John Meacham writes: > On Tue, Apr 11, 2006 at 11:35:09AM +0100, Simon Marlow wrote: > > On 11 April 2006 11:08, Ross Paterson wrote: > > > > > On Tue, Apr 11, 2006 at 11:03:22AM +0100, Simon Marlow wrote: > > >> This is a rather useful extension, and as far as I can tell it > > >> doesn't have a ticket yet: > > >> > > >> http://www.haskell.org//pipermail/libraries/2005-March/003494.html > > >> > > >> should I create a ticket? Is there any reason it might be hard > > >> to implement? > > > > > > There are a range of proposals, but none of them are implemented. > > > Wouldn't that rule them out for Haskell'? > > > > If it's not clear which is the right way to go, then yes I guess > > that does rule it out. Could you summarise the proposals? If > > there was a clear winner, and it was easy enough to implement, > > perhaps we can knock up a prototype in time. > > As I recall, this was brought up a few times during the class alias > discussion and there were good technical reasons why it would be > tricky to define a sane semantics for it. as in, it's harder than it > first looks.
The tricky part is dealing with multiple subclasses. For example, class Functor f where fmap :: (a -> b) -> f a -> f b class Functor f => Monad f where ... fmap = liftM class Functor f => Comonad f where ... fmap = liftW newtype Id a = Id a instance Functor Id instance Monad Id instance Comonad Id Which default gets used for fmap? -- David Menendez <[EMAIL PROTECTED]> | "In this house, we obey the laws <http://www.eyrie.org/~zednenem> | of thermodynamics!" _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://haskell.org/mailman/listinfo/haskell-prime