Re: LOGO-L> Re: Multiple Turtles

[George Mills <mills@softronix.com>]

Yehuda Katz wrote:
> 
> 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.

That would not be the error. It would be "SETH does not like [100 100]".

SETH TOWARDS TURTLE 4

Would be the correct way to use it.

But to make it less ambiguous POSTURTLE (or TURTLEPOS) makes most
sense and TURTLE (in MSWLogo) already returns the TURTLE number.

But ASK (ASKTURTLE) would be the most general purpose.

SETH ASKTURTLE 5 [HEADING]

This is in the Logo Rule book on page 453.

> 
> > 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]]
> 
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