Counts

concurrency.scm

(define (countdown n)
  (cond ((= n 0) 'countdown-done)
        (else
         (display "Down ")
         (displayln n)
         (call-soon (lambda () (countdown (- n 1)))))))

(define (up stop)
  (define (iter x)
    (cond ((> x stop) 'up-done)
          (else
           (display "Up ")
           (displayln x)
           (call-soon (lambda () (iter (+ x 1)))))))
  (iter 0))

(countdown 5)
; Down 5
; Down 4
; Down 3
; Down 2
; Down 1

(up 5)
; Up 1
; Up 2
; Up 3
; Up 4
; Up 5