(require 'stdlib)

(define (average-function args)
  (/ (apply + args) (length args)))

(defmacro average-macro (args)
  `(/ (+ ,@args) (length ,args)))

(let ((r '(1 2 3 4 5 6)))
  (puts (average-function r))
  (puts (average-macro r)))

;; accepts list argument or atoms
(define (foo #!rest args)
  (when (listp (car args))
    (setq args (car args)))
  (/ (apply + args) (length args)))

(puts (foo '(1 2.3 4 4)))
(puts (foo 1 2 3 4 5.6))