Proposal: Add conspicuously missing Functor instances for tuples

[Edward Kmett]

+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 at 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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