318	359	</ul>
319	360
320	361	<dl class="latex">
321		<dt class="pubdef"><a name="record/1"><strong>record</strong>(<var>+Spec</var>)</a></dt>
	362	<dt class="pubdef"><a id="record/1"><strong>record</strong>(<var>+Spec</var>)</a></dt>
322	363	<dd class="defbody">
323	364	The construct <code>:- record Spec, ...</code> is used to define access
324	365	to named fields in a compound. It is subject to term-expansion (see
325		<a name="idx:expandterm2:2169"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>)
	366	<a id="idx:expandterm2:2173"></a><a class="pred" href="consulting.html#expand_term/2">expand_term/2</a>)
326	367	and cannot be called as a predicate. See
327		<a class="sec" href="record.html">section A.31</a> for details.
	368	<a class="sec" href="record.html#sec:A.31">section A.31</a> for details.
328	369	</dd>
329	370	</dl>
330	371

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193	234	</div>
194		<h2 id="sec:reexport"><a name="sec:6.7"><span class="sec-nr">6.7</span> <span class="sec-title">Composing
	235	<h2 id="sec:reexport"><a id="sec:6.7"><span class="sec-nr">6.7</span> <span class="sec-title">Composing
195	236	modules from other modules</span></a></h2>
196	237
197		<a name="sec:reexport"></a>
	238	<a id="sec:reexport"></a>
198	239
199	240	<p>The predicates in this section are intended to create new modules
200	241	from the content of other modules. Below is an example to define a
201	242	<em>composite</em> module. The example exports all public predicates of <code>module_1</code>, <code>module_2</code>
202		and <code>module_3</code>, <a name="idx:pred1:1710"></a><span class="pred-ext">pred/1</span>
	243	and <code>module_3</code>, <a id="idx:pred1:1714"></a><span class="pred-ext">pred/1</span>
203	244	from <code>module_4</code>, all predicates from <code>module_5</code>
204	245	except
205		<a name="idx:donotuse1:1711"></a><span class="pred-ext">do_not_use/1</span>
	246	<a id="idx:donotuse1:1715"></a><span class="pred-ext">do_not_use/1</span>
206	247	and all predicates from <code>module_6</code> while renaming
207		<a name="idx:pred1:1712"></a><span class="pred-ext">pred/1</span> into <a name="idx:mypred1:1713"></a><span class="pred-ext">mypred/1</span>.
	248	<a id="idx:pred1:1716"></a><span class="pred-ext">pred/1</span> into <a id="idx:mypred1:1717"></a><span class="pred-ext">mypred/1</span>.
208	249
209	250	<pre class="code">
210	251	:- module(my_composite, []).

218	259	</pre>
219	260
220	261	<dl class="latex">
221		<dt class="pubdef"><a name="reexport/1"><strong>reexport</strong>(<var>+Files</var>)</a></dt>
	262	<dt class="pubdef"><a id="reexport/1"><strong>reexport</strong>(<var>+Files</var>)</a></dt>
222	263	<dd class="defbody">
223		Load and import predicates as <a name="idx:usemodule1:1714"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
	264	Load and import predicates as <a id="idx:usemodule1:1718"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>
224	265	and re-export all imported predicates. The reexport declarations must
225	266	immediately follow the module declaration.</dd>
226		<dt class="pubdef"><a name="reexport/2"><strong>reexport</strong>(<var>+File,
	267	<dt class="pubdef"><a id="reexport/2"><strong>reexport</strong>(<var>+File,
227	268	+Import</var>)</a></dt>
228	269	<dd class="defbody">
229		Import from <var>File</var> as <a name="idx:usemodule2:1715"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
	270	Import from <var>File</var> as <a id="idx:usemodule2:1719"></a><a class="pred" href="import.html#use_module/2">use_module/2</a>
230	271	and re-export the imported predicates. The reexport declarations must
231	272	immediately follow the module declaration.
232	273	</dd>

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193	234	</div>
194		<h2 id="sec:registry"><a name="sec:A.32"><span class="sec-nr">A.32</span> <span class="sec-title">library(registry):
	235	<h2 id="sec:registry"><a id="sec:A.32"><span class="sec-nr">A.32</span> <span class="sec-title">library(registry):
195	236	Manipulating the Windows registry</span></a></h2>
196	237
197		<a name="sec:registry"></a>
	238	<a id="sec:registry"></a>
198	239
199	240	<p>The <code>library(registry)</code> is only available on the
200	241	MS-Windows version of SWI-Prolog. It loads the foreign extension <code>plregtry.dll</code>,

214	255	<code>users</code>.
215	256
216	257	<dl class="latex">
217		<dt class="pubdef"><a name="registry_get_key/2"><strong>registry_get_key</strong>(<var>+Path,
	258	<dt class="pubdef"><a id="registry_get_key/2"><strong>registry_get_key</strong>(<var>+Path,
218	259	-Value</var>)</a></dt>
219	260	<dd class="defbody">
220	261	Get the principal (default) value associated to this key. Fails silently
221	262	if the key does not exist.</dd>
222		<dt class="pubdef"><a name="registry_get_key/3"><strong>registry_get_key</strong>(<var>+Path,
	263	<dt class="pubdef"><a id="registry_get_key/3"><strong>registry_get_key</strong>(<var>+Path,
223	264	+Name, -Value</var>)</a></dt>
224	265	<dd class="defbody">
225	266	Get a named value associated to this key.</dd>
226		<dt class="pubdef"><a name="registry_set_key/2"><strong>registry_set_key</strong>(<var>+Path,
	267	<dt class="pubdef"><a id="registry_set_key/2"><strong>registry_set_key</strong>(<var>+Path,
227	268	+Value</var>)</a></dt>
228	269	<dd class="defbody">
229	270	Set the principal (default) value of this key. Creates (a path to) the
230	271	key if it does not already exist.</dd>
231		<dt class="pubdef"><a name="registry_set_key/3"><strong>registry_set_key</strong>(<var>+Path,
	272	<dt class="pubdef"><a id="registry_set_key/3"><strong>registry_set_key</strong>(<var>+Path,
232	273	+Name, +Value</var>)</a></dt>
233	274	<dd class="defbody">
234	275	Associate a named value to this key. Creates (a path to) the key if it
235	276	does not already exist.</dd>
236		<dt class="pubdef"><a name="registry_delete_key/1"><strong>registry_delete_key</strong>(<var>+Path</var>)</a></dt>
	277	<dt class="pubdef"><a id="registry_delete_key/1"><strong>registry_delete_key</strong>(<var>+Path</var>)</a></dt>
237	278	<dd class="defbody">
238	279	Delete the indicated key.</dd>
239		<dt class="pubdef"><a name="shell_register_file_type/4"><strong>shell_register_file_type</strong>(<var>+Ext,
	280	<dt class="pubdef"><a id="shell_register_file_type/4"><strong>shell_register_file_type</strong>(<var>+Ext,
240	281	+Type, +Name, +OpenAction</var>)</a></dt>
241	282	<dd class="defbody">
242	283	Register a file-type. <var>Ext</var> is the extension to associate.

244	285	<var>Name</var> is the name visible in the Windows file-type browser.
245	286	Finally, <var>OpenAction</var> defines the action to execute when a file
246	287	with this extension is opened in the Windows explorer.</dd>
247		<dt class="pubdef"><a name="shell_register_dde/6"><strong>shell_register_dde</strong>(<var>+Type,
	288	<dt class="pubdef"><a id="shell_register_dde/6"><strong>shell_register_dde</strong>(<var>+Type,
248	289	+Action, +Service, +Topic, +Command, +IfNotRunning</var>)</a></dt>
249	290	<dd class="defbody">
250	291	Associate DDE actions to a type. <var>Type</var> is the same type as
251		used for the 2nd argument of <a name="idx:shellregisterfiletype4:2170"></a><a class="pred" href="registry.html#shell_register_file_type/4">shell_register_file_type/4</a>, <var>Action</var>
	292	used for the 2nd argument of <a id="idx:shellregisterfiletype4:2174"></a><a class="pred" href="registry.html#shell_register_file_type/4">shell_register_file_type/4</a>, <var>Action</var>
252	293	is the action to perform, <var>Service</var> and <var>Topic</var>
253	294	specify the DDE topic to address, and <var>Command</var> is the command
254	295	to execute on this topic. Finally, <var>IfNotRunning</var> defines the
255	296	command to execute if the required DDE server is not present.</dd>
256		<dt class="pubdef"><a name="shell_register_prolog/1"><strong>shell_register_prolog</strong>(<var>+Ext</var>)</a></dt>
	297	<dt class="pubdef"><a id="shell_register_prolog/1"><strong>shell_register_prolog</strong>(<var>+Ext</var>)</a></dt>
257	298	<dd class="defbody">
258	299	Default registration of SWI-Prolog, which is invoked as part of the
259	300	initialisation process on Windows systems. As the source also includes

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 6.10</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:resmodules"><a name="sec:6.10"><span class="sec-nr">6.10</span> <span class="sec-title">Reserved
	235	<h2 id="sec:resmodules"><a id="sec:6.10"><span class="sec-nr">6.10</span> <span class="sec-title">Reserved
195	236	Modules and using the `user' module</span></a></h2>
196	237
197		<a name="sec:resmodules"></a>
	238	<a id="sec:resmodules"></a>
198	239
199	240	<p>As mentioned above, SWI-Prolog contains two special modules. The
200	241	first one is the module <code>system</code>. This module contains all

208	249	implies they can use all predicates imported into <code>user</code>
209	250	without explicitly importing them. If an application loads all modules
210	251	from the
211		<code>user</code> module using <a name="idx:usemodule1:1725"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>,
	252	<code>user</code> module using <a id="idx:usemodule1:1729"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>,
212	253	one achieves a scoping system similar to the C-language, where every
213	254	module can access all exported predicates without any special
214	255	precautions.

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193	234	</div>
194		<h1 id="sec:runtime"><a name="sec:12"><span class="sec-nr">12</span> <span class="sec-title">Generating
	235	<h1 id="sec:runtime"><a id="sec:12"><span class="sec-nr">12</span> <span class="sec-title">Generating
195	236	Runtime Applications</span></a></h1>
196	237
197		<a name="sec:runtime"></a>
	238	<a id="sec:runtime"></a>
198	239
199	240	<p>This chapter describes the features of SWI-Prolog for delivering
200	241	applications that can run without the development version of the system

204	245	The first part is the <em>emulator</em>, which is machine-dependent. The
205	246	second part is the <em>resource archive</em>, which contains the
206	247	compiled program in a machine-independent format, startup options and
207		possibly user-defined <em>resources</em>; see <a name="idx:resource3:2096"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>
	248	possibly user-defined <em>resources</em>; see <a id="idx:resource3:2100"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>
208	249	and
209		<a name="idx:openresource3:2097"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>.
	250	<a id="idx:openresource3:2101"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>.
210	251
211	252	<p>These two parts can be connected in various ways. The most common way
212	253	for distributed runtime applications is to <em>concatenate</em> the two
213	254	parts. This can be achieved using external commands (Unix:
214	255	<b>cat</b>, Windows: <b>copy</b>), or using the
215		<code>stand_alone</code> option to <a name="idx:qsaveprogram2:2098"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
	256	<code>stand_alone</code> option to <a id="idx:qsaveprogram2:2102"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
216	257	The second option is to attach a startup script in front of the resource
217	258	that starts the emulator with the proper options. This is the default
218	259	under Unix. Finally, an emulator can be told to use a specified resource
219	260	file using the <strong>-x</strong> command line switch.
220	261
221	262	<dl class="latex">
222		<dt class="pubdef"><a name="qsave_program/2"><strong>qsave_program</strong>(<var>+File,
	263	<dt class="pubdef"><a id="qsave_program/2"><strong>qsave_program</strong>(<var>+File,
223	264	+Options</var>)</a></dt>
224	265	<dd class="defbody">
225	266	Saves the current state of the program to the file <var>File</var>. The

232	273	<dl class="latex">
233	274	<dt><strong>local</strong>(<var>+KBytes</var>)</dt>
234	275	<dd class="defbody">
235		Limit for the local stack. See <a class="sec" href="cmdline.html">section
	276	Limit for the local stack. See <a class="sec" href="cmdline.html#sec:2.4.3">section
236	277	2.4.3</a>.
237	278	</dd>
238	279	<dt><strong>global</strong>(<var>+KBytes</var>)</dt>
239	280	<dd class="defbody">
240		Limit for the global stack. See <a class="sec" href="cmdline.html">section
	281	Limit for the global stack. See <a class="sec" href="cmdline.html#sec:2.4.3">section
241	282	2.4.3</a>.
242	283	</dd>
243	284	<dt><strong>trail</strong>(<var>+KBytes</var>)</dt>
244	285	<dd class="defbody">
245		Limit for the trail stack. See <a class="sec" href="cmdline.html">section
	286	Limit for the trail stack. See <a class="sec" href="cmdline.html#sec:2.4.3">section
246	287	2.4.3</a>.
247	288	</dd>
248	289	<dt><strong>goal</strong>(<var>:Callable</var>)</dt>

264	305	If
265	306	<code>kernel</code>, lock all predicates as system predicates. If
266	307	<code>development</code>, save the predicates in their current state and
267		keep reading resources from their source (if present). See also <a name="idx:resource3:2099"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>.
	308	keep reading resources from their source (if present). See also <a id="idx:resource3:2103"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>.
268	309	</dd>
269	310	<dt><strong>autoload</strong>(<var>+Boolean</var>)</dt>
270	311	<dd class="defbody">
271		If <code>true</code> (default), run <a name="idx:autoload0:2100"></a><a class="pred" href="runtime.html#autoload/0">autoload/0</a>
	312	If <code>true</code> (default), run <a id="idx:autoload0:2104"></a><a class="pred" href="runtime.html#autoload/0">autoload/0</a>
272	313	first.
273	314	</dd>
274	315	<dt><strong>map</strong>(<var>+File</var>)</dt>

288	329	application has all libraries loaded, the resulting executable is
289	330	completely independent of the runtime environment or location where it
290	331	was built. See also
291		<a class="sec" href="compilation.html">section 2.10.2.4</a>.
	332	<a class="sec" href="compilation.html#sec:2.10.2.4">section 2.10.2.4</a>.
292	333	</dd>
293	334	<dt><strong>emulator</strong>(<var>+File</var>)</dt>
294	335	<dd class="defbody">

298	339	<dd class="defbody">
299	340	If <code>save</code>, include shared objects (DLLs) into the saved
300	341	state. See
301		<a name="idx:currentforeignlibrary2:2101"></a><a class="pred" href="foreignlink.html#current_foreign_library/2">current_foreign_library/2</a>.
	342	<a id="idx:currentforeignlibrary2:2105"></a><a class="pred" href="foreignlink.html#current_foreign_library/2">current_foreign_library/2</a>.
302	343	If the program <b>strip</b> is available, this is first used to reduce
303		the size of the shared object. If a state is started, <a name="idx:useforeignlibrary1:2102"></a><a class="pred" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a>
	344	the size of the shared object. If a state is started, <a id="idx:useforeignlibrary1:2106"></a><a class="pred" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a>
304	345	first tries to locate the foreign resource in the executable. When found
305	346	it copies the content of the resource to a temporary file and loads it.
306	347	If possible (Unix), the temporary object is deleted immediately after
307		opening.<sup class="fn">180<span class="fn-text">This option is
	348	opening.<sup class="fn">181<span class="fn-text">This option is
308	349	experimental and currently disabled by default. It will become the
309	350	default if it proves robust.</span></sup>
310	351	</dd>
311	352	</dl>
312	353
313	354	</dd>
314		<dt class="pubdef"><a name="qsave_program/1"><strong>qsave_program</strong>(<var>+File</var>)</a></dt>
	355	<dt class="pubdef"><a id="qsave_program/1"><strong>qsave_program</strong>(<var>+File</var>)</a></dt>
315	356	<dd class="defbody">
316	357	Equivalent to <code>qsave_program(File, [])</code>.</dd>
317		<dt class="pubdef"><a name="autoload/0"><strong>autoload</strong></a></dt>
	358	<dt class="pubdef"><a id="autoload/0"><strong>autoload</strong></a></dt>
318	359	<dd class="defbody">
319	360	Check the current Prolog program for predicates that are referred to,
320	361	are undefined and have a definition in the Prolog library. Load the
321	362	appropriate libraries.
322	363
323		<p>This predicate is used by <a name="idx:qsaveprogram12:2103"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>
	364	<p>This predicate is used by <a id="idx:qsaveprogram12:2107"></a><a class="pred" href="runtime.html#qsave_program/1">qsave_program/[1,2]</a>
324	365	to ensure the saved state does not depend on availability of the
325	366	libraries. The predicate
326		<a name="idx:autoload0:2104"></a><a class="pred" href="runtime.html#autoload/0">autoload/0</a>
	367	<a id="idx:autoload0:2108"></a><a class="pred" href="runtime.html#autoload/0">autoload/0</a>
327	368	examines all clauses of the loaded program (obtained with
328		<a name="idx:clause2:2105"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>)
	369	<a id="idx:clause2:2109"></a><a class="pred" href="examineprog.html#clause/2">clause/2</a>)
329	370	and analyzes the body for referenced goals. Such an analysis cannot be
330	371	complete in Prolog, which allows for the creation of arbitrary terms at
331	372	runtime and the use of them as a goal. The current analysis is limited

335	376	<ul class="latex">
336	377	<li>Direct goals appearing in the body
337	378	<li>Arguments of declared meta-predicates that are marked with an
338		integer (0..9). See <a name="idx:metapredicate1:2106"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>.
	379	integer (0..9). See <a id="idx:metapredicate1:2110"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>.
339	380	</ul>
340	381
341	382	<p>The analysis of meta-predicate arguments is limited to cases where

352	393
353	394	<p>But, the calls to prove_simple/1 and prove_complex/1 in the example
354	395	below are <em>not</em> discovered by the analysis and therefore the
355		modules that define these predicates must be loaded explicitly using <a name="idx:usemodule1:2107"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>,2.
	396	modules that define these predicates must be loaded explicitly using <a id="idx:usemodule1:2111"></a><a class="pred" href="import.html#use_module/1">use_module/1</a>,2.
356	397
357	398	<pre class="code">
358	399	...,

363	404	Goal)),
364	405	</pre>
365	406
366		<p>It is good practice to use <a name="idx:gxref0:2108"></a><a class="pred" href="xref.html#gxref/0">gxref/0</a>
	407	<p>It is good practice to use <a id="idx:gxref0:2112"></a><a class="pred" href="xref.html#gxref/0">gxref/0</a>
367	408	to make sure that the program has sufficient declarations such that the
368	409	analaysis tools can verify that all required predicates can be resolved
369		and that all code is called. See <a name="idx:metapredicate1:2109"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>, <a name="idx:dynamic1:2110"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>, <a name="idx:public1:2111"></a><a class="pred" href="dynamic.html#public/1">public/1</a>
	410	and that all code is called. See <a id="idx:metapredicate1:2113"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>, <a id="idx:dynamic1:2114"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>, <a id="idx:public1:2115"></a><a class="pred" href="dynamic.html#public/1">public/1</a>
370	411	and prolog:called_by/2.</dd>
371		<dt class="pubdef"><a name="volatile/1"><strong>volatile</strong> <var>+Name/Arity,
	412	<dt class="pubdef"><a id="volatile/1"><strong>volatile</strong> <var>+Name/Arity,
372	413	...</var></a></dt>
373	414	<dd class="defbody">
374	415	Declare that the clauses of specified predicates should <strong>not</strong>

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193	234	</div>
194		<h2 id="sec:sicstus-chr"><a name="sec:8.6"><span class="sec-nr">8.6</span> <span class="sec-title">Backwards
	235	<h2 id="sec:sicstus-chr"><a id="sec:8.6"><span class="sec-nr">8.6</span> <span class="sec-title">Backwards
195	236	Compatibility</span></a></h2>
196	237
197		<a name="sec:sicstus-chr"></a>
198		<h3 id="sec:chr-sicstus"><a name="sec:8.6.1"><span class="sec-nr">8.6.1</span> <span class="sec-title">The
	238	<a id="sec:sicstus-chr"></a>
	239	<h3 id="sec:chr-sicstus"><a id="sec:8.6.1"><span class="sec-nr">8.6.1</span> <span class="sec-title">The
199	240	Old SICStus CHR implemenation</span></a></h3>
200	241
201		<a name="sec:chr-sicstus"></a>
	242	<a id="sec:chr-sicstus"></a>
202	243
203	244	<p>There are small differences between the current K.U.Leuven CHR system
204	245	in SWI-Prolog, older versions of the same system, and SICStus' CHR

216	257	<ul class="latex">
217	258	<li><i>The constraints/1 declaration</i><br>
218	259	This declaration is deprecated. It has been replaced with the
219		<a name="idx:chrconstraint1:1823"></a><a class="pred" href="practical.html#chr_constraint/1">chr_constraint/1</a>
	260	<a id="idx:chrconstraint1:1827"></a><a class="pred" href="practical.html#chr_constraint/1">chr_constraint/1</a>
220	261	declaration.
221	262
222	263	<p>
223	264	<li><i>The option/2 declaration</i><br>
224	265	This declaration is deprecated. It has been replaced with the
225		<a name="idx:chroption2:1824"></a><a class="pred" href="SyntaxAndSemantics.html#chr_option/2">chr_option/2</a>
	266	<a id="idx:chroption2:1828"></a><a class="pred" href="SyntaxAndSemantics.html#chr_option/2">chr_option/2</a>
226	267	declaration.
227	268
228	269	<p>

242	283	<li><i>Guard bindings</i><br>
243	284	The <code>check_guard_bindings</code> option only turns invalid calls to
244	285	unification into failure. In SICStus this option does more: it
245		intercepts instantiation errors from Prolog built-ins such as <a name="idx:is2:1825"></a><a class="pred" href="arith.html#is/2">is/2</a>
	286	intercepts instantiation errors from Prolog built-ins such as <a id="idx:is2:1829"></a><a class="pred" href="arith.html#is/2">is/2</a>
246	287	and turns them into failure. In SWI-Prolog, we do not go this far, as we
247	288	like to separate concerns more. The CHR compiler is aware of the CHR
248	289	code, the Prolog system, and the programmer should be aware of the

250	291	rules.
251	292	</ul>
252	293
253		<p><h3 id="sec:chr-eclipse"><a name="sec:8.6.2"><span class="sec-nr">8.6.2</span> <span class="sec-title">The
	294	<p><h3 id="sec:chr-eclipse"><a id="sec:8.6.2"><span class="sec-nr">8.6.2</span> <span class="sec-title">The
254	295	Old ECLiPSe CHR implemenation</span></a></h3>
255	296
256		<a name="sec:chr-eclipse"></a>
	297	<a id="sec:chr-eclipse"></a>
257	298
258	299	<p>The old ECLiPSe CHR implementation features a label_with/1 construct
259	300	for labeling variables in CHR constraints. This feature has long since

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193	234	</div>
194		<h2 id="sec:signal"><a name="sec:4.12"><span class="sec-nr">4.12</span> <span class="sec-title">Handling
	235	<h2 id="sec:signal"><a id="sec:4.12"><span class="sec-nr">4.12</span> <span class="sec-title">Handling
195	236	signals</span></a></h2>
196	237
197		<a name="sec:signal"></a>
	238	<a id="sec:signal"></a>
198	239
199	240	<p>As of version 3.1.0, SWI-Prolog is able to handle software interrupts
200		(signals) in Prolog as well as in foreign (C) code (see <a class="sec" href="foreigninclude.html">section
	241	(signals) in Prolog as well as in foreign (C) code (see <a class="sec" href="foreigninclude.html#sec:11.4.13">section
201	242	11.4.13</a>).
202	243
203	244	<p>Signals are used to handle internal errors (execution of a

212	253	communication (Unix kill() function).
213	254
214	255	<dl class="latex">
215		<dt class="pubdef"><a name="on_signal/3"><strong>on_signal</strong>(<var>+Signal,
	256	<dt class="pubdef"><a id="on_signal/3"><strong>on_signal</strong>(<var>+Signal,
216	257	-Old, :New</var>)</a></dt>
217	258	<dd class="defbody">
218	259	Determines the reaction on <var>Signal</var>. <var>Old</var> is unified

221	262	retrieved using <code>on_signal(Signal, Current, Current)</code>.
222	263
223	264	<p>The action description is an atom denoting the name of the predicate
224		that will be called if <var>Signal</var> arrives. <a name="idx:onsignal3:773"></a><a class="pred" href="signal.html#on_signal/3">on_signal/3</a>
	265	that will be called if <var>Signal</var> arrives. <a id="idx:onsignal3:773"></a><a class="pred" href="signal.html#on_signal/3">on_signal/3</a>
225	266	is a meta-predicate, which implies that <<var>Module</var>>:<<var>Name</var>>
226	267	refers to <<var>Name</var>>/1 in module <<var>Module</var>>.
227	268	The handler is called with a single argument: the name of the signal as

229	270
230	271	<p>Two predicate names have special meaning. <code>throw</code> implies
231	272	Prolog will map the signal onto a Prolog exception as described in
232		<a class="sec" href="exception.html">section 4.11</a>. <code>default</code>
	273	<a class="sec" href="exception.html#sec:4.11">section 4.11</a>. <code>default</code>
233	274	resets the handler to the settings active before SWI-Prolog manipulated
234	275	the handler.
235	276

243	284
244	285	<p>The signal names are defined by the POSIX standard as symbols of the
245	286	form <code>SIG</code><SIGNAME>. The Prolog name for a signal is
246		the lowercase version of <SIGNAME>. The predicate <a name="idx:currentsignal3:774"></a><a class="pred" href="signal.html#current_signal/3">current_signal/3</a>
	287	the lowercase version of <SIGNAME>. The predicate <a id="idx:currentsignal3:774"></a><a class="pred" href="signal.html#current_signal/3">current_signal/3</a>
247	288	may be used to map between names and signals.
248	289
249	290	<p>Initially, some signals are mapped to <code>throw</code>, while all

251	292	exception:
252	293	<code>fpe</code>, <code>alrm</code>, <code>xcpu</code>, <code>xfsz</code>
253	294	and <code>vtalrm</code>.</dd>
254		<dt class="pubdef"><a name="current_signal/3"><strong>current_signal</strong>(<var>?Name,
	295	<dt class="pubdef"><a id="current_signal/3"><strong>current_signal</strong>(<var>?Name,
255	296	?Id, ?Handler</var>)</a></dt>
256	297	<dd class="defbody">
257	298	Enumerate the currently defined signal handling. <var>Name</var> is the
258	299	signal name, <var>Id</var> is the numerical identifier and <var>Handler</var>
259		is the currently defined handler (see <a name="idx:onsignal3:775"></a><a class="pred" href="signal.html#on_signal/3">on_signal/3</a>).
	300	is the currently defined handler (see <a id="idx:onsignal3:775"></a><a class="pred" href="signal.html#on_signal/3">on_signal/3</a>).
260	301	</dd>
261	302	</dl>
262	303
263		<p><h3 id="sec:signalhandling"><a name="sec:4.12.1"><span class="sec-nr">4.12.1</span> <span class="sec-title">Notes
	304	<p><h3 id="sec:signalhandling"><a id="sec:4.12.1"><span class="sec-nr">4.12.1</span> <span class="sec-title">Notes
264	305	on signal handling</span></a></h3>
265	306
266		<a name="sec:signalhandling"></a>
	307	<a id="sec:signalhandling"></a>
267	308
268	309	<p>Before deciding to deal with signals in your application, please
269	310	consider the following:

285	326	foreign functions called from a handler cannot safely use the SWI-Prolog
286	327	API and cannot use C longjmp(). Handlers defined as <code>throw</code>
287	328	are unsafe. Handlers defined to call a predicate are safe. Note that the
288		predicate can call <a name="idx:throw1:776"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
	329	predicate can call <a id="idx:throw1:776"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
289	330	but the delivery is delayed until Prolog is in a safe state.
290	331
291		<p>The C-interface described in <a class="sec" href="foreigninclude.html">section
	332	<p>The C-interface described in <a class="sec" href="foreigninclude.html#sec:11.4.13">section
292	333	11.4.13</a> provides the option
293	334	<code>PL_SIGSYNC</code> to select either safe synchronous or unsafe
294	335	asynchronous delivery.

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193	234	</div>
194		<h2 id="sec:simplex"><a name="sec:A.33"><span class="sec-nr">A.33</span> <span class="sec-title">library(simplex):
	235	<h2 id="sec:simplex"><a id="sec:A.33"><span class="sec-nr">A.33</span> <span class="sec-title">library(simplex):
195	236	Solve linear programming problems</span></a></h2>
196	237
197		<a name="sec:simplex"></a>
198
199		<p><a name="sec:simplex"></a>
	238	<a id="sec:simplex"></a>
	239
	240	<p><a id="sec:simplex"></a>
200	241
201	242	<dl class="tags">
202	243	<dt class="tag">author</dt>
203	244	<dd>
204		https://www.metalevel.atMarkus Triska
	245	<a class="url" href="https://www.metalevel.at">Markus Triska</a>
205	246	</dd>
206	247	</dl>
207	248
208		<p><h3 id="sec:simplex-intro"><a name="sec:A.33.1"><span class="sec-nr">A.33.1</span> <span class="sec-title">Introduction</span></a></h3>
209
210		<p><a name="sec:simplex-intro"></a>
	249	<p><h3 id="sec:simplex-intro"><a id="sec:A.33.1"><span class="sec-nr">A.33.1</span> <span class="sec-title">Introduction</span></a></h3>
	250
	251	<p><a id="sec:simplex-intro"></a>
211	252
212	253	<p>A <b>linear programming problem</b> or simply <b>linear program</b>
213	254	(LP) consists of:

253	294	<p>The most frequently used predicates are thus:
254	295
255	296	<dl class="latex">
256		<dt class="pubdef"><a name="gen_state/1"><strong>gen_state</strong>(<var>-State</var>)</a></dt>
	297	<dt class="pubdef"><a id="gen_state/1"><strong>gen_state</strong>(<var>-State</var>)</a></dt>
257	298	<dd class="defbody">
258	299	Generates an initial state corresponding to an empty linear program.</dd>
259		<dt class="pubdef"><a name="constraint/3"><strong>constraint</strong>(<var>+Constraint,
	300	<dt class="pubdef"><a id="constraint/3"><strong>constraint</strong>(<var>+Constraint,
260	301	+S0, -S</var>)</a></dt>
261	302	<dd class="defbody">
262	303	Adds a linear or integrality constraint to the linear program

268	309	or <code>>=</code>. The coefficient <code>1</code> can be omitted. An
269	310	integrality constraint is of the form <code>integral(Variable)</code>
270	311	and constrains Variable to an integral value.</dd>
271		<dt class="pubdef"><a name="maximize/3"><strong>maximize</strong>(<var>+Objective,
	312	<dt class="pubdef"><a id="maximize/3"><strong>maximize</strong>(<var>+Objective,
272	313	+S0, -S</var>)</a></dt>
273	314	<dd class="defbody">
274	315	Maximizes the objective function, stated as a list of

276	317	elements, with respect to the linear program corresponding to state
277	318	<var>S0</var>. <code>\</code>arg{<var>S</var>} is unified with an
278	319	internal representation of the solved instance.</dd>
279		<dt class="pubdef"><a name="minimize/3"><strong>minimize</strong>(<var>+Objective,
	320	<dt class="pubdef"><a id="minimize/3"><strong>minimize</strong>(<var>+Objective,
280	321	+S0, -S</var>)</a></dt>
281	322	<dd class="defbody">
282	323	Analogous to <a class="pred" href="simplex.html#maximize/3">maximize/3</a>.</dd>
283		<dt class="pubdef"><a name="variable_value/3"><strong>variable_value</strong>(<var>+State,
	324	<dt class="pubdef"><a id="variable_value/3"><strong>variable_value</strong>(<var>+State,
284	325	+Variable, -Value</var>)</a></dt>
285	326	<dd class="defbody">
286	327	<var>Value</var> is unified with the value obtained for <var>Variable</var>. <var>State</var>
287	328	must correspond to a solved instance.</dd>
288		<dt class="pubdef"><a name="objective/2"><strong>objective</strong>(<var>+State,
	329	<dt class="pubdef"><a id="objective/2"><strong>objective</strong>(<var>+State,
289	330	-Objective</var>)</a></dt>
290	331	<dd class="defbody">
291	332	Unifies <var>Objective</var> with the result of the objective function

300	341	be <i>non-negative</i>. This may change in future versions, and
301	342	non-negativity constraints should therefore be stated explicitly.
302	343
303		<p><h3 id="sec:simplex-delayed-column"><a name="sec:A.33.2"><span class="sec-nr">A.33.2</span> <span class="sec-title">Delayed
	344	<p><h3 id="sec:simplex-delayed-column"><a id="sec:A.33.2"><span class="sec-nr">A.33.2</span> <span class="sec-title">Delayed
304	345	column generation</span></a></h3>
305	346
306		<p><a name="sec:simplex-delayed-column"></a>
	347	<p><a id="sec:simplex-delayed-column"></a>
307	348
308	349	<p><i>Delayed column generation</i> means that more constraint columns
309	350	are added to an existing LP. The following predicates are frequently
310	351	used when this method is applied:
311	352
312	353	<dl class="latex">
313		<dt class="pubdef"><a name="constraint/4"><strong>constraint</strong>(<var>+Name,
	354	<dt class="pubdef"><a id="constraint/4"><strong>constraint</strong>(<var>+Name,
314	355	+Constraint, +S0, -S</var>)</a></dt>
315	356	<dd class="defbody">
316	357	Like <a class="pred" href="simplex.html#constraint/3">constraint/3</a>,
317	358	and attaches the name <var>Name</var> (an atom or compound term) to the
318	359	new constraint.</dd>
319		<dt class="pubdef"><a name="shadow_price/3"><strong>shadow_price</strong>(<var>+State,
	360	<dt class="pubdef"><a id="shadow_price/3"><strong>shadow_price</strong>(<var>+State,
320	361	+Name, -Value</var>)</a></dt>
321	362	<dd class="defbody">
322	363	Unifies <var>Value</var> with the shadow price corresponding to the
323	364	linear constraint whose name is <var>Name</var>. <var>State</var> must
324	365	correspond to a solved instance.</dd>
325		<dt class="pubdef"><a name="constraint_add/4"><strong>constraint_add</strong>(<var>+Name,
	366	<dt class="pubdef"><a id="constraint_add/4"><strong>constraint_add</strong>(<var>+Name,
326	367	+Left, +S0, -S</var>)</a></dt>
327	368	<dd class="defbody">
328	369	<var>Left</var> is a list of <code>Coefficient*Variable</code> terms.

333	374
334	375	<p>An example application of <i>delayed column generation</i> to solve a <i>bin
335	376	packing</i> task is available from:
336		https://www.metalevel.at/various/colgen/<b>metalevel.at/various/colgen/</b>
337
338		<p><h3 id="sec:simplex-special-structure"><a name="sec:A.33.3"><span class="sec-nr">A.33.3</span> <span class="sec-title">Solving
	377	<a class="url" href="https://www.metalevel.at/various/colgen/"><b>metalevel.at/various/colgen/</b></a>
	378
	379	<p><h3 id="sec:simplex-special-structure"><a id="sec:A.33.3"><span class="sec-nr">A.33.3</span> <span class="sec-title">Solving
339	380	LPs with special structure</span></a></h3>
340	381
341		<p><a name="sec:simplex-special-structure"></a>
	382	<p><a id="sec:simplex-special-structure"></a>
342	383
343	384	<p>The following predicates allow you to solve specific kinds of LPs
344	385	more efficiently:
345	386
346	387	<dl class="latex">
347		<dt class="pubdef"><a name="transportation/4"><strong>transportation</strong>(<var>+Supplies,
	388	<dt class="pubdef"><a id="transportation/4"><strong>transportation</strong>(<var>+Supplies,
348	389	+Demands, +Costs, -Transport</var>)</a></dt>
349	390	<dd class="defbody">
350	391	Solves a transportation problem. <var>Supplies</var> and <var>Demands</var>

356	397	the form of a list of lists that represents the transportation matrix,
357	398	where element (<i>i</i>,<i>j</i>) denotes how many units to ship from <i>i</i>
358	399	to <i>j</i>.</dd>
359		<dt class="pubdef"><a name="assignment/2"><strong>assignment</strong>(<var>+Cost,
	400	<dt class="pubdef"><a id="assignment/2"><strong>assignment</strong>(<var>+Cost,
360	401	-Assignment</var>)</a></dt>
361	402	<dd class="defbody">
362	403	Solves a linear assignment problem. <var>Cost</var> is a list of lists

368	409	</dd>
369	410	</dl>
370	411
371		<p><h3 id="sec:simplex-examples"><a name="sec:A.33.4"><span class="sec-nr">A.33.4</span> <span class="sec-title">Examples</span></a></h3>
372
373		<p><a name="sec:simplex-examples"></a>
	412	<p><h3 id="sec:simplex-examples"><a id="sec:A.33.4"><span class="sec-nr">A.33.4</span> <span class="sec-title">Examples</span></a></h3>
	413
	414	<p><a id="sec:simplex-examples"></a>
374	415
375	416	<p>We include a few examples for solving LPs with this library.
376	417
377		<p><h4 id="sec:simplex-ex-1"><a name="sec:A.33.4.1"><span class="sec-nr">A.33.4.1</span> <span class="sec-title">Example
	418	<p><h4 id="sec:simplex-ex-1"><a id="sec:A.33.4.1"><span class="sec-nr">A.33.4.1</span> <span class="sec-title">Example
378	419	1</span></a></h4>
379	420
380		<p><a name="sec:simplex-ex-1"></a>
	421	<p><a id="sec:simplex-ex-1"></a>
381	422
382	423	<p>This is the "radiation therapy" example, taken from
383	424	<i>Introduction to Operations Research</i> by Hillier and Lieberman.
384	425
385		<p>https://www.metalevel.at/prolog/dcg<b>Prolog DCG notation</b> is used
386		to <i>implicitly</i> thread the state through posting the constraints:
	426	<p><a class="url" href="https://www.metalevel.at/prolog/dcg"><b>Prolog
	427	DCG notation</b></a> is used to <i>implicitly</i> thread the state
	428	through posting the constraints:
387	429
388	430	<pre class="code">
389	431	:- use_module(library(simplex)).

410	452	Val2 = 9 rdiv 2.
411	453	</pre>
412	454
413		<p><h4 id="sec:simplex-ex-2"><a name="sec:A.33.4.2"><span class="sec-nr">A.33.4.2</span> <span class="sec-title">Example
	455	<p><h4 id="sec:simplex-ex-2"><a id="sec:A.33.4.2"><span class="sec-nr">A.33.4.2</span> <span class="sec-title">Example
414	456	2</span></a></h4>
415	457
416		<p><a name="sec:simplex-ex-2"></a>
	458	<p><a id="sec:simplex-ex-2"></a>
417	459
418	460	<p>Here is an instance of the knapsack problem described above, where
419	461	<code>C = 8</code>, and we have two types of items: One item with value

475	517	does not necessarily yield an optimal solution in the presence of
476	518	integrality constraints.
477	519
478		<p><h4 id="sec:simplex-ex-3"><a name="sec:A.33.4.3"><span class="sec-nr">A.33.4.3</span> <span class="sec-title">Example
	520	<p><h4 id="sec:simplex-ex-3"><a id="sec:A.33.4.3"><span class="sec-nr">A.33.4.3</span> <span class="sec-title">Example
479	521	3</span></a></h4>
480	522
481		<p><a name="sec:simplex-ex-3"></a>
	523	<p><a id="sec:simplex-ex-3"></a>
482	524
483	525	<p>We are given:
484	526

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193	234	</div>
194		<h2 id="sec:softlicense"><a name="sec:E.2"><span class="sec-nr">E.2</span> <span class="sec-title">Software
	235	<h2 id="sec:softlicense"><a id="sec:E.2"><span class="sec-nr">E.2</span> <span class="sec-title">Software
195	236	support to keep track of license conditions</span></a></h2>
196	237
197		<a name="sec:softlicense"></a>
	238	<a id="sec:softlicense"></a>
198	239
199	240	<p>Given the above, it is possible that SWI-Prolog packages and
200	241	extensions rely on the GPL, LGPL or other licenses. The predicates below
201	242	allow for registering license requirements for Prolog files and foreign
202		modules. The predicate <a name="idx:license0:2340"></a><a class="pred" href="softlicense.html#license/0">license/0</a>
	243	modules. The predicate <a id="idx:license0:2344"></a><a class="pred" href="softlicense.html#license/0">license/0</a>
203	244	reports which components from the currently configured system are
204	245	distributed under non-permissive open source licenses and therefore may
205	246	need to be replaced to suit your requirements.
206	247
207	248	<dl class="latex">
208		<dt class="pubdef"><a name="license/0"><strong>license</strong></a></dt>
	249	<dt class="pubdef"><a id="license/0"><strong>license</strong></a></dt>
209	250	<dd class="defbody">
210	251	Evaluate the license conditions of all loaded components. If the system
211	252	contains one or more components that are licenced under GPL-like
212	253	restrictions the system indicates this program may only be distributed
213	254	under the <code>GPL</code> license as well as which components prohibit
214	255	the use of other license conditions. Likewise for for LGPL components.</dd>
215		<dt class="pubdef"><a name="license/2"><strong>license</strong>(<var>+LicenseId,
	256	<dt class="pubdef"><a id="license/2"><strong>license</strong>(<var>+LicenseId,
216	257	+Component</var>)</a></dt>
217	258	<dd class="defbody">
218	259	Register the fact that <var>Component</var> is distributed under a
219	260	license identified by <var>LicenseId</var>. Known license identifiers
220		can be listed using <a name="idx:knownlicenses0:2341"></a><a class="pred" href="softlicense.html#known_licenses/0">known_licenses/0</a>.
	261	can be listed using <a id="idx:knownlicenses0:2345"></a><a class="pred" href="softlicense.html#known_licenses/0">known_licenses/0</a>.
221	262	A new license can be registered as a known language using a declaration
222	263	like below. The second argument defines the
223	264	<em>category</em> if the license, which is one of <code>gpl</code>,

235	276	</pre>
236	277
237	278	</dd>
238		<dt class="pubdef"><a name="license/1"><strong>license</strong>(<var>+LicenseId</var>)</a></dt>
	279	<dt class="pubdef"><a id="license/1"><strong>license</strong>(<var>+LicenseId</var>)</a></dt>
239	280	<dd class="defbody">
240	281	Intended as a directive in Prolog source files. It takes the current
241		filename and calls <a name="idx:license2:2342"></a><a class="pred" href="softlicense.html#license/2">license/2</a>.</dd>
242		<dt class="pubdef"><a name="PL_license()"><var>void</var> <strong>PL_license</strong>(<var>const
	282	filename and calls <a id="idx:license2:2346"></a><a class="pred" href="softlicense.html#license/2">license/2</a>.</dd>
	283	<dt class="pubdef"><a id="PL_license()"><var>void</var> <strong>PL_license</strong>(<var>const
243	284	char LicenseId, const char Component</var>)</a></dt>
244	285	<dd class="defbody">
245	286	Intended for the install() procedure of foreign libraries. This call can
246	287	be made <em>before</em> <a class="func" href="foreigninclude.html#PL_initialise()">PL_initialise()</a>.</dd>
247		<dt class="pubdef"><a name="known_licenses/0"><strong>known_licenses</strong></a></dt>
	288	<dt class="pubdef"><a id="known_licenses/0"><strong>known_licenses</strong></a></dt>
248	289	<dd class="defbody">
249	290	List all licenses <em>known</em> to the system. This does not imply the
250		system contains code covered by the listed licenses. See <a name="idx:license2:2343"></a><a class="pred" href="softlicense.html#license/2">license/2</a>.
	291	system contains code covered by the listed licenses. See <a id="idx:license2:2347"></a><a class="pred" href="softlicense.html#license/2">license/2</a>.
251	292	</dd>
252	293	</dl>
253	294

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194		<h2 id="sec:solutionsequences"><a name="sec:A.34"><span class="sec-nr">A.34</span> <span class="sec-title">library(solution_sequences):
	235	<h2 id="sec:solutionsequences"><a id="sec:A.34"><span class="sec-nr">A.34</span> <span class="sec-title">library(solution_sequences):
195	236	Modify solution sequences</span></a></h2>
196	237
197		<p><a name="sec:solutionsequences"></a>
	238	<p><a id="sec:solutionsequences"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="mtag">See also</dt>

211	252	GROUP BY.
212	253
213	254	<p>These predicates were introduced in the context of the
214		http://swish.swi-prolog.orgSWISH Prolog browser-based shell, which can
215		represent the solutions to a predicate as a table. Notably wrapping a
216		goal in <a class="pred" href="solutionsequences.html#distinct/1">distinct/1</a>
	255	<a class="url" href="http://swish.swi-prolog.org">SWISH</a> Prolog
	256	browser-based shell, which can represent the solutions to a predicate as
	257	a table. Notably wrapping a goal in <a class="pred" href="solutionsequences.html#distinct/1">distinct/1</a>
217	258	avoids duplicates in the result table and using
218	259	<a class="pred" href="solutionsequences.html#order_by/2">order_by/2</a>
219	260	produces a nicely ordered table.

260	301	</dl>
261	302
262	303	<dl class="latex">
263		<dt class="pubdef"><a name="distinct/1"><strong>distinct</strong>(<var>:Goal</var>)</a></dt>
264		<dt class="pubdef"><a name="distinct/2"><strong>distinct</strong>(<var>?Witness,
	304	<dt class="pubdef"><a id="distinct/1"><strong>distinct</strong>(<var>:Goal</var>)</a></dt>
	305	<dt class="pubdef"><a id="distinct/2"><strong>distinct</strong>(<var>?Witness,
265	306	:Goal</var>)</a></dt>
266	307	<dd class="defbody">
267	308	True if <var>Goal</var> is true and no previous solution of <var>Goal</var>

283	324	</pre>
284	325
285	326	</dd>
286		<dt class="pubdef"><a name="reduced/1"><strong>reduced</strong>(<var>:Goal</var>)</a></dt>
287		<dt class="pubdef"><a name="reduced/3"><strong>reduced</strong>(<var>?Witness,
	327	<dt class="pubdef"><a id="reduced/1"><strong>reduced</strong>(<var>:Goal</var>)</a></dt>
	328	<dt class="pubdef"><a id="reduced/3"><strong>reduced</strong>(<var>?Witness,
288	329	:Goal, +Options</var>)</a></dt>
289	330	<dd class="defbody">
290	331	Similar to <a class="pred" href="solutionsequences.html#distinct/1">distinct/1</a>,

308	349	</dl>
309	350
310	351	</dd>
311		<dt class="pubdef"><a name="limit/2"><strong>limit</strong>(<var>+Count,
	352	<dt class="pubdef"><a id="limit/2"><strong>limit</strong>(<var>+Count,
312	353	:Goal</var>)</a></dt>
313	354	<dd class="defbody">
314	355	Limit the number of solutions. True if <var>Goal</var> is true,
315	356	returning at most <var>Count</var> solutions. Solutions are returned as
316	357	soon as they become available.</dd>
317		<dt class="pubdef"><a name="offset/2"><strong>offset</strong>(<var>+Count,
	358	<dt class="pubdef"><a id="offset/2"><strong>offset</strong>(<var>+Count,
318	359	:Goal</var>)</a></dt>
319	360	<dd class="defbody">
320	361	Ignore the first <var>Count</var> solutions. True if <var>Goal</var> is
321	362	true and produces more than <var>Count</var> solutions. This predicate
322	363	computes and ignores the first <var>Count</var> solutions.</dd>
323		<dt class="pubdef"><a name="order_by/2"><strong>order_by</strong>(<var>Spec,
324		Goal</var>)</a></dt>
	364	<dt class="pubdef"><a id="call_nth/2"><strong>call_nth</strong>(<var>:Goal,
	365	?Nth</var>)</a></dt>
	366	<dd class="defbody">
	367	True when <var>Goal</var> succeeded for the <var>Nth</var> time. If <var>Nth</var>
	368	is bound on entry, the predicate succeeds deterministically if there are
	369	at least <var>Nth</var> solutions for <var>Goal</var>.</dd>
	370	<dt class="pubdef"><a id="order_by/2"><strong>order_by</strong>(<var>+Spec,
	371	:Goal</var>)</a></dt>
325	372	<dd class="defbody">
326	373	Order solutions according to <var>Spec</var>. <var>Spec</var> is a list
327	374	of terms, where each element is one of. The ordering of solutions of <var>Goal</var>

340	387	</dl>
341	388
342	389	</dd>
343		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="group_by/4"><strong>group_by</strong>(<var>+By,
	390	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="group_by/4"><strong>group_by</strong>(<var>+By,
344	391	+Template, :Goal, -Bag</var>)</a></dt>
345	392	<dd class="defbody">
346	393	Group bindings of <var>Template</var> that have the same value for <var>By</var>.

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193	234	</div>
194		<h2 id="sec:statistics"><a name="sec:4.40"><span class="sec-nr">4.40</span> <span class="sec-title">Obtaining
	235	<h2 id="sec:statistics"><a id="sec:4.40"><span class="sec-nr">4.40</span> <span class="sec-title">Obtaining
195	236	Runtime Statistics</span></a></h2>
196	237
197		<a name="sec:statistics"></a>
	238	<a id="sec:statistics"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="statistics/2"><strong>statistics</strong>(<var>+Key,
	241	<dt class="pubdef"><a id="statistics/2"><strong>statistics</strong>(<var>+Key,
201	242	-Value</var>)</a></dt>
202	243	<dd class="defbody">
203	244	Unify system statistics determined by <var>Key</var> with <var>Value</var>.

