gistfile1.txt

-module(demo).

% ...

check(Board) ->
    case winner(Board) of
        {victory, Player} -> % Player wins;
        undefined ->
            case is_full(Board) of
                true -> draw;
                false -> keep_playing
            end
    end.

winner(Board) of
    case Board of
        {x, x, x,
         _, _, _,
         _, _, _} -> {victory, x};
 
        {x, _, _,
         _, x, _,
         _, _, x} -> {victory, x};
 
        {x, _, _,
         x, _, _,
         x, _, _} -> {victory, x};
 
        %% [snip]
 
        _ -> undefined
    end.

is_full(Board) ->
    lists:all(fun(X) -> X =/= undefined end, tuple_to_list(Board)).