[Haskell-cafe] Classes in type declarations in Hugs

[Simon Peyton-Jones]

| 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.

Simon