Message-Id: <9309151314.AA23185@sc.ZIB-Berlin.DE>
Reply-To: Mailing list for the LaTeX3 project <LATEX-L@vm.urz.Uni-Heidelberg.de>
In-Reply-To:  <9309151250.AA23123@sc.ZIB-Berlin.DE>
Date:         Wed, 15 Sep 93 15:12:18 +0200
From: Rainer Schoepf <schoepf@SC>
Sender: Mailing list for the LaTeX3 project <LATEX-L@vm.urz.Uni-Heidelberg.de>
To: Multiple Recipients of <LATEX-L@vm.urz.Uni-Heidelberg.de>
Subject:      Re: when is a bug a bug? or is it? (fwd)
Status: R


"Erik-Jan Vens" writes:

 >   some time ago I provided Barbara Beeton with an example where LaTeX seemed
 > to be getting in an infinite loop. I suspected it had to do with TeX the
 > program, but yesterday I found the answer, and Barbara asked me to pass it on
 > to you:
 >
 > dixit bbeeton:
 >
 > > well, that's a good one!
 > > shows the dangers of redefining primitives.
 > > this should definitely be passed on to the latex3 folks -- would
 > > you do that, please?  (cc me, though -- i'd like to hear the
 > > answer.)
 > > i'm going to hand this over to my reliable bug-checker for his
 > > opinion.  it may be desirable to report this to knuth even though
 > > it's a bad thing in latex and a possible "misuse" of the facilities.

Oh, Barbara, here you are on the wrong track. LaTeX goes a very long
way to ensure that such an infinite loop cannot happen, *unless* you
use primitive TeX commands. In that respect it doesn't go far enough:
it doesn't prevent people from using these primitive commands.


 > This was what I did:
 >
 > \documentstyle{article}
 >
 > \begin{document}
 >
 > \begin{tabular}{rl}
 > \ &$\vbox to 2\ht\strutbox{\ \vfill}$\\
 > \end{tabular}
 >
 > \end{document}

If the box would have been produced by \makebox or \parbox, there
would have been no infinite loop. (the other possibility would be to
insert \@parboxrestore at the beginning of the box construction.)

Rainer


   Rainer Schoepf
   Konrad-Zuse-Zentrum
    fuer Informationstechnik Berlin
   Heilbronner Strasse 10
   D-10711 Berlin
   Federal Republic of Germany
   <Schoepf@sc.ZIB-Berlin.de> or <Schoepf@sc.ZIB-Berlin.d400.de>