On 07/04/2010 01:49 PM, Sjoerd Visscher wrote: > > On Jul 4, 2010, at 11:31 AM, Andrew Coppin wrote: > >>>> type family F f a :: * >>>> class RFunctor f where >>>> (%) :: f a b -> (a -> b) -> F f a -> F f b >>>> >> >> I have literally no idea what a type family is. I understand ATs (I think!), >> but TFs make no sense to me. >> >> (For this reason, most if not all of the rest of this post doesn't make >> sense.) > > I would have liked to use ATs here, like this: > >> class RFunctor f where >> type F f a :: * >> (%) :: f a b -> (a -> b) -> F f a -> F f b > > But this isn't valid as ATs require all type variables to be in scope, and > 'a' isn't. > There's a GHC ticket for this: http://hackage.haskell.org/trac/ghc/ticket/3714
This works (on my ghc-6.12.2): > class Rfunctor f where > type F f :: * -> * > (%) :: f a b -> (a -> b) -> F f a -> F f b > [...] -- Steffen _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
