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) 2016, 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('$engines', 36 [ engine_create/3, % ?Template, :Goal, -Engine 37 engine_create/4, % ?Template, :Goal, -Engine, +Options 38 engine_next_reified/2, % +Engine, -Term 39 engine_yield/1, % +Term 40 engine_self/1, % -Engine 41 current_engine/1 % ?Engine 42 ]). 43 44:- meta_predicate 45 engine_create( , , ), 46 engine_create( , , , ). 47 48/** <module> Engine (interactor) support 49 50 51*/ 52 53%! engine_create(?Template, :Goal, ?Engine) is det. 54%! engine_create(?Template, :Goal, -Engine, +Options) is det. 55% 56% Create a new engine, prepared to run Goal and return answers as 57% instances of Template. Goal is not started. 58 59engine_create(Template, Goal, Engine) :- 60 ( atom(Engine) 61 -> '$engine_create'(Engine, Template+Goal, [alias(Engine)]) 62 ; '$engine_create'(Engine, Template+Goal, ) 63 ). 64engine_create(Template, Goal, Engine, Options) :- 65 '$engine_create'(Engine, Template+Goal, Options). 66 67%! engine_next(+Engine, -Term) is semidet. 68% 69% Switch control to Engine and if engine produces a result, switch 70% control back and unify the instance of Template from 71% engine_create/3,4 with Term. Repeatedly calling engine_next/2 on 72% Engine retrieves new instances of Template by backtracking over 73% Goal. Fails of Goal has no more solutions. If Goal raises an 74% exception the exception is re-raised by this predicate. 75 76%! engine_next_reified(+Engine, -Term) is det. 77% 78% Similar to engine_next/2 but returning answers in reified form. 79% Answers are returned using the terms the(Answer), no, and 80% exception(Error). 81 82engine_next_reified(Engine, Answer) :- 83 ( catch(engine_next(Engine, Answer0), Error, true) 84 -> ( var(Error) 85 -> Answer = the(Answer0) 86 ; Answer = exception(Error) 87 ) 88 ; Answer = no 89 ). 90 91%! engine_post(+Engine, +Package) is det. 92% 93% Make the term Package available for engine_fetch/1 from within 94% the engine. At most one term can be made available. Posting a 95% package does not cause the engine to wakeup. Therefore, an 96% engine_next/2 call must follow a call to this predicate to make 97% the engine fetch the package. The predicate engine_post/3 98% combines engine_post/2 and engine_next/2. 99% 100% @error permission_error(post_to, engine, Package) if a package 101% was already posted and has not yet been fetched by the engine. 102 103%! engine_post(+Engine, +Package, -Reply) is semidet. 104% 105% Same as engine_next/2, but transfer Term to Engine if Engine 106% calls engine_fetch/1. Acts as: 107% 108% == 109% engine_post(Engine, Package, Answer) :- 110% engine_post(Engine, Package), 111% engine_next(Engine, Answer). 112% == 113 114%! engine_destroy(+Engine) is det. 115% 116% Destroy Engine. Eventually, engine destruction will also be 117% subject to symbol garbage collection. 118 119%! engine_yield(+Term) is det. 120% 121% Make engine_answer/2 return with the given term. 122 123engine_yield(Term) :- 124 '$engine_yield'(Term, 256). 125 126%! engine_self(E) is semidet. 127% 128% True if executed inside engine E 129 130engine_self(E) :- 131 thread_self(E), 132 is_engine(E). 133 134%! current_engine(?E) 135% 136% True if E is a currently know engine. 137 138current_engine(E) :- 139 thread_property(E, engine(true)). 140 141%! '$engine_yield'(?Term, +Code:integer) 142% 143% Cause PL_next_solution() to return with Code, providing access 144% to Term through PL_yielded(). Can only be called if 145% PL_open_query() is called with PL_Q_ALLOW_YIELD. Code tells the 146% code that controls PL_next_solution() what to do and the codes 147% used must be agreed upon for a specific application. Code must 148% be an integer >= 256. Other return codes are reserved by the 149% system. 150 151'$engine_yield'(_Term, _Code) :- 152 '$yield'