(define (make-int-channel n)
  (let ((channel (make-sync-channel)))
    (spawn
     (lambda ()
       (let loop ((i n))
	 (send-sync channel i)
	 (loop (+ 1 i)))))
    channel))

(define (remove-multiples factor channel)
  (let ((out-channel (make-sync-channel)))
    (spawn
     (lambda ()
       (let loop ()
	 (let ((i (receive-sync channel)))
	   (if (not (zero? (remainder i factor)))
	       (send-sync out-channel i))
	   (loop)))))
    out-channel))

(define (prime-channel)
  (let ((primes (make-sync-channel)))
    (spawn
     (lambda ()
       (let loop ((channel (make-int-channel 2)))
	 (let ((factor (receive-sync channel)))
	   (send-sync primes factor)
	   (loop (remove-multiples factor channel))))))
    primes))

(define (write-channel channel)
  (let loop ()
    (write (receive-sync channel))
    (newline)
    (loop)))