| 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.
|
