done adding LevelType.level_type as a field of GameType.game_type, and having main loop go through GameUpdate.game_type -> LevelUpdate.update

fcore/game-update.sml

@@ -0,0 +1,18 @@
+structure GameUpdate =
+struct
+  open GameType
+
+  fun update (game: GameType.game_type, input) =
+    let
+      val {mode, userKeys} = game
+
+      val mode =
+        case mode of
+          LEVEL level =>
+            let val level = LevelUpdate.update (level, input)
+            in LEVEL level
+            end
+    in
+      {mode = mode, userKeys = userKeys}
+    end
+end