Partially implement separate blocks

src/Dodge/WorldEvent/DamageBlock.hs

@@ -1,16 +1,13 @@
 module Dodge.WorldEvent.DamageBlock
-    ( damageBlocksBy
-    )
     where
 import Dodge.Data
 
-import Data.Maybe
 import Control.Lens
-{- | Given a wall, if it is a damageable block
- - then damage it and connecting walls by a certain amount.  -}
-damageBlocksBy :: Int -> Wall -> World -> World
-{-# INLINE damageBlocksBy #-}
-damageBlocksBy x wall w
-        | isJust (wall ^? blHP) = foldr (\j -> walls . ix j . blHP -~ x) w (_blIDs wall)
-        | otherwise = w
 
+damageBlocksBy :: Int -> Wall -> World -> World
+damageBlocksBy x wl = case wl ^? wlBlockID of
+    Just blid -> blocks . ix blid . blHPs %~ reduceHeadBy x
+    Nothing   -> id
+  where
+    reduceHeadBy y (z:zs) = z - y : zs
+    reduceHeadBy _ [] = []