coroutine implementation on scheme

coroutine.scm

(define proc1 '())
(define proc2 '())

(define (coroutine1)
  (define (yield-for next-cnt)
    (call/cc (lambda (cnt)
      (set! proc1 cnt)
      (next-cnt))))
  (define (setup)
    (call/cc (lambda (cnt)
      (set! proc1 cnt)
      (coroutine2))))
  (setup)
  (for-each (lambda (i) 
              (print "cor1:" i)
              (if (not (eq? i 5))
                (yield-for proc2)))
            (list 1 2 3 4 5)))

(define (coroutine2)
  (define (yield-for next-cnt)
    (call/cc (lambda (cnt)
      (set! proc2 cnt)
      (next-cnt))))
  (for-each (lambda (i) 
              (print "cor2:" i)
              (yield-for proc1))
            (list 1 2 3 4 5)))

(coroutine1)