CLHS: Function NULL

#

Function NULL

Syntax:

null object => boolean

Arguments and Values:

object---an object.

boolean---a boolean.

Description:

Returns t if object is the empty list; otherwise, returns nil.

Examples:

     (null '()) =>  T
     (null nil) =>  T
     (null t) =>  NIL
     (null 1) =>  NIL

Side Effects: None.

Affected By: None.

Exceptional Situations: None.

See Also:

not

Notes:

null is intended to be used to test for the empty list whereas not is intended to be used to invert a boolean (or generalized boolean). Operationally, null and not compute the same result; which to use is a matter of style.

     (null object) ==  (typep object 'null) ==  (eq object '())

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- NOT-AND-NULL-RETURN-VALUE:X3J13-MAR-93

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