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List:       haskell-cafe
Subject:    Re: [Haskell-cafe] ANN: generic-deepseq 1.0.0.0
From:       Gábor_Lehel <illissius () gmail ! com>
Date:       2012-02-20 9:06:38
Message-ID: CAPNUp082174c0Rb36UuEGmj8Dq5N_nzK59=ExeysrCMH1txZ0w () mail ! gmail ! com
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2012/2/20 José Pedro Magalhães <jpm@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
difference.

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