numberp

numberp Function

Syntax:

numberp object → generalized-boolean

Arguments and Values:

object—an object.

generalized-boolean—a generalized boolean.

Description:

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

Examples:

(numberp 12) → true 
(numberp (expt 2 130)) → true 
(numberp #c(5/3 7.2)) → true 
(numberp nil) → false 
(numberp (cons 1 2)) → false 

Notes:

(numberp object) ≡ (typep object ’number)

Expanded Reference: numberp

Testing if an object is a number

numberp returns true if the object is of type number, which includes integers, ratios, floats, and complex numbers.

(numberp 42)
=> T
(numberp 3.14)
=> T
(numberp 2/3)
=> T
(numberp #c(1 2))
=> T

Non-numeric objects

numberp returns false for all non-numeric types.

(numberp nil)
=> NIL
(numberp "42")
=> NIL
(numberp 'foo)
=> NIL
(numberp (cons 1 2))
=> NIL
(numberp #\0)
=> NIL

Large integers (bignums) are numbers

Arbitrarily large integers are still numbers.

(numberp (expt 2 130))
=> T
(numberp most-positive-fixnum)
=> T

Practical use: input validation

numberp is useful for validating that a value is numeric before performing arithmetic.

(defun safe-add (a b)
  (if (and (numberp a) (numberp b))
      (+ a b)
      (error "Both arguments must be numbers")))

(safe-add 3 4)
=> 7

Equivalence to typep

numberp is equivalent to (typep object 'number).

(eql (numberp 42) (typep 42 'number))
=> T
(eql (numberp "x") (typep "x" 'number))
=> T