Sum of squares. This contains two versions, one using Vector and another that takes advantage of stream fusion. The stream fusion version is sightly faster and uses constant space. You'll ALSO notice, the only difference between the two files is the 3rd import statement :)

SumOfSquaresStreamFusion.hs

{-# LANGUAGE BangPatterns #-}
{-# OPTIONS_GHC -Odph #-}

import Prelude hiding (map, sum)
import qualified Data.ByteString.Char8 as S
import Data.List.Stream

main = S.getContents >>= print . sumOfSquares . parse
  where sumOfSquares = sum . map (\x -> x * x)

-- Fill a new vector from a file containing a list of numbers.
parse = unfoldr step
  where
     step !s = case S.readInt s of
        Nothing       -> Nothing
        Just (!k, !t) -> Just (k, S.tail t)

SumOfSquaresVector.hs

{-# LANGUAGE BangPatterns #-}
{-# OPTIONS_GHC -Odph #-}

import Prelude hiding (map, sum)
import qualified Data.ByteString.Char8 as S
import Data.Vector

main = S.getContents >>= print . sumOfSquares . parse
  where sumOfSquares = sum . map (\x -> x * x)

-- Fill a new vector from a file containing a list of numbers.
parse = unfoldr step
  where
     step !s = case S.readInt s of
        Nothing       -> Nothing
        Just (!k, !t) -> Just (k, S.tail t)