带有逗号分隔可选参数的环境

Question

使用xparse，如何让这样的事情发挥作用？

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn

\NewDocumentEnvironment{ anenvironment }{ >{\SplitArgument{1}{,}}o }{
  \begin{ auxanenvironment }[#1]
}{
  \end{ auxanenvironment }
}

\NewDocumentEnvironment{ auxanenvironment }{ O{}o }{
  Do~something~with~#1\IfValueTF{ #2 }{ ,~and~something~else~with~#2. }{ . }
}{}

\ExplSyntaxOff
\begin{document}
\begin{anenvironment}[this argument, this other argument]
\end{anenvironment}

\begin{anenvironment}[this argument]
\end{anenvironment}
\end{document}

Answer 1

虽然可以使用辅助环境来实现这一点，但我不认为这是最好的方法。

您还应该处理可选参数未出现的情况：它是可选的，不是吗？

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\NewDocumentEnvironment{anenvironment}{ >{\SplitArgument{1}{,}}o }
 {
  \IfValueT{#1}{ \noibe_anenvironment_arg:nn #1 }
  %<initial code for the environment>
  \par Start\par
 }
 {
  %<final code for the environment>
  End\par
 }

\cs_new_protected:Nn \noibe_anenvironment_arg:nn
 {
  \tl_if_novalue:nF { #1 }
   {
    Do~something~with~#1
    \tl_if_novalue:nTF { #2 }
     {.}
     {
      ,~and~something~else~with~#2.
     }
   }
}

\ExplSyntaxOff

\begin{document}

\begin{anenvironment}[this argument, this other argument]
\end{anenvironment}

\medskip

\begin{anenvironment}[this argument]
\end{anenvironment}

\medskip

\begin{anenvironment}
\end{anenvironment}

\end{document}

如果不知道您的实际用例，很难做到不那么通用。如果参数用于设置选项，我建议您考虑使用键值接口。

Answer 2

这是一种完全不同的方法。

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{listofitems}
\newenvironment{anenvironment}[1][\relax]{%
  \ifx\relax#1\relax\else
    \readlist*\arglist{ #1}%
    \foreachitem\x\in\arglist[]{%
      Doing something with \detokenize\expandafter{\x}.\x\par
    }%
  \fi\par
}{%
  \par Done doing something.\par\medskip
}
\begin{document}
\begin{anenvironment}
This is a test.
\end{anenvironment}
\begin{anenvironment}[\itshape]
This is a test.
\end{anenvironment}
\begin{anenvironment}[\itshape,\bfseries, \tiny]
This is a test.
\end{anenvironment}
\end{document}

Answer 3

我不确定这是否是正确的方法，但我刚刚发现，删除第 6 行参数周围的方括号，并将auxanenvironment的参数更改为强制参数可以解决问题：

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn

\NewDocumentEnvironment{ anenvironment }{ >{\SplitArgument{1}{,}}o }{
  \begin{ auxanenvironment }#1
}{
  \end{ auxanenvironment }
}

\NewDocumentEnvironment{ auxanenvironment }{ mm }{
  Do~something~with~#1\IfValueTF{ #2 }{ ,~and~something~else~with~#2. }{ . }
}{}

\ExplSyntaxOff
\begin{document}
\begin{anenvironment}[this argument, this other argument]
\end{anenvironment}

\begin{anenvironment}[this argument]
\end{anenvironment}
\end{document}