206	247	reasons. These keys are described in <a class="tab" href="statistics.html#tab:qpstatistics">table
207	248	7</a>.
208	249
209		<p><table border="2" frame="box" rules="groups" style="margin:auto">
210		<tr valign="top"><td colspan=2 align=center>Native keys (times as float
211		in seconds)</tr>
212		<tbody>
213		<tr valign="top"><td>agc</td><td>Number of atom garbage collections
	250	<p><table class="latex frame-box center">
	251	<tr><td colspan=2 align=center>Native keys (times as float in seconds)</tr>
	252	<tr class="hline"><td>agc</td><td>Number of atom garbage collections
214	253	performed </td></tr>
215		<tr valign="top"><td>agc_gained</td><td>Number of atoms removed </td></tr>
216		<tr valign="top"><td>agc_time</td><td>Time spent in atom garbage
217		collections </td></tr>
218		<tr valign="top"><td>atoms</td><td>Total number of defined atoms </td></tr>
219		<tr valign="top"><td>c_stack</td><td>System (C-) stack limit. 0 if not
220		known. </td></tr>
221		<tr valign="top"><td>cgc</td><td>Number of clause garbage collections
222		performed </td></tr>
223		<tr valign="top"><td>cgc_gained</td><td>Number of clauses reclaimed </td></tr>
224		<tr valign="top"><td>cgc_time</td><td>Time spent in clause garbage
225		collections </td></tr>
226		<tr valign="top"><td>clauses</td><td>Total number of clauses in the
227		program </td></tr>
228		<tr valign="top"><td>codes</td><td>Total size of (virtual) executable
229		code in words </td></tr>
230		<tr valign="top"><td>cputime</td><td>(User) <span style="font-variant:small-caps">CPU</span>
	254	<tr><td>agc_gained</td><td>Number of atoms removed </td></tr>
	255	<tr><td>agc_time</td><td>Time spent in atom garbage collections </td></tr>
	256	<tr><td>atoms</td><td>Total number of defined atoms </td></tr>
	257	<tr><td>c_stack</td><td>System (C-) stack limit. 0 if not known. </td></tr>
	258	<tr><td>cgc</td><td>Number of clause garbage collections performed </td></tr>
	259	<tr><td>cgc_gained</td><td>Number of clauses reclaimed </td></tr>
	260	<tr><td>cgc_time</td><td>Time spent in clause garbage collections </td></tr>
	261	<tr><td>clauses</td><td>Total number of clauses in the program </td></tr>
	262	<tr><td>codes</td><td>Total size of (virtual) executable code in words </td></tr>
	263	<tr><td>cputime</td><td>(User) <span style="font-variant:small-caps">CPU</span>
231	264	time since thread was started in seconds </td></tr>
232		<tr valign="top"><td>epoch</td><td>Time stamp when thread was started </td></tr>
233		<tr valign="top"><td>functors</td><td>Total number of defined name/arity
234		pairs </td></tr>
235		<tr valign="top"><td>global</td><td>Allocated size of the global stack
236		in bytes </td></tr>
237		<tr valign="top"><td>globalused</td><td>Number of bytes in use on the
238		global stack </td></tr>
239		<tr valign="top"><td>globallimit</td><td>Size to which the global stack
240		is allowed to grow </td></tr>
241		<tr valign="top"><td>global_shifts</td><td>Number of global stack
242		expansions </td></tr>
243		<tr valign="top"><td>heapused</td><td>Bytes of heap in use by Prolog (0
244		if not maintained) </td></tr>
245		<tr valign="top"><td>inferences</td><td>Total number of passes via the
246		call and redo ports since Prolog was started </td></tr>
247		<tr valign="top"><td>modules</td><td>Total number of defined modules </td></tr>
248		<tr valign="top"><td>local</td><td>Allocated size of the local stack in
249		bytes </td></tr>
250		<tr valign="top"><td>local_shifts</td><td>Number of local stack
251		expansions </td></tr>
252		<tr valign="top"><td>locallimit</td><td>Size to which the local stack is
253		allowed to grow </td></tr>
254		<tr valign="top"><td>localused</td><td>Number of bytes in use on the
255		local stack </td></tr>
256		<tr valign="top"><td>table_space_used</td><td>Amount of bytes in use by
257		the thread's answer tables </td></tr>
258		<tr valign="top"><td>trail</td><td>Allocated size of the trail stack in
259		bytes </td></tr>
260		<tr valign="top"><td>trail_shifts</td><td>Number of trail stack
261		expansions </td></tr>
262		<tr valign="top"><td>traillimit</td><td>Size to which the trail stack is
263		allowed to grow </td></tr>
264		<tr valign="top"><td>trailused</td><td>Number of bytes in use on the
265		trail stack </td></tr>
266		<tr valign="top"><td>shift_time</td><td>Time spent in stack-shifts </td></tr>
267		<tr valign="top"><td>stack</td><td>Total memory in use for stacks in all
268		threads </td></tr>
269		<tr valign="top"><td>predicates</td><td>Total number of predicates. This
270		includes predicates that are undefined or not yet resolved. </td></tr>
271		<tr valign="top"><td>process_epoch</td><td>Time stamp when Prolog was
272		started </td></tr>
273		<tr valign="top"><td>process_cputime</td><td>(User) <span style="font-variant:small-caps">CPU</span>
	265	<tr><td>epoch</td><td>Time stamp when thread was started </td></tr>
	266	<tr><td>functors</td><td>Total number of defined name/arity pairs </td></tr>
	267	<tr><td>global</td><td>Allocated size of the global stack in bytes </td></tr>
	268	<tr><td>globalused</td><td>Number of bytes in use on the global stack </td></tr>
	269	<tr><td>globallimit</td><td>Size to which the global stack is allowed to
	270	grow </td></tr>
	271	<tr><td>global_shifts</td><td>Number of global stack expansions </td></tr>
	272	<tr><td>heapused</td><td>Bytes of heap in use by Prolog (0 if not
	273	maintained) </td></tr>
	274	<tr><td>inferences</td><td>Total number of passes via the call and redo
	275	ports since Prolog was started </td></tr>
	276	<tr><td>modules</td><td>Total number of defined modules </td></tr>
	277	<tr><td>local</td><td>Allocated size of the local stack in bytes </td></tr>
	278	<tr><td>local_shifts</td><td>Number of local stack expansions </td></tr>
	279	<tr><td>locallimit</td><td>Size to which the local stack is allowed to
	280	grow </td></tr>
	281	<tr><td>localused</td><td>Number of bytes in use on the local stack </td></tr>
	282	<tr><td>table_space_used</td><td>Amount of bytes in use by the thread's
	283	answer tables </td></tr>
	284	<tr><td>trail</td><td>Allocated size of the trail stack in bytes </td></tr>
	285	<tr><td>trail_shifts</td><td>Number of trail stack expansions </td></tr>
	286	<tr><td>traillimit</td><td>Size to which the trail stack is allowed to
	287	grow </td></tr>
	288	<tr><td>trailused</td><td>Number of bytes in use on the trail stack </td></tr>
	289	<tr><td>shift_time</td><td>Time spent in stack-shifts </td></tr>
	290	<tr><td>stack</td><td>Total memory in use for stacks in all threads </td></tr>
	291	<tr><td>predicates</td><td>Total number of predicates. This includes
	292	predicates that are undefined or not yet resolved. </td></tr>
	293	<tr><td>process_epoch</td><td>Time stamp when Prolog was started </td></tr>
	294	<tr><td>process_cputime</td><td>(User) <span style="font-variant:small-caps">CPU</span>
274	295	time since Prolog was started in seconds </td></tr>
275		<tr valign="top"><td>thread_cputime</td><td>MT-version: Seconds CPU time
276		used by finished threads. Basically non-portable. Works on Linux,
277		MacOSX, Windows and probably some more. </td></tr>
278		<tr valign="top"><td>threads</td><td>MT-version: number of active
279		threads </td></tr>
280		<tr valign="top"><td>threads_created</td><td>MT-version: number of
281		created threads </td></tr>
282		<tr valign="top"><td>engines</td><td>MT-version: number of existing
283		engines </td></tr>
284		<tr valign="top"><td>engines_created</td><td>MT-version: number of
285		created engines </td></tr>
	296	<tr><td>thread_cputime</td><td>MT-version: Seconds CPU time used by
	297	finished threads. Basically non-portable. Works on Linux, MacOSX,
	298	Windows and probably some more. </td></tr>
	299	<tr><td>threads</td><td>MT-version: number of active threads </td></tr>
	300	<tr><td>threads_created</td><td>MT-version: number of created threads </td></tr>
	301	<tr><td>engines</td><td>MT-version: number of existing engines </td></tr>
	302	<tr><td>engines_created</td><td>MT-version: number of created engines </td></tr>
286	303	</table>
287		<div class="caption"><b>Table 6 : </b>Keys for <a name="idx:statistics2:1562"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>.
	304	<div class="caption"><b>Table 6 : </b>Keys for <a id="idx:statistics2:1562"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>.
288	305	Space is expressed in bytes. Time is expressed in seconds, represented
289	306	as a floating point number.</div>
290		<a name="tab:statistics"></a>
291
292		<p><table border="2" frame="box" rules="groups" style="margin:auto">
293		<tr valign="top"><td colspan=2 align=center>Compatibility keys (times in
	307	<a id="tab:statistics"></a>
	308
	309	<p><table class="latex frame-box center">
	310	<tr><td colspan=2 align=center>Compatibility keys (times in
294	311	milliseconds)</tr>
295		<tbody>
296		<tr valign="top"><td>runtime</td><td>[ CPU time, CPU time since last ]
	312	<tr class="hline"><td>runtime</td><td>[ CPU time, CPU time since last ]
297	313	(milliseconds, excluding time spent in garbage collection) </td></tr>
298		<tr valign="top"><td>system_time</td><td>[ System CPU time, System CPU
299		time since last ] (milliseconds)</td></tr>
300		<tr valign="top"><td>real_time</td><td>[ Wall time, Wall time since last
301		] (integer seconds. See <a name="idx:gettime1:1563"></a><a class="pred" href="system.html#get_time/1">get_time/1</a>) </td></tr>
302		<tr valign="top"><td>walltime</td><td>[ Wall time since start, Wall time
303		since last] (milliseconds, SICStus compatibility) </td></tr>
304		<tr valign="top"><td>memory</td><td>[ Total unshared data, free memory ]
305		(Uses getrusage() if available, otherwise incomplete own statistics.) </td></tr>
306		<tr valign="top"><td>stacks</td><td>[ global use, local use ] </td></tr>
307		<tr valign="top"><td>program</td><td>[ heap, 0 ] </td></tr>
308		<tr valign="top"><td>global_stack</td><td>[ global use, global free ] </td></tr>
309		<tr valign="top"><td>local_stack</td><td>[ local use, local free ] </td></tr>
310		<tr valign="top"><td>trail</td><td>[ trail use, trail free ] </td></tr>
311		<tr valign="top"><td>garbage_collection</td><td>[ number of GC, bytes
312		gained, time spent, bytes left ] The last column is a SWI-Prolog
313		extension. It contains the sum of the memory left after each collection,
314		which can be divided by the count to find the average working set size
315		after GC. Use <code>[Count, Gained, Time\|_]</code> for compatiblity. </td></tr>
316		<tr valign="top"><td>stack_shifts</td><td>[ global shifts, local shifts,
	314	<tr><td>system_time</td><td>[ System CPU time, System CPU time since
	315	last ] (milliseconds)</td></tr>
	316	<tr><td>real_time</td><td>[ Wall time, Wall time since last ] (integer
	317	seconds. See <a id="idx:gettime1:1563"></a><a class="pred" href="system.html#get_time/1">get_time/1</a>) </td></tr>
	318	<tr><td>walltime</td><td>[ Wall time since start, Wall time since last]
	319	(milliseconds, SICStus compatibility) </td></tr>
	320	<tr><td>memory</td><td>[ Total unshared data, free memory ] (Uses
	321	getrusage() if available, otherwise incomplete own statistics.) </td></tr>
	322	<tr><td>stacks</td><td>[ global use, local use ] </td></tr>
	323	<tr><td>program</td><td>[ heap, 0 ] </td></tr>
	324	<tr><td>global_stack</td><td>[ global use, global free ] </td></tr>
	325	<tr><td>local_stack</td><td>[ local use, local free ] </td></tr>
	326	<tr><td>trail</td><td>[ trail use, trail free ] </td></tr>
	327	<tr><td>garbage_collection</td><td>[ number of GC, bytes gained, time
	328	spent, bytes left ] The last column is a SWI-Prolog extension. It
	329	contains the sum of the memory left after each collection, which can be
	330	divided by the count to find the average working set size after GC. Use <code>[Count,
	331	Gained, Time\|_]</code> for compatiblity. </td></tr>
	332	<tr><td>stack_shifts</td><td>[ global shifts, local shifts, time spent ] </td></tr>
	333	<tr><td>atoms</td><td>[ number, memory use, 0 ] </td></tr>
	334	<tr><td>atom_garbage_collection</td><td>[ number of AGC, bytes gained,
317	335	time spent ] </td></tr>
318		<tr valign="top"><td>atoms</td><td>[ number, memory use, 0 ] </td></tr>
319		<tr valign="top"><td>atom_garbage_collection</td><td>[ number of AGC,
320		bytes gained, time spent ] </td></tr>
321		<tr valign="top"><td>clause_garbage_collection</td><td>[ number of CGC,
322		clauses gained, time spent ] </td></tr>
323		<tr valign="top"><td>core</td><td>Same as memory </td></tr>
	336	<tr><td>clause_garbage_collection</td><td>[ number of CGC, clauses
	337	gained, time spent ] </td></tr>
	338	<tr><td>core</td><td>Same as memory </td></tr>
324	339	</table>
325		<div class="caption"><b>Table 7 : </b>Compatibility keys for <a name="idx:statistics2:1564"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>.
	340	<div class="caption"><b>Table 7 : </b>Compatibility keys for <a id="idx:statistics2:1564"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>.
326	341	Time is expressed in milliseconds.</div>
327		<a name="tab:qpstatistics"></a>
	342	<a id="tab:qpstatistics"></a>
328	343	</dd>
329		<dt class="pubdef"><a name="statistics/0"><strong>statistics</strong></a></dt>
	344	<dt class="pubdef"><a id="statistics/0"><strong>statistics</strong></a></dt>
330	345	<dd class="defbody">
331	346	Display a table of system statistics on the stream <code>user_error</code>.</dd>
332		<dt class="pubdef"><a name="time/1"><strong>time</strong>(<var>:Goal</var>)</a></dt>
	347	<dt class="pubdef"><a id="time/1"><strong>time</strong>(<var>:Goal</var>)</a></dt>
333	348	<dd class="defbody">
334		Execute <var>Goal</var> just like <a name="idx:call1:1565"></a><a class="pred" href="metacall.html#call/1">call/1</a>
	349	Execute <var>Goal</var> just like <a id="idx:call1:1565"></a><a class="pred" href="metacall.html#call/1">call/1</a>
335	350	and print time used, number of logical inferences and the average number
336	351	of <var>lips</var> (logical inferences per second). Note that SWI-Prolog
337	352	counts the actual executed number of inferences rather than the number

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194		<h2 id="sec:status"><a name="sec:1.2"><span class="sec-nr">1.2</span> <span class="sec-title">Status
	235	<h2 id="sec:status"><a id="sec:1.2"><span class="sec-nr">1.2</span> <span class="sec-title">Status
195	236	and releases</span></a></h2>
196	237
197		<a name="sec:status"></a>
198
199		<p>This manual describes version 7.6.2 of SWI-Prolog. SWI-Prolog is
	238	<a id="sec:status"></a>
	239
	240	<p>This manual describes version 7.7.4 of SWI-Prolog. SWI-Prolog is
200	241	widely considered to be a robust and scalable implementation of the
201	242	Prolog language. It is widely used in education and research. In
202	243	addition, it is in use for <var>24 × 7</var> mission critical

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193	234	</div>
194		<h2 id="sec:streamstat"><a name="sec:4.18"><span class="sec-nr">4.18</span> <span class="sec-title">Status
	235	<h2 id="sec:streamstat"><a id="sec:4.18"><span class="sec-nr">4.18</span> <span class="sec-title">Status
195	236	of streams</span></a></h2>
196	237
197		<a name="sec:streamstat"></a>
	238	<a id="sec:streamstat"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="wait_for_input/3"><strong>wait_for_input</strong>(<var>+ListOfStreams,
	241	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="wait_for_input/3"><strong>wait_for_input</strong>(<var>+ListOfStreams,
201	242	-ReadyList, +TimeOut</var>)</a></dt>
202	243	<dd class="defbody">
203	244	Wait for input on one of the streams in <var>ListOfStreams</var> and
204	245	return a list of streams on which input is available in <var>ReadyList</var>.
205		<a name="idx:waitforinput3:1066"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>
	246	<a id="idx:waitforinput3:1066"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>
206	247	waits for at most <var>TimeOut</var> seconds. <var>TimeOut</var> may be
207	248	specified as a floating point number to specify fractions of a second.
208		If <var>TimeOut</var> equals <code>infinite</code>, <a name="idx:waitforinput3:1067"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>
	249	If <var>TimeOut</var> equals <code>infinite</code>, <a id="idx:waitforinput3:1067"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>
209	250	waits indefinitely. If <var>Timeout</var> is 0 or 0.0 this predicate
210	251	returns without waiting.<sup class="fn">91<span class="fn-text">Prior to
211	252	7.3.23, the integer value `0' was the same as <code>infinite</code>.</span></sup>

227	268	wait_for_input([user_input, P4], Inputs, 0).
228	269	</pre>
229	270
230		<p><a name="idx:select:1068"></a><a name="idx:poll:1069"></a>When
231		available, the implementation is based on the poll() system call. The
232		poll() puts no additional restriction on the number of open files the
233		process may have. It does limit the time to <var>2^31-1</var>
234		milliseconds (a bit less than 25 days). Specifying a too large timeout
235		raises a
	271	<p><a id="idx:select:1068"></a><a id="idx:poll:1069"></a>When available,
	272	the implementation is based on the poll() system call. The poll() puts
	273	no additional restriction on the number of open files the process may
	274	have. It does limit the time to <var>2^31-1</var> milliseconds (a bit
	275	less than 25 days). Specifying a too large timeout raises a
236	276	<code>representation_error(timeout)</code> exception. If poll() is not
237	277	supported by the OS, select() is used. The select() call can only handle
238	278	file descriptors up to <code>FD_SETSIZE</code>. If the set contains a
239	279	descriptor that exceeds this limit a
240	280	<code>representation_error('FD_SETSIZE')</code> is raised.
241	281
242		<p>Note that <a name="idx:waitforinput3:1070"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>
	282	<p>Note that <a id="idx:waitforinput3:1070"></a><a class="pred" href="streamstat.html#wait_for_input/3">wait_for_input/3</a>
243	283	returns streams that have data waiting. This does not mean you can, for
244		example, call <a name="idx:read2:1071"></a><a class="pred" href="termrw.html#read/2">read/2</a>
	284	example, call <a id="idx:read2:1071"></a><a class="pred" href="termrw.html#read/2">read/2</a>
245	285	on the stream without blocking as the stream might hold an incomplete
246	286	term. The predicate
247		<a name="idx:setstream2:1072"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>
	287	<a id="idx:setstream2:1072"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>
248	288	using the option <code>timeout(Seconds)</code> can be used to make the
249	289	stream generate an exception if no new data arrives within the timeout
250	290	period. Suppose two processes communicate by exchanging Prolog terms.

261	301	</pre>
262	302
263	303	</dd>
264		<dt class="pubdef"><a name="byte_count/2"><strong>byte_count</strong>(<var>+Stream,
	304	<dt class="pubdef"><a id="byte_count/2"><strong>byte_count</strong>(<var>+Stream,
265	305	-Count</var>)</a></dt>
266	306	<dd class="defbody">
267	307	Byte position in <var>Stream</var>. For binary streams this is the same
268		as <a name="idx:charactercount2:1073"></a><a class="pred" href="streamstat.html#character_count/2">character_count/2</a>.
	308	as <a id="idx:charactercount2:1073"></a><a class="pred" href="streamstat.html#character_count/2">character_count/2</a>.
269	309	For text files the number may be different due to multi-byte encodings
270	310	or additional record separators (such as Control-M in Windows).</dd>
271		<dt class="pubdef"><a name="character_count/2"><strong>character_count</strong>(<var>+Stream,
	311	<dt class="pubdef"><a id="character_count/2"><strong>character_count</strong>(<var>+Stream,
272	312	-Count</var>)</a></dt>
273	313	<dd class="defbody">
274	314	Unify <var>Count</var> with the current character index. For input
275	315	streams this is the number of characters read since the open; for output
276	316	streams this is the number of characters written. Counting starts at 0.</dd>
277		<dt class="pubdef"><a name="line_count/2"><strong>line_count</strong>(<var>+Stream,
	317	<dt class="pubdef"><a id="line_count/2"><strong>line_count</strong>(<var>+Stream,
278	318	-Count</var>)</a></dt>
279	319	<dd class="defbody">
280	320	Unify <var>Count</var> with the number of lines read or written.
281	321	Counting starts at 1.</dd>
282		<dt class="pubdef"><a name="line_position/2"><strong>line_position</strong>(<var>+Stream,
	322	<dt class="pubdef"><a id="line_position/2"><strong>line_position</strong>(<var>+Stream,
283	323	-Count</var>)</a></dt>
284	324	<dd class="defbody">
285	325	Unify <var>Count</var> with the position on the current line. Note that

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185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="ext-lists.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="ext-syntax.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:strings"><a name="sec:5.2"><span class="sec-nr">5.2</span> <span class="sec-title">The
	235	<h2 id="sec:strings"><a id="sec:5.2"><span class="sec-nr">5.2</span> <span class="sec-title">The
195	236	string type and its double quoted syntax</span></a></h2>
196	237
197		<a name="sec:strings"></a>
	238	<a id="sec:strings"></a>
198	239
199	240	<p>As of SWI-Prolog version 7, text enclosed in double quotes
200	241	(e.g.,

203	244	on the global (term) stack. Strings represent sequences of Unicode
204	245	characters including the character code 0 (zero). The length strings is
205	246	limited by the available space on the global (term) stack (see
206		<a name="idx:setprologstack2:1594"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>).
	247	<a id="idx:setprologstack2:1594"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>).
207	248	Strings are distinct from lists, which makes it possible to detect them
208	249	at runtime and print them using the string syntax, as illustrated below:
209	250

224	265	Prolog flag and does not define the term that is produced by back quoted
225	266	text.
226	267
227		<p><table border="2" frame="hsides" rules="groups" style="margin:auto">
228		<tr valign="top"><td><b>Mode</b></td><td align=center><a class="flag" href="flags.html#flag:double_quotes">double_quotes</a> </td><td align=center><a class="flag" href="flags.html#flag:back_quotes">back_quotes</a> </td></tr>
229		<tbody>
230		<tr valign="top"><td>Version 7 default</td><td align=center>string</td><td align=center>codes </td></tr>
231		<tr valign="top"><td><strong>--traditional</strong> </td><td align=center>codes</td><td align=center>symbol_char </td></tr>
	268	<p><table class="latex frame-hsides center">
	269	<tr><td><b>Mode</b></td><td align=center><a class="flag" href="flags.html#flag:double_quotes">double_quotes</a> </td><td align=center><a class="flag" href="flags.html#flag:back_quotes">back_quotes</a> </td></tr>
	270	<tr class="hline"><td>Version 7 default</td><td align=center>string</td><td align=center>codes </td></tr>
	271	<tr><td><strong>--traditional</strong> </td><td align=center>codes</td><td align=center>symbol_char </td></tr>
232	272	</table>
233	273	<div class="caption"><b>Table 8 : </b>Mapping of double and back quoted
234	274	text in the two modes.</div>
235		<a name="tab:quote-mapping"></a>
236
237		<p><a class="sec" href="strings.html">Section 5.2.4</a> motivates the
238		introduction of strings and mapping double quoted text to this type.
239
240		<p><h3 id="sec:string-predicates"><a name="sec:5.2.1"><span class="sec-nr">5.2.1</span> <span class="sec-title">Predicates
	275	<a id="tab:quote-mapping"></a>
	276
	277	<p><a class="sec" href="strings.html#sec:5.2.4">Section 5.2.4</a>
	278	motivates the introduction of strings and mapping double quoted text to
	279	this type.
	280
	281	<p><h3 id="sec:string-predicates"><a id="sec:5.2.1"><span class="sec-nr">5.2.1</span> <span class="sec-title">Predicates
241	282	that operate on strings</span></a></h3>
242	283
243		<a name="sec:string-predicates"></a>
	284	<a id="sec:string-predicates"></a>
244	285
245	286	<p>Strings may be manipulated by a set of predicates that is similar to
246		the manipulation of atoms. In addition to the list below, <a name="idx:string1:1595"></a><a class="pred" href="typetest.html#string/1">string/1</a>
247		performs the type check for this type and is described in <a class="sec" href="typetest.html">section
	287	the manipulation of atoms. In addition to the list below, <a id="idx:string1:1595"></a><a class="pred" href="typetest.html#string/1">string/1</a>
	288	performs the type check for this type and is described in <a class="sec" href="typetest.html#sec:4.6">section
248	289	4.6</a>.
249	290
250	291	<p>SWI-Prolog's string primitives are being synchronized with
251		http://eclipseclp.org/wiki/Prolog/StringsECLiPSe. We expect the set of
252		predicates documented in this section to be stable, although it might be
253		expanded. In general, SWI-Prolog's text manipulation predicates accept
254		any form of text as input argument and produce the type indicated by the
255		predicate name as output. This policy simplifies migration and writing
256		programs that can run unmodified or with minor modifications on systems
257		that do not support strings. Code should avoid relying on this feature
258		as much as possible for clarity as well as to facilitate a more strict
259		mode and/or type checking in future releases.
	292	<a class="url" href="http://eclipseclp.org/wiki/Prolog/Strings">ECLiPSe</a>.
	293	We expect the set of predicates documented in this section to be stable,
	294	although it might be expanded. In general, SWI-Prolog's text
	295	manipulation predicates accept any form of text as input argument and
	296	produce the type indicated by the predicate name as output. This policy
	297	simplifies migration and writing programs that can run unmodified or
	298	with minor modifications on systems that do not support strings. Code
	299	should avoid relying on this feature as much as possible for clarity as
	300	well as to facilitate a more strict mode and/or type checking in future
	301	releases.
260	302
261	303	<dl class="latex">
262		<dt class="pubdef"><a name="atom_string/2"><strong>atom_string</strong>(<var>?Atom,
	304	<dt class="pubdef"><a id="atom_string/2"><strong>atom_string</strong>(<var>?Atom,
263	305	?String</var>)</a></dt>
264	306	<dd class="defbody">
265	307	Bi-directional conversion between an atom and a string. At least one of
266	308	the two arguments must be instantiated. <var>Atom</var> can also be an
267	309	integer or floating point number.</dd>
268		<dt class="pubdef"><a name="number_string/2"><strong>number_string</strong>(<var>?Number,
	310	<dt class="pubdef"><a id="number_string/2"><strong>number_string</strong>(<var>?Number,
269	311	?String</var>)</a></dt>
270	312	<dd class="defbody">
271	313	Bi-directional conversion between a number and a string. At least one of

286	328	before exponent, i.e., <code>"1e10"</code> is a valid number.
287	329	</ul>
288	330	</dd>
289		<dt class="pubdef"><a name="term_string/2"><strong>term_string</strong>(<var>?Term,
	331	<dt class="pubdef"><a id="term_string/2"><strong>term_string</strong>(<var>?Term,
290	332	?String</var>)</a></dt>
291	333	<dd class="defbody">
292	334	Bi-directional conversion between a term and a string. If <var>String</var>
293	335	is instantiated, it is parsed and the result is unified with <var>Term</var>.
294	336	Otherwise <var>Term</var> is `written' using the option <code>quoted(true)</code>
295	337	and the result is converted to <var>String</var>.</dd>
296		<dt class="pubdef"><a name="term_string/3"><strong>term_string</strong>(<var>?Term,
	338	<dt class="pubdef"><a id="term_string/3"><strong>term_string</strong>(<var>?Term,
297	339	?String, +Options</var>)</a></dt>
298	340	<dd class="defbody">
299		As <a name="idx:termstring2:1596"></a><a class="pred" href="strings.html#term_string/2">term_string/2</a>,
300		passing <var>Options</var> to either <a name="idx:readterm2:1597"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
301		or <a name="idx:writeterm2:1598"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>.
	341	As <a id="idx:termstring2:1596"></a><a class="pred" href="strings.html#term_string/2">term_string/2</a>,
	342	passing <var>Options</var> to either <a id="idx:readterm2:1597"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	343	or <a id="idx:writeterm2:1598"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>.
302	344	For example:
303	345
304	346	<pre class="code">

308	350	</pre>
309	351
310	352	</dd>
311		<dt class="pubdef"><a name="string_chars/2"><strong>string_chars</strong>(<var>?String,
	353	<dt class="pubdef"><a id="string_chars/2"><strong>string_chars</strong>(<var>?String,
312	354	?Chars</var>)</a></dt>
313	355	<dd class="defbody">
314	356	Bi-directional conversion between a string and a list of characters
315	357	(one-character atoms). At least one of the two arguments must be
316	358	instantiated.</dd>
317		<dt class="pubdef"><a name="string_codes/2"><strong>string_codes</strong>(<var>?String,
	359	<dt class="pubdef"><a id="string_codes/2"><strong>string_codes</strong>(<var>?String,
318	360	?Codes</var>)</a></dt>
319	361	<dd class="defbody">
320	362	Bi-directional conversion between a string and a list of character
321	363	codes. At least one of the two arguments must be instantiated.</dd>
322		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="text_to_string/2"><strong>text_to_string</strong>(<var>+Text,
	364	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="text_to_string/2"><strong>text_to_string</strong>(<var>+Text,
323	365	-String</var>)</a></dt>
324	366	<dd class="defbody">
325	367	Converts <var>Text</var> to a string. <var>Text</var> is an atom, string
326	368	or list of characters (codes or chars). When running in
327	369	<strong>--traditional</strong> mode, <code>'[]'</code> is ambiguous and
328	370	interpreted as an empty string.</dd>
329		<dt class="pubdef"><a name="string_length/2"><strong>string_length</strong>(<var>+String,
	371	<dt class="pubdef"><a id="string_length/2"><strong>string_length</strong>(<var>+String,
330	372	-Length</var>)</a></dt>
331	373	<dd class="defbody">
332	374	Unify <var>Length</var> with the number of characters in <var>String</var>.
333		This predicate is functionally equivalent to <a name="idx:atomlength2:1599"></a><a class="pred" href="manipatom.html#atom_length/2">atom_length/2</a>
	375	This predicate is functionally equivalent to <a id="idx:atomlength2:1599"></a><a class="pred" href="manipatom.html#atom_length/2">atom_length/2</a>
334	376	and also accepts atoms, integers and floats as its first argument.</dd>
335		<dt class="pubdef"><a name="string_code/3"><strong>string_code</strong>(<var>?Index,
	377	<dt class="pubdef"><a id="string_code/3"><strong>string_code</strong>(<var>?Index,
336	378	+String, ?Code</var>)</a></dt>
337	379	<dd class="defbody">
338	380	True when <var>Code</var> represents the character at the 1-based <var>Index</var>

343	385	<var>String</var>. The mode <code>string_code(-,+,+)</code> is
344	386	deterministic if the searched-for <var>Code</var> appears only once in <var>String</var>.
345	387	See also
346		<a name="idx:substring5:1600"></a><a class="pred" href="strings.html#sub_string/5">sub_string/5</a>.</dd>
347		<dt class="pubdef"><a name="get_string_code/3"><strong>get_string_code</strong>(<var>+Index,
	388	<a id="idx:substring5:1600"></a><a class="pred" href="strings.html#sub_string/5">sub_string/5</a>.</dd>
	389	<dt class="pubdef"><a id="get_string_code/3"><strong>get_string_code</strong>(<var>+Index,
348	390	+String, -Code</var>)</a></dt>
349	391	<dd class="defbody">
350		Semi-deterministic version of <a name="idx:stringcode3:1601"></a><a class="pred" href="strings.html#string_code/3">string_code/3</a>.
	392	Semi-deterministic version of <a id="idx:stringcode3:1601"></a><a class="pred" href="strings.html#string_code/3">string_code/3</a>.
351	393	In addition, this version provides strict range checking, throwing a
352	394	domain error if <var>Index</var> is less than 1 or greater than the
353	395	length of <var>String</var>. ECLiPSe provides this to support <code>String[Index]</code>
354	396	notation.</dd>
355		<dt class="pubdef"><a name="string_concat/3"><strong>string_concat</strong>(<var>?String1,
	397	<dt class="pubdef"><a id="string_concat/3"><strong>string_concat</strong>(<var>?String1,
356	398	?String2, ?String3</var>)</a></dt>
357	399	<dd class="defbody">
358		Similar to <a name="idx:atomconcat3:1602"></a><a class="pred" href="manipatom.html#atom_concat/3">atom_concat/3</a>,
	400	Similar to <a id="idx:atomconcat3:1602"></a><a class="pred" href="manipatom.html#atom_concat/3">atom_concat/3</a>,
359	401	but the unbound argument will be unified with a string object rather
360	402	than an atom. Also, if both <var>String1</var> and
361	403	<var>String2</var> are unbound and <var>String3</var> is bound to text,

366	408	particularly fast on long strings, as for each redo the system has to
367	409	create two entirely new strings, while the list equivalent only creates
368	410	a single new list-cell and moves some pointers around.</dd>
369		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="split_string/4"><strong>split_string</strong>(<var>+String,
	411	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="split_string/4"><strong>split_string</strong>(<var>+String,
370	412	+SepChars, +PadChars, -SubStrings</var>)</a></dt>
371	413	<dd class="defbody">
372	414	Break <var>String</var> into <var>SubStrings</var>. The <var>SepChars</var>

401	443	<var>PadChars</var> or is equivalent to handle multiple adjacent
402	444	separators as a single (often white space). The behaviour with partially
403	445	overlapping sets of padding and separators should be considered
404		undefined. See also <a name="idx:readstring5:1603"></a><a class="pred" href="strings.html#read_string/5">read_string/5</a>.</dd>
405		<dt class="pubdef"><a name="sub_string/5"><strong>sub_string</strong>(<var>+String,
	446	undefined. See also <a id="idx:readstring5:1603"></a><a class="pred" href="strings.html#read_string/5">read_string/5</a>.</dd>
	447	<dt class="pubdef"><a id="sub_string/5"><strong>sub_string</strong>(<var>+String,
406	448	?Before, ?Length, ?After, ?SubString</var>)</a></dt>
407	449	<dd class="defbody">
408	450	<var>SubString</var> is a substring of <var>String</var>. There are <var>Before</var>

410	452	contains <var>Length</var> character and is followed by <var>After</var>
411	453	characters in <var>String</var>. If not enough information is provided
412	454	to compute the start of the match, <var>String</var> is scanned
413		left-to-right. This predicate is functionally equivalent to <a name="idx:subatom5:1604"></a><a class="pred" href="manipatom.html#sub_atom/5">sub_atom/5</a>,
	455	left-to-right. This predicate is functionally equivalent to <a id="idx:subatom5:1604"></a><a class="pred" href="manipatom.html#sub_atom/5">sub_atom/5</a>,
414	456	but operates on strings. The following example splits a string of the
415	457	form
416	458	<<var>name</var>>=<<var>value</var>> into the name part (an

425	467	</pre>
426	468
427	469	</dd>
428		<dt class="pubdef"><a name="atomics_to_string/2"><strong>atomics_to_string</strong>(<var>+List,
	470	<dt class="pubdef"><a id="atomics_to_string/2"><strong>atomics_to_string</strong>(<var>+List,
429	471	-String</var>)</a></dt>
430	472	<dd class="defbody">
431	473	<var>List</var> is a list of strings, atoms, integers or floating point
432	474	numbers. Succeeds if <var>String</var> can be unified with the
433	475	concatenated elements of <var>List</var>. Equivalent to <code>atomics_to_string(List,
434	476	'', String)</code>.</dd>
435		<dt class="pubdef"><a name="atomics_to_string/3"><strong>atomics_to_string</strong>(<var>+List,
	477	<dt class="pubdef"><a id="atomics_to_string/3"><strong>atomics_to_string</strong>(<var>+List,
436	478	+Separator, -String</var>)</a></dt>
437	479	<dd class="defbody">
438		Creates a string just like <a name="idx:atomicstostring2:1605"></a><a class="pred" href="strings.html#atomics_to_string/2">atomics_to_string/2</a>,
	480	Creates a string just like <a id="idx:atomicstostring2:1605"></a><a class="pred" href="strings.html#atomics_to_string/2">atomics_to_string/2</a>,
439	481	but inserts
440	482	<var>Separator</var> between each pair of inputs. For example:
441	483

446	488	</pre>
447	489
448	490	</dd>
449		<dt class="pubdef"><a name="string_upper/2"><strong>string_upper</strong>(<var>+String,
	491	<dt class="pubdef"><a id="string_upper/2"><strong>string_upper</strong>(<var>+String,
450	492	-UpperCase</var>)</a></dt>
451	493	<dd class="defbody">
452	494	Convert <var>String</var> to upper case and unify the result with
453	495	<var>UpperCase</var>.</dd>
454		<dt class="pubdef"><a name="string_lower/2"><strong>string_lower</strong>(<var>+String,
	496	<dt class="pubdef"><a id="string_lower/2"><strong>string_lower</strong>(<var>+String,
455	497	LowerCase</var>)</a></dt>
456	498	<dd class="defbody">
457	499	Convert <var>String</var> to lower case and unify the result with
458	500	<var>LowerCase</var>.</dd>
459		<dt class="pubdef"><a name="read_string/3"><strong>read_string</strong>(<var>+Stream,
	501	<dt class="pubdef"><a id="read_string/3"><strong>read_string</strong>(<var>+Stream,
460	502	?Length, -String</var>)</a></dt>
461	503	<dd class="defbody">
462	504	Read at most <var>Length</var> characters from <var>Stream</var> and
463	505	return them in the string <var>String</var>. If <var>Length</var> is
464	506	unbound, <var>Stream</var> is read to the end and <var>Length</var> is
465	507	unified with the number of characters read.</dd>
466		<dt class="pubdef"><a name="read_string/5"><strong>read_string</strong>(<var>+Stream,
	508	<dt class="pubdef"><a id="read_string/5"><strong>read_string</strong>(<var>+Stream,
467	509	+SepChars, +PadChars, -Sep, -String</var>)</a></dt>
468	510	<dd class="defbody">
469	511	Read a string from <var>Stream</var>, providing functionality similar to
470		<a name="idx:splitstring4:1606"></a><a class="pred" href="strings.html#split_string/4">split_string/4</a>.
	512	<a id="idx:splitstring4:1606"></a><a class="pred" href="strings.html#split_string/4">split_string/4</a>.
471	513	The predicate performs the following steps:
472	514
473	515	<p>

482	524	terminated by the end of the input, <var>Sep</var> is unified with -1.
483	525	</ol>
484	526
485		<p>The predicate <a name="idx:readstring5:1607"></a><a class="pred" href="strings.html#read_string/5">read_string/5</a>
	527	<p>The predicate <a id="idx:readstring5:1607"></a><a class="pred" href="strings.html#read_string/5">read_string/5</a>
486	528	called repeatedly on an input until
487	529	<var>Sep</var> is -1 (end of file) is equivalent to reading the entire
488		file into a string and calling <a name="idx:splitstring4:1608"></a><a class="pred" href="strings.html#split_string/4">split_string/4</a>,
	530	file into a string and calling <a id="idx:splitstring4:1608"></a><a class="pred" href="strings.html#split_string/4">split_string/4</a>,
489	531	provided that <var>SepChars</var> and <var>PadChars</var> are not <em>partially
490	532	overlapping</em>.<sup class="fn">144<span class="fn-text">Behaviour that
491	533	is fully compatible would requite unlimited look-ahead.</span></sup>

501	543	</pre>
502	544
503	545	</dd>
504		<dt class="pubdef"><a name="open_string/2"><strong>open_string</strong>(<var>+String,
	546	<dt class="pubdef"><a id="open_string/2"><strong>open_string</strong>(<var>+String,
505	547	-Stream</var>)</a></dt>
506	548	<dd class="defbody">
507	549	True when <var>Stream</var> is an input stream that accesses the content

511	553	</dd>
512	554	</dl>
513	555
514		<p><h3 id="sec:text-representation"><a name="sec:5.2.2"><span class="sec-nr">5.2.2</span> <span class="sec-title">Representing
	556	<p><h3 id="sec:text-representation"><a id="sec:5.2.2"><span class="sec-nr">5.2.2</span> <span class="sec-title">Representing
515	557	text: strings, atoms and code lists</span></a></h3>
516	558
517		<a name="sec:text-representation"></a>
	559	<a id="sec:text-representation"></a>
518	560
519	561	<p>With the introduction of strings as a Prolog data type, there are
520	562	three main ways to represent text: using strings, atoms or code lists.

527	569	<dt><b>Lists of character codes</b></dt>
528	570	<dd>
529	571	is what you need if you want to <em>parse</em> text using Prolog grammar
530		rules (DCGs, see <a name="idx:phrase3:1609"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>).
	572	rules (DCGs, see <a id="idx:phrase3:1609"></a><a class="pred" href="DCG.html#phrase/3">phrase/3</a>).
531	573	Most of the text reading predicates (e.g.,
532		<a name="idx:readlinetocodes2:1610"></a><a class="pred" href="readutil.html#read_line_to_codes/2">read_line_to_codes/2</a>)
	574	<a id="idx:readlinetocodes2:1610"></a><a class="pred" href="readutil.html#read_line_to_codes/2">read_line_to_codes/2</a>)
533	575	return a list of character codes because most applications need to parse
534	576	these lines before the data can be processed.</dd>
535	577	<dt><b>Atoms</b></dt>

547	589	<dd>
548	590	typically represents text that is processed as a unit most of the time,
549	591	but which is not an identifier for something. Format specifications for
550		<a name="idx:format3:1611"></a><a class="pred" href="format.html#format/3">format/3</a>
	592	<a id="idx:format3:1611"></a><a class="pred" href="format.html#format/3">format/3</a>
551	593	is a good example. Another example is a descriptive text provided in an
552		application. Strings may be composed and decomposed using e.g., <a name="idx:stringconcat3:1612"></a><a class="pred" href="strings.html#string_concat/3">string_concat/3</a>
553		and <a name="idx:substring5:1613"></a><a class="pred" href="strings.html#sub_string/5">sub_string/5</a>
554		or converted for parsing using <a name="idx:stringcodes2:1614"></a><a class="pred" href="strings.html#string_codes/2">string_codes/2</a>
555		or created from codes generated by a generative grammar rule, also using <a name="idx:stringcodes2:1615"></a><a class="pred" href="strings.html#string_codes/2">string_codes/2</a>.
	594	application. Strings may be composed and decomposed using e.g., <a id="idx:stringconcat3:1612"></a><a class="pred" href="strings.html#string_concat/3">string_concat/3</a>
	595	and <a id="idx:substring5:1613"></a><a class="pred" href="strings.html#sub_string/5">sub_string/5</a>
	596	or converted for parsing using <a id="idx:stringcodes2:1614"></a><a class="pred" href="strings.html#string_codes/2">string_codes/2</a>
	597	or created from codes generated by a generative grammar rule, also using <a id="idx:stringcodes2:1615"></a><a class="pred" href="strings.html#string_codes/2">string_codes/2</a>.
556	598	</dd>
557	599	</dl>
558	600
559		<p><h3 id="sec:ext-dquotes-port"><a name="sec:5.2.3"><span class="sec-nr">5.2.3</span> <span class="sec-title">Adapting
	601	<p><h3 id="sec:ext-dquotes-port"><a id="sec:5.2.3"><span class="sec-nr">5.2.3</span> <span class="sec-title">Adapting
560	602	code for double quoted strings</span></a></h3>
561	603
562		<a name="sec:ext-dquotes-port"></a>
	604	<a id="sec:ext-dquotes-port"></a>
563	605
564	606	<p>The predicates in this section can help adapting your program to the
565	607	new convention for handling double quoted strings. We have adapted a
566	608	huge code base with which we were not familiar in about half a day.
567	609
568	610	<dl class="latex">
569		<dt class="pubdef"><a name="list_strings/0"><strong>list_strings</strong></a></dt>
	611	<dt class="pubdef"><a id="list_strings/0"><strong>list_strings</strong></a></dt>
570	612	<dd class="defbody">
571	613	This predicate may be used to assess compatibility issues due to the
572	614	representation of double quoted text as string objects. See
573		<a class="sec" href="strings.html">section 5.2</a> and <a class="sec" href="strings.html">section
574		5.2.4</a>. To use it, load your program into Prolog and run <a name="idx:liststrings0:1616"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>.
	615	<a class="sec" href="strings.html#sec:5.2">section 5.2</a> and <a class="sec" href="strings.html#sec:5.2.4">section
	616	5.2.4</a>. To use it, load your program into Prolog and run <a id="idx:liststrings0:1616"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>.
575	617	The predicate lists source locations of string objects encountered in
576	618	the program that are not considered safe. Such string need to be
577	619	examined manually, after which one of the actions below may be

595	637	command line option and code exploiting this mapping is also not
596	638	portable to ISO compliant systems.
597	639	<li>If the strings appear in facts and usage is safe, add a clause to
598		the multifile predicate check:string_predicate/1 to silence <a name="idx:liststrings0:1617"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>
	640	the multifile predicate check:string_predicate/1 to silence <a id="idx:liststrings0:1617"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>
599	641	on all clauses of that predicate.
600	642	<li>If the strings appear as an argument to a predicate that can handle
601	643	string objects, add a clause to the multifile predicate
602		check:valid_string_goal/1 to silence <a name="idx:liststrings0:1618"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>.
	644	check:valid_string_goal/1 to silence <a id="idx:liststrings0:1618"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>.
603	645	</ul>
604	646	</dd>
605		<dt class="pubdef"><a name="check:string_predicate/1"><strong>check:string_predicate</strong>(<var>:PredicateIndicator</var>)</a></dt>
	647	<dt class="pubdef"><a id="check:string_predicate/1"><strong>check:string_predicate</strong>(<var>:PredicateIndicator</var>)</a></dt>
606	648	<dd class="defbody">
607	649	Declare that <var>PredicateIndicator</var> has clauses that contain
608	650	strings, but that this is safe. For example, if there is a predicate
609	651	help_info/2 , where the second argument contains a double quoted string
610	652	that is handled properly by the predicates of the applications' help
611	653	system, add the following declaration to stop
612		<a name="idx:liststrings0:1619"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>
	654	<a id="idx:liststrings0:1619"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>
613	655	from complaining:
614	656
615	657	<pre class="code">

619	661	</pre>
620	662
621	663	</dd>
622		<dt class="pubdef"><a name="check:valid_string_goal/1"><strong>check:valid_string_goal</strong>(<var>:Goal</var>)</a></dt>
	664	<dt class="pubdef"><a id="check:valid_string_goal/1"><strong>check:valid_string_goal</strong>(<var>:Goal</var>)</a></dt>
623	665	<dd class="defbody">
624	666	Declare that calls to <var>Goal</var> are safe. The module qualification
625	667	is the actual module in which <var>Goal</var> is defined. For example, a
626		call to <a name="idx:format3:1620"></a><a class="pred" href="format.html#format/3">format/3</a>
	668	call to <a id="idx:format3:1620"></a><a class="pred" href="format.html#format/3">format/3</a>
627	669	is resolved by the predicate system:format/3. and the code below
628	670	specifies that the second argument may be a string (system predicates
629	671	that accept strings are defined in the library).

637	679	<p></dd>
638	680	</dl>
639	681
640		<p><h3 id="sec:ext-dquotes-motivation"><a name="sec:5.2.4"><span class="sec-nr">5.2.4</span> <span class="sec-title">Why
	682	<p><h3 id="sec:ext-dquotes-motivation"><a id="sec:5.2.4"><span class="sec-nr">5.2.4</span> <span class="sec-title">Why
641	683	has the representation of double quoted text changed?</span></a></h3>
642	684
643		<a name="sec:ext-dquotes-motivation"></a>
	685	<a id="sec:ext-dquotes-motivation"></a>
644	686
645	687	<p>Prolog defines two forms of quoted text. Traditionally, single quoted
646	688	text is mapped to atoms while double quoted text is mapped to a list of

681	723
682	724	<p>Lacking runtime information, debuggers and the toplevel can only use
683	725	heuristics to decide whether to print a list of integers as such or as a
684		string (see <a name="idx:portraytext1:1621"></a><span class="pred-ext">portray_text/1</span>).
	726	string (see <a id="idx:portraytext1:1621"></a><span class="pred-ext">portray_text/1</span>).
685	727
686	728	<p>While experienced Prolog programmers have learned to cope with this,
687	729	we still consider this an unfortunate situation.

749	791	my_class(_).
750	792	</pre>
751	793
752		<p>Finally, the predicate <a name="idx:stringcode3:1622"></a><a class="pred" href="strings.html#string_code/3">string_code/3</a>
753		can be exploited directly as a replacement for the <a name="idx:memberchk2:1623"></a><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a>
	794	<p>Finally, the predicate <a id="idx:stringcode3:1622"></a><a class="pred" href="strings.html#string_code/3">string_code/3</a>
	795	can be exploited directly as a replacement for the <a id="idx:memberchk2:1623"></a><a class="pred" href="builtinlist.html#memberchk/2">memberchk/2</a>
754	796	on a list of codes. Although the string is still pushed onto the stack,
755	797	it is more compact and only a single entity.
756	798	</dd>
757	799	</dl>
758	800
759		<p>We offer the predicate <a name="idx:liststrings0:1624"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>
	801	<p>We offer the predicate <a id="idx:liststrings0:1624"></a><a class="pred" href="strings.html#list_strings/0">list_strings/0</a>
760	802	to help porting your program.
761	803
762	804	<p></body></html>⏎

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196		<a name="sec:summary"></a>
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197	238
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193	234	</div>
194		<h2 id="sec:swiorother"><a name="sec:1.3"><span class="sec-nr">1.3</span> <span class="sec-title">Should
	235	<h2 id="sec:swiorother"><a id="sec:1.3"><span class="sec-nr">1.3</span> <span class="sec-title">Should
195	236	I be using SWI-Prolog?</span></a></h2>
196	237
197		<a name="sec:swiorother"></a>
	238	<a id="sec:swiorother"></a>
198	239
199	240	<p>There are a number of reasons why it might be better to choose a
200	241	commercial, or another free, Prolog system:

238	279	SWI-Prolog provides a good command line environment, including `Do What
239	280	I Mean', autocompletion, history and a tracer that operates on single
240	281	key strokes. The system automatically recompiles modified parts of the
241		source code using the <a name="idx:make0:1"></a><a class="pred" href="consulting.html#make/0">make/0</a>
	282	source code using the <a id="idx:make0:1"></a><a class="pred" href="consulting.html#make/0">make/0</a>
242	283	command. The system can be instructed to open an arbitrary editor on the
243	284	right file and line based on its source database. It ships with various
244	285	graphical tools and can be combined with the SWI-Prolog editor, PDT

247	288	<p>
248	289	<li><i>Fast compiler</i><br>
249	290	Even very large applications can be loaded in seconds on most machines.
250		If this is not enough, there is the Quick Load Format. See <a name="idx:qcompile1:2"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>
251		and <a name="idx:qsaveprogram2:3"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
	291	If this is not enough, there is the Quick Load Format. See <a id="idx:qcompile1:2"></a><a class="pred" href="consulting.html#qcompile/1">qcompile/1</a>
	292	and <a id="idx:qsaveprogram2:3"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>.
252	293
253	294	<p>
254	295	<li><i>Transparent compiled code</i><br>

275	316	<p>
276	317	<li><i>Flexibility</i><br>
277	318	SWI-Prolog can easily be integrated with C, supporting non-determinism
278		in Prolog calling C as well as C calling Prolog (see <a class="sec" href="foreign.html">section
	319	in Prolog calling C as well as C calling Prolog (see <a class="sec" href="foreign.html#sec:11">section
279	320	11</a>). It can also be <em>embedded</em> in external programs (see
280		<a class="sec" href="plld.html">section 11.5</a>). System predicates can
281		be redefined locally to provide compatibility with other Prolog systems.
	321	<a class="sec" href="plld.html#sec:11.5">section 11.5</a>). System
	322	predicates can be redefined locally to provide compatibility with other
	323	Prolog systems.
282	324
283	325	<p>
284	326	<li><i>Threads</i><br>

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193	234	</div>
194		<h2 id="sec:swiprolog"><a name="sec:1.1"><span class="sec-nr">1.1</span> <span class="sec-title">Positioning
	235	<h2 id="sec:swiprolog"><a id="sec:1.1"><span class="sec-nr">1.1</span> <span class="sec-title">Positioning
195	236	SWI-Prolog</span></a></h2>
196	237
197		<a name="sec:swiprolog"></a>
	238	<a id="sec:swiprolog"></a>
198	239
199	240	<p>Most implementations of the Prolog language are designed to serve a
200	241	limited set of use cases. SWI-Prolog is no exception to this rule.

237	278	<cite><a class="cite" href="Bibliography.html#Demoen:CW350">Demoen, 2002</a></cite>.
238	279	Some libraries are copied from the YAP<sup class="fn">1<span class="fn-text"><a class="url" href="http://www.dcc.fc.up.pt/\~{}vsc/Yap/">http://www.dcc.fc.up.pt/\~{}vsc/Yap/</a></span></sup>
239	280	system. Together with YAP we developed a portability framework (see
240		<a class="sec" href="dialect.html">section C</a>). This framework has
241		been filled for SICStus Prolog, YAP, IF/Prolog and Ciao. SWI-Prolog
242		version 7 introduces various extensions to the Prolog language (see <a class="sec" href="extensions.html">section
	281	<a class="sec" href="dialect.html#sec:C">section C</a>). This framework
	282	has been filled for SICStus Prolog, YAP, IF/Prolog and Ciao. SWI-Prolog
	283	version 7 introduces various extensions to the Prolog language (see <a class="sec" href="extensions.html#sec:5">section
243	284	5</a>). The
244	285	<em>string</em> data type and its supporting set of built-in predicates
245	286	is compatibility with ECLiPSe.

