Term checking utilities

Author(s): The Ciao Development Team.

This module implements a basic set of term checking utilities.

Usage and interface

Documentation on exports

PREDICATEask/2
ask(Term1,Term2)

Term1 and Term2 unify without producing bindings for the variables of Term1. I.e., instance(Term1,Term2) holds.

PROPERTYinstance/2

Usage:instance(Term1,Term2)

Term1 is an instance of Term2.

  • The following properties hold globally:
    (basic_props:native/1)This predicate is understood natively by CiaoPP.

Usage:ISOsubsumes_term(Term1,Term2)

Term2 is an instance of Term1.

    PREDICATEvariant/2
    variant(Term1,Term2)

    Term1 and Term2 are identical up to renaming.

    most_general_instance(Term1,Term2,Term)

    Term satisfies instance(Term,Term1) and instance(Term,Term2) and there is no term more general than Term (modulo variants) that satisfies it.

    most_specific_generalization(Term1,Term2,Term)

    Term satisfies instance(Term1,Term) and instance(Term2,Term) and there is no term less general than Term (modulo variants) that satisfies it.

    REGTYPEunifier/1
    unifier(Unifier) :-
            list(Unifier,unifier_elem).
    

    Usage:unifier(X)

    X is a unifier.

      PREDICATEunifiable/3

      Usage:unifiable(X,Y,Unifier)

      Unifies Unifier with the most general unifier between the terms X and Y. Fails if such unifier does not exit.

      Documentation on internals

      A regular type, defined as follows:
      unifier_elem(X=Term) :-
              var(X),
              term(Term).
      

      Documentation on imports

      This module has the following direct dependencies:

      Other information

      Currently, 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.