Re: Forcing expansions in Tex

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Article #10971

#10971

From: C.E. Thompson
Date: Wed, 06 Jan 1993 01:40

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In article <EIJKHOUT.93Jan5155258@cupid.cs.utk.edu>, eijkhout@cupid.cs.utk.edu
(Victor Eijkhout) writes:
|> 
|> No bug. The \uppercase command is *not expandable* in the
|> technical sense, and that's the one that counts.
|> 
[...]
|> 
|> The behaviour of \uppercase is often counterintuitive.
|> See a couple of cute examples in section 3.6.2 of the
|> book by yours truly.)

No argument about that. Does anyone understand the pre-history of this?
In general, TeX82 does more things by expansion than TeX78 did: for example,
conditionals were moved from the stomach to the mouth in TeX82 version 0.8
(change #45 in tex82.bug). Why did \uppercase and \lowercase get left as
mode-indepedent commands?

There is a design constraint in TeX that expansion mustn't have certain
side-effects (in particular, it mustn't alter anything in the |eqtb| array).
(In METAFONT, by the way, there is no such constraint: expanding a token can
cause almost anything to happen.) But there would seem to be no problem with
\uppercase and \lowercase in this respect.

Chris Thompson
JANET:    cet1@uk.ac.cam.phx
Internet: cet1@phx.cam.ac.uk

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References: <MANDAL.93Jan5124200@rose.cis.ohio-state.edu> <EIJKHOUT.93Jan5155258@cupid.cs.utk.edu>

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From: cet1@cus.cam.ac.uk (C.E. Thompson)
Subject: Re: Forcing expansions in Tex
Message-ID: <1993Jan6.014020.6570@infodev.cam.ac.uk>
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Date: Wed, 6 Jan 1993 01:40:20 GMT
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