gistfile1.el

(defun a-function (option callback)
  "Open the message with key."
  (interactive)
  (let* ((buffer (get-buffer-create "aprocessbuffer"))
         (command (a-build-autocomple-command option))
         (proc (start-process "aproccess" buffer "ls" "-l" )))
    (set-process-sentinel proc (lambda (process signal)
                                 (cond
                                  ((equal signal "finished\n")
                                   (let ((output (with-current-buffer (process-buffer process)
                                                   (buffer-substring (point-min) (point-max)))))
                                     (funcall callback output)
))
                                  ('t
                                   (message "signal: %s" signal)
                                   ))))))

(a-function "List" (lambda (e)
                   (message "SUPER %s" e)
                   ))
                   
;; error in process sentinel: let: Symbol's value as variable is void: callback
;; error in process sentinel: Symbol's value as variable is void: callback