How to edit and return string in Emacs Lisp?

[gnusupport]

(defun buffer-out ()
  (interactive)
  (let ((buffer (current-buffer))
	(value (buffer-string)))
    (kill-buffer buffer)))

(defun buffer-string-out ()
  (interactive)
  (buffer-string))

(defun edit-string (string)
  (interactive)
  (let ((buffer "*edit-string*"))
    (get-buffer-create buffer)
    (switch-to-buffer buffer)
    (set-buffer buffer)
    (let ((inhibit-read-only nil))
      (insert string)
      (fundamental-mode)
      (local-set-key (kbd "C-c C-c") 'buffer-out))))

;;      (add-hook 'kill-buffer-hook 'buffer-string-out))))

(setq ok (edit-string "OK"))

I am trying to get this work, could you point me to a solution to edit string, and return the string back?