[ANNOUNCE] GHC 8.4.1-rc1 available

Kazu Yamamoto (=?iso-2022-jp?B?GyRCOzNLXE9CSScbKEI=?=) kazu at iij.ad.jp
Thu Mar 8 02:05:38 UTC 2018

Hi Ben,

> What you are seeing isn't a warning, it's an error.
> 8.4.1 throws errors for Monoids missing Semigroup instances not because
> of -Wsemigroup but rather because Semigroup is now a superclass of
> Monoid.
> -Wsemigroup will likely be deprecated in a future release now since
> we've reached phase 2 of the Semigroup/Monoid proposal.

Thank you for your explanation. It's now clear to me!

>> GHC 8.4.1rc does not find Monad data types which define "fail" even
>> with -Wcompat. Now I understand that
>> -Wnoncanonical-monadfail-instances is necessary. Why doesn't -Wcampat
>> include -Wnoncanonical-monadfail-instances?
> My understanding is that the MonadFail proposal is in a bit of a state
> of limbo, so its preparatory warning flag hasn't yet been added to
> -Wcompat.

OK. I hope the proposal Wiki documents will be updated anyway.


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