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191	232	<a class="nav" href="gc.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:syntax"><a name="sec:2.16"><span class="sec-nr">2.16</span> <span class="sec-title">The
	235	<h2 id="sec:syntax"><a id="sec:2.16"><span class="sec-nr">2.16</span> <span class="sec-title">The
195	236	SWI-Prolog syntax</span></a></h2>
196	237
197		<a name="sec:syntax"></a>
	238	<a id="sec:syntax"></a>
198	239
199	240	<p>SWI-Prolog syntax is close to ISO-Prolog standard syntax, which is
200	241	based on the Edinburgh Prolog syntax. A formal description can be found
201	242	in the ISO standard document. For an informal introduction we refer to
202		Prolog text books (see <a class="sec" href="intro.html">section 1</a>)
	243	Prolog text books (see <a class="sec" href="intro.html#sec:1">section 1</a>)
203	244	and
204		http://www.swi-prolog.org/Links.htmlonline tutorials . In addition to
205		the differences from the ISO standard documented here, SWI-Prolog offers
206		several extensions, some of which also extend the syntax. See <a class="sec" href="extensions.html">section
	245	<a class="url" href="http://www.swi-prolog.org/Links.html">online
	246	tutorials</a>. In addition to the differences from the ISO standard
	247	documented here, SWI-Prolog offers several extensions, some of which
	248	also extend the syntax. See <a class="sec" href="extensions.html#sec:5">section
207	249	5</a> for more information.
208	250
209		<p><h3 id="sec:isosyntax"><a name="sec:2.16.1"><span class="sec-nr">2.16.1</span> <span class="sec-title">ISO
	251	<p><h3 id="sec:isosyntax"><a id="sec:2.16.1"><span class="sec-nr">2.16.1</span> <span class="sec-title">ISO
210	252	Syntax Support</span></a></h3>
211	253
212		<a name="sec:isosyntax"></a>
	254	<a id="sec:isosyntax"></a>
213	255
214	256	<p>This section lists various extensions w.r.t. the ISO Prolog syntax.
215	257
216		<p><h4 id="sec:processorcharset"><a name="sec:2.16.1.1"><span class="sec-nr">2.16.1.1</span> <span class="sec-title">Processor
	258	<p><h4 id="sec:processorcharset"><a id="sec:2.16.1.1"><span class="sec-nr">2.16.1.1</span> <span class="sec-title">Processor
217	259	Character Set</span></a></h4>
218	260
219		<a name="sec:processorcharset"></a>
220
221		<p><a name="idx:ISOLatin1:212"></a><a name="idx:characterset:213"></a>The
	261	<a id="sec:processorcharset"></a>
	262
	263	<p><a id="idx:ISOLatin1:212"></a><a id="idx:characterset:213"></a>The
222	264	processor character set specifies the class of each character used for
223	265	parsing Prolog source text. Character classification is fixed to
224		http://www.unicode.org/Unicode. See also <a class="sec" href="widechars.html">section
	266	<a class="url" href="http://www.unicode.org/">Unicode</a>. See also <a class="sec" href="widechars.html#sec:2.19">section
225	267	2.19</a>.
226	268
227		<p><h4 id="sec:nestedcomments"><a name="sec:2.16.1.2"><span class="sec-nr">2.16.1.2</span> <span class="sec-title">Nested
	269	<p><h4 id="sec:nestedcomments"><a id="sec:2.16.1.2"><span class="sec-nr">2.16.1.2</span> <span class="sec-title">Nested
228	270	comments</span></a></h4>
229	271
230		<a name="sec:nestedcomments"></a>
	272	<a id="sec:nestedcomments"></a>
231	273
232	274	<p>SWI-Prolog allows for nesting <code>/* ... */</code> comments. Where
233	275	the ISO standard accepts <code>/* ... /* ... */</code> as a comment,

251	293
252	294	</pre>
253	295
254		<p><h4 id="sec:charescapes"><a name="sec:2.16.1.3"><span class="sec-nr">2.16.1.3</span> <span class="sec-title">Character
	296	<p><h4 id="sec:charescapes"><a id="sec:2.16.1.3"><span class="sec-nr">2.16.1.3</span> <span class="sec-title">Character
255	297	Escape Syntax</span></a></h4>
256	298
257		<a name="sec:charescapes"></a>
	299	<a id="sec:charescapes"></a>
258	300
259	301	<p>Within quoted atoms (using single quotes: <code>'<atom>'</code>)
260	302	special characters are represented using escape sequences. An escape

400	442
401	443	<p>Character escaping is only available if
402	444	<code>current_prolog_flag(character_escapes, true)</code> is active
403		(default). See <a name="idx:currentprologflag2:214"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>.
404		Character escapes conflict with <a name="idx:writef2:215"></a><a class="pred" href="format.html#writef/2">writef/2</a>
405		in two ways: <code>\40</code> is interpreted as decimal 40 by <a name="idx:writef2:216"></a><a class="pred" href="format.html#writef/2">writef/2</a>,
406		but as octal 40 (decimal 32) by <code>read</code>. Also, the <a name="idx:writef2:217"></a><a class="pred" href="format.html#writef/2">writef/2</a>
	445	(default). See <a id="idx:currentprologflag2:214"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>.
	446	Character escapes conflict with <a id="idx:writef2:215"></a><a class="pred" href="format.html#writef/2">writef/2</a>
	447	in two ways: <code>\40</code> is interpreted as decimal 40 by <a id="idx:writef2:216"></a><a class="pred" href="format.html#writef/2">writef/2</a>,
	448	but as octal 40 (decimal 32) by <code>read</code>. Also, the <a id="idx:writef2:217"></a><a class="pred" href="format.html#writef/2">writef/2</a>
407	449	sequence
408	450	<code>\l</code> is illegal. It is advised to use the more widely
409	451	supported
410		<a name="idx:format23:218"></a><a class="pred" href="format.html#format/2">format/[2,3]</a>
411		predicate instead. If you insist upon using <a name="idx:writef2:219"></a><a class="pred" href="format.html#writef/2">writef/2</a>,
	452	<a id="idx:format23:218"></a><a class="pred" href="format.html#format/2">format/[2,3]</a>
	453	predicate instead. If you insist upon using <a id="idx:writef2:219"></a><a class="pred" href="format.html#writef/2">writef/2</a>,
412	454	either switch <a class="flag" href="flags.html#flag:character_escapes">character_escapes</a>
413	455	to <code>false</code>, or use double <code>\\</code>, as in <code>writef('\\l')</code>.
414	456
415		<p><h4 id="sec:nondecsyntax"><a name="sec:2.16.1.4"><span class="sec-nr">2.16.1.4</span> <span class="sec-title">Syntax
	457	<p><h4 id="sec:nondecsyntax"><a id="sec:2.16.1.4"><span class="sec-nr">2.16.1.4</span> <span class="sec-title">Syntax
416	458	for non-decimal numbers</span></a></h4>
417	459
418		<a name="sec:nondecsyntax"></a>
	460	<a id="sec:nondecsyntax"></a>
419	461
420	462	<p>SWI-Prolog implements both Edinburgh and ISO representations for
421	463	non-decimal numbers. According to Edinburgh syntax, such numbers are

425	467	<code>0<em>[bxo]</em><<var>number</var>></code>. For example: <code>A is 0b100 \/ 0xf00</code>
426	468	is a valid expression. Such numbers are always unsigned.
427	469
428		<p><h4 id="sec:digitgroupsyntax"><a name="sec:2.16.1.5"><span class="sec-nr">2.16.1.5</span> <span class="sec-title">Using
	470	<p><h4 id="sec:digitgroupsyntax"><a id="sec:2.16.1.5"><span class="sec-nr">2.16.1.5</span> <span class="sec-title">Using
429	471	digit groups in large integers</span></a></h4>
430	472
431		<a name="sec:digitgroupsyntax"></a>
	473	<a id="sec:digitgroupsyntax"></a>
432	474
433	475	<p>SWI-Prolog supports splitting long integers into <em>digit groups</em>.
434	476	Digit groups can be separated with the sequence <<var>underscore</var>>,

442	484	1_000_/more/000
443	485	</pre>
444	486
445		<p>Integers can be printed using this notation with <a name="idx:format2:220"></a><a class="pred" href="format.html#format/2">format/2</a>,
	487	<p>Integers can be printed using this notation with <a id="idx:format2:220"></a><a class="pred" href="format.html#format/2">format/2</a>,
446	488	using the
447	489	<code>~I</code> format specifier. For example:
448	490

454	496	<p>The current syntax has been proposed by Ulrich Neumerkel on the
455	497	SWI-Prolog mailinglist.
456	498
457		<p><h4 id="sec:floatsyntax"><a name="sec:2.16.1.6"><span class="sec-nr">2.16.1.6</span> <span class="sec-title">NaN
	499	<p><h4 id="sec:floatsyntax"><a id="sec:2.16.1.6"><span class="sec-nr">2.16.1.6</span> <span class="sec-title">NaN
458	500	and Infinity floats and their syntax</span></a></h4>
459	501
460		<a name="sec:floatsyntax"></a>
	502	<a id="sec:floatsyntax"></a>
461	503
462	504	<p>SWI-Prolog supports reading an printing `special' floating point
463	505	values according to
464		http://eclipseclp.org/Specs/core_update_float.htmlProposal for Prolog
465		Standard core update wrt floating point arithmetic by Joachim Schimpf
466		and available in ECLiPSe Prolog. In particular,
	506	<a class="url" href="http://eclipseclp.org/Specs/core_update_float.html">Proposal
	507	for Prolog Standard core update wrt floating point arithmetic</a> by
	508	Joachim Schimpf and available in ECLiPSe Prolog. In particular,
467	509
468	510	<p>
469	511	<ul class="latex">

489	531
490	532	<p>Note that, compliant with the ISO standard, SWI-Prolog arithmetic
491	533	(see
492		<a class="sec" href="arith.html">section 4.27</a>) never returns one of
493		the above values but instead raises an <em>exception</em>, e.g.,
	534	<a class="sec" href="arith.html#sec:4.27">section 4.27</a>) never
	535	returns one of the above values but instead raises an <em>exception</em>,
	536	e.g.,
494	537
495	538	<pre class="code">
496	539	?- A is 1/0.

504	547	exchange data with languages that can represent the full range of IEEE
505	548	doubles.
506	549
507		<p><h4 id="sec:varprefix"><a name="sec:2.16.1.7"><span class="sec-nr">2.16.1.7</span> <span class="sec-title">Force
	550	<p><h4 id="sec:varprefix"><a id="sec:2.16.1.7"><span class="sec-nr">2.16.1.7</span> <span class="sec-title">Force
508	551	only underscore to introduce a variable</span></a></h4>
509	552
510		<a name="sec:varprefix"></a>
	553	<a id="sec:varprefix"></a>
511	554
512	555	<p>According to the ISO standard and most Prolog systems, identifiers
513	556	that start with an uppercase letter or an underscore are variables. In

530	573	uppercase letter is another category were the readability of the code
531	574	improves using this option.
532	575
533		<p><h4 id="sec:unicodesyntax"><a name="sec:2.16.1.8"><span class="sec-nr">2.16.1.8</span> <span class="sec-title">Unicode
	576	<p><h4 id="sec:unicodesyntax"><a id="sec:2.16.1.8"><span class="sec-nr">2.16.1.8</span> <span class="sec-title">Unicode
534	577	Prolog source</span></a></h4>
535	578
536		<a name="sec:unicodesyntax"></a>
	579	<a id="sec:unicodesyntax"></a>
537	580
538	581	<p>The ISO standard specifies the Prolog syntax in ASCII characters. As
539	582	SWI-Prolog supports Unicode in source files we must extend the syntax.
540	583	This section describes the implication for the source files, while
541		writing international source files is described in <a class="sec" href="projectfiles.html">section
	584	writing international source files is described in <a class="sec" href="projectfiles.html#sec:3.1.3">section
542	585	3.1.3</a>.
543	586
544	587	<p>The SWI-Prolog Unicode character classification is based on version
545		6.0.0 of the Unicode standard. Please note that <a name="idx:chartype2:221"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>
	588	6.0.0 of the Unicode standard. Please note that <a id="idx:chartype2:221"></a><a class="pred" href="chartype.html#char_type/2">char_type/2</a>
546	589	and friends, intended to be used with all text except Prolog source
547	590	code, is based on the C library locale-based classification routines.
548	591

551	594	<li><i>Quoted atoms and strings</i><br>
552	595	Any character of any script can be used in quoted atoms and strings. The
553	596	escape sequences <code>\uXXXX</code> and <code>\UXXXXXXXX</code> (see
554		<a class="sec" href="syntax.html">section 2.16.1.3</a>) were introduced
555		to specify Unicode code points in ASCII files.
	597	<a class="sec" href="syntax.html#sec:2.16.1.3">section 2.16.1.3</a>)
	598	were introduced to specify Unicode code points in ASCII files.
556	599
557	600	<p>
558	601	<li><i>Atoms and Variables</i><br>

588	631	character of other type</i>) are currently handled as `solo'.
589	632	</ul>
590	633
591		<p><h4 id="sec:singleton"><a name="sec:2.16.1.9"><span class="sec-nr">2.16.1.9</span> <span class="sec-title">Singleton
	634	<p><h4 id="sec:singleton"><a id="sec:2.16.1.9"><span class="sec-nr">2.16.1.9</span> <span class="sec-title">Singleton
592	635	variable checking</span></a></h4>
593	636
594		<a name="sec:singleton"></a>
595
596		<p><a name="idx:singletonvariable:222"></a><a name="idx:anonymousvariable:223"></a>A <em>singleton
	637	<a id="sec:singleton"></a>
	638
	639	<p><a id="idx:singletonvariable:222"></a><a id="idx:anonymousvariable:223"></a>A <em>singleton
597	640	variable</em> is a variable that appears only one time in a clause. It
598	641	can always be replaced by <code>_</code>, the
599	642	<em>anonymous</em> variable. In some cases, however, people prefer to
600	643	give the variable a name. As mistyping a variable is a common mistake,
601		Prolog systems generally give a warning (controlled by <a name="idx:stylecheck1:224"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>)
	644	Prolog systems generally give a warning (controlled by <a id="idx:stylecheck1:224"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>)
602	645	if a variable is used only once. The system can be informed that a
603	646	variable is meant to appear once by <em>starting</em> it with an
604	647	underscore, e.g.,

630	673	<p>Any normal variable appearing exactly once in the clause <em>and</em>
631	674	any named singleton variables appearing more than once are reported.
632	675	Below are some examples with warnings in the right column. Singleton
633		messages can be suppressed using the <a name="idx:stylecheck1:225"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>
	676	messages can be suppressed using the <a id="idx:stylecheck1:225"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>
634	677	directive.
635	678
636		<p><table border="2" frame="box" rules="groups" style="margin:auto">
637		<tr valign="top"><td>test(_).</td></tr>
638		<tr valign="top"><td>test(_a).</td><td>Singleton variables: [_a] </td></tr>
639		<tr valign="top"><td>test(_12).</td><td>Singleton variables: [_12] </td></tr>
640		<tr valign="top"><td>test(A).</td><td>Singleton variables: [A] </td></tr>
641		<tr valign="top"><td>test(_A).</td></tr>
642		<tr valign="top"><td>test(__a).</td></tr>
643		<tr valign="top"><td>test(_, _).</td></tr>
644		<tr valign="top"><td>test(_a, _a).</td></tr>
645		<tr valign="top"><td>test(__a, __a).</td><td>Singleton-marked variables
646		appearing more than once: [__a] </td></tr>
647		<tr valign="top"><td>test(_A, _A).</td><td>Singleton-marked variables
648		appearing more than once: [_A] </td></tr>
649		<tr valign="top"><td>test(A, A).</td></tr>
	679	<p><table class="latex frame-box center">
	680	<tr><td>test(_).</td></tr>
	681	<tr><td>test(_a).</td><td>Singleton variables: [_a] </td></tr>
	682	<tr><td>test(_12).</td><td>Singleton variables: [_12] </td></tr>
	683	<tr><td>test(A).</td><td>Singleton variables: [A] </td></tr>
	684	<tr><td>test(_A).</td></tr>
	685	<tr><td>test(__a).</td></tr>
	686	<tr><td>test(_, _).</td></tr>
	687	<tr><td>test(_a, _a).</td></tr>
	688	<tr><td>test(__a, __a).</td><td>Singleton-marked variables appearing
	689	more than once: [__a] </td></tr>
	690	<tr><td>test(_A, _A).</td><td>Singleton-marked variables appearing more
	691	than once: [_A] </td></tr>
	692	<tr><td>test(A, A).</td></tr>
650	693	</table>
651	694
652	695	<p><b>Semantic singletons</b>
653	696
654	697	<p>Starting with version 6.5.1, SWI-Prolog has <em>syntactic singletons</em>
655	698	and <em>semantic singletons</em>. The first are checked by
656		<a name="idx:readclause3:226"></a><a class="pred" href="termrw.html#read_clause/3">read_clause/3</a>
657		(and <a name="idx:readterm3:227"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>
	699	<a id="idx:readclause3:226"></a><a class="pred" href="termrw.html#read_clause/3">read_clause/3</a>
	700	(and <a id="idx:readterm3:227"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>
658	701	using the option
659	702	<code>singletons(warning)</code>). The latter are generated by the
660	703	compiler for variables that appear alone in a <em>branch</em>. For

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	20	dt.pubdef, dt.multidef
	21	{ color: #fff;
	22	padding: 2px 10px 0px 10px;
	23	margin-bottom: 5px;
	24	font-size: 18px;
	25	vertical-align: middle;
	26	overflow: hidden;
	27	}
	28
	29	dt.pubdef { background-color: #0c3d6e; }
	30	dt.multidef { background-color: #ef9439; }
27	31
28	32	.bib dd
29	33	{ margin-bottom: 1em;

117	121	padding-top: 0.2em;
118	122	font-size: 80%;
119	123	font-style: italic;
120		color: #202020;
	124	color: #fff;
121	125	}
122	126
123	127	div.caption

127	131	}
128	132
129	133	/* Footnotes */
130
131		sup.fn { color: blue; text-decoration: underline; }
132		span.fn-text { display: none; }
133		sup.fn span {display: none;}
134		sup:hover span
135		{ display: block !important;
136		position: absolute; top: auto; left: auto; width: 80%;
137		color: #000; background: white;
138		border: 2px solid;
139		padding: 5px; margin: 10px; z-index: 100;
140		font-size: smaller;
	134	.fn {
	135	color: red;
	136	font-size: 70%;
	137	}
	138
	139	.fn-text, .fnp {
	140	position: absolute;
	141	top: auto;
	142	left: 10%;
	143	border: 1px solid #000;
	144	box-shadow: 5px 5px 5px #888;
	145	display: none;
	146	background: #fff;
	147	color: #000;
	148	margin-top: 25px;
	149	padding: 8px 12px;
	150	font-size: larger;
	151	}
	152
	153	sup:hover span.fn-text
	154	{ display: block;
141	155	}
142	156
143	157	/* Lists */

181	195	font-size: +1;
182	196	margin-top: 1ex;
183	197	}
	198
	199	/* Tables */
	200
	201	table.center
	202	{ margin: auto;
	203	}
	204
	205	table.latex
	206	{ border-collapse:collapse;
	207	}
	208
	209	table.latex tr
	210	{ vertical-align: text-top;
	211	}
	212
	213	table.latex td,th
	214	{ padding: 2px 1em;
	215	}
	216
	217	table.latex tr.hline td,th
	218	{ border-top: 1px solid black;
	219	}
	220
	221	table.frame-box
	222	{ border: 2px solid black;
	223	}
	224
184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="tty.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="files.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:system"><a name="sec:4.35"><span class="sec-nr">4.35</span> <span class="sec-title">Operating
	235	<h2 id="sec:system"><a id="sec:4.35"><span class="sec-nr">4.35</span> <span class="sec-title">Operating
195	236	System Interaction</span></a></h2>
196	237
197		<a name="sec:system"></a>
	238	<a id="sec:system"></a>
198	239
199	240	<p>The predicates in this section provide basic access to the operating
200	241	system that has been part of the Prolog legacy tradition. Note that more

203	244	<code>library(socket)</code>, <code>library(unix)</code> and <code>library(filesex)</code>.
204	245
205	246	<dl class="latex">
206		<dt class="pubdef"><a name="shell/1"><strong>shell</strong>(<var>+Command</var>)</a></dt>
207		<dd class="defbody">
208		Equivalent to `<code>shell(Command, 0)</code>'. See <a name="idx:shell2:1440"></a><a class="pred" href="system.html#shell/2">shell/2</a>
	247	<dt class="pubdef"><a id="shell/1"><strong>shell</strong>(<var>+Command</var>)</a></dt>
	248	<dd class="defbody">
	249	Equivalent to `<code>shell(Command, 0)</code>'. See <a id="idx:shell2:1440"></a><a class="pred" href="system.html#shell/2">shell/2</a>
209	250	for details.</dd>
210		<dt class="pubdef"><a name="shell/2"><strong>shell</strong>(<var>+Command,
	251	<dt class="pubdef"><a id="shell/2"><strong>shell</strong>(<var>+Command,
211	252	-Status</var>)</a></dt>
212	253	<dd class="defbody">
213	254	Execute <var>Command</var> on the operating system. <var>Command</var>
214	255	is given to the Bourne shell (/bin/sh). <var>Status</var> is unified
215	256	with the exit status of the command.
216	257
217		<p>On Windows, <a name="idx:shell12:1441"></a><a class="pred" href="system.html#shell/1">shell/[1,2]</a>
	258	<p>On Windows, <a id="idx:shell12:1441"></a><a class="pred" href="system.html#shell/1">shell/[1,2]</a>
218	259	executes the command using the CreateProcess() API and waits for the
219	260	command to terminate. If the command ends with a
220	261	<code>&</code> sign, the command is handed to the WinExec() API,
221		which does not wait for the new task to terminate. See also <a name="idx:winexec2:1442"></a><a class="pred" href="system.html#win_exec/2">win_exec/2</a>
	262	which does not wait for the new task to terminate. See also <a id="idx:winexec2:1442"></a><a class="pred" href="system.html#win_exec/2">win_exec/2</a>
222	263	and
223		<a name="idx:winshell2:1443"></a><a class="pred" href="system.html#win_shell/2">win_shell/2</a>.
	264	<a id="idx:winshell2:1443"></a><a class="pred" href="system.html#win_shell/2">win_shell/2</a>.
224	265	Please note that the CreateProcess() API does <b>not</b> imply the
225	266	Windows command interpreter (<b>cmd.exe</b> and therefore commands that
226	267	are built in the command interpreter can only be activated using the

233	274
234	275	<p>Note that many of the operations that can be achieved using the shell
235	276	built-in commands can easily be achieved using Prolog primitives. See
236		<a name="idx:makedirectory1:1444"></a><a class="pred" href="files.html#make_directory/1">make_directory/1</a>, <a name="idx:deletefile1:1445"></a><a class="pred" href="files.html#delete_file/1">delete_file/1</a>, <a name="idx:renamefile2:1446"></a><a class="pred" href="files.html#rename_file/2">rename_file/2</a>,
	277	<a id="idx:makedirectory1:1444"></a><a class="pred" href="files.html#make_directory/1">make_directory/1</a>, <a id="idx:deletefile1:1445"></a><a class="pred" href="files.html#delete_file/1">delete_file/1</a>, <a id="idx:renamefile2:1446"></a><a class="pred" href="files.html#rename_file/2">rename_file/2</a>,
237	278	etc. The clib package provides <code>library(filesex)</code>,
238		implementing various high level file operations such as <a name="idx:copyfile2:1447"></a><span class="pred-ext">copy_file/2</span>.
	279	implementing various high level file operations such as <a id="idx:copyfile2:1447"></a><span class="pred-ext">copy_file/2</span>.
239	280	Using Prolog primitives instead of shell commands improves the
240	281	portability of your program.
241	282
242		<p>The library <code>library(process)</code> provides <a name="idx:processcreate3:1448"></a><span class="pred-ext">process_create/3</span>
	283	<p>The library <code>library(process)</code> provides <a id="idx:processcreate3:1448"></a><span class="pred-ext">process_create/3</span>
243	284	and several related primitives that support more fine-grained
244	285	interaction with processes, including I/O redirection and management of
245	286	asynchronous processes.</dd>
246		<dt class="pubdef"><a name="getenv/2"><strong>getenv</strong>(<var>+Name,
	287	<dt class="pubdef"><a id="getenv/2"><strong>getenv</strong>(<var>+Name,
247	288	-Value</var>)</a></dt>
248	289	<dd class="defbody">
249	290	Get environment variable. Fails silently if the variable does not exist.
250	291	Please note that environment variable names are case-sensitive on Unix
251	292	systems and case-insensitive on Windows.</dd>
252		<dt class="pubdef"><a name="setenv/2"><strong>setenv</strong>(<var>+Name,
	293	<dt class="pubdef"><a id="setenv/2"><strong>setenv</strong>(<var>+Name,
253	294	+Value</var>)</a></dt>
254	295	<dd class="defbody">
255	296	Set an environment variable. <var>Name</var> and <var>Value</var> must
256	297	be instantiated to atoms or integers. The environment variable will be
257		passed to <a name="idx:shell02:1449"></a><a class="pred" href="system.html#shell/1">shell/[0-2]</a>
258		and can be requested using <a name="idx:getenv2:1450"></a><a class="pred" href="system.html#getenv/2">getenv/2</a>.
259		They also influence <a name="idx:expandfilename2:1451"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>.
	298	passed to <a id="idx:shell02:1449"></a><a class="pred" href="system.html#shell/1">shell/[0-2]</a>
	299	and can be requested using <a id="idx:getenv2:1450"></a><a class="pred" href="system.html#getenv/2">getenv/2</a>.
	300	They also influence <a id="idx:expandfilename2:1451"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>.
260	301	Environment variables are shared between threads. Depending on the
261		underlying C library, <a name="idx:setenv2:1452"></a><a class="pred" href="system.html#setenv/2">setenv/2</a>
262		and <a name="idx:unsetenv1:1453"></a><a class="pred" href="system.html#unsetenv/1">unsetenv/1</a>
	302	underlying C library, <a id="idx:setenv2:1452"></a><a class="pred" href="system.html#setenv/2">setenv/2</a>
	303	and <a id="idx:unsetenv1:1453"></a><a class="pred" href="system.html#unsetenv/1">unsetenv/1</a>
263	304	may not be thread-safe and may cause memory leaks. Only changing the
264	305	environment once and before starting threads is safe in all versions of
265	306	SWI-Prolog.</dd>
266		<dt class="pubdef"><a name="unsetenv/1"><strong>unsetenv</strong>(<var>+Name</var>)</a></dt>
	307	<dt class="pubdef"><a id="unsetenv/1"><strong>unsetenv</strong>(<var>+Name</var>)</a></dt>
267	308	<dd class="defbody">
268	309	Remove an environment variable from the environment. Some systems lack
269		the underlying unsetenv() library function. On these systems <a name="idx:unsetenv1:1454"></a><a class="pred" href="system.html#unsetenv/1">unsetenv/1</a>
	310	the underlying unsetenv() library function. On these systems <a id="idx:unsetenv1:1454"></a><a class="pred" href="system.html#unsetenv/1">unsetenv/1</a>
270	311	sets the variable to the empty string.</dd>
271		<dt class="pubdef"><a name="setlocale/3"><strong>setlocale</strong>(<var>+Category,
	312	<dt class="pubdef"><a id="setlocale/3"><strong>setlocale</strong>(<var>+Category,
272	313	-Old, +New</var>)</a></dt>
273	314	<dd class="defbody">
274	315	Set/Query the <em>locale</em> setting which tells the C library how to
275	316	interpret text files, write numbers, dates, etc. Category is one of
276	317	<code>all</code>, <code>collate</code>, <code>ctype</code>, <code>messages</code>,
277	318	<code>monetary</code>, <code>numeric</code> or <code>time</code>. For
278		details, please consult the C library locale documentation. See also <a class="sec" href="widechars.html">section
	319	details, please consult the C library locale documentation. See also <a class="sec" href="widechars.html#sec:2.19.1">section
279	320	2.19.1</a>. Please note that the locale is shared between all threads
280		and thread-safe usage of <a name="idx:setlocale3:1455"></a><a class="pred" href="system.html#setlocale/3">setlocale/3</a>
	321	and thread-safe usage of <a id="idx:setlocale3:1455"></a><a class="pred" href="system.html#setlocale/3">setlocale/3</a>
281	322	is in general not possible. Do locale operations before starting threads
282	323	or thoroughly study threading aspects of locale support in your
283	324	environment before using in multithreaded environments. Locale settings
284		are used by <a name="idx:formattime3:1456"></a><a class="pred" href="system.html#format_time/3">format_time/3</a>, <a name="idx:collationkey2:1457"></a><a class="pred" href="chartype.html#collation_key/2">collation_key/2</a>
285		and <a name="idx:localesort2:1458"></a><a class="pred" href="chartype.html#locale_sort/2">locale_sort/2</a>.</dd>
286		<dt class="pubdef"><a name="unix/1"><strong>unix</strong>(<var>+Command</var>)</a></dt>
	325	are used by <a id="idx:formattime3:1456"></a><a class="pred" href="system.html#format_time/3">format_time/3</a>, <a id="idx:collationkey2:1457"></a><a class="pred" href="chartype.html#collation_key/2">collation_key/2</a>
	326	and <a id="idx:localesort2:1458"></a><a class="pred" href="chartype.html#locale_sort/2">locale_sort/2</a>.</dd>
	327	<dt class="pubdef"><a id="unix/1"><strong>unix</strong>(<var>+Command</var>)</a></dt>
287	328	<dd class="defbody">
288	329	This predicate comes from the Quintus compatibility library and provides
289	330	a partial implementation thereof. It provides access to some operating

293	334	<dl class="latex">
294	335	<dt><strong>system</strong>(<var>+Command</var>)</dt>
295	336	<dd class="defbody">
296		Equivalent to calling <a name="idx:shell1:1459"></a><a class="pred" href="system.html#shell/1">shell/1</a>.
	337	Equivalent to calling <a id="idx:shell1:1459"></a><a class="pred" href="system.html#shell/1">shell/1</a>.
297	338	Use for compatibility only.</dd>
298	339	<dt><strong>shell</strong>(<var>+Command</var>)</dt>
299	340	<dd class="defbody">
300		Equivalent to calling <a name="idx:shell1:1460"></a><a class="pred" href="system.html#shell/1">shell/1</a>.
	341	Equivalent to calling <a id="idx:shell1:1460"></a><a class="pred" href="system.html#shell/1">shell/1</a>.
301	342	Use for compatibility only.</dd>
302	343	<dt><strong>shell</strong></dt>
303	344	<dd class="defbody">
304		Equivalent to calling <a name="idx:shell0:1461"></a><span class="pred-ext">shell/0</span>.
	345	Equivalent to calling <a id="idx:shell0:1461"></a><span class="pred-ext">shell/0</span>.
305	346	Use for compatibility only.</dd>
306	347	<dt><strong>cd</strong></dt>
307	348	<dd class="defbody">
308		Equivalent to calling <a name="idx:workingdirectory2:1462"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>
	349	Equivalent to calling <a id="idx:workingdirectory2:1462"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>
309	350	to the expansion (see
310		<a name="idx:expandfilename2:1463"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>)
	351	<a id="idx:expandfilename2:1463"></a><a class="pred" href="files.html#expand_file_name/2">expand_file_name/2</a>)
311	352	of <code><code>~</code></code>. For compatibility only.</dd>
312	353	<dt><strong>cd</strong>(<var>+Directory</var>)</dt>
313	354	<dd class="defbody">
314		Equivalent to calling <a name="idx:workingdirectory2:1464"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>.
	355	Equivalent to calling <a id="idx:workingdirectory2:1464"></a><a class="pred" href="files.html#working_directory/2">working_directory/2</a>.
315	356	Use for compatibility only.</dd>
316	357	<dt><strong>argv</strong>(<var>-Argv</var>)</dt>
317	358	<dd class="defbody">

329	370	</dd>
330	371	</dl>
331	372
332		<p><h3 id="sec:winsystem"><a name="sec:4.35.1"><span class="sec-nr">4.35.1</span> <span class="sec-title">Windows-specific
	373	<p><h3 id="sec:winsystem"><a id="sec:4.35.1"><span class="sec-nr">4.35.1</span> <span class="sec-title">Windows-specific
333	374	Operating System Interaction</span></a></h3>
334	375
335		<a name="sec:winsystem"></a>
	376	<a id="sec:winsystem"></a>
336	377
337	378	<p>The predicates in this section are only available on the Windows
338	379	version of SWI-Prolog. Their use is discouraged if there are portably
339		alternatives. For example, <a name="idx:winexec2:1465"></a><a class="pred" href="system.html#win_exec/2">win_exec/2</a>
340		and <a name="idx:winshell2:1466"></a><a class="pred" href="system.html#win_shell/2">win_shell/2</a>
341		can often be replaced by the more portable <a name="idx:shell2:1467"></a><a class="pred" href="system.html#shell/2">shell/2</a>
	380	alternatives. For example, <a id="idx:winexec2:1465"></a><a class="pred" href="system.html#win_exec/2">win_exec/2</a>
	381	and <a id="idx:winshell2:1466"></a><a class="pred" href="system.html#win_shell/2">win_shell/2</a>
	382	can often be replaced by the more portable <a id="idx:shell2:1467"></a><a class="pred" href="system.html#shell/2">shell/2</a>
342	383	or the more powerful
343		<a name="idx:processcreate3:1468"></a><span class="pred-ext">process_create/3</span>.
	384	<a id="idx:processcreate3:1468"></a><span class="pred-ext">process_create/3</span>.
344	385
345	386	<dl class="latex">
346		<dt class="pubdef"><a name="win_exec/2"><strong>win_exec</strong>(<var>+Command,
	387	<dt class="pubdef"><a id="win_exec/2"><strong>win_exec</strong>(<var>+Command,
347	388	+Show</var>)</a></dt>
348	389	<dd class="defbody">
349	390	Windows only. Spawns a Windows task without waiting for its completion. <var>Show</var>

363	404	<code>shownormal</code>. In addition, <code>iconic</code> is a synonym
364	405	for <code>minimize</code> and
365	406	<code>normal</code> for <code>shownormal</code>.</dd>
366		<dt class="pubdef"><a name="win_shell/3"><strong>win_shell</strong>(<var>+Operation,
	407	<dt class="pubdef"><a id="win_shell/3"><strong>win_shell</strong>(<var>+Operation,
367	408	+File, +Show</var>)</a></dt>
368	409	<dd class="defbody">
369	410	Windows only. Opens the document <var>File</var> using the Windows shell
370	411	rules for doing so. <var>Operation</var> is one of <code>open</code>,
371	412	<code>print</code> or <code>explore</code> or another operation
372	413	registered with the shell for the given document type. On modern systems
373		it is also possible to pass a <a name="idx:URL:1469"></a>URL as <var>File</var>,
	414	it is also possible to pass a <a id="idx:URL:1469"></a>URL as <var>File</var>,
374	415	opening the URL in Windows default browser. This call interfaces to the
375	416	Win32 API ShellExecute(). The <var>Show</var> argument determines the
376		initial state of the opened window (if any). See <a name="idx:winexec2:1470"></a><a class="pred" href="system.html#win_exec/2">win_exec/2</a>
	417	initial state of the opened window (if any). See <a id="idx:winexec2:1470"></a><a class="pred" href="system.html#win_exec/2">win_exec/2</a>
377	418	for defined values.</dd>
378		<dt class="pubdef"><a name="win_shell/2"><strong>win_shell</strong>(<var>+Operation,
	419	<dt class="pubdef"><a id="win_shell/2"><strong>win_shell</strong>(<var>+Operation,
379	420	+File</var>)</a></dt>
380	421	<dd class="defbody">
381	422	Same as <code>win_shell(Operation, File, normal)</code></dd>
382		<dt class="pubdef"><a name="win_registry_get_value/3"><strong>win_registry_get_value</strong>(<var>+Key,
	423	<dt class="pubdef"><a id="win_registry_get_value/3"><strong>win_registry_get_value</strong>(<var>+Key,
383	424	+Name, -Value</var>)</a></dt>
384	425	<dd class="defbody">
385	426	Windows only. Fetches the value of a Windows registry key. <var>Key</var>

405	446	</pre>
406	447
407	448	</dd>
408		<dt class="pubdef"><a name="win_folder/2"><strong>win_folder</strong>(<var>?Name,
	449	<dt class="pubdef"><a id="win_folder/2"><strong>win_folder</strong>(<var>?Name,
409	450	-Directory</var>)</a></dt>
410	451	<dd class="defbody">
411	452	True if <var>Name</var> is the Windows `CSIDL' of <var>Directory</var>.

424	465	</pre>
425	466
426	467	</dd>
427		<dt class="pubdef"><a name="win_add_dll_directory/1"><strong>win_add_dll_directory</strong>(<var>+AbsDir</var>)</a></dt>
	468	<dt class="pubdef"><a id="win_add_dll_directory/1"><strong>win_add_dll_directory</strong>(<var>+AbsDir</var>)</a></dt>
428	469	<dd class="defbody">
429	470	This predicate adds a directory to the search path for dependent DLL
430		files. If possible, this is achieved with <a name="idx:winadddlldirectory2:1471"></a><a class="pred" href="system.html#win_add_dll_directory/2">win_add_dll_directory/2</a>.
	471	files. If possible, this is achieved with <a id="idx:winadddlldirectory2:1471"></a><a class="pred" href="system.html#win_add_dll_directory/2">win_add_dll_directory/2</a>.
431	472	Otherwise, <code>%PATH%</code> is extended with the provided directory.
432	473	<var>AbsDir</var> may be specified in the Prolog canonical syntax. See
433		<a name="idx:prologtoosfilename2:1472"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>.
434		Note that <a name="idx:useforeignlibrary1:1473"></a><a class="pred" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a>
	474	<a id="idx:prologtoosfilename2:1472"></a><a class="pred" href="files.html#prolog_to_os_filename/2">prolog_to_os_filename/2</a>.
	475	Note that <a id="idx:useforeignlibrary1:1473"></a><a class="pred" href="foreignlink.html#use_foreign_library/1">use_foreign_library/1</a>
435	476	passes an absolute path to the DLL if the destination DLL can be located
436		from the specification using <a name="idx:absolutefilename3:1474"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.</dd>
437		<dt class="pubdef"><a name="win_add_dll_directory/2"><strong>win_add_dll_directory</strong>(<var>+AbsDir,
	477	from the specification using <a id="idx:absolutefilename3:1474"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>.</dd>
	478	<dt class="pubdef"><a id="win_add_dll_directory/2"><strong>win_add_dll_directory</strong>(<var>+AbsDir,
438	479	-Cookie</var>)</a></dt>
439	480	<dd class="defbody">
440	481	This predicate adds a directory to the search path for dependent DLL
441	482	files. If the call is successful it unifies <var>Cookie</var> with a
442		handle that must be passed to <a name="idx:winremovedlldirectory1:1475"></a><a class="pred" href="system.html#win_remove_dll_directory/1">win_remove_dll_directory/1</a>
	483	handle that must be passed to <a id="idx:winremovedlldirectory1:1475"></a><a class="pred" href="system.html#win_remove_dll_directory/1">win_remove_dll_directory/1</a>
443	484	to remove the directory from the search path. Error conditions:
444	485
445	486	<p>

453	494	or the underlying Windows API returns an error.
454	495	</ul>
455	496
456		<p>If <a name="idx:opensharedobject2:1476"></a><a class="pred" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a>
	497	<p>If <a id="idx:opensharedobject2:1476"></a><a class="pred" href="foreignlink.html#open_shared_object/2">open_shared_object/2</a>
457	498	is passed an <em>absolute</em> path to a DLL on a Windows installation
458	499	that supports AddDllDirectory() and friends,<sup class="fn">130<span class="fn-text">Windows 7
459	500	with up-to-date patches or Windows 8.</span></sup> SWI-Prolog uses

461	502	<code>LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR</code> and
462	503	<code>LOAD_LIBRARY_SEARCH_DEFAULT_DIRS</code>. In this scenario,
463	504	directories from <code>%PATH%</code> and <em>not</em> searched.
464		Additional directories can be added using <a name="idx:winadddlldirectory2:1477"></a><a class="pred" href="system.html#win_add_dll_directory/2">win_add_dll_directory/2</a>.</dd>
465		<dt class="pubdef"><a name="win_remove_dll_directory/1"><strong>win_remove_dll_directory</strong>(<var>-Cookie</var>)</a></dt>
466		<dd class="defbody">
467		Remove a DLL search directory installed using <a name="idx:winadddlldirectory2:1478"></a><a class="pred" href="system.html#win_add_dll_directory/2">win_add_dll_directory/2</a>.
	505	Additional directories can be added using <a id="idx:winadddlldirectory2:1477"></a><a class="pred" href="system.html#win_add_dll_directory/2">win_add_dll_directory/2</a>.</dd>
	506	<dt class="pubdef"><a id="win_remove_dll_directory/1"><strong>win_remove_dll_directory</strong>(<var>-Cookie</var>)</a></dt>
	507	<dd class="defbody">
	508	Remove a DLL search directory installed using <a id="idx:winadddlldirectory2:1478"></a><a class="pred" href="system.html#win_add_dll_directory/2">win_add_dll_directory/2</a>.
468	509	</dd>
469	510	</dl>
470	511
471		<p><h3 id="sec:timedate"><a name="sec:4.35.2"><span class="sec-nr">4.35.2</span> <span class="sec-title">Dealing
	512	<p><h3 id="sec:timedate"><a id="sec:4.35.2"><span class="sec-nr">4.35.2</span> <span class="sec-title">Dealing
472	513	with time and date</span></a></h3>
473	514
474		<a name="sec:timedate"></a>
	515	<a id="sec:timedate"></a>
475	516
476	517	<p>Representing time in a computer system is surprisingly complicated.
477	518	There are a large number of time representations in use, and the correct

509	550
510	551	<p>Where older versions of SWI-Prolog relied on the POSIX conversion
511	552	functions, the current implementation uses
512		http://cr.yp.to/libtai.htmllibtai to realise conversion between
513		time-stamps and calendar dates for a period of 10 million years.
514
515		<p><h4 id="sec:dattimedata"><a name="sec:4.35.2.1"><span class="sec-nr">4.35.2.1</span> <span class="sec-title">Time
	553	<a class="url" href="http://cr.yp.to/libtai.html">libtai</a> to realise
	554	conversion between time-stamps and calendar dates for a period of 10
	555	million years.
	556
	557	<p><h4 id="sec:dattimedata"><a id="sec:4.35.2.1"><span class="sec-nr">4.35.2.1</span> <span class="sec-title">Time
516	558	and date data structures</span></a></h4>
517	559
518		<a name="sec:dattimedata"></a>
	560	<a id="sec:dattimedata"></a>
519	561
520	562	<p>We use the following time representations
521	563

531	573	and minute (0..59). The <var>S</var> field holds the seconds as a
532	574	floating point number between 0.0 and 60.0. <var>Off</var> is an integer
533	575	representing the offset relative to UTC in seconds, where positive
534		values are west of Greenwich. If converted from local time (see <a name="idx:stampdatetime3:1479"></a><a class="pred" href="system.html#stamp_date_time/3">stamp_date_time/3</a>),
	576	values are west of Greenwich. If converted from local time (see <a id="idx:stampdatetime3:1479"></a><a class="pred" href="system.html#stamp_date_time/3">stamp_date_time/3</a>),
535	577	<var>TZ</var> holds the name of the local timezone. If the timezone is
536	578	not known, <var>TZ</var> is the atom <code><code>-</code></code>. <var>DST</var>
537	579	is <code>true</code> if daylight saving time applies to the current

541	583	<dt><strong>date</strong>(<var>Y,M,D</var>)</dt>
542	584	<dd class="defbody">
543	585	Date using the same values as described above. Extracted using
544		<a name="idx:datetimevalue3:1480"></a><a class="pred" href="system.html#date_time_value/3">date_time_value/3</a>.</dd>
	586	<a id="idx:datetimevalue3:1480"></a><a class="pred" href="system.html#date_time_value/3">date_time_value/3</a>.</dd>
545	587	<dt><strong>time</strong>(<var>H,Mn,S</var>)</dt>
546	588	<dd class="defbody">
547	589	Time using the same values as described above. Extracted using
548		<a name="idx:datetimevalue3:1481"></a><a class="pred" href="system.html#date_time_value/3">date_time_value/3</a>.
	590	<a id="idx:datetimevalue3:1481"></a><a class="pred" href="system.html#date_time_value/3">date_time_value/3</a>.
549	591	</dd>
550	592	</dl>
551	593
552		<p><h4 id="sec:datimepreds"><a name="sec:4.35.2.2"><span class="sec-nr">4.35.2.2</span> <span class="sec-title">Time
	594	<p><h4 id="sec:datimepreds"><a id="sec:4.35.2.2"><span class="sec-nr">4.35.2.2</span> <span class="sec-title">Time
553	595	and date predicates</span></a></h4>
554	596
555		<a name="sec:datimepreds"></a>
	597	<a id="sec:datimepreds"></a>
556	598
557	599	<dl class="latex">
558		<dt class="pubdef"><a name="get_time/1"><strong>get_time</strong>(<var>-TimeStamp</var>)</a></dt>
	600	<dt class="pubdef"><a id="get_time/1"><strong>get_time</strong>(<var>-TimeStamp</var>)</a></dt>
559	601	<dd class="defbody">
560	602	Return the current time as a <var>TimeStamp</var>. The granularity is
561		system-dependent. See <a class="sec" href="system.html">section 4.35.2.1</a>.</dd>
562		<dt class="pubdef"><a name="stamp_date_time/3"><strong>stamp_date_time</strong>(<var>+TimeStamp,
	603	system-dependent. See <a class="sec" href="system.html#sec:4.35.2.1">section
	604	4.35.2.1</a>.</dd>
	605	<dt class="pubdef"><a id="stamp_date_time/3"><strong>stamp_date_time</strong>(<var>+TimeStamp,
563	606	-DateTime, +TimeZone</var>)</a></dt>
564	607	<dd class="defbody">
565	608	Convert a <var>TimeStamp</var> to a <var>DateTime</var> in the given
566		timezone. See <a class="sec" href="system.html">section 4.35.2.1</a> for
567		details on the data types. <var>TimeZone</var> describes the timezone
568		for the conversion. It is one of <code>local</code> to extract the local
569		time, <code>'UTC'</code> to extract a UTC time or an integer describing
570		the seconds west of Greenwich.</dd>
571		<dt class="pubdef"><a name="date_time_stamp/2"><strong>date_time_stamp</strong>(<var>+DateTime,
	609	timezone. See <a class="sec" href="system.html#sec:4.35.2.1">section
	610	4.35.2.1</a> for details on the data types. <var>TimeZone</var>
	611	describes the timezone for the conversion. It is one of <code>local</code>
	612	to extract the local time, <code>'UTC'</code> to extract a UTC time or
	613	an integer describing the seconds west of Greenwich.</dd>
	614	<dt class="pubdef"><a id="date_time_stamp/2"><strong>date_time_stamp</strong>(<var>+DateTime,
572	615	-TimeStamp</var>)</a></dt>
573	616	<dd class="defbody">
574	617	Compute the timestamp from a date/9 term. Values for month, day, hour,
575	618	minute or second need not be normalized. This flexibility allows for
576	619	easy computation of the time at any given number of these units from a
577		given timestamp. Normalization can be achieved following this call with <a name="idx:stampdatetime3:1482"></a><a class="pred" href="system.html#stamp_date_time/3">stamp_date_time/3</a>.
	620	given timestamp. Normalization can be achieved following this call with <a id="idx:stampdatetime3:1482"></a><a class="pred" href="system.html#stamp_date_time/3">stamp_date_time/3</a>.
578	621	This example computes the date 200 days after 2006-7-14:
579	622
580	623	<pre class="code">

617	660	<p>Note that DST and offset calculation are based on the POSIX function
618	661	mktime(). If mktime() returns an error, a representation_error
619	662	<code>dst</code> is generated.</dd>
620		<dt class="pubdef"><a name="date_time_value/3"><strong>date_time_value</strong>(<var>?Key,
	663	<dt class="pubdef"><a id="date_time_value/3"><strong>date_time_value</strong>(<var>?Key,
621	664	+DateTime, ?Value</var>)</a></dt>
622	665	<dd class="defbody">
623	666	Extract values from a date/9 term. Provided keys are:
624	667
625		<p><table border="2" frame="hsides" rules="groups" style="margin:auto">
626		<tr valign="top"><td><b>key</b></td><td><b>value </b></td></tr>
627		<tbody>
628		<tr valign="top"><td><code>year</code> </td><td>Calendar year as an
	668	<p><table class="latex frame-hsides center">
	669	<tr><td><b>key</b></td><td><b>value </b></td></tr>
	670	<tr class="hline"><td><code>year</code> </td><td>Calendar year as an
629	671	integer </td></tr>
630		<tr valign="top"><td><code>month</code> </td><td>Calendar month as an
631		integer 1..12 </td></tr>
632		<tr valign="top"><td><code>day</code> </td><td>Calendar day as an
633		integer 1..31 </td></tr>
634		<tr valign="top"><td><code>hour</code> </td><td>Clock hour as an integer
635		0..23 </td></tr>
636		<tr valign="top"><td><code>minute</code> </td><td>Clock minute as an
637		integer 0..59 </td></tr>
638		<tr valign="top"><td><code>second</code> </td><td>Clock second as a
639		float 0.0..60.0 </td></tr>
640		<tr valign="top"><td><code>utc_offset</code> </td><td>Offset to UTC in
641		seconds (positive is west) </td></tr>
642		<tr valign="top"><td><code>time_zone</code> </td><td>Name of timezone;
643		fails if unknown </td></tr>
644		<tr valign="top"><td><code>daylight_saving</code> </td><td>Bool <code>daylight_saving</code>true)
	672	<tr><td><code>month</code> </td><td>Calendar month as an integer 1..12 </td></tr>
	673	<tr><td><code>day</code> </td><td>Calendar day as an integer 1..31 </td></tr>
	674	<tr><td><code>hour</code> </td><td>Clock hour as an integer 0..23 </td></tr>
	675	<tr><td><code>minute</code> </td><td>Clock minute as an integer 0..59 </td></tr>
	676	<tr><td><code>second</code> </td><td>Clock second as a float 0.0..60.0 </td></tr>
	677	<tr><td><code>utc_offset</code> </td><td>Offset to UTC in seconds
	678	(positive is west) </td></tr>
	679	<tr><td><code>time_zone</code> </td><td>Name of timezone; fails if
	680	unknown </td></tr>
	681	<tr><td><code>daylight_saving</code> </td><td>Bool <code>daylight_saving</code>true)
645	682	if dst is in effect </td></tr>
646		<tr valign="top"><td><code>date</code> </td><td>Term <code>date(Y,M,D)</code> </td></tr>
647		<tr valign="top"><td><code>time</code> </td><td>Term <code>time(H,M,S)</code> </td></tr>
	683	<tr><td><code>date</code> </td><td>Term <code>date(Y,M,D)</code> </td></tr>
	684	<tr><td><code>time</code> </td><td>Term <code>time(H,M,S)</code> </td></tr>
648	685	</table>
649	686	</dd>
650		<dt class="pubdef"><a name="format_time/3"><strong>format_time</strong>(<var>+Out,
	687	<dt class="pubdef"><a id="format_time/3"><strong>format_time</strong>(<var>+Out,
651	688	+Format, +StampOrDateTime</var>)</a></dt>
652	689	<dd class="defbody">
653	690	Modelled after POSIX strftime(), using GNU extensions. <var>Out</var> is
654		a destination as specified with <a name="idx:withoutputto2:1483"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>. <var>Format</var>
	691	a destination as specified with <a id="idx:withoutputto2:1483"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>. <var>Format</var>
655	692	is an atom or string with the following conversions. Conversions start
656	693	with a percent (%) character.<sup class="fn">132<span class="fn-text">Descriptions
657	694	taken from Linux Programmer's Manual</span></sup>

662	699	<ul class="latex">
663	700	<li><code>a</code><br>
664	701	The abbreviated weekday name according to the current locale. Use
665		<a name="idx:formattime4:1484"></a><a class="pred" href="system.html#format_time/4">format_time/4</a>
	702	<a id="idx:formattime4:1484"></a><a class="pred" href="system.html#format_time/4">format_time/4</a>
666	703	for POSIX locale.
667	704	<li><code>A</code><br>
668	705	The full weekday name according to the current locale. Use
669		<a name="idx:formattime4:1485"></a><a class="pred" href="system.html#format_time/4">format_time/4</a>
	706	<a id="idx:formattime4:1485"></a><a class="pred" href="system.html#format_time/4">format_time/4</a>
670	707	for POSIX locale.
671	708	<li><code>b</code><br>
672	709	The abbreviated month name according to the current locale. Use
673		<a name="idx:formattime4:1486"></a><a class="pred" href="system.html#format_time/4">format_time/4</a>
	710	<a id="idx:formattime4:1486"></a><a class="pred" href="system.html#format_time/4">format_time/4</a>
674	711	for POSIX locale.
675	712	<li><code>B</code><br>
676	713	The full month name according to the current locale. Use
677		<a name="idx:formattime4:1487"></a><a class="pred" href="system.html#format_time/4">format_time/4</a>
	714	<a id="idx:formattime4:1487"></a><a class="pred" href="system.html#format_time/4">format_time/4</a>
678	715	for POSIX locale.
679	716	<li><code>c</code><br>
680	717	The preferred date and time representation for the current locale.

