[Haskell-cafe] Eta Reduction
jwlato at gmail.com
Wed Apr 2 21:25:55 UTC 2014
On Apr 2, 2014 4:32 PM, "Niklas Haas" <haskell at nand.wakku.to> wrote:
> On Wed, 2 Apr 2014 09:51:46 -0400, Edward Kmett <ekmett at gmail.com> wrote:
> > We're not storing the instance as a slot in the constructor, so this
> > data Foo a where
> > Foo :: Seq a => Int -> a -> Foo a
> > or equivalently
> > data Foo a = Seq a => Foo !Int !a
> Why not? Say we define Seq to something like
> > type family Seq (a :: *) :: Constraint where
> > Seq (a -> b) = 1 ~ 0
> > Seq t = ()
> What would be the drawback in this scenario?
I think that would be acceptable if we posit the existence of a valid Seq a
dictionary. I think that would be possible for all builtin types and
anything defined via data. But what about e.g.
newtype F = F (forall x. Show x => x-> String)
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Haskell-Cafe