Proposal: Remove Semigroup and Monoid instances for Data.Map, Data.IntMap, Data.HashMap

[Bardur Arantsson]

[ blahblah :) ]

+1 for the original suggestion.

+2 for Kris' newtype-only suggestion -- especially if we can actually
prevent orphan instances effectively. (I think I got that right, it's a
big thread at this point.). IMO, it's fine to force people to at least
*consider* which instance they want absent a "best" answer. I do think
it's important that we are actually able to effectively prevent people
from just declaring orphans willy-nilly.

+0 for _hvr's dual-incompatible releases. It would be a +1, but my worry
here is (as usual) the worry about *forcing* the whole ecosystem to
upgrade all at once. Usually this is not actually a big deal, but
"containers" is used by almost *everything*, so it's effectively a
"split" until everything upgrades. (Obviously, things are not quite are
dramatic as that since, presumably, relatively few packages actually use
the instance in question, but...)

Cheers,