GNU Emacs Lisp Reference Manual

3.3: Type Predicates for Numbers

The functions in this section test whether the argument is a number or whether it is a certain sort of number. The functions integerp and floatp can take any type of Lisp object as argument (the predicates would not be of much use otherwise); but the zerop predicate requires a number as its argument. See also integer-or-marker-p and number-or-marker-p, in Predicates on Markers.

Function: floatp object

This predicate tests whether its argument is a floating point number and returns t if so, nil otherwise.

floatp does not exist in Emacs versions 18 and earlier.

Function: integerp object

This predicate tests whether its argument is an integer, and returns t if so, nil otherwise.

Function: numberp object

This predicate tests whether its argument is a number (either integer or floating point), and returns t if so, nil otherwise.

Function: wholenump object

The wholenump predicate (whose name comes from the phrase ``whole-number-p'') tests to see whether its argument is a nonnegative integer, and returns t if so, nil otherwise. 0 is considered non-negative.

natnump is an obsolete synonym for wholenump.

Function: zerop number

This predicate tests whether its argument is zero, and returns t if so, nil otherwise. The argument must be a number.

These two forms are equivalent: (zerop x) == (= x 0).