I’m afraid I don’t understand the question.
type instance XIPBinds (GhcPass 'Parsed) = NoExt
type instance XIPBinds (GhcPass 'Renamed) = NoExt
type instance XIPBinds (GhcPass 'Typechecked) = TcEvBinds
it works fine for
type instance XIPBinds (GhcPass _) = NoExt
You mean, the first group does not work, but the latter does?? I’m not even
sure what “work” means. I’m perplexed and need more context
Simon
From: ghc-devs <ghc-devs-boun...@haskell.org> On Behalf Of Alan & Kim Zimmerman
Sent: 23 April 2018 11:57
To: ghc-devs <ghc-devs@haskell.org>
Subject: Type family constraints
Given
data GhcPass (c :: Pass)
deriving instance Eq (GhcPass c)
deriving instance Typeable c => Data (GhcPass c)
data Pass = Parsed | Renamed | Typechecked
deriving (Data)
Is there any way to express that `pass` must be valid for each value of `Pass`
in the following instance head?
instance (p ~ GhcPass pass, OutputableBndrId p)
=> Outputable (HsIPBinds p) where
This comes from a problem where setting each type family instance separately
does not get picked up during instance resolution (and can't be, according to
earlier questions by me on this)
i.e.
type instance XIPBinds (GhcPass 'Parsed) = NoExt
type instance XIPBinds (GhcPass 'Renamed) = NoExt
type instance XIPBinds (GhcPass 'Typechecked) = TcEvBinds
it works fine for
type instance XIPBinds (GhcPass _) = NoExt
Alan
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