MonadFail decisions

Edward Kmett ekmett at
Fri Oct 16 16:41:19 UTC 2015

Hi David,

I took the time to update the MonadFail wiki page to include both the
timeline currently under consideration, lengthening the timeline to finish
in 8.8 to comply with the "3 release policy" and to ensure that folks
always have a notification of pending breaking changes.

I included a couple of personal comments about the desugaring in 1.3 where
we could do better. The improvements in 1.3 could be made any time over the
8.0 and 8.2 releases before we start expecting people to cut over in 8.4
without impact.

As for the "mob", please keep in mind that the vast majority of feedback
about the MonadFail proposal has been positive and draw heart from that.
Many of the folks who were against the Foldable/Traversable generalizations
(e.g. Lennart) are heavily in favor of MFP.


On Fri, Oct 16, 2015 at 12:09 PM, David Luposchainsky <
dluposchainsky at> wrote:

> On 13.10.2015 16:29, Simon Peyton Jones wrote:
> > Also, David, did our conversation at HX help you get un-stuck?
> Hi Simon,
> yes, it was definitely a good pointer. On the other hand, I found the
> Haskell
> Exchange to be quite a frustrating event with respect to current events:
> there
> was a load of very loud, but in my opinion very wrong, categorical
> opposition to
> breaking changes in general.
> I spent quite a bit of time worrying about MonadFail in the past, but
> right now
> I'd like to wait for a "tentative yes" from the CLC before I keep going,
> because
> I'm really not sure the mob is going to make me throw away my patch.
> Granted, a
> lot of the discussion is about MRP, but many of the points brought up
> there are
> equally valid against the MFP.
> David
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the ghc-devs mailing list