描述列表中的自动交替标签

Question

我需要以这样一种方式使用描述环境，这样我就不必一遍又一遍地写交替标签（如下例所示）。有没有办法让这些标签自动生成？这将节省大量时间和麻烦。谢谢。

\begin{description}
\item[A:] text
\item[B:] text
\item[A:] text
\item[B:] text
\item[A:] text
\item[B:] text
\item[A:] text
\item[B:] text
\item[A:] text
\item[B:] text
\end{description}

Answer 1

基于enumerate环境的变体，具有enumitem和etoolbox：

\documentclass{article}
\usepackage{enumitem}
\usepackage{etoolbox}
\newlist{alternate}{enumerate}{1}
\renewcommand\labelalternatei{\bfseries\protect\ifnumodd{\value{alternatei}}{A:}{B:}}

\begin{document}

Some text some text some text some text some text some text some text some text some text some text some text some text some text.
\begin{alternate}[wide=0pt]
  \item First
  \item Second
  \item Third
  \item Fourth
  \item Fifth
  \item Sixth
\end{alternate}

\end{document} 

Answer 2

借助包裹enumitem和一些我无法解释的黑魔法。

\documentclass{article}

\usepackage{enumitem}
\protected\def\mylabel#1{\ifodd#1A:\else B:\fi}
\AtBeginDocument{\sbox0{\bfseries A:\hspace\labelsep}%
                 %\edef\Ahmad{\dimexpr\number\wd0 sp\relax}% pleasing but slower
                 \edef\Ahmad{\the\wd0}%
}

\begin{document}

\begin{enumerate}[label=\bfseries\mylabel{\value*},
                  itemindent=\dimexpr-\leftmargin+\Ahmad\relax, 
                  labelwidth=\Ahmad]
\item text
\item text
\item text
\item text
\item text
\item text
\item text
\item text
\item text
\item text
\end{enumerate}

\begin{description}
\item[A:] text
\item[B:] text
\item[A:] text
\item[B:] text
\item[A:] text
\item[B:] text
\item[A:] text
\item[B:] text
\item[A:] text
\item[B:] text
\end{description}
\end{document}