Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!think!snorkelwacker!bloom-beacon!HPLABS.HP.COM!mayer%hplnpm
From: mayer%hplnpm@HPLABS.HP.COM (Niels P. Mayer)
Newsgroups: comp.windows.x
Subject: Re: WINTERP Questions
Message-ID: <9297.630088747@hplnpm>
Date: 19 Dec 89 16:39:07 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: Hewlett-Packard Labs, Software Technology Lab, Palo Alto, CA.
Lines: 64

Newsflash! WINTERP now has documentation! 
see expo.lcs.mit.edu:contrib/winterp.tar.Z for details....

In article <1971@eric.mpr.ca> parker@zaphod.mpr.ca (Ross Parker) writes:
>I've just finished building winterp (version 1.0), and it
>looks pretty neat...

Thanks! Please send me any enhancements you make.

>and have a couple of questions. The documentation that came
>with winterp is a little skimpy (as can be expected - I'm
>not complaining).

I just updated the file on expo with approx 200kbytes of plaintext
documentation.  Hope this will make you happy. The documentation is no
substitute for the standard Motif documentation, the Xtoolkit
documentation, or Doug Young's upcoming Motif Book. The documentation
should serve as a good supplement to the official Motif documetation and
should help you in translating example code from C to WINTERP-Lisp syntax.

> I got the idea from the doc that it is
>possible to write out C code, but I couldn't figure out
>how to do it. Is it easy? If so, can it be explained in
>a paragraph or so?

The documentation explains some of the philosophy behind writing hybrid
Lisp/C programs. XLISP makes it very easy to merge in new C-implemented
primitives and methods into an application. JonnyG did a good job of
explaining in one paragraph what needs to be done, and which things you
should look at. 

Writing Lisp callable C code in WINTERP is easy once you get the hang of
it. All of the WINTERP source code should serve as an example of how to
implement methods and primitives in C. As JonnyG said, the toughest part is
remembering to protect newly created objects from getting garbage
collected. Also take a look at ./winterp/src-server/w_funtab.{c,h} to see
how to add new methods and functions to XLISP's functiontable.

I was going to write up a document on how to add new primitives to XLISP
and WINTERP, but I didn't find the time. Send me mail if you're interested
and I'll mail you something if I ever get around to documenting that aspect
of WINTERP.

> Are winterp lisp functions only capable of calling other
> winterp lisp functions, or can I build a library of 'C'
> callbacks that are called by winterp lisp functions?

Winterp lisp functions can call other lisp-implemented functions, or they
can call C-implemented functions. Similarly, methods for particular object
classes can be implemented in C or in Lisp. 

You can then call these C-implemented lisp primitives via callbacks
(XtAddCallback()), event handlers (XtAdd{Raw}Eventhandler()), and timeouts
(XtAddTimeout()) . I've even provided a special ActionProc "Lisp()" which
will allow you to call the lisp evaluator through translation and
accelerator tables (it's lotsa fun)...

				-- Niels Mayer
				   Hewlett-Packard Laboratories
				   Human-Computer Interaction Department.

PS: If anybody sends e-mail questions about WINTERP, be forewarned that I
will not be able to answer e-mail until after the first week of January --
I will be on vacation, and I'm leaving tonight.