CheckWhetherLeadingSpace.tex

CheckWhetherLeadingSpace.tex

% Time-stamp: <10-09-2018 à 17:03:05>

% cf https://tex.stackexchange.com/a/449979/4686

\catcode`@ 11

\long\def\@gobble#1{}
\long\def\@gobbletwo#1#2{}

%\long\def\JFB@stop@firstoftwo#1#2{\z@#1}
\long\def\JFB@stop@secondoftwo#1#2{\z@#2}
\long\def\JFB@stop@thirdoffour#1#2#3#4{\z@#3}

%\long\def\JFB@stop@firstofthree#1#2#3{\z@#1}
\long\def\JFB@stop@secondofthree#1#2#3{\z@#2}
\long\def\JFB@stop@thirdofthree#1#2#3{\z@#3}


%%%%%%%%%%%%%%%%
% \JFB@CheckWhetherBrace
% (branches according to whether #1 starts or not with explicit
% character token of catcode 1)

\long\def\JFB@CheckWhetherBrace#1{%
  \romannumeral
  \expandafter\@gobble\expandafter
  {\expandafter{\string#1.}\expandafter\JFB@stop@thirdoffour\string}%
  \JFB@stop@secondoftwo
}%

testing checkwhetherbrace

\JFB@CheckWhetherBrace{cccc{aaaa}bbbb}{WRONG}{OK}

\JFB@CheckWhetherBrace{{aaaa}bbbb}{OK}{WRONG}

%%%%%%%%%%%%%%%%
% \JFB@CheckWhetherNull
% (branches according to whether #1 is or not empty)

\long\def\JFB@CheckWhetherNull#1{%
  \romannumeral
  \expandafter\expandafter\expandafter\@gobbletwo
  \expandafter\string\expandafter{\expandafter{%
  \expandafter{\string#1}\expandafter\@gobble\string}%
                         \iffalse}\JFB@stop@thirdoffour\fi
  \JFB@stop@secondoftwo
}%

testing checkwhethernull

\JFB@CheckWhetherNull{}{OK}{WRONG}

\JFB@CheckWhetherNull{{}}{WRONG}{OK}

\JFB@CheckWhetherNull{ }{WRONG}{OK}

\JFB@CheckWhetherNull{ {}}{WRONG}{OK}

\JFB@CheckWhetherNull{{} }{WRONG}{OK}

\JFB@CheckWhetherNull{{ }}{WRONG}{OK}

\JFB@CheckWhetherNull{a}{WRONG}{OK}

\JFB@CheckWhetherNull{\error}{WRONG}{OK}


%%%%%%%%%%%%%%%%
% \JFB@CheckWhetherLeadingSpace
% (branches according to whether #1 starts or not
%  with character code 32 space token)
% as in the other macros we could simplify with "delimiter" tokens
% but this would limit generality as they would be forbidden
% from argument

\long\def\JFB@CheckWhetherLeadingSpace#1{%
  \romannumeral
  \expandafter\JFB@CheckWhetherLeadingSpace@a\string{{}#1. }%
}%

\long\def\JFB@CheckWhetherLeadingSpace@a#1#2 {%
    \JFB@CheckWhetherNull{#2}%
    {\expandafter\JFB@stop@secondofthree}%
    {\expandafter\JFB@stop@thirdofthree}%
    \expandafter{\string}%
}

testing checkwhetherleadingspace

\JFB@CheckWhetherLeadingSpace{}{WRONG}{OK}

\JFB@CheckWhetherLeadingSpace{{}}{WRONG}{OK}

\JFB@CheckWhetherLeadingSpace{ }{OK}{WRONG}

\JFB@CheckWhetherLeadingSpace{ {}}{OK}{WRONG}

\JFB@CheckWhetherLeadingSpace{{} }{WRONG}{OK}

\JFB@CheckWhetherLeadingSpace{{ }}{WRONG}{OK}

\JFB@CheckWhetherLeadingSpace{a}{WRONG}{OK}

\JFB@CheckWhetherLeadingSpace{\error}{WRONG}{OK}

\JFB@CheckWhetherLeadingSpace{ \error}{OK}{WRONG}
\bye