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Type tests are semi-deterministic predicates that succeed if the
argument satisfies the requested type. Type-test predicates have no
error condition and do not instantiate their argument. See also library
"hello".51In traditional Prolog systems, double quoted text is often mapped to a list of character codes. See also the Prolog flag double_quotes.
atomic(Term) :- nonvar(Term), \+ compound(Term).
SWI-Prolog defines the following atomic datatypes: atom (atom/1),
floating point number (float/1)
and blob (blob/2).
In addition, the symbol
 (empty list) is atomic, but not
an atom. See section 5.1.
causes callable to succeed on any meta-argument.52We 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:  p(user:22)