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haskell / deepseq

Deep evaluation of data structures
http://hackage.haskell.org/package/deepseq
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NFData instances for unboxed arrays from array #102

Open meooow25 opened 1 month ago

meooow25 commented 1 month ago

NFData instances could be provided for UArray, STUArray and IOUArray from the array package: https://hackage.haskell.org/package/array

PS: I find it a little odd that deepseq depends on array and has to provide these, rather than the other way around.

Bodigrim commented 1 month ago

PS: I find it a little odd that deepseq depends on array and has to provide these, rather than the other way around.

It should rather be other way around indeed.

meooow25 commented 1 month ago

I looked into this a bit, and it seems there are two ways we can go about it.

A. deepseq provides the instances

This is simple enough. I can make a PR for it.

B. Reverse the deepseq->array dependency

It turns out that the Array type is defined not in array, but in base's GHC.Arr. So deepseq never required a dependency on array in the first place. The steps here are:

  1. deepseq drops the dependency on array and provides NFData for Array using GHC.Arr. This is released as version deepseq-x.
  2. array-y provides NFData instances for unboxed arrays by taking a dependency on deepseq >= x. Users of array >= y get the instances.

Sidenote: I found that there was a plan to reverse deepseq->containers and deepseq->array dependencies in GHC #5468, but they stopped at containers due to undocumented reasons.

What do you think?

meooow25 commented 1 week ago

Hi, any thoughts on this?

Bodigrim commented 1 week ago

Given that deepseq is a dependency of template-haskell, the former is practically non-reinstallable and such are its dependencies as well, including array. I think "B. Reverse the deepseq->array dependency" would be most beneficial.

The steps here are:

I think the same could be achieved with automatic Cabal flags: a dependency cycle should be automatically rejected by Cabal solver, forcing flipping a flag. But this requires testing, and being boot packages is likely to complicate things.

Bodigrim commented 1 week ago

(@mixphix is a maintainer here, I'm just passing by)

meooow25 commented 1 week ago

Could you explain what you mean be automatic Cabal flags? I didn't get that, but then again I'm not too familiar with Cabal stuff.
As I see it, for B the only thing deepseq needs to do is simply drop the array dependency. Nothing would be lost with this. Further changes are required only to add new NFData instances.

Bodigrim commented 1 week ago

Ah, that's even simpler then. I guess the only relevant part of my comment is that array-y does not even need to demand deepseq >= x, because Cabal solver would imply such bound automatically to avoid circular dependencies.