Possible bug within GNU Prolog ?
"Vic Bancroft" <[email protected]>
| Newsgroups | gmane.comp.gnu.prolog.general |
|---|---|
| Message-ID | <[email protected]> |
The second clause in the predicate occured_once/2 relies on the behavior of member/2 in that if the list contains an unbound variable, it counts as an occurrance, e.g., | ?- member( 1, [2,X]). X = 1 ? yes If an unbound variable is an element of the list, then the variable can unify with operand one and occurs, e.g., | ?- occured_once(1, [V]). V = 1 ? yes If more than one unbound variable is an element of the list, then the occured_once predicate will always fail, e.g., | ?- occured_once(1, [V,W]). no The example is even more interesting when using structures, | ?- occured_once( v(c(1)), [ v(2), v(c(X)) ]). X = 1 ? yes more, l8r, v _______________________________________________ Users-prolog mailing list [email protected] http://lists.gnu.org/mailman/listinfo/users-prolog