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Re: LOGO-L> quirky problem




Michael Tempel (michaelt@media.mit.edu)
Tue, 21 Jan 1997 06:27:30 -0500

>Well I hung in there for 90 minutes and finally solve the MWorld 2
>problem... but i am not sure why it worked. It was only doing a little
>something I used to do with Logo on the Apple II that fixed things. Here's
>the situation:
>
>Fourth graders are making a Guide to the El. School for new students.
>Pairs make Projects entitled Health Center, Library Rules, Cafeteria, etc.
>I link these projects from a main page with buttons programmed as follows:
>
>To Cafeteria
>getproject "cafe
>end
>
>Cafeteria is the button name and the project is called cafe.
>
>there are 10 projects to link to the main page in this way.
>
>Some of the button commands worked and others didn't. The syntax was
>correct, I tried all sort of changes. FINALLY by moving the ones that
>DIDN'T work to the top of the list of procedures they began to connect to
>the projects.
>
>I will fiddle around some this am to see if it still works but what I don't
>get is why the order affected things. Seems as though Logo should be able
>to scan down my list of procedures and find the right one.
>
>
>Regards,
>
>Peter
>

Here's what I think may be happening:

There's an error in one of your procedures somewhere midway down the
procedures page. When you leave the procedures page, Logo reads through
what you've written, top to bottom, and defines each procedure as it goes.
If there's a certain type of error, Logo stops and doesn't get to the rest
of the procedures.

The kinds of errors that cause this are those that intefere with defining.
Here's an example:

to square
repeat 4 [fd 50 rt 90]
end

to repeat
end

to circle
repeat 36 [fd 10 rt 10]
end

This will cause the message "repeat is already used" - it's a primitive so
you can't define it on your own. (Actually, you can, but that's another
story.)

In this case CIRCLE won't be defined and you'll get the message "I don't
know how to circle" if you try to run it.

I suspect that this is the problem you had. By moving procdures to the top
of the procedures page you put them before the offending procedure.

I hope this helps.

-Michael

Michael Tempel tel: 212 579 8028
Logo Foundation fax: 212 579 8013
250 West 85th Street michaelt@media.mit.edu
New York NY 10024
http://el.www.media.mit.edu/groups/logo-foundation/

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