完全展开使用 expl3 创建的新环境的参数

Question

在这答案是，我得到了下面的代码，解决了我原来的问题。

\ExplSyntaxOn

\NewDocumentEnvironment{withalignment}{m}
 {
  \begin{\vincent_alignment:n { #1 }}
 }
 {
  \end{\vincent_alignment:n { #1 }}
 }

\cs_new:Nn \vincent_alignment:n
 {
  \str_case:nn { #1 }
   {
    {c}{center}
    {center}{center}
    {l}{flushleft}
    {left}{flushleft}
    {r}{flushright}
    {right}{flushright}
   }
 }
\ExplSyntaxOff

可以这样使用：

\begin{withalignment}{left}
\lipsum[1][1-4]
\end{withalignment}

\begin{withalignment}{center}
\lipsum[1][1-4]
\end{withalignment}

然而，问题是当我通过宏/命令提供对齐时：

\newcommand{\myalignment}{center}
\begin{withalignment}{\myalignment}
\lipsum[1][1-4]
\end{withalignment}

似乎不起作用。如何在处理参数之前充分展开它以使其起作用？

Answer 1

我做的改变：

• [必填] 在定义中\vincent_alignment:n，\str_case:nn被替换为\str_case:en
• [可选] 在定义withalignment环境时，分别在和\exp_args:Ne前面添加一个。此更改是可选的，但应该会提高效率。\begin\endwithalignment

\documentclass{article}
\usepackage{lipsum}

\ExplSyntaxOn
\NewDocumentEnvironment{withalignment}{m}
 {
  \exp_args:Ne \begin {\vincent_alignment:n { #1 }}
 }
 {
  \exp_args:Ne \end {\vincent_alignment:n { #1 }}
 }

\cs_new:Nn \vincent_alignment:n
 {
  \str_case:en { #1 }
   {
    {c}{center}
    {center}{center}
    {l}{flushleft}
    {left}{flushleft}
    {r}{flushright}
    {right}{flushright}
   }
 }
\ExplSyntaxOff

\begin{document}
\begin{withalignment}{left}
\lipsum[1][1-4]
\end{withalignment}

\begin{withalignment}{center}
\lipsum[1][1-4]
\end{withalignment}

\newcommand{\myalignment}{center}
\begin{withalignment}{\myalignment}
\lipsum[1][1-4]
\end{withalignment}

\renewcommand{\myalignment}{right}
\begin{withalignment}{\myalignment}
\lipsum[1][1-4]
\end{withalignment}
\end{document}

奖励：应用第二种解决方案Ulrike Fischer 建议在问题评论中

\documentclass{article}
\usepackage{lipsum}

\ExplSyntaxOn
\NewDocumentEnvironment{withalignment}{m}
 {
  \exp_args:Ne \begin {\vincent_alignment:e { #1 }}
 }
 {
  \exp_args:Ne \end {\vincent_alignment:e { #1 }}
 }

\cs_new:Nn \vincent_alignment:n
 {
  \str_case:nn { #1 }
   {
    {c}{center}
    {center}{center}
    {l}{flushleft}
    {left}{flushleft}
    {r}{flushright}
    {right}{flushright}
   }
 }
\cs_generate_variant:Nn \vincent_alignment:n {e}
\ExplSyntaxOff

\begin{document}
\begin{withalignment}{left}
\lipsum[1][1-4]
\end{withalignment}

\begin{withalignment}{center}
\lipsum[1][1-4]
\end{withalignment}

\newcommand{\myalignment}{center}
\begin{withalignment}{\myalignment}
\lipsum[1][1-4]
\end{withalignment}

\renewcommand{\myalignment}{right}
\begin{withalignment}{\myalignment}
\lipsum[1][1-4]
\end{withalignment}
\end{document}