“知道”周围环境名称的 LaTeX 2e 环境

Question

我希望有一个 LaTeX 2e 环境，当它出现在另一个环境中时，它会“知道”周围环境的名称。这可能吗？

我知道这\@currenvir提供了当前环境的名称。

我寻求某种\@surroundenvir能够提供周围环境名称的东西。

例如

\documentclass{article}
\makeatletter
\newenvironment{FOO}{\message{\@currenvir-begin: Surrounding environment's name is \@surroundenvir}}%
                    {\message{\@currenvir-end: Surrounding environment's name is \@surroundenvir}}
\newenvironment{BAR}{\message{\@currenvir-begin: Surrounding environment's name is \@surroundenvir}}%
                    {\message{\@currenvir-end: Surrounding environment's name is \@surroundenvir}}
\newenvironment{FOOBAR}{\message{\@currenvir-begin: Surrounding environment's name is \@surroundenvir}}%
                       {\message{\@currenvir-end: Surrounding environment's name is \@surroundenvir}}
\makeatother
\begin{document}
\begin{FOO}
\end{FOO}
\begin{BAR}
\end{BAR}
\begin{FOOBAR}
\end{FOOBAR}
\begin{FOO}
\begin{BAR}
\begin{FOOBAR}
\end{FOOBAR}
\end{BAR}
\end{FOO}
\end{document}

应提供控制台输出：

FOO-begin: Surrounding environment's name is document
FOO-end: Surrounding environment's name is document
BAR-begin: Surrounding environment's name is document
BAR-end: Surrounding environment's name is document
FOOBAR-begin: Surrounding environment's name is document
FOOBAR-end: Surrounding environment's name is document
FOO-begin: Surrounding environment's name is document
BAR-begin: Surrounding environment's name is FOO
FOOBAR-begin: Surrounding environment's name is BAR
FOOBAR-end: Surrounding environment's name is BAR
BAR-end: Surrounding environment's name is FOO
FOO-end: Surrounding environment's name is document

Answer 1

环境通常使用\begin-\end子句来调用。你可以\begin使用etoolbox\@currenvir）在更新之前存储其值：

\documentclass{article}

\usepackage{etoolbox}

\makeatletter
% \patchcmd{<cmd>}{<search>}{<replace>}{<success>}{<failure>}
\patchcmd{\begin}{\begingroup}{\begingroup\let\@surroundenvir\@currenvir}{}{}

\newenvironment{FOO}{\message{\@currenvir-begin: Surrounding environment's name is \@surroundenvir}}%
                    {\message{\@currenvir-end: Surrounding environment's name is \@surroundenvir}}
\newenvironment{BAR}{\message{\@currenvir-begin: Surrounding environment's name is \@surroundenvir}}%
                    {\message{\@currenvir-end: Surrounding environment's name is \@surroundenvir}}
\newenvironment{FOOBAR}{\message{\@currenvir-begin: Surrounding environment's name is \@surroundenvir}}%
                       {\message{\@currenvir-end: Surrounding environment's name is \@surroundenvir}}
\makeatother

\begin{document}

\begin{FOO}
\end{FOO}
\begin{BAR}
\end{BAR}
\begin{FOOBAR}
\end{FOOBAR}
\begin{FOO}
  \begin{BAR}
    \begin{FOOBAR}
    \end{FOOBAR}
  \end{BAR}
\end{FOO}

\end{document}

得出的结果是.log：

FOO-begin：周围环境的名称是文档
FOO-end: 周围环境的名称是文档
BAR-begin：周围环境的名称是文档
BAR-end: 周围环境的名称是文档
FOOBAR-begin：周围环境的名称是文档
FOOBAR-end: 周围环境的名称是 document
FOO-begin：周围环境的名称是文档
BAR-begin：周围环境的名称是FOO
FOOBAR-begin：周围环境的名称为BAR
FOOBAR-end: 周围环境名称为BAR
BAR-end: 周围环境的名称是 FOO
FOO-end: 周围环境的名称是文档

请注意，\@currenvir默认值为document，在LaTeX2e 内核。

Answer 2

例如“test.tex”：

\documentclass{article}
\usepackage{etoolbox}
\makeatletter
\newcommand*\@surroundenvir{}
\newcommand*\@surroundenvirtemp{}
\BeforeBeginEnvironment{FOO}{\let\@surroundenvirtemp=\@currenvir}
\AtBeginEnvironment{FOO}{\let\@surroundenvir=\@surroundenvirtemp}
\BeforeBeginEnvironment{BAR}{\let\@surroundenvirtemp=\@currenvir}
\AtBeginEnvironment{BAR}{\let\@surroundenvir=\@surroundenvirtemp}
\BeforeBeginEnvironment{FOOBAR}{\let\@surroundenvirtemp=\@currenvir}
\AtBeginEnvironment{FOOBAR}{\let\@surroundenvir=\@surroundenvirtemp}
\newenvironment{FOO}{\message{Begin \@currenvir: Surrounding env is: \@surroundenvir^^J}}%
                    {\message{End \@currenvir: Surrounding env is: \@surroundenvir^^J}}%%
\newenvironment{BAR}{\message{Begin \@currenvir: Surrounding env is: \@surroundenvir^^J}}%
                    {\message{End \@currenvir: Surrounding env is: \@surroundenvir^^J}}%%
\newenvironment{FOOBAR}{\message{Begin \@currenvir: Surrounding env is: \@surroundenvir^^J}}%
                       {\message{End \@currenvir: Surrounding env is: \@surroundenvir^^J}}%%
\makeatother

\begin{document}

\begin{FOO}
\end{FOO}

\begin{BAR}
\end{BAR}

\begin{FOOBAR}
\end{FOOBAR}

\begin{FOO}
\begin{BAR}
\begin{FOOBAR}
\end{FOOBAR}
\end{BAR}
\end{FOO}


\end{document}