[plt-scheme] pause or wait?

> When running recursive procedures that have an effect on the screen 
> (such as an animation) it sometimes nice to have them pause between each 
> call. I looked for such a PAUSE or WAIT primitive but couldn't find one. 
> Any pointers?

Hi Knubee,


If we're using the draw.ss teachpack from How to Design Programs,

http://htdp.org/2003-09-26/Book/curriculum-Z-H-9.html#node_sec_6.6

then we should be able to use the function sleep-for-a-while mentioned in 
exercise 6.6.6.


If we're using the module language, you can still access teachpacks by 
requiring the appropriate one from the 'htdp' collection.  For example:


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(module test-drawing mzscheme
   (require (lib "posn.ss" "lang")
            (lib "draw.ss" "htdp")
            (lib "etc.ss"))


   ;; draw-shrinking-circle: posn number number
   ;; draws a circle that shrinks.
   (define (draw-shrinking-circle center-posn current-radius min-radius)
     (cond
       [(> current-radius min-radius)
        (and
         (draw-circle center-posn current-radius 'black)
         (sleep-for-a-while .05)
         (draw-circle center-posn current-radius 'white)
         (draw-shrinking-circle center-posn
                                (sub1 current-radius)
                                min-radius))]
       [else true]))


   (start 300 300)
   (draw-shrinking-circle (make-posn 150 150) 100 50))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;



Best of wishes!