[Haskell-cafe] ANN: generic-deepseq

Gábor Lehel illissius at gmail.com
Mon Feb 20 10:06:38 CET 2012

2012/2/20 José Pedro Magalhães <jpm at cs.uu.nl>:
>> One last issue: Say I have a type like: "data T = C !Int"
>> Currently GHC Generics can't express the strictness annotation. This
>> means that your deepseq will unnecessarily evaluate the Int (since it
>> will always be evaluated already). It would be nice if the strictness
>> information could be added to the K1 type. (José, would it be hard to
>> add this to GHC.Generics?)
> I don't think so; I think the right place to put it is as a method of the
> Selector class, though.
> But, I'm wondering, for your example, wouldn't/couldn't GHC optimize away
> `seq` calls to strict arguments?

Isn't it also an issue that bang patterns only guarantee WHNF, but
there might be unevaluated data "further inside"? Obviously not a
problem for !Int; I don't know if the logic is there to tell the

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