Path: utzoo!attcan!uunet!husc6!bloom-beacon!WHEATIES.AI.MIT.EDU!sundar
From: sundar@WHEATIES.AI.MIT.EDU (Sundar Narasimhan)
Newsgroups: comp.windows.x
Subject: Deficiency in the translation mechanism
Message-ID: <8901241952.AA05880@special-k.ai.mit.edu>
Date: 24 Jan 89 19:52:40 GMT
References: <6312@eagle.ukc.ac.uk>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 39


   Current solution (2):

   Write a new widget which replicates most of the code in the text
   widget.

You are right. I decided after careful evaluation (and actually using
the text widgets provided in the Athena and Hp Widget sets) to do just
this. (But I don't think that it is the translation mechanism that is
at fault, but rather the poor interface or hooks provided by current
text widgets to the application writer).

The way I think it should have been done is to have before, during,
and after procedures that an application can alter or supply (these
could be just callbacks but you really want to have something more
like Lisp machine method combinations). The hp widget actually
provides you such a facility (it has Verify callbacks on modification,
for example).

With this capability writing a field editor that returns on carriage
return would be simple. I have, in fact a command and argument parser,
that for example dispatches on characters like ' ' to attempt
completing what the user typed, provide help etc. Notice that some of
these operations may involve modifying the text, the cursor position
etc.. operations which are very cumbersome to do in the current text
edit widgets at the application level. It will also provide you a
simple way to implement a tty window -- (a widget that just scrolls
error messages is actually hard to do with the present text widgets --
I know this facility can also be gotten by running xterm in slave mode but
then you'd have a whole extra process to contend with).

I think that such an interface to a text widget is more powerful than
the ones provided by the current widgets, and will make the widget
useable in more applications. (Mine is currently being used by
programs in a multiprocessor development environment, a plotter
program, and an experimenatal motion vision analysis package -- but it
runs only on Suns at this time).

-Sundar