Strongly +1 from me. I very highly value instances of standard type classes for standard type constructions, particularly products, sums, and functions, not just for some library wrappers around them. And consistency usually ends up the best practical choice, whether or not many uses are clear beforehand.

On Tue, Jan 19, 2016 at 6:38 AM, Edward Kmett <ekmett@gmail.com> wrote:
+1 from me. 

We routinely supply instances for tuples of up to 4 or 5 elements elsewhere. 

There is no need to be randomly inconsistent here.

-Edward

On Mon, Jan 18, 2016 at 3:10 PM, David Feuer <david.feuer@gmail.com> wrote:
For some reason I really can't imagine, it seems the only tuple type
with a Functor instance is (,) a. I was astonished to find that

fmap (+1) (1,2,3)

doesn't work. Since this is *useful*, and there is *only one way to do
it*, I propose we add the following:

instance Functor ((,,) a b) where
  fmap f (a,b,c) = (a,b,f c)
instance Functor ((,,,) a b c) where
  fmap f (a,b,c,d) = (a,b,c,f d)
etc.

I would really love to see these make 8.0.0, but if that's impossible
then so be it.
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