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

An updated Zipper version is uploaded here: http://www.haskell.org/haskellwiki/User_talk:Kr.angelov It doesn't use State monad anymore and it returns Maybe. This seems to be the common preference, is it? Feel free to vote against. Should we change Data.Map also? There is another proposal for changes in findMin/findMax so it is better to make this two breaking changes together rather than in a later release. It also allows to pass whole new subtree in insert{Left/Right/Down}. On Sat, May 24, 2008 at 3:41 AM, wrote:

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 _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe