[Proposal] Add instance Monoid a => Monoid (Const a b)

Ross Paterson R.Paterson at city.ac.uk
Sat Oct 12 19:15:25 UTC 2013

On Sat, Oct 12, 2013 at 01:32:33PM -0400, Edward Kmett wrote:
> I am strongly in favor of removing Constant from transformers.

No objection to that: we obviously don't need both.

> It isn't used by the vast majority of the ecosystem, but Const is in very
> active use.
> The only major consumer of Constant at this time I think is Rusell O'Connor's
> multiplate library.

And presumably you want to keep the shorter name for backward compatibility.

> On a related note Simon recently asked the core libraries committee if we
> should move Data.Functor.Identity into base.
> I'm very strongly inclined to say yes, as was the rest of the committee.
> Do you have any objection there?

I don't object to moving Data.Functor.Identity, but I wish that
discussion had happened in a place where the rest of us could see it.
On this tangent, I note on


that the process is described as:

	It is expected the committee will discuss any matters brought
	to it amongst themselves, and if they think appropriate, with
	the wider community, to try to reach consensus.  Ultimately,
	the committee will make decisions by more than half of the
	membership voting for a particular outcome.  These rules of
	operation may also be changed in the same way.

That's a more closed model than I thought was envisaged when the
committee was set up, and I think it's problematic.  I'd suggest that
open discussion with the committee making the final decision is likely
to produce better results.

More information about the Libraries mailing list