Macro Help -- transform arguments

example.lisp

;; A macro that would transform this:
(my-macro my-function (medium pathname options)
	  (list medium pathname options))

;; Into:
(defun my-function (&rest rest)
  (let ((medium (nth 0 rest))
	(pathname (nth 1 rest))
	(options (nth 1 rest)))
    (list medium pathname options)))

;; I.e. change function signature without changing semantics.