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forces a failure.
fail/0
fail/0 fails always. It can force backtracing.
Conjuncted subgoals that follow after fail/0 can never be executed.
Be careful with calling fail/0 after a never-ending loop (for
example see repeat/0).
Examples
| write('this is going to fail'), fail. | Fails with output on the current outputstream 'this is going to fail'. |
| repeat,write(endless),nl,fail. | writes infinitely on the current outputstream 'endless'. |
Standard
This predicate is part of the ISO-Prolog Standard.
See also
abort/0, break/0, call/1, fcall/1, catch/3, ','(conjunction)/2, '!'(cut)/0, ';'(disjunction)/2, true/0, halt/0/1, '->'(if-then)/2, ';'(if-then-else)/2, '\+'(not provable)/1, once/1, repeat/0, throw/1.
| document: http://www.ifcomputer.co.jp/MINERVA/Manual/Reference/Predicates/logic_and_control/fail/print_de.html published 2008/12/1 update 2001/2/7 (c) 1996-2006 IF Computer Japan | ||||||||
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