/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2019-2020, VU University 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
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/
:- module(prolog_wrap,
[ wrap_predicate/4, % :Head, +Name, -Wrapped, +Body
unwrap_predicate/2, % :PI, ?Name
current_predicate_wrapper/4 % :Head, -Name, -Wrapped, -Body
]).
:- autoload(library(lists),[member/2]).
:- autoload(library(pairs),[pairs_keys/2]).
:- meta_predicate
wrap_predicate(:, +, -, +),
% unwrap_predicate(:, ?),
current_predicate_wrapper(:, -, -, -).
/** <module> Wrapping predicates
This library allows adding _wrappers_ to predicates. The notion of
wrappers is known in various languages under several names. For example
Logtalk knows these as _before methods_ or _after methods_ and Python
has _decorators_. A SWI-Prolog wrapper is a _body term_ that normally
calls the original wrapped definition somewhere.
*/
%! wrap_predicate(:Head, +Name, -Wrapped, +Body) is det.
%
% Wrap the predicate referenced by Head using Body. Subsequent calls
% to Head call the given Body term. Body may call the original
% definition through Wrapped. Wrapped is a term of the shape below,
% where _Closure_ is an opaque _blob_.
%
% call(Closure(A1, ...))
%
% Name names the wrapper for inspection using predicate_property/2 or
% deletion using unwrap_predicate/2. If Head has a wrapper with Name
% the Body of the existing wrapper is updated without changing the
% order of the registered wrappers. The same predicate may be wrapped
% multiple times. Multiple wrappers are executed starting with the
% last registered (outermost).
%
% The predicate referenced by Head does not need to be defined at the
% moment the wrapper is installed. If Head is undefined, the predicate
% is created instead of _searched for_ using e.g., the auto loader.
%
% Registered wrappers __are not part of saved states__ (see
% qsave_program/2) and thus need to be re-registered, for example
% using initialization/1.
wrap_predicate(M:Head, WName, Wrapped, Body) :-
'$wrap_predicate'(M:Head, WName, _Closure, Wrapped, Body).
%! unwrap_predicate(:PI, ?Name) is semidet.
%
% Remove the outermost wrapper whose name unifies with Name. Fails if
% no matching wrapper exists.
%! current_predicate_wrapper(:Head, -Name, -Wrapped, -Body) is nondet.
%
% True if Head is wrapped with Body. The arguments are compatible with
% wrap_predicate/4 such that the result may be used to re-create the
% wrapper.
%
% Wrappers are enumerated starting with the first registered
% (innermost) wrapper.
current_predicate_wrapper(M:Head, Name, Wrapped, Body) :-
'$wrapped_predicate'(M:Head, Pairs),
Head =.. [_|Args],
member(Name-CRef, Pairs),
clause(M:WHead, Body0, CRef),
WHead =.. [_|Args],
body_closure(Body0, Wrapped, Body).
body_closure(call(ClosureTerm), Wrapped, Wrapped) :-
callable(ClosureTerm),
functor(ClosureTerm, Closure, _Arity),
blob(Closure, closure),
!.
body_closure(Body0, Wrapped, Body) :-
compound(Body0),
!,
compound_name_arity(Body0, Name, Arity),
compound_name_arity(Body, Name, Arity),
body_closure_args(0, Arity, Body0, Wrapped, Body).
body_closure(Body, _, Body).
body_closure_args(I, Arity, Body0, Closure, Body) :-
I < Arity,
!,
I2 is I+1,
arg(I2, Body0, Arg0),
arg(I2, Body, Arg),
body_closure(Arg0, Closure, Arg),
body_closure_args(I2, Arity, Body0, Closure, Body).
body_closure_args(_, _, _, _, _).
% Not for public docs!
% '$syspreds':'$predicate_property'(?Property, +Value) is nondet.
%
% Extend predicate_property/2 to provide the `wrapped` property
:- multifile
'$syspreds':'$predicate_property'/2.
'$syspreds':'$predicate_property'(wrapped(List), Pred) :-
'$wrapped_predicate'(Pred, Pairs),
pairs_keys(Pairs, List).