Monad of no `return` Proposal (MRP): Moving `return` out of `Monad`

Edward Kmett ekmett at
Tue Sep 29 15:16:10 UTC 2015

The standard is pretty much what was driving the timing of this proposal.

With warnings put in place in 8.0, we can have the situation set up so that
this process completes in time for a Haskell 2017 that incorporates much of
the current state of the world, AMP, Foldable/Traversable, etc.

Then knock-on effects like Traversable simplification can be in place by a
Haskell 2020, which can try to be more ambitious.

If we don't start it now, however, then we won't have sufficient warning
time for users.

On Mon, Sep 28, 2015 at 5:42 PM, wren romano <wren at>

> On Sat, Sep 26, 2015 at 6:04 PM, Richard Eisenberg <eir at>
> wrote:
> > Thanks for making this proposal.
> >
> > I'm leery of the breakage that this would cause. But, there has been no
> chorus of voices complaining about breaking changes in the recent past (AMP
> and changes to Typeable are top on my mind), so perhaps our community is
> more tolerant of breakage than I would guess.
> Though I'd love to see pure/return unified, I almost wonder if it'd be
> a good idea to wait a bit on this. By which I mean, rather than having
> a bunch of little breaking changes as we try to fix things piecemeal,
> perhaps it'd be better to fold this proposal (and similar ones) into
> the next Haskell' report (assuming we can actually ship it this time).
> That way we can just have a big break-the-world change in the
> transition to Haskell2020 (or whatever).
> Not sure if that's the best approach, especially given the difficulty
> in getting Haskell2020 finalized, but it might be worth thinking
> about...
> --
> Live well,
> ~wren
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