バブルソート in Haskell

bubble_sort.hs

module BubbleSort where

-- |
-- Bubble Sort
--
-- >>> bubbleSort [1,2,3]
-- [1,2,3]
--
-- >>> bubbleSort [2,3,1]
-- [1,2,3]
--
-- >>> bubbleSort [3,2,1]
-- [1,2,3]
bubbleSort :: Ord a => [a] -> [a]
bubbleSort [] = []
bubbleSort xs = y : (bubbleSort ys)
    where y:ys = swapList xs

-- |
-- Swap List Items
--
-- >>> swapList [1,2,3]
-- [1,2,3]
--
-- >>> swapList [2,3,1]
-- [1,2,3]
--
-- >>> swapList [3,2,1]
-- [1,3,2]
swapList :: Ord a => [a] -> [a]
swapList [] = []
swapList (x:[]) = x:[]
swapList (x:xs)
    | x > y     = y : x : ys
    | otherwise = x : y : ys
    where y:ys = swapList xs