Term checking utilitiesAuthor(s): The CLIP Group.
This module implements a basic set of term checking utilities.
Usage and interface
- Library usage:
Documentation on exports
Term1 and Term2 unify without producing bindings for the variables of Term1. I.e., instance(Term1,Term2) holds.
Term1 is an instance of Term2.
- The following properties hold globally:
(basic_props:native/1)This predicate is understood natively by CiaoPP.
Term2 is an instance of Term1.
Term1 and Term2 are identical up to renaming.
Term satisfies instance(Term,Term1) and instance(Term,Term2) and there is no term more general than Term (modulo variants) that satisfies it.
Term satisfies instance(Term1,Term) and instance(Term2,Term) and there is no term less general than Term (modulo variants) that satisfies it.
unifier(Unifier) :- list(Unifier,unifier_elem).
X is a unifier.
Unifies Unifier with the most general unifier between the terms X and Y. Fails if such unifier does not exit.
- The following properties should hold at call time:
(basic_props:term/1)X is any term.
(basic_props:term/1)Y is any term.
- The following properties hold upon exit:
(terms_check:unifier/1)Unifier is a unifier.
Documentation on internals
unifier_elem(X=Term) :- var(X), term(Term).
Other informationCurrently, ask/2 and instance/2 are exactly the same. However, ask/2 is intended to be more general, since it is also applicable to constraint domains (although not yet implemented): i.e., for the particular case of Herbrand terms, ask/2 is just instance/2.
Known bugs and planned improvements
- Run-time checks have been reported not to work with this code. That means that either the assertions here, or the code that implements the run-time checks are erroneous.