On Fri, 26 Mar 2010 19:28:18 +0000, Ross Paterson
On Fri, Mar 26, 2010 at 05:24:18AM -0700, Nicolas Pouillard wrote:
Could we have functors products, sums, fixpoints as well? It would really avoid to redefine them each time.
Do you mean
data Product f g a = Product (f a) (g a)
Yes, I was thinking of using :*: instead of Product: data (:*:) f g a = (:*:) (f a) (g a)
with Functor, Foldable, Traversable and Applicative instances?
Yes.
Not sure if the other two count as transformers.
Why not: data (:+:) f g a = Inl (f a) | Inr (g a) And sure, no applicative nor monad instance for this one. And Fix like in category-extras: http://hackage.haskell.org/packages/archive/category-extras/0.53.5/doc/html/... Best regards, -- Nicolas Pouillard http://nicolaspouillard.fr