11.3.54 current_predicate/[1,2] [ISO]

Synopsis

current_predicate(?PredSpec)

Unifies PredSpec with a predicate specifications of the form Name/Arity.

current_predicate(?Name, ?Term)

Unifies Name with the name of a user-defined predicate, and Term with the most general term corresponding to that predicate.

Arguments

:PredSpec

pred_spec

Name

atom

:Term

callable

Description

If you have loaded the predicates foo/1 and foo/3 into Prolog, current_predicate/2 would return the following:

      | ?- current_predicate(foo, T).
     
     T = foo(_A) ;
     
     T = foo(_A,_B,_C) ;
     
     no

Examples

• The following goals can be used to backtrack through every predicate in your program.

            | ?- current_predicate(Name, Module:Term).
            
            | ?- current_predicate(Module:PredSpec).
       

• If a module is specified, current_predicate/[1,2] only succeeds for those predicates that are defined in the module. It fails for those predicates that are imported into a module.

            | ?- current_predicate(m:P).
       

  will backtrack through all predicates P that are defined in module m. To backtrack through all predicates imported by a module use predicate_property/2 (see ref-lps-ove).

To find out whether a predicate is built-in, use predicate_property/2.

     % Is there a callable predicate named gc?
     
     | ?- current_predicate(gc, Term).
     
     no
     | ?- predicate_property(gc, Prop)
     
     Prop = built_in

Exceptions

instantiation_error

type_error

in PredSpec

Comments

current_predicate/1 is part of the ISO Prolog standard; current_predicate/2 is not.

See Also

predicate_property/2, ref-lps-ove.