Rehome launcher

src/IntMapHelp.hs

@@ -3,6 +3,7 @@ module IntMapHelp
     , newKey
     , insertNewKey
     , insertWithNewKeys
+    , swapKeys
     )
     where
 --import Data.List hiding (foldr,insert)
@@ -19,3 +20,6 @@ insertNewKey x m = case lookupMax m of
 {- | Insert a list of values with new keys -}
 insertWithNewKeys :: [a] -> IntMap a -> IntMap a
 insertWithNewKeys xs m = union m $ fromList $ zip [newKey m..] xs
+{- | Swaps two keys. Unsafe: assumes both keys exist. -}
+swapKeys :: Int -> Int -> IntMap a -> IntMap a
+swapKeys i j m = insert i (m ! j) $ insert j (m ! i) m