797	834
798	835	<p>The table below gives some format strings for popular time
799	836	representations. RFC1123 is used by HTTP. The full implementation of
800		<a name="idx:httptimestamp2:1488"></a><span class="pred-ext">http_timestamp/2</span>
	837	<a id="idx:httptimestamp2:1488"></a><span class="pred-ext">http_timestamp/2</span>
801	838	as available from <code>library(http/http_header)</code> is here.
802	839
803	840	<pre class="code">

808	845	Date, posix).
809	846	</pre>
810	847
811		<p><table border="2" frame="hsides" rules="groups" style="margin:auto">
812		<tr valign="top"><td><b>Standard</b> </td><td><b>Format string</b> </td></tr>
813		<tbody>
814		<tr valign="top"><td><b>xsd</b> </td><td><code>'%FT%T%:z'</code> </td></tr>
815		<tr valign="top"><td><b>ISO8601</b> </td><td><code>'%FT%T%z'</code> </td></tr>
816		<tr valign="top"><td><b>RFC822</b> </td><td><code>'%a, %d %b %Y %T %z'</code> </td></tr>
817		<tr valign="top"><td><b>RFC1123</b> </td><td><code>'%a, %d %b %Y %T GMT'</code> </td></tr>
	848	<p><table class="latex frame-hsides center">
	849	<tr><td><b>Standard</b> </td><td><b>Format string</b> </td></tr>
	850	<tr class="hline"><td><b>xsd</b> </td><td><code>'%FT%T%:z'</code> </td></tr>
	851	<tr><td><b>ISO8601</b> </td><td><code>'%FT%T%z'</code> </td></tr>
	852	<tr><td><b>RFC822</b> </td><td><code>'%a, %d %b %Y %T %z'</code> </td></tr>
	853	<tr><td><b>RFC1123</b> </td><td><code>'%a, %d %b %Y %T GMT'</code> </td></tr>
818	854	</table>
819	855	</dd>
820		<dt class="pubdef"><a name="format_time/4"><strong>format_time</strong>(<var>+Out,
	856	<dt class="pubdef"><a id="format_time/4"><strong>format_time</strong>(<var>+Out,
821	857	+Format, +StampOrDateTime, +Locale</var>)</a></dt>
822	858	<dd class="defbody">
823	859	Format time given a specified <var>Locale</var>. This predicate is a

828	864	and <code>B</code> format specifiers. The predicate is used to be able
829	865	to emit POSIX locale week and month names for emitting standardised
830	866	time-stamps such as RFC1123.</dd>
831		<dt class="pubdef"><a name="parse_time/2"><strong>parse_time</strong>(<var>+Text,
	867	<dt class="pubdef"><a id="parse_time/2"><strong>parse_time</strong>(<var>+Text,
832	868	-Stamp</var>)</a></dt>
833	869	<dd class="defbody">
834		Same as <code>parse_time(Text, _Format, Stamp)</code>. See <a name="idx:parsetime3:1489"></a><a class="pred" href="system.html#parse_time/3">parse_time/3</a>.</dd>
835		<dt class="pubdef"><a name="parse_time/3"><strong>parse_time</strong>(<var>+Text,
	870	Same as <code>parse_time(Text, _Format, Stamp)</code>. See <a id="idx:parsetime3:1489"></a><a class="pred" href="system.html#parse_time/3">parse_time/3</a>.</dd>
	871	<dt class="pubdef"><a id="parse_time/3"><strong>parse_time</strong>(<var>+Text,
836	872	?Format, -Stamp</var>)</a></dt>
837	873	<dd class="defbody">
838	874	Parse a textual time representation, producing a time-stamp. Supported

841	877	Otherwise,
842	878	<var>Format</var> is unified with the format encountered.
843	879
844		<p><table border="2" frame="box" rules="groups" style="margin:auto">
845		<tr valign="top"><td><b>Name</b></td><td><b>Example </b></td></tr>
846		<tbody>
847		<tr valign="top"><td>rfc_1123</td><td><code>Fri, 08 Dec 2006 15:29:44
	880	<p><table class="latex frame-box center">
	881	<tr><td><b>Name</b></td><td><b>Example </b></td></tr>
	882	<tr class="hline"><td>rfc_1123</td><td><code>Fri, 08 Dec 2006 15:29:44
848	883	GMT </code></td></tr>
849		<tr valign="top"><td></td><td><code>Fri, 08 Dec 2006 15:29:44 +0000 </code></td></tr>
850		<tbody>
851		<tr valign="top"><td>iso_8601</td><td><code>2006-12-08T17:29:44+02:00 </code></td></tr>
852		<tr valign="top"><td></td><td><code>20061208T172944+0200 </code></td></tr>
853		<tr valign="top"><td></td><td><code>2006-12-08T15:29Z </code></td></tr>
854		<tr valign="top"><td></td><td><code>2006-12-08 </code></td></tr>
855		<tr valign="top"><td></td><td><code>20061208 </code></td></tr>
856		<tr valign="top"><td></td><td><code>2006-12 </code></td></tr>
857		<tr valign="top"><td></td><td><code>2006-W49-5 </code></td></tr>
858		<tr valign="top"><td></td><td><code>2006-342 </code></td></tr>
	884	<tr><td></td><td><code>Fri, 08 Dec 2006 15:29:44 +0000 </code></td></tr>
	885	<tr class="hline"><td>iso_8601</td><td><code>2006-12-08T17:29:44+02:00 </code></td></tr>
	886	<tr><td></td><td><code>20061208T172944+0200 </code></td></tr>
	887	<tr><td></td><td><code>2006-12-08T15:29Z </code></td></tr>
	888	<tr><td></td><td><code>2006-12-08 </code></td></tr>
	889	<tr><td></td><td><code>20061208 </code></td></tr>
	890	<tr><td></td><td><code>2006-12 </code></td></tr>
	891	<tr><td></td><td><code>2006-W49-5 </code></td></tr>
	892	<tr><td></td><td><code>2006-342 </code></td></tr>
859	893	</table>
860	894	</dd>
861		<dt class="pubdef"><a name="day_of_the_week/2"><strong>day_of_the_week</strong>(<var>+Date,-DayOfTheWeek</var>)</a></dt>
	895	<dt class="pubdef"><a id="day_of_the_week/2"><strong>day_of_the_week</strong>(<var>+Date,-DayOfTheWeek</var>)</a></dt>
862	896	<dd class="defbody">
863	897	Computes the day of the week for a given date.
864	898	<code><var>Date</var> = date(<var>Year</var>,<var>Month</var>,<var>Day</var>)</code>.

867	901	</dd>
868	902	</dl>
869	903
870		<p><h3 id="sec:plwin"><a name="sec:4.35.3"><span class="sec-nr">4.35.3</span> <span class="sec-title">Controlling
	904	<p><h3 id="sec:plwin"><a id="sec:4.35.3"><span class="sec-nr">4.35.3</span> <span class="sec-title">Controlling
871	905	the <b>swipl-win.exe</b> console window</span></a></h3>
872	906
873		<a name="sec:plwin"></a>
	907	<a id="sec:plwin"></a>
874	908
875	909	<p>The Windows executable <b>swipl-win.exe</b> console has a number of
876	910	predicates to control the appearance of the console. Being totally

879	913	predicates for reference here.
880	914
881	915	<dl class="latex">
882		<dt class="pubdef"><a name="window_title/2"><strong>window_title</strong>(<var>-Old,
	916	<dt class="pubdef"><a id="window_title/2"><strong>window_title</strong>(<var>-Old,
883	917	+New</var>)</a></dt>
884	918	<dd class="defbody">
885	919	Unify <var>Old</var> with the title displayed in the console and change
886	920	the title to <var>New</var>.<sup class="fn">bug<span class="fn-text">This
887	921	predicate should have been called <code>win_window_title</code> for
888	922	consistent naming.</span></sup></dd>
889		<dt class="pubdef"><a name="win_window_pos/1"><strong>win_window_pos</strong>(<var>+ListOfOptions</var>)</a></dt>
	923	<dt class="pubdef"><a id="win_window_pos/1"><strong>win_window_pos</strong>(<var>+ListOfOptions</var>)</a></dt>
890	924	<dd class="defbody">
891	925	Interface to the MS-Windows SetWindowPos() function, controlling size,
892	926	position and stacking order of the window. <var>ListOfOptions</var> is a

921	955	</dl>
922	956
923	957	</dd>
924		<dt class="pubdef"><a name="win_has_menu/0"><strong>win_has_menu</strong></a></dt>
925		<dd class="defbody">
926		True if <a name="idx:wininsertmenu2:1490"></a><a class="pred" href="system.html#win_insert_menu/2">win_insert_menu/2</a>
927		and <a name="idx:wininsertmenuitem4:1491"></a><a class="pred" href="system.html#win_insert_menu_item/4">win_insert_menu_item/4</a>
	958	<dt class="pubdef"><a id="win_has_menu/0"><strong>win_has_menu</strong></a></dt>
	959	<dd class="defbody">
	960	True if <a id="idx:wininsertmenu2:1490"></a><a class="pred" href="system.html#win_insert_menu/2">win_insert_menu/2</a>
	961	and <a id="idx:wininsertmenuitem4:1491"></a><a class="pred" href="system.html#win_insert_menu_item/4">win_insert_menu_item/4</a>
928	962	are present.</dd>
929		<dt class="pubdef"><a name="win_insert_menu/2"><strong>win_insert_menu</strong>(<var>+Label,
	963	<dt class="pubdef"><a id="win_insert_menu/2"><strong>win_insert_menu</strong>(<var>+Label,
930	964	+Before</var>)</a></dt>
931	965	<dd class="defbody">
932	966	Insert a new entry (pulldown) in the menu. If the menu already contains

942	976	</pre>
943	977
944	978	</dd>
945		<dt class="pubdef"><a name="win_insert_menu_item/4"><strong>win_insert_menu_item</strong>(<var>+Pulldown,
	979	<dt class="pubdef"><a id="win_insert_menu_item/4"><strong>win_insert_menu_item</strong>(<var>+Pulldown,
946	980	+Label, +Before, :Goal</var>)</a></dt>
947	981	<dd class="defbody">
948	982	Add an item to the named <var>Pulldown</var> menu. <var>Label</var> and
949		<var>Before</var> are handled as in <a name="idx:wininsertmenu2:1492"></a><a class="pred" href="system.html#win_insert_menu/2">win_insert_menu/2</a>,
	983	<var>Before</var> are handled as in <a id="idx:wininsertmenu2:1492"></a><a class="pred" href="system.html#win_insert_menu/2">win_insert_menu/2</a>,
950	984	but the label <code><code>-</code></code> inserts a <em>separator</em>. <var>Goal</var>
951	985	is called if the user selects the item.
952	986	</dd>

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194		<h2 id="sec:tabling"><a name="sec:A.35"><span class="sec-nr">A.35</span> <span class="sec-title">library(tabling):
	235	<h2 id="sec:tabling"><a id="sec:A.35"><span class="sec-nr">A.35</span> <span class="sec-title">library(tabling):
195	236	Tabled execution (SLG)</span></a></h2>
196	237
197		<a name="sec:tabling"></a>
198
199		<p><a name="idx:SLGresolution:2171"></a>The library <code>library(tabling)</code>
	238	<a id="sec:tabling"></a>
	239
	240	<p><a id="idx:SLGresolution:2175"></a>The library <code>library(tabling)</code>
200	241	provides support for <em>Tabled execution</em> of one or more Prolog
201	242	predicates, also called <em>SLG resolution</em>. Tabling a predicate
202	243	provides two properties:

206	247	<li>Re-evaluation of a tabled predicate is avoided by
207	248	<em>memoizing</em> the answers. This can realise huge performance
208	249	enhancements as illustrated in
209		<a class="sec" href="tabling.html">section A.35.1</a>. It also comes
210		with two downsides: the memoized answers are not automatically updated
211		or invalidated if the world (set of predicates on which the answers
212		depend) changes and the answer tables must be stored (in memory).
	250	<a class="sec" href="tabling.html#sec:A.35.1">section A.35.1</a>. It
	251	also comes with two downsides: the memoized answers are not
	252	automatically updated or invalidated if the world (set of predicates on
	253	which the answers depend) changes and the answer tables must be stored
	254	(in memory).
213	255
214	256	<p>
215	257	<li><em>Left recursion</em>, a goal calling a <em>variant</em> of itself
216	258	recursively and thus <i>looping</i> under the normal Prolog SLD
217	259	resolution is avoided by suspending the variant call and resuming it
218		with answers from the table. This is illustrated in <a class="sec" href="tabling.html">section
	260	with answers from the table. This is illustrated in <a class="sec" href="tabling.html#sec:A.35.2">section
219	261	A.35.2</a>.
220	262	</ol>
221	263

227	269	evaluation, i.e., applying rules on the axioms and derived facts until a
228	270	fixed point is reached. However, bottom-up evaluation typically derives
229	271	many facts that are never used. Tabling provides a <em>goal oriented</em>
230		resolution strategy for such problems and is enabled simply by adding a <a name="idx:table1:2172"></a><a class="pred" href="tabling.html#table/1">table/1</a>
	272	resolution strategy for such problems and is enabled simply by adding a <a id="idx:table1:2176"></a><a class="pred" href="tabling.html#table/1">table/1</a>
231	273	directive to the program.
232	274
233		<p><h4 id="sec:tabling-memoize"><a name="sec:A.35.1"><span class="sec-nr">A.35.1</span> <span class="sec-title">Example
	275	<p><h4 id="sec:tabling-memoize"><a id="sec:A.35.1"><span class="sec-nr">A.35.1</span> <span class="sec-title">Example
234	276	1: using tabling for memoizing</span></a></h4>
235	277
236		<a name="sec:tabling-memoize"></a>
	278	<a id="sec:tabling-memoize"></a>
237	279
238	280	<p>As a first classical example we use tabling for <em>memoizing</em>
239	281	intermediate results. We use Fibonacci numbers to illustrate the

318	360	fib(F1, F2, I2, N, F).
319	361	</pre>
320	362
321		<p><h4 id="sec:tabling-non-termination"><a name="sec:A.35.2"><span class="sec-nr">A.35.2</span> <span class="sec-title">Example
	363	<p><h4 id="sec:tabling-non-termination"><a id="sec:A.35.2"><span class="sec-nr">A.35.2</span> <span class="sec-title">Example
322	364	2: avoiding non-termination</span></a></h4>
323	365
324		<a name="sec:tabling-non-termination"></a>
	366	<a id="sec:tabling-non-termination"></a>
325	367
326	368	<p>SLD resolution easily results in an infinite loop due to <em>left
327	369	recursion</em>, a goal that (indirectly) calls a variant of itself or

370	412	X = 'Leiden'.
371	413	</pre>
372	414
373		<p>Again, the fact that a simple <a name="idx:table1:2173"></a><a class="pred" href="tabling.html#table/1">table/1</a>
	415	<p>Again, the fact that a simple <a id="idx:table1:2177"></a><a class="pred" href="tabling.html#table/1">table/1</a>
374	416	directive turns the pure logical specification into a fairly efficient
375	417	algorithm is a clear advantage. Without tabling the program needs to be <em>stratified</em>,
376	418	introducing a base layer with the raw connections, a second layer that

386	428	and does not need to deal with maintaining consistency between the
387	429	tables and ground facts.
388	430
389		<p><h4 id="sec:tabling-mode-directed"><a name="sec:A.35.3"><span class="sec-nr">A.35.3</span> <span class="sec-title">Mode
	431	<p><h4 id="sec:tabling-mode-directed"><a id="sec:A.35.3"><span class="sec-nr">A.35.3</span> <span class="sec-title">Mode
390	432	directed tabling</span></a></h4>
391	433
392		<a name="sec:tabling-mode-directed"></a>
393
394		<p><a name="idx:answersubsumptiontabling:2174"></a>Tabling as defined
	434	<a id="sec:tabling-mode-directed"></a>
	435
	436	<p><a id="idx:answersubsumptiontabling:2178"></a>Tabling as defined
395	437	above has a serious limitation. Although the definition of connection/2
396	438	from section
397		<a class="sec" href="tabling.html">section A.35.2</a> can compute the
398		transitive closure of connected cities, it cannot provide you with a
399		route to travel. The reason is that there are infinitely many routes if
400		there are cycles in the network and each new route found will be added
401		to the answer table and cause the tabled execution's completion
	439	<a class="sec" href="tabling.html#sec:A.35.2">section A.35.2</a> can
	440	compute the transitive closure of connected cities, it cannot provide
	441	you with a route to travel. The reason is that there are infinitely many
	442	routes if there are cycles in the network and each new route found will
	443	be added to the answer table and cause the tabled execution's completion
402	444	algorithm to search for more routes, eventually running out of memory.
403	445
404	446	<p>The solution to this problem is called <em>mode directed tabling</em>
405	447	or
406		<em>answer subsumption</em>.<sup class="fn">183<span class="fn-text">The
	448	<em>answer subsumption</em>.<sup class="fn">184<span class="fn-text">The
407	449	term <em>answer subsumption</em> is used by XSB and <em>mode directed
408	450	tabling</em> by YAP and B-Prolog. The idea is that some arguments are
409	451	considered `outputs', where multiple values for the same `input' are

411	453	name.</span></sup> In this execution model one or more arguments are <em>not</em>
412	454	added to the table. Instead, we remember a single <em>aggregated</em>
413	455	value for these arguments. The example below is derived from
414		<a class="sec" href="tabling.html">section A.35.2</a> and returns the
415		connection as a list of cities. This argument is defined as a <em>moded</em>
416		argument using the
417		<code>lattice(PI)</code> mode.<sup class="fn">184<span class="fn-text">This
	456	<a class="sec" href="tabling.html#sec:A.35.2">section A.35.2</a> and
	457	returns the connection as a list of cities. This argument is defined as
	458	a <em>moded</em> argument using the
	459	<code>lattice(PI)</code> mode.<sup class="fn">185<span class="fn-text">This
418	460	mode is compatible to XSB Prolog.</span></sup> This causes the tabling
419	461	engine each time that it finds an new path to call shortest/3 and keep
420	462	the shortest route.

493	535	</dd>
494	536	</dl>
495	537
496		<p><h3 id="sec:tabling-memoize"><a name="sec:A.35.1"><span class="sec-nr">A.35.1</span> <span class="sec-title">Tabling
	538	<p><h3 id="sec:tabling-memoize"><a id="sec:A.35.1"><span class="sec-nr">A.35.1</span> <span class="sec-title">Tabling
497	539	predicate reference</span></a></h3>
498	540
499	541	<dl class="latex">
500		<dt class="pubdef"><a name="table/1"><strong>table</strong> <var>+PredicateIndicators</var></a></dt>
	542	<dt class="pubdef"><a id="table/1"><strong>table</strong> <var>+PredicateIndicators</var></a></dt>
501	543	<dd class="defbody">
502	544	Prepare the given <var>PredicateIndicators</var> for tabling. Can only
503	545	be used as a directive. The example below prepares the predicate
504		<span class="pred-ext">edge/2</span> and the non-terminal <span class="pred-ext">statement/3</span>
	546	<span class="pred-ext">edge/2</span> and the non-terminal <span class="pred-ext">statement//1</span>
505	547	for tabled execution.
506	548
507	549	<pre class="code">

518	560
519	561	<p><i>Mode directed tabling</i> is discussed in the general introduction
520	562	section about tabling.</dd>
521		<dt class="pubdef"><a name="abolish_all_tables/0"><strong>abolish_all_tables</strong></a></dt>
	563	<dt class="pubdef"><a id="abolish_all_tables/0"><strong>abolish_all_tables</strong></a></dt>
522	564	<dd class="defbody">
523	565	Remove all tables. This is normally used to free up the space or
524	566	recompute the result after predicates on which the result for some

533	575	</dl>
534	576
535	577	</dd>
536		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="abolish_table_subgoals/1"><strong>abolish_table_subgoals</strong>(<var>:Subgoal</var>)</a></dt>
	578	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="abolish_table_subgoals/1"><strong>abolish_table_subgoals</strong>(<var>:Subgoal</var>)</a></dt>
537	579	<dd class="defbody">
538	580	Abolish all tables that unify with SubGoal.
539	581	</dd>
540	582	</dl>
541	583
542		<p><h4 id="sec:tabling-about"><a name="sec:A.35.1.1"><span class="sec-nr">A.35.1.1</span> <span class="sec-title">About
	584	<p><h4 id="sec:tabling-about"><a id="sec:A.35.1.1"><span class="sec-nr">A.35.1.1</span> <span class="sec-title">About
543	585	the tabling implementation</span></a></h4>
544	586
545		<a name="sec:tabling-about"></a>
	587	<a id="sec:tabling-about"></a>
546	588
547	589	<p>The SWI-Prolog implementation uses <em>Delimited continuations</em>
548	590	(see
549		<a class="sec" href="delcont.html">section 4.10</a> to realise
	591	<a class="sec" href="delcont.html#sec:4.10">section 4.10</a> to realise
550	592	suspension of variant calls. The initial version was written by Benoit
551	593	Desouter and described in
552	594	<cite><a class="cite" href="Bibliography.html#DBLP:journals/tplp/DesouterDS15">Desouter <em>et
553	595	al.</em>, 2015</a></cite>. We moved the main data structures required
554	596	for tabling, the <em>answer tables</em> (see
555		<a class="sec" href="db.html">section 4.14.4</a>) and the <em>worklist</em>
	597	<a class="sec" href="db.html#sec:4.14.4">section 4.14.4</a>) and the <em>worklist</em>
556	598	to SWI-Prolog's C core.
557		<em>Mode directed tabling</em> (<a class="sec" href="tabling.html">section
	599	<em>Mode directed tabling</em> (<a class="sec" href="tabling.html#sec:A.35.3">section
558	600	A.35.3</a>) is based on a prototype implementation by Fabrizio Riguzzi.
559	601
560		<p>The <a name="idx:table1:2175"></a><a class="pred" href="tabling.html#table/1">table/1</a>
	602	<p>The <a id="idx:table1:2179"></a><a class="pred" href="tabling.html#table/1">table/1</a>
561	603	directive causes the creation of a wrapper calling the renamed original
562	604	predicate. For example, the program in
563		<a class="sec" href="tabling.html">section A.35.2</a> is translated into
564		the following program. We give this information to improve your
565		understanding of the current tabling implementation. Future versions are
566		likely to use a more low-level translation that is not based on
567		wrappers.
	605	<a class="sec" href="tabling.html#sec:A.35.2">section A.35.2</a> is
	606	translated into the following program. We give this information to
	607	improve your understanding of the current tabling implementation. Future
	608	versions are likely to use a more low-level translation that is not
	609	based on wrappers.
568	610
569	611	<pre class="code">
570	612	connection(A, B) :-

583	625	'connection tabled'('Haarlem', 'Leiden').
584	626	</pre>
585	627
586		<p><h4 id="sec:tabling-status"><a name="sec:A.35.1.2"><span class="sec-nr">A.35.1.2</span> <span class="sec-title">Status
	628	<p><h4 id="sec:tabling-status"><a id="sec:A.35.1.2"><span class="sec-nr">A.35.1.2</span> <span class="sec-title">Status
587	629	of tabling</span></a></h4>
588	630
589		<a name="sec:tabling-status"></a>
	631	<a id="sec:tabling-status"></a>
590	632
591	633	<p>The current implementation is merely a first prototype. It needs
592	634	several enhancements before we can consider it a serious competitor to

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193	234	</div>
194		<h2 id="sec:termrw"><a name="sec:4.20"><span class="sec-nr">4.20</span> <span class="sec-title">Term
	235	<h2 id="sec:termrw"><a id="sec:4.20"><span class="sec-nr">4.20</span> <span class="sec-title">Term
195	236	reading and writing</span></a></h2>
196	237
197		<a name="sec:termrw"></a>
	238	<a id="sec:termrw"></a>
198	239
199	240	<p>This section describes the basic term reading and writing predicates.
200		The predicates <a name="idx:format12:1114"></a><a class="pred" href="format.html#format/1">format/[1,2]</a>
201		and <a name="idx:writef2:1115"></a><a class="pred" href="format.html#writef/2">writef/2</a>
	241	The predicates <a id="idx:format12:1114"></a><a class="pred" href="format.html#format/1">format/[1,2]</a>
	242	and <a id="idx:writef2:1115"></a><a class="pred" href="format.html#writef/2">writef/2</a>
202	243	provide formatted output. Writing to Prolog data structures such as
203		atoms or code-lists is supported by <a name="idx:withoutputto2:1116"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
204		and <a name="idx:format3:1117"></a><a class="pred" href="format.html#format/3">format/3</a>.
	244	atoms or code-lists is supported by <a id="idx:withoutputto2:1116"></a><a class="pred" href="IO.html#with_output_to/2">with_output_to/2</a>
	245	and <a id="idx:format3:1117"></a><a class="pred" href="format.html#format/3">format/3</a>.
205	246
206	247	<p>Reading is sensitive to the Prolog flag <a class="flag" href="flags.html#flag:character_escapes">character_escapes</a>,
207	248	which controls the interpretation of the <code><code>\</code></code>
208	249	character in quoted atoms and strings.
209	250
210	251	<dl class="latex">
211		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="write_term/2"><strong>write_term</strong>(<var>+Term,
	252	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="write_term/2"><strong>write_term</strong>(<var>+Term,
212	253	+Options</var>)</a></dt>
213	254	<dd class="defbody">
214		The predicate <a name="idx:writeterm2:1118"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	255	The predicate <a id="idx:writeterm2:1118"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
215	256	is the generic form of all Prolog term-write predicates. Valid options
216	257	are:
217	258
218	259	<dl class="latex">
219	260	<dt><strong>attributes</strong>(<var>Atom</var>)</dt>
220	261	<dd class="defbody">
221		Define how attributed variables (see <a class="sec" href="attvar.html">section
	262	Define how attributed variables (see <a class="sec" href="attvar.html#sec:7.1">section
222	263	7.1</a>) are written. The default is determined by the Prolog flag <a class="flag" href="flags.html#flag:write_attributes">write_attributes</a>.
223	264	Defined values are <code>ignore</code> (ignore the attribute), <code>dots</code>
224	265	(write the attributes as <code>{...}</code>), <code>write</code> (simply
225		hand the attributes recursively to <a name="idx:writeterm2:1119"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>)
226		and <code>portray</code> (hand the attributes to <a name="idx:attrportrayhook2:1120"></a><a class="pred" href="attvar.html#attr_portray_hook/2">attr_portray_hook/2</a>).</dd>
	266	hand the attributes recursively to <a id="idx:writeterm2:1119"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>)
	267	and <code>portray</code> (hand the attributes to <a id="idx:attrportrayhook2:1120"></a><a class="pred" href="attvar.html#attr_portray_hook/2">attr_portray_hook/2</a>).</dd>
227	268	<dt><strong>back_quotes</strong>(<var>Atom</var>)</dt>
228	269	<dd class="defbody">
229	270	Fulfills the same role as the <a class="flag" href="flags.html#flag:back_quotes">back_quotes</a>

240	281	<dd class="defbody">
241	282	Define how non-text blobs are handled. By default, this is left to the
242	283	write handler specified with the blob type. Using <code>portray</code>,
243		<a name="idx:portray1:1121"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
244		is called for each blob encountered. See <a class="sec" href="foreigninclude.html">section
	284	<a id="idx:portray1:1121"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	285	is called for each blob encountered. See <a class="sec" href="foreigninclude.html#sec:11.4.7">section
245	286	11.4.7</a>.</dd>
246	287	<dt><strong>character_escapes</strong>(<var>Bool</var>)</dt>
247	288	<dd class="defbody">

254	295	<code>@(Template, Substitutions)</code>, where <var>Substitutions</var>
255	296	is a list
256	297	<var>Var</var> = <var>Value</var>. If <code>cycles</code> is <code>false</code>,
257		<code>max_depth</code> is not given, and <var>Term</var> is cyclic, <a name="idx:writeterm2:1122"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	298	<code>max_depth</code> is not given, and <var>Term</var> is cyclic, <a id="idx:writeterm2:1122"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
258	299	raises a <code>domain_error</code>.<sup class="fn">92<span class="fn-text">The
259	300	cycles option and the cyclic term representation using the @-term are
260	301	copied from SICStus Prolog. However, the default in SICStus is set to <code>false</code>
261	302	and SICStus writes an infinite term if not protected by, e.g., the <code>depth_limit</code>
262	303	option.</span></sup> See also the <code>cycles</code> option in
263		<a name="idx:readterm2:1123"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.</dd>
	304	<a id="idx:readterm2:1123"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.</dd>
264	305	<dt><strong>dotlists</strong>(<var>Bool</var>)</dt>
265	306	<dd class="defbody">
266	307	If <code>true</code> (default <code>false</code>), write lists using the
267	308	dotted term notation rather than the list notation.<sup class="fn">93<span class="fn-text">Copied
268	309	from ECLiPSe.</span></sup> Note that as of version 7, the list
269	310	constructor is
270		<code>'[\|]'</code>. Using <code>dotlists(true)</code>, <a name="idx:writeterm2:1124"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	311	<code>'[\|]'</code>. Using <code>dotlists(true)</code>, <a id="idx:writeterm2:1124"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
271	312	writes a list using `.' as constructor. This is intended for
272	313	communication with programs such as other Prolog systems, that rely on
273	314	this notation.</dd>

276	317	If <code>true</code> (default <code>false</code>), add a fullstop token
277	318	to the output. The dot is preceeded by a space if needed and followed by
278	319	a space (default) or newline if the <code>nl(true)</code> option is also
279		given.<sup class="fn">94<span class="fn-text">Compatible with http://eclipseclp.org/doc/bips/kernel/ioterm/write_term-3.htmlECLiPSe</span></sup></dd>
	320	given.<sup class="fn">94<span class="fn-text">Compatible with <a class="url" href="http://eclipseclp.org/doc/bips/kernel/ioterm/write_term-3.html">ECLiPSe</a></span></sup></dd>
280	321	<dt><strong>ignore_ops</strong>(<var>Bool</var>)</dt>
281	322	<dd class="defbody">
282	323	If <code>true</code>, the generic term representation (<<var>functor</var>>(<<var>args</var>>

307	348	<dd class="defbody">
308	349	Define the reference module (default <code>user</code>). This defines
309	350	the default value for the <a class="flag" href="flags.html#flag:character_escapes">character_escapes</a>
310		option as well as the operator definitions to use. See also <a name="idx:op3:1125"></a><a class="pred" href="operators.html#op/3">op/3</a>.</dd>
	351	option as well as the operator definitions to use. See also <a id="idx:op3:1125"></a><a class="pred" href="operators.html#op/3">op/3</a>.</dd>
311	352	<dt><strong>nl</strong>(<var>Bool</var>)</dt>
312	353	<dd class="defbody">
313	354	Add a newline to the output. See also the <code>fullstop</code> option.</dd>

317	358	is a non-negative integer, will be written as a variable name. If <var>N</var>
318	359	is an atom it is written without quotes. This extension allows for
319	360	writing variables with user-provided names. The default is <code>false</code>.
320		See also <a name="idx:numbervars3:1126"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>
	361	See also <a id="idx:numbervars3:1126"></a><a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>
321	362	and the option <code>variable_names</code>.</dd>
322	363	<dt><strong>partial</strong>(<var>Bool</var>)</dt>
323	364	<dd class="defbody">

326	367	is intended to solve the problems with the code below. Calling <code>write_value(<code>.</code>)</code>
327	368	writes <code>..</code>, which cannot be read. By adding <code>partial(true)</code>
328	369	to the option list, it correctly emits <code>. .</code>. Similar
329		problems appear when emitting operators using multiple calls to <a name="idx:writeterm3:1127"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>.
	370	problems appear when emitting operators using multiple calls to <a id="idx:writeterm3:1127"></a><a class="pred" href="termrw.html#write_term/3">write_term/3</a>.
330	371
331	372	<pre class="code">
332	373	write_value(Value) :-

341	382	<dt><strong>portray_goal</strong>(<var>:Goal</var>)</dt>
342	383	<dd class="defbody">
343	384	Implies <code>portray(true)</code>, but calls <var>Goal</var> rather
344		than the predefined hook <a name="idx:portray1:1128"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>. <var>Goal</var>
345		is called through <a name="idx:call3:1129"></a><span class="pred-ext">call/3</span>,
	385	than the predefined hook <a id="idx:portray1:1128"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>. <var>Goal</var>
	386	is called through <a id="idx:call3:1129"></a><span class="pred-ext">call/3</span>,
346	387	where the first argument is <var>Goal</var>, the second is the term to
347	388	be printed and the 3rd argument is the current write option list. The
348	389	write option list is copied from the write_term call, but the list is

350	391	current priority.</dd>
351	392	<dt><strong>portrayed</strong>(<var>Bool</var>)</dt>
352	393	<dd class="defbody">
353		If <code>true</code>, the hook <a name="idx:portray1:1130"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
354		is called before printing a term that is not a variable. If <a name="idx:portray1:1131"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
355		succeeds, the term is considered printed. See also <a name="idx:print1:1132"></a><a class="pred" href="termrw.html#print/1">print/1</a>.
	394	If <code>true</code>, the hook <a id="idx:portray1:1130"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	395	is called before printing a term that is not a variable. If <a id="idx:portray1:1131"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	396	succeeds, the term is considered printed. See also <a id="idx:print1:1132"></a><a class="pred" href="termrw.html#print/1">print/1</a>.
356	397	The default is <code>false</code>. This option is an extension to the
357	398	ISO write_term options.</dd>
358	399	<dt><strong>priority</strong>(<var>Integer</var>)</dt>

375	416	<dd class="defbody">
376	417	Determines whether and where extra white space is added to enhance
377	418	readability. The default is <code>standard</code>, adding only space
378		where needed for proper tokenization by <a name="idx:readterm3:1133"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.
	419	where needed for proper tokenization by <a id="idx:readterm3:1133"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.
379	420	Currently, the only other value is <code>next_argument</code>, adding a
380	421	space after a comma used to separate arguments in a term or list.</dd>
381	422	<dt><strong>variable_names</strong>(<var>+List</var>)</dt>

391	432	<var>Name</var> does not represent a valid Prolog variable name.
392	433
393	434	<p>The implementation binds the variables from <var>List</var> to a term
394		<code>'$VAR'</code>(<var>Name</var>). Like <a name="idx:writecanonical1:1134"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>,
	435	<code>'$VAR'</code>(<var>Name</var>). Like <a id="idx:writecanonical1:1134"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>,
395	436	terms that where already bound to <code>'$VAR'</code>(<var>X</var>)
396		before <a name="idx:writeterm2:1135"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	437	before <a id="idx:writeterm2:1135"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
397	438	are printed normally, unless the option <code>numbervars(true)</code> is
398	439	also provided. If the option <code>numbervars(true)</code> is used, the
399	440	user is responsible for avoiding collisions between assigned names and
400	441	numbered names. See also the <code>variable_names</code> option of
401		<a name="idx:readterm2:1136"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.
402
403		<p>Possible variable attributes (see <a class="sec" href="attvar.html">section
404		7.1</a>) are ignored. In most cases one should use <a name="idx:copyterm3:1137"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>
	442	<a id="idx:readterm2:1136"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.
	443
	444	<p>Possible variable attributes (see <a class="sec" href="attvar.html#sec:7.1">section
	445	7.1</a>) are ignored. In most cases one should use <a id="idx:copyterm3:1137"></a><a class="pred" href="attvar.html#copy_term/3">copy_term/3</a>
405	446	to obtain a copy that is free of attributed variables and handle the
406	447	associated constraints as appropriate for the use-case.
407	448	</dd>
408	449	</dl>
409	450
410	451	</dd>
411		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="write_term/3"><strong>write_term</strong>(<var>+Stream,
	452	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="write_term/3"><strong>write_term</strong>(<var>+Stream,
412	453	+Term, +Options</var>)</a></dt>
413	454	<dd class="defbody">
414		As <a name="idx:writeterm2:1138"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>,
	455	As <a id="idx:writeterm2:1138"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>,
415	456	but output is sent to <var>Stream</var> rather than the current output.</dd>
416		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="write_length/3"><strong>write_length</strong>(<var>+Term,
	457	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="write_length/3"><strong>write_length</strong>(<var>+Term,
417	458	-Length, +Options</var>)</a></dt>
418	459	<dd class="defbody">
419	460	True when <var>Length</var> is the number of characters emitted for
420	461	<var>write_term</var>Term, Options . In addition to valid options for
421		<a name="idx:writeterm2:1139"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>,
	462	<a id="idx:writeterm2:1139"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>,
422	463	it processes the option:
423	464
424	465	<dl class="latex">

431	472	</dl>
432	473
433	474	</dd>
434		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="write_canonical/1"><strong>write_canonical</strong>(<var>+Term</var>)</a></dt>
	475	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="write_canonical/1"><strong>write_canonical</strong>(<var>+Term</var>)</a></dt>
435	476	<dd class="defbody">
436	477	Write <var>Term</var> on the current output stream using standard
437	478	parenthesised prefix notation (i.e., ignoring operator declarations).
438	479	Atoms that need quotes are quoted. Terms written with this predicate can
439	480	always be read back, regardless of current operator declarations.
440		Equivalent to <a name="idx:writeterm2:1140"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	481	Equivalent to <a id="idx:writeterm2:1140"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
441	482	using the options <code>ignore_ops</code>,
442		<code>quoted</code> and <code>numbervars</code> after <a name="idx:numbervars4:1141"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>
	483	<code>quoted</code> and <code>numbervars</code> after <a id="idx:numbervars4:1141"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>
443	484	using the
444	485	<code>singletons</code> option.
445	486
446		<p>Note that due to the use of <a name="idx:numbervars4:1142"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>,
447		non-ground terms must be written using a <em>single</em> <a name="idx:writecanonical1:1143"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>
	487	<p>Note that due to the use of <a id="idx:numbervars4:1142"></a><a class="pred" href="manipterm.html#numbervars/4">numbervars/4</a>,
	488	non-ground terms must be written using a <em>single</em> <a id="idx:writecanonical1:1143"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>
448	489	call. This used to be the case anyhow, as garbage collection between
449	490	multiple calls to one of the write predicates can change the <code>_G</code><NNN>
450	491	identity of the variables.</dd>
451		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="write_canonical/2"><strong>write_canonical</strong>(<var>+Stream,
	492	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="write_canonical/2"><strong>write_canonical</strong>(<var>+Stream,
452	493	+Term</var>)</a></dt>
453	494	<dd class="defbody">
454	495	Write <var>Term</var> in canonical form on <var>Stream</var>.</dd>
455		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="write/1"><strong>write</strong>(<var>+Term</var>)</a></dt>
	496	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="write/1"><strong>write</strong>(<var>+Term</var>)</a></dt>
456	497	<dd class="defbody">
457	498	Write <var>Term</var> to the current output, using brackets and
458	499	operators where appropriate.</dd>
459		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="write/2"><strong>write</strong>(<var>+Stream,
	500	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="write/2"><strong>write</strong>(<var>+Stream,
460	501	+Term</var>)</a></dt>
461	502	<dd class="defbody">
462	503	Write <var>Term</var> to <var>Stream</var>.</dd>
463		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="writeq/1"><strong>writeq</strong>(<var>+Term</var>)</a></dt>
	504	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="writeq/1"><strong>writeq</strong>(<var>+Term</var>)</a></dt>
464	505	<dd class="defbody">
465	506	Write <var>Term</var> to the current output, using brackets and
466	507	operators where appropriate. Atoms that need quotes are quoted. Terms
467		written with this predicate can be read back with <a name="idx:read1:1144"></a><a class="pred" href="termrw.html#read/1">read/1</a>
	508	written with this predicate can be read back with <a id="idx:read1:1144"></a><a class="pred" href="termrw.html#read/1">read/1</a>
468	509	provided the currently active operator declarations are identical.</dd>
469		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="writeq/2"><strong>writeq</strong>(<var>+Stream,
	510	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="writeq/2"><strong>writeq</strong>(<var>+Stream,
470	511	+Term</var>)</a></dt>
471	512	<dd class="defbody">
472	513	Write <var>Term</var> to <var>Stream</var>, inserting quotes.</dd>
473		<dt class="pubdef"><a name="writeln/1"><strong>writeln</strong>(<var>+Term</var>)</a></dt>
	514	<dt class="pubdef"><a id="writeln/1"><strong>writeln</strong>(<var>+Term</var>)</a></dt>
474	515	<dd class="defbody">
475	516	Equivalent to <code>write(Term), nl.</code>. The output stream is
476	517	locked, which implies no output from other threads can appear between
477	518	the term and newline.</dd>
478		<dt class="pubdef"><a name="writeln/2"><strong>writeln</strong>(<var>+Stream,
	519	<dt class="pubdef"><a id="writeln/2"><strong>writeln</strong>(<var>+Stream,
479	520	+Term</var>)</a></dt>
480	521	<dd class="defbody">
481	522	Equivalent to <code>write(Stream, Term), nl(Stream).</code>. The output
482	523	stream is locked, which implies no output from other threads can appear
483	524	between the term and newline.</dd>
484		<dt class="pubdef"><a name="print/1"><strong>print</strong>(<var>+Term</var>)</a></dt>
485		<dd class="defbody">
486		Print a term for debugging purposes. The predicate <a name="idx:print1:1145"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	525	<dt class="pubdef"><a id="print/1"><strong>print</strong>(<var>+Term</var>)</a></dt>
	526	<dd class="defbody">
	527	Print a term for debugging purposes. The predicate <a id="idx:print1:1145"></a><a class="pred" href="termrw.html#print/1">print/1</a>
487	528	acts as if defined as below.
488	529
489	530	<pre class="code">

497	538	]).
498	539	</pre>
499	540
500		<p>The <a name="idx:print1:1146"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	541	<p>The <a id="idx:print1:1146"></a><a class="pred" href="termrw.html#print/1">print/1</a>
501	542	predicate is used primarily through the <code>~p</code> escape sequence
502		of <a name="idx:format2:1147"></a><a class="pred" href="format.html#format/2">format/2</a>,
	543	of <a id="idx:format2:1147"></a><a class="pred" href="format.html#format/2">format/2</a>,
503	544	which is commonly used in the recipies used by
504		<a name="idx:printmessage2:1148"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	545	<a id="idx:printmessage2:1148"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
505	546	to emit messages.
506	547
507	548	<p>The classical definition of this predicate is equivalent to the ISO
508		predicate <a name="idx:writeterm2:1149"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	549	predicate <a id="idx:writeterm2:1149"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
509	550	using the options <code>portray(true)</code> and
510	551	<code>numbervars(true)</code>. The <code>portray(true)</code> option
511	552	allows the user to implement application-specific printing of terms
512	553	printed during debugging to facilitate easy understanding of the output.
513	554	See also
514		<a name="idx:portray1:1150"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	555	<a id="idx:portray1:1150"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
515	556	and <code>library(portray_text)</code>. SWI-Prolog adds <code>quoted(true)</code>
516	557	to (1) facilitate the copying/pasting of terms that are not affected by
517		<a name="idx:portray1:1151"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	558	<a id="idx:portray1:1151"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
518	559	and to (2) allow numbers, atoms and strings to be more easily
519	560	distinguished, e.g., <code>42</code>, <code>'42'</code> and <code>"42"</code>.</dd>
520		<dt class="pubdef"><a name="print/2"><strong>print</strong>(<var>+Stream,
	561	<dt class="pubdef"><a id="print/2"><strong>print</strong>(<var>+Stream,
521	562	+Term</var>)</a></dt>
522	563	<dd class="defbody">
523	564	Print <var>Term</var> to <var>Stream</var>.</dd>
524		<dt class="pubdef"><a name="portray/1"><strong>portray</strong>(<var>+Term</var>)</a></dt>
	565	<dt class="pubdef"><a id="portray/1"><strong>portray</strong>(<var>+Term</var>)</a></dt>
525	566	<dd class="defbody">
526	567	A dynamic predicate, which can be defined by the user to change the
527		behaviour of <a name="idx:print1:1152"></a><a class="pred" href="termrw.html#print/1">print/1</a>
528		on (sub)terms. For each subterm encountered that is not a variable <a name="idx:print1:1153"></a><a class="pred" href="termrw.html#print/1">print/1</a>
529		first calls <a name="idx:portray1:1154"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	568	behaviour of <a id="idx:print1:1152"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	569	on (sub)terms. For each subterm encountered that is not a variable <a id="idx:print1:1153"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	570	first calls <a id="idx:portray1:1154"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
530	571	using the term as argument. For lists, only the list as a whole is given
531		to <a name="idx:portray1:1155"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>.
	572	to <a id="idx:portray1:1155"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>.
532	573	If
533		<a name="idx:portray1:1156"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
534		succeeds <a name="idx:print1:1157"></a><a class="pred" href="termrw.html#print/1">print/1</a>
	574	<a id="idx:portray1:1156"></a><a class="pred" href="termrw.html#portray/1">portray/1</a>
	575	succeeds <a id="idx:print1:1157"></a><a class="pred" href="termrw.html#print/1">print/1</a>
535	576	assumes the term has been written.</dd>
536		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="read/1"><strong>read</strong>(<var>-Term</var>)</a></dt>
	577	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="read/1"><strong>read</strong>(<var>-Term</var>)</a></dt>
537	578	<dd class="defbody">
538	579	Read the next Prolog term from the current input stream and unify it
539		with <var>Term</var>. On a syntax error <a name="idx:read1:1158"></a><a class="pred" href="termrw.html#read/1">read/1</a>
	580	with <var>Term</var>. On a syntax error <a id="idx:read1:1158"></a><a class="pred" href="termrw.html#read/1">read/1</a>
540	581	displays an error message, attempts to skip the erroneous term and
541	582	fails. On reaching end-of-file
542	583	<var>Term</var> is unified with the atom <code>end_of_file</code>.</dd>
543		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="read/2"><strong>read</strong>(<var>+Stream,
	584	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="read/2"><strong>read</strong>(<var>+Stream,
544	585	-Term</var>)</a></dt>
545	586	<dd class="defbody">
546	587	Read <var>Term</var> from <var>Stream</var>.</dd>
547		<dt class="pubdef"><a name="read_clause/3"><strong>read_clause</strong>(<var>+Stream,
	588	<dt class="pubdef"><a id="read_clause/3"><strong>read_clause</strong>(<var>+Stream,
548	589	-Term, +Options</var>)</a></dt>
549	590	<dd class="defbody">
550		Equivalent to <a name="idx:readterm3:1159"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>,
	591	Equivalent to <a id="idx:readterm3:1159"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>,
551	592	but sets options according to the current compilation context and
552	593	optionally processes comments. Defined options:
553	594
554	595	<dl class="latex">
555	596	<dt><strong>syntax_errors</strong>(<var>+Atom</var>)</dt>
556	597	<dd class="defbody">
557		See <a name="idx:readterm3:1160"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>,
	598	See <a id="idx:readterm3:1160"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>,
558	599	but the default is <code>dec10</code> (report and restart).</dd>
559	600	<dt><strong>term_position</strong>(<var>-TermPos</var>)</dt>
560	601	<dd class="defbody">
561		Same as for <a name="idx:readterm3:1161"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.</dd>
	602	Same as for <a id="idx:readterm3:1161"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.</dd>
562	603	<dt><strong>subterm_positions</strong>(<var>-TermPos</var>)</dt>
563	604	<dd class="defbody">
564		Same as for <a name="idx:readterm3:1162"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.</dd>
	605	Same as for <a id="idx:readterm3:1162"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.</dd>
565	606	<dt><strong>variable_names</strong>(<var>-Bindings</var>)</dt>
566	607	<dd class="defbody">
567		Same as for <a name="idx:readterm3:1163"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.</dd>
	608	Same as for <a id="idx:readterm3:1163"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.</dd>
568	609	<dt><strong>process_comment</strong>(<var>+Boolean</var>)</dt>
569	610	<dd class="defbody">
570	611	If <code>true</code> (default), call

579	620	</dd>
580	621	</dl>
581	622
582		<p>The <code>singletons</code> option of <a name="idx:readterm3:1164"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>
	623	<p>The <code>singletons</code> option of <a id="idx:readterm3:1164"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>
583	624	is initialised from the active style-checking mode. The <code>module</code>
584		option is initialised to the current compilation module (see <a name="idx:prologloadcontext2:1165"></a><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a>).</dd>
585		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="read_term/2"><strong>read_term</strong>(<var>-Term,
	625	option is initialised to the current compilation module (see <a id="idx:prologloadcontext2:1165"></a><a class="pred" href="consulting.html#prolog_load_context/2">prolog_load_context/2</a>).</dd>
	626	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="read_term/2"><strong>read_term</strong>(<var>-Term,
586	627	+Options</var>)</a></dt>
587	628	<dd class="defbody">
588	629	Read a term from the current input stream and unify the term with
589	630	<var>Term</var>. The reading is controlled by options from the list of
590	631	<var>Options</var>. If this list is empty, the behaviour is the same as
591	632	for
592		<a name="idx:read1:1166"></a><a class="pred" href="termrw.html#read/1">read/1</a>.
	633	<a id="idx:read1:1166"></a><a class="pred" href="termrw.html#read/1">read/1</a>.
593	634	The options are upward compatible with Quintus Prolog. The argument
594	635	order is according to the ISO standard. Syntax errors are always
595		reported using exception-handling (see <a name="idx:catch3:1167"></a><a class="pred" href="exception.html#catch/3">catch/3</a>).
	636	reported using exception-handling (see <a id="idx:catch3:1167"></a><a class="pred" href="exception.html#catch/3">catch/3</a>).
596	637	Options:
597	638
598	639	<dl class="latex">

600	641	<dd class="defbody">
601	642	If <code>true</code>, read <code>`</code>...<code>`</code> to a string
602	643	object (see
603		<a class="sec" href="strings.html">section 5.2</a>). The default depends
604		on the Prolog flag
	644	<a class="sec" href="strings.html#sec:5.2">section 5.2</a>). The default
	645	depends on the Prolog flag
605	646	<a class="flag" href="flags.html#flag:back_quotes">back_quotes</a>.</dd>
606	647	<dt><strong>character_escapes</strong>(<var>Bool</var>)</dt>
607	648	<dd class="defbody">
608	649	Defines how to read <code>\</code> escape sequences in quoted atoms. See
609	650	the Prolog flag <a class="flag" href="flags.html#flag:character_escapes">character_escapes</a>
610		in <a name="idx:currentprologflag2:1168"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>.
	651	in <a id="idx:currentprologflag2:1168"></a><a class="pred" href="flags.html#current_prolog_flag/2">current_prolog_flag/2</a>.
611	652	(SWI-Prolog).</dd>
612	653	<dt><strong>comments</strong>(<var>-Comments</var>)</dt>
613	654	<dd class="defbody">
614	655	Unify <var>Comments</var> with a list of <var>Position</var>-<var>Comment</var>,
615	656	where
616		<var>Position</var> is a stream position object (see <a name="idx:streampositiondata3:1169"></a><a class="pred" href="IO.html#stream_position_data/3">stream_position_data/3</a>)
	657	<var>Position</var> is a stream position object (see <a id="idx:streampositiondata3:1169"></a><a class="pred" href="IO.html#stream_position_data/3">stream_position_data/3</a>)
617	658	indicating the start of a comment and <var>Comment</var> is a string
618	659	object containing the text including delimiters of a comment. It returns
619		all comments from where the <a name="idx:readterm2:1170"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	660	all comments from where the <a id="idx:readterm2:1170"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
620	661	call started up to the end of the term read.</dd>
621	662	<dt><strong>cycles</strong>(<var>Bool</var>)</dt>
622	663	<dd class="defbody">
623	664	If <code>true</code> (default <code>false</code>), re-instantiate
624		templates as produced by the corresponding <a name="idx:writeterm2:1171"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	665	templates as produced by the corresponding <a id="idx:writeterm2:1171"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
625	666	option. Note that the default is <code>false</code> to avoid
626	667	misinterpretation of <code>@(Template, Substutions)</code>, while the
627		default of <a name="idx:writeterm2:1172"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
	668	default of <a id="idx:writeterm2:1172"></a><a class="pred" href="termrw.html#write_term/2">write_term/2</a>
628	669	is <code>true</code> because emitting cyclic terms without using the
629	670	template construct produces an infinitely large term (read: it will
630	671	generate an error after producing a huge amount of output).</dd>

