Refactor wall zoning, remove streaming

src/ListHelp.hs

@@ -10,8 +10,13 @@ module ListHelp
     , foldPairs
     , loopPairs
     , slideWindow
+    
+    , merge
+    , mergeBy
+    , mergeOn
     ) where
 import Data.List
+import Data.Ord
 
 loopPairs :: [a] -> [(a,a)]
 loopPairs (a:as) = snd $ foldr f (Just a,[]) (a:as)
@@ -65,3 +70,18 @@ errorHead s [] = error s
 
 slideWindow :: Int -> [a] -> [[a]]
 slideWindow n = foldr (zipWith (:)) (repeat []) . take n . tails
+
+merge :: Ord a => [a] -> [a] -> [a]
+merge = mergeBy compare
+
+mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a]
+mergeBy _ xs [] = xs
+mergeBy _ [] ys = ys
+mergeBy f (x:xs) (y:ys)
+    | f x y /= GT = x : mergeBy f xs (y:ys)
+    | otherwise   = y : mergeBy f (x:xs) ys
+
+mergeOn :: Ord b => (a -> b) -> [a] -> [a] -> [a]
+mergeOn f xs = map snd . mergeBy (comparing fst) (g xs) . g
+  where
+    g = map (\x -> let y = f x in y `seq` (y,x))