merge_sort.hs

mergeSort :: Ord a => [a] -> [a]
mergeSort [] = []
mergeSort [x] = [x]
mergeSort xs = merge (mergeSort l) (mergeSort r)
    where
        s = length xs `div` 2
        (l,r) = splitAt s xs
        merge :: Ord a => [a] -> [a] -> [a]
        merge [] ys = ys
        merge xs [] = xs
        merge (x:xs) (y:ys) | x<=y = x:merge xs (y:ys)
                            | x>y  = y:merge (x:xs) ys

main = do
    print $ mergeSort [4,1,3,6,7,3,2]