;; ** An implementation of producer functions

#lang racket

(define (make-producer producer)
  (let ([resume #f]
        [return-to-caller #f])
    (lambda (raw-yield)
      (define (yield value)
        (let/cc k (set! resume k) (return-to-caller value)))
      (set! return-to-caller raw-yield)
      (if resume
        (resume 'blah)
        (producer yield)))))

(define (get producer)
  (let/cc k (producer k)))

(define producer
  (make-producer (lambda (yield)
                   (yield 1)
                   (yield 2)
                   (yield 3))))