SICStus Prolog 中的 current_predicate

Question

SICStus Prolog offers both current_predicate/1 and current_predicate/2.

The manual page states:

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.

They appear to have the same features: both predicates work for enumerating predicates, both work with modules.

The manual page comments:

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

Should I ever use current_predicate/2 in new (= non-legacy) code?

Answer 1

Short answer, no. Don't use it in new code.

The benefit of current_predicate/2 was to allow querying, using a predicate call template , if the predicate is defined, unlike current_predicate/1 . Eg

...,
(   current_predicate(_, foo(_, _)) ->
    foo(A, B)
;   ...
),
...

But you can often use instead the standard predicate_property/2 predicate, which takes a template as first argument.

PS The Logtalk linter will scream at you (and suggest a more standard alternative) if it finds you calling current_predicate/2 :-)