;;; Shift and Reset (Filinski and Danvy)

(define (mk v)
  (error "Missing reset!"))

(define (abort v)
  (mk v))

(define (reset exp)
  (call-with-current-continuation
   (lambda (k)
     (let ((m mk))
       (set! mk 
	     (lambda (r)
	       (set! mk m)
	       (k r)))
       (abort (exp))))))

(define (shift f)
  (call-with-current-continuation
   (lambda (k)
     (abort (f (lambda (v) (reset (lambda () (k v)))))))))