A quicksort implementation in Haskell

qsort.hs

-- the middle integer item from a list
middle :: [Integer] -> Integer
middle list = list !! (fromIntegral midInd)
  where midInd = length list `div` 2

-- the median of three integer values
-- thanks to Tony Jiang from HH Coding for the improved algo!
qMed3 :: Integer -> Integer -> Integer -> Integer
qMed3 a b c = min firstMax (max firstMin c)
  where firstMax = max a b
        firstMin = min a b

{- attempted to use quicksort to get the median 8|
    --> this resulted in infinite recursion :'(
qsMed3 :: [Integer] -> Integer
qsMed3 list = if (length list == 3) then middle $ quicksort list else undefined
-}

quicksort :: [Integer] -> [Integer]
quicksort []     = []
quicksort list   = (quicksort lesser) ++ pivots ++ (quicksort greater)
  where pivotVal = qMed3 (head list) (middle list) (last list)
        pivots   = filter (\x -> x == pivotVal) list -- possible duplicates
        lesser   = filter (\x -> x <  pivotVal) list
        greater  = filter (\x -> x >  pivotVal) list

-- Now, test our implementation
main :: IO ()
main = do
  print $ quicksort [3]
  print $ quicksort [1,2]
  print $ quicksort [1,2,3]
  print $ quicksort [3,1,2]
  print $ quicksort [5,3,4,2,1]
  print $ quicksort $ reverse [1..10]
  -- test for duplicates
  print $ quicksort $ reverse $ [4..10] ++ [-5..12]