[Haskell-cafe] Re: Interesting problem from Bird (4.2.13)

Here's my attempt though it's not really different from using built-in lists: viewCL CatNil = Nothing viewCL (Wrap a) = Just (a, CatNil) viewCL (Cat a b) = case viewCL a of Nothing -> viewCL b Just (x, xs) -> Just (x, Cat xs b) instance Eq a => Eq (CatList a) where a == b = case (viewCL a, viewCL b) of (Just (x, xs), Just (y, ys)) -> x==y && xs == ys (Nothing, Nothing) -> True _ -> False