Finding the slice of an input array that has the largest total

largest_slice.hs

import Data.List

data SummedIntList = SummedIntList {
  listElements :: [Int],
  elementTotal :: Int
} deriving (Show)

emptySummedList = SummedIntList [] 0

addIntToList (SummedIntList xs t) x = SummedIntList (xs ++ [x]) (t + x)

largestSlice = scanList emptySummedList emptySummedList
  where
    scanList store curr []       = largestElements store curr
    scanList store curr (x:xs)
      | x >= 0                   = scanList store (addIntToList curr x) xs
      | otherwise                = scanList (largest store curr) emptySummedList xs

    largest a b
      | elementTotal a > elementTotal b = a
      | otherwise                       = b

    largestElements = (listElements . ) . largest