strict.sty

%% $Header: /cvsroot-fuse/texd/latex/sty/strict.sty,v 1.2 2007/10/02 19:18:49 jfine Exp $
%% Copyright 2007 Jonathan Fine
%% Licensed under the Apache License, Version 2.0

% Like Perl's "use strict", this package places conditions on a
% document, for it to process without error.  To use it, place
% "\usepackage{strict}" in the document preamble.

% The purpose of the package is to help the user keep to the straight
% and narrow.

% So far, only one condition, which is on environment names.

% The LaTeX macros all 'environments' such as \begin{alpha}
% ... \end{alpha}, simply because \alpha is defined.  This package
% redefines \begin{xxx} and \end{xxx} to produce an error and do nothing
% unless both \xxx and \endxxx are defined.  However, if \xxx and
% \endxxx are both defined, then \begin{xxx} and \end{xxx} work just as
% before.

% Although the name of the package is 'strict', the license is not.
% If you want to add a feature to 'strict.sty', you're welcome to modify
% your local copy (carefully).  When you're done, I'd like to have a
% copy of your changes.

% TODO:  Allow \begin{em} ... \end{em} and so forth.


% Copied from /usr/share/texmf/tex/latex/base/latex.ltx
\def\begin#1{%
  \@ifundefined{#1}%
    {\def\reserved@a{\@latex@error{Environment #1 undefined}\@eha}}%
    {\def\reserved@a{\def\@currenvir{#1}%
     \edef\@currenvline{\on@line}%
     \csname #1\endcsname}}%
 \@ignorefalse \begingroup\@endpefalse\reserved@a}

\def\end#1{%
  \csname end#1\endcsname\@checkend{#1}%
  \expandafter\endgroup\if@endpe\@doendpe\fi
  \if@ignore\@ignorefalse\ignorespaces\fi}


% New values.  If \#1 and \end#1 are both defined, continue
% as above.  If not, do nothing other than produce an undefined
% environment error.
\def\begin#1{%
  \strict@ifenvironment{#1}%
    {%
      \@ignorefalse
      \begingroup
        \@endpefalse
        \def\@currenvir{#1}%
        \edef\@currenvline{\on@line}%
        \csname #1\endcsname
    }%
    {\@latex@error{Environment #1 undefined}\@eha}%
  }

\def\end#1{%
  \strict@ifenvironment{#1}%
    {%
      \csname end#1\endcsname\@checkend{#1}%
      \expandafter\endgroup\if@endpe\@doendpe\fi
      \if@ignore\@ignorefalse\ignorespaces\fi
    }%
    {\@latex@error{Environment #1 undefined}\@eha}%
  }


% True only if \#1 and \end#1 are defined.
\def\strict@ifenvironment #1%
{%
  \begingroup
    \expandafter
  \endgroup
  \expandafter
  \strict@ifenvironmentA
    \csname #1\expandafter\endcsname
    \csname end#1\endcsname
  }

\def\strict@ifenvironmentA #1#2%
{%
  \ifcase
    \ifx #1\undefined\@ne\fi
    \ifx #2\undefined\@ne\fi
    \z@
    \expandafter\@firstoftwo
  \else
    \expandafter\@secondoftwo
  \fi
}

% Self-test, and \ddt if the test fails.
\strict@ifenvironment{itemize}{}{\ddt}
\strict@ifenvironment{xxx}{\ddt}{}
\strict@ifenvironment{alpha}{\ddt}{}

\ProvidesPackage{strict}