Re: [Haskell-cafe] Extending constraints

What you want seems a bit tricky.

p :: ProxyWrapper Num p = ProxyWrapper (Proxy :: Proxy Int)

At this point, all you know about p is that it is a Num. You don't know that it is Typeable, because you choose to forget about that. You could give p the type 'ProxyWrapper (Ext Typeable Num)' and it would work.

then the following would give a type error:

oops :: TypeRep oops = typeOfInnerProxy p

Yes, and correctly so. Because Typeable isn't even a superclass of Num. So there's no way to know that p actually contains a Typeable proxy. Cheers, Andres -- Andres Löh, Haskell Consultant Well-Typed LLP, http://www.well-typed.com