On Mon, Aug 15, 2016 at 02:48:58PM +0100, Tom Ellis wrote:
> I find that message equally puzzling. It seems to me that the most
> helpful message > would have to mention that Eq B is required to
> satisfy Eq A.
Time to file a feature request then! :)
https://ghc.haskell.org/trac/ghc/wiki/ReportABug