Re: X and Ada?

[hyland@esosun.UUCP (Steve Hyland)]

In article <249@sandia.UUCP> pjatter@sandia.UUCP (Paul Attermeier) writes:

>Is X and Ada a practical combination? 

Yes. We are currently using a subset Ada binding to X.

More pertinent:

>From what little I've seen of the X toolkits, it appears that
>X makes 'callbacks' to the application program. If X is in C
>(which would be acceptable in our 'Ada' system) and the application
>is in Ada, it looks like we still have the same problem.

Yes, the current X toolkit allows the user to include a call-back
routine in the argument list. Since this would violate the spirit of
Ada, we will not allow this. We have a similar problem in the intrinsics,
with the use of event handlers in widgets. The answer ? Its not completely
obvious to me at this point.

More to the point, however; the toolkit is a SUGGESTED set of sample
widgets. How they are implemented is very specific to C. How they are
implemented in our version will be very specific to Ada. In other words,
to the interface user, the widgets will appear the same. To the
application programmer, C widgets and Ada widgets will be different from
each other. And for the widget programmer, as with the C version, the
toolkit will be a template for creating other widgets.

Some of the ways in which we are considering implementing widgets:
  Tasking : seems to be more in the spirit of Widgets-As-Objects,
  Procedure Calls: that is, you create a widget with a procedure call,
  and must handle the events that occur in that widget.

We are leaning toward widgets as task types, since this seems (at least,
intuitively) the correct approach. My only concern is overhead associated
with lots of tasks. Anyone else have any thoughts ?

>Do we need to wait for an Ada implementation of X? Will such a thing
>be available in my lifetime? Am I missing a more obvious solution?

No, you do not need to wait if you are in a hurry. A basic binding can
be hacked out fairly quickly. On the other hand, we have a STARS contract
to build the Ada binding (which will become public domain, I believe) to
X and the X Toolkit. The final versions of these, to be deliverable in
about a year, will be completely written in Ada. An interim version,
which binds to the C version of X11 will be available in about 6 months.

>Paul Attermeier
>uucp: ...{ucbvax | gatech}!unmvax!sandia!pjatter
>arpanet: pjatter@sandia-2

Steve Hyland
SAIC