% MAP.TEX

% Marek Ry\'cko

% Macro \map
% for applying operations to token sequences

% uses SPLIT.TEX

% version 0.0 24.07.1993
% version 0.1 1.5.1996
%   -- english description

\def\map
      % for each element E of the token list #2
      % ``execute'' the token list #1
      % possibly making use of the following macros:
      %   \mappre   the token list before E (without E)
      %   \mapcur   the token E
      %   \mappost  the token list after E (without E)
      %   \mapupto  the token list from the beginning till and including E
      %   \mapfrom  the token list from and including E till the end
      %   \mapent   the entire token list
      %
      %   -------------\mapent----------------
      %                   ---\mapfrom---------
      %   ----\mapupto-----
      %   ................E...................
      %   ----\mappre----- ---\mappost--------
      %                   
      %                   |
      %                   |
      %                \mapcur
      %
    #1% operation
    #2% token list
    {{%
    \def\mapent{#2}%
    \def\mappre{}%
    \let\mapfrom\mapent
    % \mappre contains already processed sequence
    % \mapfrom contains the sequence to be processed
    % while nonempty \mapfrom do:
    \ifx\empty\mapfrom \mapcontfalse \else \mapconttrue \fi
    \loop \ifmapcont
        % \mapfrom nonempty, so it can be split:
        % split \mapfrom to head and tail:
        \split\mapfrom\mapcur\mappost
        % set \mapupto as the concatenation of \mappre and \mapcur:
        \expandafter\expandafter\expandafter
        \def\expandafter\expandafter\expandafter
        \mapupto\expandafter\expandafter\expandafter
        {\expandafter\mappre\mapcur}%
        % execute operation(s):
        #1%
        % define new values of \mappre and \mapfrom
        \expandafter\def\expandafter\mappre\expandafter{\mapupto}%
        \expandafter\def\expandafter\mapfrom\expandafter{\mappost}%
        % \mappre contains already processed sequence
        % \mapfrom contains the sequence to be processed
        \ifx\empty\mapfrom \mapcontfalse \else \mapconttrue \fi
    \repeat}}%
\newif\ifmapcont