Kazu Yamamoto (山本和彦) <k...@iij.ad.jp> writes: > Hello Ben, > Hi Kazu,
>> As always, do let us know if you encounter any trouble in the course of >> testing. Thanks for your help! > > I tried GHC 8.4.1rc1 to understand how SemigroupMonoid and MonadFail > proposals work. > > GHC 8.4.1rc1 surely detects Monoid data types if they are not > instances of Semigroup. However, GHC users guide still says that both > -Wcompat and -Wsemigroup are disabled by default. Should we update the > document or am I missing something? > 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. > 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. Cheers, - Ben
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