; Expoliting reuse of continuations.
; Debugging:
; (define (ex m v) (write (list m v))(newline) v)
; Pattern support:
(call/cc (lambda (finish)
(let* ((found (let ((tskList '())) (cons (lambda () (if (null? tskList) (finish "done")
           (let ((nxt (car tskList))) (set! tskList (cdr tskList)) (nxt))))
         (lambda (t) (set! tskList (cons t tskList))))))
       (yield (car found))(newTsk (cdr found))
       (DoS (lambda (n p) (let q ((n n)) (if (zero? n) (yield)
         (begin (call/cc (lambda (C) (newTsk C) (p n))) (q (- n 1))))))))
; version of sqrt and point-plot within pattern:
(let (
  (sqrt (lambda (x) (if (< x 0) (yield) (if (= x 0) 0
     (let ((root (sqrt x))) (call/cc (lambda (c)
       (newTsk (lambda () (c (- root)))) (c root))))))))
  (plot (lambda (x y) (write (list "pt=" x y))(newline)(yield))))
; Application:
(let ((gr 5)) (DoS (+ (* 4 gr) 1)
  (lambda (i) (let ((x (/ (- i (* 2 gr)) gr))) (plot x (sqrt (- 1 (* x x))))))))))))