Re: Building STk on HP-UX

From: Erik Ostrom <eostrom_at_ccs.neu.edu>
Date: Tue, 14 Feb 95 15:53:23 -0500

> Does this approach make sense?
>
>
> (button "Frob" :command
> (create-callback table (lambda () (frob ...))))
>
> Create-callback interns the closure and associates it with a string. It
> returns a string that when executed by Tk looks up the calback by name and
> funcalls it. If you had one table per application, you could throw it away
> when the application is deactivated.

I did something related to this for bindings in STklos objects.
Here's an example from my code:

    (define-binding bb '<3> (|X| |Y|)
      (menu-post ih (- |X| 6) (- |Y| 6)))

What this does, roughly, is:

  * Create a closure of two arguments, |X| and |Y|, with the obvious
    definition. (bb and ih are of course defined in the scope.)
  * Store the closure in a hash table associated with bb.
  * Bind <3> in bb to "(XXXX %X %Y)", where XXXX is the address of the
    closure.

The hash table ensures that if you later bind <3> to something else,
the old closure will get GCd.

There are a number of things I don't like about this--for example, it
doesn't work for various non-bind entities like menus, and it creates
a hash table for every Tk-object (actually every Tk-object that uses
define-binding). However, if I ignore the implementation and its
limitations, I really like using it.

If anyone's interested, I can mail out the code. It's a pretty
horrendous macro and an associated function, along with an extra slot
in Tk-object; it's not great, but it could be hacked into shape.
Received on Tue Feb 14 1995 - 22:30:16 CET