Conor,
I'm scared. What about this?
data EQ :: * -> * -> * where
Refl :: EQ x x
class Public x where
blah :: EQ x Fred
instance Public Fred where
blah = Refl
What happens when I say
newtype Jim = Hide Fred deriving Public
? I tried it. I get
blah :: EQ Jim Fred
It's clear that GeneralizedNewtypeDeriving goes too far.
Now, I am scared. This should be regarded as a bug in generalised
newtype deriving, shouldn't it? I would expect newtype deriving to be
unable to come up with instances that cannot be written by hand.
I would have expected people out on the streets marching to GHC
headquarters by now; how can you stay so calm?
Cheers,
Stefan
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