SWI-Prolog -- callable/1

Availability:built-in

[ISO]callable(@Term)

True if Term is bound to an atom or a compound term. This was intended as a type-test for arguments to call/1, call/2 etc. Note that callable only tests the surface term. Terms such as (22,true) are considered callable, but cause call/1 to raise a type error. Module-qualification of meta-argument (see meta_predicate/1) using :/2 causes callable to succeed on any meta-argument.^{66We think that callable/1
should be deprecated and there should be two new predicates, one
performing a test for callable that is minimally module aware and
possibly consistent with type-checking in call/1
and a second predicate that tests for atom or compound.} Consider the program and query below:

:- meta_predicate p(0).

p(G) :- callable(G), call(G).

?- p(22).
ERROR: Type error: `callable' expected, found `22'
ERROR: In:
ERROR:    [6] p(user:22)