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@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@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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