% \iffalse meta-comment
%
% Copyright (C) 2004 by Scott Pakin <scott+pt@pakin.org>
% ------------------------------------------------------
%
% This file may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.2
% of this license or (at your option) any later version.
% The latest version of this license is in:
%
%    http://www.latex-project.org/lppl.txt
%
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\usepackage{varioref}
\usepackage{flafter}
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    hyperindex=false,
    bookmarksopen,
    pdftitle={PerlTeX: defining LaTeX macros in terms of Perl code},
    pdfauthor={Scott Pakin, scott+pt@pakin.org},
    pdfsubject={Using Perl to define LaTeX macros},
    pdfkeywords={programming, LaTeX, macros, Perl}
  }
}{}
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%   Digits        \0\1\2\3\4\5\6\7\8\9
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% \newcommand{\perltex}{\texttt{perltex.pl}}  ^^A  Name of the Perl script
% \newcommand{\perlmac}{\texttt{perltex.sty}} ^^A  Name of the LaTeX package
%
% ^^A  Define an environment just like macro but for Perl scalars or lists.
% \makeatletter
% \newenvironment{perlmacro}[1]{^^A
%   \begingroup
%     \def\PrintMacroName##1{\strut\MacroFont\string##1\ }^^A
%     \def\SpecialIndex@##1##2{^^A
%       \@bsphack
%       \special@index{\expandafter\@gobble\string##1\actualchar
%         \string\verb\quotechar*\verbatimchar\string##1\verbatimchar##2}^^A
%       \@esphack
%     }^^A
%     \begin{macro}{#1}^^A
% }{^^A
%     \end{macro}^^A
%   \endgroup
% }
% \makeatother
%
% \title{\PerlTeX---defining \LaTeX{} macros in terms of Perl code^^A
%   \thanks{This document corresponds to \PerlTeX~\fileversion, dated
%   \filedate.}}
% \author{Scott Pakin \\ \texttt{scott+pt@pakin.org}}
%
% \maketitle
% \sloppy
%
% \begin{abstract}
%   \PerlTeX{} is a combination Perl script (\perltex) and \LaTeXe{}
%   style file (\perlmac) that, together, give the user the ability to
%   define \LaTeX{} macros in terms of Perl code.  Once defined, a Perl
%   macro becomes indistinguishable from any other \LaTeX{} macro.
%   \PerlTeX{} thereby combines \LaTeX's typesetting power with Perl's
%   programmability.
% \end{abstract}
%
% \section{Introduction}
%
% \TeX{} is a professional-quality typesetting system.  However, its
% programming language is rather hard to use for anything but the most
% simple forms of text substitution.  Even \LaTeX, the most popular
% macro package for \TeX, does little to simplify \TeX{} programming.
%
% Perl is a general-purpose programming language whose forte is in text
% manipulation.  However, it has no support whatsoever for typesetting.
%
% \PerlTeX's goal is to bridge these two worlds.  It enables the
% construction of documents that are primarily \LaTeX-based but contain
% a modicum of Perl.  \PerlTeX{} seamlessly integrates Perl code into a
% \LaTeX{} document, enabling the user to define macros whose bodies
% consist of Perl code instead of \TeX{} and \LaTeX{} code.
%
% As an example, suppose you need to define a macro that reverses a set
% of words.  Although it sounds like it should be simple, few \LaTeX{}
% authors are sufficiently versed in the \TeX{} language to be able to
% express such a macro.  However, a word-reversal function is easy to
% express in Perl: one need only |split| a string into a list of words,
% |reverse| the list, and |join| it back together.  The following is how
% a |\reversewords| macro could be defined using \PerlTeX:
%
% \begin{verbatim}
%    \perlnewcommand{\reversewords}[1]{join " ", reverse split " ", $_[0]}
% \end{verbatim}
%
% \noindent
% Then, executing ``\texttt{\string\reversewords\string{Try doing this
% without Perl!\string}}'' in a document would produce the text ``Perl!
% without this doing Try''.  Simple, isn't it?
%
% As another example, think about how you'd write a macro in \LaTeX{} to
% extract a substring of a given string when provided with a starting
% position and a length.  Perl has an built-in |substr| function and
% \PerlTeX{} makes it easy to export this to \LaTeX:
%
% \begin{verbatim}
%    \perlnewcommand{\substr}[3]{substr $_[0], $_[1], $_[2]}
% \end{verbatim}
%
% |\substr| can then be used just like any other \LaTeX{} macro---and as
% simply as Perl's |substr| function:
%
% \bigskip
%
% \noindent|   |^^A
% \begin{tabular}{@{}l@{}}
%    |\newcommand{\str}{superlative}| \\
%    |A sample substring of ``\str'' is ``\substr{\str}{2}{4}''.| \\[1ex]
%    \multicolumn{1}{@{}c@{}}{\Huge$\Downarrow$} \\[2ex]
%    \multicolumn{1}{@{}c@{}}{A sample substring of ``superlative'' is ``perl''.}
% \end{tabular}
%
% \bigskip
%
% To present a somewhat more complex example, observe how much
% easier it is to generate a repetitive matrix using Perl code than
% ordinary \LaTeX{} commands:
%
% \begin{verbatim}
%    \perlnewcommand{\hilbertmatrix}[1]{
%      my $result = '
%    \[
%    \renewcommand{\arraystretch}{1.3}
%    ';
%      $result .= '\begin{array}{' . 'c' x $_[0] . "}\n";
%      foreach $j (0 .. $_[0]-1) {
%        my @row;
%        foreach $i (0 .. $_[0]-1) {
%          push @row, ($i+$j) ? (sprintf '\frac{1}{%d}', $i+$j+1) : '1';
%        }
%        $result .= join (' & ', @row) . " \\\\\n";
%      }
%      $result .= '\end{array}
%    \]';
%      return $result;
%    }
%
%    \hilbertmatrix{20}
% \end{verbatim}
%
% \begin{center}
% {\Huge$\Downarrow$}
% \end{center}
%
% \[
% \renewcommand{\arraystretch}{1.3}
% \begin{array}{ccccccccccccccc}
% 1 & \frac{1}{2} & \frac{1}{3} & \frac{1}{4} & \frac{1}{5} & \frac{1}{6} & \frac{1}{7} & \frac{1}{8} & \frac{1}{9} & \frac{1}{10} & \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} \\
% \frac{1}{2} & \frac{1}{3} & \frac{1}{4} & \frac{1}{5} & \frac{1}{6} & \frac{1}{7} & \frac{1}{8} & \frac{1}{9} & \frac{1}{10} & \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} \\
% \frac{1}{3} & \frac{1}{4} & \frac{1}{5} & \frac{1}{6} & \frac{1}{7} & \frac{1}{8} & \frac{1}{9} & \frac{1}{10} & \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} \\
% \frac{1}{6} & \frac{1}{7} & \frac{1}{8} & \frac{1}{9} & \frac{1}{10} & \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} \\
% \frac{1}{7} & \frac{1}{8} & \frac{1}{9} & \frac{1}{10} & \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} \\
% \frac{1}{8} & \frac{1}{9} & \frac{1}{10} & \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} & \frac{1}{22} \\
% \frac{1}{9} & \frac{1}{10} & \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} & \frac{1}{22} & \frac{1}{23} \\
% \frac{1}{10} & \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} & \frac{1}{22} & \frac{1}{23} & \frac{1}{24} \\
% \frac{1}{11} & \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} & \frac{1}{22} & \frac{1}{23} & \frac{1}{24} & \frac{1}{25} \\
% \frac{1}{12} & \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} & \frac{1}{22} & \frac{1}{23} & \frac{1}{24} & \frac{1}{25} & \frac{1}{26} \\
% \frac{1}{13} & \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} & \frac{1}{22} & \frac{1}{23} & \frac{1}{24} & \frac{1}{25} & \frac{1}{26} & \frac{1}{27} \\
% \frac{1}{14} & \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} & \frac{1}{22} & \frac{1}{23} & \frac{1}{24} & \frac{1}{25} & \frac{1}{26} & \frac{1}{27} & \frac{1}{28} \\
% \frac{1}{15} & \frac{1}{16} & \frac{1}{17} & \frac{1}{18} & \frac{1}{19} & \frac{1}{20} & \frac{1}{21} & \frac{1}{22} & \frac{1}{23} & \frac{1}{24} & \frac{1}{25} & \frac{1}{26} & \frac{1}{27} & \frac{1}{28} & \frac{1}{29} \\
% \end{array}
% \]
%
% \bigskip
%
% In addition to |\perlnewcommand| and |\perlrenewcommand|, \PerlTeX{}
% supports |\perlnewenvironment| and |\perlrenewenvironment| macros.
% These enable environments to be defined using Perl code.  The
% following example, a |spreadsheet| environment, generates a |tabular|
% environment plus a predefined header row.  This example would have
% been much more difficult to implement without \PerlTeX:
%
% \begin{verbatim}
% \newcounter{ssrow}
% \perlnewenvironment{spreadsheet}[1]{
%   my $cols = $_[0];
%   my $header = "A";
%   my $tabular = "\\setcounter{ssrow}{1}\n";
%   $tabular .= '\newcommand*{\rownum}{\thessrow\addtocounter{ssrow}{1}}' . "\n";
%   $tabular .= '\begin{tabular}{@{}r|*{' . $cols . '}{r}@{}}' . "\n";
%   $tabular .= '\\multicolumn{1}{@{}c}{} &' . "\n";
%   foreach (1 .. $cols) {
%     $tabular .= "\\multicolumn{1}{c";
%     $tabular .= '@{}' if $_ == $cols;
%     $tabular .= "}{" . $header++ . "}";
%     if ($_ == $cols) {
%       $tabular .= " \\\\ \\cline{2-" . ($cols+1) . "}"
%     }
%     else {
%       $tabular .= " &";
%     }
%     $tabular .= "\n";
%   }
%   return $tabular;
% }{
%   return "\\end{tabular}\n";
% }
%
% \begin{center}
%   \begin{spreadsheet}{4}
%     \rownum &  1 &  8 & 10 & 15 \\
%     \rownum & 12 & 13 &  3 &  6 \\
%     \rownum &  7 &  2 & 16 &  9 \\
%     \rownum & 14 & 11 &  5 &  4
%   \end{spreadsheet}
% \end{center}
% \end{verbatim}
%
% \begin{center}
% {\Huge$\Downarrow$}
% \end{center}
%
% \DeleteShortVerb{\|}
% \begin{center}
%   \begin{tabular}{@{}r|*{4}{r}@{}}
%     \multicolumn{1}{@{}c}{} &
%     \multicolumn{1}{c}{A} &
%     \multicolumn{1}{c}{B} &
%     \multicolumn{1}{c}{C} &
%     \multicolumn{1}{c@{}}{D} \\ \cline{2-5}
%     1 &  1 &  8 & 10 & 15 \\
%     2 & 12 & 13 &  3 &  6 \\
%     3 &  7 &  2 & 16 &  9 \\
%     4 & 14 & 11 &  5 &  4
%   \end{tabular}
% \end{center}
% \MakeShortVerb{\|}
%
%
% \section{Usage}
%
% There are two components to using \PerlTeX\@.  First, documents must
% include a ``|\usepackage{perltex}|'' line in their preamble in
% order to define |\perlnewcommand|, |\perlrenewcommand|,
% |\perlnewenvironment|, and |\perlrenewenvironment|.  Second, \LaTeX{}
% documents must be compiled using the \perltex{} wrapper script.
%
% \subsection{Defining and redefining Perl macros}
%
% \DescribeMacro{\perlnewcommand}
% \DescribeMacro{\perlrenewcommand}
% \DescribeMacro{\perlnewenvironment}
% \DescribeMacro{\perlrenewenvironment}
% \perlmac{} defines four macros: |\perlnewcommand|,
% |\perlrenewcommand|, |\perlnewenvironment|, and
% |\perlrenewenvironment|.  These behave exactly like their \LaTeXe{}
% counterparts---|\newcommand|, |\renewcommand|, |\newenvironment|, and
% |\renewenvironment|---except that the macro body consists of Perl code
% that dynamically generates \LaTeX{} code.  \perlmac{} even includes
% support for optional arguments and the starred forms of its commands
% (i.e.~|\perlnewcommand*|, |\perlrenewcommand*|, |\perlnewenvironment*|,
% and |\perlrenewenvironment*|).
%
% When the Perl code is executed, it is placed within a subroutine named
% after the macro name but with ``|\|'' replaced with ``|latex_|''.  For
% example, a \PerlTeX-defined \LaTeX{} macro called |\myMacro| produces
% a Perl subroutine called |latex_myMacro|.  Macro arguments are
% converted to subroutine arguments.  A \LaTeX{} macro's |#1| argument
% is referred to as |$_[0]| in Perl; |#2| is referred to as |$_[1]|; and
% so forth.
%
% Any valid Perl code can be used in the body of a macro.  However,
% \PerlTeX{} executes the Perl code within a secure sandbox.  This means
% that potentially harmful Perl operations, such as |unlink|, |rmdir|,
% and |system| will result in a run-time error.  (It is possible to
% disable the safety checks, however, as will be explained in
% Section~\ref{sec:perltex-man}.)  Having a secure sandbox implies that
% it is safe to build \PerlTeX{} documents written by other people
% without worrying about what they may do to your computer system.
%
% A single sandbox is used for the entire |latex| run.  This means that
% multiple macros defined by |\perlnewcommand| can invoke each other.
% It also means that global variables persist across macro calls:
%
% \bigskip
%
% \noindent|   |^^A
% \begin{tabular}{@{}l@{}}
%    |\perlnewcommand{\setX}[1]{$x = $_[0]; return ""}| \\
%    |\perlnewcommand{\getX}{'$x$ was set to ' . $x . '.'}| \\
%    |\setX{123}| \\
%    |\getX| \\
%    |\setX{456}| \\
%    |\getX| \\[1ex]
%    \multicolumn{1}{@{}c@{}}{\Huge$\Downarrow$} \\[2ex]
%    \multicolumn{1}{@{}c@{}}{$x$ was set to 123.  $x$ was set to 456.} \\
% \end{tabular}
%
% \bigskip
%
% Macro arguments are expanded by \LaTeX{} before being passed to Perl.
% Consider the following macro definition, which wraps its argument
% within |\begin{verbatim*}|\dots\linebreak[0]|\end{verbatim*}|:
%
