PROPOSAL: Add instances to Data.Monoid newtype wrappers

Oliver Charles ollie at
Thu Dec 11 16:00:26 UTC 2014

Sean Leather <sean.leather at> writes:

> As of base, 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?

+1, I believe the general feeling is: add canonical type class instances
whether one exists. These instances certainly make sense.

-- ocharles
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