1/* Part of SWI-Prolog 2 3 Author: Jan Wielemaker 4 E-mail: J.Wielemaker@vu.nl 5 WWW: http://www.swi-prolog.org 6 Copyright (c) 2019-2020, VU University Amsterdam 7 All rights reserved. 8 9 Redistribution and use in source and binary forms, with or without 10 modification, are permitted provided that the following conditions 11 are met: 12 13 1. Redistributions of source code must retain the above copyright 14 notice, this list of conditions and the following disclaimer. 15 16 2. Redistributions in binary form must reproduce the above copyright 17 notice, this list of conditions and the following disclaimer in 18 the documentation and/or other materials provided with the 19 distribution. 20 21 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 22 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 23 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 24 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 25 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 26 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 27 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 28 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 29 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 31 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 32 POSSIBILITY OF SUCH DAMAGE. 33*/ 34 35:- module(prolog_wrap, 36 [ wrap_predicate/4, % :Head, +Name, -Wrapped, +Body 37 unwrap_predicate/2, % :PI, ?Name 38 current_predicate_wrapper/4 % :Head, -Name, -Wrapped, -Body 39 ]). 40:- autoload(library(lists),[member/2]). 41:- autoload(library(pairs),[pairs_keys/2]). 42 43 44:- meta_predicate 45 wrap_predicate( , , , ), 46% unwrap_predicate(:, ?), 47 current_predicate_wrapper( , , , ). 48 49/** <module> Wrapping predicates 50 51This library allows adding _wrappers_ to predicates. The notion of 52wrappers is known in various languages under several names. For example 53Logtalk knows these as _before methods_ or _after methods_ and Python 54has _decorators_. A SWI-Prolog wrapper is a _body term_ that normally 55calls the original wrapped definition somewhere. 56*/ 57 58%! wrap_predicate(:Head, +Name, -Wrapped, +Body) is det. 59% 60% Wrap the predicate referenced by Head using Body. Subsequent calls 61% to Head call the given Body term. Body may call the original 62% definition through Wrapped. Wrapped is a term of the shape below, 63% where _Closure_ is an opaque _blob_. 64% 65% call(Closure(A1, ...)) 66% 67% Name names the wrapper for inspection using predicate_property/2 or 68% deletion using unwrap_predicate/2. If Head has a wrapper with Name 69% the Body of the existing wrapper is updated without changing the 70% order of the registered wrappers. The same predicate may be wrapped 71% multiple times. Multiple wrappers are executed starting with the 72% last registered (outermost). 73% 74% The predicate referenced by Head does not need to be defined at the 75% moment the wrapper is installed. If Head is undefined, the predicate 76% is created instead of _searched for_ using e.g., the auto loader. 77% 78% Registered wrappers __are not part of saved states__ (see 79% qsave_program/2) and thus need to be re-registered, for example 80% using initialization/1. 81 82wrap_predicate(M:Head, WName, Wrapped, Body) :- 83 '$wrap_predicate'(M:Head, WName, _Closure, Wrapped, Body). 84 85%! unwrap_predicate(:PI, ?Name) is semidet. 86% 87% Remove the outermost wrapper whose name unifies with Name. Fails if 88% no matching wrapper exists. 89 90%! current_predicate_wrapper(:Head, -Name, -Wrapped, -Body) is nondet. 91% 92% True if Head is wrapped with Body. The arguments are compatible with 93% wrap_predicate/4 such that the result may be used to re-create the 94% wrapper. 95% 96% Wrappers are enumerated starting with the first registered 97% (innermost) wrapper. 98 99current_predicate_wrapper(M:Head, Name, Wrapped, Body) :- 100 '$wrapped_predicate'(M:Head, Pairs), 101 Head =.. [_|Args], 102 member(Name-CRef, Pairs), 103 clause(M:, Body0, CRef), 104 WHead =.. [_|Args], 105 body_closure(Body0, Wrapped, Body). 106 107body_closure(call(ClosureTerm), Wrapped, Wrapped) :- 108 callable(ClosureTerm), 109 functor(ClosureTerm, Closure, _Arity), 110 blob(Closure, closure), 111 !. 112body_closure(Body0, Wrapped, Body) :- 113 compound(Body0), 114 !, 115 compound_name_arity(Body0, Name, Arity), 116 compound_name_arity(Body, Name, Arity), 117 body_closure_args(0, Arity, Body0, Wrapped, Body). 118body_closure(Body, _, Body). 119 120body_closure_args(I, Arity, Body0, Closure, Body) :- 121 I < Arity, 122 !, 123 I2 is I+1, 124 arg(I2, Body0, Arg0), 125 arg(I2, Body, Arg), 126 body_closure(Arg0, Closure, Arg), 127 body_closure_args(I2, Arity, Body0, Closure, Body). 128body_closure_args(_, _, _, _, _). 129 130 131% Not for public docs! 132% '$syspreds':'$predicate_property'(?Property, +Value) is nondet. 133% 134% Extend predicate_property/2 to provide the `wrapped` property 135 136:- multifile 137 '$syspreds':'$predicate_property'/2. 138 139'$syspreds''$predicate_property'(wrapped(List), Pred) :- 140 '$wrapped_predicate'(Pred, Pairs), 141 pairs_keys(Pairs, List)