[Haskell-cafe] Typeclass resolution errors quite puzzling

[Francesco Ariis]

On Mon, Aug 15, 2016 at 02:35:15PM +0100, Tom Ellis wrote:
> My complaint is about the confusing error message, not the failure to
> type check.

For reference, feeding that program to Hugs (which I usually
find a bit better in terms of error reporting) leads to:

    ERROR "prova.hs":5 - Instance of Eq B required for definition of main

Slightly clearer but not much. I don't have UHC handy to test
its error messages!