replace tokens

nidan.tex

%%% replace all tokens; 
%%% space -> +, leftbrace -> (, rightbrace -> ), others -> *, 
%%% provided that the argument doesn' have ! and \end. 

\def\length#1{\spaces{#1!}\notspaces{#1!}}

\def\notspaces#1{\beforegroup#1\iffalse{}\fi}
\def\beforegroup#1#{\recur#1!\futurelength}
\def\recur#1{%
  \ifx!#1\else*\expandafter\recur\fi}
\def\futurelength#1#2!{%
  \ifx!#1\notspaces{#1!}\else(\length{#1})\notspaces{#2!}\fi}

\def\spaces#1{%
  \ifx!#1\ifEnd%
    \else%
      \expandafter\expandafter\expandafter\crash%
      \expandafter\ifx\space#1%
                    \end+\expandafter\restSpace{#1}%
                  \else%
                    \end\expandafter\rest\noexpand#1%
                  \fi%
  \fi}
\def\rest#1#2\fi{\fi\expandafter\spaces\expandafter{\noexpand#2}}
\def\restSpace#1{\expandafter\expandafter\expandafter\spaces%
                 \expandafter\expandafter\expandafter{\expandafter\chopSpace#1}}
\def\ifEnd#1\fi\fi{\fi}
\def\crash#1\end{}
\def\chop#1{}
\def\chopSpace#1 {}


%\edef\result{\length{a bcd }}
%\edef\result{\length{ \a {b\cd ef{g} }\h}}
%\edef\result{\length{{ }{ {}} {}}}
%\edef\result{\length{ \a {b\cd ef{g} }\h}}
%\edef\result{\length{{ a} {bc ef{g} }h {} }}
%\edef\result{\length{{>>+<+<\-}}}
%\edef\result{\length{{s}}}
%\edef\result{\length{\expandafter\expandafter\expandafter}}
%\edef\result{\expandafter\length\expandafter{\csname ?TeX\endcsname}}
\edef\next{\noexpand\length{a\space\space\space b}}\edef\result{\next}

\show\result

\end