Type family equation violates injectivity?

[Carter Schonwald]

were you using the same version of vector in both setups?

in the most recent  vector release  we made mutable type family injective
in the vector package for ghc's that support it ...

On Sat, Dec 29, 2018 at 1:50 PM Dominick Samperi <djsamperi at gmail.com>
wrote:

> When I use v8.6.3 of GHC under Ubuntu to install the inline-r package
> I get the error "Type family equation violates injectivity annotation," and
> a type variable on the LHS cannot be inferred from the RHS, due to
> the lack of injectivity (I suppose).
>
> On the other hand, v8.0.2 of GHC (shipped with Haskell Platform under
> Ubuntu) does not have this problem (it has other problems).
>
> Has something changed in the latest version of the compiler that might
> cause this? Possible work-around?
>
> FYI, the line that triggers the error is:
> type instance G.Mutable (W t ty s) = Mutable.W t ty
>
> The variable that cannot be inferred is 's'.
>
> Thanks,
> Dominick
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