Is there an alternative to `mapOrAccumulate` and `...

# arrow

[jean]

Is there an alternative to mapOrAccumulate and parMapOrAccumulate that fails at the first “left” rather than accumulating it? I’m trying to map a list of object to another type and wish to either get a “left” error at the first fail or get the whole new list.

[jean]

I’m doing this for now

objects.mapOrAccumulate { it.toOtherType().bind() }
    .mapLeft { it.first() }

It’s fine enough but it might be an function in the library doing that already?

[Emil Kantis]

couldn't you just do 🤔

either { objects.map { it.toOtherType().bind() } }?

[Alejandro Serrano.Mena]

for a more general reply, every "normal" collection function (map., foreach, ...) already works in a left-biased way, so you don't need special operators for them. You only need to use OrAccumulate versions when you want processing to continue after the first error

[jean]

If I use a normal map I end up with a List<Either<Error, OtherType>> rather than a Either<Error, List<OtherType>> . Wasn’t there a traverse() method to convert a list of either to a either of list actually?

[Alejandro Serrano.Mena]

the trick is to call the map inside an either context, as mentioned by @Emil Kantis above

[jean]

Yes, I just find it a little less elegant, but it works. Thanks for the tips!

[simon.vergauwen]

Quiver will support this kind-of fluent operators if you still prefer to use traverse in the future. I don't think they'll go as far as to also support parTraverse, etc.

This also points to the reason for the DSL, it doesn't require any of these APIs and thus the regular APIs "just work".

Additionally, after working with it a lot we felt it consistently resulted in less code than before.