(define-record-type :get-request
  (make-get-request)
  get-request?)

(define-record-type :put-request
  (make-put-request value)
  put-request?
  (value put-request-value))

(define-record-type :cell
  (really-make-cell request-channel reply-channel)
  cell?
  (request-channel cell-request-channel)
  (reply-channel cell-reply-channel))

(define (make-cell value)
  (let ((request-channel (make-sync-channel))
	(reply-channel (make-sync-channel)))
    (spawn
     (lambda ()
       (let loop ((value value))
	 (let ((request (receive-sync request-channel)))
	   (cond
	    ((get-request? request)
	     (send-sync reply-channel value)
	     (loop value))
	    ((put-request? request)
	     (loop (put-request-value request))))))))
    (really-make-cell request-channel reply-channel)))

(define (cell-ref cell)
  (send-sync (cell-request-channel cell)
	     (make-get-request))
  (receive-sync (cell-reply-channel cell)))

(define (cell-set! cell value)
  (send-sync (cell-request-channel cell)
	(make-put-request value)))