% Global Vars
%
% (c) Charles Baynham 2019
%
% License: LaTeX Project Public License 1.3c
%
% This package allow the user to declare a variable which can then be used
% anywhere else in a document, including before it was declared. This is done
% by putting the definitions into the .aux files, therefore requiring two runs
% to get it right.
%
% It implements two commands: \defVal{<value>} and \useVal{<value>}. \defVal
% sets up a global variable and \useVal recalls it.
%
% Using \defVal twice will result in an error. Using \useVal for an undefined
% value will output the text "??"
%

\NeedsTeXFormat{LaTeX2e}
\def\@globalvalsPkgName{globalvals}
\ProvidesPackage{\@globalvalsPkgName}
  [2019/02/06 v1.1 Define and use global variables throughout a document, including before their definition]



% useVal@#1 will hold the value of the variable: it's defined by an .aux file
% somewhere
\newcommand{\useVal}[1]{%
  \ifcsname useVal@#1\endcsname
    \csname useVal@#1\endcsname
  \else
    ??%
    \PackageWarning{\@globalvalsPkgName}{Value "#1" has not yet been defined. This may be fine, you may need to recompile. If you keep getting this message it's because you haven't defined it yet. }
  \fi
}

% useVal@#1 is defined in the .aux file to be used on the next run.
% useVal@#1@defined is defined immediately to mark that useVal@#1 has already
% been used and cannot be used again
\newcommand{\defVal}[2]{%
\ifcsname useVal@#1@defined\endcsname
  \PackageError{\@globalvalsPkgName}{Value "#1" already defined}%
    {You have two defVal commands which have the same parameter name. This error is occurring on the 2nd (or 3rd, or 4th...).}%
\else%
  \write\@auxout{%
    \unexpanded{\global\@namedef{useVal@#1}{#2}}%
  }%
  \global\@namedef{useVal@#1@defined}{}%
  \global\@namedef{useVal@#1}{#2}%
  \PackageInfo{\@globalvalsPkgName}{Defining new variable "#1" with value "#2"}%
\fi%
}

\endinput
%%
%% End of file `globalvals.sty'.