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Message-ID:  <4A7A906B.6080709@morningstar2.co.uk>
Date:         Thu, 6 Aug 2009 09:12:27 +0100
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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: xparse
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
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Status: R

Will Robertson wrote:
> I'm more in favour of having the single letter with a possible optional
> default.
> I still think that { o } and { o{default} } make the most sense.

Well, in a way so do I (it was my suggestion :-))

> I like this way of doing coordinates. Could 'd{}{-default-}' be
> shoe-horned into this syntax as well? I suppose that would mean
> completely re-writing the parser. But then we wouldn't need another
> letter for my feature of limited value.

I thought about this.  There is an issue, though.  For a standard
delimited argument, the two "ends" are arbitrary: [) will work as well
as [].  You can easily pick up:

d{ ...

for the opening-group token, but in this case you have to have a closing
group token as the closing token (both for d{} and for gathering the
argument).  So d[]{default} and d{}{default} are subtly but importantly
different.  I'm not opposed, though:

"d{}{<default>} can be used to include an optional argument surrounded
by braces.  Note that in this case the closing token *must* be a
close-group token (usually `}')."
-- 
Joseph Wright