http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions. html#NEWTYPE-DERIVING | -----Original Message----- | From: Graham Klyne [mailto:GK@ninebynine.org] | Sent: 07 December 2004 10:46 | To: Simon Peyton-Jones; haskell-cafe@haskell.org | Subject: RE: [Haskell-cafe] Classes in type declarations in Hugs | | At 10:15 06/12/04 +0000, Simon Peyton-Jones wrote: | >| This is where I find ghc's newtype deriving to be incredibly useful. | >| | >| newtype CPError a = CPError (Either Error a) | >| deriving(Monad,MonadError) | >| | >| now CPError is a monad and an instance of MonadError and you are free | >to | >| override or inherit more interesting instances at will without | >| conflicting with the basic types for Either :) | > | >Aha! I've always wondered whether anyone uses this feature, which I | >implemented at John Hughes's suggestion. I'd be interested to know if | >you are alone, or whether others do so too. | | Not a user, but sounds maybe interesting. Can you point to documentation? | | #g | | | ------------ | Graham Klyne | For email: | http://www.ninebynine.org/#Contact