life_engine.tex

% !TEX root = life.tex

%% ## The Game of Life Engine. ##
%% Display board.
\def\lb@print{\l@input@header@make\lb@loop{\csname lc@\the\i;\the\j\endcsname}{\endgraf}\vfill\eject}

\def\lb@print@next{%
    \advance\lb@iter1
    \lb@diff=0
    \lb@loop{%
        \expandafter\ifx\csname lc@\the\i;\the\j\expandafter\endcsname\csname lc@next@\the\i;\the\j\endcsname
        \else
            \global\advance\lb@diff1
        \fi
        \global\expandafter\let\csname lc@\the\i;\the\j\expandafter\endcsname\csname lc@next@\the\i;\the\j\endcsname
        }{}%
    \ifnum\lb@diff=0
        \lb@stop
    \fi
    \lb@print
}

%% ## Update processing. ##
\def\lb@tick{\lb@loop{\lc@update}{}}
\def\lc@update{%
    \expandafter\ifx\csname lc@\the\i;\the\j\endcsname\lc@alive
        \lc@update@alive
    \else
        \lc@update@dead
    \fi
}

%% Offset the "cursor" by specified coordinates, checking if an alive cell exists.
\def\lc@check@numalive@peek#1#2{%
    \begingroup
        \l@modadvance{\i}{\lb@size@y}{#1}\l@modadvance{\j}{\lb@size@x}{#2}
        %\advance\i#1 \advance\j#2
        \expandafter\ifx\csname lc@\the\i;\the\j\endcsname\lc@alive
            \global\advance\k1\relax
        \fi
    \endgroup
}
%% Count the number of neighbours alive.
\def\lc@check@numalive{%
    \k=0\relax
    \lc@check@numalive@peek{1}{0}%
    \lc@check@numalive@peek{1}{1}%
    \lc@check@numalive@peek{0}{1}%
    \lc@check@numalive@peek{-1}{1}%
    \lc@check@numalive@peek{-1}{0}%
    \lc@check@numalive@peek{-1}{-1}%
    \lc@check@numalive@peek{0}{-1}%
    \lc@check@numalive@peek{1}{-1}%
}

\def\lc@update@alive{%
    \lc@check@numalive
    \ifcase\k
        \csname lc@update@alive@hook@0\endcsname
    \or
        \csname lc@update@alive@hook@1\endcsname
    \or
        \csname lc@update@alive@hook@2\endcsname
    \or
        \csname lc@update@alive@hook@3\endcsname
    \or
        \csname lc@update@alive@hook@4\endcsname
    \or
        \csname lc@update@alive@hook@5\endcsname
    \or
        \csname lc@update@alive@hook@6\endcsname
    \or
        \csname lc@update@alive@hook@7\endcsname
    \or
        \csname lc@update@alive@hook@8\endcsname
    \else
        \errmessage{Undefined behavior!}
    \fi
}
\def\lc@update@dead{%
    \lc@check@numalive
    \ifcase\k
        \csname lc@update@dead@hook@0\endcsname
    \or
        \csname lc@update@dead@hook@1\endcsname
    \or
        \csname lc@update@dead@hook@2\endcsname
    \or
        \csname lc@update@dead@hook@3\endcsname
    \or
        \csname lc@update@dead@hook@4\endcsname
    \or
        \csname lc@update@dead@hook@5\endcsname
    \or
        \csname lc@update@dead@hook@6\endcsname
    \or
        \csname lc@update@dead@hook@7\endcsname
    \or
        \csname lc@update@dead@hook@8\endcsname
    \else
        \errmessage{Undefined behavior!}
    \fi
}
\def\lc@update@to@dead{\global\expandafter\let\csname lc@next@\the\i;\the\j\endcsname\lc@dead}
\def\lc@update@to@alive{\global\expandafter\let\csname lc@next@\the\i;\the\j\endcsname\lc@alive}