Better solution for evenOddListMerge

epi_judge_haskell_solutions/evenOddListMerge.hs

@@ -1,14 +1,12 @@
 import TestFramework.TestRunner
+import Data.List (partition)
 
 evenOddMerge :: [a] -> [a]
-evenOddMerge xs = fmap snd ls ++ fmap snd rs where 
-    (ls,rs) = partition (even . fst) ([0..] `zip` xs)
-
-partition :: (a -> Bool) -> [a] -> ([a],[a])
-partition f [] = ([],[])
-partition f (x:xs) = let (ls,rs) = partition f xs 
-                     in  if f x then (x:ls,rs) else (ls,x:rs)
+evenOddMerge xs = 
+    let (evens, odds) = partition (even . fst) . zip (iterate (+1) 0) $ xs
+    in fmap snd evens ++ fmap snd odds 
 
+main :: IO ()
 main = goTest 
     evenOddMerge
     (intList . head)