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

Henning Thielemann lemming at
Mon Jan 11 19:12:39 UTC 2016

On Mon, 11 Jan 2016, Richard Eisenberg wrote:

> On Jan 9, 2016, at 6:44 PM, Henning Thielemann <lemming at> 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.

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