deepseq: Add more instances. #50

[Zemyla]

We do have Eq instances for those types, though, and they say that they
compare the references rather than the values. Is NFData more like Eq or
Show?

On Wed, Jan 15, 2020, 02:59 John Villarreal via Libraries <
libraries at haskell.org> wrote:

> I too agree that NFData instances for reference types are more trouble
> than worth the modest convenience they buy us. We don't have Show instances
> for reference-like types either and I don't think anybody would be arguing
> for those either.
>
> John
>
> On Wednesday, 15 January 2020, 07:55:40 UTC, Henning Thielemann <
> lemming at henning-thielemann.de> wrote:
>
> > David put my thoughts pretty clearly: is it more useful or more
> > confusing? I am also leaning toward more confusing. Hopefully more can
> > weigh in on this.
>
> I also think NFData instances for reference types are more dangerous than
> helpful. Since laziness and strictness account for subtle programming
> mistakes, it is better if GHC tells you that 'rnf tvar' does possibly not
> perform what you expect. I'd even consider to add an instance with a type
> error message to show the user that this instance has been omitted by
> intention.
>
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