Re: RFC for a change in EmptyDataDecls instance deriving

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 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 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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