% \begin{verbatim}
%     \perlnewcommand{\verbit}[1]{
%       "\\begin{verbatim*}\n$_[0]\n\\end{verbatim*}\n"
%     }
% \end{verbatim}
%
% \noindent
% An invocation of
% ``|\verbit{\TeX}|'' would therefore typeset the \emph{expansion} of
% ``|\TeX|'', namely ``|T\kern| |-.1667em\lower| |.5ex\hbox| |{E}\kern|
% |-.125emX\spacefactor| |\@m|'', which might be a bit unexpected.  The
% solution is to use |\noexpand|:
% |\verbit{\noexpand\TeX}|~$\Rightarrow$ |\TeX|\@.  ``Robust'' macros as
% well as |\begin| and |\end| are implicitly preceded by |\noexpand|.
%
%
% \subsection{Invoking \perltex}
% \label{sec:perltex-man}
%
% The following pages reproduce the \perltex{} program documentation.
% Key parts of the documentation are excerpted when \perltex{} is
% invoked with the |--help| option.  The various Perl
% |pod2|\meta{something} tools can be used to generate the complete
% program documentation in a variety of formats such as \LaTeX, HTML,
% plain text, or Unix man-page format.  For example, the following
% command is the recommended way to produce a Unix man page from
% \perltex:
%
% \begin{verbatim}
%   pod2man --center=" " --release=" " perltex.pl > perltex.1
% \end{verbatim}
%
% \clearpage
% \begingroup
% \def\index#1{}
% \def\section#1{}
% \let\subsection=\subsubsection
%
% ^^A  ***************************************************************
% ^^A  * The following was generated using pod2latex and touched up  *
% ^^A  * slightly to make it better match the rest of this document. *
% ^^A  ***************************************************************
%
% \def\C++{{\rm C\kern-.05em\raise.3ex\hbox{\footnotesize ++}}}
% \def\underscore{\leavevmode\kern.04em\vbox{\hrule width 0.4em height 0.3pt}}
% \setlength{\parindent}{0pt}
%
% \section{PERLTEX.PL}%
% \index{PERLTEX.PL}
%
% \subsection*{NAME}
% perltex --- enable \LaTeX{} macros to be defined in terms of Perl code
%
% \subsection*{SYNOPSIS}
% perltex
% {\tt [}{\bf {\tt --}help}{\tt ]}
% {\tt [}{\bf {\tt --}latex}={\em program\/}{\tt ]}
% {\tt [}{\bf {\tt --}}{\tt [}{\bf no}{\tt ]}{\bf safe}{\tt ]}
% {\tt [}{\bf {\tt --}permit}={\em feature\/}{\tt ]}
% {\tt [}{\em latex options\/}{\tt ]}
%
% \subsection*{DESCRIPTION}
% \LaTeX{} --- through the underlying \TeX{} typesetting system --- produces
% beautifully typeset documents but has a macro language that is
% difficult to program.  In particular, support for complex string
% manipulation is largely lacking.  Perl is a popular general-purpose
% programming language whose forte is string manipulation.  However, it
% has no typesetting capabilities whatsoever.
%
% \bigskip
%
% Clearly, Perl's programmability could complement \LaTeX{}'s typesetting
% strengths.  {\bf perltex} is the tool that enables a symbiosis between
% the two systems.  All a user needs to do is compile a \LaTeX{} document
% using {\bf perltex} instead of {\bf latex}.  ({\bf perltex} is actually a
% wrapper for {\bf latex}, so no {\bf latex} functionality is lost.)  If the
% document includes a {\tt \char`\\usepackage\{perltex\}} in its preamble, then
% {\tt \char`\\perlnewcommand} and {\tt \char`\\perlrenewcommand} macros will be made
% available.  These behave just like \LaTeX{}'s {\tt \char`\\newcommand} and
% {\tt \char`\\renewcommand} except that the macro body contains Perl code instead
% of \LaTeX{} code.
%
% \subsection*{OPTIONS}%
% \index{OPTIONS}
%
% {\bf perltex} accepts the following command-line options:
%
% \begin{description}
%
% \item[{\bf {\tt --}help}]%
% \index{--help@{\bf {\tt --}help}}%
% \hfil\\
% Display basic usage information.
%
% \item[{\bf {\tt --}latex}={\em program\/}]%
% \index{--latex=program@{\bf {\tt --}latex}={\em program\/}}%
% \hfil\\
% Specify a program to use instead of {\bf latex}.  For example,
% {\tt --latex=pdf{}latex} would typeset the given document using
% {\bf pdf{}latex} instead of ordinary {\bf latex}.
%
% \item[{\bf {\tt --}}{\tt [}{\bf no}{\tt ]}{\bf safe}]%
% \index{--[no]safe@{\bf {\tt --}}{\tt [}{\bf no}{\tt ]}{\bf safe}}%
% \hfil\\
% Enable or disable sandboxing.  With the default of {\tt --safe},
% {\bf perltex} executes the code from a {\tt \char`\\perlnewcommand} or
% {\tt \char`\\perlrenewcommand} macro within a protected environment that
% prohibits ``unsafe'' operations such as accessing files or executing
% external programs.  Specifying {\tt --nosafe} gives the \LaTeX{} document
% {\em carte blanche\/} to execute any arbitrary Perl code, including that
% which can harm the user's files.  See the {\em Safe\/} manpage for more information.
%
% \item[{\bf {\tt --}permit}={\em feature\/}]%
% \index{--permit=feature@{\bf {\tt --}permit}={\em feature\/}}%
% \hfil\\
% Permit particular Perl operations to be performed.  The {\tt --permit}
% option, which can be specified more than once on the command line,
% enables finer-grained control over the {\bf perltex} sandbox.  See
% the {\em Opcode\/} manpage for more information.
%
% \end{description}
%
% These options are then followed by whatever options are normally
% passed to {\bf latex} (or whatever program was specified with
% {\tt --latex}), including, for instance, the name of the {\em .tex\/} file to
% compile.
%
% \subsection*{EXAMPLES}
% In its simplest form, {\bf perltex} is run just like {\bf latex}:
% \begin{verbatim}
%     perltex myfile.tex
% \end{verbatim}
%
% To use {\bf pdf{}latex} instead of regular {\bf latex}, use the {\tt --latex}
% option:
% \begin{verbatim}
%     perltex --latex=pdflatex myfile.tex
% \end{verbatim}
%
% If \LaTeX{} gives a ``{\tt trapped by operation mask}'' error and you
% trust the {\em .tex\/} file you're trying to compile not to execute
% malicious Perl code (e.g., because you wrote it yourself), you can
% disable {\bf perltex}'s safety mechansisms with {\tt --nosafe}:
% \begin{verbatim}
%     perltex --nosafe myfile.tex
% \end{verbatim}
%
% The following command gives documents only {\bf perltex}'s default
% permissions ({\tt :browse}) plus the ability to open files and invoke the
% {\tt time} command:
% \begin{verbatim}
%     perltex --permit=:browse --permit=:filesys_open
%       --permit=time myfile.tex
% \end{verbatim}
%
% \subsection*{ENVIRONMENT}
% {\bf perltex} honors the following environment variables:
%
% \begin{description}
%
% \item[PERLTEX]%
% \index{PERLTEX@PERLTEX}%
% \hfil\\
% Specify the filename of the \LaTeX{} compiler.  The \LaTeX{} compiler
% defaults to ``{\tt latex}''.  The {\tt PERLTEX} environment variable
% overrides this default, and the {\tt --latex} command-line option (see
% the {\tt OPTIONS} entry elsewhere in this document) overrides that.
%
% \end{description}
%
% \subsection*{FILES}
% While compiling {\em jobname.tex\/}, {\bf perltex} makes use of the following
% files:
%
% \begin{description}
%
% \item[{\em jobname.lgpl\/}]%
% \index{jobname.lgpl@{\em jobname.lgpl\/}}%
% \hfil\\
% log file written by Perl; helpful for debugging Perl macros
%
% \item[{\em jobname.topl\/}]%
% \index{jobname.topl@{\em jobname.topl\/}}%
% \hfil\\
% information sent from \LaTeX{} to Perl
%
% \item[{\em jobname.frpl\/}]%
% \index{jobname.frpl@{\em jobname.frpl\/}}%
% \hfil\\
% information sent from Perl to \LaTeX{}
%
% \item[{\em jobname.tfpl\/}]%
% \index{jobname.tfpl@{\em jobname.tfpl\/}}%
% \hfil\\
% ``flag'' file whose existence indicates that {\em jobname.topl\/} contains
% valid data
%
% \item[{\em jobname.ffpl\/}]%
% \index{jobname.ffpl@{\em jobname.ffpl\/}}%
% \hfil\\
% ``flag'' file whose existence indicates that {\em jobname.frpl\/} contains
% valid data
%
% \item[{\em jobname.dfpl\/}]%
% \index{jobname.dfpl@{\em jobname.dfpl\/}}%
% \hfil\\
% ``flag'' file whose existence indicates that {\em jobname.ffpl\/} has been
% deleted
%
% \end{description}
%
% \subsection*{NOTES}
% {\bf perltex}'s sandbox defaults to what the {\em Opcode\/} manpage calls ``{\tt :browse}''.
%
% \subsection*{SEE ALSO}
% {\em latex\/}(1), {\em pdf{}latex\/}(1), {\em perl\/}(1), {\em Safe\/}(3pm), {\em Opcode\/}(3pm)
%
% \subsection*{AUTHOR}
% Scott Pakin, {\em scott+pt@pakin.org\/}
%
% ^^A  ***********************************
% ^^A  * End of generated pod2latex text *
% ^^A  ***********************************
% \endgroup
% \clearpage
%
%
% \StopEventually{^^A
%   \section{License agreement}
%   \label{sec:license}
%
%   \begin{center}
%   Copyright \textcopyright{} 2004 by Scott Pakin \texttt{<scott+pt@pakin.org>}
%   \end{center}
%
%   \providecommand{\url}[1]{\texttt{##1}}
%
%   \noindent
%   These files may be distributed and/or modified under the conditions of
%   the \LaTeX{} Project Public License, either version~1.2 of this
%   license or (at your option) any later version.  The latest version of
%   this license is in \url{http://www.latex-project.org/lppl.txt} and
%   version~1.2 or later is part of all distributions of \LaTeX{} version
%   1999/12/01 or later.
%
%   \PrintChanges
%   \PrintIndex
% }
%
% \section{Implementation}
% \label{sec:implementation}
%
% Users interested only in \emph{using} \PerlTeX{} can skip
% Section~\ref{sec:implementation}, which presents the complete
% \PerlTeX{} source code.  This section should be of interest primarily
% to those who wish to extend \PerlTeX{} or modify it to use a language
% other than Perl.
%
% Section~\ref{sec:implementation} is split into two main parts.
% Section~\ref{sec:perlmacros} presents the source code for \perlmac,
% the \LaTeX{} side of \PerlTeX, and Section~\ref{sec:perltex} presents
% the source code for \perltex, the Perl side of \PerlTeX\@.
% \makeatletter
% \@ifundefined{perlmaclines}{}{^^A
%   \newcount\perltex@lines
%   \perltex@lines=\perltexlines
%   \advance\perltex@lines by -\perlmaclines
%   In toto, \PerlTeX{} consists of a relatively small amount of code.
%   \perlmac{} is only \perlmaclines{} lines of \LaTeX{} and \perltex{}
%   is only \the\perltex@lines{} lines of Perl.
% }
% \makeatother
% \perltex{} is fairly straightforward Perl code and shouldn't be too
% difficult to understand by anyone comfortable with Perl programming.
% \perlmac, in contrast, contains a bit of \LaTeX{} trickery and is
% probably impenetrable to anyone who hasn't already tried his hand at
% \LaTeX{} programming.  Fortunately for the reader, the code is
% profusely commented so the aspiring \LaTeX{} guru may yet learn
% something from it.
%
% After documenting the \perlmac{} and \perltex{} source code, a few
% suggestions are provided for porting \PerlTeX{} to use a backend
% language other than Perl (Section~\ref{sec:porting}).
%
% \subsection{\perlmac}
% \label{sec:perlmacros}
%
% \iffalse
%<*package>
% \fi
%
% Although I've written a number of \LaTeX{} packages, \perlmac{} was
% the most challenging to date.  The key things I needed to learn how to
% do include the following:
%
% \begin{enumerate}
%   \item storing brace-matched---but otherwise not valid \LaTeX---code
%   for later use
%
%   \item iterating over a macro's arguments
% \end{enumerate}
%
% Storing non-\LaTeX{} code in a variable involves beginning a group in
% an argumentless macro, fiddling with category codes, using
% |\afterassignment| to specify a continuation function, and storing the
% subsequent brace-delimited tokens in the input stream into a token
% register.  The continuation function, which also takes no arguments,
% ends the group begun in the first function and proceeds using the
% correctly |\catcode|d token register.  This technique appears in
% |\plmac@haveargs| and |\plmac@havecode| and in a simpler form
% (i.e.,~without the need for storing the argument) in
% |\plmac@write@perl| and |\plmac@write@perl@i|.
%
% Iterating over a macro's arguments is hindered by \TeX's requirement
% that ``|#|'' be followed by a number or another ``|#|''.  The
% technique I discovered (which is used by the Texinfo source code) is
% first to |\let| a variable be |\relax|, thereby making it
% unexpandable, then to define a macro that uses that variable followed
% by a loop variable, and finally to expand the loop variable and |\let|
% the |\relax|ed variable be ``|#|'' right before invoking the macro.
% This technique appears in |\plmac@havecode|.
%
% I hope you find reading the \perlmac{} source code instructive.
% Writing it certainly was.
%
%
% \subsubsection{Package initialization}
% \label{sec:package-init}
%
% \PerlTeX{} defines six macros that are used for communication between
% Perl and \LaTeX\@.  |\plmac@tag| is a string of characters that should
