(define resume '*)

(define (makecoroutine proc)
  (let ((lcs '*))
    (letrec ((localres (lambda (co v) 
			 (let ((v (call/cc (lambda (k)
					     (set! lcs k)
					     (co v)))))
			   (set! resume localres)
			   v)))
	     (newcoroutine (lambda (v) (lcs v))))
      (call/cc (lambda (exit)
		 (proc (localres exit newcoroutine))
		 (error "End of coroutine"))))))