[Haskell-cafe] Classes in type declarations in Hugs

Graham Klyne GK at ninebynine.org
Tue Dec 7 05:45:32 EST 2004

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
>| 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?


Graham Klyne
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