Lines: 50
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
User-Agent: 40tude_Dialog/2.0.15.41de
Message-ID:  <lhuvb7mshjkb$.dlg@nililand.de>
Date:         Tue, 27 Sep 2011 14:10:20 +0200
Reply-To: Mailing list for the LaTeX3 project
              <LATEX-L@listserv.uni-heidelberg.de>
Sender: Mailing list for the LaTeX3 project <LATEX-L@listserv.uni-heidelberg.de>
From: Ulrike Fischer <news3@NILILAND.DE>
Subject: o and V-type functions
To: LATEX-L@listserv.uni-heidelberg.de
Precedence: list
Status: R

The documentations source3 says at the start "In general, the V and
v specifiers are favoured over o for recovering stored information". 

But everytime I start to define functions which should expand their
argument I end either with x or o types. 

As an example I tried to write a function which process key-val
lists. The list can also be given through a command. With o this
works fine, with V normal and empty lists gives errors:

\documentclass[parskip]{scrartcl}
\usepackage{expl3}


\begin{document}

\section{expl3}
\ExplSyntaxOn

\keys_define:nn {test}
 {testa .code:n = {#1},
  testb .code:n = {#1},
 }

 
\cs_new:Npn \test_usekeys:n #1 {keys:~[\keys_set:nn {test}{#1}]}
\cs_generate_variant:Nn \test_usekeys:n {V}
\cs_generate_variant:Nn \test_usekeys:n {o}

\def\mykeylist{testa=A,testb=B}

 \test_usekeys:V {\mykeylist}
%\test_usekeys:V {testa=A,testb=B}
%\test_usekeys:V {}

\par 

\test_usekeys:o {\mykeylist}\\
\test_usekeys:o {testa=A,testb=B}\\
\test_usekeys:o {}\\
\test_usekeys:o {\mykeylist}\\

\end{document}


Could someone explain me when arguments of type V are actually
useful and "better" than o and how they should be used?

-- 
Ulrike Fischer