% never occur within one of the user's macro names, macro arguments, or
% macro bodies.  \perltex{} therefore defines |\plmac@tag| as a long
% string of random uppercase letters.  |\plmac@tofile| is the name of a
% file used for communication from \LaTeX{} to Perl.  |\plmac@fromfile|
% is the name of a file used for communication from Perl to \LaTeX.
% |\plmac@toflag| signals that |\plmac@tofile| can be read safely.
% |\plmac@fromflag| signals that |\plmac@fromfile| can be read safely.
% |\plmac@doneflag| signals that |\plmac@fromflag| has been deleted.
% Table~\ref{tbl:variables} lists all of these variables along with the
% value assigned to each by \perltex.
%
% \begin{table}[htbp]
%   \centering
%   \caption{Variables used for communication between Perl and \LaTeX}
%   \label{tbl:variables}
%   \begin{tabular}{@{}lll@{}}
%     \hline
%     Variable & Purpose & \perltex{} assignment \\
%     \hline
%
%     |\plmac@tag| & |\plmac@tofile| field separator &
%     (20 random letters) \\
%
%     |\plmac@tofile| & \LaTeX{} $\rightarrow$ Perl communication &
%     |\jobname.topl| \\
%
%     |\plmac@fromfile| & Perl $\rightarrow$ \LaTeX{} communication &
%     |\jobname.frpl| \\
%
%     |\plmac@toflag| & |\plmac@tofile| synchronization &
%     |\jobname.tfpl| \\
%
%     |\plmac@fromflag| & |\plmac@fromfile| synchronization &
%     |\jobname.ffpl| \\
%
%     |\plmac@doneflag| & |\plmac@fromflag| synchronization &
%     |\jobname.dfpl| \\
%
%     \hline
%   \end{tabular}
% \end{table}
%
% \begin{macro}{\ifplmac@have@perltex}
% \begin{macro}{\plmac@have@perltextrue}
% \begin{macro}{\plmac@have@perltexfalse}
% The following block of code checks the existence of each of the
% variables listed in Table~\ref{tbl:variables}.  If any variable is not
% defined, \perlmac{} gives an error message and---as we shall see on
% page~\pageref{page:define-dummies}---defines dummy versions of
% |\perl|[|re|]|newcommand| and |\perl|[|re|]|newenvironment|.
%    \begin{macrocode}
\newif\ifplmac@have@perltex
\plmac@have@perltextrue
\@ifundefined{plmac@tag}{\plmac@have@perltexfalse}{}
\@ifundefined{plmac@tofile}{\plmac@have@perltexfalse}{}
\@ifundefined{plmac@fromfile}{\plmac@have@perltexfalse}{}
\@ifundefined{plmac@toflag}{\plmac@have@perltexfalse}{}
\@ifundefined{plmac@fromflag}{\plmac@have@perltexfalse}{}
\@ifundefined{plmac@doneflag}{\plmac@have@perltexfalse}{}
\ifplmac@have@perltex
\else
  \PackageError{perltex}{Document must be compiled using perltex}
    {Instead of compiling your document directly with latex, you need
     to\MessageBreak use the perltex script.  \space perltex sets up
     a variety of macros needed by\MessageBreak the perltex
     package as well as a listener process needed for\MessageBreak
     communication between LaTeX and Perl.}
\fi
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \subsubsection{Defining Perl macros}
% \label{sec:perl-mac}
%
% \PerlTeX{} defines four macros intended to be called by the user.
% Section~\ref{sec:perl-mac} details the implementation of two of them:
% |\perlnewcommand| and |\perlrenewcommand|.
% (Section~\ref{sec:perl-env} details the implementation of the other
% two, |\perlnewenvironment| and |\perlrenewenvironment|.)  The goal is
% for these two macros to behave \emph{exactly} like |\newcommand| and
% |\renewcommand|, respectively, except that the author macros they in
% turn define have Perl bodies instead of \LaTeX{} bodies.
%
% The sequence of the operations defined in this section is as follows:
%
% \begin{enumerate}
%   \item The user invokes |\perl|[|re|]|newcommand|, which stores
%   |\|[|re|]|newcommand| in |\plmac@command|.  The
%   |\perl|[|re|]|newcommand| macro then invokes |\plmac@newcommand@i|
%   with a first argument of ``|*|'' for |\perl|[|re|]|newcommand*| or
%   ``|!|'' for ordinary |\perl|[|re|]|newcommand|.
%
%   \item |\plmac@newcommand@i| defines |\plmac@starchar| as ``|*|'' if
%   it was passed a ``|*|'' or \meta{empty} if it was passed a ``|!|''.
%   It then stores the name of the user's macro in |\plmac@macname|, a
%   |\write|able version of the name in |\plmac@cleaned@macname|, and
%   the macro's previous definition (needed by |\perlrenewcommand|) in
%   |\plmac@oldbody|.  Finally, |\plmac@newcommand@i| invokes
%   |\plmac@newcommand@ii|.
%
%   \item |\plmac@newcommand@ii| stores the number of arguments to the
%   user's macro (which may be zero) in |\plmac@numargs|.  It then
%   invokes |\plmac@newcommand@iii@opt| if the first argument is
%   supposed to be optional or |\plmac@newcommand@iii@no@opt| if all
%   arguments are supposed to be required.
%
%   \item |\plmac@newcommand@iii@opt| defines |\plmac@defarg| as the
%   default value of the optional argument.
%   |\plmac@newcommand@iii@no@opt| defines it as \meta{empty}.  Both
%   functions then call |\plmac@haveargs|.
%
%   \item |\plmac@haveargs| stores the user's macro body (written in
%   Perl) verbatim in |\plmac@perlcode|.  |\plmac@haveargs| then invokes
%   |\plmac@havecode|.
%
%   \item By the time |\plmac@havecode| is invoked all of the
%   information needed to define the user's macro is available.  Before
%   defining a \LaTeX{} macro, however, |\plmac@havecode| invokes
%   |\plmac@write@perl| to tell \perltex{} to define a Perl subroutine
%   with a name based on |\plmac@cleaned@macname| and the code contained
%   in |\plmac@perlcode|.  Figure~\ref{fig:tofile-define} illustrates
%   the data that |\plmac@write@perl| passes to \perltex.
%
% \begin{figure}[htbp]
%   \centering
%   \DeleteShortVerb\|
%   \begin{tabular}{|l|}
%     \hline
%     \verb|DEF|                    \\ \hline
%     \verb|\plmac@tag|             \\ \hline
%     \verb|\plmac@cleaned@macname| \\ \hline
%     \verb|\plmac@tag|             \\ \hline
%     \verb|\plmac@perlcode|        \\ \hline
%   \end{tabular}
%   \MakeShortVerb\|
%   \caption{Data written to \texttt{\string\plmac@tofile} to define a
%     Perl subroutine}
%   \label{fig:tofile-define}
% \end{figure}
%
%   \item |\plmac@havecode| invokes |\newcommand| or |\renewcommand|, as
%   appropriate, defining the user's macro as a call to
%   |\plmac@write@perl|.  An invocation of the user's \LaTeX{} macro
%   causes |\plmac@write@perl| to pass the information shown in
%   Figure~\ref{fig:tofile-use} to \perltex.
%
% \begin{figure}[htbp]
%   \centering
%   \DeleteShortVerb\|
%   \begin{tabular}{|l|}
%     \hline
%     \verb|USE|                    \\ \hline
%     \verb|\plmac@tag|             \\ \hline
%     \verb|\plmac@cleaned@macname| \\ \hline
%     \verb|\plmac@tag|             \\ \hline
%     \verb|#1|                     \\ \hline
%     \verb|\plmac@tag|             \\ \hline
%     \verb|#2|                     \\ \hline
%     \verb|\plmac@tag|             \\ \hline
%     \verb|#3|                     \\ \hline
%     \multicolumn{1}{c}{$\vdots$}  \\ \hline
%     \verb|#|\meta{last}           \\ \hline
%   \end{tabular}
%   \MakeShortVerb\|
%   \caption{Data written to \texttt{\string\plmac@tofile} to invoke a
%     Perl subroutine}
%   \label{fig:tofile-use}
% \end{figure}
%
%   \item Whenever |\plmac@write@perl| is invoked it writes its argument
%   verbatim to |\plmac@tofile|; \perltex{} evaluates the code and
%   writes |\plmac@fromfile|; finally, |\plmac@write@perl| |\input|s
%   |\plmac@fromfile|.
% \end{enumerate}
%
% An example might help distinguish the myriad macros used internally by
% \perlmac.  Consider the following call made by the user's
% document:\label{text:example-cmd}
%
% \begin{center}
% |\perlnewcommand*{\example}[3][frobozz]{join("---", @_)}|
% \end{center}
%
% \noindent
% Table~\ref{tbl:example-cmd} shows how \perlmac{} parses that command
% into its constituent components and which components are bound to
% which \perlmac{} macros.
%
% \begin{table}[htbp]
%   \centering
%   \caption{Macro assignments corresponding to an sample
%     \texttt{\string\perlnewcommand*}}
%   \label{tbl:example-cmd}
%   \begin{tabular}{@{}lll@{}}
%     \hline
%     Macro & \multicolumn{2}{l@{}}{Sample definition} \\
%     \hline
%     |\plmac@command|          & |\newcommand|                    \\
%     |\plmac@starchar|         & |*|                              \\
%     |\plmac@macname|          & |\example|                       \\
%     |\plmac@cleaned@macname|  & |\example| & (catcode~11)        \\
%     |\plmac@oldbody|          & |\relax| & (presumably)          \\
%     |\plmac@numargs|          & |3|                              \\
%     |\plmac@defarg|           & |frobozz|                        \\
%     |\plmac@perlcode|         & |join("---", @_)| & (catcode~11) \\
%     \hline
%   \end{tabular}
% \end{table}
%
% \bigskip
%
% \begin{macro}{\perlnewcommand}
% \begin{macro}{\perlrenewcommand}
% \begin{macro}{\plmac@command}
% \begin{macro}{\plmac@next}
% |\perlnewcommand| and |\perlrenewcommand| are the first two commands
% exported to the user by \perlmac.  |\perlnewcommand| is analogous to
% |\newcommand| except that the macro body consists of Perl code instead
% of \LaTeX{} code.  Likewise, |\perlrenewcommand| is analogous to
% |\renewcommand| except that the macro body consists of Perl code
% instead of \LaTeX{} code.  |\perlnewcommand| and |\perlrenewcommand|
% merely define |\plmac@command| and |\plmac@next| and invoke
% |\plmac@newcommand@i|.
%    \begin{macrocode}
\def\perlnewcommand{%
  \let\plmac@command=\newcommand
  \let\plmac@next=\relax
  \@ifnextchar*{\plmac@newcommand@i}{\plmac@newcommand@i!}%
}
%    \end{macrocode}
%    \begin{macrocode}
\def\perlrenewcommand{%
  \let\plmac@next=\relax
  \let\plmac@command=\renewcommand
  \@ifnextchar*{\plmac@newcommand@i}{\plmac@newcommand@i!}%
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\plmac@newcommand@i}
% \begin{macro}{\plmac@starchar}
% \begin{macro}{\plmac@macname}
% \begin{macro}{\plmac@oldbody}
% \begin{macro}{\plmac@cleaned@macname}
% If\label{page:newcommand-i} the user invoked
% |\perl|[|re|]|newcommand*| then |\plmac@newcommand@i| is passed a
% ``|*|'' and, in turn, defines |\plmac@starchar| as ``|*|''.  If the
% user invoked |\perl|[|re|]|newcommand| (no ``|*|'') then
% |\plmac@newcommand@i| is passed a ``|!|'' and, in turn, defines
% |\plmac@starchar| as \meta{empty}.  In either case,
% |\plmac@newcommand@i| defines |\plmac@macname| as the name of the
% user's macro, |\plmac@cleaned@macname| as a |\write|able
% (i.e.,~category code~11) version of |\plmac@macname|, and
% |\plmac@oldbody| and the previous definition of the user's macro.
% (|\plmac@oldbody| is needed by |\perlrenewcommand|.)  It then invokes
% |\plmac@newcommand@ii|.
%    \begin{macrocode}
\def\plmac@newcommand@i#1#2{%
  \ifx#1*%
    \def\plmac@starchar{*}%
  \else
    \def\plmac@starchar{}%
  \fi
  \def\plmac@macname{#2}%
  \let\plmac@oldbody=#2\relax
  \expandafter\def\expandafter\plmac@cleaned@macname\expandafter{%
    \expandafter\string\plmac@macname}%
  \@ifnextchar[{\plmac@newcommand@ii}{\plmac@newcommand@ii[0]}%]
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\plmac@newcommand@ii}
% \begin{macro}{\plmac@numargs}
% |\plmac@newcommand@i| invokes |\plmac@newcommand@ii| with the number
% of arguments to the user's macro in brackets.  |\plmac@newcommand@ii|
% stores that number in |\plmac@numargs| and invokes
% |\plmac@newcommand@iii@opt| if the first argument is to be optional or
% |\plmac@newcommand@iii@no@opt| if all arguments are to be mandatory.
%    \begin{macrocode}
\def\plmac@newcommand@ii[#1]{%
  \def\plmac@numargs{#1}%
  \@ifnextchar[{\plmac@newcommand@iii@opt}
               {\plmac@newcommand@iii@no@opt}%]
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\plmac@newcommand@iii@opt}
% \begin{macro}{\plmac@newcommand@iii@no@opt}
% \begin{macro}{\plmac@defarg}
% Only one of these two macros is executed per invocation of
% |\perl|[|re|]|newcommand|, depending on whether or not the first
% argument of the user's macro is an optional argument.
% |\plmac@newcommand@iii@opt| is invoked if the argument is optional.
% It defines |\plmac@defarg| to the default value of the optional
% argument.  |\plmac@newcommand@iii@no@opt| is invoked if all arguments
% are mandatory.  It defines |\plmac@defarg| as |\relax|.  Both
% |\plmac@newcommand@iii@opt| and |\plmac@newcommand@iii@no@opt| then
% invoke |\plmac@haveargs|.
%    \begin{macrocode}
\def\plmac@newcommand@iii@opt[#1]{%
  \def\plmac@defarg{#1}%
  \plmac@haveargs
}
%    \end{macrocode}
%    \begin{macrocode}
