LOGO-L> Re: LOGO-L> Re: LOGO-L> Is Logo old technology?

["Wen \"Wayne\" Su" <Wen.Su@gte.net>]

I think that, if my understanding is correct, there is a major difference
between MW and TT here. Suppose in the code below, both subprocesses (called
Circle and Square)  that are launched try to modify a variable owned by the
current process (called Parent), in MW, there is no directly built-in
mechanism that allows the Parent process to tell which launched process
modifies the variable first, for example. Of course, this can be done by
users by other means. The same issue arised in low-level hardware driver
code, or when both the interrupt handler code (the code that is triggered to
be executed by a hardware interrupt event) and the main line code try  to
modify the same variable. In TT, the data change requests are sent from
Circle and Square to Parent and the requests are placed in a queue, and the
Parent process can tell which data modification request comes in first by
means of its built-in message passing method(bird).

This above comment (if correct), does not imply that MW is inferior as far
as its education value is concerned, IMHO. Maybe MW developers happen to
believe this feature is not that important for children students. Some
people (Ken Kahn?) may believe this is very very important ( I think that is
the reason why he talked about the "global variable" accessing issue.); some
may not.

Regards,
Wen

Bill Kerr wrote in message ....
>I think this MicroWorlds procedure (from MW help on waituntil and also
>done?) does synchronise parallel processes:
>
>to sq-circ
>t1, pd launch [repeat 36 [fd 10 rt 10]]
>; t1 draws a circle
>t2, pd launch [repeat 4 [fd 50 rt 90]]
>; t2 draws a square
>waituntil [done? [repeat 36 [fd 10 rt 10]]]
>; the procedure does not continue until the circle is finished
>; so that the drawings of circles and square are synchronised
>t1, pu rt random 360 fd random 50
>t2, pu rt random 360 fd random 50
>; repositions turtles for next drawing
>sq-circ
>end







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