Implement game engine

src/Game/Engine.hs

@@ -31,8 +31,17 @@ handleEvents = mapMaybe getDir <$> liftTransS (constM ask)
     getDir _ = Nothing
 
 tick :: Monad m => MSF (DrawerT m) (Maybe Direction) GameState
-tick = next initialState $ feedback initialState $ proc (dir, state) -> do
-  returnA -< (state, state)
+tick =
+  next initialState $
+    mealy
+      ( \input state ->
+          let moveDir = setDir state.moveDir input
+              snakePos = movePos moveDir <$> state.snakePos
+              berryPos = state.berryPos
+              newstate = GameState {..}
+           in (newstate, newstate)
+      )
+      initialState
 
 mainSF :: Monad m => MSF (DrawerT m) () ()
 mainSF = proc () -> do

src/Game/State.hs

@@ -1,7 +1,6 @@
 module Game.State where
 
 data Direction = U | D | L | R
-  deriving (Show, Eq)
 
 movePos :: Direction -> (Int, Int) -> (Int, Int)
 movePos U (x, y) = (x, y - 1)
@@ -9,6 +8,17 @@ movePos D (x, y) = (x, y + 1)
 movePos L (x, y) = (x - 1, y)
 movePos R (x, y) = (x + 1, y)
 
+opposite :: Direction -> Direction -> Bool
+opposite U D = True
+opposite D U = True
+opposite L R = True
+opposite R L = True
+opposite _ _ = False
+
+setDir :: Direction -> Maybe Direction -> Direction
+setDir d Nothing = d
+setDir d (Just d') = if opposite d d' then d else d'
+
 data GameState = GameState
   { snakePos :: [(Int, Int)],
     moveDir :: Direction,