632	673	<dd class="defbody">
633	674	If <code>true</code> (default <code>false</code>), read <code>.(a,[])</code>
634	675	as a list, even if lists are internally nor constructed using the dot as
635		functor. This is primarily intended to read the output from <a name="idx:writecanonical1:1173"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>
636		from other Prolog systems. See <a class="sec" href="ext-lists.html">section
	676	functor. This is primarily intended to read the output from <a id="idx:writecanonical1:1173"></a><a class="pred" href="termrw.html#write_canonical/1">write_canonical/1</a>
	677	from other Prolog systems. See <a class="sec" href="ext-lists.html#sec:5.1">section
637	678	5.1</a>.</dd>
638	679	<dt><strong>double_quotes</strong>(<var>Atom</var>)</dt>
639	680	<dd class="defbody">

644	685	<dd class="defbody">
645	686	Specify <var>Module</var> for operators, <a class="flag" href="flags.html#flag:character_escapes">character_escapes</a>
646	687	flag and <a class="flag" href="flags.html#flag:double_quotes">double_quotes</a>
647		flag. The value of the latter two is overruled if the corresponding <a name="idx:readterm3:1174"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>
	688	flag. The value of the latter two is overruled if the corresponding <a id="idx:readterm3:1174"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>
648	689	option is provided. If no module is specified, the current `source
649	690	module' is used. (SWI-Prolog).</dd>
650	691	<dt><strong>quasi_quotations</strong>(<var>-List</var>)</dt>
651	692	<dd class="defbody">
652	693	If present, unify <var>List</var> with the quasi quotations (see
653		<a class="sec" href="quasiquotations.html">section A.28</a>) instead of
654		evaluating quasi quotations. Each quasi quotation is a term <code>quasi_quotation(+Syntax,
	694	<a class="sec" href="quasiquotations.html#sec:A.28">section A.28</a>)
	695	instead of evaluating quasi quotations. Each quasi quotation is a term <code>quasi_quotation(+Syntax,
655	696	+Quotation, +VarDict, -Result)</code>, where <var>Syntax</var> is the
656	697	term in
657	698	<code>{\|Syntax\|\|..\|}</code>, <var>Quotation</var> is a list of character

666	707	underscore (`<code>_</code>') are not included in this list. (ISO). If <var>Vars</var>
667	708	is the constant <code>warning</code>, singleton variables are reported
668	709	using
669		<a name="idx:printmessage2:1175"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
	710	<a id="idx:printmessage2:1175"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
670	711	The variables appear in the order they have been read.</dd>
671	712	<dt><strong>syntax_errors</strong>(<var>Atom</var>)</dt>
672	713	<dd class="defbody">
673	714	If <code>error</code> (default), throw an exception on a syntax error.
674	715	Other values are <code>fail</code>, which causes a message to be printed
675	716	using
676		<a name="idx:printmessage2:1176"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>,
	717	<a id="idx:printmessage2:1176"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>,
677	718	after which the predicate fails, <code>quiet</code> which causes the
678	719	predicate to fail silently, and <code>dec10</code> which causes syntax
679		errors to be printed, after which <a name="idx:readterm23:1177"></a><a class="pred" href="termrw.html#read_term/2">read_term/[2,3]</a>
680		continues reading the next term. Using <code>dec10</code>, <a name="idx:readterm23:1178"></a><a class="pred" href="termrw.html#read_term/2">read_term/[2,3]</a>
	720	errors to be printed, after which <a id="idx:readterm23:1177"></a><a class="pred" href="termrw.html#read_term/2">read_term/[2,3]</a>
	721	continues reading the next term. Using <code>dec10</code>, <a id="idx:readterm23:1178"></a><a class="pred" href="termrw.html#read_term/2">read_term/[2,3]</a>
681	722	never fails. (Quintus, SICStus).</dd>
682	723	<dt><strong>subterm_positions</strong>(<var>TermPos</var>)</dt>
683	724	<dd class="defbody">

711	752	corresponding subterm.</dd>
712	753	<dt><strong>dict_position</strong>(<var><var>From</var>, <var>To</var>, <var>TagFrom</var>, <var>TagTo</var>, <var>KeyValuePosList</var></var>)</dt>
713	754	<dd class="defbody">
714		Used for a dict (see <a class="sec" href="dicts.html">section 5.4</a>).
715		The position of the key-value pairs is described by <var>KeyValuePosList</var>,
	755	Used for a dict (see <a class="sec" href="dicts.html#sec:5.4">section
	756	5.4</a>). The position of the key-value pairs is described by <var>KeyValuePosList</var>,
716	757	which is a list of
717	758	<code>key_value_position/7</code> terms. The <code>key_value_position/7</code>
718	759	terms appear in the order of the input. Because maps to not preserve
719	760	ordering, the key is provided in the position description.</dd>
720	761	<dt><strong>key_value_position</strong>(<var><var>From</var>, <var>To</var>, <var>SepFrom</var>, <var>SepTo</var>, <var>Key</var>, <var>KeyPos</var>, <var>ValuePos</var></var>)</dt>
721	762	<dd class="defbody">
722		Used for key-value pairs in a map (see <a class="sec" href="dicts.html">section
	763	Used for key-value pairs in a map (see <a class="sec" href="dicts.html#sec:5.4">section
723	764	5.4</a>). It is similar to the <code>term_position/5</code> that would
724	765	be created, except that the key and value positions do not need an
725	766	intermediate list and the key is provided in <var>Key</var> to enable

739	780	<dt><strong>term_position</strong>(<var>Pos</var>)</dt>
740	781	<dd class="defbody">
741	782	Unifies <var>Pos</var> with the starting position of the term read. <var>Pos</var>
742		is of the same format as used by <a name="idx:streamproperty2:1179"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>.</dd>
	783	is of the same format as used by <a id="idx:streamproperty2:1179"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>.</dd>
743	784	<dt><strong>var_prefix</strong>(<var>Bool</var>)</dt>
744	785	<dd class="defbody">
745	786	If <code>true</code>, demand variables to start with an underscore. See
746		<a class="sec" href="syntax.html">section 2.16.1.7</a>.</dd>
	787	<a class="sec" href="syntax.html#sec:2.16.1.7">section 2.16.1.7</a>.</dd>
747	788	<dt><strong>variables</strong>(<var>Vars</var>)</dt>
748	789	<dd class="defbody">
749	790	Unify <var>Vars</var> with a list of variables in the term. The
750		variables appear in the order they have been read. See also <a name="idx:termvariables2:1180"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>.
	791	variables appear in the order they have been read. See also <a id="idx:termvariables2:1180"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>.
751	792	(ISO).</dd>
752	793	<dt><strong>variable_names</strong>(<var>Vars</var>)</dt>
753	794	<dd class="defbody">

760	801	</dl>
761	802
762	803	</dd>
763		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="read_term/3"><strong>read_term</strong>(<var>+Stream,
	804	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="read_term/3"><strong>read_term</strong>(<var>+Stream,
764	805	-Term, +Options</var>)</a></dt>
765	806	<dd class="defbody">
766		Read term with options from <var>Stream</var>. See <a name="idx:readterm2:1181"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.</dd>
767		<dt class="pubdef"><a name="read_term_from_atom/3"><strong>read_term_from_atom</strong>(<var>+Atom,
	807	Read term with options from <var>Stream</var>. See <a id="idx:readterm2:1181"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>.</dd>
	808	<dt class="pubdef"><a id="read_term_from_atom/3"><strong>read_term_from_atom</strong>(<var>+Atom,
768	809	-Term, +Options</var>)</a></dt>
769	810	<dd class="defbody">
770		Use <a name="idx:readterm3:1182"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>
	811	Use <a id="idx:readterm3:1182"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>
771	812	to read the next term from <var>Atom</var>. <var>Atom</var> is either an
772		atom or a string object (see <a class="sec" href="strings.html">section
	813	atom or a string object (see <a class="sec" href="strings.html#sec:5.2">section
773	814	5.2</a>). It is not required for <var>Atom</var> to end with a
774		full-stop. This predicate supersedes <a name="idx:atomtoterm3:1183"></a><a class="pred" href="manipatom.html#atom_to_term/3">atom_to_term/3</a>.</dd>
775		<dt class="pubdef"><a name="read_history/6"><strong>read_history</strong>(<var>+Show,
	815	full-stop. This predicate supersedes <a id="idx:atomtoterm3:1183"></a><a class="pred" href="manipatom.html#atom_to_term/3">atom_to_term/3</a>.</dd>
	816	<dt class="pubdef"><a id="read_history/6"><strong>read_history</strong>(<var>+Show,
776	817	+Help, +Special, +Prompt, -Term, -Bindings</var>)</a></dt>
777	818	<dd class="defbody">
778		Similar to <a name="idx:readterm2:1184"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
	819	Similar to <a id="idx:readterm2:1184"></a><a class="pred" href="termrw.html#read_term/2">read_term/2</a>
779	820	using the option <code>variable_names</code>, but allows for history
780		substitutions. <a name="idx:readhistory6:1185"></a><a class="pred" href="termrw.html#read_history/6">read_history/6</a>
	821	substitutions. <a id="idx:readhistory6:1185"></a><a class="pred" href="termrw.html#read_history/6">read_history/6</a>
781	822	is used by the top level to read the user's actions. <var>Show</var> is
782	823	the command the user should type to show the saved events. <var>Help</var>
783	824	is the command to get an overview of the capabilities. <var>Special</var>
784	825	is a list of commands that are not saved in the history. <var>Prompt</var>
785	826	is the first prompt given. Continuation prompts for more lines are
786		determined by <a name="idx:prompt2:1186"></a><a class="pred" href="termrw.html#prompt/2">prompt/2</a>.
	827	determined by <a id="idx:prompt2:1186"></a><a class="pred" href="termrw.html#prompt/2">prompt/2</a>.
787	828	A
788	829	<code>%w</code> in the prompt is substituted by the event number. See
789		<a class="sec" href="history.html">section 2.7</a> for available
	830	<a class="sec" href="history.html#sec:2.7">section 2.7</a> for available
790	831	substitutions.
791	832
792		<p>SWI-Prolog calls <a name="idx:readhistory6:1187"></a><a class="pred" href="termrw.html#read_history/6">read_history/6</a>
	833	<p>SWI-Prolog calls <a id="idx:readhistory6:1187"></a><a class="pred" href="termrw.html#read_history/6">read_history/6</a>
793	834	as follows:
794	835
795	836	<pre class="code">

797	838	</pre>
798	839
799	840	</dd>
800		<dt class="pubdef"><a name="prompt/2"><strong>prompt</strong>(<var>-Old,
	841	<dt class="pubdef"><a id="prompt/2"><strong>prompt</strong>(<var>-Old,
801	842	+New</var>)</a></dt>
802	843	<dd class="defbody">
803		Set prompt associated with <a name="idx:read1:1188"></a><a class="pred" href="termrw.html#read/1">read/1</a>
	844	Set prompt associated with <a id="idx:read1:1188"></a><a class="pred" href="termrw.html#read/1">read/1</a>
804	845	and its derivatives. <var>Old</var> is first unified with the current
805	846	prompt. On success the prompt will be set to <var>New</var> if this is
806	847	an atom. Otherwise an error message is displayed. A prompt is printed if

808	849	margin. It is also printed whenever a newline is given and the term has
809	850	not been terminated. Prompts are only printed when the current input
810	851	stream is <var>user</var>.</dd>
811		<dt class="pubdef"><a name="prompt1/1"><strong>prompt1</strong>(<var>+Prompt</var>)</a></dt>
	852	<dt class="pubdef"><a id="prompt1/1"><strong>prompt1</strong>(<var>+Prompt</var>)</a></dt>
812	853	<dd class="defbody">
813	854	Sets the prompt for the next line to be read. Continuation lines will be
814		read using the prompt defined by <a name="idx:prompt2:1189"></a><a class="pred" href="termrw.html#prompt/2">prompt/2</a>.
	855	read using the prompt defined by <a id="idx:prompt2:1189"></a><a class="pred" href="termrw.html#prompt/2">prompt/2</a>.
815	856	</dd>
816	857	</dl>
817	858

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 9.2</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 9.2</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="threadcreate.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="threadcom.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:thmonitor"><a name="sec:9.2"><span class="sec-nr">9.2</span> <span class="sec-title">Monitoring
	235	<h2 id="sec:thmonitor"><a id="sec:9.2"><span class="sec-nr">9.2</span> <span class="sec-title">Monitoring
195	236	threads</span></a></h2>
196	237
197		<a name="sec:thmonitor"></a>
	238	<a id="sec:thmonitor"></a>
198	239
199	240	<p>Normal multithreaded applications should not need the predicates from
200	241	this section because almost any usage of these predicates is unsafe. For
201	242	example checking the existence of a thread before signalling it is of no
202		use as it may vanish between the two calls. Catching exceptions using <a name="idx:catch3:1872"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	243	use as it may vanish between the two calls. Catching exceptions using <a id="idx:catch3:1876"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
203	244	is the only safe way to deal with thread-existence errors.
204	245
205	246	<p>These predicates are provided for diagnosis and monitoring tasks. See
206		also <a class="sec" href="thutil.html">section 9.5</a>, describing more
207		high-level primitives.
	247	also <a class="sec" href="thutil.html#sec:9.5">section 9.5</a>,
	248	describing more high-level primitives.
208	249
209	250	<dl class="latex">
210		<dt class="pubdef"><a name="is_thread/1"><strong>is_thread</strong>(<var>@Term</var>)</a></dt>
	251	<dt class="pubdef"><a id="is_thread/1"><strong>is_thread</strong>(<var>@Term</var>)</a></dt>
211	252	<dd class="defbody">
212	253	True if <var>Term</var> is a handle to an existing thread.</dd>
213		<dt class="pubdef"><a name="thread_property/2"><strong>thread_property</strong>(<var>?Id,
	254	<dt class="pubdef"><a id="thread_property/2"><strong>thread_property</strong>(<var>?Id,
214	255	?Property</var>)</a></dt>
215	256	<dd class="defbody">
216	257	True if thread <var>Id</var> has <var>Property</var>. Either or both
217	258	arguments may be unbound, enumerating all relations on backtracking.
218		Calling <a name="idx:threadproperty2:1873"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>
	259	Calling <a id="idx:threadproperty2:1877"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>
219	260	does not influence any thread. See also
220		<a name="idx:threadjoin2:1874"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>.
	261	<a id="idx:threadjoin2:1878"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>.
221	262	For threads that have an alias name, this name is returned in <var>Id</var>
222	263	instead of the opaque thread identifier. Defined properties are:
223	264

244	285	note that threads waiting for something are considered running too.</dd>
245	286	<dt><strong>suspended</strong></dt>
246	287	<dd class="defbody">
247		Only if the thread is an engine (see <a class="sec" href="engines.html">section
	288	Only if the thread is an engine (see <a class="sec" href="engines.html#sec:10">section
248	289	10</a>). Indicates that the engine is currently not associated with an
249	290	OS thread.</dd>
250	291	<dt><strong>false</strong></dt>

255	296	The <var>Goal</var> of the thread has been completed and succeeded.</dd>
256	297	<dt><strong>exited</strong>(<var>Term</var>)</dt>
257	298	<dd class="defbody">
258		The <var>Goal</var> of the thread has been terminated using <a name="idx:threadexit1:1875"></a><a class="pred" href="threadcreate.html#thread_exit/1">thread_exit/1</a>
	299	The <var>Goal</var> of the thread has been terminated using <a id="idx:threadexit1:1879"></a><a class="pred" href="threadcreate.html#thread_exit/1">thread_exit/1</a>
259	300	with <var>Term</var> as argument. If the underlying native thread has
260	301	exited (using pthread_exit()) <var>Term</var> is unbound.</dd>
261	302	<dt><strong>exception</strong>(<var>Term</var>)</dt>
262	303	<dd class="defbody">
263	304	The <var>Goal</var> of the thread has been terminated due to an uncaught
264		exception (see <a name="idx:throw1:1876"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
265		and <a name="idx:catch3:1877"></a><a class="pred" href="exception.html#catch/3">catch/3</a>).
	305	exception (see <a id="idx:throw1:1880"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
	306	and <a id="idx:catch3:1881"></a><a class="pred" href="exception.html#catch/3">catch/3</a>).
266	307	</dd>
267	308	</dl>
268	309
269	310	</dd>
270	311	<dt><strong>engine</strong>(<var>Boolean</var>)</dt>
271	312	<dd class="defbody">
272		If the thread is an engine (see <a class="sec" href="engines.html">chapter
	313	If the thread is an engine (see <a class="sec" href="engines.html#sec:10">chapter
273	314	10</a>), <var>Boolean</var> is
274	315	<code>true</code>. Othwerwise the property is not present.</dd>
275	316	<dt><strong>thread</strong>(<var>ThreadId</var>)</dt>

287	328	</dd>
288	329	</dl>
289	330
290		<p>See also <a name="idx:threadstatistics3:1878"></a><a class="pred" href="thmonitor.html#thread_statistics/3">thread_statistics/3</a>
	331	<p>See also <a id="idx:threadstatistics3:1882"></a><a class="pred" href="thmonitor.html#thread_statistics/3">thread_statistics/3</a>
291	332	to obtain resource usage information and
292		<a name="idx:messagequeueproperty2:1879"></a><a class="pred" href="threadcom.html#message_queue_property/2">message_queue_property/2</a>
	333	<a id="idx:messagequeueproperty2:1883"></a><a class="pred" href="threadcom.html#message_queue_property/2">message_queue_property/2</a>
293	334	to get the number of queued messages for a thread.</dd>
294		<dt class="pubdef"><a name="thread_statistics/3"><strong>thread_statistics</strong>(<var>+Id,
	335	<dt class="pubdef"><a id="thread_statistics/3"><strong>thread_statistics</strong>(<var>+Id,
295	336	+Key, -Value</var>)</a></dt>
296	337	<dd class="defbody">
297		Obtains statistical information on thread <var>Id</var> as <a name="idx:statistics2:1880"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>
298		does in single-threaded applications. This call supports all keys of <a name="idx:statistics2:1881"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>,
	338	Obtains statistical information on thread <var>Id</var> as <a id="idx:statistics2:1884"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>
	339	does in single-threaded applications. This call supports all keys of <a id="idx:statistics2:1885"></a><a class="pred" href="statistics.html#statistics/2">statistics/2</a>,
299	340	although only stack sizes, <code>cputime</code>,
300	341	<code>inferences</code> and <code>epoch</code> yield different values
301		for each thread.<sup class="fn">159<span class="fn-text">There is no
	342	for each thread.<sup class="fn">160<span class="fn-text">There is no
302	343	portable interface to obtain thread-specific CPU time and some operating
303	344	systems provide no access to this information at all. On such systems
304	345	the total process CPU is returned. Thread CPU time is supported on
305	346	MS-Windows, Linux and MacOSX.</span></sup></dd>
306		<dt class="pubdef"><a name="mutex_statistics/0"><strong>mutex_statistics</strong></a></dt>
	347	<dt class="pubdef"><a id="mutex_statistics/0"><strong>mutex_statistics</strong></a></dt>
307	348	<dd class="defbody">
308	349	Print usage statistics on internal mutexes and mutexes associated with
309	350	dynamic predicates. For each mutex two numbers are printed: the number

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 9.3</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 9.3</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
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27	31
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191	232	<a class="nav" href="thmonitor.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:threadcom"><a name="sec:9.3"><span class="sec-nr">9.3</span> <span class="sec-title">Thread
	235	<h2 id="sec:threadcom"><a id="sec:9.3"><span class="sec-nr">9.3</span> <span class="sec-title">Thread
195	236	communication</span></a></h2>
196	237
197		<a name="sec:threadcom"></a>
198
199		<p><h3 id="sec:msgqueue"><a name="sec:9.3.1"><span class="sec-nr">9.3.1</span> <span class="sec-title">Message
	238	<a id="sec:threadcom"></a>
	239
	240	<p><h3 id="sec:msgqueue"><a id="sec:9.3.1"><span class="sec-nr">9.3.1</span> <span class="sec-title">Message
200	241	queues</span></a></h3>
201	242
202		<a name="sec:msgqueue"></a>
	243	<a id="sec:msgqueue"></a>
203	244
204	245	<p>Prolog threads can exchange data using dynamic predicates, database
205	246	records, and other globally shared data. These provide no suitable means

208	249	threads to wait for data or conditions without using the CPU.
209	250
210	251	<p>Each thread has a message queue attached to it that is identified by
211		the thread. Additional queues are created using <a name="idx:messagequeuecreate1:1882"></a><a class="pred" href="threadcom.html#message_queue_create/1">message_queue_create/1</a>.
	252	the thread. Additional queues are created using <a id="idx:messagequeuecreate1:1886"></a><a class="pred" href="threadcom.html#message_queue_create/1">message_queue_create/1</a>.
212	253	Explicitly created queues come in two flavours. When given an
213	254	<em>alias</em>, they must be destroyed by the user. <em>Anonymous</em>
214		message queues are identified by a <em>blob</em> (see <a class="sec" href="foreigninclude.html">section
	255	message queues are identified by a <em>blob</em> (see <a class="sec" href="foreigninclude.html#sec:11.4.7">section
215	256	11.4.7</a>) and subject to garbage collection.
216	257
217	258	<dl class="latex">
218		<dt class="pubdef"><a name="thread_send_message/2"><strong>thread_send_message</strong>(<var>+QueueOrThreadId,
	259	<dt class="pubdef"><a id="thread_send_message/2"><strong>thread_send_message</strong>(<var>+QueueOrThreadId,
219	260	+Term</var>)</a></dt>
220	261	<dd class="defbody">
221	262	Place <var>Term</var> in the given queue or default queue of the
222	263	indicated thread (which can even be the message queue of itself, see
223		<a name="idx:threadself1:1883"></a><a class="pred" href="threadcreate.html#thread_self/1">thread_self/1</a>).
	264	<a id="idx:threadself1:1887"></a><a class="pred" href="threadcreate.html#thread_self/1">thread_self/1</a>).
224	265	Any term can be placed in a message queue, but note that the term is
225	266	copied to the receiving thread and variable bindings are thus lost. This
226	267	call returns immediately.

233	274	the same queue as all-but-the-winner perform a useless scan of the
234	275	queue. If there is only one waiting thread or all waiting threads wait
235	276	with an unbound variable, an arbitrary thread is restarted to scan the
236		queue.<sup class="fn">160<span class="fn-text">See the documentation for
	277	queue.<sup class="fn">161<span class="fn-text">See the documentation for
237	278	the POSIX thread functions pthread_cond_signal() v.s. pthread_cond_broadcast()
238	279	for background information.</span></sup></dd>
239		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="thread_send_message/3"><strong>thread_send_message</strong>(<var>+Queue,
	280	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="thread_send_message/3"><strong>thread_send_message</strong>(<var>+Queue,
240	281	+Term, +Options</var>)</a></dt>
241	282	<dd class="defbody">
242		As <a name="idx:threadsendmessage2:1884"></a><a class="pred" href="threadcom.html#thread_send_message/2">thread_send_message/2</a>,
	283	As <a id="idx:threadsendmessage2:1888"></a><a class="pred" href="threadcom.html#thread_send_message/2">thread_send_message/2</a>,
243	284	but providing additional <var>Options</var>. These are to deal with the
244		case that the queue has a finite maximum size and is full: whereas <a name="idx:threadsendmessage2:1885"></a><a class="pred" href="threadcom.html#thread_send_message/2">thread_send_message/2</a>
	285	case that the queue has a finite maximum size and is full: whereas <a id="idx:threadsendmessage2:1889"></a><a class="pred" href="threadcom.html#thread_send_message/2">thread_send_message/2</a>
245	286	will block until the queue has drained sufficiently to accept a new
246		message, <a name="idx:threadsendmessage3:1886"></a><a class="pred" href="threadcom.html#thread_send_message/3">thread_send_message/3</a>
247		can accept a time-out or deadline analogously to <a name="idx:threadgetmessage3:1887"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>.
	287	message, <a id="idx:threadsendmessage3:1890"></a><a class="pred" href="threadcom.html#thread_send_message/3">thread_send_message/3</a>
	288	can accept a time-out or deadline analogously to <a id="idx:threadgetmessage3:1891"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>.
248	289	The options are:
249	290
250	291	<dl class="latex">
251	292	<dt><strong>deadline</strong>(<var>+AbsTime</var>)</dt>
252	293	<dd class="defbody">
253	294	The call fails (silently) if no space has become available before
254		<var>AbsTime</var>. See <a name="idx:gettime1:1888"></a><a class="pred" href="system.html#get_time/1">get_time/1</a>
	295	<var>AbsTime</var>. See <a id="idx:gettime1:1892"></a><a class="pred" href="system.html#get_time/1">get_time/1</a>
255	296	for the representation of absolute time. If <var>AbsTime</var> is
256		earlier then the current time, <a name="idx:threadsendmessage3:1889"></a><a class="pred" href="threadcom.html#thread_send_message/3">thread_send_message/3</a>
	297	earlier then the current time, <a id="idx:threadsendmessage3:1893"></a><a class="pred" href="threadcom.html#thread_send_message/3">thread_send_message/3</a>
257	298	fails immediately. Both resolution and maximum wait time is
258		platform-dependent.<sup class="fn">161<span class="fn-text">The
	299	platform-dependent.<sup class="fn">162<span class="fn-text">The
259	300	implementation uses MsgWaitForMultipleObjects() on MS-Windows and
260	301	pthread_cond_timedwait() on other systems.</span></sup></dd>
261	302	<dt><strong>timeout</strong>(<var>+Time</var>)</dt>

264	305	wait in seconds. This is a relative-time version of the <code>deadline</code>
265	306	option. If both options are provided, the earlier time is effective.
266	307
267		<p>If <var>Time</var> is 0 or 0.0, <a name="idx:threadsendmessage3:1890"></a><a class="pred" href="threadcom.html#thread_send_message/3">thread_send_message/3</a>
	308	<p>If <var>Time</var> is 0 or 0.0, <a id="idx:threadsendmessage3:1894"></a><a class="pred" href="threadcom.html#thread_send_message/3">thread_send_message/3</a>
268	309	examines the queue and sends the message if space is availabel, but does
269	310	not suspend if no space is available, failing immediately instead.
270	311
271		<p>If <var>Time</var> <var>< 0</var>, <a name="idx:threadsendmessage3:1891"></a><a class="pred" href="threadcom.html#thread_send_message/3">thread_send_message/3</a>
	312	<p>If <var>Time</var> <var>< 0</var>, <a id="idx:threadsendmessage3:1895"></a><a class="pred" href="threadcom.html#thread_send_message/3">thread_send_message/3</a>
272	313	fails immediately without sending the message.
273	314	</dd>
274	315	</dl>
275	316
276	317	</dd>
277		<dt class="pubdef"><a name="thread_get_message/1"><strong>thread_get_message</strong>(<var>?Term</var>)</a></dt>
	318	<dt class="pubdef"><a id="thread_get_message/1"><strong>thread_get_message</strong>(<var>?Term</var>)</a></dt>
278	319	<dd class="defbody">
279	320	Examines the thread message queue and if necessary blocks execution
280	321	until a term that unifies to <var>Term</var> arrives in the queue. After

294	335	thread_send_message(Thread_1, a(gnat)),
295	336	</pre>
296	337
297		<p>See also <a name="idx:threadpeekmessage1:1892"></a><a class="pred" href="threadcom.html#thread_peek_message/1">thread_peek_message/1</a>.</dd>
298		<dt class="pubdef"><a name="thread_peek_message/1"><strong>thread_peek_message</strong>(<var>?Term</var>)</a></dt>
	338	<p>See also <a id="idx:threadpeekmessage1:1896"></a><a class="pred" href="threadcom.html#thread_peek_message/1">thread_peek_message/1</a>.</dd>
	339	<dt class="pubdef"><a id="thread_peek_message/1"><strong>thread_peek_message</strong>(<var>?Term</var>)</a></dt>
299	340	<dd class="defbody">
300	341	Examines the thread message queue and compares the queued terms with <var>Term</var>
301	342	until one unifies or the end of the queue has been reached. In the first
302	343	case the call succeeds, possibly instantiating
303	344	<var>Term</var>. If no term from the queue unifies, this call fails.
304	345	I.e.,
305		<a name="idx:threadpeekmessage1:1893"></a><a class="pred" href="threadcom.html#thread_peek_message/1">thread_peek_message/1</a>
306		never waits and does not remove any term from the queue. See also <a name="idx:threadgetmessage3:1894"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>.</dd>
307		<dt class="pubdef"><a name="message_queue_create/1"><strong>message_queue_create</strong>(<var>?Queue</var>)</a></dt>
	346	<a id="idx:threadpeekmessage1:1897"></a><a class="pred" href="threadcom.html#thread_peek_message/1">thread_peek_message/1</a>
	347	never waits and does not remove any term from the queue. See also <a id="idx:threadgetmessage3:1898"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>.</dd>
	348	<dt class="pubdef"><a id="message_queue_create/1"><strong>message_queue_create</strong>(<var>?Queue</var>)</a></dt>
308	349	<dd class="defbody">
309	350	Equivalent to <code>message_queue_create(Queue,[])</code>. For
310	351	compatibility, calling <code>message_queue_create(+Atom)</code> is
311	352	equivalent to
312	353	<code>message_queue_create(Queue, [alias(Atom)])</code>. New code should
313	354	use
314		<a name="idx:messagequeuecreate2:1895"></a><a class="pred" href="threadcom.html#message_queue_create/2">message_queue_create/2</a>
	355	<a id="idx:messagequeuecreate2:1899"></a><a class="pred" href="threadcom.html#message_queue_create/2">message_queue_create/2</a>
315	356	to create a named queue.</dd>
316		<dt class="pubdef"><a name="message_queue_create/2"><strong>message_queue_create</strong>(<var>-Queue,
	357	<dt class="pubdef"><a id="message_queue_create/2"><strong>message_queue_create</strong>(<var>-Queue,
317	358	+Options</var>)</a></dt>
318	359	<dd class="defbody">
319	360	Create a message queue from <var>Options</var>. Defined options are:

324	365	Create a message queue that is identified by the atom <var>Alias</var>.
325	366	Message queues created this way must be explicitly destroyed by the
326	367	user. If the alias option is omitted, an <em>Anonymous</em> queue is
327		created that is indentified by a <em>blob</em> (see <a class="sec" href="foreigninclude.html">section
328		11.4.7</a>) and subject to garbage collection.<sup class="fn">162<span class="fn-text">Garbage
	368	created that is indentified by a <em>blob</em> (see <a class="sec" href="foreigninclude.html#sec:11.4.7">section
	369	11.4.7</a>) and subject to garbage collection.<sup class="fn">163<span class="fn-text">Garbage
329	370	collecting anonymous message queues is not part of the ISO proposal and
330	371	most likely not a widely implemented feature.</span></sup></dd>
331	372	<dt><strong>max_size</strong>(<var>+Size</var>)</dt>
332	373	<dd class="defbody">
333	374	Maximum number of terms in the queue. If this number is reached,
334		<a name="idx:threadsendmessage2:1896"></a><a class="pred" href="threadcom.html#thread_send_message/2">thread_send_message/2</a>
	375	<a id="idx:threadsendmessage2:1900"></a><a class="pred" href="threadcom.html#thread_send_message/2">thread_send_message/2</a>
335	376	will suspend until the queue is drained. The option can be used if the
336	377	source, sending messages to the queue, is faster than the drain,
337	378	consuming the messages.

339	380	</dl>
340	381
341	382	</dd>
342		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="message_queue_destroy/1"><strong>message_queue_destroy</strong>(<var>+Queue</var>)</a></dt>
343		<dd class="defbody">
344		Destroy a message queue created with <a name="idx:messagequeuecreate1:1897"></a><a class="pred" href="threadcom.html#message_queue_create/1">message_queue_create/1</a>.
	383	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="message_queue_destroy/1"><strong>message_queue_destroy</strong>(<var>+Queue</var>)</a></dt>
	384	<dd class="defbody">
	385	Destroy a message queue created with <a id="idx:messagequeuecreate1:1901"></a><a class="pred" href="threadcom.html#message_queue_create/1">message_queue_create/1</a>.
345	386	A permission error is raised if <var>Queue</var> refers to (the default
346	387	queue of) a thread. Other threads that are waiting for <var>Queue</var>
347	388	using
348		<a name="idx:threadgetmessage2:1898"></a><a class="pred" href="threadcom.html#thread_get_message/2">thread_get_message/2</a>
	389	<a id="idx:threadgetmessage2:1902"></a><a class="pred" href="threadcom.html#thread_get_message/2">thread_get_message/2</a>
349	390	receive an existence error.</dd>
350		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="thread_get_message/2"><strong>thread_get_message</strong>(<var>+Queue,
	391	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="thread_get_message/2"><strong>thread_get_message</strong>(<var>+Queue,
351	392	?Term</var>)</a></dt>
352	393	<dd class="defbody">
353		As <a name="idx:threadgetmessage1:1899"></a><a class="pred" href="threadcom.html#thread_get_message/1">thread_get_message/1</a>,
	394	As <a id="idx:threadgetmessage1:1903"></a><a class="pred" href="threadcom.html#thread_get_message/1">thread_get_message/1</a>,
354	395	operating on a given queue. It is allowed (but not advised) to get
355	396	messages from the queue of other threads. This predicate raises an
356	397	existence error exception if <var>Queue</var> doesn't exist or is
357		destroyed using <a name="idx:messagequeuedestroy1:1900"></a><a class="pred" href="threadcom.html#message_queue_destroy/1">message_queue_destroy/1</a>
	398	destroyed using <a id="idx:messagequeuedestroy1:1904"></a><a class="pred" href="threadcom.html#message_queue_destroy/1">message_queue_destroy/1</a>
358	399	while this predicate is waiting.</dd>
359		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="thread_get_message/3"><strong>thread_get_message</strong>(<var>+Queue,
	400	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="thread_get_message/3"><strong>thread_get_message</strong>(<var>+Queue,
360	401	?Term, +Options</var>)</a></dt>
361	402	<dd class="defbody">
362		As <a name="idx:threadgetmessage2:1901"></a><a class="pred" href="threadcom.html#thread_get_message/2">thread_get_message/2</a>,
	403	As <a id="idx:threadgetmessage2:1905"></a><a class="pred" href="threadcom.html#thread_get_message/2">thread_get_message/2</a>,
363	404	but providing additional <var>Options</var>:
364	405
365	406	<dl class="latex">
366	407	<dt><strong>deadline</strong>(<var>+AbsTime</var>)</dt>
367	408	<dd class="defbody">
368	409	The call fails (silently) if no message has arrived before
369		<var>AbsTime</var>. See <a name="idx:gettime1:1902"></a><a class="pred" href="system.html#get_time/1">get_time/1</a>
	410	<var>AbsTime</var>. See <a id="idx:gettime1:1906"></a><a class="pred" href="system.html#get_time/1">get_time/1</a>
370	411	for the representation of absolute time. If <var>AbsTime</var> is
371		earlier then the current time, <a name="idx:threadgetmessage3:1903"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>
	412	earlier then the current time, <a id="idx:threadgetmessage3:1907"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>
372	413	fails immediately. Both resolution and maximum wait time is
373		platform-dependent.<sup class="fn">163<span class="fn-text">The
	414	platform-dependent.<sup class="fn">164<span class="fn-text">The
374	415	implementation uses MsgWaitForMultipleObjects() on MS-Windows and
375	416	pthread_cond_timedwait() on other systems.</span></sup></dd>
376	417	<dt><strong>timeout</strong>(<var>+Time</var>)</dt>

379	420	wait in seconds. This is a relative-time version of the <code>deadline</code>
380	421	option. If both options are provided, the earlier time is effective.
381	422
382		<p>If <var>Time</var> is 0 or 0.0, <a name="idx:threadgetmessage3:1904"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>
	423	<p>If <var>Time</var> is 0 or 0.0, <a id="idx:threadgetmessage3:1908"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>
383	424	examines the queue but does not suspend if no matching term is
384	425	available. Note that unlike
385		<a name="idx:threadpeekmessage2:1905"></a><a class="pred" href="threadcom.html#thread_peek_message/2">thread_peek_message/2</a>,
	426	<a id="idx:threadpeekmessage2:1909"></a><a class="pred" href="threadcom.html#thread_peek_message/2">thread_peek_message/2</a>,
386	427	a matching term is removed from the queue.
387	428
388		<p>If <var>Time</var> <var>< 0</var>, <a name="idx:threadgetmessage3:1906"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>
	429	<p>If <var>Time</var> <var>< 0</var>, <a id="idx:threadgetmessage3:1910"></a><a class="pred" href="threadcom.html#thread_get_message/3">thread_get_message/3</a>
389	430	fails immediately without removing any message from the queue.
390	431	</dd>
391	432	</dl>
392	433
393	434	</dd>
394		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="thread_peek_message/2"><strong>thread_peek_message</strong>(<var>+Queue,
	435	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="thread_peek_message/2"><strong>thread_peek_message</strong>(<var>+Queue,
395	436	?Term</var>)</a></dt>
396	437	<dd class="defbody">
397		As <a name="idx:threadpeekmessage1:1907"></a><a class="pred" href="threadcom.html#thread_peek_message/1">thread_peek_message/1</a>,
	438	As <a id="idx:threadpeekmessage1:1911"></a><a class="pred" href="threadcom.html#thread_peek_message/1">thread_peek_message/1</a>,
398	439	operating on a given queue. It is allowed to peek into another thread's
399	440	message queue, an operation that can be used to check whether a thread
400	441	has swallowed a message sent to it.</dd>
401		<dt class="pubdef"><a name="message_queue_property/2"><strong>message_queue_property</strong>(<var>?Queue,
	442	<dt class="pubdef"><a id="message_queue_property/2"><strong>message_queue_property</strong>(<var>?Queue,
402	443	?Property</var>)</a></dt>
403	444	<dd class="defbody">
404	445	True if <var>Property</var> is a property of <var>Queue</var>. Defined

412	453	<dt><strong>max_size</strong>(<var>Size</var>)</dt>
413	454	<dd class="defbody">
414	455	Maximum number of terms that can be in the queue. See
415		<a name="idx:messagequeuecreate2:1908"></a><a class="pred" href="threadcom.html#message_queue_create/2">message_queue_create/2</a>.
	456	<a id="idx:messagequeuecreate2:1912"></a><a class="pred" href="threadcom.html#message_queue_create/2">message_queue_create/2</a>.
416	457	This property is not present if there is no limit (default).
417	458	</dd>
418	459	<dt><strong>size</strong>(<var>Size</var>)</dt>

468	509	thread_send_message(Id, Goal).
469	510	</pre>
470	511
471		<p><h3 id="sec:thread-signal"><a name="sec:9.3.2"><span class="sec-nr">9.3.2</span> <span class="sec-title">Signalling
	512	<p><h3 id="sec:thread-signal"><a id="sec:9.3.2"><span class="sec-nr">9.3.2</span> <span class="sec-title">Signalling
472	513	threads</span></a></h3>
473	514
474		<a name="sec:thread-signal"></a>
	515	<a id="sec:thread-signal"></a>
475	516
476	517	<p>These predicates provide a mechanism to make another thread execute
477	518	some goal as an <em>interrupt</em>. Signalling threads is safe as these
478	519	interrupts are only checked at safe points in the virtual machine.
479	520	Nevertheless, signalling in multithreaded environments should be handled
480		with care as the receiving thread may hold a <em>mutex</em> (see <a name="idx:withmutex2:1909"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>).
	521	with care as the receiving thread may hold a <em>mutex</em> (see <a id="idx:withmutex2:1913"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>).
481	522	Signalling probably only makes sense to start debugging threads and to
482		cancel no-longer-needed threads with <a name="idx:throw1:1910"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
	523	cancel no-longer-needed threads with <a id="idx:throw1:1914"></a><a class="pred" href="exception.html#throw/1">throw/1</a>,
483	524	where the receiving thread should be designed carefully to handle
484	525	exceptions at any point.
485	526
486	527	<dl class="latex">
487		<dt class="pubdef"><a name="thread_signal/2"><strong>thread_signal</strong>(<var>+ThreadId,
	528	<dt class="pubdef"><a id="thread_signal/2"><strong>thread_signal</strong>(<var>+ThreadId,
488	529	:Goal</var>)</a></dt>
489	530	<dd class="defbody">
490	531	Make thread <var>ThreadId</var> execute <var>Goal</var> at the first
491	532	opportunity. In the current implementation, this implies at the first
492		pass through the <em>Call port</em>. The predicate <a name="idx:threadsignal2:1911"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>
	533	pass through the <em>Call port</em>. The predicate <a id="idx:threadsignal2:1915"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>
493	534	itself places <var>Goal</var> into the signalled thread's signal queue
494	535	and returns immediately.
495	536

498	539	guaranteed easily. At the call port, the Prolog virtual machine holds no
499	540	locks and therefore the asynchronous execution is safe.
500	541
501		<p><var>Goal</var> can be any valid Prolog goal, including <a name="idx:throw1:1912"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
502		to make the receiving thread generate an exception, and <a name="idx:trace0:1913"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
	542	<p><var>Goal</var> can be any valid Prolog goal, including <a id="idx:throw1:1916"></a><a class="pred" href="exception.html#throw/1">throw/1</a>
	543	to make the receiving thread generate an exception, and <a id="idx:trace0:1917"></a><a class="pred" href="debugger.html#trace/0">trace/0</a>
503	544	to start tracing the receiving thread.
504	545
505	546	<p>In the Windows version, the receiving thread immediately executes the

508	549	</dd>
509	550	</dl>
510	551
511		<p><h3 id="sec:threadlocal"><a name="sec:9.3.3"><span class="sec-nr">9.3.3</span> <span class="sec-title">Threads
	552	<p><h3 id="sec:threadlocal"><a id="sec:9.3.3"><span class="sec-nr">9.3.3</span> <span class="sec-title">Threads
512	553	and dynamic predicates</span></a></h3>
513	554
514		<a name="sec:threadlocal"></a>
515
516		<p>Besides queues (<a class="sec" href="threadcom.html">section 9.3.1</a>)
517		threads can share and exchange data using dynamic predicates. The
518		multithreaded version knows about two types of dynamic predicates. By
519		default, a predicate declared
520		<em>dynamic</em> (see <a name="idx:dynamic1:1914"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>)
	555	<a id="sec:threadlocal"></a>
	556
	557	<p>Besides queues (<a class="sec" href="threadcom.html#sec:9.3.1">section
	558	9.3.1</a>) threads can share and exchange data using dynamic predicates.
	559	The multithreaded version knows about two types of dynamic predicates.
	560	By default, a predicate declared
	561	<em>dynamic</em> (see <a id="idx:dynamic1:1918"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>)
521	562	is shared by all threads. Each thread may assert, retract and run the
522	563	dynamic predicate. Synchronisation inside Prolog guarantees the
523	564	consistency of the predicate. Updates are
524	565	<em>logical</em>: visible clauses are not affected by assert/retract
525	566	after a query started on the predicate. In many cases primitives from
526		<a class="sec" href="threadsync.html">section 9.4</a> should be used to
527		ensure that application invariants on the predicate are maintained.
	567	<a class="sec" href="threadsync.html#sec:9.4">section 9.4</a> should be
	568	used to ensure that application invariants on the predicate are
	569	maintained.
528	570
529	571	<p>Besides shared predicates, dynamic predicates can be declared with
530	572	the
531		<a name="idx:threadlocal1:1915"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>
	573	<a id="idx:threadlocal1:1919"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>
532	574	directive. Such predicates share their attributes, but the clause list
533	575	is different in each thread.
534	576
535	577	<dl class="latex">
536		<dt class="pubdef"><a name="thread_local/1"><strong>thread_local</strong> <var>+Functor/+Arity,
	578	<dt class="pubdef"><a id="thread_local/1"><strong>thread_local</strong> <var>+Functor/+Arity,
537	579	...</var></a></dt>
538	580	<dd class="defbody">
539		This directive is related to the <a name="idx:dynamic1:1916"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
540		directive. It tells the system that the predicate may be modified using <a name="idx:assert1:1917"></a><a class="pred" href="db.html#assert/1">assert/1</a>, <a name="idx:retract1:1918"></a><a class="pred" href="db.html#retract/1">retract/1</a>,
	581	This directive is related to the <a id="idx:dynamic1:1920"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>
	582	directive. It tells the system that the predicate may be modified using <a id="idx:assert1:1921"></a><a class="pred" href="db.html#assert/1">assert/1</a>, <a id="idx:retract1:1922"></a><a class="pred" href="db.html#retract/1">retract/1</a>,
541	583	etc., during execution of the program. Unlike normal shared dynamic
542	584	data, however, each thread has its own clause list for the predicate. As
543	585	a thread starts, this clause list is empty. If there are still clauses
544	586	when the thread terminates, these are automatically reclaimed by the
545		system (see also <a name="idx:volatile1:1919"></a><a class="pred" href="runtime.html#volatile/1">volatile/1</a>).
	587	system (see also <a id="idx:volatile1:1923"></a><a class="pred" href="runtime.html#volatile/1">volatile/1</a>).
546	588	The thread_local property implies the properties <em>dynamic</em> and <em>volatile</em>.
547	589
548	590	<p>Thread-local dynamic predicates are intended for maintaining

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 9.1</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 9.1</title><link rel="home" href="index.html">
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186	227	<body style="background:white">

191	232	<a class="nav" href="threads.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="thmonitor.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:threadcreate"><a name="sec:9.1"><span class="sec-nr">9.1</span> <span class="sec-title">Creating
	235	<h2 id="sec:threadcreate"><a id="sec:9.1"><span class="sec-nr">9.1</span> <span class="sec-title">Creating
195	236	and destroying Prolog threads</span></a></h2>
196	237
197		<a name="sec:threadcreate"></a>
	238	<a id="sec:threadcreate"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="thread_create/2"><strong>thread_create</strong>(<var>:Goal,
	241	<dt class="pubdef"><a id="thread_create/2"><strong>thread_create</strong>(<var>:Goal,
201	242	-Id</var>)</a></dt>
202	243	<dd class="defbody">
203		Shorthand for <code>thread_create(Goal, Id, [])</code>. See <a name="idx:threadcreate3:1827"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>.</dd>
204		<dt class="pubdef"><a name="thread_create/3"><strong>thread_create</strong>(<var>:Goal,
	244	Shorthand for <code>thread_create(Goal, Id, [])</code>. See <a id="idx:threadcreate3:1831"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>.</dd>
	245	<dt class="pubdef"><a id="thread_create/3"><strong>thread_create</strong>(<var>:Goal,
205	246	-Id, +Options</var>)</a></dt>
206	247	<dd class="defbody">
207	248	Create a new Prolog thread (and underlying operating system thread) and

212	253	is given. Otherwise it is a <em>blob</em> of type <code>thread</code>.
213	254	The anonymous blobs are subject to atom garbage collection. If a thread
214	255	handle is garbage collected and the thread is not <em>detached</em>, it
215		is <em>joined</em> if it has already terminated (see <a name="idx:threadjoin2:1828"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>)
216		and detached otherwise (see <a name="idx:threaddetach1:1829"></a><a class="pred" href="threadcreate.html#thread_detach/1">thread_detach/1</a>).<sup class="fn">156<span class="fn-text">Up
	256	is <em>joined</em> if it has already terminated (see <a id="idx:threadjoin2:1832"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>)
	257	and detached otherwise (see <a id="idx:threaddetach1:1833"></a><a class="pred" href="threadcreate.html#thread_detach/1">thread_detach/1</a>).<sup class="fn">157<span class="fn-text">Up
217	258	to version 7.3.23, anonymous thread handles were integers. Using
218	259	integers did not allow for safe checking of the thread's status as the
219	260	thread may have died and the handle may have been reused and did not

222	263	where <var>I</var> is the internal thread identifier and <var>Ptr</var>
223	264	is the unique address of the identifier. The <var>I</var> is accepted as
224	265	input argument for all thread APIs that accept a thread identifier for
225		convenient interaction from the toplevel. See also <a name="idx:threadproperty2:1830"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>.
	266	convenient interaction from the toplevel. See also <a id="idx:threadproperty2:1834"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>.
226	267
227	268	<p><var>Options</var> is a list of options. The currently defined
228	269	options are below. Stack size options can also take the value <code>inf</code>

235	276	<dd class="defbody">
236	277	Associate an `alias name' with the thread. This name may be used to
237	278	refer to the thread and remains valid until the thread is joined (see
238		<a name="idx:threadjoin2:1831"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>).
	279	<a id="idx:threadjoin2:1835"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>).
239	280	If the OS supports it (e.g., Linux), the operating system thread is
240	281	named as well.</dd>
241	282	<dt><strong>at_exit</strong>(<var>:AtExit</var>)</dt>
242	283	<dd class="defbody">
243		Register <var>AtExit</var> as using <a name="idx:threadatexit1:1832"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
244		before entering the thread goal. Unlike calling <a name="idx:threadatexit1:1833"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
	284	Register <var>AtExit</var> as using <a id="idx:threadatexit1:1836"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
	285	before entering the thread goal. Unlike calling <a id="idx:threadatexit1:1837"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
245	286	as part of the normal
246	287	<var>Goal</var>, this <em>ensures</em> the <var>AtExit</var> is called.
247	288	Using
248		<a name="idx:threadatexit1:1834"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>,
249		the thread may be signalled or run out of resources before <a name="idx:threadatexit1:1835"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
	289	<a id="idx:threadatexit1:1838"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>,
	290	the thread may be signalled or run out of resources before <a id="idx:threadatexit1:1839"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
250	291	is reached.</dd>
251	292	<dt><strong>debug</strong>(<var>+Bool</var>)</dt>
252	293	<dd class="defbody">
253	294	Enable/disable debugging the new thread. If <code>false</code> (default
254	295	<code>true</code>), the new thread is created with the property
255	296	<code>debug(false)</code> and debugging is disabled before the new
256		thread is started. The thread debugging predicates such as <a name="idx:tspy1:1836"></a><a class="pred" href="thutil.html#tspy/1">tspy/1</a>
257		and <a name="idx:tdebug0:1837"></a><a class="pred" href="thutil.html#tdebug/0">tdebug/0</a>
	297	thread is started. The thread debugging predicates such as <a id="idx:tspy1:1840"></a><a class="pred" href="thutil.html#tspy/1">tspy/1</a>
	298	and <a id="idx:tdebug0:1841"></a><a class="pred" href="thutil.html#tdebug/0">tdebug/0</a>
258	299	do not signal threads with the debug property set to
259		<code>false</code>.<sup class="fn">157<span class="fn-text">Currently,
	300	<code>false</code>.<sup class="fn">158<span class="fn-text">Currently,
260	301	the flag is only used as a hint for the the various debugging
261	302	primitives, i.e., the system does not really enforce that the target
262	303	thread stays in <em>nodebug</em> mode.</span></sup></dd>
263	304	<dt><strong>detached</strong>(<var>Bool</var>)</dt>
264	305	<dd class="defbody">
265	306	If <code>false</code> (default), the thread can be waited for using
266		<a name="idx:threadjoin2:1838"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>. <a name="idx:threadjoin2:1839"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
	307	<a id="idx:threadjoin2:1842"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>. <a id="idx:threadjoin2:1843"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
267	308	must be called on this thread to reclaim all resources associated with
268	309	the thread. If <code>true</code>, the system will reclaim all associated
269	310	resources automatically after the thread finishes. Please note that
270	311	thread identifiers are freed for reuse after a detached thread finishes
271		or a normal thread has been joined. See also <a name="idx:threadjoin2:1840"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
272		and <a name="idx:threaddetach1:1841"></a><a class="pred" href="threadcreate.html#thread_detach/1">thread_detach/1</a>.
	312	or a normal thread has been joined. See also <a id="idx:threadjoin2:1844"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
	313	and <a id="idx:threaddetach1:1845"></a><a class="pred" href="threadcreate.html#thread_detach/1">thread_detach/1</a>.
273	314
274	315	<p>If a detached thread dies due to failure or exception of the initial
275		goal, the thread prints a message using <a name="idx:printmessage2:1842"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
	316	goal, the thread prints a message using <a id="idx:printmessage2:1846"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>.
276	317	If such termination is considered normal, the code must be wrapped using
277		<a name="idx:ignore1:1843"></a><a class="pred" href="metacall.html#ignore/1">ignore/1</a>
278		and/or <a name="idx:catch3:1844"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
	318	<a id="idx:ignore1:1847"></a><a class="pred" href="metacall.html#ignore/1">ignore/1</a>
	319	and/or <a id="idx:catch3:1848"></a><a class="pred" href="exception.html#catch/3">catch/3</a>
279	320	to ensure successful completion.</dd>
280	321	<dt><strong>inherit_from</strong>(<var>+ThreadId</var>)</dt>
281	322	<dd class="defbody">
282	323	Inherit defaults from the given <var>ThreadId</var> instead of the
283	324	calling thread. This option was added to ensure that the
284		<code>__thread_pool_manager</code> (see <a name="idx:threadcreateinpool4:1845"></a><a class="pred" href="threadpool.html#thread_create_in_pool/4">thread_create_in_pool/4</a>),
	325	<code>__thread_pool_manager</code> (see <a id="idx:threadcreateinpool4:1849"></a><a class="pred" href="threadpool.html#thread_create_in_pool/4">thread_create_in_pool/4</a>),
285	326	which is created lazily, has a predictable state. The following
286	327	properties are inherited:
287	328
288	329	<p>
289	330	<ul class="latex">
290		<li>The prompt (see <a name="idx:prompt2:1846"></a><a class="pred" href="termrw.html#prompt/2">prompt/2</a>)
291		<li>The <em>typein</em> module (see <a name="idx:module1:1847"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>)
	331	<li>The prompt (see <a id="idx:prompt2:1850"></a><a class="pred" href="termrw.html#prompt/2">prompt/2</a>)
	332	<li>The <em>typein</em> module (see <a id="idx:module1:1851"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a>)
292	333	<li>The standard streams (<code>user_input</code>, etc.)
293	334	<li>The default encoding (see <a class="flag" href="flags.html#flag:encoding">encoding</a>)
294		<li>The default locale (see <a name="idx:setlocale1:1848"></a><span class="pred-ext">setlocale/1</span>)
	335	<li>The default locale (see <a id="idx:setlocale1:1852"></a><span class="pred-ext">setlocale/1</span>)
295	336	<li>All prolog flags
296		<li>The limits of Prolog stacks (see <a name="idx:setprologstack2:1849"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>)
	337	<li>The limits of Prolog stacks (see <a id="idx:setprologstack2:1853"></a><a class="pred" href="memory.html#set_prolog_stack/2">set_prolog_stack/2</a>)
297	338	</ul>
298	339	</dd>
299	340	<dt><strong>global</strong>(<var>K-Bytes</var>)</dt>

