Re: [Haskell-cafe] Extending constraints

On 5 June 2012 17:52, Andres Löh wrote:

Hi Bas.

I haven't thought about this for long, but ...

...

data ProxyWrapper constraint =    forall a. constraint a => ProxyWrapper (Proxy a)

I'm assuming adding Typable a in ProxyWrapper is not an option for you?

No, I would rather keep that type as unconstrained as possible.

So then what about:

class (c1 a, c2 a) => Ext c1 c2 a instance (c1 a, c2 a) => Ext c1 c2 a

typeOfInnerProxy :: ProxyWrapper (Ext Typeable constraint) -> TypeRep typeOfInnerProxy (ProxyWrapper p) = typeOfArg p

This will certainly require all sorts of undecidable instances :) But does it work for you?

It works. Thanks a lot! Cheers, Bas