PROPOSAL: Add instances to Data.Monoid newtype wrappers

[Edward Kmett]

I'm a very strong +1 on this.

We've already sat down to add some of these, and there was a general
resolution by the core libraries committee in response to a similar raised
issue for the types in GHC.Generics that missing instances like this that
have obvious canonical implementations should be added wherever possible.

-Edward

On Fri, Dec 12, 2014 at 2:30 AM, Sean Leather <sean.leather at gmail.com>
wrote:

> As of base 4.7.0.1, none of the newtype wrappers in Data.Monoid have
> instances for:
>
>    - Typeable
>    - Data
>    - Functor
>
>
> It looks like the base library repository has AutoDeriveTypeable, so I
> presume that takes care of the Typeable instances. It also looks like First
> and Last now have Functor instances, amongst others.
>
> In particular, I would like to add Functor instances for all parameterized
> types, where applicable (i.e. Dual, Sum, Product).
>
> In general, I think we should add whatever other instances make sense.
> Data came to mind. Others?
>
> Discussion period: 2 weeks (or perhaps until after the beginning of the
> new year)
>
> Regards,
> Sean
>
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