LOGO-L> Re: Logo Grammar 
Author Message
 LOGO-L> Re: Logo Grammar


>There is no standard Logo grammar.

>At one of the Logo conferences several years ago I ran a session in
>which the possibility of a standard was discussed.  Many of the Logo
>implementors were there, as well as many users.  We ended up with
>the conclusion that no standard was possible, because there were too
>many serious disagreements about syntax, and also because the set of
>primitive procedures was constantly in flux.

>The main syntactic disagreement was about special forms.

Which confirms that there is, in fact, a standard.  The disagreements are
about what exceptions to the standard there should be.

>In LCSI Logo
>and products derived from it, TO is the only exception to the rule that
>inputs are evaluated before a procedure is invoked.  For example, to
>edit a procedure named FOO you must say
>    EDIT "FOO
>so that the word FOO, the procedure's name, is the value of the input
>to EDIT.  By contrast, in MIT-derived dialects (such as Terrapin), several
>primitive procedures are treated as exceptions, so you must say
>to edit the procedure named FOO.

>The advantage of the latter (special form) syntax is that it's more
>obvious to a beginner, especially a young one.

>The advantage of the former (evaluated) syntax is that it's a more
>general mechanism.  For example, suppose I have a bunch of procedures
>that I want to consider as a unit.  I can say
>    END
>and then use the instruction
>to edit those three procedures.  In Terrapin syntax it would instead
>edit the procedure MYPROCS itself, which isn't what I want this time.
>Also, in the long run (some of us think) it's easier to understand;
>in MIT-derived dialects you still have to say
>    MAKE "VAR value
>to assign a value to the variable VAR, so you have to explain to
>students why you need quotes in that case but not for EDIT!

Yes, I agree with you, but I think that everyone would agree that EDIT FOO
is an exception to standard Logo syntax.

>Some really recent versions have even more different notations, moving
>away from the whole idea of variables, so instead of using MAKE to set
>the value and using :VAR to retrieve it, you have procedures SETVAR
>and VAR for those purposes, and there are no variables at all.

This isn't new.  We've always had HEADING and SETHEADING, POS and SETPOS.
This innovation lets the user create these command-reporter pairs, but the
form is the same as what we've always had.


>As for the semantics, what are the essential features of Logo?  There
>have been versions without turtle graphics, such as the "Music Logo"
>that Terrapin sold for the Apple II in which graphics primitives were
>replaced with sound generation primitives.  At MIT there is a project
>in which a small computer is mounted in a Lego brick; it has a different
>primitive set from the typical keyboard-and-screen computer.  At the
>meeting all we agreed on was that anything called Logo should have
>the word and list processing primitives (FIRST, BUTFIRST, LAST, BUTLAST,

...although the first version of StarLogo didn't have lists, (but it did
have lots of turtles).  Maybe it wasn't Logo (or maybe it was).


Michael Tempel                    tel: 212 579 8028
Logo Foundation                   fax: 212 579 8013

New York  NY 10024


Sun, 12 Mar 2000 03:00:00 GMT  
 LOGO-L> Re: Logo Grammar

> At MIT there is a project in which a small computer is mounted in
> a Lego brick; it has a different primitive set from the typical
> keyboard-and-screen computer.  At the meeting all we agreed on was
> that anything called Logo should have the word and list processing


Is able to download the sources of this different primitive set of
Logo ?


* * * * * * * * * * * * * * * * * * * * * *
  Ing. Hazel Diaz Morales                
  Departamento de Computacion                  
  Instituto Tecnologico de Costa Rica    

  Tel     : (506) 552-5333, exts. 2449, 2447
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                              Anthony de Mello

Wed, 15 Mar 2000 03:00:00 GMT  
 [ 2 post ] 

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