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Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!purdue!avr
From: avr@cs.purdue.EDU (Andrew V. Royappa)
Newsgroups: comp.windows.x,comp.lang.lisp
Subject: Re: X windows and Lisp
Summary: X windows and Lisp
Keywords: X windows and Lisp
Message-ID: <7217@medusa.cs.purdue.edu>
Date: 21 Jul 89 18:47:04 GMT
References: <1281@mmm.UUCP>
Followup-To: comp.windows.x,comp.lang.lisp
Organization: Department of Computer Science, Purdue University
Lines: 52

In article <1281@mmm.UUCP>, kozak@mmm.UUCP (Darryn Kozak) writes:
> 	We are interested in "combining" the X window system and Common 
> Lisp together. We are writing our  application on Unix and X based
> workstations. Our current intentions are to use X and Motif for our 
> user interface, but to keep our application in Lisp.
> 
> 	Is anyone else doing this? 

I have implemented some algebra algorithms in Lisp and am building
a front-end for them based on X. I chose a display-oriented front-end 
since it would be friendlier and because my application needs to produce
graphical output (draw curves, surfaces, etc.). I would like my application 
to be widely used and so I try to minimize the environment necessary to
run it in, meaning I decided not to use packages such as CLX and CLOS.
My application will need Common Lisp, X, and a Lisp <-> C interface.

The basic design is that the Lisp process will call a certain C
routine to start up the user interface (call is "UI()"). 
This routine will not return until the application quits. What the
UI() routine will do is present the user with a tool containing
a few windows, mainly a text window and a graphics window. When
the user types in some text and selects a button, the text is
passed by the UI() routine to the Lisp program, by calling a
Lisp function (the text is passed as a string argument). The
Lisp function computes whatever command the text string describes,
and returns a string containing a series of graphics commands to the UI().
The UI() displays the graphics commands on the graphics window.


> 	Where should the line between C and Lisp lie. That is, where should
> the control of the application be? It appears that all of the Xlib and Xt
> data structures must remain in C. 
> 

So to summarize, although the Lisp program starts up the (C based)
user interface, the user interface really has control over the
application (uses subroutine calls to Lisp to perform computations).

I am comfortable coding in both Lisp and C, but prefer
coding graphics/window operations in C, and symbolic math type 
operations in Lisp. So I separate the two portions and have
a simple well-defined interface between them (subroutine calls
passing and returning strings), and neither side needs to know
anything about the other.

More discussion on this would be interesting. I invite comments
on my approach (always willing to listen to good ideas).

				Andrew V. Royappa
				Purdue University
				avr@purdue.edu
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