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% bxenclose.sty
%% package declaration
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{bxenclose}[2016/04/01 v0.2]
\def\bxew@pkgame{bxenclose}
%--------------------------------------- main
%% \bxew@begin@body@hook
% Things to be prepended to the document body.
\let\bxew@begin@body@hook\@empty
%% \bxew@end@body@hook
% Things to be appended to the document body.
\let\bxew@end@body@hook\@empty
% The insertion of \bxew@begin@body@hook is realized by appending
% the token to \document macro. But of course there are dozens of
% packages that do the same thing, and in order to "win the race"
% and put \bxew@begin@body@hook immediately before the actual body
% content, I need to postpone the patching to \document as late as
% possible. Hence comes my tactics, where the patching will be done
% in invocation of "\begin{document}", just before expanding the
% \document macro.
%%<*> \enclosebodywith{<begin>}{<end>}
\@onlypreamble\enclosebodywith
\newcommand\enclosebodywith[2]{%
\begingroup
\ifx\bxew@patch@begin\@undefined\else
\bxew@patch@begin
\fi
\toks@\expandafter{\bxew@begin@body@hook}%
\toks\tw@{#1}%
\xdef\bxew@begin@body@hook{%
\the\toks@\the\toks\tw@}%
\toks@\expandafter{\bxew@end@body@hook}%
\toks\tw@{#2}%
\xdef\bxew@end@body@hook{%
\the\toks\tw@\the\toks@}%
\endgroup
}
%% \bxew@patch@begin
% Patches to \begin macro. Specifically, it prepends
% "\bxew@begin@hook{#1}" to \begin.
\def\bxew@patch@begin{%
\global\let\bxew@patch@begin\@undefined % one-shot
\begingroup
\toks@\expandafter{\begin{##1}}%
\edef\bxew@tempa{\gdef\noexpand\begin####1{%
\noexpand\bxew@begin@hook{####1}\the\toks@}}%
\bxew@tempa
\endgroup
}
%% \bxew@unpatch@begin
% Revokes the patch of \bxew@patch@begin. That is, it removes
% "\bxew@begin@hook{#1}" from \begin macro.
\def\bxew@unpatch@begin{%
\global\let\bxew@unpatch@begin\@undefined % one-shot
\begingroup
% check the target
\long\def\bxew@tempa##1\bxew@begin@hook##2##3\bxew@end{%
\def\bxew@tempa{##2}}%
\expandafter\bxew@tempa\begin{}\bxew@begin@hook!\bxew@end
\ifx\bxew@tempa\@empty % if target is there
\long\def\bxew@tempa##1\bxew@begin@hook##2{##1}%
\toks@\expandafter\expandafter\expandafter
{\expandafter\bxew@tempa\begin{##1}}%
\edef\bxew@tempa{\gdef\noexpand\begin####1{\the\toks@}}%
\bxew@tempa
\fi % if not there, then do nothing
\endgroup
}
%% \bxew@begin@hook{<envname>}
% The patch attached to \begin. When "\begin{document}"
% is called, this macro patches to \document, before
% \document is expanded.
\def\bxew@begin@hook#1{%
\begingroup
\def\bxew@tempa{#1}\def\bxew@tempb{document}%
\ifx\bxew@tempa\bxew@tempb % if it is \begin{document}
% just in case unpatching failed
\global\let\bxew@begin@hook\@gobble % neutralize
\bxew@unpatch@begin
\bxew@patch@document
\fi
\endgroup
}
%% \bxew@patch@document
% Appends something and \bxew@begin@body@hook to \document macro.
\def\bxew@patch@document{%
\begingroup
\global\let\bxew@patch@document\@undefined % one-shot
\g@addto@macro\document{%
\bxew@patch@enddocument
% and \bxew@begin@body@hook will come last
\let\reserved@a\bxew@begin@body@hook
\global\let\bxew@begin@body@hook\@undefined
\reserved@a}%
\endgroup
}
% Just like \bxew@begin@body@hook, prepending \bxew@end@body@hook
% to \enddocument need to be deferred as much as possible. So I
% decided to patch \enddocument just before executing the
% \bxew@begin@body@hook macro.
%% \bxew@patch@enddocument
% Prepends \bxew@end@body@hook to \enddocument.
\def\bxew@patch@enddocument{%
\global\let\bxew@patch@enddocument\@undefined % one-shot
\begingroup
\toks@\expandafter{\enddocument}%
\toks\tw@{\bxew@end@body@hook
\global\let\bxew@end@body@hook\@undefined}%
\xdef\enddocument{\the\toks\tw@\the\toks@}%
\endgroup
}
%--------------------------------------- done
\endinput
%% EOF
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