make player's heatth decrement when attacked, and when player's health reaches 0, boot player back to title screen

fcore/level/level-update.sml

@@ -17,31 +17,40 @@ struct
 
       val enemyTree = Enemy.generateTree enemies
       val player = Player.checkEnemyCollisions (player, enemies, enemyTree)
-
-      val (player, enemies, fallingEnemies) =
-        PlayerAttack.attackEnemies (player, enemies, enemyTree, fallingEnemies)
-
-      val projectiles = #projectiles player
-      val (fallingEnemies, enemies) =
-        PlayerAttack.projectileHitEnemy
-          (projectiles, enemies, enemyTree, fallingEnemies)
-
-      val enemies = Enemy.update
-        (enemies, walls, wallTree, platforms, platformTree, player, graph)
-
-      val fallingEnemies = FallingEnemies.update fallingEnemies
-
-      val mode =
-        { player = player
-        , walls = walls
-        , wallTree = wallTree
-        , platforms = platforms
-        , platformTree = platformTree
-        , enemies = enemies
-        , graph = graph
-        , fallingEnemies = fallingEnemies
-        }
     in
-      {mode = GameType.LEVEL mode, userKeys = userKeys, saveKeys = false}
+      if #health player > 0 then
+        let
+          val (player, enemies, fallingEnemies) =
+            PlayerAttack.attackEnemies
+              (player, enemies, enemyTree, fallingEnemies)
+
+          val projectiles = #projectiles player
+          val (fallingEnemies, enemies) =
+            PlayerAttack.projectileHitEnemy
+              (projectiles, enemies, enemyTree, fallingEnemies)
+
+          val enemies = Enemy.update
+            (enemies, walls, wallTree, platforms, platformTree, player, graph)
+
+          val fallingEnemies = FallingEnemies.update fallingEnemies
+
+          val mode =
+            { player = player
+            , walls = walls
+            , wallTree = wallTree
+            , platforms = platforms
+            , platformTree = platformTree
+            , enemies = enemies
+            , graph = graph
+            , fallingEnemies = fallingEnemies
+            }
+        in
+          {mode = GameType.LEVEL mode, userKeys = userKeys, saveKeys = false}
+        end
+      else
+        { mode = GameType.TITLE (TitleType.initial)
+        , userKeys = userKeys
+        , saveKeys = false
+        }
     end
 end