我如何制作可扩展的引用列表？

Question

我尝试制作一个引用列表，可用于xstring。以下是 MWE：

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{xstring}

\makeatletter
\NewDocumentCommand{\citelist}{m}
  {%
    \@for\citeitem:={#1}\do{\@nameuse{b@\citeitem}, }%
  }
\makeatother

\begin{document}

`\citelist{a,b}'

\StrChar{\citelist{a,b}}{1}[\temp]

`\meaning\temp'  (instead of `macro:->A')

\begin{thebibliography}{A}
\bibitem[A]{a} A
\bibitem[B]{b} B
\end{thebibliography}

\end{document}

不幸的\citelist是 不适用于\StrChar。我该怎么办？

Answer 1

\@for使用不可扩展的赋值。递归定义应该可行。

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{xstring}

\makeatletter
\newcommand{\citelist}[1]{\@citelist#1,\relax,}
\newcommand*{\@citelist}{}% better safe than sorry
\def\@citelist#1,{\ifx#1\relax\else\@nameuse{b@#1}, \expandafter\@citelist\fi}%
\makeatother

\begin{document}

`\citelist{a,b}'

\StrChar{\citelist{a,b}}{1}[\temp]

`\meaning\temp'  (instead of `macro:->A')

\begin{thebibliography}{A}
\bibitem[A]{a} A
\bibitem[B]{b} B
\end{thebibliography}

\end{document}