309	350	<dt><strong>c_stack</strong>(<var>K-Bytes</var>)</dt>
310	351	<dd class="defbody">
311	352	Set the limit to which the system stack of this thread may grow. The
312		default, minimum and maximum values are system-dependent.<sup class="fn">158<span class="fn-text">Older
	353	default, minimum and maximum values are system-dependent.<sup class="fn">159<span class="fn-text">Older
313	354	versions used <code>stack</code>. This is still accepted as a synonym.</span></sup></dd>
314	355	<dt><strong>trail</strong>(<var>K-Bytes</var>)</dt>
315	356	<dd class="defbody">

323	364	engine. This implies that further instantiation of this term in either
324	365	thread does not have consequences for the other thread: Prolog threads
325	366	do not share data from their stacks.</dd>
326		<dt class="pubdef"><a name="thread_self/1"><strong>thread_self</strong>(<var>-Id</var>)</a></dt>
	367	<dt class="pubdef"><a id="thread_self/1"><strong>thread_self</strong>(<var>-Id</var>)</a></dt>
327	368	<dd class="defbody">
328	369	Get the Prolog thread identifier of the running thread. If the thread
329	370	has an alias, the alias name is returned.</dd>
330		<dt class="pubdef"><a name="thread_join/2"><strong>thread_join</strong>(<var>+Id</var>)</a></dt>
331		<dd class="defbody">
332		Calls <a name="idx:threadjoin2:1850"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
	371	<dt class="pubdef"><a id="thread_join/2"><strong>thread_join</strong>(<var>+Id</var>)</a></dt>
	372	<dd class="defbody">
	373	Calls <a id="idx:threadjoin2:1854"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
333	374	and succeeds if thread <var>Id</var> terminated with success. Otherwise
334	375	the exception
335	376	<code>error(<code>thread_error(Status)</code>, _)</code> is raised.</dd>
336		<dt class="pubdef"><a name="thread_join/2"><strong>thread_join</strong>(<var>+Id,
	377	<dt class="pubdef"><a id="thread_join/2"><strong>thread_join</strong>(<var>+Id,
337	378	-Status</var>)</a></dt>
338	379	<dd class="defbody">
339	380	Wait for the termination of the thread with the given <var>Id</var>.
340	381	Then unify the result status of the thread with <var>Status</var>. After
341	382	this call, <var>Id</var> becomes invalid and all resources associated
342	383	with the thread are reclaimed. Note that threads with the attribute
343		<code>detached(true)</code> cannot be joined. See also <a name="idx:threadproperty2:1851"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>.
344
345		<p>A thread that has been completed without <a name="idx:threadjoin2:1852"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
	384	<code>detached(true)</code> cannot be joined. See also <a id="idx:threadproperty2:1855"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>.
	385
	386	<p>A thread that has been completed without <a id="idx:threadjoin2:1856"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
346	387	being called on it is partly reclaimed: the Prolog stacks are released
347	388	and the C thread is destroyed. A small data structure representing the
348		exit status of the thread is retained until <a name="idx:threadjoin2:1853"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
	389	exit status of the thread is retained until <a id="idx:threadjoin2:1857"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
349	390	is called on the thread. Defined values for <var>Status</var> are:
350	391
351	392	<dl class="latex">

357	398	The goal has failed.</dd>
358	399	<dt><strong>exception</strong>(<var>Term</var>)</dt>
359	400	<dd class="defbody">
360		The thread is terminated on an exception. See <a name="idx:printmessage2:1854"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
	401	The thread is terminated on an exception. See <a id="idx:printmessage2:1858"></a><a class="pred" href="exception.html#print_message/2">print_message/2</a>
361	402	to turn system exceptions into readable messages.</dd>
362	403	<dt><strong>exited</strong>(<var>Term</var>)</dt>
363	404	<dd class="defbody">
364		The thread is terminated on <a name="idx:threadexit1:1855"></a><a class="pred" href="threadcreate.html#thread_exit/1">thread_exit/1</a>
	405	The thread is terminated on <a id="idx:threadexit1:1859"></a><a class="pred" href="threadcreate.html#thread_exit/1">thread_exit/1</a>
365	406	using the argument <var>Term</var>.
366	407	</dd>
367	408	</dl>
368	409
369	410	</dd>
370		<dt class="pubdef"><a name="thread_detach/1"><strong>thread_detach</strong>(<var>+Id</var>)</a></dt>
	411	<dt class="pubdef"><a id="thread_detach/1"><strong>thread_detach</strong>(<var>+Id</var>)</a></dt>
371	412	<dd class="defbody">
372	413	Switch thread into detached state (see <code>detached(Bool)</code>
373	414	option at
374		<a name="idx:threadcreate3:1856"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>)
	415	<a id="idx:threadcreate3:1860"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>)
375	416	at runtime. <var>Id</var> is the identifier of the thread placed in
376		detached state. This may be the result of <a name="idx:threadself1:1857"></a><a class="pred" href="threadcreate.html#thread_self/1">thread_self/1</a>.
	417	detached state. This may be the result of <a id="idx:threadself1:1861"></a><a class="pred" href="threadcreate.html#thread_self/1">thread_self/1</a>.
377	418
378	419	<p>One of the possible applications is to simplify debugging. Threads
379	420	that are created as <em>detached</em> leave no traces if they crash. For
380	421	non-detached threads the status can be inspected using
381		<a name="idx:threadproperty2:1858"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>.
	422	<a id="idx:threadproperty2:1862"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>.
382	423	Threads nobody is waiting for may be created normally and detach
383	424	themselves just before completion. This way they leave no traces on
384	425	normal completion and their reason for failure can be inspected.</dd>
385		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="thread_exit/1"><strong>thread_exit</strong>(<var>+Term</var>)</a></dt>
	426	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="thread_exit/1"><strong>thread_exit</strong>(<var>+Term</var>)</a></dt>
386	427	<dd class="defbody">
387	428	Terminates the thread immediately, leaving <code>exited(Term)</code> as
388		result state for <a name="idx:threadjoin2:1859"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>.
	429	result state for <a id="idx:threadjoin2:1863"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>.
389	430	If the thread has the attribute
390	431	<code>detached(true)</code> it terminates, but its exit status cannot be
391		retrieved using <a name="idx:threadjoin2:1860"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>,
	432	retrieved using <a id="idx:threadjoin2:1864"></a><a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>,
392	433	making the value of <var>Term</var> irrelevant. The Prolog stacks and C
393	434	thread are reclaimed.
394	435
395	436	<p>The current implementation does not guarantee proper releasing of all
396		mutexes and proper cleanup in <a name="idx:setupcallcleanup3:1861"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>,
397		etc. Please use the exception mechanism (<a name="idx:throw1:1862"></a><a class="pred" href="exception.html#throw/1">throw/1</a>)
	437	mutexes and proper cleanup in <a id="idx:setupcallcleanup3:1865"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>,
	438	etc. Please use the exception mechanism (<a id="idx:throw1:1866"></a><a class="pred" href="exception.html#throw/1">throw/1</a>)
398	439	to abort execution using non-standard control.</dd>
399		<dt class="pubdef"><a name="thread_initialization/1"><strong>thread_initialization</strong>(<var>:Goal</var>)</a></dt>
	440	<dt class="pubdef"><a id="thread_initialization/1"><strong>thread_initialization</strong>(<var>:Goal</var>)</a></dt>
400	441	<dd class="defbody">
401	442	Run <var>Goal</var> when thread is started. This predicate is similar to
402		<a name="idx:initialization1:1863"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>,
	443	<a id="idx:initialization1:1867"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>,
403	444	but is intended for initialization operations of the runtime stacks,
404	445	such as setting global variables as described in
405		<a class="sec" href="gvar.html">section 4.33</a>. <var>Goal</var> is run
406		on four occasions: at the call to this predicate, after loading a saved
407		state, on starting a new thread and on creating a Prolog engine through
408		the C interface. On loading a saved state, <var>Goal</var> is executed <em>after</em>
409		running the
410		<a name="idx:initialization1:1864"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
	446	<a class="sec" href="gvar.html#sec:4.33">section 4.33</a>. <var>Goal</var>
	447	is run on four occasions: at the call to this predicate, after loading a
	448	saved state, on starting a new thread and on creating a Prolog engine
	449	through the C interface. On loading a saved state, <var>Goal</var> is
	450	executed <em>after</em> running the
	451	<a id="idx:initialization1:1868"></a><a class="pred" href="consulting.html#initialization/1">initialization/1</a>
411	452	hooks.</dd>
412		<dt class="pubdef"><a name="thread_at_exit/1"><strong>thread_at_exit</strong>(<var>:Goal</var>)</a></dt>
	453	<dt class="pubdef"><a id="thread_at_exit/1"><strong>thread_at_exit</strong>(<var>:Goal</var>)</a></dt>
413	454	<dd class="defbody">
414	455	Run <var>Goal</var> just before releasing the thread resources. This is
415		to be compared to <a name="idx:athalt1:1865"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>,
	456	to be compared to <a id="idx:athalt1:1869"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>,
416	457	but only for the current thread. These hooks are run regardless of why
417	458	the execution of the thread has been completed. When these hooks are
418	459	run, the return code is already available through
419		<a name="idx:threadproperty2:1866"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>
420		using the result of <a name="idx:threadself1:1867"></a><a class="pred" href="threadcreate.html#thread_self/1">thread_self/1</a>
	460	<a id="idx:threadproperty2:1870"></a><a class="pred" href="thmonitor.html#thread_property/2">thread_property/2</a>
	461	using the result of <a id="idx:threadself1:1871"></a><a class="pred" href="threadcreate.html#thread_self/1">thread_self/1</a>
421	462	as thread identifier. Note that there are two scenarios for using exit
422		hooks. Using <a name="idx:threadatexit1:1868"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
	463	hooks. Using <a id="idx:threadatexit1:1872"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
423	464	is typically used if the thread creates a side-effect that must be
424	465	reverted if the thread dies. Another scenario is where the creator of
425	466	the thread wants to be informed when the thread ends. That cannot be
426		guaranteed by means of <a name="idx:threadatexit1:1869"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
	467	guaranteed by means of <a id="idx:threadatexit1:1873"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
427	468	because it is possible that the thread cannot be created or dies almost
428	469	instantly due to a signal or resource error. The <code>at_exit(Goal)</code>
429	470	option of
430		<a name="idx:threadcreate3:1870"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>
	471	<a id="idx:threadcreate3:1874"></a><a class="pred" href="threadcreate.html#thread_create/3">thread_create/3</a>
431	472	is designed to deal with this scenario.</dd>
432		<dt class="pubdef"><a name="thread_setconcurrency/2"><strong>thread_setconcurrency</strong>(<var>-Old,
	473	<dt class="pubdef"><a id="thread_setconcurrency/2"><strong>thread_setconcurrency</strong>(<var>-Old,
433	474	+New</var>)</a></dt>
434	475	<dd class="defbody">
435		<a name="idx:Solaris:1871"></a>Determine the concurrency of the process,
	476	<a id="idx:Solaris:1875"></a>Determine the concurrency of the process,
436	477	which is defined as the maximum number of concurrently active threads.
437	478	`Active' here means they are using CPU time. This option is provided if
438	479	the thread implementation provides pthread_setconcurrency(). Solaris is

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193	234	</div>
194		<h2 id="sec:threadpool"><a name="sec:A.36"><span class="sec-nr">A.36</span> <span class="sec-title">library(thread_pool):
	235	<h2 id="sec:threadpool"><a id="sec:A.36"><span class="sec-nr">A.36</span> <span class="sec-title">library(thread_pool):
195	236	Resource bounded thread management</span></a></h2>
196	237
197		<p><a name="sec:threadpool"></a>
	238	<p><a id="sec:threadpool"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">See also</dt>

237	278	directive or otherwise during startup of the application.
238	279
239	280	<dl class="latex">
240		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="thread_pool_create/3"><strong>thread_pool_create</strong>(<var>+Pool,
	281	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="thread_pool_create/3"><strong>thread_pool_create</strong>(<var>+Pool,
241	282	+Size, +Options</var>)</a></dt>
242	283	<dd class="defbody">
243	284	Create a pool of threads. A pool of threads is a declaration for

264	305	state of a thread. Threads can be created both <code>detached</code> and
265	306	normal and must be joined using <a class="pred" href="threadcreate.html#thread_join/2">thread_join/2</a>
266	307	if they are not detached.</dd>
267		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="thread_pool_destroy/1"><strong>thread_pool_destroy</strong>(<var>+Name</var>)</a></dt>
	308	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="thread_pool_destroy/1"><strong>thread_pool_destroy</strong>(<var>+Name</var>)</a></dt>
268	309	<dd class="defbody">
269	310	Destroy the thread pool named <var>Name</var>.
270	311

276	317	</dl>
277	318
278	319	</dd>
279		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="current_thread_pool/1"><strong>current_thread_pool</strong>(<var>?Name</var>)</a></dt>
	320	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="current_thread_pool/1"><strong>current_thread_pool</strong>(<var>?Name</var>)</a></dt>
280	321	<dd class="defbody">
281	322	True if <var>Name</var> refers to a defined thread pool.</dd>
282		<dt class="pubdef"><span class="pred-tag">[nondet]</span><a name="thread_pool_property/2"><strong>thread_pool_property</strong>(<var>?Name,
	323	<dt class="pubdef"><span class="pred-tag">[nondet]</span><a id="thread_pool_property/2"><strong>thread_pool_property</strong>(<var>?Name,
283	324	?Property</var>)</a></dt>
284	325	<dd class="defbody">
285	326	True if <var>Property</var> is a property of thread pool <var>Name</var>.

313	354	</dl>
314	355
315	356	</dd>
316		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="thread_create_in_pool/4"><strong>thread_create_in_pool</strong>(<var>+Pool,
	357	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="thread_create_in_pool/4"><strong>thread_create_in_pool</strong>(<var>+Pool,
317	358	:Goal, -Id, +Options</var>)</a></dt>
318	359	<dd class="defbody">
319	360	Create a thread in <var>Pool</var>. <var>Options</var> overrule default

339	380	</dl>
340	381
341	382	</dd>
342		<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a name="create_pool/1"><strong>create_pool</strong>(<var>+PoolName</var>)</a></dt>
	383	<dt class="multidef"><span class="pred-tag">[semidet,multifile]</span><a id="create_pool/1"><strong>create_pool</strong>(<var>+PoolName</var>)</a></dt>
343	384	<dd class="defbody">
344	385	Hook to create a thread pool lazily. The hook is called if
345	386	<a class="pred" href="threadpool.html#thread_create_in_pool/4">thread_create_in_pool/4</a>

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193	234	</div>
194		<h1 id="sec:threads"><a name="sec:9"><span class="sec-nr">9</span> <span class="sec-title">Multithreaded
	235	<h1 id="sec:threads"><a id="sec:9"><span class="sec-nr">9</span> <span class="sec-title">Multithreaded
195	236	applications</span></a></h1>
196	237
197		<a name="sec:threads"></a>
	238	<a id="sec:threads"></a>
198	239
199	240	<p>SWI-Prolog multithreading is based on standard C language
200	241	multithreading support. It is not like <em>ParLog</em> or other parallel

210	251	applications. Such applications often have need for communication
211	252	between services and/or fast non-blocking service to multiple concurrent
212	253	clients. The shared heap provides fast communication, and thread
213		creation is relatively cheap.<sup class="fn">154<span class="fn-text">On
	254	creation is relatively cheap.<sup class="fn">155<span class="fn-text">On
214	255	an Intel i7-2600K, running Ubuntu Linux 12.04, SWI-Prolog 6.2 creates
215	256	and joins 32,000 threads per second elapsed time.</span></sup>
216	257

220	261	such computations are executed in a new thread, the main thread can
221	262	process events and allow the user to cancel the ongoing computation.
222	263	User interfaces can also use multiple threads, each thread dealing with
223		input from a distinct group of windows. See also <a class="sec" href="mt-xpce.html">section
	264	input from a distinct group of windows. See also <a class="sec" href="mt-xpce.html#sec:9.7">section
224	265	9.7</a>.
225	266
226	267	<p>

235	276	<cite><a class="cite" href="Bibliography.html#Butenhof:1997:PPT">Butenhof,
236	277	1997</a></cite> used on most popular systems except for MS-Windows. On
237	278	Windows it uses the
238		http://sources.redhat.com/pthreads-win32/pthread-win32 emulation of
239		POSIX threads mixed with the Windows native API for smoother and faster
240		operation. The SWI-Prolog thread implementation has been discussed in
241		the ISO WG17 working group and is largely addopted by YAP and XSB
242		Prolog.<sup class="fn">155<span class="fn-text">The latest version of
243		the ISO draft can be found at <a class="url" href="http://logtalk.org/plstd/threads.pdf">http://logtalk.org/plstd/threads.pdf</a>.
	279	<a class="url" href="http://sources.redhat.com/pthreads-win32/">pthread-win32</a>
	280	emulation of POSIX threads mixed with the Windows native API for
	281	smoother and faster operation. The SWI-Prolog thread implementation has
	282	been discussed in the ISO WG17 working group and is largely addopted by
	283	YAP and XSB Prolog.<sup class="fn">156<span class="fn-text">The latest
	284	version of the ISO draft can be found at <a class="url" href="http://logtalk.org/plstd/threads.pdf">http://logtalk.org/plstd/threads.pdf</a>.
244	285	It appears to have dropped from the ISO WG17 agenda.</span></sup>
245	286
246	287	<p>

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193	234	</div>
194		<h2 id="sec:threadsync"><a name="sec:9.4"><span class="sec-nr">9.4</span> <span class="sec-title">Thread
	235	<h2 id="sec:threadsync"><a id="sec:9.4"><span class="sec-nr">9.4</span> <span class="sec-title">Thread
195	236	synchronisation</span></a></h2>
196	237
197		<a name="sec:threadsync"></a>
	238	<a id="sec:threadsync"></a>
198	239
199	240	<p>All internal Prolog operations are thread-safe. This implies that two
200	241	Prolog threads can operate on the same dynamic predicate without

215	256	assert/retract order.
216	257
217	258	<p>The code below provides a solution to this problem based on
218		<a name="idx:withmutex2:1920"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>.
	259	<a id="idx:withmutex2:1924"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>.
219	260	It also illustrates the problem of mutexes. The predicate
220		<a name="idx:withmutex2:1921"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>
221		behaves as <a name="idx:once1:1922"></a><a class="pred" href="metacall.html#once/1">once/1</a>
	261	<a id="idx:withmutex2:1925"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>
	262	behaves as <a id="idx:once1:1926"></a><a class="pred" href="metacall.html#once/1">once/1</a>
222	263	with respect to the guarded goal. This means that our predicate
223	264	address/2 is no longer a nice logical non-deterministic relation. This
224		could be solved by explicit locking and unlocking a mutex using <a name="idx:setupcallcleanup2:1923"></a><span class="pred-ext">setup_call_cleanup/2</span>,
	265	could be solved by explicit locking and unlocking a mutex using <a id="idx:setupcallcleanup2:1927"></a><span class="pred-ext">setup_call_cleanup/2</span>,
225	266	but at the risk of deadlocking the program if the choice point is left
226	267	open by accident.
227	268

237	278	address_db(Id, Address)).
238	279	</pre>
239	280
240		<p>Message queues (see <a name="idx:messagequeuecreate3:1924"></a><span class="pred-ext">message_queue_create/3</span>)
	281	<p>Message queues (see <a id="idx:messagequeuecreate3:1928"></a><span class="pred-ext">message_queue_create/3</span>)
241	282	often provide simpler and more robust ways for threads to communicate.
242	283	Still, mutexes can be a sensible solution and are therefore provided.
243	284
244	285	<dl class="latex">
245		<dt class="pubdef"><a name="mutex_create/1"><strong>mutex_create</strong>(<var>?MutexId</var>)</a></dt>
	286	<dt class="pubdef"><a id="mutex_create/1"><strong>mutex_create</strong>(<var>?MutexId</var>)</a></dt>
246	287	<dd class="defbody">
247	288	Create a mutex. If <var>MutexId</var> is an atom, a <em>named</em> mutex
248	289	is created. If it is a variable, an anonymous mutex reference is
249	290	returned. Anonymous mutexes are subject to (atom) garbage collection.</dd>
250		<dt class="pubdef"><a name="mutex_create/2"><strong>mutex_create</strong>(<var>-MutexId,
	291	<dt class="pubdef"><a id="mutex_create/2"><strong>mutex_create</strong>(<var>-MutexId,
251	292	+Options</var>)</a></dt>
252	293	<dd class="defbody">
253	294	Create a mutex using options. Defined options are:

261	302	</dl>
262	303
263	304	</dd>
264		<dt class="pubdef"><a name="mutex_destroy/1"><strong>mutex_destroy</strong>(<var>+MutexId</var>)</a></dt>
	305	<dt class="pubdef"><a id="mutex_destroy/1"><strong>mutex_destroy</strong>(<var>+MutexId</var>)</a></dt>
265	306	<dd class="defbody">
266	307	Destroy a mutex. If the mutex is not locked, it is destroyed and further
267	308	access yields an <code>existence_error</code> exception. As of version
268	309	7.1.19, this behaviour is reliable. If the mutex is locked, the mutex is
269	310	sheduled for <em>delayed destruction</em>: it will be destroyed when it
270	311	becomes unlocked.</dd>
271		<dt class="pubdef"><a name="with_mutex/2"><strong>with_mutex</strong>(<var>+MutexId,
	312	<dt class="pubdef"><a id="with_mutex/2"><strong>with_mutex</strong>(<var>+MutexId,
272	313	:Goal</var>)</a></dt>
273	314	<dd class="defbody">
274	315	Execute <var>Goal</var> while holding <var>MutexId</var>. If <var>Goal</var>
275		leaves choice points, these are destroyed (as in <a name="idx:once1:1925"></a><a class="pred" href="metacall.html#once/1">once/1</a>).
	316	leaves choice points, these are destroyed (as in <a id="idx:once1:1929"></a><a class="pred" href="metacall.html#once/1">once/1</a>).
276	317	The mutex is unlocked regardless of whether <var>Goal</var> succeeds,
277	318	fails or raises an exception. An exception thrown by <var>Goal</var> is
278		re-thrown after the mutex has been successfully unlocked. See also <a name="idx:mutexcreate1:1926"></a><a class="pred" href="threadsync.html#mutex_create/1">mutex_create/1</a>
279		and <a name="idx:setupcallcleanup3:1927"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>.
	319	re-thrown after the mutex has been successfully unlocked. See also <a id="idx:mutexcreate1:1930"></a><a class="pred" href="threadsync.html#mutex_create/1">mutex_create/1</a>
	320	and <a id="idx:setupcallcleanup3:1931"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>.
280	321
281	322	<p>Although described in the thread section, this predicate is also
282	323	available in the single-threaded version, where it behaves simply as
283		<a name="idx:once1:1928"></a><a class="pred" href="metacall.html#once/1">once/1</a>.</dd>
284		<dt class="pubdef"><a name="mutex_lock/1"><strong>mutex_lock</strong>(<var>+MutexId</var>)</a></dt>
	324	<a id="idx:once1:1932"></a><a class="pred" href="metacall.html#once/1">once/1</a>.</dd>
	325	<dt class="pubdef"><a id="mutex_lock/1"><strong>mutex_lock</strong>(<var>+MutexId</var>)</a></dt>
285	326	<dd class="defbody">
286	327	Lock the mutex. Prolog mutexes are <em>recursive</em> mutexes: they can
287	328	be locked multiple times by the same thread. Only after unlocking it as

290	331	thread is suspended until the mutex is unlocked.
291	332
292	333	<p>If <var>MutexId</var> is an atom, and there is no current mutex with
293		that name, the mutex is created automatically using <a name="idx:mutexcreate1:1929"></a><a class="pred" href="threadsync.html#mutex_create/1">mutex_create/1</a>.
	334	that name, the mutex is created automatically using <a id="idx:mutexcreate1:1933"></a><a class="pred" href="threadsync.html#mutex_create/1">mutex_create/1</a>.
294	335	This implies named mutexes need not be declared explicitly.
295	336
296	337	<p>Please note that locking and unlocking mutexes should be paired
297	338	carefully. Especially make sure to unlock mutexes even if the protected
298	339	code fails or raises an exception. For most common cases, use
299		<a name="idx:withmutex2:1930"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>,
	340	<a id="idx:withmutex2:1934"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>,
300	341	which provides a safer way for handling Prolog-level mutexes. The
301		predicate <a name="idx:setupcallcleanup3:1931"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
	342	predicate <a id="idx:setupcallcleanup3:1935"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>
302	343	is another way to guarantee that the mutex is unlocked while retaining
303	344	non-determinism.</dd>
304		<dt class="pubdef"><a name="mutex_trylock/1"><strong>mutex_trylock</strong>(<var>+MutexId</var>)</a></dt>
305		<dd class="defbody">
306		As <a name="idx:mutexlock1:1932"></a><a class="pred" href="threadsync.html#mutex_lock/1">mutex_lock/1</a>,
	345	<dt class="pubdef"><a id="mutex_trylock/1"><strong>mutex_trylock</strong>(<var>+MutexId</var>)</a></dt>
	346	<dd class="defbody">
	347	As <a id="idx:mutexlock1:1936"></a><a class="pred" href="threadsync.html#mutex_lock/1">mutex_lock/1</a>,
307	348	but if the mutex is held by another thread, this predicates fails
308	349	immediately.</dd>
309		<dt class="pubdef"><a name="mutex_unlock/1"><strong>mutex_unlock</strong>(<var>+MutexId</var>)</a></dt>
	350	<dt class="pubdef"><a id="mutex_unlock/1"><strong>mutex_unlock</strong>(<var>+MutexId</var>)</a></dt>
310	351	<dd class="defbody">
311	352	Unlock the mutex. This can only be called if the mutex is held by the
312	353	calling thread. If this is not the case, a <code>permission_error</code>
313	354	exception is raised.</dd>
314		<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a name="mutex_unlock_all/0"><strong>mutex_unlock_all</strong></a></dt>
	355	<dt class="pubdef"><span class="pred-tag">[deprecated]</span><a id="mutex_unlock_all/0"><strong>mutex_unlock_all</strong></a></dt>
315	356	<dd class="defbody">
316	357	Unlock all mutexes held by the current thread. This predicate should not
317		be needed if mutex unlocking is guaranteed with <a name="idx:withmutex2:1933"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>
	358	be needed if mutex unlocking is guaranteed with <a id="idx:withmutex2:1937"></a><a class="pred" href="threadsync.html#with_mutex/2">with_mutex/2</a>
318	359	or
319		<a name="idx:setupcallcleanup3:1934"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>.<sup class="fn">164<span class="fn-text">The
320		also deprecated <a name="idx:threadexit1:1935"></a><a class="pred" href="threadcreate.html#thread_exit/1">thread_exit/1</a>
	360	<a id="idx:setupcallcleanup3:1938"></a><a class="pred" href="metacall.html#setup_call_cleanup/3">setup_call_cleanup/3</a>.<sup class="fn">165<span class="fn-text">The
	361	also deprecated <a id="idx:threadexit1:1939"></a><a class="pred" href="threadcreate.html#thread_exit/1">thread_exit/1</a>
321	362	bypasses the automatic cleanup.</span></sup></dd>
322		<dt class="pubdef"><a name="mutex_property/2"><strong>mutex_property</strong>(<var>?MutexId,
	363	<dt class="pubdef"><a id="mutex_property/2"><strong>mutex_property</strong>(<var>?MutexId,
323	364	?Property</var>)</a></dt>
324	365	<dd class="defbody">
325	366	True if <var>Property</var> is a property of <var>MutexId</var>. Defined

328	369	<dl class="latex">
329	370	<dt><strong>alias</strong>(<var>Alias</var>)</dt>
330	371	<dd class="defbody">
331		Mutex has the defined alias name. See <a name="idx:mutexcreate2:1936"></a><a class="pred" href="threadsync.html#mutex_create/2">mutex_create/2</a>
	372	Mutex has the defined alias name. See <a id="idx:mutexcreate2:1940"></a><a class="pred" href="threadsync.html#mutex_create/2">mutex_create/2</a>
332	373	using the `alias' option.</dd>
333	374	<dt><strong>status</strong>(<var>Status</var>)</dt>
334	375	<dd class="defbody">

+97

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193	234	</div>
194		<h2 id="sec:thutil"><a name="sec:9.5"><span class="sec-nr">9.5</span> <span class="sec-title">Thread
	235	<h2 id="sec:thutil"><a id="sec:9.5"><span class="sec-nr">9.5</span> <span class="sec-title">Thread
195	236	support library(threadutil)</span></a></h2>
196	237
197		<a name="sec:thutil"></a>
	238	<a id="sec:thutil"></a>
198	239
199	240	<p>This library defines a couple of useful predicates for demonstrating
200	241	and debugging multithreaded applications. This library is certainly not
201	242	complete.
202	243
203	244	<dl class="latex">
204		<dt class="pubdef"><a name="threads/0"><strong>threads</strong></a></dt>
	245	<dt class="pubdef"><a id="threads/0"><strong>threads</strong></a></dt>
205	246	<dd class="defbody">
206	247	Lists all current threads and their status.</dd>
207		<dt class="pubdef"><a name="join_threads/0"><strong>join_threads</strong></a></dt>
	248	<dt class="pubdef"><a id="join_threads/0"><strong>join_threads</strong></a></dt>
208	249	<dd class="defbody">
209	250	Join all terminated threads. For normal applications, dealing with
210	251	terminated threads must be part of the application logic, either
211	252	detaching the thread before termination or making sure it will be
212		joined. The predicate <a name="idx:jointhreads0:1937"></a><a class="pred" href="thutil.html#join_threads/0">join_threads/0</a>
	253	joined. The predicate <a id="idx:jointhreads0:1941"></a><a class="pred" href="thutil.html#join_threads/0">join_threads/0</a>
213	254	is intended for interactive sessions to reclaim resources from threads
214	255	that died unexpectedly during development.</dd>
215		<dt class="pubdef"><a name="interactor/0"><strong>interactor</strong></a></dt>
	256	<dt class="pubdef"><a id="interactor/0"><strong>interactor</strong></a></dt>
216	257	<dd class="defbody">
217	258	Create a new console and run the Prolog top level in this new console.
218		See also <a name="idx:attachconsole0:1938"></a><a class="pred" href="thutil.html#attach_console/0">attach_console/0</a>.
	259	See also <a id="idx:attachconsole0:1942"></a><a class="pred" href="thutil.html#attach_console/0">attach_console/0</a>.
219	260	In the Windows version a new interactor can also be created from the <b>Run/New
220	261	thread</b> menu.
221	262	</dd>
222	263	</dl>
223	264
224		<p><h3 id="sec:threaddebug"><a name="sec:9.5.1"><span class="sec-nr">9.5.1</span> <span class="sec-title">Debugging
	265	<p><h3 id="sec:threaddebug"><a id="sec:9.5.1"><span class="sec-nr">9.5.1</span> <span class="sec-title">Debugging
225	266	threads</span></a></h3>
226	267
227		<a name="sec:threaddebug"></a>
	268	<a id="sec:threaddebug"></a>
228	269
229	270	<p>Support for debugging threads is still very limited. Debug and trace
230	271	mode are flags that are local to each thread. Individual threads can be
231	272	debugged either using the graphical debugger described in
232		<a class="sec" href="guitracer.html">section 3.5</a> (see <a name="idx:tspy1:1939"></a><a class="pred" href="thutil.html#tspy/1">tspy/1</a>
	273	<a class="sec" href="guitracer.html#sec:3.5">section 3.5</a> (see <a id="idx:tspy1:1943"></a><a class="pred" href="thutil.html#tspy/1">tspy/1</a>
233	274	and friends) or by attaching a console to the thread and running the
234	275	traditional command line debugger (see
235		<a name="idx:attachconsole0:1940"></a><a class="pred" href="thutil.html#attach_console/0">attach_console/0</a>).
	276	<a id="idx:attachconsole0:1944"></a><a class="pred" href="thutil.html#attach_console/0">attach_console/0</a>).
236	277	When using the graphical debugger, the debugger must be <em>loaded</em>
237		from the main thread (for example using guitracer) before <a name="idx:gtrace0:1941"></a><a class="pred" href="guitracer.html#gtrace/0">gtrace/0</a>
	278	from the main thread (for example using guitracer) before <a id="idx:gtrace0:1945"></a><a class="pred" href="guitracer.html#gtrace/0">gtrace/0</a>
238	279	can be called from a thread.
239	280
240	281	<dl class="latex">
241		<dt class="pubdef"><a name="attach_console/0"><strong>attach_console</strong></a></dt>
	282	<dt class="pubdef"><a id="attach_console/0"><strong>attach_console</strong></a></dt>
242	283	<dd class="defbody">
243	284	If the current thread has no console attached yet, attach one and
244	285	redirect the user streams (input, output, and error) to the new console

256	297	</pre>
257	298
258	299	</dd>
259		<dt class="pubdef"><a name="tdebug/1"><strong>tdebug</strong>(<var>+ThreadId</var>)</a></dt>
	300	<dt class="pubdef"><a id="tdebug/1"><strong>tdebug</strong>(<var>+ThreadId</var>)</a></dt>
260	301	<dd class="defbody">
261	302	Prepare <var>ThreadId</var> for debugging using the graphical tracer.
262	303	This implies installing the tracer hooks in the thread and switching the
263		thread to debug mode using <a name="idx:debug0:1942"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.
264		The call is injected into the thread using <a name="idx:threadsignal2:1943"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>.
	304	thread to debug mode using <a id="idx:debug0:1946"></a><a class="pred" href="debugger.html#debug/0">debug/0</a>.
	305	The call is injected into the thread using <a id="idx:threadsignal2:1947"></a><a class="pred" href="threadcom.html#thread_signal/2">thread_signal/2</a>.
265	306	We refer to the documentation of this predicate for asynchronous
266	307	interaction with threads. New threads created inherit their debug mode
267	308	from the thread that created them.</dd>
268		<dt class="pubdef"><a name="tdebug/0"><strong>tdebug</strong></a></dt>
269		<dd class="defbody">
270		Call <a name="idx:tdebug1:1944"></a><a class="pred" href="thutil.html#tdebug/1">tdebug/1</a>
	309	<dt class="pubdef"><a id="tdebug/0"><strong>tdebug</strong></a></dt>
	310	<dd class="defbody">
	311	Call <a id="idx:tdebug1:1948"></a><a class="pred" href="thutil.html#tdebug/1">tdebug/1</a>
271	312	in all running threads.</dd>
272		<dt class="pubdef"><a name="tnodebug/1"><strong>tnodebug</strong>(<var>+ThreadId</var>)</a></dt>
	313	<dt class="pubdef"><a id="tnodebug/1"><strong>tnodebug</strong>(<var>+ThreadId</var>)</a></dt>
273	314	<dd class="defbody">
274	315	Disable debugging thread <var>ThreadId</var>.</dd>
275		<dt class="pubdef"><a name="tnodebug/0"><strong>tnodebug</strong></a></dt>
	316	<dt class="pubdef"><a id="tnodebug/0"><strong>tnodebug</strong></a></dt>
276	317	<dd class="defbody">
277	318	Disable debugging in all threads.</dd>
278		<dt class="pubdef"><a name="tspy/2"><strong>tspy</strong>(<var>:Spec,
	319	<dt class="pubdef"><a id="tspy/2"><strong>tspy</strong>(<var>:Spec,
279	320	+ThreadId</var>)</a></dt>
280	321	<dd class="defbody">
281		Set a spy point as <a name="idx:spy1:1945"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
	322	Set a spy point as <a id="idx:spy1:1949"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
282	323	and enable the thread for debugging using
283		<a name="idx:tdebug1:1946"></a><a class="pred" href="thutil.html#tdebug/1">tdebug/1</a>.
	324	<a id="idx:tdebug1:1950"></a><a class="pred" href="thutil.html#tdebug/1">tdebug/1</a>.
284	325	Note that a spy point is a global flag on a predicate that is visible
285	326	from all threads. Spy points are honoured in all threads that are in
286	327	debug mode and ignored in threads that are in nodebug mode.</dd>
287		<dt class="pubdef"><a name="tspy/1"><strong>tspy</strong>(<var>:Spec</var>)</a></dt>
288		<dd class="defbody">
289		Set a spy point as <a name="idx:spy1:1947"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
	328	<dt class="pubdef"><a id="tspy/1"><strong>tspy</strong>(<var>:Spec</var>)</a></dt>
	329	<dd class="defbody">
	330	Set a spy point as <a id="idx:spy1:1951"></a><a class="pred" href="debugger.html#spy/1">spy/1</a>
290	331	and enable debugging in all threads using
291		<a name="idx:tdebug0:1948"></a><a class="pred" href="thutil.html#tdebug/0">tdebug/0</a>.
292		Note that removing spy points can be done using <a name="idx:nospy1:1949"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>.
293		Disabling spy points in a specific thread is achieved by <a name="idx:tnodebug1:1950"></a><a class="pred" href="thutil.html#tnodebug/1">tnodebug/1</a>.
	332	<a id="idx:tdebug0:1952"></a><a class="pred" href="thutil.html#tdebug/0">tdebug/0</a>.
	333	Note that removing spy points can be done using <a id="idx:nospy1:1953"></a><a class="pred" href="debugger.html#nospy/1">nospy/1</a>.
	334	Disabling spy points in a specific thread is achieved by <a id="idx:tnodebug1:1954"></a><a class="pred" href="thutil.html#tnodebug/1">tnodebug/1</a>.
294	335	</dd>
295	336	</dl>
296	337
297		<p><h3 id="sec:tprofile"><a name="sec:9.5.2"><span class="sec-nr">9.5.2</span> <span class="sec-title">Profiling
	338	<p><h3 id="sec:tprofile"><a id="sec:9.5.2"><span class="sec-nr">9.5.2</span> <span class="sec-title">Profiling
298	339	threads</span></a></h3>
299	340
300		<a name="sec:tprofile"></a>
	341	<a id="sec:tprofile"></a>
301	342
302	343	<p>In the current implementation, at most one thread can be profiled at
303		any moment. Any thread can call <a name="idx:profile1:1951"></a><a class="pred" href="profile.html#profile/1">profile/1</a>
304		to profile the execution of some part of its code. The predicate <a name="idx:tprofile1:1952"></a><a class="pred" href="thutil.html#tprofile/1">tprofile/1</a>
	344	any moment. Any thread can call <a id="idx:profile1:1955"></a><a class="pred" href="profile.html#profile/1">profile/1</a>
	345	to profile the execution of some part of its code. The predicate <a id="idx:tprofile1:1956"></a><a class="pred" href="thutil.html#tprofile/1">tprofile/1</a>
305	346	allows for profiling the execution of another thread until the user
306	347	stops collecting profile data.
307	348
308	349	<dl class="latex">
309		<dt class="pubdef"><a name="tprofile/1"><strong>tprofile</strong>(<var>+ThreadId</var>)</a></dt>
	350	<dt class="pubdef"><a id="tprofile/1"><strong>tprofile</strong>(<var>+ThreadId</var>)</a></dt>
310	351	<dd class="defbody">
311	352	Start collecting profile data in <var>ThreadId</var> and ask the user to
312	353	hit
313		<<var>return</var>> to stop the profiler. See <a class="sec" href="profile.html">section
	354	<<var>return</var>> to stop the profiler. See <a class="sec" href="profile.html#sec:4.41">section
314	355	4.41</a> for details on the execution profiler.
315	356	</dd>
316	357	</dl>

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193	234	</div>
194		<h2 id="sec:toplevel"><a name="sec:4.37"><span class="sec-nr">4.37</span> <span class="sec-title">User
	235	<h2 id="sec:toplevel"><a id="sec:4.37"><span class="sec-nr">4.37</span> <span class="sec-title">User
195	236	Top-level Manipulation</span></a></h2>
196	237
197		<a name="sec:toplevel"></a>
	238	<a id="sec:toplevel"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="break/0"><strong>break</strong></a></dt>
	241	<dt class="pubdef"><a id="break/0"><strong>break</strong></a></dt>
201	242	<dd class="defbody">
202	243	Recursively start a new Prolog top level. This Prolog top level shares
203	244	everything from the environment it was started in. Debugging is switched

207	248	<code>end_of_file.</code> can be entered to return from the break
208	249	environment. If the <strong>-t</strong> <var>toplevel</var> command line
209	250	option is given, this goal is started instead of entering the default
210		interactive top level (<a name="idx:prolog0:1525"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>).
	251	interactive top level (<a id="idx:prolog0:1525"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>).
211	252
212	253	<p>Notably the gui based versions (<b>swipl-win</b> on Windows and
213	254	MacOS) provide the menu <b>Run/New thread</b> that opens a new toplevel
214	255	that runs concurrently with the initial toplevel. The concurrent
215	256	toplevel can be used to examine the program, in particular global
216	257	dynamic predicates. It can not access <em>global variables</em> or
217		thread-local dynamic predicates (see <a name="idx:threadlocal1:1526"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>)
	258	thread-local dynamic predicates (see <a id="idx:threadlocal1:1526"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a>)
218	259	of the main thread.</dd>
219		<dt class="pubdef"><a name="abort/0"><strong>abort</strong></a></dt>
	260	<dt class="pubdef"><a id="abort/0"><strong>abort</strong></a></dt>
220	261	<dd class="defbody">
221	262	Abort the Prolog execution and restart the top level. If the
222	263	<strong>-t</strong> <var>toplevel</var> command line option is given,

224	265	level.
225	266
226	267	<p>Aborting is implemented by throwing the reserved exception
227		<code>'$aborted'</code>. This exception can be caught using <a name="idx:catch3:1527"></a><a class="pred" href="exception.html#catch/3">catch/3</a>,
	268	<code>'$aborted'</code>. This exception can be caught using <a id="idx:catch3:1527"></a><a class="pred" href="exception.html#catch/3">catch/3</a>,
228	269	but the recovery goal is wrapped with a predicate that prunes the choice
229		points of the recovery goal (i.e., as <a name="idx:once1:1528"></a><a class="pred" href="metacall.html#once/1">once/1</a>)
	270	points of the recovery goal (i.e., as <a id="idx:once1:1528"></a><a class="pred" href="metacall.html#once/1">once/1</a>)
230	271	and re-throws the exception. This is illustrated in the example below,
231		where we press control-C and `a'. See also <a class="sec" href="exception.html">section
	272	where we press control-C and `a'. See also <a class="sec" href="exception.html#sec:4.11.1">section
232	273	4.11.1</a>.
233	274
234	275	<pre class="code">

238	279	</pre>
239	280
240	281	</dd>
241		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="halt/0"><strong>halt</strong></a></dt>
	282	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="halt/0"><strong>halt</strong></a></dt>
242	283	<dd class="defbody">
243	284	Terminate Prolog execution. This is the same as <code>halt(0)</code>.
244	285	See
245		<a name="idx:halt1:1529"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a>
	286	<a id="idx:halt1:1529"></a><a class="pred" href="toplevel.html#halt/1">halt/1</a>
246	287	for details.</dd>
247		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="halt/1"><strong>halt</strong>(<var>+Status</var>)</a></dt>
	288	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="halt/1"><strong>halt</strong>(<var>+Status</var>)</a></dt>
248	289	<dd class="defbody">
249	290	Terminate Prolog execution with <var>Status</var>. This predicate calls
250	291	<a class="func" href="foreigninclude.html#PL_halt()">PL_halt()</a> which

256	297	to <var>Status</var>.
257	298
258	299	<p>
259		<li>Call all hooks registered using <a name="idx:athalt1:1530"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>.
260		If <var>Status</var> equals 0 (zero), any of these hooks calls <a name="idx:cancelhalt1:1531"></a><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a>,
	300	<li>Call all hooks registered using <a id="idx:athalt1:1530"></a><a class="pred" href="consulting.html#at_halt/1">at_halt/1</a>.
	301	If <var>Status</var> equals 0 (zero), any of these hooks calls <a id="idx:cancelhalt1:1531"></a><a class="pred" href="consulting.html#cancel_halt/1">cancel_halt/1</a>,
261	302	termination is cancelled.
262	303
263	304	<p>

270	311
271	312	<p>
272	313	<ul class="latex">
273		<li>Cancel all threads, calling <a name="idx:threadatexit1:1532"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
	314	<li>Cancel all threads, calling <a id="idx:threadatexit1:1532"></a><a class="pred" href="threadcreate.html#thread_at_exit/1">thread_at_exit/1</a>
274	315	registered termination hooks. Threads not responding within 1 second are
275	316	cancelled forcefully.
276	317	<li>Flush I/O and close all streams except for standard I/O.

