# expandable optional parameter to enumerate environment

The MWE below, by using paralist package, is supposed to allow \begin{enumerate}[...] where ... is flexible in "some way" (inherits from enumerates above).

\documentclass[a4paper,10pt]{report}

\usepackage{paralist,xargs}

\newcommand\mwe[2]{[{\ref{#1}.}.#2]}

\begin{document}

\newenvironmentx{enumwe}[2][2=1]{%
\begin{enumerate}\mwe{#1}{#2}%
%\expandafter\begin\expandafter{\expandafter enumerate\expandafter}\mwe{#1}{#2}%
\ignorespaces%
}{\end{enumerate}%
\ignorespacesafterend%
}

\begin{enumerate}[{A}1]

\item \label{one} {\bfseries~Appendix One}

\begin{enumwe}{one}
\item text
\end{enumwe}

\end{enumerate}

\end{document}


However, the commented line seems a wrong attempt, while the MWE typesets wrong.

The expanded result expected would be the following.

\begin{enumerate}[{A}1]
\item \label{one} {\bfseries~Appendix One}
\begin{enumerate}[{A1.}1.]
\item text
\end{enumerate}
\end{enumerate}


I appreciate any help or suggestions.

P.S.: I actually need to expand a macro in the optional parameter to enumerate environment, like \begin{enumerate}[\mwe{...}1.], but it's not working (the ?? occurs everywhere) and this MWE is my approach, but I got stuck with the weird error:

! LaTeX Error: \begin{enumerate} on input line 21 ended by \end{enumerate}.

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You should use the package enumitem instead which is more flexible and allows what you want to achieve. –  Marco Daniel Aug 17 '12 at 16:24
@MarcoDaniel: sorry, all the rest of the class core code involved is based on paralist, for now. –  sjb Aug 17 '12 at 16:58

\expandafter only steps over a single token not brace groups, so the simplest thing is to put everything you want to step over into a single token:

\documentclass[a4paper,10pt]{report}

\usepackage{paralist,xargs}

\newcommand\mwe[2]{[{\ref{#1}.}.#2]}

\begin{document}

\newenvironmentx{enumwe}[2][2=1]{%
\def\temp{\begin{enumerate}}%
\expandafter\temp\mwe{#1}{#2}%
\ignorespaces%
}{\end{enumerate}%
\ignorespacesafterend%
}

\begin{enumerate}[{A}1]

\item \label{one} {\bfseries~Appendix One}

\begin{enumwe}{one}
\item text
\end{enumwe}

\end{enumerate}

\end{document}

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