[Haskell-cafe] diff implementation in haskell

Are there pure haskell implementations of diff and diff3 algorithms. Like:

data Diff a = Deleted [a] | Common [a] | Added [a]

diff :: Eq a => [a] -> [a] -> [Diff a]

diff3 :: Eq a => [a] -> [a] -> [a] -> [a]

or smth more general like:

class Diff a where type Difference a diff :: a -> a -> Difference a patch :: a -> Difference a -> a

prop_diffpatch a b = patch a (diff a b) == b

? If not, where can I start towards the implementation? What's the way to do it more functionally? -- Victor Nazarov