[Haskell-cafe] Typechecker complains about untouchable types

[宮里洸司]

Hi rowan,

This seems like a bug (at least inconvenience) in the constraint
solver. But it's already
fixed to accept both versions in the newer releases of GHC.

I've checked that ghc-8.8.3 and ghc-8.10.7 rejects with the type error
you reported,
while ghc-9.0.1 or newer accepts without any error.

I think there's a filed issue in the issue tracker, but sorry I couldn't find.

-- 
/* Koji Miyazato <viercc at gmail.com> */