283	324	<li>Call exit(Status) to terminate the process
284	325	</ol>
285	326	</dd>
286		<dt class="pubdef"><a name="prolog/0"><strong>prolog</strong></a></dt>
	327	<dt class="pubdef"><a id="prolog/0"><strong>prolog</strong></a></dt>
287	328	<dd class="defbody">
288	329	This goal starts the default interactive top level. Queries are read
289	330	from the stream <code>user_input</code>. See also the Prolog flag
290		<a class="flag" href="flags.html#flag:history">history</a>. The <a name="idx:prolog0:1533"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>
	331	<a class="flag" href="flags.html#flag:history">history</a>. The <a id="idx:prolog0:1533"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>
291	332	predicate is terminated (succeeds) by typing the end-of-file character
292	333	(typically control-D).
293	334	</dd>

295	336
296	337	<p>The following two hooks allow for expanding queries and handling the
297	338	result of a query. These hooks are used by the top level variable
298		expansion mechanism described in <a class="sec" href="topvars.html">section
	339	expansion mechanism described in <a class="sec" href="topvars.html#sec:2.8">section
299	340	2.8</a>.
300	341
301	342	<dl class="latex">
302		<dt class="pubdef"><a name="expand_query/4"><strong>expand_query</strong>(<var>+Query,
	343	<dt class="pubdef"><a id="expand_query/4"><strong>expand_query</strong>(<var>+Query,
303	344	-Expanded, +Bindings, -ExpandedBindings</var>)</a></dt>
304	345	<dd class="defbody">
305	346	Hook in module <code>user</code>, normally not defined. <var>Query</var>
306	347	and
307	348	<var>Bindings</var> represents the query read from the user and the
308		names of the free variables as obtained using <a name="idx:readterm3:1534"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.
	349	names of the free variables as obtained using <a id="idx:readterm3:1534"></a><a class="pred" href="termrw.html#read_term/3">read_term/3</a>.
309	350	If this predicate succeeds, it should bind <var>Expanded</var> and <var>ExpandedBindings</var>
310	351	to the query and bindings to be executed by the top level. This
311		predicate is used by the top level (<a name="idx:prolog0:1535"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>).
312		See also <a name="idx:expandanswer2:1536"></a><a class="pred" href="toplevel.html#expand_answer/2">expand_answer/2</a>
	352	predicate is used by the top level (<a id="idx:prolog0:1535"></a><a class="pred" href="toplevel.html#prolog/0">prolog/0</a>).
	353	See also <a id="idx:expandanswer2:1536"></a><a class="pred" href="toplevel.html#expand_answer/2">expand_answer/2</a>
313	354	and
314		<a name="idx:termexpansion2:1537"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>.</dd>
315		<dt class="pubdef"><a name="expand_answer/2"><strong>expand_answer</strong>(<var>+Bindings,
	355	<a id="idx:termexpansion2:1537"></a><a class="pred" href="consulting.html#term_expansion/2">term_expansion/2</a>.</dd>
	356	<dt class="pubdef"><a id="expand_answer/2"><strong>expand_answer</strong>(<var>+Bindings,
316	357	-ExpandedBindings</var>)</a></dt>
317	358	<dd class="defbody">
318	359	Hook in module <code>user</code>, normally not defined. Expand the

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193	234	</div>
194		<h2 id="sec:topvars"><a name="sec:2.8"><span class="sec-nr">2.8</span> <span class="sec-title">Reuse
	235	<h2 id="sec:topvars"><a id="sec:2.8"><span class="sec-nr">2.8</span> <span class="sec-title">Reuse
195	236	of top-level bindings</span></a></h2>
196	237
197		<a name="sec:topvars"></a>
	238	<a id="sec:topvars"></a>
198	239
199	240	<p>Bindings resulting from the successful execution of a top-level goal
200	241	are asserted in a database <em>if they are not too large</em>. These

214	255	</pre>
215	256
216	257	<div class="caption"><b>Figure 1 : </b>Reusing top-level bindings</div>
217		<a name="fig:topevelvars"></a>
	258	<a id="fig:topevelvars"></a>
218	259
219	260	<p>Note that variables may be set by executing <a class="pred" href="compare.html#=/2">=/2</a>:
220	261

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193	234	</div>
194		<h2 id="sec:tracehook"><a name="sec:B.3"><span class="sec-nr">B.3</span> <span class="sec-title">Intercepting
	235	<h2 id="sec:tracehook"><a id="sec:B.3"><span class="sec-nr">B.3</span> <span class="sec-title">Intercepting
195	236	the Tracer</span></a></h2>
196	237
197		<a name="sec:tracehook"></a>
	238	<a id="sec:tracehook"></a>
198	239
199	240	<dl class="latex">
200		<dt class="pubdef"><a name="prolog_trace_interception/4"><strong>prolog_trace_interception</strong>(<var>+Port,
	241	<dt class="pubdef"><a id="prolog_trace_interception/4"><strong>prolog_trace_interception</strong>(<var>+Port,
201	242	+Frame, +Choice, -Action</var>)</a></dt>
202	243	<dd class="defbody">
203	244	Dynamic predicate, normally not defined. This predicate is called from

228	269	<dd class="defbody">
229	270	The unify port represents the <em>neck</em> instruction, signalling the
230	271	end of the head-matching process. This port is normally invisible. See
231		<a name="idx:leash1:2189"></a><a class="pred" href="debugger.html#leash/1">leash/1</a>
232		and <a name="idx:visible1:2190"></a><a class="pred" href="debugger.html#visible/1">visible/1</a>.</dd>
	272	<a id="idx:leash1:2193"></a><a class="pred" href="debugger.html#leash/1">leash/1</a>
	273	and <a id="idx:visible1:2194"></a><a class="pred" href="debugger.html#visible/1">visible/1</a>.</dd>
233	274	<dt><strong>exit</strong></dt>
234	275	<dd class="defbody">
235	276	The exit port signals the goal is proved. It is possible for the goal to
236		have alternatives. See <a name="idx:prologframeattribute3:2191"></a><a class="pred" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a>
	277	have alternatives. See <a id="idx:prologframeattribute3:2195"></a><a class="pred" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a>
237	278	to examine the goal stack.</dd>
238	279	<dt><strong>fail</strong></dt>
239	280	<dd class="defbody">

260	301	</dl>
261	302
262	303	<p><var>Frame</var> is a reference to the current local stack frame,
263		which can be examined using <a name="idx:prologframeattribute3:2192"></a><a class="pred" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a>. <var>Choice</var>
	304	which can be examined using <a id="idx:prologframeattribute3:2196"></a><a class="pred" href="manipstack.html#prolog_frame_attribute/3">prolog_frame_attribute/3</a>. <var>Choice</var>
264	305	is a reference to the last choice point and can be examined using
265		<a name="idx:prologchoiceattribute3:2193"></a><a class="pred" href="manipstack.html#prolog_choice_attribute/3">prolog_choice_attribute/3</a>. <var>Action</var>
	306	<a id="idx:prologchoiceattribute3:2197"></a><a class="pred" href="manipstack.html#prolog_choice_attribute/3">prolog_choice_attribute/3</a>. <var>Action</var>
266	307	must be unified with a term that specifies how execution must continue.
267	308	The following actions are defined:
268	309
269	310	<dl class="latex">
270	311	<dt><strong>abort</strong></dt>
271	312	<dd class="defbody">
272		Abort execution. See <a name="idx:abort0:2194"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
	313	Abort execution. See <a id="idx:abort0:2198"></a><a class="pred" href="toplevel.html#abort/0">abort/0</a>.
273	314	</dd>
274	315	<dt><strong>continue</strong></dt>
275	316	<dd class="defbody">

285	326	</dd>
286	327	<dt><strong>nodebug</strong></dt>
287	328	<dd class="defbody">
288		Continue execution in normal nodebugging mode. See <a name="idx:nodebug0:2195"></a><a class="pred" href="debugger.html#nodebug/0">nodebug/0</a>.
	329	Continue execution in normal nodebugging mode. See <a id="idx:nodebug0:2199"></a><a class="pred" href="debugger.html#nodebug/0">nodebug/0</a>.
289	330	</dd>
290	331	<dt><strong>retry</strong></dt>
291	332	<dd class="defbody">

307	348	</dd>
308	349	</dl>
309	350
310		<p>Together with the predicates described in <a class="sec" href="debugger.html">section
	351	<p>Together with the predicates described in <a class="sec" href="debugger.html#sec:4.39">section
311	352	4.39</a> and the other predicates of this chapter, this predicate
312	353	enables the Prolog user to define a complete new debugger in Prolog.
313	354	Besides this, it enables the Prolog programmer to monitor the execution

329	370	</pre>
330	371
331	372	</dd>
332		<dt class="pubdef"><a name="prolog_skip_frame/1"><strong>prolog_skip_frame</strong>(<var>-Frame</var>)</a></dt>
	373	<dt class="pubdef"><a id="prolog_skip_frame/1"><strong>prolog_skip_frame</strong>(<var>-Frame</var>)</a></dt>
333	374	<dd class="defbody">
334	375	Indicate <var>Frame</var> as a skipped frame and set the `skip level'
335	376	(see
336		<a name="idx:prologskiplevel2:2196"></a><a class="pred" href="tracehook.html#prolog_skip_level/2">prolog_skip_level/2</a>
	377	<a id="idx:prologskiplevel2:2200"></a><a class="pred" href="tracehook.html#prolog_skip_level/2">prolog_skip_level/2</a>
337	378	to the recursion depth of <var>Frame</var>. The effect of the skipped
338	379	flag is that a redo on a child of this frame is handled differently.
339	380	First, a <code>redo</code> trace is called for the child, where the skip
340	381	level is set to <code>redo_in_skip</code>. Next, the skip level is set
341	382	to skip level of the skipped frame.</dd>
342		<dt class="pubdef"><a name="prolog_skip_level/2"><strong>prolog_skip_level</strong>(<var>-Old,
	383	<dt class="pubdef"><a id="prolog_skip_level/2"><strong>prolog_skip_level</strong>(<var>-Old,
343	384	+New</var>)</a></dt>
344	385	<dd class="defbody">
345	386	Unify <var>Old</var> with the old value of `skip level' and then set
346	387	this level according to <var>New</var>. <var>New</var> is an integer,
347	388	the atom
348	389	<code>very_deep</code> (meaning don't skip) or the atom <code>skip_in_redo</code>
349		(see <a name="idx:prologskipframe1:2197"></a><a class="pred" href="tracehook.html#prolog_skip_frame/1">prolog_skip_frame/1</a>).
	390	(see <a id="idx:prologskipframe1:2201"></a><a class="pred" href="tracehook.html#prolog_skip_frame/1">prolog_skip_frame/1</a>).
350	391	The `skip level' is a setting of each Prolog thread that disables the
351	392	debugger on all recursion levels deeper than the level of the variable.
352		See also <a name="idx:prologskipframe1:2198"></a><a class="pred" href="tracehook.html#prolog_skip_frame/1">prolog_skip_frame/1</a>.
	393	See also <a id="idx:prologskipframe1:2202"></a><a class="pred" href="tracehook.html#prolog_skip_frame/1">prolog_skip_frame/1</a>.
353	394	</dd>
354	395	</dl>
355	396

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193	234	</div>
194		<h2 id="sec:tty"><a name="sec:4.34"><span class="sec-nr">4.34</span> <span class="sec-title">Terminal
	235	<h2 id="sec:tty"><a id="sec:4.34"><span class="sec-nr">4.34</span> <span class="sec-title">Terminal
195	236	Control</span></a></h2>
196	237
197		<a name="sec:tty"></a>
	238	<a id="sec:tty"></a>
198	239
199	240	<p>The following predicates form a simple access mechanism to the Unix
200	241	termcap library to provide terminal-independent I/O for screen

202	243	SWI-Prolog Windows console accepts the ANSI escape sequences.
203	244
204	245	<dl class="latex">
205		<dt class="pubdef"><a name="tty_get_capability/3"><strong>tty_get_capability</strong>(<var>+Name,
	246	<dt class="pubdef"><a id="tty_get_capability/3"><strong>tty_get_capability</strong>(<var>+Name,
206	247	+Type, -Result</var>)</a></dt>
207	248	<dd class="defbody">
208	249	Get the capability named <var>Name</var> from the termcap library. See

215	256	are only computed once. Successive queries on the same capability are
216	257	fast.
217	258	</dd>
218		<dt class="pubdef"><a name="tty_goto/2"><strong>tty_goto</strong>(<var>+X,
	259	<dt class="pubdef"><a id="tty_goto/2"><strong>tty_goto</strong>(<var>+X,
219	260	+Y</var>)</a></dt>
220	261	<dd class="defbody">
221	262	Goto position (<var>X</var>, <var>Y</var>) on the screen. Note that the
222	263	predicates
223		<a name="idx:linecount2:1435"></a><a class="pred" href="streamstat.html#line_count/2">line_count/2</a>
224		and <a name="idx:lineposition2:1436"></a><a class="pred" href="streamstat.html#line_position/2">line_position/2</a>
	264	<a id="idx:linecount2:1435"></a><a class="pred" href="streamstat.html#line_count/2">line_count/2</a>
	265	and <a id="idx:lineposition2:1436"></a><a class="pred" href="streamstat.html#line_position/2">line_position/2</a>
225	266	will not have a well-defined behaviour while using this predicate.
226	267	</dd>
227		<dt class="pubdef"><a name="tty_put/2"><strong>tty_put</strong>(<var>+Atom,
	268	<dt class="pubdef"><a id="tty_put/2"><strong>tty_put</strong>(<var>+Atom,
228	269	+Lines</var>)</a></dt>
229	270	<dd class="defbody">
230	271	Put an atom via the termcap library function tputs(). This function
231		decodes padding information in the strings returned by <a name="idx:ttygetcapability3:1437"></a><a class="pred" href="tty.html#tty_get_capability/3">tty_get_capability/3</a>
	272	decodes padding information in the strings returned by <a id="idx:ttygetcapability3:1437"></a><a class="pred" href="tty.html#tty_get_capability/3">tty_get_capability/3</a>
232	273	and should be used to output these strings. <var>Lines</var> is the
233	274	number of lines affected by the operation, or 1 if not applicable (as in
234	275	almost all cases).
235	276	</dd>
236		<dt class="pubdef"><a name="tty_size/2"><strong>tty_size</strong>(<var>-Rows,
	277	<dt class="pubdef"><a id="tty_size/2"><strong>tty_size</strong>(<var>-Rows,
237	278	-Columns</var>)</a></dt>
238	279	<dd class="defbody">
239	280	Determine the size of the terminal. Platforms:

241	282	<dl class="latex">
242	283	<dt><b>Unix</b></dt>
243	284	<dd>
244		If the system provides <em>ioctl</em> calls for this, these are used and <a name="idx:ttysize2:1438"></a><a class="pred" href="tty.html#tty_size/2">tty_size/2</a>
	285	If the system provides <em>ioctl</em> calls for this, these are used and <a id="idx:ttysize2:1438"></a><a class="pred" href="tty.html#tty_size/2">tty_size/2</a>
245	286	properly reflects the actual size after a user resize of the window. The <em>ioctl</em>
246	287	is issued on teh file descriptor associated with the <code>user_input</code>
247		stream. As a fallback, the system uses <a name="idx:ttygetcapability3:1439"></a><a class="pred" href="tty.html#tty_get_capability/3">tty_get_capability/3</a>
	288	stream. As a fallback, the system uses <a id="idx:ttygetcapability3:1439"></a><a class="pred" href="tty.html#tty_get_capability/3">tty_get_capability/3</a>
248	289	using <code>li</code> and <code>co</code> capabilities. In this case the
249	290	reported size reflects the size at the first call and is not updated
250	291	after a user-initiated resize of the terminal.</dd>

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193	234	</div>
194		<h2 id="sec:typetest"><a name="sec:4.6"><span class="sec-nr">4.6</span> <span class="sec-title">Verify
	235	<h2 id="sec:typetest"><a id="sec:4.6"><span class="sec-nr">4.6</span> <span class="sec-title">Verify
195	236	Type of a Term</span></a></h2>
196	237
197		<a name="sec:typetest"></a>
	238	<a id="sec:typetest"></a>
198	239
199	240	<p>Type tests are semi-deterministic predicates that succeed if the
200	241	argument satisfies the requested type. Type-test predicates have no

202	243	<code>library(error)</code>.
203	244
204	245	<dl class="latex">
205		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="var/1"><strong>var</strong>(<var>@Term</var>)</a></dt>
	246	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="var/1"><strong>var</strong>(<var>@Term</var>)</a></dt>
206	247	<dd class="defbody">
207	248	True if <var>Term</var> currently is a free variable.
208	249	</dd>
209		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="nonvar/1"><strong>nonvar</strong>(<var>@Term</var>)</a></dt>
	250	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="nonvar/1"><strong>nonvar</strong>(<var>@Term</var>)</a></dt>
210	251	<dd class="defbody">
211	252	True if <var>Term</var> currently is not a free variable.
212	253	</dd>
213		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="integer/1"><strong>integer</strong>(<var>@Term</var>)</a></dt>
	254	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="integer/1"><strong>integer</strong>(<var>@Term</var>)</a></dt>
214	255	<dd class="defbody">
215	256	True if <var>Term</var> is bound to an integer.
216	257	</dd>
217		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="float/1"><strong>float</strong>(<var>@Term</var>)</a></dt>
	258	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="float/1"><strong>float</strong>(<var>@Term</var>)</a></dt>
218	259	<dd class="defbody">
219	260	True if <var>Term</var> is bound to a floating point number.
220	261	</dd>
221		<dt class="pubdef"><a name="rational/1"><strong>rational</strong>(<var>@Term</var>)</a></dt>
	262	<dt class="pubdef"><a id="rational/1"><strong>rational</strong>(<var>@Term</var>)</a></dt>
222	263	<dd class="defbody">
223	264	True if <var>Term</var> is bound to a rational number. Rational numbers
224	265	include integers.
225	266	</dd>
226		<dt class="pubdef"><a name="rational/3"><strong>rational</strong>(<var>@Term,
	267	<dt class="pubdef"><a id="rational/3"><strong>rational</strong>(<var>@Term,
227	268	-Numerator, -Denominator</var>)</a></dt>
228	269	<dd class="defbody">
229	270	True if <var>Term</var> is a rational number with given <var>Numerator</var>

233	274	integer and there are no common divisors between <var>Numerator</var>
234	275	and <var>Denominator</var>.
235	276	</dd>
236		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="number/1"><strong>number</strong>(<var>@Term</var>)</a></dt>
	277	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="number/1"><strong>number</strong>(<var>@Term</var>)</a></dt>
237	278	<dd class="defbody">
238	279	True if <var>Term</var> is bound to an integer or floating point number.<sup class="fn">55<span class="fn-text">As
239	280	rational numbers are not atomic in the current implementation and we do
240		not want to break the rule that <a name="idx:number1:601"></a><a class="pred" href="typetest.html#number/1">number/1</a>
241		implies <a name="idx:atomic1:602"></a><a class="pred" href="typetest.html#atomic/1">atomic/1</a>, <a name="idx:number1:603"></a><a class="pred" href="typetest.html#number/1">number/1</a>
	281	not want to break the rule that <a id="idx:number1:601"></a><a class="pred" href="typetest.html#number/1">number/1</a>
	282	implies <a id="idx:atomic1:602"></a><a class="pred" href="typetest.html#atomic/1">atomic/1</a>, <a id="idx:number1:603"></a><a class="pred" href="typetest.html#number/1">number/1</a>
242	283	fails on rational numbers. This will change if rational numbers become
243	284	atomic.</span></sup></dd>
244		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="atom/1"><strong>atom</strong>(<var>@Term</var>)</a></dt>
	285	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="atom/1"><strong>atom</strong>(<var>@Term</var>)</a></dt>
245	286	<dd class="defbody">
246	287	True if <var>Term</var> is bound to an atom.</dd>
247		<dt class="pubdef"><a name="blob/2"><strong>blob</strong>(<var>@Term,
	288	<dt class="pubdef"><a id="blob/2"><strong>blob</strong>(<var>@Term,
248	289	?Type</var>)</a></dt>
249	290	<dd class="defbody">
250	291	True if <var>Term</var> is a <em>blob</em> of type <var>Type</var>. See
251		<a class="sec" href="foreigninclude.html">section 11.4.7</a>.</dd>
252		<dt class="pubdef"><a name="string/1"><strong>string</strong>(<var>@Term</var>)</a></dt>
	292	<a class="sec" href="foreigninclude.html#sec:11.4.7">section 11.4.7</a>.</dd>
	293	<dt class="pubdef"><a id="string/1"><strong>string</strong>(<var>@Term</var>)</a></dt>
253	294	<dd class="defbody">
254	295	True if <var>Term</var> is bound to a string. Note that string here
255		refers to the built-in atomic type string as described in <a class="sec" href="strings.html">section
	296	refers to the built-in atomic type string as described in <a class="sec" href="strings.html#sec:5.2">section
256	297	5.2</a>. Starting with version 7, the syntax for a string object is
257	298	text between double quotes, such as <code>"hello"</code>.<sup class="fn">56<span class="fn-text">In
258	299	traditional Prolog systems, double quoted text is often mapped to a list
259	300	of <em>character codes</em>.</span></sup> See also the Prolog flag
260	301	<a class="flag" href="flags.html#flag:double_quotes">double_quotes</a>.</dd>
261		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="atomic/1"><strong>atomic</strong>(<var>@Term</var>)</a></dt>
	302	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="atomic/1"><strong>atomic</strong>(<var>@Term</var>)</a></dt>
262	303	<dd class="defbody">
263	304	True if <var>Term</var> is bound (i.e., not a variable) and is not
264	305	compound. Thus, atomic acts as if defined by:

269	310	\+ compound(Term).
270	311	</pre>
271	312
272		<p>SWI-Prolog defines the following atomic datatypes: atom (<a name="idx:atom1:604"></a><a class="pred" href="typetest.html#atom/1">atom/1</a>),
273		string (<a name="idx:string1:605"></a><a class="pred" href="typetest.html#string/1">string/1</a>),
274		integer (<a name="idx:integer1:606"></a><a class="pred" href="typetest.html#integer/1">integer/1</a>),
275		floating point number (<a name="idx:float1:607"></a><a class="pred" href="typetest.html#float/1">float/1</a>)
276		and blob (<a name="idx:blob2:608"></a><a class="pred" href="typetest.html#blob/2">blob/2</a>).
	313	<p>SWI-Prolog defines the following atomic datatypes: atom (<a id="idx:atom1:604"></a><a class="pred" href="typetest.html#atom/1">atom/1</a>),
	314	string (<a id="idx:string1:605"></a><a class="pred" href="typetest.html#string/1">string/1</a>),
	315	integer (<a id="idx:integer1:606"></a><a class="pred" href="typetest.html#integer/1">integer/1</a>),
	316	floating point number (<a id="idx:float1:607"></a><a class="pred" href="typetest.html#float/1">float/1</a>)
	317	and blob (<a id="idx:blob2:608"></a><a class="pred" href="typetest.html#blob/2">blob/2</a>).
277	318	In addition, the symbol <code>[]</code> (empty list) is atomic, but not
278		an atom. See <a class="sec" href="ext-lists.html">section 5.1</a>.</dd>
279		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="compound/1"><strong>compound</strong>(<var>@Term</var>)</a></dt>
280		<dd class="defbody">
281		True if <var>Term</var> is bound to a compound term. See also <a name="idx:functor3:609"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
282		=../2, <a name="idx:compoundnamearity3:610"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>
283		and <a name="idx:compoundnamearguments3:611"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>.</dd>
284		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="callable/1"><strong>callable</strong>(<var>@Term</var>)</a></dt>
	319	an atom. See <a class="sec" href="ext-lists.html#sec:5.1">section 5.1</a>.</dd>
	320	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="compound/1"><strong>compound</strong>(<var>@Term</var>)</a></dt>
	321	<dd class="defbody">
	322	True if <var>Term</var> is bound to a compound term. See also <a id="idx:functor3:609"></a><a class="pred" href="manipterm.html#functor/3">functor/3</a>
	323	=../2, <a id="idx:compoundnamearity3:610"></a><a class="pred" href="manipterm.html#compound_name_arity/3">compound_name_arity/3</a>
	324	and <a id="idx:compoundnamearguments3:611"></a><a class="pred" href="manipterm.html#compound_name_arguments/3">compound_name_arguments/3</a>.</dd>
	325	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="callable/1"><strong>callable</strong>(<var>@Term</var>)</a></dt>
285	326	<dd class="defbody">
286	327	True if <var>Term</var> is bound to an atom or a compound term. This was
287		intended as a type-test for arguments to <a name="idx:call1:612"></a><a class="pred" href="metacall.html#call/1">call/1</a>
288		and <a name="idx:call2:613"></a><a class="pred" href="metacall.html#call/2">call/2</a>..
	328	intended as a type-test for arguments to <a id="idx:call1:612"></a><a class="pred" href="metacall.html#call/1">call/1</a>
	329	and <a id="idx:call2:613"></a><a class="pred" href="metacall.html#call/2">call/2</a>..
289	330	Note that callable only tests the <em>surface term</em>. Terms such as
290		(22,true) are considered callable, but cause <a name="idx:call1:614"></a><a class="pred" href="metacall.html#call/1">call/1</a>
291		to raise a type error. Module-qualification of meta-argument (see <a name="idx:metapredicate1:615"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>)
	331	(22,true) are considered callable, but cause <a id="idx:call1:614"></a><a class="pred" href="metacall.html#call/1">call/1</a>
	332	to raise a type error. Module-qualification of meta-argument (see <a id="idx:metapredicate1:615"></a><a class="pred" href="metapred.html#meta_predicate/1">meta_predicate/1</a>)
292	333	using
293	334	<code><code>:</code>/2</code> causes callable to succeed on any
294		meta-argument.<sup class="fn">57<span class="fn-text">We think that <a name="idx:callable1:616"></a><a class="pred" href="typetest.html#callable/1">callable/1</a>
	335	meta-argument.<sup class="fn">57<span class="fn-text">We think that <a id="idx:callable1:616"></a><a class="pred" href="typetest.html#callable/1">callable/1</a>
295	336	should be deprecated and there should be two new predicates, one
296	337	performing a test for callable that is minimally module aware and
297		possibly consistent with type-checking in <a name="idx:call1:617"></a><a class="pred" href="metacall.html#call/1">call/1</a>
	338	possibly consistent with type-checking in <a id="idx:call1:617"></a><a class="pred" href="metacall.html#call/1">call/1</a>
298	339	and a second predicate that tests for atom or compound.</span></sup>
299	340	Consider the program and query below:
300	341

310	351	</pre>
311	352
312	353	</dd>
313		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="ground/1"><strong>ground</strong>(<var>@Term</var>)</a></dt>
314		<dd class="defbody">
315		True if <var>Term</var> holds no free variables. See also <a name="idx:nonground2:618"></a><a class="pred" href="manipterm.html#nonground/2">nonground/2</a>
316		and <a name="idx:termvariables2:619"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>.</dd>
317		<dt class="pubdef"><a name="cyclic_term/1"><strong>cyclic_term</strong>(<var>@Term</var>)</a></dt>
	354	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="ground/1"><strong>ground</strong>(<var>@Term</var>)</a></dt>
	355	<dd class="defbody">
	356	True if <var>Term</var> holds no free variables. See also <a id="idx:nonground2:618"></a><a class="pred" href="manipterm.html#nonground/2">nonground/2</a>
	357	and <a id="idx:termvariables2:619"></a><a class="pred" href="manipterm.html#term_variables/2">term_variables/2</a>.</dd>
	358	<dt class="pubdef"><a id="cyclic_term/1"><strong>cyclic_term</strong>(<var>@Term</var>)</a></dt>
318	359	<dd class="defbody">
319	360	True if <var>Term</var> contains cycles, i.e. is an infinite term. See
320		also <a name="idx:acyclicterm1:620"></a><a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a>
321		and <a class="sec" href="cyclic.html">section 2.17</a>.<sup class="fn">58<span class="fn-text">The
322		predicates <a name="idx:cyclicterm1:621"></a><a class="pred" href="typetest.html#cyclic_term/1">cyclic_term/1</a>
323		and <a name="idx:acyclicterm1:622"></a><a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a>
	361	also <a id="idx:acyclicterm1:620"></a><a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a>
	362	and <a class="sec" href="cyclic.html#sec:2.17">section 2.17</a>.<sup class="fn">58<span class="fn-text">The
	363	predicates <a id="idx:cyclicterm1:621"></a><a class="pred" href="typetest.html#cyclic_term/1">cyclic_term/1</a>
	364	and <a id="idx:acyclicterm1:622"></a><a class="pred" href="typetest.html#acyclic_term/1">acyclic_term/1</a>
324	365	are compatible with SICStus Prolog. Some Prolog systems supporting
325	366	cyclic terms use is_cyclic/1 .</span></sup></dd>
326		<dt class="pubdef"><span class="pred-tag">[ISO]</span><a name="acyclic_term/1"><strong>acyclic_term</strong>(<var>@Term</var>)</a></dt>
	367	<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="acyclic_term/1"><strong>acyclic_term</strong>(<var>@Term</var>)</a></dt>
327	368	<dd class="defbody">
328	369	True if <var>Term</var> does not contain cycles, i.e. can be processed
329		recursively in finite time. See also <a name="idx:cyclicterm1:623"></a><a class="pred" href="typetest.html#cyclic_term/1">cyclic_term/1</a>
330		and <a class="sec" href="cyclic.html">section 2.17</a>.
	370	recursively in finite time. See also <a id="idx:cyclicterm1:623"></a><a class="pred" href="typetest.html#cyclic_term/1">cyclic_term/1</a>
	371	and <a class="sec" href="cyclic.html#sec:2.17">section 2.17</a>.
331	372	</dd>
332	373	</dl>
333	374

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191	232	<a class="nav" href="threadpool.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:ugraphs"><a name="sec:A.37"><span class="sec-nr">A.37</span> <span class="sec-title">library(ugraphs):
	235	<h2 id="sec:ugraphs"><a id="sec:A.37"><span class="sec-nr">A.37</span> <span class="sec-title">library(ugraphs):
195	236	Unweighted Graphs</span></a></h2>
196	237
197		<a name="sec:ugraphs"></a>
198		<a name="sec:lib:ugraphs"></a> Authors: <em>Richard O'Keefe & Vitor
	238	<a id="sec:ugraphs"></a>
	239	<a id="sec:lib:ugraphs"></a> Authors: <em>Richard O'Keefe & Vitor
199	240	Santos Costa</em>
200	241	<blockquote><i>Implementation and documentation are copied from YAP
201	242	5.0.1. The

226	267	has no neighbors.
227	268
228	269	<dl class="latex">
229		<dt class="pubdef"><a name="vertices_edges_to_ugraph/3"><strong>vertices_edges_to_ugraph</strong>(<var>+Vertices,
	270	<dt class="pubdef"><a id="vertices_edges_to_ugraph/3"><strong>vertices_edges_to_ugraph</strong>(<var>+Vertices,
230	271	+Edges, -Graph</var>)</a></dt>
231	272	<dd class="defbody">
232	273	Given a graph with a set of <var>Vertices</var> and a set of <var>Edges</var>,

250	291	</pre>
251	292
252	293	</dd>
253		<dt class="pubdef"><a name="vertices/2"><strong>vertices</strong>(<var>+Graph,
	294	<dt class="pubdef"><a id="vertices/2"><strong>vertices</strong>(<var>+Graph,
254	295	-Vertices</var>)</a></dt>
255	296	<dd class="defbody">
256	297	Unify <var>Vertices</var> with all vertices appearing in <var>Graph</var>.

262	303	</pre>
263	304
264	305	</dd>
265		<dt class="pubdef"><a name="edges/2"><strong>edges</strong>(<var>+Graph,
	306	<dt class="pubdef"><a id="edges/2"><strong>edges</strong>(<var>+Graph,
266	307	-Edges</var>)</a></dt>
267	308	<dd class="defbody">
268	309	Unify <var>Edges</var> with all edges appearing in <var>Graph</var>.

274	315	</pre>
275	316
276	317	</dd>
277		<dt class="pubdef"><a name="add_vertices/3"><strong>add_vertices</strong>(<var>+Graph,
	318	<dt class="pubdef"><a id="add_vertices/3"><strong>add_vertices</strong>(<var>+Graph,
278	319	+Vertices, -NewGraph</var>)</a></dt>
279	320	<dd class="defbody">
280	321	Unify <var>NewGraph</var> with a new graph obtained by adding the list

287	328	</pre>
288	329
289	330	</dd>
290		<dt class="pubdef"><a name="del_vertices/3"><strong>del_vertices</strong>(<var>+Graph,
	331	<dt class="pubdef"><a id="del_vertices/3"><strong>del_vertices</strong>(<var>+Graph,
291	332	+Vertices, -NewGraph</var>)</a></dt>
292	333	<dd class="defbody">
293	334	Unify <var>NewGraph</var> with a new graph obtained by deleting the list

304	345	</pre>
305	346
306	347	</dd>
307		<dt class="pubdef"><a name="add_edges/3"><strong>add_edges</strong>(<var>+Graph,
	348	<dt class="pubdef"><a id="add_edges/3"><strong>add_edges</strong>(<var>+Graph,
308	349	+Edges, -NewGraph</var>)</a></dt>
309	350	<dd class="defbody">
310	351	Unify <var>NewGraph</var> with a new graph obtained by adding the list

321	362	</pre>
322	363
323	364	</dd>
324		<dt class="pubdef"><a name="del_edges/3"><strong>del_edges</strong>(<var>+Graph,
	365	<dt class="pubdef"><a id="del_edges/3"><strong>del_edges</strong>(<var>+Graph,
325	366	+Edges, -NewGraph</var>)</a></dt>
326	367	<dd class="defbody">
327	368	Unify <var>NewGraph</var> with a new graph obtained by removing the list

337	378	</pre>
338	379
339	380	</dd>
340		<dt class="pubdef"><a name="transpose_ugraph/2"><strong>transpose_ugraph</strong>(<var>+Graph,
	381	<dt class="pubdef"><a id="transpose_ugraph/2"><strong>transpose_ugraph</strong>(<var>+Graph,
341	382	-NewGraph</var>)</a></dt>
342	383	<dd class="defbody">
343	384	Unify <var>NewGraph</var> with a new graph obtained from <var>Graph</var>

352	393	</pre>
353	394
354	395	</dd>
355		<dt class="pubdef"><a name="neighbours/3"><strong>neighbours</strong>(<var>+Vertex,
	396	<dt class="pubdef"><a id="neighbours/3"><strong>neighbours</strong>(<var>+Vertex,
356	397	+Graph, -Vertices</var>)</a></dt>
357	398	<dd class="defbody">
358	399	Unify <var>Vertices</var> with the list of neighbours of vertex <var>Vertex</var>

365	406	</pre>
366	407
367	408	</dd>
368		<dt class="pubdef"><a name="neighbors/3"><strong>neighbors</strong>(<var>+Vertex,
	409	<dt class="pubdef"><a id="neighbors/3"><strong>neighbors</strong>(<var>+Vertex,
369	410	+Graph, -Vertices</var>)</a></dt>
370	411	<dd class="defbody">
371		American version of <a name="idx:neighbours3:2176"></a><a class="pred" href="ugraphs.html#neighbours/3">neighbours/3</a>.</dd>
372		<dt class="pubdef"><a name="complement/2"><strong>complement</strong>(<var>+Graph,
	412	American version of <a id="idx:neighbours3:2180"></a><a class="pred" href="ugraphs.html#neighbours/3">neighbours/3</a>.</dd>
	413	<dt class="pubdef"><a id="complement/2"><strong>complement</strong>(<var>+Graph,
373	414	-NewGraph</var>)</a></dt>
374	415	<dd class="defbody">
375	416	Unify <var>NewGraph</var> with the graph complementary to <var>Graph</var>.

384	425	</pre>
385	426
386	427	</dd>
387		<dt class="pubdef"><a name="compose/3"><strong>compose</strong>(<var>+LeftGraph,
	428	<dt class="pubdef"><a id="compose/3"><strong>compose</strong>(<var>+LeftGraph,
388	429	+RightGraph, -NewGraph</var>)</a></dt>
389	430	<dd class="defbody">
390	431	Compose <var>NewGraph</var> by connecting the <em>drains</em> of <var>LeftGraph</var>

396	437	</pre>
397	438
398	439	</dd>
399		<dt class="pubdef"><a name="ugraph_union/3"><strong>ugraph_union</strong>(<var>+Graph1,
	440	<dt class="pubdef"><a id="ugraph_union/3"><strong>ugraph_union</strong>(<var>+Graph1,
400	441	+Graph2, -NewGraph</var>)</a></dt>
401	442	<dd class="defbody">
402	443	<var>NewGraph</var> is the union of <var>Graph1</var> and <var>Graph2</var>.

408	449	</pre>
409	450
410	451	</dd>
411		<dt class="pubdef"><a name="top_sort/2"><strong>top_sort</strong>(<var>+Graph,
	452	<dt class="pubdef"><a id="top_sort/2"><strong>top_sort</strong>(<var>+Graph,
412	453	-Sort</var>)</a></dt>
413	454	<dd class="defbody">
414	455	Generate the set of nodes <var>Sort</var> as a topological sorting of

422	463	</pre>
423	464
424	465	</dd>
425		<dt class="pubdef"><a name="top_sort/3"><strong>top_sort</strong>(<var>+Graph,
	466	<dt class="pubdef"><a id="top_sort/3"><strong>top_sort</strong>(<var>+Graph,
426	467	-Sort0, -Sort</var>)</a></dt>
427	468	<dd class="defbody">
428	469	Generate the difference list Sort-Sort0 as a topological sorting of
429	470	<var>Graph</var>, if one is possible.</dd>
430		<dt class="pubdef"><a name="transitive_closure/2"><strong>transitive_closure</strong>(<var>+Graph,
	471	<dt class="pubdef"><a id="transitive_closure/2"><strong>transitive_closure</strong>(<var>+Graph,
431	472	-Closure</var>)</a></dt>
432	473	<dd class="defbody">
433	474	Generate the graph Closure as the transitive closure of

439	480	</pre>
440	481
441	482	</dd>
442		<dt class="pubdef"><a name="reachable/3"><strong>reachable</strong>(<var>+Vertex,
	483	<dt class="pubdef"><a id="reachable/3"><strong>reachable</strong>(<var>+Vertex,
443	484	+Graph, -Vertices</var>)</a></dt>
444	485	<dd class="defbody">
445	486	Unify <var>Vertices</var> with the set of all vertices in <var>Graph</var>

+77

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193	234	</div>
194		<h2 id="sec:url"><a name="sec:A.38"><span class="sec-nr">A.38</span> <span class="sec-title">library(url):
	235	<h2 id="sec:url"><a id="sec:A.38"><span class="sec-nr">A.38</span> <span class="sec-title">library(url):
195	236	Analysing and constructing URL</span></a></h2>
196	237
197		<p><a name="sec:url"></a>
	238	<p><a id="sec:url"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="mtag">author</dt>

221	262	of the standard encountered in practical use.
222	263
223	264	<dl class="latex">
224		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="global_url/3"><strong>global_url</strong>(<var>+URL,
	265	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="global_url/3"><strong>global_url</strong>(<var>+URL,
225	266	+Base, -Global</var>)</a></dt>
226	267	<dd class="defbody">
227	268	Translate a possibly relative <var>URL</var> into an absolute one.

234	275	</dl>
235	276
236	277	</dd>
237		<dt class="pubdef"><a name="is_absolute_url/1"><strong>is_absolute_url</strong>(<var>+URL</var>)</a></dt>
	278	<dt class="pubdef"><a id="is_absolute_url/1"><strong>is_absolute_url</strong>(<var>+URL</var>)</a></dt>
238	279	<dd class="defbody">
239	280	True if <var>URL</var> is an absolute <var>URL</var>. That is, a <var>URL</var>
240	281	that starts with a protocol identifier.</dd>
241		<dt class="pubdef"><a name="http_location/2"><strong>http_location</strong>(<var>?Parts,
	282	<dt class="pubdef"><a id="http_location/2"><strong>http_location</strong>(<var>?Parts,
242	283	?Location</var>)</a></dt>
243	284	<dd class="defbody">
244	285	Construct or analyze an HTTP location. This is similar to

252	293	</pre>
253	294
254	295	<table class="arglist">
255		<tr valign="top"><td><var>Location</var> </td><td>Atom or list of
256		character codes. </td></tr>
	296	<tr><td><var>Location</var> </td><td>Atom or list of character codes. </td></tr>
257	297	</table>
258	298	</dd>
259		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="parse_url/2"><strong>parse_url</strong>(<var>?URL,
	299	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="parse_url/2"><strong>parse_url</strong>(<var>?URL,
260	300	?Attributes</var>)</a></dt>
261	301	<dd class="defbody">
262	302	Construct or analyse a <var>URL</var>. <var>URL</var> is an atom holding

324	364
325	365	<p>By instantiating the parts-list this predicate can be used to create
326	366	a <var>URL</var>.</dd>
327		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="parse_url/3"><strong>parse_url</strong>(<var>+URL,
	367	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="parse_url/3"><strong>parse_url</strong>(<var>+URL,
328	368	+BaseURL, -Attributes</var>)</a></dt>
329	369	<dd class="defbody">
330	370	Similar to <a class="pred" href="url.html#parse_url/2">parse_url/2</a>
331	371	for relative URLs. If <var>URL</var> is relative, it is resolved using
332	372	the absolute <var>URL</var> <var>BaseURL</var>.</dd>
333		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="www_form_encode/2"><strong>www_form_encode</strong>(<var>+Value,
	373	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="www_form_encode/2"><strong>www_form_encode</strong>(<var>+Value,
334	374	-XWWWFormEncoded</var>)</a></dt>
335		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="www_form_encode/2"><strong>www_form_encode</strong>(<var>-Value,
	375	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="www_form_encode/2"><strong>www_form_encode</strong>(<var>-Value,
336	376	+XWWWFormEncoded</var>)</a></dt>
337	377	<dd class="defbody">
338	378	En/decode to/from application/x-www-form-encoded. Encoding encodes all

353	393	</dl>
354	394
355	395	</dd>
356		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="set_url_encoding/2"><strong>set_url_encoding</strong>(<var>?Old,
	396	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="set_url_encoding/2"><strong>set_url_encoding</strong>(<var>?Old,
357	397	+New</var>)</a></dt>
358	398	<dd class="defbody">
359	399	Query and set the encoding for URLs. The default is <code>utf8</code>.

368	408	</dl>
369	409
370	410	</dd>
371		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="url_iri/2"><strong>url_iri</strong>(<var>+Encoded,
	411	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="url_iri/2"><strong>url_iri</strong>(<var>+Encoded,
372	412	-Decoded</var>)</a></dt>
373		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="url_iri/2"><strong>url_iri</strong>(<var>-Encoded,
	413	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="url_iri/2"><strong>url_iri</strong>(<var>-Encoded,
374	414	+Decoded</var>)</a></dt>
375	415	<dd class="defbody">
376	416	Convert between a URL, encoding in US-ASCII and an IRI. An IRI is a
377	417	fully expanded Unicode string. Unicode strings are first encoded into
378	418	UTF-8, after which %-encoding takes place.</dd>
379		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="parse_url_search/2"><strong>parse_url_search</strong>(<var>?Spec,
	419	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="parse_url_search/2"><strong>parse_url_search</strong>(<var>?Spec,
380	420	?Fields:list(Name=Value)</var>)</a></dt>
381	421	<dd class="defbody">
382	422	Construct or analyze an HTTP search specification. This deals with form
383	423	data using the MIME-type
384	424	<code>application/x-www-form-urlencoded</code> as used in HTTP GET
385	425	requests.</dd>
386		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="file_name_to_url/2"><strong>file_name_to_url</strong>(<var>+File,
	426	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="file_name_to_url/2"><strong>file_name_to_url</strong>(<var>+File,
387	427	-URL</var>)</a></dt>
388		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="file_name_to_url/2"><strong>file_name_to_url</strong>(<var>-File,
	428	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="file_name_to_url/2"><strong>file_name_to_url</strong>(<var>-File,
389	429	+URL</var>)</a></dt>
390	430	<dd class="defbody">
391	431	Translate between a filename and a file:<code>//</code> <var>URL</var>.

+79

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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 12.3</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:useresource"><a name="sec:12.3"><span class="sec-nr">12.3</span> <span class="sec-title">Using
	235	<h2 id="sec:useresource"><a id="sec:12.3"><span class="sec-nr">12.3</span> <span class="sec-title">Using
195	236	program resources</span></a></h2>
196	237
197		<a name="sec:useresource"></a>
	238	<a id="sec:useresource"></a>
198	239
199	240	<p>A <em>resource</em> is very similar to a file. Resources, however,
200	241	can be represented in two different formats: on files, as well as part
201		of the resource <em>archive</em> of a saved state (see <a name="idx:qsaveprogram2:2119"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>).
	242	of the resource <em>archive</em> of a saved state (see <a id="idx:qsaveprogram2:2123"></a><a class="pred" href="runtime.html#qsave_program/2">qsave_program/2</a>).
202	243
203	244	<p>A resource has a <em>name</em> and a <em>class</em>. The <em>source</em>
204	245	data of the resource is a file. Resources are declared by declaring the
205		predicate <a name="idx:resource3:2120"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>.
	246	predicate <a id="idx:resource3:2124"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>.
206	247	They are accessed using the predicate
207		<a name="idx:openresource3:2121"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>.
	248	<a id="idx:openresource3:2125"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>.
208	249
209	250	<p>Before going into details, let us start with an example. Short texts
210	251	can easily be expressed in Prolog source code, but long texts are

223	264	close(In)).
224	265	</pre>
225	266
226		<p>The predicate <a name="idx:help0:2122"></a><a class="pred" href="help.html#help/0">help/0</a>
	267	<p>The predicate <a id="idx:help0:2126"></a><a class="pred" href="help.html#help/0">help/0</a>
227	268	opens the resource as a Prolog stream. If we are executing this from the
228	269	development environment, this will actually return a stream to the file <code>help.txt</code>
229	270	itself. When executed from the saved state, the stream will actually be
230	271	a stream opened on the program resource file, taking care of the offset
231	272	and length of the resource.
232	273
233		<p><h3 id="sec:runtime-predicates"><a name="sec:12.3.1"><span class="sec-nr">12.3.1</span> <span class="sec-title">Resource
	274	<p><h3 id="sec:runtime-predicates"><a id="sec:12.3.1"><span class="sec-nr">12.3.1</span> <span class="sec-title">Resource
234	275	manipulation predicates</span></a></h3>
235	276
236		<a name="sec:runtime-predicates"></a>
	277	<a id="sec:runtime-predicates"></a>
237	278
238	279	<dl class="latex">
239		<dt class="pubdef"><a name="resource/3"><strong>resource</strong>(<var>+Name,
	280	<dt class="pubdef"><a id="resource/3"><strong>resource</strong>(<var>+Name,
240	281	+Class, +FileSpec</var>)</a></dt>
241	282	<dd class="defbody">
242	283	This predicate is defined as a dynamic predicate in the module

246	287	:, which are reserved for internal usage by the resource library. <var>Class</var>
247	288	describes the kind of object stored in the resource. In the current
248	289	implementation, it is just an atom. <var>FileSpec</var> is a file
249		specification that may exploit <a name="idx:filesearchpath2:2123"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	290	specification that may exploit <a id="idx:filesearchpath2:2127"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
250	291	(see
251		<a name="idx:absolutefilename2:2124"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>).
	292	<a id="idx:absolutefilename2:2128"></a><a class="pred" href="files.html#absolute_file_name/2">absolute_file_name/2</a>).
252	293
253	294	<p>Normally, resources are defined as unit clauses (facts), but the
254	295	definition of this predicate also allows for rules. For proper

258	299
259	300	<p>Dynamic rules are useful to turn all files in a certain directory
260	301	into resources, without specifying a resource for each file. For
261		example, assume the <a name="idx:filesearchpath2:2125"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a> <code>icons</code>
	302	example, assume the <a id="idx:filesearchpath2:2129"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a> <code>icons</code>
262	303	refers to the resource directory containing icon files. The following
263	304	definition makes all these images available as resources:
264	305

275	316	</pre>
276	317
277	318	</dd>
278		<dt class="pubdef"><a name="open_resource/3"><strong>open_resource</strong>(<var>+Name,
	319	<dt class="pubdef"><a id="open_resource/3"><strong>open_resource</strong>(<var>+Name,
279	320	?Class, -Stream</var>)</a></dt>
280	321	<dd class="defbody">
281	322	Opens the resource specified by <var>Name</var> and <var>Class</var>. If

284	325	<var>Stream</var> becomes a handle to a binary input stream, providing
285	326	access to the content of the resource.
286	327
287		<p>The predicate <a name="idx:openresource3:2126"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>
288		first checks <a name="idx:resource3:2127"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>.
	328	<p>The predicate <a id="idx:openresource3:2130"></a><a class="pred" href="useresource.html#open_resource/3">open_resource/3</a>
	329	first checks <a id="idx:resource3:2131"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>.
289	330	When successful it will open the returned resource source file.
290	331	Otherwise it will look in the program's resource database. When creating
291	332	a saved state, the system normally saves the resource contents into the
292	333	resource archive, but does not save the resource clauses.
293	334
294	335	<p>This way, the development environment uses the files (and
295		modifications) to the <a name="idx:resource3:2128"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>
	336	modifications) to the <a id="idx:resource3:2132"></a><a class="pred" href="useresource.html#resource/3">resource/3</a>
296	337	declarations and/or files containing resource info, thus immediately
297	338	affecting the running environment, while the runtime system quickly
298	339	accesses the system resources.
299	340	</dd>
300	341	</dl>
301	342
302		<p><h3 id="sec:swiplrc"><a name="sec:12.3.2"><span class="sec-nr">12.3.2</span> <span class="sec-title">The <b>swipl-rc</b>
	343	<p><h3 id="sec:swiplrc"><a id="sec:12.3.2"><span class="sec-nr">12.3.2</span> <span class="sec-title">The <b>swipl-rc</b>
303	344	program</span></a></h3>
304	345
305		<a name="sec:swiplrc"></a>
	346	<a id="sec:swiplrc"></a>
306	347
307	348	<p>The utility program <b>swipl-rc</b> can be used to examine and
308	349	manipulate the contents of a SWI-Prolog resource file. The options are

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193	234	</div>
194		<h2 id="sec:usingmodules"><a name="sec:3.2"><span class="sec-nr">3.2</span> <span class="sec-title">Using
	235	<h2 id="sec:usingmodules"><a id="sec:3.2"><span class="sec-nr">3.2</span> <span class="sec-title">Using
195	236	modules</span></a></h2>
196	237
197		<a name="sec:usingmodules"></a>
	238	<a id="sec:usingmodules"></a>
198	239
199	240	<p>Modules have been debated fiercely in the Prolog world. Despite all
200	241	counter-arguments we feel they are extremely useful because:

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4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.39</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.39</title><link rel="home" href="index.html">
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193	234	</div>
194		<h2 id="sec:varnumbers"><a name="sec:A.39"><span class="sec-nr">A.39</span> <span class="sec-title">library(varnumbers):
	235	<h2 id="sec:varnumbers"><a id="sec:A.39"><span class="sec-nr">A.39</span> <span class="sec-title">library(varnumbers):
195	236	Utilities for numbered terms</span></a></h2>
196	237
197		<p><a name="sec:varnumbers"></a>
	238	<p><a id="sec:varnumbers"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">See also</dt>

226	267	</pre>
227	268
228	269	<dl class="latex">
229		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="numbervars/1"><strong>numbervars</strong>(<var>+Term</var>)</a></dt>
	270	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="numbervars/1"><strong>numbervars</strong>(<var>+Term</var>)</a></dt>
230	271	<dd class="defbody">
231	272	Number variables in <var>Term</var> using $VAR(N). Equivalent to
232	273	<code>numbervars(Term, 0, _)</code>.

239	280	</dl>
240	281
241	282	</dd>
242		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="varnumbers/2"><strong>varnumbers</strong>(<var>+Term,
	283	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="varnumbers/2"><strong>varnumbers</strong>(<var>+Term,
243	284	-Copy</var>)</a></dt>
244	285	<dd class="defbody">
245	286	Inverse of <a class="pred" href="varnumbers.html#numbervars/1">numbervars/1</a>.
246	287	Equivalent to <code>varnumbers(Term, 0, Copy)</code>.</dd>
247		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="varnumbers/3"><strong>varnumbers</strong>(<var>+Term,
	288	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="varnumbers/3"><strong>varnumbers</strong>(<var>+Term,
248	289	+Start, -Copy</var>)</a></dt>
249	290	<dd class="defbody">
250	291	Inverse of <a class="pred" href="manipterm.html#numbervars/3">numbervars/3</a>.

266	307	</dl>
267	308
268	309	</dd>
269		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="max_var_number/3"><strong>max_var_number</strong>(<var>+Term,
	310	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="max_var_number/3"><strong>max_var_number</strong>(<var>+Term,
270	311	+Start, -Max</var>)</a></dt>
271	312	<dd class="defbody">
272	313	True when <var>Max</var> is the max of <var>Start</var> and the highest

285	326	</dl>
286	327
287	328	</dd>
288		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="varnumbers_names/3"><strong>varnumbers_names</strong>(<var>+Term,
	329	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="varnumbers_names/3"><strong>varnumbers_names</strong>(<var>+Term,
289	330	-Copy, -VariableNames</var>)</a></dt>
290	331	<dd class="defbody">
291	332	If <var>Term</var> is a term with numbered and named variables using the

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2	2	<html>
3	3	<head>
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	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 6.1</title><link rel="home" href="index.html">
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191	232	<a class="nav" href="modules.html"><img src="prev.gif" alt="Previous"></a>
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193	234	</div>
194		<h2 id="sec:whymodules"><a name="sec:6.1"><span class="sec-nr">6.1</span> <span class="sec-title">Why
	235	<h2 id="sec:whymodules"><a id="sec:6.1"><span class="sec-nr">6.1</span> <span class="sec-title">Why
195	236	Use Modules?</span></a></h2>
196	237
197		<a name="sec:whymodules"></a>
	238	<a id="sec:whymodules"></a>
198	239
199	240	<p>In classic Prolog systems, all predicates are organised in a single
200	241	namespace and any predicate can call any predicate. Because each

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193	234	</div>
194		<h2 id="sec:widechars"><a name="sec:2.19"><span class="sec-nr">2.19</span> <span class="sec-title">Wide
	235	<h2 id="sec:widechars"><a id="sec:2.19"><span class="sec-nr">2.19</span> <span class="sec-title">Wide
195	236	character support</span></a></h2>
196	237
197		<a name="sec:widechars"></a>
198
199		<p><a name="idx:UTF8:262"></a><a name="idx:Unicode:263"></a><a name="idx:UCS:264"></a><a name="idx:internationalization:265"></a>SWI-Prolog
	238	<a id="sec:widechars"></a>
	239
	240	<p><a id="idx:UTF8:262"></a><a id="idx:Unicode:263"></a><a id="idx:UCS:264"></a><a id="idx:internationalization:265"></a>SWI-Prolog
200	241	supports <em>wide characters</em>, characters with character codes above
201	242	255 that cannot be represented in a single <em>byte</em>.
202	243	<em>Universal Character Set</em> (UCS) is the ISO/IEC 10646 standard

208	249	as case conversion are unambiguously defined.
209	250
210	251	<p>For this reason SWI-Prolog has two representations for atoms and
211		string objects (see <a class="sec" href="strings.html">section 5.2</a>).
212		If the text fits in ISO Latin-1, it is represented as an array of 8-bit
213		characters. Otherwise the text is represented as an array of 32-bit
214		numbers. This representational issue is completely transparent to the
215		Prolog user. Users of the foreign language interface as described in <a class="sec" href="foreign.html">chapter
	252	string objects (see <a class="sec" href="strings.html#sec:5.2">section
	253	5.2</a>). If the text fits in ISO Latin-1, it is represented as an array
	254	of 8-bit characters. Otherwise the text is represented as an array of
	255	32-bit numbers. This representational issue is completely transparent to
	256	the Prolog user. Users of the foreign language interface as described in <a class="sec" href="foreign.html#sec:11">chapter
216	257	11</a> sometimes need to be aware of these issues though.
217	258
218	259	<p>Character coding comes into view when characters of strings need to

221	262	section we only deal with I/O through streams, which includes file I/O
222	263	as well as I/O through network sockets.
223	264
224		<p><h3 id="sec:encoding"><a name="sec:2.19.1"><span class="sec-nr">2.19.1</span> <span class="sec-title">Wide
	265	<p><h3 id="sec:encoding"><a id="sec:2.19.1"><span class="sec-nr">2.19.1</span> <span class="sec-title">Wide
225	266	character encodings on streams</span></a></h3>
226	267
227		<a name="sec:encoding"></a>
	268	<a id="sec:encoding"></a>
228	269
229	270	<p>Although characters are uniquely coded using the UCS standard
230	271	internally, streams and files are byte (8-bit) oriented and there are a

237	278	pairs of bytes, is also popular.
238	279
239	280	<p>Prolog I/O streams have a property called <em>encoding</em> which
240		specifies the used encoding that influences <a name="idx:getcode2:266"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>
241		and <a name="idx:putcode2:267"></a><a class="pred" href="chario.html#put_code/2">put_code/2</a>
	281	specifies the used encoding that influences <a id="idx:getcode2:266"></a><a class="pred" href="chario.html#get_code/2">get_code/2</a>
	282	and <a id="idx:putcode2:267"></a><a class="pred" href="chario.html#put_code/2">put_code/2</a>
242	283	as well as all the other text I/O predicates.
243	284
244	285	<p>The default encoding for files is derived from the Prolog flag

248	289	and the translation is left to the wide-character functions of the C
249	290	library.<sup class="fn">34<span class="fn-text">The Prolog native UTF-8
250	291	mode is considerably faster than the generic mbrtowc() one.</span></sup>
251		The encoding can be specified explicitly in <a name="idx:loadfiles2:268"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
252		for loading Prolog source with an alternative encoding, <a name="idx:open4:269"></a><a class="pred" href="IO.html#open/4">open/4</a>
253		when opening files or using <a name="idx:setstream2:270"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>
254		on any open stream. For Prolog source files we also provide the <a name="idx:encoding1:271"></a><a class="pred" href="consulting.html#encoding/1">encoding/1</a>
	292	The encoding can be specified explicitly in <a id="idx:loadfiles2:268"></a><a class="pred" href="consulting.html#load_files/2">load_files/2</a>
	293	for loading Prolog source with an alternative encoding, <a id="idx:open4:269"></a><a class="pred" href="IO.html#open/4">open/4</a>
	294	when opening files or using <a id="idx:setstream2:270"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>
	295	on any open stream. For Prolog source files we also provide the <a id="idx:encoding1:271"></a><a class="pred" href="consulting.html#encoding/1">encoding/1</a>
255	296	directive that can be used to switch between encodings that are
256	297	compatible with US-ASCII (<code>ascii</code>, <code>iso_latin_1</code>, <code>utf8</code>
257		and many locales). See also <a class="sec" href="projectfiles.html">section
258		3.1.3</a> for writing Prolog files with non-US-ASCII characters and <a class="sec" href="syntax.html">section
	298	and many locales). See also <a class="sec" href="projectfiles.html#sec:3.1.3">section
	299	3.1.3</a> for writing Prolog files with non-US-ASCII characters and <a class="sec" href="syntax.html#sec:2.16.1.8">section
259	300	2.16.1.8</a> for syntax issues. For additional information and Unicode
260	301	resources, please visit
261	302	<a class="url" href="http://www.unicode.org/">http://www.unicode.org/</a>.

