/*-------------------------------------------------------------------------*
 * GNU Prolog                                                              *
 *                                                                         *
 * Part  : Prolog buit-in predicates                                       *
 * File  : catch.pl                                                        *
 * Descr.: exception management (catch)                                    *
 * Author: Daniel Diaz                                                     *
 *                                                                         *
 * Copyright (C) 1999-2012 Daniel Diaz                                     *
 *                                                                         *
 * This file is part of GNU Prolog                                         *
 *                                                                         *
 * GNU Prolog is free software: you can redistribute it and/or             *
 * modify it under the terms of either:                                    *
 *                                                                         *
 *   - the GNU Lesser General Public License as published by the Free      *
 *     Software Foundation; either version 3 of the License, or (at your   *
 *     option) any later version.                                          *
 *                                                                         *
 * or                                                                      *
 *                                                                         *
 *   - 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.                                          *
 *                                                                         *
 * or both in parallel, as here.                                           *
 *                                                                         *
 * GNU Prolog 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 copies of the GNU General Public License and   *
 * the GNU Lesser General Public License along with this program.  If      *
 * not, see http://www.gnu.org/licenses/.                                  *
 *-------------------------------------------------------------------------*/

/* $Id: catch.pl,v 1.22 2012/11/22 13:23:40 diaz Exp $ */

:-	built_in.

'$use_catch'.



          % Warning the name '$catch_internal1' is tested by the debugger

'$catch'(Goal, Catch, Recovery, Func, Arity, DebugCall) :-
	'$call_c'('Pl_Save_Call_Info_3'(Func, Arity, DebugCall)),
	'$catch1'(Goal, Catch, Recovery, 0).

'$catch1'(Goal, Catch, Recovery, CallInfo) :-
	'$call_c'('Pl_Load_Call_Info_Arg_1'(3)),   % to ensure CallInfo is deref
	'$catch_internal'(Goal, Catch, Recovery, CallInfo).


'$catch_internal'(Goal, Catch, Recovery, CallInfo) :-
	'$sys_var_read'(7, Handler),
	'$sys_var_put'(8, '$no_ball$'),
	'$catch_internal1'(Goal, Catch, Recovery, CallInfo, Handler).


'$catch_internal1'(Goal, _Catch, _Recovery, CallInfo, Handler) :-
	'$get_current_B'(B),
	'$sys_var_write'(7, B),
% for debug
% format('~N*** ~d for catch(~w,~w,~w)~n', [B, Goal, _Catch, _Recovery]),
	'$call_internal'(Goal, CallInfo),
	'$get_current_B'(B1),
	(   B1 > B ->
	    '$trail_handler'(B)
	;   !
	),
	'$sys_var_write'(7, Handler).

% for debug
% '$catch_internal1'(_, _, _, _, _):-
%	'$get_current_B'(B),
%	'$sys_var_get'(8, Ball),
%	format('~N*** ~d catching throw(~w)~n', [B, Ball]),
%	fail.

'$catch_internal1'(_, Catch, Recovery, CallInfo, Handler) :-
	'$sys_var_write'(7, Handler), % after throw or fail
	'$sys_var_get'(8, Ball),
	Ball \== '$no_ball$',
	'$catch_a_throw'(Ball, Catch, Recovery, CallInfo, Handler).




'$catch_a_throw'(Ball, _, _, _, Handler) :-                       % for abort
% for debug
% write(catch(Ball, Handler)), nl,
	nonvar(Ball),
	Ball = '$catch_sync'(B), !,
	(   Handler > B ->
	    '$unwind'('$catch_sync'(B))
	;   '$catch_fail_now'(B)
	).

'$catch_a_throw'(Ball, Ball1, Recovery, CallInfo, _) :-
% for debug
%write(catch1(Ball, Ball1, Recovery)), nl,
	Ball = Ball1,
% for debug
% write(catch2(Ball, Ball1, Recovery)), nl,
	!,                                           % normal throw - unifies
	'$sys_var_put'(8, '$no_ball$'),
	'$call_internal'(Recovery, CallInfo).

'$catch_a_throw'(Ball, _, _, _, _) :-         % normal throw - does not unify
	'$unwind'(Ball).




'$trail_handler'(_).

'$trail_handler'(Handler) :-
	'$sys_var_write'(7, Handler),
	fail.




'$catch_sync_for_fail_at'(B) :-
	'$sys_var_read'(7, Handler),
% for debug
% write(catch_sync(Handler, B)), nl,
	(   Handler > B ->
	    throw('$catch_sync'(B))
	;   '$catch_fail_now'(Handler)
	).




'$catch_fail_now'(B) :-
	'$set_current_B'(B),
	fail.
