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ekmett / adjunctions

Simple adjunctions
http://hackage.haskell.org/package/adjunctions
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Make `Functor` the superclass of `Representable` #13

Closed sjoerdvisscher closed 7 years ago

sjoerdvisscher commented 9 years ago

I think we should drop the Distributive superclass constraint, and make it just Functor.

Any code that needs distribute given Representable f can just use distributeRep, and get no performance penalty, because indexing under fmap and then tabulating is the only way to implement distribute anyway.

So the Distributive superclass constraint is just an annoyance. Removing it will also make it easier to merge the TH and Generics pull requests by @bgamari.

treeowl commented 7 years ago

While this is morally correct, Representable forces users to commit to a specific Rep, which becomes part of their public API. They may not be ready to do that yet.

RyanGlScott commented 7 years ago

Also note that the annoyance of the GHC.Generics representation types not having Distributive instances will be resolved in the next version of distributive (which reminds me, I should try and push out a new release sometime soon...)

treeowl commented 7 years ago

Those (aside from sums, of course) should also have reasonable Representable instances. The most obvious thing would be

instance (Representable f, Representable f) => Representable (f :: g) where type Rep (f :: g) = Either (Rep f) (Rep g) index (fa :: ) (Left x) = index fa x index ( :: ga) (Right y) = index ga y

but I fear the type family may loop when deriving the instance for an infinite stream.

On Nov 29, 2016 7:28 PM, "Ryan Scott" notifications@github.com wrote:

Also note that the annoyance of the GHC.Generics representation types not having Distributive instances will be resolved in the next version of distributive (which reminds me, I should try and push out a new release sometime soon...)

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/ekmett/adjunctions/pull/13#issuecomment-263745184, or mute the thread https://github.com/notifications/unsubscribe-auth/ABzi_eAjZ4-A16JSzmO-_VtBNviGk6d2ks5rDMMVgaJpZM4EDvEY .

RyanGlScott commented 7 years ago

distributive-0.5.1 has been released, which includes Distributive instances for the datatypes in GHC.Generics.