As a data point I now get thousands of occurrences of this warning across my packages. It is quite annoying. class Foo a where type Bar a instance Foo [a] where type Bar [a] = Int is enough to trigger it. And you can't turn it off by using _ as instance Foo [_] where type Bar [_] = Int isn't legal. I've been avoiding it for now by using if impl(ghc >= 8) ghc-options: -fno-warn-unused-matches but this is a pretty awful addition to this warning as it stands. -Edward On Mon, Jan 11, 2016 at 2:12 PM, Henning Thielemann < lemming@henning-thielemann.de> wrote:
On Mon, 11 Jan 2016, Richard Eisenberg wrote:
On Jan 9, 2016, at 6:44 PM, Henning Thielemann <
lemming@henning-thielemann.de> 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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