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integerp

integerp Function

Syntax:

integerp object → generalized-boolean

Arguments and Values:

object—an object.

generalized-boolean—a generalized boolean.

Description:

Returns true if object is of type integer; otherwise, returns false.

Examples:

(integerp 1) → true 
(integerp (expt 2 130)) → true 
(integerp 6/5) → false 
(integerp nil) → false

Notes:

(integerp object) ≡ (typep object ’integer)

Expanded Reference: integerp​

Testing if an object is an integer​

integerp returns true if the object is an integer (fixnum or bignum).

(integerp 1)
=> T
(integerp 0)
=> T
(integerp -100)
=> T
(integerp (expt 2 130))
=> T

Non-integer numbers​

Ratios, floats, and complex numbers are not integers.

(integerp 6/5)
=> NIL
(integerp 3.0)
=> NIL
(integerp #c(1 2))
=> NIL

Non-numeric objects​

integerp returns false for all non-numeric types.

(integerp nil)
=> NIL
(integerp "42")
=> NIL
(integerp 'hello)
=> NIL

Practical use: ensuring integer arguments​

integerp can guard functions that require integer inputs.

(defun factorial (n)
  (assert (and (integerp n) (>= n 0))
          (n) "~A is not a non-negative integer" n)
  (if (zerop n) 1 (* n (factorial (1- n)))))

(factorial 5)
=> 120

Equivalence to typep​

integerp is equivalent to (typep object 'integer).

(eql (integerp 42) (typep 42 'integer))
=> T
(eql (integerp 3.0) (typep 3.0 'integer))
=> T