SWI-Prolog -- current

Documentation
- Reference manual
  - Built-in Predicates
    - Examining the program
- Packages

Availability:built-in

current_predicate(?Name, :Head)

Classical pre-ISO implementation of current_predicate/1, where the predicate is represented by the head term. The advantage is that this can be used for checking the existence of a predicate before calling it without the need for functor/3:

call_if_exists(G) :-
        current_predicate(_, G),
        call(G).

Because of this intended usage, current_predicate/2 also succeeds if the predicate can be autoloaded. Unfortunately, checking the autoloader makes this predicate relatively slow, in particular because a failed lookup of the autoloader will cause the autoloader to verify that its index is up-to-date.