update state of falling enemies per loop

fcore/enemy/enemy-behaviour.sml

@@ -405,12 +405,7 @@ struct
          * fallingEnemies *)
         let
           val fallingList =
-            { falling = false
-            , x = x
-            , y = y
-            , variant = #variant enemy
-            , jumped = 0
-            } :: fallingList
+            {x = x, y = y, variant = #variant enemy, jumped = 0} :: fallingList
         in
           (enemyList, fallingList)
         end
@@ -457,12 +452,7 @@ struct
          * fallingEnemies *)
         let
           val fallingList =
-            { falling = false
-            , x = x
-            , y = y
-            , variant = #variant enemy
-            , jumped = 0
-            } :: fallingList
+            {x = x, y = y, variant = #variant enemy, jumped = 0} :: fallingList
         in
           (enemyList, fallingList)
         end

fcore/enemy/falling-enemies.sml

@@ -0,0 +1,61 @@
+structure FallingEnemies =
+struct
+  open GameType
+
+  fun helpGenerateTree (pos, fallingVec: falling_enemy vector, acc) =
+    if pos = Vector.length fallingVec then
+      acc
+    else
+      let
+        val {x, y, ...} = Vector.sub (fallingVec, pos)
+
+        val size = Constants.enemySize
+
+        val acc = QuadTree.insert (x, y, size, size, pos + 1, acc)
+      in
+        helpGenerateTree (pos + 1, fallingVec, acc)
+      end
+
+  fun generateTree fallingVec =
+    helpGenerateTree
+      ( 0
+      , fallingVec
+      , QuadTree.create (Constants.worldWidth, Constants.worldHeight)
+      )
+
+  fun updateList (pos, vec, acc) =
+    if pos < 0 then
+      acc
+    else
+      let
+        val {x, y, jumped, variant} = Vector.sub (vec, pos)
+
+        val size = Constants.enemySize
+        val ww = Constants.worldWidth
+        val wh = Constants.worldHeight
+      in
+        if Collision.isColliding (x, y, size, size, 0, 0, ww, wh) then
+          (* move falling enemy up or down depending on jumped *)
+          let
+            val updated =
+              if jumped < Constants.jumpLimit then
+                { x = x
+                , y = y - Constants.moveEnemyBy
+                , jumped = jumped + Constants.moveEnemyBy
+                , variant = variant
+                }
+              else
+                { x = x
+                , y = y + Constants.moveEnemyBy
+                , jumped = jumped
+                , variant = variant
+                }
+          in
+            updateList (pos - 1, vec, updated :: acc)
+          end
+        else
+          (* if current is not colliding with world's bounds, then filter out 
+           * as it is off screen *)
+          updateList (pos - 1, vec, acc)
+      end
+end

fcore/game-type.sml

@@ -58,8 +58,7 @@ sig
     , nextPlatID: int
     }
 
-  type falling_enemy =
-    {falling: bool, x: int, y: int, variant: EnemyVariants.t, jumped: int}
+  type falling_enemy = {x: int, y: int, variant: EnemyVariants.t, jumped: int}
 
   type game_type =
     { player: player
@@ -136,8 +135,7 @@ struct
     , nextPlatID: int
     }
 
-  type falling_enemy =
-    {falling: bool, x: int, y: int, variant: EnemyVariants.t, jumped: int}
+  type falling_enemy = {x: int, y: int, variant: EnemyVariants.t, jumped: int}
 
   type game_type =
     { player: player

fcore/game-update.sml

@@ -19,7 +19,11 @@ struct
       val projectiles = #projectiles player
       val projectileTree = Projectile.generateTree projectiles
 
-      val (enemies, newFallingEnemies) = Enemy.updateEnemyList
+      (* update state of falling enemies and possibly filter *)
+      val fallingEnemies = FallingEnemies.updateList
+        (Vector.length fallingEnemies - 1, fallingEnemies, [])
+
+      val (enemies, fallingEnemies) = Enemy.updateEnemyList
         ( Vector.length enemies - 1
         , enemies
         , projectiles
@@ -31,10 +35,10 @@ struct
         , player
         , graph
         , []
-        , []
+        , fallingEnemies
         )
 
-      val fallingEnemies = Vector.fromList newFallingEnemies
+      val fallingEnemies = Vector.fromList fallingEnemies
     in
       { player = player
       , walls = walls