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

Henning Thielemann lemming at
Sat Jan 9 23:44:41 UTC 2016

On Sat, 9 Jan 2016, Carter Schonwald wrote:

> Have you tried _x instead?

Ah, this solves the problem! Almost.

I have an instance like this one:

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.

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