Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!uakari.primate.wisc.edu!ames!dftsrv!mimsy!brillig.umd.edu!don
From: don@brillig.umd.edu (Don Hopkins)
Newsgroups: comp.lang.postscript
Subject: debugging PostScript
Summary: do it on the screen
Keywords: PostScript debugging, NeWS, PSIBER Space Deck
Message-ID: <21248@mimsy.umd.edu>
Date: 13 Dec 89 02:37:10 GMT
References: <89@<POLLACK> <49400001@primerd>
Sender: news@mimsy.umd.edu
Reply-To: don@brillig.umd.edu (Don Hopkins)
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 57

In article <49400001@primerd> choinski@primerd.prime.com writes:
>
>||It seems like it might be possible, in principle, to get a cheap and
>||accurate postscript previewer given you already have postscript in a
>||printer.
>
>The hell with any pre-viewers!   Does anyone out there have a postscript
>lexer?  I've just about had it with sending a large PS file to the
>printer and find the entire job flushed because I misspelled "setgray".
>And of course, it only reports one error at a time, so any additional
>problems are found ONE AT A TIME!
>
>A PS-lexer would be great, and having a syntax checker as well would
>be optimal.  I don't need a full pre-viewer, just something to catch
>simple errors.  I can handle the semantic problems when I see the
>output.
>
>Anyone have something that will do?  
>
>-============================================================================-
> Burton Choinski                                       choinski@env.prime.com
>   Prime Computer, Inc.                                  (508) 879-2960 x3233
>   Framingham, Ma.  01701
> Disclaimer:  Hey, not me man; musta been my evil twin.
>-============================================================================-

PostScript syntax is so trivial that most of the bugs you enounter are
semantic. How could a mere lexer know that "setgary" was a user
defined procedure rather than a typo, without actually interpreting
the code? What you probably need is a PostScript interpreter with a
stubbed-off graphics library. I'm not saying that such a beast (a
graphics-less postscript interpreter) would not be useful (it would be
very useful, and relativly easy to write). You could lexically analyze
the document structuring comments, without actually interpreting the
PostScript code, but no matter how badly formed the document structure
is, it'll never cause any of the types of bugs you want to detect,
since comments are ignored by the interpreter, of course!

The best way to debug PostScript is on the screen. I have heard that
Adobe sells some sort of PostScript debugging system for Display
PostScript, but I have never seen it. (and I've only seen ads for
LaserTalk.)  I've written an extensive PostScript debugger for NeWS
(The PSIBER Space Deck -- PostScript Interactive Bug Eradication
Routines), that is described in a paper I presented at the Usenix
Monterey graphics conference. I use it all the time, and it seemed to
work last time I tried (it's been most useful for debugging itsself).
If you'd like a copy of the paper and/or the source code to the NeWS
PostScript debugger and associated paraphernalia, send me a note
(don@brillig.umd.edu, ...!uunet!mimsy!don) and I'll try to email it to
you. (It's pretty big, but it's free!).  (I recently posted it all to
comp.windows.news, so check there first if you can.) The NeWS debugger
is written entirely in PostScript.  It runs on NeWS 1.1 and X11/NeWS.
It would be impossible to run it in a laser printer though, because of
its extremely interactive nature (direct stack manipulation, graphical
data structure editor, etc...).

	-Don