-- Quick sort 

quicksort :: Ord a => [a] -> [a]
quicksort []     = []
quicksort (p:xs) = (quicksort lesser) ++ [p] ++ (quicksort greater)
    where
        lesser  = filter (< p) xs
        greater = filter (>= p) xs
        
-- Quick sort v2

qsort [] = []
qsort (p:xs) = qsort [x | x<-xs, x<p] ++ [p] ++ qsort [x | x<-xs, x>=p]

-- Unit Testing

import Test.HUnit

tests = TestList[
  TestLabel "should_display_hello_world" should_display_hello_world]
  
should_display_operator = TestCase (
  assertEqual
  "Display Hello World"
  (show HelloWorld)
  "Hello Word"
  )