apply (Function)

Syntax:

Arguments and Values:

function—a function designator.

args—a spreadable argument list designator.

results—the values returned by function.

Description:

Applies the function to the args.

When the function receives its arguments via &rest, it is permissible (but not required) for the implementation to bind the rest parameter to an object that shares structure with the last argument to apply. Because a function can neither detect whether it was called via apply nor whether (if so) the last argument to apply was a constant, conforming programs must neither rely on the list structure of a rest list to be freshly consed, nor modify that list structure.

setf can be used with apply in certain circumstances; see Section 5.1.2.5 (APPLY Forms as Places).

Examples:

 (setq f '+) → +
 (apply f '(1 2)) → 3
 (setq f #'-) → #<FUNCTION ->
 (apply f '(1 2)) → -1
 (apply #'max 3 5 '(2 7 3)) → 7
 (apply 'cons '((+ 2 3) 4)) → ((+ 2 3) . 4)
 (apply #'+ '()) → 0

 (defparameter *some-list* '(a b c))
 (defun strange-test (&rest x) (eq x *some-list*))
 (apply #'strange-test *some-list*) → implementation-dependent

 (defun bad-boy (&rest x) (rplacd x 'y))
 (bad-boy 'a 'b 'c) has undefined consequences.
 (apply #'bad-boy *some-list*) has undefined consequences.

 (defun foo (size &rest keys &key double &allow-other-keys)
   (let ((v (apply #'make-array size :allow-other-keys t keys)))
     (if double (concatenate (type-of v) v v) v)))
 (foo 4 :initial-contents '(a b c d) :double t)
    → #(A B C D A B C D)

See Also:

funcall, fdefinition, function (Special Operator), Section 3.1 (Evaluation), Section 5.1.2.5 (APPLY Forms as Places)