gistfile1.scm

;; http://repository.readscheme.org/ftp/papers/PLoP2001_dferguson0_1.pdf

(define coroutine-maker 
  (lambda (proc) 
    (let ((saved-continuation '())) 
      (let ((update-continuation! (lambda (v) 
                                    (display "updating") 
                                    (set! saved-continuation v)))) 
        (let ((resumer (resume-maker update-continuation!)) 
              (first-time #t)) 
          (lambda (value) 
            (if first-time 
                (begin 
                  (set! first-time #f) 
                  (proc resumer value)) 
                (saved-continuation value)))))))) 


(define resume-maker 
  (lambda (update-proc!) 
    (lambda (next-coroutine value) 
      (let ((receiver (lambda (continuation) 
                        (update-proc! continuation) 
                        (next-coroutine value)))) 
        (call-with-current-continuation receiver)))))