Re: suppress warning "Defined but not used: type variable ‘x’" in GHC-8.0

11 Jan 2016


      On Mon, 11 Jan 2016, Richard Eisenberg wrote:
...
On Jan 9, 2016, at 6:44 PM, Henning Thielemann  wrote:
...
instance (Natural n) => Num.Integer (Un n) where
   type Repr (Un _n) = Unary
GHC-7.6.3 and GHC-7.4.2 complain:
   Type indexes must match class instance head
   Found `Un _n' but expected `Un n'
   In the type synonym instance declaration for `Num.Repr'
   In the instance declaration for `Num.Integer (Un n)'
GHC-7.8.4, GHC-7.10.3 and GHC-8.0 are happy with the difference.
I'm surprised this is accepted at all. Looks like hogwash to me. I think you should post a bug report.
Ok, but then GHC must not warn about the unused argument of Repr.