Write basic game structure

src/Game/Engine.hs

@@ -0,0 +1,33 @@
+{-# LANGUAGE Arrows #-}
+
+module Game.Engine where
+
+import Data.MonadicStreamFunction
+import Game.State
+import Game.Utils
+
+handleEvents :: Monad m => MSF (DrawerT m) () [Direction]
+handleEvents = proc () -> do
+  returnA -< []
+
+tick :: Monad m => MSF (DrawerT m) (Maybe Direction) GameState
+tick = next initialState $ feedback initialState $ proc (dir, state) -> do
+  returnA -< (state, state)
+
+mainSF :: Monad m => MSF (DrawerT m) () ()
+mainSF = proc () -> do
+  n <- count -< ()
+  let isTick = n `mod` 20 == 1
+
+  -- handle inputs (buffer)
+  dirs <- handleEvents -< ()
+  dir <- fifoGate -< (dirs, isTick)
+
+  state' <-
+    if isTick
+      then fmap Just tick -< dir
+      else returnA -< Nothing
+  -- undefined is safe here because the first frame is guaranteed to be a tick
+  state <- hold undefined -< state'
+
+  returnA -< ()