RE: LOGO-L> Tessellation program

[RAY CATZEL <learn@computerpals.on.ca>]

Hi Brian,
Thanks for your feedback. Please let send me a list of your books.

I work with MicroWorlds which provides an attractive multimedia interface for 
the students. They enjoy programming their own games which can incorporate a 
lot of programming challenges.

I like your recursion examples because of the combination of problem solving 
and playful experimentation (to obtain different graphical results). I now must 
design a project that will require a background  design drawn using recursion 
for one of the games.  The advantage in drawing the background this way is that 
the total project size is smaller than having to load a graphics file.  The 
size of their project is significant when they are published on the Web.
Ray.

-----Original Message-----
From:	jstclair@omsd.cerf.fred.org [SMTP:jstclair@omsd.cerf.fred.org]
Sent:	Tuesday, December 30, 1997 4:52 AM
To:	logo-list@gsn.org
Subject:	Re: LOGO-L> Tessellation program

Please reply to bh@anarres.CS.Berkeley.EDU (Brian Harvey)  or
logo-l@gsn.org   NOT   logo-list@gsn.org  or  me.

-John
--Message below re-posted by <jstclair@omsd.cerf.fred.org>
Date - 30 Dec 1997 04:07:03 GMT
>From - bh@anarres.CS.Berkeley.EDU (Brian Harvey)
To - jcstclair@omsd
Subject - Re: LOGO-L> Tessellation program
Usenet: comp.lang.logo
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Post Usenet mail to comp-lang-logo@ucbvax.berkeley.edu
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>RAY CATZEL wrote:
>> I must admit that I have a tough time unraveling the logic of these 
recursive
>> stacks. Has anyone found that this type of exercise is reasonable for kids 
of
>> 13 years?

My guess is that the age is less of an issue than the context of prior
learning.  What kind of prior experience with recursion do these kids
have?  What kind of prior graphics experience?

One thing that might help with recursive graphic designs is to start with
a bunch of simpler examples, like a recursive tree.  Here is the simplest
possible example, which I learned from Paul Goldenberg:  You start by
making a few small simple non-recursive shapes:

to square
repeat 4 [fd 10 rt 90]
end

to triangle
repeat 3 [fd 10 rt 120]
end

and so on.  Then you say

to vee
lt 45
fd 40
run pick [square triangle]
bk 40
rt 90
fd 40
run pick [square triangle]
bk 40
lt 45
end

If your version of Logo doesn't provide PICK, here it is:

to pick :stuff
output item (1 + random count :stuff) :stuff
end

And if the RUN in your version of Logo insists on lists, make it

run pick [[square] [triangle]]

So far, no recursion.  Try VEE several times to get used to how it works.

Then you edit VEE so that it says (in both places)

run pick [square triangle vee]

and ask the kids to predict what will happen!


For more complicated recursive designs, try writing non-recursive
versions that draw first-level and then second-level pictures,
and understand them thoroughly, before going on to the multi-level
recursive version.  (This is essentially the "combining method" of
understanding recursion that I discuss in my books.)




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