request for reviews for my first patch -- ticket 7401

Richard Eisenberg eir at
Mon Aug 12 16:33:48 CEST 2013

My proposal below doesn't really give different behavior for EmptyDataDecls in the two scenarios… the available constructs are the same under either H98 or H2010. It's just that the "distance" from the spec is different.

Personally, I'm loathe to stray from a well-defined note in a standard for this. I see my proposal below as a feasible solution to #7401, but I would actually favor not implementing any change here, because the workaround -- using standalone deriving -- is so easy and doesn't seem to have any real drawbacks (e.g. performance).


On Aug 12, 2013, at 12:55 AM, Austin Seipp wrote:

> On Sun, Aug 11, 2013 at 10:00 PM, Richard Eisenberg <eir at> wrote:
>> But, instead of creating a new extension for this feature, what about just co-opting EmptyDataDecls? More concretely, I propose this:
>> Under H98: EmptyDataDecls allows both the declaration of empty data decls and deriving instances for them.
>> Under H2010: EmptyDataDecls allows deriving instances for empty data decls.
>> This proposal brings the annoyance that H2010 no longer implies EmptyDataDecls.
>> Thoughts?
>> Richard
> IMHO, I'd find this inconsistency in extension behavior much more
> annoying than just going against the standard on this note. But that's
> just my 0.02c.
> -- 
> Regards,
> Austin - PGP: 4096R/0x91384671

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