Fix wall bug, refactor placements

src/Dodge/Zone.hs

@@ -16,6 +16,8 @@ module Dodge.Zone
     , cloudsNearPoint
     , wallsNearZones
     , zoneOfSight
+    , flattenIMIMIM
+    , module Dodge.Zone.Data
     )
     where
 import Dodge.Data
@@ -87,7 +89,9 @@ zoneOfSight w =
 
 wallsDoubleScreen :: World -> IM.IntMap Wall
 wallsDoubleScreen w
-    = foldl' (flip $ IM.union . \i -> innerFold (f i (_znObjects $ _wallsZone w))) IM.empty xs
+    -- = foldl' (flip $ IM.union . \i -> innerFold (f i (_znObjects $ _wallsZone w))) IM.empty xs
+    -- for some reason (TODO diagnose) the foldl' version causes errors
+    = foldr (IM.union . \i -> innerFold (f i (_znObjects $ _wallsZone w))) IM.empty xs
   where 
     innerFold m = foldl' (flip $ IM.union . \ j -> f j m) IM.empty ys
     f i m = case IM.lookup i m of 
@@ -168,3 +172,6 @@ wallsNearPoint p w =  IM.unions [f b $ f a $ _znObjects $ _wallsZone w | a<-[x-1
     f i m = case IM.lookup i m of 
         Just val -> val
         _ -> IM.empty
+
+flattenIMIMIM :: IM.IntMap (IM.IntMap (IM.IntMap a)) -> IM.IntMap a
+flattenIMIMIM = IM.unions . fmap IM.unions