update positions of falling enemies per frame (and filter them out too)

fcore/enemy/falling-enemies.sml

@@ -28,6 +28,40 @@ struct
       , QuadTree.create (Constants.worldWidth, Constants.worldHeight)
       )
 
+  (* - Updating position of fallingEnemies 
+   * - and filtering out enemies which are no longer in world bounds - *)
+  structure UpdateFalling =
+    MakeGapMapFolder
+      (struct
+         structure Pair = FallingEnemyPair
+
+         type env = unit
+
+         type state = FallingEnemyMap.t
+
+         fun fold (fallingID, fallingEnemy, (), fallingMap) =
+           let
+             val {x, y, variant} = fallingEnemy
+             val size = Constants.enemySize
+             val ww = Constants.worldWidth
+             val wh = Constants.worldHeight
+           in
+             if Collision.isCollidingPlus (x, y, size, size, 0, 0, ww, wh) then
+               let
+                 val newFalling =
+                   {x = x, y = y - Constants.moveEnemyBy, variant = variant}
+               in
+                 FallingEnemyMap.add (fallingID, newFalling, fallingMap)
+               end
+             else
+               (* filter out since not in world bounds *)
+               fallingMap
+           end
+       end)
+
+  fun update fallingEnemies =
+    UpdateFalling.foldUnordered (fallingEnemies, (), FallingEnemyMap.empty)
+
   (* - Drawing falling enemies - *)
   structure FallingDrawVec =
     MakeGapMapFolder

fcore/game-update.sml

@@ -29,13 +29,7 @@ struct
       val enemies = Enemy.update
         (enemies, walls, wallTree, platforms, platformTree, player, graph)
 
-    (* update state of falling enemies and possibly filter *)
+      val fallingEnemies = FallingEnemies.update fallingEnemies
-    (* todo: use enemy map
-    val fallingEnemies = FallingEnemies.updateList
-      (Vector.length fallingEnemies - 1, fallingEnemies, player, [])
-    
-    val fallingEnemies = Vector.fromList fallingEnemies
-      *)
     in
       { player = player
       , walls = walls