[plt-scheme] event binding help

From: briand at aracnet.com (briand at aracnet.com)
Date: Sat Feb 28 19:30:12 EST 2004

>>>>> "Bruce" == Bruce Hauman <bhauman at cs.wcu.edu> writes:

  Bruce>   For list-related administrative tasks:
  Bruce> http://list.cs.brown.edu/mailman/listinfo/plt-scheme

  Bruce> Hey Brian,

  Bruce> There are many ways to do what you are asking.  Here is some
  Bruce> code that only implements two different ways.  One uses the
  Bruce> event delegation model that Java uses heavily in its GUI API.
  Bruce> The other just uses straight mutation of the button's
  Bruce> callback.

  Bruce> I would advise against making a bunch of global event
  Bruce> handlers.  It would really be good to find the lowest points
  Bruce> on the event chain and introduce your handlers there.

Thanks for the example Bruce.

I think I found a more succinct way of expressing what I'm trying to do.

Given the way the event-handling currently works, with keypresses and
mouse-events being separate methods (or even if they aren't), the code
ends up looking like :

  state=line do...
  state=circle do...

later in the code...

  state=in-line do
  state=in-circle do

  state=in-line do
  state=in-circle do


This breaks up the "tool" operation through several points in the
code, which is not useful.

What I want is the "inverse" of the above, i.e.

  event=button-down do...
  event=motion do ...
  event=key-press do...

The bind methodology makes for code which is much easier to
understand, i.e. the 2nd form.  I was hoping that the eventspace
functionality would allow me to do something similar, but if it does I
can't figure it out.

I believe that the "java-like" portion of your example demonstrates
that this functionality must be explicitly provided.

Thank you for your help.


Posted on the users mailing list.