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Message-ID:  <4B24C7FB.1040604@morningstar2.co.uk>
Date:         Sun, 13 Dec 2009 10:54:51 +0000
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              <LATEX-L@listserv.uni-heidelberg.de>
Sender: Mailing list for the LaTeX3 project <LATEX-L@listserv.uni-heidelberg.de>
From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: \peek_ ... in tables
To: LATEX-L@listserv.uni-heidelberg.de
Precedence: list
Status: R

Hello all,

I've been working on some code to do peek-ahead stuff in tables. It 
looks to me as though the \peek_...:NTF functions are broken in this 
context:

\documentclass{article}
\usepackage{array,expl3}
\begin{document}
\ExplSyntaxOn
\cs_new:Npn \CollectTokens {
   \peek_meaning:NTF \ignorespaces { } { }
}
\ExplSyntaxOff

\begin{tabular}{>{\CollectTokens}cc}
   a & \\
     & \\
       \\
\end{tabular}

\ExplSyntaxOn
\cs_set:Npn \CollectTokens {
   \cs_set_eq:NN \l_peek_search_token \ignorespaces
   \tl_set:Nn \l_peek_true_tl  { }
   \tl_set:Nn \l_peek_false_tl { }
   \peek_after:NN \peek_execute_branches_meaning:
}
\ExplSyntaxOff

\begin{tabular}{>{\CollectTokens}cc}
   a & \\
     & \\
       \\
\end{tabular}

\end{document}

The second version here omits the \group_align_safe_(begin/end): 
functions which the standard \peek_meaning:NTF, etc., functions add.

Any ideas what is up? Am I getting something wrong?
--
Joseph Wright