Re: Data.Functor.{Product,Sum} functions

Data.Bifoldable has already been dragged into base: https://ghc.haskell.org/trac/ghc/ticket/9682 On 12/24/2016 03:43 PM, David Feuer wrote:

This |||| is the sum eliminator. We can't call it `sum`, but maybe `sumE`? I do think it should be included with some name. Another option might be to drag Data.Bifoldable into base from bifunctors; (||||) = bifoldMap, but I think the case for a specialized name is still pretty good.

&&&& is definitely a nice thing to have. However, (&&&&) = liftA2 Pair, so I'm not convinced we need to give it its own name.

On Fri, Dec 23, 2016 at 7:02 PM, Baldur Blöndal wrote:

...

Let's see if any of these are useful (a lot more at https://ghc.haskell.org/trac/ghc/ticket/13026)

(||||) :: (f a -> b) -> (g a -> b) -> ((Sum f g) a -> b) f |||| g = \case InL fa -> f fa InR ga -> g ga

(&&&&) :: (a -> f b) -> (a -> g b) -> (a -> (Product f g) b) (f &&&& g) a = f a `Pair` g a

I couldn't think of any for Data.Functor.Compose, names are up for bikeshedding

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