How to force a fail in Prolog?

Question

In prolog, is it possible to force a fail? Something like:

check(F,A,[1,2,3]) :- FAIL.
check(F,A,_) : greater_than(F,A).

This may be a bad example, but something along the lines of this.

So if it does a pattern match on F,A,[1,2,3], then we just stop the who unifying process, and return a false.

See http://stackoverflow.com/questions/3001825/what-are-the-uses-of-the-fail-predicate-in-prolog?rq=1, esp. the last answer — , Apr 03 '13 at 02:53

score 1 · Answer 1 · answered Apr 03 '13 at 14:44

1

Prolog has a built-in fail/0 predicate, which always fails. You need a cut ! in front of it in order to prevent further matching of the same check/3 rule:

check(F,A,[1,2,3]) :- !, fail.

answered Apr 03 '13 at 14:44

Sergey Kalinichenko

714,442
84
1,110
1,523

How to force a fail in Prolog?

1 Answers1