Added fromInt

[reactormonk]

Description of the change

Pasta from https://discourse.purescript.org/t/create-a-guide-for-porting-haskell-numbers-to-purescript-numbers/1261/2 as discussed with @hdgarrood on slack.

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Checklist:

• Added the change to the changelog's "Unreleased" section with a reference to this PR (e.g. "- Made a change (#0000)")
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation
• Added a test for the contribution (if applicable)

[hdgarrood]

Could you add tests for 2 and 5 please? Just in case.

[hdgarrood]

From the outside, it makes little sense to put this function into Data.Ring.Extra rather than just putting it into Data.Ring. What if we move abs and signum from Data.Ord into Data.Ring? I think that would mean that Data.Ord no longer needs to import Data.Ring, which would allow us to use >= here.

I think we should basically inline the definitions of power and Additive too, since importing either of those in Data.Ring will also cause a cycle.

[reactormonk]

That'd be a breaking change though, if Data.Ord doesn't export abs/signum anymore.

[hdgarrood]

Correct, so this would have to wait until the next round of breaking changes. Even though it is breaking, I prefer it over adding a new Data.Ring.Extra module because:

• the API surface makes more sense,
• we'd end up wanting to merge Data.Ring.Extra back into Data.Ring at some point in the future, which would also be breaking, and
• I think it makes more sense to put abs and signum into Data.Ring anyway

[JordanMartinez]

Ord also depends on negate in its usage of -1:

instance ordArray :: Ord a => Ord (Array a) where
  compare = \xs ys -> compare 0 (ordArrayImpl toDelta xs ys)
    where
    toDelta x y =
      case compare x y of
        EQ -> 0
        LT -> 1
        GT -> -1 -- here it is

[JordanMartinez]

Since it's not clear to me how to resolve this comment #261 (comment) I'm going to say this won't be included in 0.15.0.