complement (Function)

Syntax:

Arguments and Values:

function—a function.

complement-function—a function.

Description:

Returns a function that takes the same arguments as function, and has the same side-effect behavior as function, but returns only a single value: a generalized boolean with the opposite truth value of that which would be returned as the primary value of function. That is, when the function would have returned true as its primary value the complement-function returns false, and when the function would have returned false as its primary value the complement-function returns true.

Examples:

 (funcall (complement #'zerop) 1) → true
 (funcall (complement #'characterp) #\A) → false
 (funcall (complement #'member) 'a '(a b c)) → false
 (funcall (complement #'member) 'd '(a b c)) → true

See Also:

not (Function)

Notes:

 (complement x) ≡ #'(lambda (&rest arguments) (not (apply x arguments)))

In Common Lisp, functions with names like “xxx-if-not” are related to functions with names like “xxx-if” in that

(xxx-if-not f . arguments) ≡ (xxx-if (complement f) . arguments)

For example,

 (find-if-not #'zerop '(0 0 3)) ≡
 (find-if (complement #'zerop) '(0 0 3)) → 3

Note that since the “xxx-if-not” functions and the :test-not arguments have been deprecated, uses of “xxx-if” functions or :test arguments with complement are preferred.