299	340	<p>Note that not all encodings can represent all characters. This
300	341	implies that writing text to a stream may cause errors because the
301	342	stream cannot represent these characters. The behaviour of a stream on
302		these errors can be controlled using <a name="idx:setstream2:272"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.
	343	these errors can be controlled using <a id="idx:setstream2:272"></a><a class="pred" href="IO.html#set_stream/2">set_stream/2</a>.
303	344	Initially the terminal stream writes the characters using Prolog escape
304	345	sequences while other streams generate an I/O exception.
305	346
306		<p><h4 id="sec:bom"><a name="sec:2.19.1.1"><span class="sec-nr">2.19.1.1</span> <span class="sec-title">BOM:
	347	<p><h4 id="sec:bom"><a id="sec:2.19.1.1"><span class="sec-nr">2.19.1.1</span> <span class="sec-title">BOM:
307	348	Byte Order Mark</span></a></h4>
308	349
309		<a name="sec:bom"></a>
310
311		<p><a name="idx:BOM:273"></a><a name="idx:ByteOrderMark:274"></a>From <a class="sec" href="widechars.html">section
	350	<a id="sec:bom"></a>
	351
	352	<p><a id="idx:BOM:273"></a><a id="idx:ByteOrderMark:274"></a>From <a class="sec" href="widechars.html#sec:2.19.1">section
312	353	2.19.1</a>, you may have got the impression that text files are
313	354	complicated. This section deals with a related topic, making life often
314	355	easier for the user, but providing another worry to the programmer.

325	366	additional information revealing the encoding, making the use of a BOM
326	367	redundant or even illegal.
327	368
328		<p>The BOM is handled by SWI-Prolog <a name="idx:open4:275"></a><a class="pred" href="IO.html#open/4">open/4</a>
	369	<p>The BOM is handled by SWI-Prolog <a id="idx:open4:275"></a><a class="pred" href="IO.html#open/4">open/4</a>
329	370	predicate. By default, text files are probed for the BOM when opened for
330	371	reading. If a BOM is found, the encoding is set accordingly and the
331		property <code>bom(true)</code> is available through <a name="idx:streamproperty2:276"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>.
	372	property <code>bom(true)</code> is available through <a id="idx:streamproperty2:276"></a><a class="pred" href="IO.html#stream_property/2">stream_property/2</a>.
332	373	When opening a file for writing, writing a BOM can be requested using
333	374	the option <code>bom(true)</code> with
334		<a name="idx:open4:277"></a><a class="pred" href="IO.html#open/4">open/4</a>.
	375	<a id="idx:open4:277"></a><a class="pred" href="IO.html#open/4">open/4</a>.
335	376
336	377	<p></body></html>⏎

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2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section A.18</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section A.18</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
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193	234	</div>
194		<h2 id="sec:www_browser"><a name="sec:A.18"><span class="sec-nr">A.18</span> <span class="sec-title">library(www_browser):
	235	<h2 id="sec:www_browser"><a id="sec:A.18"><span class="sec-nr">A.18</span> <span class="sec-title">library(www_browser):
195	236	Activating your Web-browser</span></a></h2>
196	237
197		<a name="sec:www_browser"></a>
	238	<a id="sec:www_browser"></a>
198	239
199	240	<p>This library deals with the very system-dependent task of opening a
200	241	web page in a browser. See also <code>library(url)</code> and the HTTP
201	242	package.
202	243
203	244	<dl class="latex">
204		<dt class="pubdef"><a name="www_open_url/1"><strong>www_open_url</strong>(<var>+URL</var>)</a></dt>
	245	<dt class="pubdef"><a id="www_open_url/1"><strong>www_open_url</strong>(<var>+URL</var>)</a></dt>
205	246	<dd class="defbody">
206	247	Open <var>URL</var> in an external web browser. The reason to place this
207	248	in the library is to centralise the maintenance on this highly platform-

210	251	<p>
211	252	<ul class="latex">
212	253	<li><i>MS-Windows</i><br>
213		If it detects MS-Windows it uses <a name="idx:winshell2:2148"></a><a class="pred" href="system.html#win_shell/2">win_shell/2</a>
	254	If it detects MS-Windows it uses <a id="idx:winshell2:2152"></a><a class="pred" href="system.html#win_shell/2">win_shell/2</a>
214	255	to open the <var>URL</var>. The behaviour and browser started depends on
215	256	the version of Windows and Windows-shell configuration, but in general
216	257	it should be the behaviour expected by the user.
217	258
218	259	<p>
219	260	<li><i>Other platforms</i><br>
220		On other platforms it tests the environment variable (see <a name="idx:getenv2:2149"></a><a class="pred" href="system.html#getenv/2">getenv/2</a>)
	261	On other platforms it tests the environment variable (see <a id="idx:getenv2:2153"></a><a class="pred" href="system.html#getenv/2">getenv/2</a>)
221	262	named <code>BROWSER</code> or uses <b>netscape</b> if this variable is
222	263	not set. If the browser is either <code>mozilla</code> or <code>netscape</code>,
223		<a name="idx:wwwopenurl1:2150"></a><a class="pred" href="www_browser.html#www_open_url/1">www_open_url/1</a>
	264	<a id="idx:wwwopenurl1:2154"></a><a class="pred" href="www_browser.html#www_open_url/1">www_open_url/1</a>
224	265	first tries to open a new window on a running browser using the <code>-remote</code>
225	266	option of Netscape. If this fails or the browser is not <code>mozilla</code>
226	267	or <code>netscape</code> the system simply passes the URL as first

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1	1
2	2	<html>
3	3	<head>
4		<title>SWI-Prolog 7.6.2 Reference Manual: Section 3.7</title><link rel="home" href="index.html">
	4	<title>SWI-Prolog 7.7.4 Reference Manual: Section 3.7</title><link rel="home" href="index.html">
5	5	<link rel="contents" href="Contents.html">
6	6	<link rel="index" href="DocIndex.html">
7	7	<link rel="summary" href="summary.html">

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193	234	</div>
194		<h2 id="sec:xref"><a name="sec:3.7"><span class="sec-nr">3.7</span> <span class="sec-title">Cross-referencer</span></a></h2>
195
196		<a name="sec:xref"></a>
	235	<h2 id="sec:xref"><a id="sec:3.7"><span class="sec-nr">3.7</span> <span class="sec-title">Cross-referencer</span></a></h2>
	236
	237	<a id="sec:xref"></a>
197	238
198	239	<p>A cross-referencer is a tool that examines the caller-callee relation
199	240	between predicates, and, using this information to explicate dependency

201	242	and predicates for which no callers can be found. Cross-referencing is
202	243	useful during program development, reorganisation, clean-up, porting and
203	244	other program maintenance tasks. The dynamic nature of Prolog makes the
204		task non-trivial. Goals can be created dynamically using <a name="idx:call1:322"></a><a class="pred" href="metacall.html#call/1">call/1</a>
	245	task non-trivial. Goals can be created dynamically using <a id="idx:call1:322"></a><a class="pred" href="metacall.html#call/1">call/1</a>
205	246	after construction of a goal term. Abstract interpretation can find some
206	247	of these calls, but they can also come from external communication,
207	248	making it impossible to predict the callee. In other words, the

211	252
212	253	<p>SWI-Prolog's cross-referencer is split into two parts. The standard
213	254	Prolog library <code>library(prolog_xref)</code> is an extensible
214		library for information gathering described in <a class="sec" href="prolog_xref.html">section
	255	library for information gathering described in <a class="sec" href="prolog_xref.html#sec:A.27">section
215	256	A.27</a>, and the XPCE library <code>library(pce_xref)</code> provides a
216	257	graphical front-end for the cross-referencer described here. We
217	258	demonstrate the tool on CHAT80, a natural language question and answer
218	259	system by Fernando C.N. Pereira and David H.D. Warren.
219	260
220	261	<dl class="latex">
221		<dt class="pubdef"><a name="gxref/0"><strong>gxref</strong></a></dt>
	262	<dt class="pubdef"><a id="gxref/0"><strong>gxref</strong></a></dt>
222	263	<dd class="defbody">
223	264	Run cross-referencer on all currently loaded files and present a
224	265	graphical overview of the result. As the predicate operates on the

227	268	</dd>
228	269	</dl>
229	270
230		<p><a name="fig:xrefchatfile"></a><div style="text-align:center"><img src="xrefchatfile.gif"></div>
	271	<p><a id="fig:xrefchatfile"></a><div style="text-align:center"><img src="xrefchatfile.gif"></div>
231	272	<div class="caption"><b>Figure 3 : </b>File info for <code>chattop.pl</code>,
232	273	part of CHAT80</div>
233	274

235	276	3</a>) provides browsers for loaded files and predicates. To avoid long
236	277	file paths, the file hierarchy has three main branches. The first is the
237	278	current directory holding the sources. The second is marked <code>alias</code>,
238		and below it are the file-search-path aliases (see <a name="idx:filesearchpath2:323"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
	279	and below it are the file-search-path aliases (see <a id="idx:filesearchpath2:323"></a><a class="pred" href="consulting.html#file_search_path/2">file_search_path/2</a>
239	280	and
240		<a name="idx:absolutefilename3:324"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>).
	281	<a id="idx:absolutefilename3:324"></a><a class="pred" href="files.html#absolute_file_name/3">absolute_file_name/3</a>).
241	282	Here you find files loaded from the system as well as modules of the
242	283	program loaded from other locations using the file search path. All
243	284	loaded files that fall outside these categories are below the last

262	303	file. Left-clicking opens a menu to open the definition or select one of
263	304	the callers.
264	305
265		<p><a name="fig:xrefchatdep"></a><div style="text-align:center"><img src="xrefchatdep.gif"></div>
	306	<p><a id="fig:xrefchatdep"></a><div style="text-align:center"><img src="xrefchatdep.gif"></div>
266	307	<div class="caption"><b>Figure 4 : </b>Dependencies between source files
267	308	of CHAT80</div>
268	309

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184	225	</style>
185	226	</head>
186	227	<body style="background:white">

191	232	<a class="nav" href="varnumbers.html"><img src="prev.gif" alt="Previous"></a>
192	233	<a class="nav" href="hack.html"><img src="next.gif" alt="Next"></a>
193	234	</div>
194		<h2 id="sec:yall"><a name="sec:A.40"><span class="sec-nr">A.40</span> <span class="sec-title">library(yall):
	235	<h2 id="sec:yall"><a id="sec:A.40"><span class="sec-nr">A.40</span> <span class="sec-title">library(yall):
195	236	Lambda expressions</span></a></h2>
196	237
197		<p><a name="sec:yall"></a>
	238	<p><a id="sec:yall"></a>
198	239
199	240	<dl class="tags">
200	241	<dt class="tag">author</dt>

282	323	development of this module was sponsored by Kyndi, Inc.
283	324
284	325	<dl class="latex">
285		<dt class="pubdef"><a name=">>/2"><var>+Parameters</var> <strong>>></strong> <var>+Lambda</var></a></dt>
286		<dt class="pubdef"><a name=">>/3"><strong>>></strong>(<var>+Parameters,
	326	<dt class="pubdef"><a id=">>/2"><var>+Parameters</var> <strong>>></strong> <var>+Lambda</var></a></dt>
	327	<dt class="pubdef"><a id=">>/3"><strong>>></strong>(<var>+Parameters,
287	328	+Lambda, ?A1</var>)</a></dt>
288		<dt class="pubdef"><a name=">>/4"><strong>>></strong>(<var>+Parameters,
	329	<dt class="pubdef"><a id=">>/4"><strong>>></strong>(<var>+Parameters,
289	330	+Lambda, ?A1, ?A2</var>)</a></dt>
290		<dt class="pubdef"><a name=">>/5"><strong>>></strong>(<var>+Parameters,
	331	<dt class="pubdef"><a id=">>/5"><strong>>></strong>(<var>+Parameters,
291	332	+Lambda, ?A1, ?A2, ?A3</var>)</a></dt>
292		<dt class="pubdef"><a name=">>/6"><strong>>></strong>(<var>+Parameters,
	333	<dt class="pubdef"><a id=">>/6"><strong>>></strong>(<var>+Parameters,
293	334	+Lambda, ?A1, ?A2, ?A3, ?A4</var>)</a></dt>
294		<dt class="pubdef"><a name=">>/7"><strong>>></strong>(<var>+Parameters,
	335	<dt class="pubdef"><a id=">>/7"><strong>>></strong>(<var>+Parameters,
295	336	+Lambda, ?A1, ?A2, ?A3, ?A4, ?A5</var>)</a></dt>
296		<dt class="pubdef"><a name=">>/8"><strong>>></strong>(<var>+Parameters,
	337	<dt class="pubdef"><a id=">>/8"><strong>>></strong>(<var>+Parameters,
297	338	+Lambda, ?A1, ?A2, ?A3, ?A4, ?A5, ?A6</var>)</a></dt>
298		<dt class="pubdef"><a name=">>/9"><strong>>></strong>(<var>+Parameters,
	339	<dt class="pubdef"><a id=">>/9"><strong>>></strong>(<var>+Parameters,
299	340	+Lambda, ?A1, ?A2, ?A3, ?A4, ?A5, ?A6, ?A7</var>)</a></dt>
300	341	<dd class="defbody">
301	342	Calls a copy of <var>Lambda</var>. This is similar to <code>call(Lambda,A1,...)</code>,

309	350	<li>Possible excess arguments are passed by position.
310	351	</ul>
311	352	<table class="arglist">
312		<tr valign="top"><td><var>Parameters</var> </td><td>is either a plain
313		list of parameters or a term
	353	<tr><td><var>Parameters</var> </td><td>is either a plain list of
	354	parameters or a term
314	355	<code>{Free}/List</code>. <var>Free</var> represents variables that are
315	356	shared between the context and the <var>Lambda</var> term. This is
316	357	needed for compiling <var>Lambda</var> expressions. </td></tr>
317	358	</table>
318	359	</dd>
319		<dt class="pubdef"><a name="//2"><var>+Free</var> <strong>/</strong> <var>:Lambda</var></a></dt>
320		<dt class="pubdef"><a name="//3"><strong>/</strong>(<var>+Free, :Lambda,
	360	<dt class="pubdef"><a id="//2"><var>+Free</var> <strong>/</strong> <var>:Lambda</var></a></dt>
	361	<dt class="pubdef"><a id="//3"><strong>/</strong>(<var>+Free, :Lambda,
321	362	?A1</var>)</a></dt>
322		<dt class="pubdef"><a name="//4"><strong>/</strong>(<var>+Free, :Lambda,
	363	<dt class="pubdef"><a id="//4"><strong>/</strong>(<var>+Free, :Lambda,
323	364	?A1, ?A2</var>)</a></dt>
324		<dt class="pubdef"><a name="//5"><strong>/</strong>(<var>+Free, :Lambda,
	365	<dt class="pubdef"><a id="//5"><strong>/</strong>(<var>+Free, :Lambda,
325	366	?A1, ?A2, ?A3</var>)</a></dt>
326		<dt class="pubdef"><a name="//6"><strong>/</strong>(<var>+Free, :Lambda,
	367	<dt class="pubdef"><a id="//6"><strong>/</strong>(<var>+Free, :Lambda,
327	368	?A1, ?A2, ?A3, ?A4</var>)</a></dt>
328		<dt class="pubdef"><a name="//7"><strong>/</strong>(<var>+Free, :Lambda,
	369	<dt class="pubdef"><a id="//7"><strong>/</strong>(<var>+Free, :Lambda,
329	370	?A1, ?A2, ?A3, ?A4, ?A5</var>)</a></dt>
330		<dt class="pubdef"><a name="//8"><strong>/</strong>(<var>+Free, :Lambda,
	371	<dt class="pubdef"><a id="//8"><strong>/</strong>(<var>+Free, :Lambda,
331	372	?A1, ?A2, ?A3, ?A4, ?A5, ?A6</var>)</a></dt>
332		<dt class="pubdef"><a name="//9"><strong>/</strong>(<var>+Free, :Lambda,
	373	<dt class="pubdef"><a id="//9"><strong>/</strong>(<var>+Free, :Lambda,
333	374	?A1, ?A2, ?A3, ?A4, ?A5, ?A6, ?A7</var>)</a></dt>
334	375	<dd class="defbody">
335	376	Shorthand for <code>Free/[]>>Lambda</code>. This is the same as

357	398	</pre>
358	399
359	400	</dd>
360		<dt class="pubdef"><span class="pred-tag">[semidet]</span><a name="is_lambda/1"><strong>is_lambda</strong>(<var>@Term</var>)</a></dt>
	401	<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="is_lambda/1"><strong>is_lambda</strong>(<var>@Term</var>)</a></dt>
361	402	<dd class="defbody">
362	403	True if <var>Term</var> is a valid Lambda expression.</dd>
363		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="lambda_calls/2"><strong>lambda_calls</strong>(<var>+LambdaExpression,
	404	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="lambda_calls/2"><strong>lambda_calls</strong>(<var>+LambdaExpression,
364	405	-Goal</var>)</a></dt>
365		<dt class="pubdef"><span class="pred-tag">[det]</span><a name="lambda_calls/3"><strong>lambda_calls</strong>(<var>+LambdaExpression,
	406	<dt class="pubdef"><span class="pred-tag">[det]</span><a id="lambda_calls/3"><strong>lambda_calls</strong>(<var>+LambdaExpression,
366	407	+ExtraArgs, -Goal</var>)</a></dt>
367	408	<dd class="defbody">
368	409	<var>Goal</var> is the goal called if call/N is applied to

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63	63	\newcommand{\vmonth}{November}
64	64	\newcommand{\vyear}{2017}

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179	220	</head>
180	221	<body style="background:white">

189	230	started using SWI-Prolog on MS-Windows. It also describes the components
190	231	and issues that are specific to MS-Windows. It is by no means a manual
191	232	or Prolog tutorial. The reference manual is available online or can be
192		downloaded in HTML and PDF format from the http://www.swi-prolog.org/SWI-Prolog
193		website , which also provides links to books, online tutorials and other
194		Prolog-related material.
	233	downloaded in HTML and PDF format from the <a class="url" href="http://www.swi-prolog.org/">SWI-Prolog
	234	website</a>, which also provides links to books, online tutorials and
	235	other Prolog-related material.
195	236	</div>
196	237
197		<h1><a name="document-contents">Table of Contents</a></h1>
	238	<h1><a id="document-contents">Table of Contents</a></h1>
198	239
199	240	<div class="toc">
200	241	<div class="toc-h2"><a class="sec" href="#sec:1"><span class="sec-nr">1</span> <span class="sec-title">Using

239	280	SWI-Prolog</span></a></div>
240	281	</div>
241	282
242		<h2><a name="sec:1"><span class="sec-nr">1</span> <span class="sec-title">Using
	283	<h2><a id="sec:1"><span class="sec-nr">1</span> <span class="sec-title">Using
243	284	SWI-Prolog</span></a></h2>
244	285
245	286	<p>
246	287
247		<h3><a name="sec:1.1"><span class="sec-nr">1.1</span> <span class="sec-title">Starting
	288	<h3><a id="sec:1.1"><span class="sec-nr">1.1</span> <span class="sec-title">Starting
248	289	Prolog and loading a program</span></a></h3>
249	290
250	291	<p>The SWI-Prolog executable <b>swipl-win.exe</b> can be started from

270	311	<code>MyDocuments\Prolog</code>. This folder is created if it does not
271	312	exist.
272	313
273		<p><h3 id="sec:execquery"><a name="sec:1.2"><span class="sec-nr">1.2</span> <span class="sec-title">Executing
	314	<p><h3 id="sec:execquery"><a id="sec:1.2"><span class="sec-nr">1.2</span> <span class="sec-title">Executing
274	315	a query</span></a></h3>
275	316
276		<a name="sec:execquery"></a>
	317	<a id="sec:execquery"></a>
277	318
278	319	<p>After loading a program, one can ask Prolog queries about the
279	320	program. The query below asks Prolog what food `sam' likes. The system

302	343	that, when executed, produces the same set of answers as the original
303	344	program.
304	345
305		<p><h3 id="sec:menu"><a name="sec:1.3"><span class="sec-nr">1.3</span> <span class="sec-title">Menu
	346	<p><h3 id="sec:menu"><a id="sec:1.3"><span class="sec-nr">1.3</span> <span class="sec-title">Menu
306	347	commands</span></a></h3>
307	348
308		<a name="sec:menu"></a>
	349	<a id="sec:menu"></a>
309	350
310	351	<p>The SWI-Prolog console provided by <b>swipl-win.exe</b> has a menu
311	352	for accessing the most commonly used commands. We assume not all menu

315	356	<dt><b>File/Reload modified files</b></dt>
316	357	<dd class="defbody">
317	358	This menu reloads all loaded source files that have been modified using
318		the <a name="idx:make0:1"></a><a class="pred" href="#make/0">make/0</a>
	359	the <a id="idx:make0:1"></a><a class="pred" href="#make/0">make/0</a>
319	360	command described in <a class="sec" href="#sec:1.5">section 1.5</a>.</dd>
320	361	<dt><b>File/Navigator ...</b></dt>
321	362	<dd class="defbody">

367	408	</dd>
368	409	</dl>
369	410
370		<p><h3 id="sec:edit"><a name="sec:1.4"><span class="sec-nr">1.4</span> <span class="sec-title">Editing
	411	<p><h3 id="sec:edit"><a id="sec:1.4"><span class="sec-nr">1.4</span> <span class="sec-title">Editing
371	412	Prolog programs</span></a></h3>
372	413
373		<a name="sec:edit"></a>
	414	<a id="sec:edit"></a>
374	415
375	416	<p>There are three options for editing. One is to run an editor of
376		choice in a separate window and use the <a name="idx:make0:2"></a><a class="pred" href="#make/0">make/0</a>
	417	choice in a separate window and use the <a id="idx:make0:2"></a><a class="pred" href="#make/0">make/0</a>
377	418	command described below to reload modified files. In addition to this
378	419	option Prolog can be used to locate predicates, modules and loaded files
379		by specifying the editor of choice for use with the <a name="idx:edit1:3"></a><a class="pred" href="#edit/1">edit/1</a>
	420	by specifying the editor of choice for use with the <a id="idx:edit1:3"></a><a class="pred" href="#edit/1">edit/1</a>
380	421	command, described below. This is achieved by editing the
381	422	personalisation file (see <a class="sec" href="#sec:1.3">section 1.3</a>)
382	423	and following the instructions in the comments.

390	431	<a class="url" href="http://www.swi-prolog.org/IDE.html">http://www.swi-prolog.org/IDE.html</a>
391	432	for an up-to-date overview.
392	433
393		<p><h3 id="sec:commands"><a name="sec:1.5"><span class="sec-nr">1.5</span> <span class="sec-title">Some
	434	<p><h3 id="sec:commands"><a id="sec:1.5"><span class="sec-nr">1.5</span> <span class="sec-title">Some
394	435	useful commands</span></a></h3>
395	436
396		<a name="sec:commands"></a>
	437	<a id="sec:commands"></a>
397	438
398	439	<p>This section provides a very brief overview of important or commonly
399	440	used SWI-Prolog predicates to control the environment.
400	441
401	442	<dl class="latex">
402		<dt class="pubdef"><a name="consult/1"><strong>consult</strong>(<var>:File</var>)</a></dt>
	443	<dt class="pubdef"><a id="consult/1"><strong>consult</strong>(<var>:File</var>)</a></dt>
403	444	<dd class="defbody">
404	445	Load a source file. On Windows, folders may be specified with the
405	446	DOS/Windows <code><code>\</code></code>, which must be escaped, or by

410	451	as well as the selected alternative) can be omitted. Here are some
411	452	examples:
412	453
413		<p><table border="0" frame="void" rules="groups" style="margin:auto">
414		<tr valign="top"><td><code>?- consult(likes).</code></td><td>Load <code>likes.pl</code>
415		from the current folder (see <a name="idx:pwd0:4"></a><a class="pred" href="#pwd/0">pwd/0</a>). </td></tr>
416		<tr valign="top"><td><code>?- ['C:/Program Files/pl/demo/likes']</code></td><td>Load <code>likes.pl</code>
	454	<p><table class="latex frame-void center">
	455	<tr><td><code>?- consult(likes).</code></td><td>Load <code>likes.pl</code>
	456	from the current folder (see <a id="idx:pwd0:4"></a><a class="pred" href="#pwd/0">pwd/0</a>). </td></tr>
	457	<tr><td><code>?- ['C:/Program Files/pl/demo/likes']</code></td><td>Load <code>likes.pl</code>
417	458	using absolute path. </td></tr>
418		<tr valign="top"><td><code>?- ['C:<code>\</code><code>\</code>Program Files<code>\</code><code>\</code>pl<code>\</code><code>\</code>demo<code>\</code><code>\</code>likes']</code></td><td>Same
	459	<tr><td><code>?- ['C:<code>\</code><code>\</code>Program Files<code>\</code><code>\</code>pl<code>\</code><code>\</code>demo<code>\</code><code>\</code>likes']</code></td><td>Same
419	460	using Windows-style path name </td></tr>
420	461	</table>
421	462	</dd>
422		<dt class="pubdef"><a name="pwd/0"><strong>pwd</strong></a></dt>
	463	<dt class="pubdef"><a id="pwd/0"><strong>pwd</strong></a></dt>
423	464	<dd class="defbody">
424	465	Print working directory (folder).</dd>
425		<dt class="pubdef"><a name="ls/0"><strong>ls</strong></a></dt>
	466	<dt class="pubdef"><a id="ls/0"><strong>ls</strong></a></dt>
426	467	<dd class="defbody">
427	468	List files in current directory.</dd>
428		<dt class="pubdef"><a name="edit/0"><strong>edit</strong></a></dt>
	469	<dt class="pubdef"><a id="edit/0"><strong>edit</strong></a></dt>
429	470	<dd class="defbody">
430	471	If Prolog is started by opening a <code>.pl</code> file in the explorer,
431	472	edit this file. Also available from the menu.</dd>
432		<dt class="pubdef"><a name="edit/1"><strong>edit</strong>(<var>+Spec</var>)</a></dt>
	473	<dt class="pubdef"><a id="edit/1"><strong>edit</strong>(<var>+Spec</var>)</a></dt>
433	474	<dd class="defbody">
434	475	Edit file, predicate, module, etc., with the given name. If multiple
435	476	items are named <var>Spec</var> it prompts for the desired alternative.</dd>
436		<dt class="pubdef"><a name="make/0"><strong>make</strong></a></dt>
	477	<dt class="pubdef"><a id="make/0"><strong>make</strong></a></dt>
437	478	<dd class="defbody">
438	479	Reload all files that have been changed since they were last loaded.
439	480	Normally used after editing one or more files.</dd>
440		<dt class="pubdef"><a name="gtrace/0"><strong>gtrace</strong></a></dt>
	481	<dt class="pubdef"><a id="gtrace/0"><strong>gtrace</strong></a></dt>
441	482	<dd class="defbody">
442	483	Start the graphical debugger. There are three ways to use this. Entered
443	484	as a single goal at the top level, the next query will be traced.

453	494	</pre>
454	495
455	496	</dd>
456		<dt class="pubdef"><a name="trace/0"><strong>trace</strong></a></dt>
	497	<dt class="pubdef"><a id="trace/0"><strong>trace</strong></a></dt>
457	498	<dd class="defbody">
458	499	Same as gtrace, but text-based on the console.</dd>
459		<dt class="pubdef"><a name="apropos/1"><strong>apropos</strong>(<var>+Keyword</var>)</a></dt>
	500	<dt class="pubdef"><a id="apropos/1"><strong>apropos</strong>(<var>+Keyword</var>)</a></dt>
460	501	<dd class="defbody">
461	502	Search for all predicates that contain <var>Keyword</var> in their name
462	503	or short description. If a GUI environment is available the results are
463		hyperlinks. Otherwise use <a name="idx:help1:5"></a><a class="pred" href="#help/1">help/1</a>
	504	hyperlinks. Otherwise use <a id="idx:help1:5"></a><a class="pred" href="#help/1">help/1</a>
464	505	to get details on selected hits.</dd>
465		<dt class="pubdef"><a name="help/1"><strong>help</strong>(<var>+Spec</var>)</a></dt>
	506	<dt class="pubdef"><a id="help/1"><strong>help</strong>(<var>+Spec</var>)</a></dt>
466	507	<dd class="defbody">
467	508	Give help on <var>Spec</var>, which is normally the name of a predicate
468	509	or C interface function.

471	512
472	513	<p>
473	514
474		<h2><a name="sec:2"><span class="sec-nr">2</span> <span class="sec-title">Using
	515	<h2><a id="sec:2"><span class="sec-nr">2</span> <span class="sec-title">Using
475	516	SWI-Prolog with C/C++</span></a></h2>
476	517
477		<p>Using http://www.mingw.orgMinGW or a compiler with a compatible
478		calling format you can write C or C++ code that can be loaded into
479		SWI-Prolog and called as a predicate. You can also embed SWI-Prolog in
480		C/C++ applications.
	518	<p>Using <a class="url" href="http://www.mingw.org">MinGW</a> or a
	519	compiler with a compatible calling format you can write C or C++ code
	520	that can be loaded into SWI-Prolog and called as a predicate. You can
	521	also embed SWI-Prolog in C/C++ applications.
481	522
482	523	<p>Details on how to interact with Prolog are in the
483		http://www.swi-prolog.org/pldoc/refman/SWI-Prolog reference manual . The
484		mailing list archives and TWiki web provide problems and solutions to
485		the many problems that may occur. Documentation of the
	524	<a class="url" href="http://www.swi-prolog.org/pldoc/refman/">SWI-Prolog
	525	reference manual</a>. The mailing list archives and TWiki web provide
	526	problems and solutions to the many problems that may occur.
	527	Documentation of the
486	528	<code>SWI-cpp.h</code> C++ include file is available from the
487		http://www.swi-prolog.org/pldoc/package/pl2cpp.htmlpackage documentation
488		. This section only discusses some Windows-specific issues.
489
490		<p>
491
492		<h3><a name="sec:2.1"><span class="sec-nr">2.1</span> <span class="sec-title">Using
	529	<a class="url" href="http://www.swi-prolog.org/pldoc/package/pl2cpp.html">package
	530	documentation</a>. This section only discusses some Windows-specific
	531	issues.
	532
	533	<p>
	534
	535	<h3><a id="sec:2.1"><span class="sec-nr">2.1</span> <span class="sec-title">Using
493	536	MSVC</span></a></h3>
494	537
495	538	<blockquote> Because the current versions of SWI-Prolog are compiled and

529	572
530	573	<p>To create an executable that does not rely on Prolog one must create
531	574	a saved state of the required Prolog code and attach this to the
532		executable. Creating saved states is described with <a name="idx:qsaveprogram2:6"></a><span class="pred-ext">qsave_program/2</span>
	575	executable. Creating saved states is described with <a id="idx:qsaveprogram2:6"></a><span class="pred-ext">qsave_program/2</span>
533	576	in the reference manual. This can be attached to a state using the DOS
534	577	command below to create <code>final.exe</code> from the executable
535	578	produced by MSVC and the generated saved state.

540	583
541	584	<p>
542	585
543		<h3><a name="sec:2.2"><span class="sec-nr">2.2</span> <span class="sec-title">Using
	586	<h3><a id="sec:2.2"><span class="sec-nr">2.2</span> <span class="sec-title">Using
544	587	swipl-ld.exe</span></a></h3>
545	588
546	589	<p>The <b>swipl-ld.exe</b> automates most of the above complications and

564	607
565	608	<p>
566	609
567		<h2><a name="sec:3"><span class="sec-nr">3</span> <span class="sec-title">The
	610	<h2><a id="sec:3"><span class="sec-nr">3</span> <span class="sec-title">The
568	611	installation</span></a></h2>
569	612
570		<p><h3 id="sec:winver"><a name="sec:3.1"><span class="sec-nr">3.1</span> <span class="sec-title">Supported
	613	<p><h3 id="sec:winver"><a id="sec:3.1"><span class="sec-nr">3.1</span> <span class="sec-title">Supported
571	614	Windows versions</span></a></h3>
572	615
573		<a name="sec:winver"></a>
	616	<a id="sec:winver"></a>
574	617
575	618	<p>SWI-Prolog requiring Windows XP or later (XP, Vista, Windows-7). The
576	619	download site of SWI-Prolog contains older binaries that run on older
577	620	versions of Windows. We provide both 32-bit and 64-bit installers.
578	621
579		<p><h3 id="sec:ext"><a name="sec:3.2"><span class="sec-nr">3.2</span> <span class="sec-title">Choosing
	622	<p><h3 id="sec:ext"><a id="sec:3.2"><span class="sec-nr">3.2</span> <span class="sec-title">Choosing
580	623	the file extension</span></a></h3>
581	624
582		<a name="sec:ext"></a>
	625	<a id="sec:ext"></a>
583	626
584	627	<p>By default, Prolog uses the <code>.pl</code> extension to indicate
585	628	Prolog source files. Unfortunately this extension conflicts with the

594	637
595	638	<p>
596	639
597		<h3><a name="sec:3.3"><span class="sec-nr">3.3</span> <span class="sec-title">Installed
	640	<h3><a id="sec:3.3"><span class="sec-nr">3.3</span> <span class="sec-title">Installed
598	641	programs</span></a></h3>
599	642
600	643	<p>The table below lists the installed components. Some components are

603	646	of required libraries using different naming conventions. This will
604	647	probably be synchronised in the future.
605	648
606		<p><table border="2" frame="box" rules="groups" style="margin:auto">
607		<tr valign="top"><td colspan=2 align=center>Programs</tr>
608		<tbody>
609		<tr valign="top"><td><code>bin\swipl-win.exe</code> </td><td>Default
	649	<p><table class="latex frame-box center">
	650	<tr><td colspan=2 align=center>Programs</tr>
	651	<tr class="hline"><td><code>bin\swipl-win.exe</code> </td><td>Default
610	652	Windows application for interactive use. </td></tr>
611		<tr valign="top"><td><code>bin\swipl.exe</code> </td><td>Console-based
612		version for scripting purposes. </td></tr>
613		<tbody>
614		<tr valign="top"><td colspan=2 align=center>Utilities</tr>
615		<tbody>
616		<tr valign="top"><td><code>bin\swipl-ld.exe</code> </td><td>Linker
	653	<tr><td><code>bin\swipl.exe</code> </td><td>Console-based version for
	654	scripting purposes. </td></tr>
	655	<tr class="hline"><td colspan=2 align=center>Utilities</tr>
	656	<tr class="hline"><td><code>bin\swipl-ld.exe</code> </td><td>Linker
617	657	front-end to make single-file mixed Prolog/C/C++ executables. </td></tr>
618		<tr valign="top"><td><code>bin\swipl-rc.exe</code> </td><td>Manipulate
619		Prolog resource files. </td></tr>
620		<tbody>
621		<tr valign="top"><td colspan=2 align=center>Important directories</tr>
622		<tbody>
623		<tr valign="top"><td><code>bin</code> </td><td>Executables and DLL files </td></tr>
624		<tr valign="top"><td><code>library</code> </td><td>Prolog library </td></tr>
625		<tr valign="top"><td><code>boot</code> </td><td>Sources for system
626		predicates </td></tr>
627		<tr valign="top"><td><code>include</code> </td><td>C/C++ header files
628		for embedding or to create extensions </td></tr>
629		<tr valign="top"><td><code>xpce</code> </td><td>XPCE graphics system </td></tr>
630		<tr valign="top"><td><code>xpce\prolog\lib</code> </td><td>XPCE/Prolog
631		library </td></tr>
632		<tbody>
633		<tr valign="top"><td colspan=2 align=center>DLLs and other supporting
	658	<tr><td><code>bin\swipl-rc.exe</code> </td><td>Manipulate Prolog
	659	resource files. </td></tr>
	660	<tr class="hline"><td colspan=2 align=center>Important directories</tr>
	661	<tr class="hline"><td><code>bin</code> </td><td>Executables and DLL
	662	files </td></tr>
	663	<tr><td><code>library</code> </td><td>Prolog library </td></tr>
	664	<tr><td><code>boot</code> </td><td>Sources for system predicates </td></tr>
	665	<tr><td><code>include</code> </td><td>C/C++ header files for embedding
	666	or to create extensions </td></tr>
	667	<tr><td><code>xpce</code> </td><td>XPCE graphics system </td></tr>
	668	<tr><td><code>xpce\prolog\lib</code> </td><td>XPCE/Prolog library </td></tr>
	669	<tr class="hline"><td colspan=2 align=center>DLLs and other supporting
634	670	files</tr>
635		<tbody>
636		<tr valign="top"><td><code>boot32.prc</code> </td><td>Initial Prolog
	671	<tr class="hline"><td><code>boot32.prc</code> </td><td>Initial Prolog
637	672	state (32-bits) </td></tr>
638		<tr valign="top"><td><code>boot64.prc</code> </td><td>Initial Prolog
639		state (64-bits) </td></tr>
640		<tr valign="top"><td><code>\bin\libswipl.dll</code> </td><td>The Prolog
641		kernel </td></tr>
642		<tr valign="top"><td><code>\bin\plterm.dll</code> </td><td>The window
643		for <b>swipl-win.exe</b> </td></tr>
644		<tr valign="top"><td><code>\bin\pthreadVC2.dll</code></td><td>POSIX
645		thread runtime library (64-bits) </td></tr>
646		<tbody>
647		<tr valign="top"><td colspan=2 align=center>Extension DLLs (plugins)</tr>
648		<tbody>
649		<tr valign="top"><td><code>\bin\cgi.dll</code> </td><td>Gather CGI GET
	673	<tr><td><code>boot64.prc</code> </td><td>Initial Prolog state (64-bits) </td></tr>
	674	<tr><td><code>\bin\libswipl.dll</code> </td><td>The Prolog kernel </td></tr>
	675	<tr><td><code>\bin\plterm.dll</code> </td><td>The window for <b>swipl-win.exe</b> </td></tr>
	676	<tr><td><code>\bin\pthreadVC2.dll</code></td><td>POSIX thread runtime
	677	library (64-bits) </td></tr>
	678	<tr class="hline"><td colspan=2 align=center>Extension DLLs (plugins)</tr>
	679	<tr class="hline"><td><code>\bin\cgi.dll</code> </td><td>Gather CGI GET
650	680	and POST arguments </td></tr>
651		<tr valign="top"><td><code>\bin\double_metaphone.dll</code> </td><td>Soundex
652		(sounds similar) </td></tr>
653		<tr valign="top"><td><code>\bin\memfile.dll</code> </td><td>In-memory
654		temporary `files' </td></tr>
655		<tr valign="top"><td><code>\bin\odbc4pl.dll</code> </td><td>ODBC
	681	<tr><td><code>\bin\double_metaphone.dll</code> </td><td>Soundex (sounds
	682	similar) </td></tr>
	683	<tr><td><code>\bin\memfile.dll</code> </td><td>In-memory temporary
	684	`files' </td></tr>
	685	<tr><td><code>\bin\odbc4pl.dll</code> </td><td>ODBC interface </td></tr>
	686	<tr><td><code>\bin\plregtry.dll</code> </td><td>Windows registry
656	687	interface </td></tr>
657		<tr valign="top"><td><code>\bin\plregtry.dll</code> </td><td>Windows
658		registry interface </td></tr>
659		<tr valign="top"><td><code>\bin\porter_stem.dll</code> </td><td>Porter
660		stemming implementation </td></tr>
661		<tr valign="top"><td><code>\bin\random.dll</code> </td><td>Portable
662		random number generator </td></tr>
663		<tr valign="top"><td><code>\bin\rdf_db.dll</code> </td><td>RDF database </td></tr>
664		<tr valign="top"><td><code>\bin\readutil.dll</code> </td><td>Fast
665		reading utility </td></tr>
666		<tr valign="top"><td><code>\bin\sgml2pl.dll</code> </td><td>SGML/XML
667		parser </td></tr>
668		<tr valign="top"><td><code>\bin\socket.dll</code> </td><td>Prolog socket
	688	<tr><td><code>\bin\porter_stem.dll</code> </td><td>Porter stemming
	689	implementation </td></tr>
	690	<tr><td><code>\bin\random.dll</code> </td><td>Portable random number
	691	generator </td></tr>
	692	<tr><td><code>\bin\rdf_db.dll</code> </td><td>RDF database </td></tr>
	693	<tr><td><code>\bin\readutil.dll</code> </td><td>Fast reading utility </td></tr>
	694	<tr><td><code>\bin\sgml2pl.dll</code> </td><td>SGML/XML parser </td></tr>
	695	<tr><td><code>\bin\socket.dll</code> </td><td>Prolog socket interface </td></tr>
	696	<tr><td><code>\bin\table.dll</code> </td><td>Access structured files as
	697	tables </td></tr>
	698	<tr><td><code>\bin\time.dll</code> </td><td>Timing and alarm library </td></tr>
	699	<tr><td><code>\bin\xpce2pl.dll</code> </td><td>The XPCE graphics system </td></tr>
	700	<tr><td><code>\bin\zlib1.dll</code> </td><td>Compression library
	701	(32-bits) </td></tr>
	702	<tr><td><code>\bin\zlibwapi.dll</code> </td><td>Compression library
	703	(64-bits) </td></tr>
	704	<tr><td><code>\bin\zlib4pl.dll</code> </td><td>Compression library
669	705	interface </td></tr>
670		<tr valign="top"><td><code>\bin\table.dll</code> </td><td>Access
671		structured files as tables </td></tr>
672		<tr valign="top"><td><code>\bin\time.dll</code> </td><td>Timing and
673		alarm library </td></tr>
674		<tr valign="top"><td><code>\bin\xpce2pl.dll</code> </td><td>The XPCE
675		graphics system </td></tr>
676		<tr valign="top"><td><code>\bin\zlib1.dll</code> </td><td>Compression
677		library (32-bits) </td></tr>
678		<tr valign="top"><td><code>\bin\zlibwapi.dll</code> </td><td>Compression
679		library (64-bits) </td></tr>
680		<tr valign="top"><td><code>\bin\zlib4pl.dll</code> </td><td>Compression
681		library interface </td></tr>
682	706	</table>
683	707
684	708	<p>
685	709
686		<h3><a name="sec:3.4"><span class="sec-nr">3.4</span> <span class="sec-title">Installed
	710	<h3><a id="sec:3.4"><span class="sec-nr">3.4</span> <span class="sec-title">Installed
687	711	Registry keys and menus</span></a></h3>
688	712
689	713	<p>The filetype <code>.pl</code> or chosen alternative (see <a class="sec" href="#sec:3.2">section

696	720	<code>.pl</code> file can be associated with one of the installed Prolog
697	721	versions only.
698	722
699		<p><table border="2" frame="box" rules="groups" style="margin:auto">
700		<tr valign="top"><td colspan=2 align=center><code>HKEY_LOCAL_MACHINE<code>\</code>Software<code>\</code>SWI<code>\</code>Prolog</code></tr>
701		<tbody>
702		<tr valign="top"><td><code>fileExtension</code> </td><td>Extension used
	723	<p><table class="latex frame-box center">
	724	<tr><td colspan=2 align=center><code>HKEY_LOCAL_MACHINE<code>\</code>Software<code>\</code>SWI<code>\</code>Prolog</code></tr>
	725	<tr class="hline"><td><code>fileExtension</code> </td><td>Extension used
703	726	for Prolog files </td></tr>
704		<tr valign="top"><td><code>group</code> </td><td>Start menu group </td></tr>
705		<tr valign="top"><td><code>home</code> </td><td>Installation directory </td></tr>
706		<tbody>
707		<tr valign="top"><td colspan=2 align=center><code>HKEY_CURRENT_USER<code>\</code>Software<code>\</code>SWI<code>\</code>Plwin<code>\</code>Console</code></tr>
708		<tr valign="top"><td colspan=2 align=center>Note: thread-windows store
709		the same info in sub-keys</tr>
710		<tbody>
711		<tr valign="top"><td><code>Height</code> </td><td>Height of window in
	727	<tr><td><code>group</code> </td><td>Start menu group </td></tr>
	728	<tr><td><code>home</code> </td><td>Installation directory </td></tr>
	729	<tr class="hline"><td colspan=2 align=center><code>HKEY_CURRENT_USER<code>\</code>Software<code>\</code>SWI<code>\</code>Plwin<code>\</code>Console</code></tr>
	730	<tr><td colspan=2 align=center>Note: thread-windows store the same info
	731	in sub-keys</tr>
	732	<tr class="hline"><td><code>Height</code> </td><td>Height of window in
712	733	character units </td></tr>
713		<tr valign="top"><td><code>Width</code> </td><td>Width of window in
714		character units </td></tr>
715		<tr valign="top"><td><code>X</code> </td><td>Left edge of window in
716		pixel units </td></tr>
717		<tr valign="top"><td><code>Y</code> </td><td>Top edge of window in pixel
718		units </td></tr>
719		<tr valign="top"><td><code>SaveLines</code> </td><td>Number of lines
720		available for scrollback </td></tr>
	734	<tr><td><code>Width</code> </td><td>Width of window in character units </td></tr>
	735	<tr><td><code>X</code> </td><td>Left edge of window in pixel units </td></tr>
	736	<tr><td><code>Y</code> </td><td>Top edge of window in pixel units </td></tr>
	737	<tr><td><code>SaveLines</code> </td><td>Number of lines available for
	738	scrollback </td></tr>
721	739	</table>
722	740
723	741	<p>
724	742
725		<h3><a name="sec:3.5"><span class="sec-nr">3.5</span> <span class="sec-title">Execution
	743	<h3><a id="sec:3.5"><span class="sec-nr">3.5</span> <span class="sec-title">Execution
726	744	level</span></a></h3>
727	745
728	746	<p>The installer asks for the <code>admin</code> execution level (Vista

730	748
731	749	<p>
732	750
733		<h3><a name="sec:3.6"><span class="sec-nr">3.6</span> <span class="sec-title">Creating
	751	<h3><a id="sec:3.6"><span class="sec-nr">3.6</span> <span class="sec-title">Creating
734	752	a desktop menu item</span></a></h3>
735	753
736	754	<p>If you want a desktop entry for SWI-Prolog, right-drag

740	758
741	759	<p>
742	760
743		<h2><a name="sec:4"><span class="sec-nr">4</span> <span class="sec-title">The
	761	<h2><a id="sec:4"><span class="sec-nr">4</span> <span class="sec-title">The
744	762	SWI-Prolog community and foundation</span></a></h2>
745	763
746	764	<p>
747	765
748		<h3><a name="sec:4.1"><span class="sec-nr">4.1</span> <span class="sec-title">Website
	766	<h3><a id="sec:4.1"><span class="sec-nr">4.1</span> <span class="sec-title">Website
749	767	and mailing lists</span></a></h3>
750	768
751	769	<p>The SWI-Prolog website is located at <a class="url" href="http://www.swi-prolog.org/">http://www.swi-prolog.org/</a>.
752	770
753	771	<p>
754	772
755		<h3><a name="sec:4.2"><span class="sec-nr">4.2</span> <span class="sec-title">About
	773	<h3><a id="sec:4.2"><span class="sec-nr">4.2</span> <span class="sec-title">About
756	774	license conditions</span></a></h3>
757	775
758	776	<p>The SWI-Prolog license allows it to be used in a wide variety of

778	796
779	797	<p>
780	798
781		<h3><a name="sec:4.3"><span class="sec-nr">4.3</span> <span class="sec-title">Supporting
	799	<h3><a id="sec:4.3"><span class="sec-nr">4.3</span> <span class="sec-title">Supporting
782	800	SWI-Prolog</span></a></h3>
783	801
784	802	<p>There are several ways to support SWI-Prolog:

803	821	programmers.
804	822	</ul>
805	823
806		<h1><a name="document-index">Index</a></h1>
	824	<h1><a id="document-index">Index</a></h1>
807	825
808	826	<dl>
809	827	<dt class="index-sep">?</dt>

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-1

src/SWI-Prolog.h less more

67	67	/* PLVERSION_TAG: a string, normally "", but for example "rc1" */
68	68
69	69	#ifndef PLVERSION
70		#define PLVERSION 70602
	70	#define PLVERSION 70603
71	71	#endif
72	72	#ifndef PLVERSION_TAG
73	73	#define PLVERSION_TAG ""

-1

src/pl-gc.c less more

338	338	{ const char *s = stringAtom(val);
339	339	if ( strlen(s) > 10 )
340	340	{ strncpy(o, s, 10);
341		strcat(o, "...");
	341	strcpy(o+10, "...");
342	342	} else
343	343	{ strcpy(o, s);
344	344	}

1738	1738	case C_LCUT:
1739	1739	case C_SOFTCUT:
1740	1740	case C_LCUTIFTHEN:
	1741	case C_FASTCUT:
1741	1742	mark_choice_mark(state, PC[0]);
1742	1743	break;
1743	1744	/* variable access */

3978	3979	if ( gc_status.blocked \|\| !truePrologFlag(PLFLAG_GC) )
3979	3980	return FALSE;
3980	3981
	3982	assert(LD->fast_condition == NULL);
	3983
3981	3984	#ifdef O_MAINTENANCE
3982	3985	save_backtrace("GC");
3983	3986	#endif

+14

-23

src/pl-vmi.c less more

2726	2726
2727	2727	VMI(S_VIRGIN, 0, 0, ())
2728	2728	{ lTop = (LocalFrame)argFrameP(FR, FR->predicate->functor->arity);
2729		SAVE_REGISTERS(qid);
2730		DEF = getProcDefinedDefinition(DEF PASS_LD);
2731		LOAD_REGISTERS(qid);
2732
2733		if ( FR->predicate != DEF ) /* auto imported/loaded */
2734		{ FR->predicate = DEF;
	2729
	2730	if ( !DEF->impl.any && false(DEF, PROC_DEFINED) )
	2731	{ SAVE_REGISTERS(qid);
	2732	DEF = getProcDefinedDefinition(DEF PASS_LD);
	2733	LOAD_REGISTERS(qid);
	2734
	2735	FR->predicate = DEF;
2735	2736	#ifdef O_PROFILE
2736	2737	if ( FR->prof_node )
2737	2738	profSetHandle(FR->prof_node, DEF);
2738	2739	#endif
2739	2740	goto retry_continue;
	2741	#ifdef O_PLMT
	2742	} else if ( true(DEF, P_THREAD_LOCAL) )
	2743	{ DEF = getProcDefinition__LD(DEF PASS_LD);
	2744	FR->predicate = DEF;
	2745	#endif
2740	2746	}
2741	2747
2742	2748	if ( createSupervisor(DEF) )

3085	3091	- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
3086	3092
3087	3093	/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
3088		A_ENTER: Ensure the alignment of ARGP allows for efficient pushing of
3089		the number structure. We must check for availaible space to support
3090		bindConst() (wakeup and trail) because the resulting value may possibly
3091		not be shifted. See is/2 in pl-arith.c for details.
	3094	A_ENTER: Prepare for arithmetic operations.
3092	3095	- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
3093	3096
3094	3097	VMI(A_ENTER, 0, 0, ())
3095		{ if ( !hasGlobalSpace(0) )
3096		{ int rc;
3097
3098		SAVE_REGISTERS(qid);
3099		rc = ensureGlobalSpace(0, ALLOW_GC);
3100		LOAD_REGISTERS(qid);
3101		if ( rc != TRUE )
3102		{ raiseStackOverflow(rc);
3103		THROW_EXCEPTION;
3104		}
3105		}
3106
3107		AR_BEGIN();
	3098	{ AR_BEGIN();
3108	3099	NEXT_INSTRUCTION;
3109	3100	}
3110	3101