;;; File:
;;;   cont.scm
;;; Author:
;;;   Samuel A. Rebelsky
;;; Contents:
;;;   Some simple continuation examples.

; A place to store continuations.
(define cont null)

; Like (+ 3 (* 4 5))), except we grab the current continuation 
; with the 5
(+ 3 (* 4 (let/cc k (set! cont k) 5)))

(define print-squares
  (lambda (lst)
    (let/cc exit
      (map (lambda (x) 
             (if (< x 0) (exit)
                 (begin (display (* x x)) (newline))))
           lst))))

(define exit null)
(let/cc k (set! exit k))
(define resume null)
(define pause
  (lambda ()
    (let/cc k 
      (set! resume k))
    (exit)))

(define stupid
  (lambda ()
    (display "Alpha") (newline)
    (pause)
    (display "Beta") (newline)
    (pause)
    (display "Gamma") (newline)
    ))





(define stop 0)
(let/cc stopc (set! stop stopc))

; I'm not sure if I'll use the following example, but it's here
; for my notes.
(define interact
  (let* ((resume #f)
         (pause
          (lambda ()
            (let/cc p
              (set! resume p)
              (stop))))
         (done
          (lambda ()
            (set! resume #f))))
    (lambda ()
      (if resume
          (resume)
          (begin
            (display "Hi!")
            (newline)
            (pause)
            (display "Goodbye")
            (newline)
            (pause)
            (display "Still running")
            (newline)
            (done))))))