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Message-ID:  <D6C19E2C-AAB5-4237-8102-0FCE69E1F442@gmail.com>
Date:         Sun, 29 Jan 2012 23:26:50 +1030
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              <LATEX-L@listserv.uni-heidelberg.de>
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From: Will Robertson <wspr81@GMAIL.COM>
Subject: Unexpandability inside \csname
To: LATEX-L@listserv.uni-heidelberg.de
Precedence: list
Status: R

Hello,

I've been away from LaTeX for a little while and now that I come back again I've almost immediately stumbled upon an area that I don't think I've fully understood previously.

Consider:

  \csname\ifnum 3 > 2 foo\fi\endcsname

This (probably obviously to all of you) complains with the standard "Missing \endcsname inserted." presumably because there's an unexpandable implicit \relax inserted somewhere in there.

In expl3 we've discussed the concept of "restricted expandability", which refers to an expandable function that doesn't fully expand inside an "f" function (which is expandable \romannumeral-style expansion).

Does it make sense to also indicate how/where expandable functions won't behave correctly inside "c" arguments? I must admit I haven't considered the ramifications of what these mean entirely. It does seem there's not necessarily much overlap between the f-unexpandable functions and the c-unexpandable ones.

Cheers,
-- Will