/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2001-2012, University of Amsterdam
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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*/
:- module(occurs,
[ contains_term/2, % +SubTerm, +Term
contains_var/2, % +SubTerm, +Term
free_of_term/2, % +SubTerm, +Term
free_of_var/2, % +SubTerm, +Term
occurrences_of_term/3, % +SubTerm, +Term, ?Tally
occurrences_of_var/3, % +SubTerm, +Term, ?Tally
sub_term/2, % -SubTerm, +Term
sub_var/2 % -SubTerm, +Term (SWI extra)
]).
/** <module> Finding and counting sub-terms
This is a SWI-Prolog implementation of the corresponding Quintus
library, based on the generalised arg/3 predicate of SWI-Prolog.
@see library(terms) provides similar predicates and is probably
more wide-spread than this library.
*/
%! contains_term(+Sub, +Term) is semidet.
%
% Succeeds if Sub is contained in Term (=, deterministically)
contains_term(X, X) :- !.
contains_term(X, Term) :-
compound(Term),
arg(_, Term, Arg),
contains_term(X, Arg),
!.
%! contains_var(+Sub, +Term) is det.
%
% Succeeds if Sub is contained in Term (==, deterministically)
contains_var(X0, X1) :-
X0 == X1,
!.
contains_var(X, Term) :-
compound(Term),
arg(_, Term, Arg),
contains_var(X, Arg),
!.
%! free_of_term(+Sub, +Term)
%
% Succeeds of Sub does not unify to any subterm of Term
free_of_term(Sub, Term) :-
\+ contains_term(Sub, Term).
%! free_of_var(+Sub, +Term)
%
% Succeeds of Sub is not equal (==) to any subterm of Term
free_of_var(Sub, Term) :-
\+ contains_var(Sub, Term).
%! occurrences_of_term(+SubTerm, +Term, ?Count)
%
% Count the number of SubTerms in Term
occurrences_of_term(Sub, Term, Count) :-
count(sub_term(Sub, Term), Count).
%! occurrences_of_var(+SubTerm, +Term, ?Count)
%
% Count the number of SubTerms in Term
occurrences_of_var(Sub, Term, Count) :-
count(sub_var(Sub, Term), Count).
%! sub_term(-Sub, +Term)
%
% Generates (on backtracking) all subterms of Term.
sub_term(X, X).
sub_term(X, Term) :-
compound(Term),
arg(_, Term, Arg),
sub_term(X, Arg).
%! sub_var(-Sub, +Term)
%
% Generates (on backtracking) all subterms (==) of Term.
sub_var(X0, X1) :-
X0 == X1.
sub_var(X, Term) :-
compound(Term),
arg(_, Term, Arg),
sub_var(X, Arg).
/*******************************
* UTIL *
*******************************/
%! count(:Goal, -Count)
%
% Count number of times Goal succeeds.
:- meta_predicate count(0,-).
count(Goal, Count) :-
State = count(0),
( Goal,
arg(1, State, N0),
N is N0 + 1,
nb_setarg(1, State, N),
fail
; arg(1, State, Count)
).