hi, I see `Option` is deprecated in 0.11. What's t...

# arrow

[Mickey Donaghy]

hi, I see Option is deprecated in 0.11. What's the migration path for functions that I was calling on Option (specifically traverse and foldMapM) - is there an import that will make them available on nullable types or anything like that?

[simon.vergauwen]

To replace Option#traverse we can project new syntax in Functor.

fun <F, A : Any, B> Kind<F, A?>.mapNullable(FA: Functor<F>, f: (A) -> B): Kind<F, B?> =
  FA.run { 
    map { it?.let(f) }
  }

and foldMapM could be replaced by syntax on Monad but I'm not sure what we could name it best there 😅 It'd be like flatMapNullable but it takes a Monoid instead of returning ? like the mapNullable version of traverse.

fun <F, A : Any, B, MA, MO> Kind<F, A?>.foldMapM(ma: MA, mo: MO, f: (A) -> Kind<F, B>): Kind<F, B>
  where MA : Monad<F>, MO : Monoid<B> = ma.run {
  mo.run {
    flatMap { a ->
      a?.let(f)?.map { b ->
        b.combine(mo.empty())
      } ?: just(mo.empty())
    }
  }
}

[simon.vergauwen]

Both don't currently exist yet, but I think would be welcomed contributions.

[Mickey Donaghy]

hmm, tbh most of the value of using those functions on option is in the uniformity

[Mickey Donaghy]

custom monad/traversable types are still supported, right? I think I'd sooner define my own option type then.

[simon.vergauwen]

Totally valid! Option is being moved to a separate module btw, so you can still keep using it if you want to for uniformity! We're moving it our of Arrow-Core since we felt it didn't feel like a "core" data type given ? in the language.

Reference: https://github.com/arrow-kt/arrow-core/pull/239

[Mickey Donaghy]

ah cool. I'll stick with it then. Where's the module it's going to? (Also, is there a similar thing for IO in that case?)

[simon.vergauwen]

That module will probably stat within the arrow-core repository. There is no such thing for IO, mostly since the maintenance and/or further of IO cannot be justified there where as it can for Option.