References: <20150911094655.GA29867@hzdr.de>
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Message-ID:  <55F2A790.9090709@morningstar2.co.uk>
Date:         Fri, 11 Sep 2015 11:06:08 +0100
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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: non-intuitive behaviour of clist with empty items
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
In-Reply-To:  <20150911094655.GA29867@hzdr.de>
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Envelope-To: <rainer.schoepf@GMX.NET>
Status: R

On 11/09/2015 10:46, Alexander Grahn wrote:
> Good afternoon,
> 
> consider the following example:
> 
>   \documentclass{article}
>   \usepackage{expl3}
>   
>   \begin{document}
>     \ExplSyntaxOn
>       \clist_set:Nn\l_tmpa_clist{,,foo,bar,}
>       \typeout{\clist_count:N\l_tmpa_clist}    %expected:  5,    I get 2.
>       \typeout{\clist_item:Nn\l_tmpa_clist{3}} %expected: `foo`, I get `'.
>       \typeout{\clist_item:Nn\l_tmpa_clist{4}} %expected: `bar`, I get `'.
>     \ExplSyntaxOff
>   \end{document}
> 
> Why does \clist_set:Nn ignore empty items when initialising a clist
> variable from a token list? Is this intended behaviour? Is there a
> work-around?
> 
> Kind regards
> Alexander

This is by-design. Comma lists can't contain empty items, commas, etc.:
sequences can. The reason is comma lists are 'close' to the user level,
and there stray empty entries are normally best ignored.

Joseph