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Message-ID:  <4F2BFFA6.1020306@morningstar2.co.uk>
Date:         Fri, 3 Feb 2012 15:39:18 +0000
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Sender: Mailing list for the LaTeX3 project <LATEX-L@listserv.uni-heidelberg.de>
From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: Mapping Functions Versions for All and Some
To: LATEX-L@listserv.uni-heidelberg.de
In-Reply-To:  <20120203151218.GA30208@csmvddesktop>
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Status: R

On 03/02/2012 15:12, dongen wrote:
> I'm having some problem with expansion. The following is a
> contrived example of what's going wrong. I must be missing
> something obvious.
> 
>     \expandafter
>     \xdef\csname #1\endcsname ##1{%
>         \regex_match:nnTF{o}{o}{{0}{0}}{{1}{1}}
>     }
> 
> This defines some macro with the following definition:
> 
>     macro:#1->\regex_match:nnTF {o}{o}{{0}{0}}{{1}{1}}
> 
> I'd have thought the body of an xdef would be fully expanded
> (unless you put an explicit \noexpand in front of an expression).
> 
> Why doesn't the \regex_match expand? If there's any documentation
> I should read in order to understand this, please let me know where
> to find it.

All LaTeX3 functions are either fully expandable or engine-protected. In
this case, we are talking about protected functions: these are not
expandable. (In the documentation, expandable functions are marked with
a star.)
-- 
Joseph Wright