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zerop

zerop Function

Syntax:

zerop number → generalized-boolean

Pronunciation:

[ z—e( )r—o( )p—e ]

Arguments and Values:

number—a number .

generalized-boolean—a generalized boolean.

Description:

Returns true if number is zero (integer , float, or complex ); otherwise, returns false.

Regardless of whether an implementation provides distinct representations for positive and negative floating-point zeros, (zerop -0.0) always returns true.

Examples:

(zerop 0) → true 
(zerop 1) → false 
(zerop -0.0) → true 
(zerop 0/100) → true 
(zerop #c(0 0.0)) → true

Exceptional Situations:

Should signal an error of type type-error if number is not a number .

Notes:

(zerop number) ≡ (= number 0)

Expanded Reference: zerop​

Testing for zero​

zerop returns true if the number is zero, regardless of its numeric type.

(zerop 0)
=> T
(zerop 1)
=> NIL
(zerop -1)
=> NIL

With floating-point numbers​

zerop recognizes both positive and negative floating-point zero.

(zerop 0.0)
=> T
(zerop -0.0)
=> T
(zerop 0.0d0)
=> T
(zerop 0.001)
=> NIL

With rationals​

Zero ratios are also recognized as zero.

(zerop 0/100)
=> T
(zerop 0/1)
=> T
(zerop 1/1000000)
=> NIL

With complex numbers​

A complex number is zero only if both its real and imaginary parts are zero.

(zerop #c(0 0))
=> T
(zerop #c(0 0.0))
=> T
(zerop #c(0 1))
=> NIL

Practical use: safe division guard​

zerop is commonly used to guard against division by zero.

(defun safe-divide (a b)
  (if (zerop b)
      (values nil "division by zero")
      (/ a b)))

(safe-divide 10 3)
=> 10/3
(safe-divide 10 0)
=> NIL
=> "division by zero"