\def\plmac@newcommand@iii@no@opt{%
  \let\plmac@defarg=\relax
  \plmac@haveargs
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\plmac@perlcode}
% \begin{macro}{\plmac@haveargs}
% Now things start to get tricky.  We have all of the arguments we need
% to define the user's command so all that's left is to grab the macro
% body.  But there's a catch: Valid Perl code is unlikely to be valid
% \LaTeX{} code.  We therefore have to read the macro body in a
% |\verb|-like mode.  Furthermore, we actually need to \emph{store} the
% macro body in a variable, as we don't need it right away.
%
% The approach we take in |\plmac@haveargs| is as follows.  First, we
% give all ``special'' characters category code~12 (``other'').  We then
% indicate that the carriage return character (control-M) marks the end
% of a line and that curly braces retain their normal meaning.  With the
% aforementioned category-code definitions, we now have to store the
% next curly-brace-delimited fragment of text, end the current group to
% reset all category codes to their previous value, and continue
% processing the user's macro definition.  How do we do that?  The
% answer is to assign the upcoming text fragment to a token register
% (|\plmac@perlcode|) while an |\afterassignment| is in effect.  The
% |\afterassignment| causes control to transfer to |\plmac@havecode|
% right after |\plmac@perlcode| receives the macro body with all of the
% ``special'' characters made impotent.
%    \begin{macrocode}
\newtoks\plmac@perlcode
%    \end{macrocode}
%    \begin{macrocode}
\def\plmac@haveargs{%
  \begingroup
    \let\do\@makeother\dospecials
    \catcode`\^^M=\active
    \newlinechar`\^^M
    \endlinechar=`\^^M
    \catcode`\{=1
    \catcode`\}=2
    \afterassignment\plmac@havecode
    \global\plmac@perlcode
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% Control is transfered to |\plmac@havecode| from |\plmac@haveargs|
% right after the user's macro body is assigned to |\plmac@perlcode|.
% We now have everything we need to define the user's macro.  The goal
% is to define it as ``|\plmac@write@perl{|\meta{contents of
% Figure~\ref{fig:tofile-use}}|}|''.  This is easier said than done
% because the number of arguments in the user's macro is not known
% statically, yet we need to iterate over however many arguments there
% are.  Because of this complexity, we will explain |\plmac@perlcode|
% piece-by-piece.
%
% \begin{macro}{\plmac@sep}
% Define a character to separate each of the items presented in
% Figures~\ref{fig:tofile-define} and~\ref{fig:tofile-use}.  Perl will
% need to strip this off each argument.  For convenience in porting to
% languages with less powerful string manipulation than Perl's, we
% define |\plmac@sep| as a carriage-return character of category code~11
% (``letter'').
%    \begin{macrocode}
{\catcode`\^^M=11\gdef\plmac@sep{^^M}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\plmac@argnum}
% Define a loop variable that will iterate from |1| to the number of
% arguments in the user's function, i.e.,~|\plmac@numargs|.
%    \begin{macrocode}
\newcount\plmac@argnum
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\plmac@havecode}
% Now comes the final piece of what started as a call to
% |\perl|[|re|]|newcommand|.  First, to reset all category codes back to
% normal, |\plmac@havecode| ends the group that was begun in
% |\plmac@haveargs|.
% \changes{v1.1}{2004/02/24}{Added a \texttt{\string\string\string\plmac@next}
%   hook to support \PerlTeX's new environment-defining macros}
%    \begin{macrocode}
\def\plmac@havecode{%
  \endgroup
%    \end{macrocode}
%
% \begin{macro}{\plmac@define@sub}
% We invoke |\plmac@write@perl| to define a Perl subroutine named after
% |\plmac@cleaned@macname|.  |\plmac@define@sub| sends Perl the
% information shown in Figure~\vref{fig:tofile-define}.
%    \begin{macrocode}
  \edef\plmac@define@sub{%
    \noexpand\plmac@write@perl{DEF\plmac@sep
      \plmac@tag\plmac@sep
      \plmac@cleaned@macname\plmac@sep
      \plmac@tag\plmac@sep
      \the\plmac@perlcode
    }%
  }%
  \plmac@define@sub
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\plmac@body}
% The rest of |\plmac@havecode| is preparation for defining the user's
% macro.  (\LaTeXe's |\newcommand| or |\renewcommand| will do the actual
% work, though.)  |\plmac@body| will eventually contain the complete
% (\LaTeX) body of the user's macro.  Here, we initialize it to the
% first three items listed in Figure~\vref{fig:tofile-use} (with
% intervening |\plmac@sep|s).
%    \begin{macrocode}
  \edef\plmac@body{%
    USE\plmac@sep
    \plmac@tag\plmac@sep
    \plmac@cleaned@macname
  }%
%    \end{macrocode}
%
% \begin{macro}{\plmac@hash}
% Now, for each argument |#1|, |#2|,~\dots, |#\plmac@numargs| we append
% a |\plmac@tag| plus the argument to |\plmac@body| (as always, with a
% |\plmac@sep| after each item).  This requires more trickery, as \TeX{}
% requires a macro-parameter character (``|#|'') to be followed by a
% literal number, not a variable.  The approach we take, which I first
% discovered in the Texinfo source code (although it's used by \LaTeX{}
% and probably other \TeX-based systems as well), is to |\let|-bind
% |\plmac@hash| to |\relax|.  This makes |\plmac@hash| unexpandable, and
% because it's not a ``|#|'', \TeX{} doesn't complain.  After
% |\plmac@body| has been extended to include |\plmac@hash1|,
% |\plmac@hash2|,~\dots, |\plmac@hash\plmac@numargs|, we then
% |\let|-bind |\plmac@hash| to |##|, which \TeX{} lets us do because
% we're within a macro definition (|\plmac@havecode|).  |\plmac@body|
% will then contain |#1|, |#2|,~\dots, |#\plmac@numargs|, as desired.
%    \begin{macrocode}
  \let\plmac@hash=\relax
  \plmac@argnum=1%
  \loop
    \ifnum\plmac@numargs<\plmac@argnum
    \else
      \edef\plmac@body{%
        \plmac@body\plmac@sep\plmac@tag\plmac@sep
        \plmac@hash\plmac@hash\number\plmac@argnum}%
      \advance\plmac@argnum by 1%
  \repeat
  \let\plmac@hash=##\relax
%    \end{macrocode}
%
% \begin{macro}{\plmac@define@command}
% We're ready to execute a |\|[|re|]|newcommand|.  Because we need to
% expand many of our variables, we |\edef| |\plmac@define@command| to
% the appropriate |\|[|re|]|newcommand| call, which we will soon
% execute.  The user's macro must first be |\let|-bound to |\relax| to
% prevent it from expanding.  Then, we handle two cases: either all
% arguments are mandatory (and |\plmac@defarg| is |\relax|) or the
% user's macro has an optional argument (with default value
% |\plmac@defarg|).
%    \begin{macrocode}
  \expandafter\let\plmac@macname=\relax
  \ifx\plmac@defarg\relax
    \edef\plmac@define@command{%
      \noexpand\plmac@command\plmac@starchar{\plmac@macname}%
      [\plmac@numargs]{%
        \noexpand\plmac@write@perl{\plmac@body}%
      }%
  }%
  \else
    \edef\plmac@define@command{%
      \noexpand\plmac@command\plmac@starchar{\plmac@macname}%
      [\plmac@numargs][\plmac@defarg]{%
        \noexpand\plmac@write@perl{\plmac@body}%
      }%
  }%
  \fi
%    \end{macrocode}
%
% The final steps are to restore the previous definition of the user's
% macro---we had set it to |\relax| above to make the name
% unexpandable---then redefine it by invoking |\plmac@define@command|.
% Why do we need to restore the previous definition if we're just going
% to redefine it?  Because |\newcommand| needs to produce an error if
% the macro was previously defined and |\renewcommand| needs to produce
% an error if the macro was \emph{not} previously defined.
%
% |\plmac@havecode| concludes by invoking |\plmac@next|, which is a
% no-op for |\perlnewcommand| and |\perlrenewcommand| but processes the
% end-environment code for |\perlnewenvironment| and
% |\perlrenewenvironment|.
%    \begin{macrocode}
  \expandafter\let\plmac@macname=\plmac@oldbody
  \plmac@define@command
  \plmac@next
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
%
% \subsubsection{Defining Perl environments}
% \label{sec:perl-env}
%
% \changes{v1.1}{2004/02/24}{Added new
%   \texttt{\string\string\string\perlnewenvironment} and
%   \texttt{\string\string\string\perlrenewenvironment} macros}
%
% Section~\ref{sec:perl-mac} detailed the implementation of
% |\perlnewcommand| and |\perlrenewcommand|.  Section~\ref{sec:perl-env}
% does likewise for \PerlTeX's remaining two macros,
% |\perlnewenvironment| and |\perlrenewenvironment|, which are the
% Perl-bodied analogues of |\newenvironment| and |\renewenvironment|.
% This section is significantly shorter than the previous because
% |\perlnewenvironment| and |\perlrenewenvironment| are largely built
% atop the macros already defined in Section~\ref{sec:perl-mac}.
%
% \begin{macro}{\perlnewenvironment}
% \begin{macro}{\perlrenewenvironment}
% \begin{macro}{\plmac@command}
% \begin{macro}{\plmac@next}
% |\perlnewenvironment| and |\perlrenewenvironment| are the remaining
% two commands exported to the user by \perlmac.  |\perlnewenvironment|
% is analogous to |\newenvironment| except that the macro body consists
% of Perl code instead of \LaTeX{} code.  Likewise,
% |\perlrenewenvironment| is analogous to |\renewenvironment| except
% that the macro body consists of Perl code instead of \LaTeX{} code.
% |\perlnewenvironment| and |\perlrenewenvironment| merely define
% |\plmac@command| and |\plmac@next| and invoke
% |\plmac@newenvironment@i|.
%
% The significance of |\plmac@next| (which was let-bound to |\relax| for
% |\perl|[|re|]|newcommand| but is let-bound to |\plmac@end@environment|
% here) is that a \LaTeX{} environment definition is really two macro
% definitions: |\|\meta{name} and |\end|\meta{name}.  Because we want to
% reuse as much code as possible the idea is to define the ``begin''
% code as one macro, then inject---by way of |plmac@next|---a call to
% |\plmac@end@environment|, which defines the ``end'' code as a second
% macro.
%    \begin{macrocode}
\def\perlnewenvironment{%
  \let\plmac@command=\newcommand
  \let\plmac@next=\plmac@end@environment
  \@ifnextchar*{\plmac@newenvironment@i}{\plmac@newenvironment@i!}%
}
%    \end{macrocode}
%    \begin{macrocode}
\def\perlrenewenvironment{%
  \let\plmac@command=\renewcommand
  \let\plmac@next=\plmac@end@environment
  \@ifnextchar*{\plmac@newenvironment@i}{\plmac@newenvironment@i!}%
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\plmac@newenvironment@i}
% \begin{macro}{\plmac@starchar}
% \begin{macro}{\plmac@envname}
% \begin{macro}{\plmac@macname}
% \begin{macro}{\plmac@oldbody}
% \begin{macro}{\plmac@cleaned@macname}
% The |\plmac@newenvironment@i| macro is analogous to
% |\plmac@newcommand@i|; see the description of
% |\plmac@newcommand@i|~\vpageref{page:newcommand-i} to understand the
% basic structure.  The primary difference is that the environment name
% (|#2|) is just text, not a control sequence.  We store this text in
% |\plmac@envname| to facilitate generating the names of the two macros
% that constitute an environment definition.  Note that there is no
% |\plmac@newenvironment@ii|; control passes instead to
% |\plmac@newcommand@ii|.
%    \begin{macrocode}
\def\plmac@newenvironment@i#1#2{%
  \ifx#1*%
    \def\plmac@starchar{*}%
  \else
    \def\plmac@starchar{}%
  \fi
  \def\plmac@envname{#2}%
  \expandafter\def\expandafter\plmac@macname\expandafter{\csname#2\endcsname}%
  \expandafter\let\expandafter\plmac@oldbody\plmac@macname\relax
  \expandafter\def\expandafter\plmac@cleaned@macname\expandafter{%
    \expandafter\string\plmac@macname}%
  \@ifnextchar[{\plmac@newcommand@ii}{\plmac@newcommand@ii[0]}%]
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\plmac@end@environment}
% \begin{macro}{\plmac@next}
% \begin{macro}{\plmac@macname}
% \begin{macro}{\plmac@oldbody}
% \begin{macro}{\plmac@cleaned@macname}
% Recall that an environment definition is a shortcut for two macro
% definitions: |\|\meta{name} and |\end|\meta{name} (where \meta{name}
% was stored in |\plmac@envname| by |\plmac@newenvironment@i|).  After
% defining |\|\meta{name}, |\plmac@havecode| transfers control to
% |\plmac@end@environment| because |\plmac@next| was let-bound to
% |\plmac@end@environment| in |\perl|[|re|]|newenvironment|.
%
% |\plmac@end@environment|'s purpose is to define |\end|\meta{name}.
% This is a little tricky, however, because \LaTeX's
% |\|[|re|]|newcommand| refuses to (re)define a macro whose name begins
% with ``|end|''.  The solution that |\plmac@end@environment| takes is
