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 <
lemm...@henning-thielemann.de> wrote:
>
> On Mon, 11 Jan 2016, Richard Eisenberg wrote:
>
> On Jan 9, 2016, at 6:44 PM, Henning Thielemann <
>> lemm...@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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