% exa.sty
% modified after example.sty by J.Schrod, xitijsch@ddathd21.bitnet
% Guido Gonzato, guido.gonzato@univr.it

\chardef\escape=0
\chardef\open=1
\chardef\close=2
\chardef\letter=11
\chardef\other=12
%\chardef\active=13              % is defined in Plain already

\chardef\uscode=\catcode`\_      % top level macro file!

\catcode`\_=\letter

\oddsidemargin=0pt
\evensidemargin=\oddsidemargin

\newwrite\example_file
\def\example_name{\jobname.tmp }        % <-- space!

\newdimen\ExampleWidth
      \ExampleWidth=\textwidth
      \advance\ExampleWidth by \marginparwidth  % stick into margins
      \advance\ExampleWidth by \columnsep       % between columns
      \divide\ExampleWidth by 2

\def\ExampleSet{%
   \begin{boxedminipage}[c]{0.5\textwidth}%
      \hrule height\z@
      \def\markboth##1##2{}%
      \def\markright##1{}%
      \def\addcontentsline##1##2##3{}%
      \input \example_name
      \par
      \hrule height\z@
   \end{boxedminipage}%
   }

\begingroup
   \catcode`\^^I=\active
   \gdef\@vobeytabs{\catcode`\^^I\active \let^^I\@xobeytab}
   \global\let^^I=\@xobeytab%           % for \write's
\endgroup
\def\@xobeytab{\space\space\space\space\space\space\space\space}

\def\ExampleVerb{%
   \begin{minipage}[c]{0.5\textwidth}%
      \hrule height\z@
      \begingroup
         \small
         \parindent\z@
         \rightskip\@flushglue
         \@makeother\"\@verbatim
         \frenchspacing \@vobeyspaces \@vobeytabs
         \input \example_name
         \endverbatim
      \endgroup
      %\hrule height\z@
   \end{minipage}%
   }

\def\example{
   \par
   \immediate\openout\example_file\example_name
   \begingroup
      \@makeother\"\let\do\@makeother \dospecials
      \obeylines \obeyspaces
      \@ignoretrue \copy_line
   }

\begingroup
   \catcode`\|=\escape  % | is temporary escape character
   \catcode`\[=\open    % [ and ] are temporary grouping symbols
   \catcode`\]=\close
   \catcode`\{=\other   % these are `other' in verbatim mode
   \catcode`\}=\other
   \catcode`\\=|other
   |gdef|end_of_example[\end{example}]
|endgroup

\begingroup
   \obeylines \gdef\copy_line#1^^M{\write_line{#1}}%
\endgroup

\def\write_line#1{%
   \def\Next{#1}%
   \ifx \Next\end_of_example
      \def\Next{\end{example}}% % finish example
   \else
      \ifx \Next\empty
         \if@ignore             % ignore empty lines at the beginning
         \else                  % but write them out later
            \immediate\write\example_file{\Next}%
         \fi
      \else
         \immediate\write\example_file{\Next}%
         \@ignorefalse          % at least one non-empty line written
      \fi
      \let\Next\copy_line       % next line of example
   \fi
   \Next
   }

\def\endexample{%
   \endgroup
   \immediate\closeout\example_file
   \penalty \predisplaypenalty
   \vskip \abovedisplayskip
   % \leftline{\ExampleVerb \hskip\columnsep \ExampleSet}%
   \leftline{\ExampleVerb \hfill \ExampleSet}%
   \penalty \postdisplaypenalty
   \vskip \belowdisplayskip
   }

\catcode`\_=\uscode

\endinput