% first to define a |\plmac@end@macro| macro then (in |plmac@next|)
% let-bind |\end|\meta{name} to it.  Other than that,
% |\plmac@end@environment| is a combined and simplified version of
% |\perlnewenvironment|, |\perlrenewenvironment|, and
% |\plmac@newenvironment@i|.
%    \begin{macrocode}
\def\plmac@end@environment{%
  \expandafter\def\expandafter\plmac@next\expandafter{\expandafter
    \let\csname end\plmac@envname\endcsname=\plmac@end@macro
    \let\plmac@next=\relax
  }%
  \def\plmac@macname{\plmac@end@macro}%
  \expandafter\let\expandafter\plmac@oldbody\csname end\plmac@envname\endcsname
  \expandafter\def\expandafter\plmac@cleaned@macname\expandafter{%
    \expandafter\string\plmac@macname}%
  \@ifnextchar[{\plmac@newcommand@ii}{\plmac@newcommand@ii[0]}%]
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
%
% \subsubsection{Communication between \LaTeX{} and Perl}
%
% As shown in the previous section, when a document invokes
% |\perl|[|re|]|newcommand| to define a macro, \perlmac{} defines the
% macro in terms of a call to |\plmac@write@perl|.  In this section, we
% learn how |\plmac@write@perl| operates.
%
% At the highest level, \LaTeX-to-Perl communication is performed via
% the filesystem.  In essence, \LaTeX{} writes a file (|\plmac@tofile|)
% corresponding to the information in either
% Figure~\ref{fig:tofile-define} or Figure~\ref{fig:tofile-use}; Perl
% reads the file, executes the code within it, and writes a |.tex| file
% (|\plmac@fromfile|); and, finally, \LaTeX{} reads and executes the new
% |.tex| file.  However, the actual communication protocol is a bit more
% involved than that.  The problem is that Perl needs to know when
% \LaTeX{} has finished writing Perl code and \LaTeX{} needs to know
% when Perl has finished writing \LaTeX{} code.  The solution involves
% introducing three extra files---|\plmac@toflag|, |\plmac@fromflag|,
% and |\plmac@doneflag|---which are used exclusively for \LaTeX-to-Perl
% synchronization.
%
% There's a catch: Although Perl can create and delete files, \LaTeX{}
% can only create them.  Even worse, \LaTeX{} (more specifically,
% te\TeX, which is the \TeX{} distribution under which I developed
% \PerlTeX) cannot reliably poll for a file's \emph{non}existence; if a
% file is deleted in the middle of an |\immediate\openin|, |latex|
% aborts with an error message.  These restrictions led to the
% regrettably convoluted protocol illustrated in
% Figure~\ref{fig:comm-protocol}.  In the figure, ``Touch'' means
% ``create a zero-length file''; ``Await'' means ``wait until the file
% exists''; and, ``Read'', ``Write'', and ``Delete'' are defined as
% expected.  Assuming the filesystem performs these operations in a
% sequentially consistent order (not necessarily guaranteed on all
% filesystems, unfortunately), \PerlTeX{} should behave as expected.
%
% \begin{figure}[htbp]
%   \centering
%   \makeatletter\setlength{\unitlength}{\baselineskip}\makeatother
%   \DeleteShortVerb\|
%   \def\topl{\texttt{\string\plmac@tofile}}
%   \def\frpl{\texttt{\string\plmac@fromfile}}
%   \def\tfpl{\texttt{\string\plmac@toflag}}
%   \def\ffpl{\texttt{\string\plmac@fromflag}}
%   \def\dfpl{\texttt{\string\plmac@doneflag}}
%   \begin{tabular}{@{}c@{\hspace*{1cm}}|l@{~}l|c|l@{~}l|@{}}
%     \multicolumn{1}{@{}c@{\hspace*{1cm}}}{Time} &
%     \multicolumn{2}{c}{\LaTeX} &
%     \multicolumn{1}{c}{} &
%     \multicolumn{2}{c@{}}{Perl} \\
%
%     \cline{2-3}\cline{5-6}
%     \smash{\vector(0,-1){11}}
%     & Write & \topl &               &        &       \\
%     & Touch & \tfpl & $\rightarrow$ & Await  & \tfpl \\
%     &       &       &               & Read   & \topl \\
%     &       &       &               & Write  & \frpl \\
%     &       &       &               & Delete & \tfpl \\
%     &       &       &               & Delete & \topl \\
%     &       &       &               & Delete & \dfpl \\
%     & Await & \ffpl & $\leftarrow$  & Touch  & \ffpl \\
%     & Read  & \frpl &               &        &       \\
%     & Touch & \topl & $\rightarrow$ & Await  & \topl \\
%     &       &       &               & Delete & \ffpl \\
%     & Await & \dfpl & $\leftarrow$  & Touch  & \dfpl \\
%     \cline{2-3}\cline{5-6}
%   \end{tabular}
%   \MakeShortVerb\|
%   \caption{\LaTeX-to-Perl communication protocol}
%   \label{fig:comm-protocol}
% \end{figure}
%
% \begin{macro}{\plmac@await@existence}
% \begin{macro}{\ifplmac@file@exists}
% \begin{macro}{\plmac@file@existstrue}
% \begin{macro}{\plmac@file@existsfalse}
% The purpose of the |\plmac@await@existence| macro is to repeatedly
% check the existence of a given file until the file actually exists.
% For convenience, we use \LaTeXe's |\IfFileExists| macro to check the
% file and invoke |\plmac@file@existstrue| or |\plmac@file@existsfalse|,
% as appropriate.
%    \begin{macrocode}
\newif\ifplmac@file@exists
%    \end{macrocode}
%    \begin{macrocode}
\newcommand{\plmac@await@existence}[1]{%
  \loop
    \IfFileExists{#1}%
                 {\plmac@file@existstrue}%
                 {\plmac@file@existsfalse}%
    \ifplmac@file@exists
    \else
  \repeat
}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\plmac@outfile}
% We define a file handle for |\plmac@write@perl@i| to use to create and
% write |\plmac@tofile| and |\plmac@toflag|.
%    \begin{macrocode}
\newwrite\plmac@outfile
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\plmac@write@perl}
% |\plmac@write@perl| begins the \LaTeX-to-Perl data exchange, following
% the protocol illustrated in Figure~\ref{fig:comm-protocol}.
% |\plmac@write@perl| prepares for the next piece of text in the input
% stream to be read with ``special'' characters marked as category
% code~12 (``other'').  This prevents \LaTeX{} from complaining if the
% Perl code contains invalid \LaTeX{} (which it usually will).
% |\plmac@write@perl| ends by passing control to |\plmac@write@perl@i|,
% which performs the bulk of the work.
%    \begin{macrocode}
\newcommand{\plmac@write@perl}{%
  \begingroup
    \let\do\@makeother\dospecials
    \catcode`\^^M=\active
    \newlinechar`\^^M
    \endlinechar=`\^^M
    \catcode`\{=1
    \catcode`\}=2
    \plmac@write@perl@i
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\plmac@write@perl@i}
% When |\plmac@write@perl@i| begins executing, the category codes are
% set up so that the macro's argument will be evaluated ``verbatim''
% except for the part consisting of the \LaTeX\ code passed in by the
% author, which is partially expanded.  Thus, everything is in place for
% |\plmac@write@perl@i| to send its argument to Perl and read back the
% (\LaTeX) result.
%
% Because\label{page:define-dummies} all of \perlmac's protocol
% processing is encapsulated within |\plmac@write@perl@i|, this is the
% only macro that strictly requires \perltex.  Consequently, we wrap the
% entire macro definition within a check for \perltex.
%    \begin{macrocode}
\ifplmac@have@perltex
  \newcommand{\plmac@write@perl@i}[1]{%
%    \end{macrocode}
% The first step is to write argument |#1| to |\plmac@tofile|:
% \changes{v1.1}{2004/02/19}{Made argument-handling more rational by
%   making \texttt{\string\string\string\protect},
%   \texttt{\string\string\string\begin}, and
%   \texttt{\string\string\string\end} non-expandable}
%    \begin{macrocode}
      \immediate\openout\plmac@outfile=\plmac@tofile\relax
      \let\protect=\noexpand
      \def\begin{\noexpand\begin}%
      \def\end{\noexpand\end}%
      \immediate\write\plmac@outfile{#1}%
      \immediate\closeout\plmac@outfile
%    \end{macrocode}
% \noindent
% (In the future, it might be worth redefining |\def|, |\edef|, |\gdef|,
% |\xdef|, |\let|, and maybe some other control sequences as
% ``|\noexpand|\meta{control sequence}|\noexpand|'' so that |\write|
% doesn't try to expand an undefined control sequence.)
%
% We're now finished using |#1| so we can end the group begun by
% |\plmac@write@perl|, thereby resetting each character's category code
% back to its previous value.
%    \begin{macrocode}
    \endgroup
%    \end{macrocode}
%
% Continuing the protocol illustrated in Figure~\ref{fig:comm-protocol},
% we create a zero-byte |\plmac@toflag| in order to notify \perltex{}
% that it's now safe to read |\plmac@tofile|.
%    \begin{macrocode}
    \immediate\openout\plmac@outfile=\plmac@toflag\relax
    \immediate\closeout\plmac@outfile
%    \end{macrocode}
%
% To avoid reading |\plmac@fromfile| before \perltex{} has finished
% writing it we must wait until \perltex{} creates |\plmac@fromflag|,
% which it does only after it has written |\plmac@fromfile|.
%    \begin{macrocode}
    \plmac@await@existence\plmac@fromflag
%    \end{macrocode}
%
% At this point, |\plmac@fromfile| should contain valid \LaTeX{} code.
% However, we defer inputting it until we the very end.  Doing so
% enables recursive and mutually recursive invocations of \PerlTeX{}
% macros.
% \changes{v1.2}{2004/10/07}{Moved the
%   \texttt{\string\string\string\input} of the generated Perl code to
%   the end of the routine in order to support recursive \PerlTeX{}
%   macro invocations.}
%
% Because \TeX{} can't delete files we require an additional
% \LaTeX-to-Perl synchronization step.  For convenience, we recycle
% |\plmac@tofile| as a synchronization file rather than introduce yet
% another flag file to complement |\plmac@toflag|, |\plmac@fromflag|,
% and |\plmac@doneflag|.
%    \begin{macrocode}
    \immediate\openout\plmac@outfile=\plmac@tofile\relax
    \immediate\closeout\plmac@outfile
    \plmac@await@existence\plmac@doneflag
%    \end{macrocode}
%
% The only thing left to do is to |\input| and evaluate
% |\plmac@fromfile|, which contains the \LaTeX{} output from the Perl
% subroutine.
%    \begin{macrocode}
    \input\plmac@fromfile\relax
  }
%    \end{macrocode}
%
% \changes{v1.1}{2004/02/24}{Added a dummy version of the macro to use
%   if \texttt{latex} was launched directly, without \perltex}
% The foregoing code represents the ``real'' definition of
% |\plmac@write@perl@i|.  For the user's convenience, we define a dummy
% version of |\plmac@write@perl@i| so that a document which utilizes
% \perlmac{} can still compile even if not built using \perltex.  All
% calls to macros defined with |\perl|[|re|]|newcommand| and all
% invocations of environments defined with |\perl|[|re|]|newenvironment|
% are replaced with ``\fbox{Perl\TeX}''.  A minor complication is that
% text can't be inserted before the |\begin{document}|.  Hence, we
% initially define |\plmac@write@perl@i| as a do-nothing macro and
% redefine it as ``|\fbox{Perl\TeX}|'' at the |\begin{document}|.
%    \begin{macrocode}
\else
  \newcommand{\plmac@write@perl@i}[1]{\endgroup}
  \AtBeginDocument{%
    \renewcommand{\plmac@write@perl@i}[1]{%
%    \end{macrocode}
% \begin{macro}{\plmac@show@placeholder}
% There's really no point in outputting a framed ``Perl\TeX'' when a
% macro is defined \emph{and} when it's used.  |\plmac@show@placeholder|
% checks the first character of the protocol header.  If it's
% ``D''~(|DEF|), nothing is output.  Otherwise, it'll be ``U''~(|USE|)
% and ``Perl\TeX'' will be output.
%    \begin{macrocode}
      \def\plmac@show@placeholder##1##2\@empty{%
        \ifx##1D\relax
          \endgroup
        \else
          \endgroup
          \fbox{Perl\TeX}%
        \fi
      }%
      \plmac@show@placeholder#1\@empty
    }%
  }
\fi
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \iffalse
%</package>
% \fi
%
% ^^A  Keep track of the number of lines of code in perltex.
% \makeatletter
% \immediate\write\@auxout{^^A
%   \noexpand\gdef\noexpand\perlmaclines{\the\c@CodelineNo}}
% \makeatother
%
%
% \subsection{\perltex}
% \label{sec:perltex}
%
% \perltex{} is a wrapper script for |latex| (or any other \LaTeX{}
% compiler).  It sets up client-server communication between \LaTeX{}
% and Perl, with \LaTeX{} as the client and Perl as the server.  When a
% \LaTeX{} document sends a piece of Perl code to \perltex{} (with the
% help of \perlmac, as detailed in Section~\ref{sec:perlmacros}),
% \perltex{} executes it within a secure sandbox and transmits the
% resulting \LaTeX{} code back to the document.
%
% \iffalse
%<*perltex>
% \fi
%
% \subsubsection{Header comments}
%
% Because \perltex{} is generated without a \textsf{DocStrip}
% preamble or postamble we have to manually include the desired
% text as Perl comments.
%
%    \begin{macrocode}
#! /usr/bin/env perl

