continuation6.scm

(use util.stream)

; ストリームの負数番目を取ると死ねる(GCが落ちる)

(define fib
  (stream-cons 0
    (stream-cons 1
      (stream-map + fib (stream-cdr fib)))))

; ------------------------------------------------
(define next #f)
(define prev #f)
(define runaway #f)

;; main
(define (main args)

  (print "enter Ctrl-D(or Ctrl-Z on Windows) to escape.")
  (newline)

  (let/cc break
    (let loop [(n 0) (boom #f)]
      (when boom
        (print (stream-ref fib n))
        (loop (+ n 1) #t))

      (display (stream-ref fib n))
      (flush)

      (set! next
        (lambda () (loop (+ n 1) #f)))
      (set! prev
        (lambda () (if (<= 0 (- n 1)) (loop (- n 1) #f))))
      (set! runaway
        (lambda () (loop (+ n 1) #t)))

      (break #f)
      ))

  ; 終了したければ^Dを押す
  (let1 c (read-byte)
    (cond
     [(eof-object? c)]
     [(char-ci=? #\p (integer->char c)) (prev)]
     [(char=? #\! (integer->char c)) (runaway)]
     [else (next)]
     ))


  0)