Re: [Haskell-cafe] Data.Tree.Zipper in the standard libraries

G'day all. Quoting Don Stewart :

This is Haskell, we should use Maybe.

This is Haskell, more abstract is good. I do agree, though, that Monad is arguably the wrong abstraction. Something like this would arguably be better: class (Functor f) => Fail f where return :: a -> f a fail :: String -> f a (And yes, the String is arguably important; Maybe doesn't give you that.) Cheers, Andrew Bromage