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/* $Id: broadcast.pl,v 1.7 2002/02/01 15:04:49 jan Exp $
Part of XPCE --- The SWI-Prolog GUI toolkit
Author: Jan Wielemaker and Anjo Anjewierden
E-mail: jan@swi.psy.uva.nl
WWW: http://www.swi.psy.uva.nl/projects/xpce/
Copyright (C): 1985-2002, University of Amsterdam
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
As a special exception, if you link this library with other files,
compiled with a Free Software compiler, to produce an executable, this
library does not by itself cause the resulting executable to be covered
by the GNU General Public License. This exception does not however
invalidate any other reasons why the executable file might be covered by
the GNU General Public License.
*/
:- module(broadcast,
[ listen/3, % Listener x Templ x Goal
listen/2, % Templ x Goal
unlisten/1, % Listener
unlisten/2, % Listener x Templ
unlisten/3, % Listener x Templ x Goal
listening/3, % Listener x Templ x Goal
broadcast/1, % Templ
broadcast_request/1 % Templ
]).
:- meta_predicate
listen(+, :),
listen(+, +, :),
unlisten(+, +, :).
:- use_module(library(pce)). % actually, only for require/1
:- require([ strip_module/3
]).
:- dynamic
listener/4.
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Generic broadcasting service. Broadcasts are made using the predicate
broadcast(+Templ). All registered `listeners' will have their goal
called. Success or failure of this is ignored. The listener can not bind
arguments.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
% listen([+Listener], +Templ, :Goal)
%
% Open a channel for listening for events of the given `Templ'.
listen(Listener0, Templ, Goal) :-
canonical_listener(Listener0, Listener),
strip_module(Goal, Module, TheGoal),
assert_listener(Templ, Listener, Module, TheGoal).
listen(Templ, Goal) :-
strip_module(Goal, Module, TheGoal),
assert_listener(Templ, Module, Module, TheGoal).
% unlisten(+Listener, [+Templ, [:Goal]])
%
% Destroy a channel. Arguments may be variables
unlisten(Listener0) :-
canonical_listener(Listener0, Listener),
retractall(listener(_, Listener, _, _)).
unlisten(Listener0, Templ) :-
canonical_listener(Listener0, Listener),
retractall(listener(Templ, Listener, _, _)).
unlisten(Listener0, Templ, Goal) :-
canonical_listener(Listener0, Listener),
( var(Goal)
-> true
; strip_module(Goal, Module, TheGoal)
),
retract_listener(Templ, Listener, Module, TheGoal).
% listening(-Listener, -Templ, -Goal)
%
% returns currently open channels
listening(Listener0, Templ, Module:Goal) :-
canonical_listener(Listener0, Listener),
listener(Templ, Listener, Module, Goal).
% broadcast(+Templ, +Arg)
%
% Broadcast given event. Always succeeds.
broadcast(Templ) :-
( listener(Templ, _Listener, Module, Goal),
( Module:Goal
-> fail
)
; true
).
% broadcast_request(+Templ)
%
% Broadcast given event till accepted. Succeeds then, fail if no
% listener accepts the call. Bindings made by the listener goal
% are maintained. May be used to make broadcast requests. Can
% backtrack.
broadcast_request(Templ) :-
listener(Templ, _Listener, Module, Goal),
Module:Goal.
% {assert,retract}_listener(+Templ, +Listener, +Module, +Goal)
%
% Implemented as sub-predicate to ensure storage in this module.
% Second registration is ignored. Is this ok? It avoids problems
% using multiple registration of global listen channels.
assert_listener(Templ, Listener, Module, TheGoal) :-
listener(Templ, Listener, Module, TheGoal), !.
assert_listener(Templ, Listener, Module, TheGoal) :-
asserta(listener(Templ, Listener, Module, TheGoal)).
retract_listener(Templ, Listener, Module, TheGoal) :-
retractall(listener(Templ, Listener, Module, TheGoal)).
% canonical_listener(+Raw, -Canonical)
%
% Entry for later optimization.
canonical_listener(Templ, Templ).
|
