To count the maximum length of \expandafter-chains

bxcountxac.sty

%
% bxcountxac.sty

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{bxcountxac}

%% variables
\newread\xx@file
\newcount\xx@count
\newcount\xx@maxcount
%
%% \xx@scan@line
\def\xx@scan@line{%
  \expandafter\xx@scan@line@a\xx@line_%
}
\long\def\xx@scan@line@a#1{%
  \ifx#1_\else
    \ifx#1\expandafter
      \advance\xx@count\@ne
      \ifnum\xx@maxcount<\xx@count
        \xx@maxcount\xx@count
      \fi
    \else
      \xx@count\z@
    \fi
    \expandafter\xx@scan@line@a
  \fi
}
%
%% \xx@set@verbatim
\def\xx@set@verbatim{%
  \def\do##1{\catcode`##1=12\relax}%
  \do\{\do\}\do\#\do\_%
}
%
%% \xx@inspect@maxcount
\def\xx@inspect@maxcount{%
  \begingroup
    \xx@set@verbatim
    \endlinechar=13\relax
    \xx@count\z@ \xx@maxcount\z@
    \xx@inspect@maxcount@a
}
\def\xx@inspect@maxcount@a{%
  \read\xx@file to\xx@line
  \ifeof\xx@file
    \expandafter\xx@inspect@maxcount@b
  \else
    \xx@scan@line
    \expandafter\xx@inspect@maxcount@a
  \fi
}
\def\xx@inspect@maxcount@b{%
    \xdef\xx@gtempa{\xx@count\the\xx@maxcount\relax}%
  \endgroup
  \xx@gtempa
}
%
%%<*> \getxaccount{<filename>}
\newcommand\getxaccount[1]{%
  \IfFileExists{#1}{%
    \openin\xx@file=#1\relax
    \xx@inspect@maxcount
    \closein\xx@file
    \edef\xaccount{\the\xx@count}%
  }{}%
}
%
%%<*> \showxaccount{<filename>}
\newcommand\showxaccount[1]{%
  \getxaccount{#1}%
  \typeout{#1:\xaccount}%
}
%
%%-------- all done
\endinput