1 files changed, 51 insertions, 0 deletions
diff --git a/ttt/src/ttt.erl b/ttt/src/ttt.erl
new file mode 100644
index 0000000..a9fc4d1
--- /dev/null
+++ b/ttt/src/ttt.erl
@@ -0,0 +1,51 @@
+-module(ttt).
+
+-export_type([
+  player/0,
+  square/0,
+  board/0,
+  game_result/0]).
+
+-export([
+  who_wins/1,
+  empty_board/0,
+  move/4,
+  format/1]).
+
+-type player() :: 'X' | 'O'.
+-type square() :: player() | 'E'.
+-type board() :: list(square()).
+-type game_result() :: player() | 'draw' | 'running'.
+
+-define(EMPTY_BOARD, ['E', 'E', 'E', 'E', 'E', 'E', 'E', 'E', 'E']).
+
+-spec empty_board() -> board().
+empty_board() -> ?EMPTY_BOARD.
+
+-spec who_wins(Board :: board()) -> game_result().
+who_wins([A, A, A, _, _, _, _, _, _]) when A == 'X' orelse A == 'O' -> A;
+who_wins([_, _, _, A, A, A, _, _, _]) when A == 'X' orelse A == 'O' -> A;
+who_wins([_, _, _, _, _, _, A, A, A]) when A == 'X' orelse A == 'O' -> A;
+who_wins([A, _, _, A, _, _, A, _, _]) when A == 'X' orelse A == 'O' -> A;
+who_wins([_, A, _, _, A, _, _, A, _]) when A == 'X' orelse A == 'O' -> A;
+who_wins([_, _, A, _, _, A, _, _, A]) when A == 'X' orelse A == 'O' -> A;
+who_wins([A, _, _, _, A, _, _, _, A]) when A == 'X' orelse A == 'O' -> A;
+who_wins([_, _, A, _, A, _, A, _, _]) when A == 'X' orelse A == 'O' -> A;
+who_wins(Board) ->
+  case lists:member('E', Board) of
+    true -> running;
+    false -> draw
+  end.
+
+move(_, _, Row, _) when Row < 0 orelse Row > 2 -> {bad_arg};
+move(_, _, _, Col) when Col < 0 orelse Col > 2 -> {bad_arg};
+move(_, Move, _, _) when not (Move == 'X') -> {bad_arg};
+move(Board, Move, Row, Col) ->
+  I = Row * 3 + Col,
+  Updated = lists:sublist(Board, I) ++ [Move] ++ lists:nthtail(I + 1, Board),
+  {ok, Updated}.
+
+format(Board) when length(Board) == 9 ->
+  B = lists:map(fun(C) -> case C of 'E' -> ' '; _ -> C end end, Board),
+  io:format("+---+~n|~s~s~s|~n|~s~s~s|~n|~s~s~s|~n+---+~n", B);
+format(_) -> "bad board".