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From: diamant@hpfclp.HP.COM (John Diamant)
Newsgroups: comp.windows.x
Subject: Re: X and Ada?
Message-ID: <9740003@hpfclp.HP.COM>
Date: Sun, 20-Sep-87 19:51:58 EDT
Article-I.D.: hpfclp.9740003
Posted: Sun Sep 20 19:51:58 1987
Date-Received: Sat, 26-Sep-87 00:53:07 EDT
References: <64@kvasir.esosun.UUCP>
Organization: HP, Fort Collins, CO
Lines: 44

> >*Any* toolkit is going to depend on the use of call-back functions.
> 
>   I don't agree with this.  It bothers me that X has two different
> mechanisms for sending messages when it would considerably simplify
> things if only one were used.  The X event mechanism is sufficient
> to handle all the message passing requirements that the callback
> mechanism handles.

This is true, I think.  They are both turing equivalent mechanisms.  You're
also probably right that having two different mechanisms complicates things,
but the question still remains which one is better.

> I think that X events should be extended and
> generalized so that they would allow events generated by toolkit
> gadgets to be handled in the same way that normal X events are
> handled.

Personally, I would prefer the opposite direction.  I prefer callbacks, because
it places the procedural burden on the toolkit instead of the user/programmer.
I find it very appealing that I can declaratively state the times in which
my callbacks are to be executed, and not have to worry about passage of
control.

>   Does anybody know why X has two different kinds of message passing
> mechanisms?  Couldn't we just get rid of call-backs?  Does anybody have
> any ideas on what the "right" message passing mechanism for X should be?

I suspect that the reason is simply that others had the same ideas that
I do about the implicit control information achievable through callbacks,
and chose to implement it that way.

I too, would like to see only one mechanism for message passing, but I 
would rather it be callbacks.  Multiple callbacks for the same event have
to be supported, of course, for this to be meaningful.

> -- 
> Bruce Karsh
> {uwvax,ihnp4}!nicmad!karsh


John Diamant
TSBU				UUCP:  {hplabs,hpfcla}!hpfclp!diamant
Hewlett Packard Co.		ARPA Internet: diamant%hpfclp@hplabs.HP.COM
Fort Collins, CO