apply function &rest args⁺ → {result}*

function — a function designator.

args — a spreadable argument list designator.

results — the values returned by function.

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).

(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)

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