Emacs Lisp: Apply Function (List to Args)

Sometimes you have a list, you want to feed them as arguments to a function.

There 2 ways to do that:

• Use the function apply
• Use the Backquote Reader Macro

apply

(apply FUNCTION &rest args_or_list)

Call FUNCTION with args_or_list.

The last argument in args_or_list, if it is a list, it'll be flattened out and feed as args to the function.

;; test function
(defun ff (x y z)
  "return args as one string"
  (format "%s %s %s" x y z))

;; normal usage
(equal
 (ff 2 3 4)
 "2 3 4")

;; define a list
(setq xx '(2 3 4))

;; use apply, to turn a list into args
(equal
 (apply 'ff xx)
 "2 3 4")
;; true

;; the list can be shorter
(setq xx '(3 4))

;; use apply, to turn a list into args
(equal
 (apply 'ff 2 xx)
 "2 3 4")
;; true

funcall

(funcall FUNCTION &rest args)

Call FUNCTION with args.

Tip: this is useful when the function name is a variable, value known only at run-time.

;; test function
(defun ff (x y z)
  "return args as one string"
  (format "%s %s %s" x y z))

;; normal usage
(equal
 (ff 2 3 4)
 "2 3 4")

;; use funcall
(equal
 (funcall 'ff 2 3 4)
 "2 3 4")
;; t