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% (This file is public domain.)
% Demonstrate how Eplain can be used to include a TeX source file
% verbatim, typesetting comments in colored italic typewriter type.
% Load Eplain and LaTeX's color.sty package.
\input eplain
\beginpackages \usepackage{color} \endpackages
\nopagenumbers % Disable page numbers.
\font\commentfont = cmitt10 % Font for the comments (italic \tt).
% We'll define some `protected' macros with `@' in their names.
\makeatletter
% Define an equivalent of Eplain's \letreturn, to be able to assign
% various actions to the (active) percent character.
\begingroup \makeactive\%
\gdef\letpercent{\let%}
\endgroup
% The listing hook to be called in \setuplistinghook, see below. It
% makes `%' active and assigns it a `start comment' action.
\def\hlightcommentslisting{\makeactive\% \letpercent\start@comment}%
% This is what `%' is aliased to before a comment is started.
\def\start@comment{%
\leavevmode % Needed in the very first line of the input to process
% the new par (possibly inserting line number) before we
% kick in with the color and stuff.
\begingroup % Isolate color and font changes and the redefinitions.
\commentfont
\color[cmyk]{0.28,1,1,0.35}%
\percentchar % Produce the actual `%' and
\letpercent\percentchar % make all following `%'s do the same.
\letreturn\end@comment % Call \end@comment at end-of-line.
}
% \end@comment (alias for ^^M inside a comment) will end the comment
% started by \start@comment. We make ^^M active temporarily so that
% the active version of ^^M gets "frozen" into \end@comment.
\begingroup \makeactive\^^M % Avoid ^^M's from here on.
\gdef\end@comment{\endgroup ^^M}%
\endgroup
\resetatcatcode % Make `@' again inaccessible for use in macro names.
% Define \setuplistinghook to setup comments highlighting, line
% numbering and omitting the last (empty) line of input.
\def\setuplistinghook{\hlightcommentslisting \linenumberedlisting
\nolastlinelisting}
% Isn't this fun? This file typesets itself, with the extra bonus of
% the pretty-printed comments and numbered source lines!
\listing{lscommnt}
\bye
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