Re: LOGO-L> Re: Multiple Turtles

[Yehuda Katz <yehuka@beitberl.ac.il>]

Brian Harvey wrote:
> 
> Yehuda Katz <yehuka@beitberl.ac.il> writes:
> >I'm expecting a *primitive* function (instead of the 5 suggested library
> >functions), named maybe TURTLE, that will enable commands like:
> >
> >        SETXY TURTLE 5, SETH TOWARDS TURTLE 4, etc.
> 
> I don't understand the semantics of this proposed function.  Does this
> example mean "set the current turtle's position to turtle 5's position,
> and set the current turtle's heading towards turtle 4's position"?

Brian,

Thank your for your input.

My proposed TURTLE :N function reports the location ( as a list) of that
turtle.
So, saying SETPOS TURTLE 5 (not SETXY, sorry) is exactly as unique as
SETPOS [100 100], 
SETH TOWARDS TURTLE 4 is exactly as unique as SETH TOWARDS [100 100],
DIST TURTLE 5 is exactly as unique as DIST [100 100]..
 
> But I gather that it doesn't always mean the position.

What I propose is always the position, and only the position.

> Do you expect
> to be able to say
> 
>         SETH TURTLE 4
> 
> to mean "set the current turtle's heading equal to turtle 4's heading"?

No, SETH TURTLE 4 is exactly as meaningless as SETH [100 100], so you
will get a "did not output" error message.

> Because if so, then TURTLE is not a proper function; its result depends
> on something other than the arguments you give, namely, the context in
> which you use it.  

> (That is, if you just said SETH it returns a heading;

No, as I said, SETH TURTLE 4 will give an error message.  

> I think that example would have to be SETPOS anyway.)

Correct, sorry about that.
 
> Starting in LogoWriter and even more in Microworlds, LCSI has hacked up
> their syntax quite a bit so that it's no longer true that everything is
> a procedure call.  Their goal has been to make the notation "do the
> right thing" in common cases, at the cost of making the syntax itself
> quite tricky if you really look at it.
> 
> I dunno if I'd want to go down that path.

What about going the path I propose?

Regards...

[[Yehuda]]

---------------------------------------------------------------
Please post messages to the Logo forum to logo-l@gsn.org.  Mail
questions about the list administration to logofdn@gsn.org.  To
unsubscribe send    unsubscribe logo-l    to majordomo@gsn.org.