Term checking utilities

Author(s): The CLIP Group.

This module implements the term checking utilities.

Usage and interface

Documentation on exports


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


Usage: instance(Term1,Term2)

  • Description: Term1 is an instance of Term2.
  • The following properties hold globally:
    (basic_props:native/1)This predicate is understood natively by CiaoPP.


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.

Other information

Currently, ask/2 and instance/2 are exactly the same. However, ask/2 is more general, since it is also applicable to constraint domains (although not yet implemented): for the particular case of Herbrand terms, it is just instance/2 (which is the only ask check currently implemented).

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.