Type checking

• atom(X):   The term X is an atom.

• atomic(X):   The term X is an atom or a number.

• float(X):   The term X is a floating-point number.

• real(X):   The same as float(X).

• integer(X):   The term X is an integer.

• number(X):   The term X is a number.

• nonvar(X):   The term X is not a variable.

• var(X):   The term X is a free variable.

• compound(X):   The term X is a compound term. It is true if X is either a structure or a list.

• ground(X):   The term X is ground.

• callable(X):   The term X is a callable term, i.e., an atom or a compound term. No type error will occur in a meta call such as call(X) if X is callable. Notice that a callable term does not mean that the predicate is defined.