[Haskell-cafe] ANN: generic-deepseq 188.8.131.52
mhenrion at gmail.com
Sat Feb 25 01:52:26 CET 2012
On Thu, 2012-02-23 at 23:24 +0100, Bas van Dijk wrote:
> Some nitpicking:
> * In the instance:
> instance GDeepSeq U1 where grnf _ = ()
> I think it makes sense to pattern match on the U1 constructor, as in:
> grnf U1 = ().
> I haven't checked if that's necessary but my fear is that assuming:
> data Unit = Unit deriving Generic; instance DeepSeq Unit
> rnf (⊥ :: Unit) would equal: () while I would expect it to equal ⊥.
I just tested this and you were right; I have corrected the code in the
> * Why do you have the instance:
> instance GDeepSeq V1 where grnf _ = ()
> The only way to construct values of a void type is using ⊥. And I
> would expect that rnf ⊥ = ⊥, not (). I think the best thing is to just
> remove the V1 instance.
I have confirmed what Jos explained, and V1 instances are indeed not
necessary for the use case I originally intended them for, that is for
types tagged with void types. I have removed the V1 instance for now.
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