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Kind unification bug #3077

kcsongor opened this issue Sep 16, 2017 · 2 comments


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commented Sep 16, 2017

As discussed on slack, there seems to be an issue with how kinds are unified, here's a minimal, self-contained example:

data TProxy (t :: Type) = TProxy
data SProxy (s :: Symbol) = SProxy

put :: forall proxy a. proxy a -> TProxy a
put _ = TProxy

--wrong :: TProxy "apple"
wrong = put (SProxy :: SProxy "apple")

This typechecks (on both HEAD and 0.11.6), and we managed to force a Symbol into TProxy.

@paf31 paf31 added the bug label Sep 18, 2017

@paf31 paf31 added this to the 0.12.0 milestone Sep 18, 2017


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commented Sep 18, 2017

I think the problem here is that only the kinds of written types are checked. The only incorrect type is the type of wrong, which isn't checked.


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commented Oct 2, 2017

I made a quick attempt to fix this, but it's a bit trickier than I thought. I think it actually needs some of the same changes that we would need for polykinds, namely adding kind information to the types of values.

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