| - Will it be possible to write e.g. deriving instance Typeable Eq? Not at the moment; we've only been thinking about Typable for things whose kinds bottom out in *, not Constraint. There doesn't seem to be any fundamental obstacle -- but I can't yet see how it would be useful. | - How about deriving instance Typeable Typeable? (It seems Proxy Proxy | works, so maybe this would too.) Ditto. | - Does it make sense to have an instance for (~)? Ditto. | - Will instances be provided for the types in base and built-in to GHC? Yes, that would make sense. | Automatically generate Typeable instances for every type constructor | that is declared. 'deriving Typeable' becomes a no-op. Well, at the moment a type ONLY becomes an instance of a class if you ask for it to be so, so your proposal would be a change of principle. Sometimes *omitting* an instance declaration may be important (eg to prevent a type being serialisable). That said, I can't see when I'd want a type not to be Typeable. I suppose it could be a compiler option. I think the questions here are ones of software engineering rather than being technical. Simon