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From: seiler@HUDSON.DEC.COM ("LARRY SEILER")
Newsgroups: mod.computers.laser-printers
Subject: Flaw in Postscript?
Message-ID: <8601150115.AA28861@ucbvax.berkeley.edu>
Date: Tue, 14-Jan-86 20:16:46 EST
Article-I.D.: ucbvax.8601150115.AA28861
Posted: Tue Jan 14 20:16:46 1986
Date-Received: Thu, 16-Jan-86 00:44:20 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: "LARRY SEILER" <seiler@hudson.dec.com>
Organization: The ARPA Internet
Lines: 31
Approved: laser-lovers@washington.arpa

There's something that's bothered me since I first heard of Postscript,
and now that people are doing fancy stuff like N-up headers, it might
actually start biting people.  

Early criticisms of Postscript pointed out things like the absence of
any built in accounting, bugs in ROM'd code, and so forth.  To each of 
the criticisms, the reply was that Postscript allows builtin operations
to be redefined, so that a piece of patch code can be downloaded to
correct known bugs, a site that wants per-page accounting can define
a new ShowPage that provides this, and so forth.

For bug fixes, this is great.  But when it is used to add new features
to an existing function, there is trouble.  Say that the system redefines
ShowPage to include per-page accounting, and I use a header that redefines
ShowPage to do 2-up printing.  Either I've just defeated the accounting,
or else the definition of ShowPage was locked in and my 2-up header fails
on this machine.

Can any Postscript gurus out there point out a way around this problem?
It would suffice in this case to allow ShowPage to be redefined by an N-up 
header that itself calls the previous definition of ShowPage (not the original 
version, which might be buggy or might not include desired accounting).
Is that possible in PostScript?  Can anyone come up with other examples
like this where nesting of function redefinitions causes trouble?

	Larry

PS - Please, no straw men: don't say "but you have the same problem in
page description languages X, Y, and Z as well."  The question is, can
PostScript cope with it.
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