2011-09-17 - Erlang Conway Game Of Life

erl-conway-game-of-life.erl

-module(gol).
-include_lib("eunit/include/eunit.hrl").

next(World) ->
    sets:fold(fun(Member, Result) ->
                Count = sets:size(live_neighbours(Member, World)),
                case Count of
                    2 ->
                        sets:add_element(Member, Result);
                    _ ->
                        Result
                end
              end,
              sets:new(),
              World).

live_neighbours(Cell, World) ->
    {Row, Column} = Cell,
    sets:filter(
        fun(Member) ->
            {X, Y} = Member,
            (abs(Row - X) == 1) or (abs(Column - Y) == 1)
        end,
        World).


%% Any live cell with fewer than two live neighbours dies, as if caused by underpopulation.
rule1_survive_test() ->
    World = sets:from_list([{0, 0}, {0, 1}, {0, 2}]),
    New = next(World),
    ?assertEqual(1, sets:size(New)),
    ?assertMatch(true, sets:is_element({0, 1}, New)).

rule1_empty_test() ->
    World = sets:from_list([{0, 0}]),
    ?assertEqual(0, sets:size(next(World))).