Hi guys, We're starting to use arrow on my project...

# arrow

[Jérémy CROS]

Hi guys,
We're starting to use arrow on my project but I'm realizing I'm seriously rusty with my eithers 😞
Trying to transform a result of type Either<Error, List<A>> into Either<Error, List<B>>
So far I have :
call.map { it.map { B(a.value) } }
Seems to me like there should be something simpler but I can't for the life of me find it 😅

[Youssef Shoaib [MOD]]

That's probably the easiest way, but you can also do

either {
  call.bind().map { B(it.value) }
}

[Jérémy CROS]

oh ok 🤔 I've seen that syntax before but not used to it yet...
not sure why I thought there would be something else 🤔
anyway, thanks! 🙏 will submit to the team to see which one they find the easier to read 🙂

[simon.vergauwen]

There is nothing specific for drilling into a nested List, using Optics it's should also possible... Not entirely sure on the syntax..

Either.right<List<A>>().every.modify(original, f)

[Jérémy CROS]

Thanks for the final alternative! 🙂
Submitted to a vote, 100% of the team went for the double map since it's completely explicit and easier to understand at first sight

[stojan]

the either {} block + bind() enables you to work with the right side of the Either and short-circuits on left.

either {
    call.bind() // the result of this is `List<A>`
}

IMO this scales better if you do multiple ops with the right value.

I'd argue it's also explicit, but maybe less familiar

[simon.vergauwen]

@Jérémy CROS I also vote for the other solution 😂 Double map is the way to go IMO. Easy and explicit 👍 Just wanted to give an alternative ☺️