###########################################################
# Prepare a LaTeX run for two-way communication with Perl #
# By Scott Pakin <scott+pt@pakin.org>                     #
###########################################################

#-------------------------------------------------------------------
# This is file `perltex.pl',
# generated with the docstrip utility.
#
# The original source files were:
#
# perltex.dtx  (with options: `perltex')
#
# This is a generated file.
#
# Copyright (C) 2004 by Scott Pakin <scott+pt@pakin.org>
#
# This file may be distributed and/or modified under the conditions
# of the LaTeX Project Public License, either version 1.2 of this
# license or (at your option) any later version.  The latest
# version of this license is in:
#
#    http://www.latex-project.org/lppl.txt
#
# and version 1.2 or later is part of all distributions of LaTeX
# version 1999/12/01 or later.
#-------------------------------------------------------------------

%    \end{macrocode}
%
% \subsubsection{Perl modules and pragmas}
%
% We use |Safe| and |Opcode| to implement the secure sandbox,
% |Getopt::Long| and |Pod::Usage| to parse the command line, and
% various other modules and pragmas for miscellaneous things.
%    \begin{macrocode}
use Safe;
use Opcode;
use Getopt::Long;
use Pod::Usage;
use File::Basename;
use POSIX;
use warnings;
use strict;
%    \end{macrocode}
%
% \subsubsection{Variable declarations}
%
% With |use strict| in effect, we need to declare all of our variables.
% For clarity, we separate our global-variable declarations into
% variables corresponding to command-line options and other global
% variables.
%
% \paragraph{Variables corresponding to command-line arguments}
% \begin{perlmacro}{$latexprog}
% \begin{perlmacro}{$runsafely}
% \begin{perlmacro}{@permittedops}
% |$latexprog| is the name of the \LaTeX{} executable
% (e.g.,~``|latex|'').  If |$runsafely| is~|1| (the default), then the
% user's Perl code runs in a secure sandbox; if it's |0|, then arbitrary
% Perl code is allowed to run.  |@permittedops| is a list of features
% made available to the user's Perl code.  Valid values are described in
% Perl's |Opcode| manual page.  \perltex's default is a list containing
% only |:browse|.
%    \begin{macrocode}
my $latexprog;
my $runsafely = 1;
my @permittedops;
%    \end{macrocode}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
%
% \paragraph{Other global variables}
% \begin{perlmacro}{$progname}
% \begin{perlmacro}{$jobname}
% \begin{perlmacro}{@latexcmdline}
% \begin{perlmacro}{$toperl}
% \begin{perlmacro}{$fromperl}
% \begin{perlmacro}{$toflag}
% \begin{perlmacro}{$fromflag}
% \begin{perlmacro}{$doneflag}
% \begin{perlmacro}{$logfile}
% \begin{perlmacro}{$sandbox}
% \begin{perlmacro}{$latexpid}
% |$progname| is the run-time name of the \perltex{} program.
% |$jobname| is the base name of the user's |.tex| file, which defaults
% to the \TeX{} default of |texput|.  |@latexcmdline| is the command
% line to pass to the \LaTeX{} executable.  |$toperl| defines the
% filename used for \LaTeX{}$\rightarrow$Perl communication.
% |$fromperl| defines the filename used for Perl$\rightarrow$\LaTeX{}
% communication.  |$toflag| is the name of a file that will exist only
% after \LaTeX{} creates |$tofile|.  |$fromflag| is the name of a file
% that will exist only after Perl creates |$fromfile|.  |$doneflag| is
% the name of a file that will exist only after Perl deletes
% |$fromflag|.  |$logfile| is the name of a log file to which \perltex{}
% writes verbose execution information.  |$sandbox| is a secure sandbox
% in which to run code that appeared in the \LaTeX{} document.
% |$latexpid| is the process~ID of the |latex| process.
%    \begin{macrocode}
my $progname = basename $0;
my $jobname = "texput";
my @latexcmdline;
my $toperl;
my $fromperl;
my $toflag;
my $fromflag;
my $doneflag;
my $logfile;
my $sandbox = new Safe;
my $latexpid;
%    \end{macrocode}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
%
% \subsubsection{Command-line conversion}
%
% In this section, \perltex{} parses its own command line and prepares a
% command line to pass to |latex|.
%
% \paragraph{Parsing \perltex's command line}
% We first set |$latexprog| to be the contents of the environment
% variable |PERLTEX| or the value ``|latex|'' if |PERLTEX| is not
% specified.  We then use |Getopt::Long| to parse the command line,
% leaving any parameters we don't recognize in the argument vector
% (|@ARGV|) because these are presumably |latex| options.
%    \begin{macrocode}
$latexprog = $ENV{"PERLTEX"} || "latex";
Getopt::Long::Configure("require_order", "pass_through");
GetOptions("help"     => sub {pod2usage(-verbose => 1)},
           "latex=s"  => \$latexprog,
           "safe!"    => \$runsafely,
           "permit=s" => \@permittedops) || pod2usage(2);
%    \end{macrocode}
%
% \paragraph{Preparing a \LaTeX{} command line}
% \begin{perlmacro}{$firstcmd}
% \begin{perlmacro}{$option}
% We start by searching |@ARGV| for the first string that does not start
% with ``|-|'' or ``|\|''.  This string, which represents a filename, is
% used to set |$jobname|.
%    \begin{macrocode}
@latexcmdline = @ARGV;
my $firstcmd = 0;
for ($firstcmd=0; $firstcmd<=$#latexcmdline; $firstcmd++) {
    my $option = $latexcmdline[$firstcmd];
    next if substr($option, 0, 1) eq "-";
    if (substr ($option, 0, 1) ne "\\") {
        $jobname = basename $option, ".tex" ;
        $latexcmdline[$firstcmd] = "\\input $option";
    }
    last;
}
push @latexcmdline, "" if $#latexcmdline==-1;
%    \end{macrocode}
% \end{perlmacro}
% \end{perlmacro}
%
% \begin{perlmacro}{$separator}
% To avoid conflicts with the code and parameters passed to Perl from
% \LaTeX{} (see Figure~\vref{fig:tofile-define} and
% Figure~\vref{fig:tofile-use}) we define a separator string,
% |$separator|, containing 20 random uppercase letters.
%    \begin{macrocode}
my $separator = "";
foreach (1 .. 20) {
    $separator .= chr(ord("A") + rand(26));
}
%    \end{macrocode}
% \end{perlmacro}
%
% Now that we have the name of the \LaTeX{} job (|$jobname|) we can
% assign |$toperl|, |$fromperl|, |$toflag|, |$fromflag|, |$doneflag|,
% and |$logfile| in terms of |$jobname| plus a suitable extension.
%    \begin{macrocode}
$toperl = $jobname . ".topl";
$fromperl = $jobname . ".frpl";
$toflag = $jobname . ".tfpl";
$fromflag = $jobname . ".ffpl";
$doneflag = $jobname . ".dfpl";
$logfile = $jobname . ".lgpl";
%    \end{macrocode}
%
% We now replace the filename of the |.tex| file passed to \perltex{}
% with a |\def|inition of the separator character, |\def|initions of the
% various files, and the original file with |\input| prepended if
% necessary.
%    \begin{macrocode}
$latexcmdline[$firstcmd] =
    sprintf '\makeatletter' . '\def%s{%s}' x 6 . '\makeatother%s',
    '\plmac@tag', $separator,
    '\plmac@tofile', $toperl,
    '\plmac@fromfile', $fromperl,
    '\plmac@toflag', $toflag,
    '\plmac@fromflag', $fromflag,
    '\plmac@doneflag', $doneflag,
    $latexcmdline[$firstcmd];
%    \end{macrocode}
%
% \subsubsection{Launching \LaTeX}
%
% We start by deleting the |$toperl|, |$fromperl|, |$toflag|,
% |$fromflag|, and |$doneflag| files, in case any of these were left
% over from a previous (aborted) run.  We also create a log file,
% |$logfile|.  As |@latexcmdline| contains the complete command line to
% pass to |latex| we need only |fork| a new process and have the child
% process overlay itself with |latex|.  \perltex{} continues running as
% the parent.
%
% Note that here and elsewhere in \perltex, |unlink| is called
% repeatedly until the file is actually deleted.  This works around a
% race condition that occurs in some filesystems in which file deletions
% are executed somewhat lazily.
% \changes{v1.0a}{2003/08/21}{Made all \texttt{unlink} calls wait for the
%   file to actually disappear}
%    \begin{macrocode}
foreach my $file ($toperl, $fromperl, $toflag, $fromflag, $doneflag) {
    unlink $file while -e $file;
}
open (LOGFILE, ">$logfile") || die "open(\"$logfile\"): $!\n";
%    \end{macrocode}
%    \begin{macrocode}
defined ($latexpid = fork) || die "fork: $!\n";
unshift @latexcmdline, $latexprog;
if (!$latexpid) {
    exec {$latexcmdline[0]} @latexcmdline;
    die "exec('@latexcmdline'): $!\n";
}
%    \end{macrocode}
%
% \subsubsection{Preparing a sandbox}
%
% \perltex{} uses Perl's |Safe| and |Opcode| modules to declare a secure
% sandbox (|$sandbox|) in which to run Perl code passed to it from
% \LaTeX{}\@.  When the sandbox compiles and executes Perl code, it
% permits only operations that are deemed safe.  For example, the Perl
% code is allowed by default to assign variables, call functions, and
% execute loops.  However, it is not normally allowed to delete files,
% kill processes, or invoke other programs.
%    \begin{macrocode}
@permittedops=(":browse") if $#permittedops==-1;
@permittedops=(Opcode::full_opset()) if !$runsafely;
$sandbox->permit_only (@permittedops);
%    \end{macrocode}
%
% \subsubsection{Communicating with \LaTeX{}}
%
% The following code constitutes \perltex's main loop.  Until |latex|
% exits, the loop repeatedly reads Perl code from \LaTeX{}, evaluates
% it, and returns the result as per the protocol described in
% Figure~\vref{fig:comm-protocol}.
% \changes{v1.0a}{2003/08/21}{Undefined \texttt{\string\string\string$/}
%   only locally}
%
%    \begin{macrocode}
while (1) {
%    \end{macrocode}
%
% \begin{perlmacro}{$awaitexists}
% We define a local subroutine |$awaitexists| which waits for a given
% file to exist.  If |latex| exits while |$awaitexists| is waiting, then
