Yes, I could quite easily write the generator in TemplateHaskell (have played with it before) _but_ I don't like the $(xxx) syntax... Perhaps if Simon could be persuaded to allow deriving clauses to be defined in TH? data X x = X x $(deriveMyClass (reify X)) could perhaps be defined from data X x = X x deriving MyClass I saw the same suggestion earlier today on the Haskell list... Keean. Andre Pang wrote:
On 13/10/2004, at 10:02 AM, MR K P SCHUPKE wrote:
Okay, I see the Generic type class stuff does not support multi parameter type classes. I guess I am stuck - any suggestions as to how best do this?
I wish to be able to derive type level labels for datatypes, like the following:
data Fred a = Fred a deriving TTypeable
generates the instance:
instance TTypeable a al => TTypeable (Fred a) (NCons (N3 (N4 (N5 Nil))) (TCons al Nil))
If you are happy to live on the edge a bit (which you seem to be happy with, considering that you're playing with GHC CVS ;), Template Haskell might be one way to do it. See "Template Haskell: A Report from the Field", a paper where Ian Lynagh does exactly what you're trying to do: