request for reviews for my first patch -- ticket 7401

Austin Seipp aseipp at
Mon Aug 12 06:55:49 CEST 2013

On Sun, Aug 11, 2013 at 10:00 PM, Richard Eisenberg <eir at> wrote:
> According to the Haskell 2010 report (, a datatype with no constructors cannot derive any instances.

You're quite right! I should have looked over the ticket first, where
Adam pointed this out.

> 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.

Austin - PGP: 4096R/0x91384671

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