Allow for stacking of items and combining sensibly

src/IntMapHelp.hs

@@ -4,6 +4,7 @@ module IntMapHelp
     , insertNewKey
     , insertWithNewKeys
     , swapKeys
+    , findIndex
     )
     where
 --import Data.List hiding (foldr,insert)
@@ -23,3 +24,13 @@ 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
+
+-- ideally this should short circuit, I am not sure whether it does or not
+-- though
+findIndex :: (a -> Bool) -> IntMap a -> Maybe Int
+findIndex t = foldrWithKey f Nothing
+  where
+    f _ _ (Just k) = Just k
+    f k x _
+        | t x = Just k
+        | otherwise = Nothing