alg.rb

def qsort (arr, left=0, right=arr.length-1, pl=left, pr=right)
  x = arr[(left+right)/2]
  begin
    pl+=1 while arr[pl] < x
    pr-=1 while arr[pr] > x
    arr[pl], arr[pr] = arr[pr], arr[pl]
  end while arr[pl] != arr[pr]
  qsort(arr, left, pl-1) if pl-left > 1
  qsort(arr, pr+1, right) if right-pr > 1
end

arr =(1..10).sort_by {rand}
qsort(arr)
p "result:#{arr}"

qsort.hs

{-# LANGUAGE TemplateHaskell #-}
{-|
 - dependency other hackage packages
	-
 - test-framework, test-framework-th,
	- test-framework-hunit, test-framework-quickcheck,
 - HUnit, QuickCheck, data-ordlist
|-}
import Test.Framework.TH ( defaultMainGenerator )
import Test.Framework ( defaultMain, Test )
import Test.Framework.Providers.HUnit ( testCase )
import Test.Framework.Providers.QuickCheck2 ( testProperty )
import Test.HUnit ( (@=?) )
import Data.List.Ordered

{-| QuickSort Implementation |-}
qsort []     = []
qsort (x:xs) = rest (<= x) ++ x : rest (> x) where
  rest that = qsort $ filter that xs

{-| Tests |-}
main = $(defaultMainGenerator)

case_empty_list_qsort 
 = []  @=? qsort ([] :: [Int])

case_only_one_value_list_qsort
 = [1] @=? qsort [1]

case_some_values =
  [-5..5] @=? qsort [5, -2, 0, 4, 1, -1, 3, -5, 2, -3, -4]

prop_list_that_sort_by_qsort_is_sorted
 = isSorted . (qsort :: [Int] -> [Int])

自動テスト追加して Haskell で実装してみた (2行)