/usr/lib/swi-prolog/boot/engines.pl is in swi-prolog-nox 7.6.4+dfsg-1build1.
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Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2016, 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('$engines',
[ engine_create/3, % ?Template, :Goal, -Engine
engine_create/4, % ?Template, :Goal, -Engine, +Options
engine_next_reified/2, % +Engine, -Term
engine_yield/1, % +Term
engine_self/1, % -Engine
current_engine/1 % ?Engine
]).
:- meta_predicate
engine_create(?, 0, -),
engine_create(?, 0, -, +).
/** <module> Engine (interactor) support
*/
%! engine_create(?Template, :Goal, ?Engine) is det.
%! engine_create(?Template, :Goal, -Engine, +Options) is det.
%
% Create a new engine, prepared to run Goal and return answers as
% instances of Template. Goal is not started.
engine_create(Template, Goal, Engine) :-
( atom(Engine)
-> '$engine_create'(Engine, Template+Goal, [alias(Engine)])
; '$engine_create'(Engine, Template+Goal, [])
).
engine_create(Template, Goal, Engine, Options) :-
'$engine_create'(Engine, Template+Goal, Options).
%! engine_next(+Engine, -Term) is semidet.
%
% Switch control to Engine and if engine produces a result, switch
% control back and unify the instance of Template from
% engine_create/3,4 with Term. Repeatedly calling engine_next/2 on
% Engine retrieves new instances of Template by backtracking over
% Goal. Fails of Goal has no more solutions. If Goal raises an
% exception the exception is re-raised by this predicate.
%! engine_next_reified(+Engine, -Term) is det.
%
% Similar to engine_next/2 but returning answers in reified form.
% Answers are returned using the terms the(Answer), no, and
% exception(Error).
engine_next_reified(Engine, Answer) :-
( catch(engine_next(Engine, Answer0), Error, true)
-> ( var(Error)
-> Answer = the(Answer0)
; Answer = exception(Error)
)
; Answer = no
).
%! engine_post(+Engine, +Package) is det.
%
% Make the term Package available for engine_fetch/1 from within
% the engine. At most one term can be made available. Posting a
% package does not cause the engine to wakeup. Therefore, an
% engine_next/2 call must follow a call to this predicate to make
% the engine fetch the package. The predicate engine_post/3
% combines engine_post/2 and engine_next/2.
%
% @error permission_error(post_to, engine, Package) if a package
% was already posted and has not yet been fetched by the engine.
%! engine_post(+Engine, +Package, -Reply) is semidet.
%
% Same as engine_next/2, but transfer Term to Engine if Engine
% calls engine_fetch/1. Acts as:
%
% ==
% engine_post(Engine, Package, Answer) :-
% engine_post(Engine, Package),
% engine_next(Engine, Answer).
% ==
%! engine_destroy(+Engine) is det.
%
% Destroy Engine. Eventually, engine destruction will also be
% subject to symbol garbage collection.
%! engine_yield(+Term) is det.
%
% Make engine_answer/2 return with the given term.
engine_yield(Term) :-
'$engine_yield'(Term, 256).
%! engine_self(E) is semidet.
%
% True if executed inside engine E
engine_self(E) :-
thread_self(E),
is_engine(E).
%! current_engine(?E)
%
% True if E is a currently know engine.
current_engine(E) :-
thread_property(E, engine(true)).
%! '$engine_yield'(?Term, +Code:integer)
%
% Cause PL_next_solution() to return with Code, providing access
% to Term through PL_yielded(). Can only be called if
% PL_open_query() is called with PL_Q_ALLOW_YIELD. Code tells the
% code that controls PL_next_solution() what to do and the codes
% used must be agreed upon for a specific application. Code must
% be an integer >= 256. Other return codes are reserved by the
% system.
'$engine_yield'(_Term, _Code) :-
'$yield'.
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