Type Checking

The following predicates take a term as their argument. They are provided to check the type of that term.

Predicate

Succeeds if term is:

var/1

a variable; the term is currently uninstantiated.

nonvar/1

a non-variable; the term is currently instantiated.

integer/1

an integer

atom/1

an atom

float/1

a float

number/1

an integer or float.

atomic/1

an atom, number or database reference.

simple/1

an atom, number, variable or database reference.

compound/1

a compound term (arity > 0).

callable/1

a term that call/1 would take as an argument; atom or compound term.

ground/1

ground; the term contains no uninstantiated variables.

db_reference/1

a Prolog database reference

Please note: Although database references are read and written as compound terms, and formerly were, they now are a distinct atomic term type (see ref-mdb-dre).

The reference pages for these predicates include examples of their use.