> | Why not even simply > | > | instance Typeable (T a) > | > | In other words, derivable classes define default > | implementations for all their methods. > > But that has an existing meaning! It means "use the default methods for > all methods of the class". Which is not the same as "derive all > methods".
I was thinking about the proposed syntax in the "Derivable Type Classes" paper, which was just this. In classic Haskell, I can see that it is problematic whenever default methods are specified in terms of each other, like (==) and (/=) in Eq. I would then vote for > It'd have to be > instance Typeable (T a) deriving Perhaps it would be not much harder to allow instance Show MyChar deriving where showList = ... to partially override derived functions as well. > The trouble is, as you mention, that instance decls usually have a > context. I'd be quite happy to require a context in these derived > instances too, so you have to write > derive instance Typeable a => Typeable (T a) > Then it looks more like a regular instance decl. Yes, even though it's more to write, I think it's cleaner if the context is specified. After all, the old "deriving" syntax within the "data" declaration will continue to be available for compatibility. Cheers, Andres _______________________________________________ Glasgow-haskell-users mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
