RFC for a change in EmptyDataDecls instance deriving

[Erik Hesselink]

Do you have an example of things made possible by the version returning True?

Erik

On Thu, Jul 16, 2015 at 2:29 PM, Edward Kmett <ekmett at gmail.com> wrote:
> I'd caution against randomly changing Eq and Ord for Void to be less defined
> in the ill-considered name of consistency.
>
> We rather deliberately made them as "defined as possible" back in 2012 after
> a very long discussion in which the pendulum swung the other way using a few
> examples where folks tied knots with fixed points to get inhabitants of Void
> and it was less consistent to rule them out than it was to define equality
> on _|_ to be True.
>
> I'd challenge that nothing is gained by making these combinators strict in
> their arguments.
>
> -Edward
>
> On Thu, Jul 16, 2015 at 7:14 AM, Herbert Valerio Riedel <hvr at gnu.org> wrote:
>>
>> On 2015-07-16 at 05:28:03 +0200, David Feuer wrote:
>> > It's all a bit weird. I think the Proxy instance is lazy too. I would
>> > tend
>> > to think that empty types shouldn't have these instances, and that if
>> > they
>> > do that should be strict (empty case), but I can't prove that's the
>> > right
>> > way.
>>
>> Btw, something similiar came up for deepseq, regarding NFData instances
>> for types only inhabited by ⊥ (and the issue of H2010 forbidding
>> instance auto-derivation for constructor-less types was mentioned too):
>>
>>  https://github.com/haskell/deepseq/pull/1#issuecomment-61914093
>>
>> -- hvr
>
>
>
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