% \perltex{} cleans up and exits, too.
% \changes{v1.0a}{2003/08/06}{Bug fix: Added ``\texttt{undef
%   \$latexpid}'' to make the \texttt{END} block correctly return a
%   status code of~0 on success}
%    \begin{macrocode}
    my $awaitexists = sub {
      while (!-e $_[0]) {
          sleep 0;
          if (waitpid($latexpid, &WNOHANG)==-1) {
              foreach my $file ($toperl, $fromperl, $toflag,
                                $fromflag, $doneflag) {
                  unlink $file while -e $file;
              }
              undef $latexpid;
              exit 0;
          }
      }
    };
%    \end{macrocode}
% \end{perlmacro}
%
% \begin{perlmacro}{$entirefile}
% Wait for |$toflag| to exist.  When it does, this implies that
% |$toperl| must exist as well.  We read the entire contents of
% |$toperl| into the |$entirefile| variable and process it.
% Figures~\ref{fig:tofile-define} and~\ref{fig:tofile-use} illustrate
% the contents of |$toperl|.
%    \begin{macrocode}
    $awaitexists->($toflag);
    my $entirefile;
    {
        local $/ = undef;
        open (TOPERL, "<$toperl") || die "open($toperl): $!\n";
        $entirefile = <TOPERL>;
        close TOPERL;
    }
%    \end{macrocode}
% \end{perlmacro}
%
% \begin{perlmacro}{$optag}
% \begin{perlmacro}{$macroname}
% \begin{perlmacro}{@otherstuff}
% We split the contents of |$entirefile| into an operation tag (either
% |DEF| or |USE|), the macro name, and everything else (|@otherstuff|).
% If |$optag| is |DEF| then |@otherstuff| will contain the Perl code to
% define.  If |$optag| is |USE| then |@otherstuff| will be a list of
% subroutine arguments.
%    \begin{macrocode}
    my ($optag, $macroname, @otherstuff) =
        map {chomp; $_} split "$separator\n", $entirefile;
%    \end{macrocode}
% \end{perlmacro}
% \end{perlmacro}
% \end{perlmacro}
%
% We clean up the macro name by deleting all leading non-letters,
% replacing all subsequent non-alphanumerics with ``|_|'', and
% prepending ``|latex_|'' to the macro name.
%    \begin{macrocode}
    $macroname =~ s/^[^A-Za-z]+//;
    $macroname =~ s/\W/_/g;
    $macroname = "latex_" . $macroname;
%    \end{macrocode}
%
% If we're calling a subroutine, then we make the arguments more
% palatable to Perl by single-quoting them and replacing every
% occurrence of ``|\|'' with ``|\\|'' and every occurrence of ``|'|''
% with ``|\'|''.
%    \begin{macrocode}
    if ($optag eq "USE") {
      foreach (@otherstuff) {
          s/\\/\\\\/g;
          s/\'/\\\'/g;
          $_ = "'$_'";
      }
    }
%    \end{macrocode}
%
% \begin{perlmacro}{$perlcode}
% There are two possible values that can be assigned to |$perlcode|.  If
% |$optag| is |DEF|, then |$perlcode| is made to contain a definition of
% the user's subroutine, named |$macroname|.  If |$optag| is |USE|, then
% |$perlcode| becomes an invocation of |$macroname| which gets passed
% all of the macro arguments.  Figure~\ref{fig:latex-perl-define}
% presents an example of how the following code converts a \PerlTeX{}
% macro definition into a Perl subroutine definition and
% Figure~\ref{fig:latex-perl-use} presents an example of how the
% following code converts a \PerlTeX{} macro invocation into a Perl
% subroutine invocation.
%
% \begin{figure}[tbp]
%   \centering
%   \DeleteShortVerb\|
%   \begin{tabular}{l|l|}
%     \cline{2-2}
%     \LaTeX: & \verb|\perlnewcommand{\mymacro}[2]{%| \\
%             & \verb|  sprintf "Isn't $_[0] %s $_[1]?\n",| \\
%             & \verb|    $_[0]>=$_[1] ? ">=" : "<"| \\
%             & \verb|}| \\
%     \cline{2-2}
%     \multicolumn{2}{c}{} \\
%     \multicolumn{1}{c}{} & \multicolumn{1}{c}{\Huge$\Downarrow$} \\
%     \multicolumn{2}{c}{} \\
%     \cline{2-2}
%     Perl:   & \verb|sub latex_mymacro {| \\
%             & \verb|  sprintf "Isn't $_[0] %s $_[1]?\n",| \\
%             & \verb|    $_[0]>=$_[1] ? ">=" : "<"| \\
%             & \verb|}| \\
%     \cline{2-2}
%   \end{tabular}
%   \MakeShortVerb\|
%   \caption{Conversion from \LaTeX{} to Perl (subroutine definition)}
%   \label{fig:latex-perl-define}
% \end{figure}
%
% \begin{figure}[tbp]
%   \centering
%   \DeleteShortVerb\|
%   \begin{tabular}{l|l|}
%     \cline{2-2}
%     \LaTeX: & \verb|\mymacro{12}{34}| \\
%     \cline{2-2}
%     \multicolumn{2}{c}{} \\
%     \multicolumn{1}{c}{} & \multicolumn{1}{c}{\Huge$\Downarrow$} \\
%     \multicolumn{2}{c}{} \\
%     \cline{2-2}
%     Perl:   & \verb|latex_mymacro ('12', '34');| \\
%     \cline{2-2}
%   \end{tabular}
%   \MakeShortVerb\|
%   \caption{Conversion from \LaTeX{} to Perl (subroutine invocation)}
%   \label{fig:latex-perl-use}
% \end{figure}
%
%    \begin{macrocode}
    my $perlcode;
    if ($optag eq "DEF") {
      $perlcode =
          sprintf "sub %s {%s}\n",
          $macroname, $otherstuff[0];
    }
    else {
      $perlcode = sprintf "%s (%s);\n", $macroname, join(", ", @otherstuff);
    }
%    \end{macrocode}
% \end{perlmacro}
%
% Log what we're about to evaluate.
%    \begin{macrocode}
    print LOGFILE "#" x 31, " PERL CODE ", "#" x 32, "\n";
    print LOGFILE $perlcode, "\n";
%    \end{macrocode}
%
% \begin{perlmacro}{$result}
% \begin{perlmacro}{$msg}
% We're now ready to execute the user's code using the |$sandbox->reval|
% function.  If a warning occurs we write it as a Perl comment to the
% log file.  If an error occurs (i.e.,~|$@| is defined) we replace the
% result (|$result|) with a call to \LaTeXe's |\PackageError| macro to
% return a suitable error message.  We produce one error message for
% sandbox policy violations (detected by the error message, |$@|,
% containing the string ``\texttt{trapped by}'') and a different error
% message for all other errors caused by executing the user's code.  For
% clarity of reading both warning and error messages, we elide the
% string ``\texttt{at (eval} \meta{number}\texttt{) line}
% \meta{number}''.
%    \begin{macrocode}
    undef $_;
    my $result;
    {
        my $warningmsg;
        local $SIG{__WARN__} =
            sub {chomp ($warningmsg=$_[0]); return 0};
        $result = $sandbox->reval ($perlcode);
        if (defined $warningmsg) {
            $warningmsg =~ s/at \(eval \d+\) line \d+\W+//;
            print LOGFILE "# ===> $warningmsg\n\n";
        }
    }
    $result="" if !$result;
    if ($@) {
        my $msg = $@;
        $msg =~ s/at \(eval \d+\) line \d+\W+//;
        $msg =~ s/\s+/ /;
        $result = "\\PackageError{perltex}{$msg}";
        my @helpstring;
        if ($msg =~ /\btrapped by\b/) {
            @helpstring =
                ("The preceding error message comes from Perl.  Apparently,",
                 "the Perl code you tried to execute attempted to perform an",
                 "`unsafe' operation.  If you trust the Perl code (e.g., if",
                 "you wrote it) then you can invoke perltex with the --nosafe",
                 "option to allow arbitrary Perl code to execute.",
                 "Alternatively, you can selectively enable Perl features",
                 "using perltex's --permit option.  Don't do this if you don't",
                 "trust the Perl code, however; malicious Perl code can do a",
                 "world of harm to your computer system.");
        }
        else {
            @helpstring =
              ("The preceding error message comes from Perl.  Apparently,",
               "there's a bug in your Perl code.  You'll need to sort that",
               "out in your document and re-run perltex.");
        }
        my $helpstring = join ("\\MessageBreak\n", @helpstring);
        $helpstring =~ s/\.  /.\\space\\space /g;
        $result .= "{$helpstring}";
    }
%    \end{macrocode}
% \end{perlmacro}
% \end{perlmacro}
%
% Log the resulting \LaTeX{} code.
%    \begin{macrocode}
    print LOGFILE "%" x 30, " LATEX RESULT ", "%" x 30, "\n";
    print LOGFILE $result, "\n\n";
%    \end{macrocode}
%
% We add |\endinput| to the generated \LaTeX{} code to suppress an
% extraneous end-of-line character that \TeX{} would otherwise insert.
%    \begin{macrocode}
    $result .= '\endinput';
%    \end{macrocode}
%
% Continuing the protocol described in Figure~\vref{fig:comm-protocol}
% we now write |$result| (which contains either the result of executing
% the user's or a |\PackageError|) to the |$fromperl| file, delete
% |$toflag|, |$toperl|, and |$doneflag|, and notify \LaTeX{} by touching
% the |$fromflag| file.
%    \begin{macrocode}
    open (FROMPERL, ">$fromperl") || die "open($fromperl): $!\n";
    syswrite FROMPERL, $result;
    close FROMPERL;
%    \end{macrocode}
%    \begin{macrocode}
    unlink $toflag while -e $toflag;
    unlink $toperl while -e $toperl;
    unlink $doneflag while -e $doneflag;
%    \end{macrocode}
%    \begin{macrocode}
    open (FROMFLAG, ">$fromflag") || die "open($fromflag): $!\n";
    close FROMFLAG;
%    \end{macrocode}
%
% We have to perform one final \LaTeX-to-Perl synchronization step.
% Otherwise, a subsequent |\perl|[|re|]|newcommand| would see that
% |$fromflag| already exists and race ahead, finding that |$fromperl|
% does not contain what it's supposed to.
%    \begin{macrocode}
    $awaitexists->($toperl);
    unlink $fromflag while -e $fromflag;
    open (DONEFLAG, ">$doneflag") || die "open($doneflag): $!\n";
    close DONEFLAG;
}
%    \end{macrocode}
%
% \subsubsection{Final cleanup}
%
% If we exit abnormally we should do our best to kill the child |latex|
% process so that it doesn't continue running forever, holding onto
% system resources.
%    \begin{macrocode}
END {
    close LOGFILE;
    if (defined $latexpid) {
        kill (9, $latexpid);
        exit 1;
    }
    exit 0;
}

