Dear devs, The `NumericUnderscores` extension was added to Cabal for ghc 8.6. [1] I'm sending this mail referring to `BlockArguments`. [2] [1] https://github.com/haskell/cabal/pull/5130 [2] https://mail.haskell.org/pipermail/ghc-devs/2018-February/015341.html Regards, Takenobu