[plt-scheme] on-tick in 2htdp/universe.ss

From: Mitchell Wand (wand at ccs.neu.edu)
Date: Sun Apr 5 12:34:32 EDT 2009

On Sat, Apr 4, 2009 at 3:57 PM, Robby Findler
<robby at eecs.northwestern.edu>wrote:

> I'm not sure, but it looks like that is a buggy error check. You might
> try changing the 1 to a 2 in collects/2htdp/universe.ss and seeing
> what happens. (Search for "(define-keywords AllSpec" and go down two
> lines, I think.)
> Robby
Yup, that was it, but it wasn't the obvious occurrence of 1.  The correct
patch is as follows:

(define-keywords AllSpec
  [on-tick (function-with-arity
            [(x rate)
             #'(list (proc> 'on-tick (f2h x) 2)    ; last arg was 1
                     (num> 'on-tick rate positive? "pos. number"

Changing the number on line 3 doesn't do anything, but changing the one in
the line that says proc> does the trick.

Perhaps somebody can install this patch?

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