sentinel based cps in emacs-lisp. bit wierd

cps-foreach-bg.el

(defun cps-foreach-bg (proc l cont &optional command-args)
  "Call PROC with each element of L, in the background.

When there are no more elements of L call CONT with L.

Optionally use the COMMAND-ARGS as the command to run in the
operating system to do the queueing."
  (let* ((process-args (or command-args '("sleep" "1")))
         (qproc (apply
                 'start-process
                 "queue" (get-buffer-create "*queue*")
                 process-args)))
    (set-process-sentinel
     qproc
     (lambda (process status)
       (when (string-match ".*finished\n" status)
         (if l
             (funcall
              proc (car l)
              (lambda (a) (cps-foreach-bg proc (cdr l) cont)))
             ;; Else
             (funcall cont l)))))))