autoleftright.sty

%% autoleftright --- Automatically prepends
%%  \left and \right delimiter calls to parenthesis,
%%  brackets, and other symbols in math mode.
%% Copyright (C) 2020 by Shervin Sahba
%% E-mail: shervin@tuta.io


\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{autoleftright}[2020/05/07 v1.0 Automatically prepends left and right calls to parenthesis and brackets in math mode.]

\@ifpackageloaded{amsmath}{}{\RequirePackage{amsmath}}


%% OLD DELIMITERS
\let\oldlangle\langle
\let\oldrangle\rangle
\let\oldlceil\lceil
\let\oldrceil\rceil
\let\oldlfloor\lfloor
\let\oldrfloor\rfloor
% TODO: Need to preserve normal parenthesis and brackets.
% For now, these options are close to normal height.
\def\lp{\texttt{\big(}}
\def\rp{\texttt{\big)}}
\def\lb{\texttt{\big[}}
\def\rb{\texttt{\big]}}


\def\setautolrangle{
  \xdef\langle{\left \oldlangle}
  \xdef\rangle{\right\oldrangle}
}

\def\setautolrceil{
  \xdef\lceil{\left \oldlceil}
  \xdef\rceil{\right\oldrceil}
}

\def\setautolrfloor{
  \xdef\lfloor{\left \oldlfloor}
  \xdef\rfloor{\right\oldrfloor}
}


\def\setautolrpb{
  \def\resetMathstrut@{ %% compare with amsmath.sty
  % resetMathstrut builds a box around math mode tex, like \strut does for text mode. We redefine resetMathstrut to permit modification of character-based delimiters
    \begingroup
      \setbox\z@\hbox{} %% create a horizontal box, z@
      \edef\@tempa{ %% match height/depth of math box to z@
        \ht\Mathstrutbox@\the\ht\z@\relax
        \dp\Mathstrutbox@\the\dp\z@\relax
      }
    \expandafter\endgroup\@tempa
  }
  % set char delimeters to active mathcode, allowing them to be defined.
  \mathcode`(="8000
  \mathcode`)="8000
  \mathcode`[="8000
  \mathcode`]="8000
  % TODO work on | delimiters, alternating left and right
}


\def\autoleftright{
  \setautolrfloor
  \setautolrceil
  \setautolrangle
  \setautolrpb
}

\begingroup
  \catcode`(\active
  \catcode`)\active
  \xdef({\left \string(}
  \xdef){\right\string)}
\endgroup

\begingroup
  \catcode`[\active
  \catcode`]\active
  \xdef[{\left \string[}
  \xdef]{\right\string]}
\endgroup