__END__
%    \end{macrocode}
%
% \subsubsection{\perltex{} POD documentation}
%
% \perltex{} includes documentation in Perl's POD (Plain Old
% Documentation) format.  This is used both to produce manual pages and
% to provide usage information when \perltex{} is invoked with the
% |--help| option.  The POD documentation is not listed here as part of
% the documented \perltex{} source code because it contains essentially
% the same information as that shown in Section~\ref{sec:perltex-man}.
% If you're curious what the POD source looks like then see the
% generated \perltex{} file.
%
% \iffalse
%    \begin{macrocode}

=head1 NAME

perltex - enable LaTeX macros to be defined in terms of Perl code


=head1 SYNOPSIS

perltex
[B<--help>]
[B<--latex>=I<program>]
[B<-->[B<no>]B<safe>]
[B<--permit>=I<feature>]
[I<latex options>]


=head1 DESCRIPTION

LaTeX -- through the underlying TeX typesetting system -- produces
beautifully typeset documents but has a macro language that is
difficult to program.  In particular, support for complex string
manipulation is largely lacking.  Perl is a popular general-purpose
programming language whose forte is string manipulation.  However, it
has no typesetting capabilities whatsoever.

Clearly, Perl's programmability could complement LaTeX's typesetting
strengths.  B<perltex> is the tool that enables a symbiosis between
the two systems.  All a user needs to do is compile a LaTeX document
using B<perltex> instead of B<latex>.  (B<perltex> is actually a
wrapper for B<latex>, so no B<latex> functionality is lost.)  If the
document includes a C<\usepackage{perltex}> in its preamble, then
C<\perlnewcommand> and C<\perlrenewcommand> macros will be made
available.  These behave just like LaTeX's C<\newcommand> and
C<\renewcommand> except that the macro body contains Perl code instead
of LaTeX code.


=head1 OPTIONS

B<perltex> accepts the following command-line options:

=over 4

=item B<--help>

Display basic usage information.

=item B<--latex>=I<program>

Specify a program to use instead of B<latex>.  For example,
C<--latex=pdflatex> would typeset the given document using
B<pdflatex> instead of ordinary B<latex>.

=item B<-->[B<no>]B<safe>

Enable or disable sandboxing.  With the default of C<--safe>,
B<perltex> executes the code from a C<\perlnewcommand> or
C<\perlrenewcommand> macro within a protected environment that
prohibits ``unsafe'' operations such as accessing files or executing
external programs.  Specifying C<--nosafe> gives the LaTeX document
I<carte blanche> to execute any arbitrary Perl code, including that
which can harm the user's files.  See L<Safe> for more information.

=item B<--permit>=I<feature>

Permit particular Perl operations to be performed.  The C<--permit>
option, which can be specified more than once on the command line,
enables finer-grained control over the B<perltex> sandbox.  See
L<Opcode> for more information.

=back

These options are then followed by whatever options are normally
passed to B<latex> (or whatever program was specified with
C<--latex>), including, for instance, the name of the F<.tex> file to
compile.


=head1 EXAMPLES

In its simplest form, B<perltex> is run just like B<latex>:

    perltex myfile.tex

To use B<pdflatex> instead of regular B<latex>, use the C<--latex>
option:

    perltex --latex=pdflatex myfile.tex

If LaTeX gives a ``C<trapped by operation mask>'' error and you trust
the F<.tex> file you're trying to compile not to execute malicious
Perl code (e.g., because you wrote it yourself), you can disable
B<perltex>'s safety mechansisms with C<--nosafe>:

    perltex --nosafe myfile.tex

The following command gives documents only B<perltex>'s default
permissions (C<:browse>) plus the ability to open files and invoke the
C<time> command:

    perltex --permit=:browse --permit=:filesys_open
      --permit=time myfile.tex


=head1 ENVIRONMENT

B<perltex> honors the following environment variables:

=over 4

=item PERLTEX

Specify the filename of the LaTeX compiler.  The LaTeX compiler
defaults to ``C<latex>''.  The C<PERLTEX> environment variable
overrides this default, and the C<--latex> command-line option (see
L</OPTIONS>) overrides that.

=back


=head1 FILES

While compiling F<jobname.tex>, B<perltex> makes use of the following
files:

=over 4

=item F<jobname.lgpl>

log file written by Perl; helpful for debugging Perl macros

=item F<jobname.topl>

information sent from LaTeX to Perl

=item F<jobname.frpl>

information sent from Perl to LaTeX

=item F<jobname.tfpl>

``flag'' file whose existence indicates that F<jobname.topl> contains
valid data

=item F<jobname.ffpl>

``flag'' file whose existence indicates that F<jobname.frpl> contains
valid data

=item F<jobname.dfpl>

``flag'' file whose existence indicates that F<jobname.ffpl> has been
deleted

=back


=head1 NOTES

B<perltex>'s sandbox defaults to what L<Opcode> calls ``C<:browse>''.


=head1 SEE ALSO

latex(1), pdflatex(1), perl(1), Safe(3pm), Opcode(3pm)


=head1 AUTHOR

Scott Pakin, I<scott+pt@pakin.org>
%    \end{macrocode}
% \fi
%
% \iffalse
%</perltex>
% \fi
%
% ^^A  Keep track of the number of lines of code in perltex.
% \makeatletter
% \immediate\write\@auxout{^^A
%   \noexpand\gdef\noexpand\perltexlines{\the\c@CodelineNo}}
% \makeatother
%
%
% \subsection{Porting to other languages}
% \label{sec:porting}
%
% Perl is a natural choice for a \LaTeX{} macro language because of its
% excellent support for text manipulation including extended regular
% expressions, string interpolation, and ``here'' strings, to name a few
% nice features.  However, Perl's syntax is unusual and its semantics
% are rife with annoying special cases.  Some users will therefore long
% for a \meta{some-language-other-than-Perl}\TeX\@.  Fortunately,
% porting \PerlTeX{} to use a different language should be fairly
% straightforward.  \perltex{} will need to be rewritten in the target
% language, of course, but \perlmac{} modifications will likely be
% fairly minimal.  In all probability, only the following changes will
% need to be made:
%
% \begin{itemize}
%   \item Rename \perlmac{} and \perltex{} (and choose a package name
%   other than ``\PerlTeX'') as per the \PerlTeX{} license agreement
%   (Section~\ref{sec:license}).
%
%   \item In your replacement for \perlmac, replace all occurrences of
%   ``|plmac|'' with a different string.
%
%   \item In your replacement for \perltex, choose different file
%   extensions for the various helper files.
% \end{itemize}
%
% The importance of these changes is that they help ensure version
% consistency and that they make it possible to run
% \meta{some-language-other-than-Perl}\TeX{} alongside \PerlTeX,
% enabling multiple programming languages to be utilized in the same
% \LaTeX{} document.
%
% \Finale
\endinput
