Hey, is there something like `switchMap` in Arrow ...

# arrow

[Robert Menke]

Hey, is there something like switchMap in Arrow that can be used for scenarios like this:

Option
    .fromNullable(someValue)
    .map { /* calls a function that returns Either<Error, Value> */}

After calling map I have Option<Either<Error, Value>>

wondering if there’s any way to avoid the extra wrapping. CC @Derek Seroky

[kioba]

Option.fromNullable(someValue)
            .map { /* calls a function*/ }
            .toEither { Error.AbsentValue }

or

Either.cond(someValue != null, { Error.AbsentValue }, { callTheFunction(someValue) })

[Imran/Malic]

@Robert Menke If you think about it this type

Option<Either<Error, Value>>

is isomorphic aka ‘equal’ to

Either<Nothing, Either<Error, Value>>

If there is a chance to flatten this stack, I recommend you to do it.
You may have to see that Option<A> is isomorphic to Either<Nothing, A>

[Imran/Malic]

It’s similar to the problem one faces with overly nested types. They’re hard to dig into, you’ll have to do a lot of fmap’s, unless you use arrow-optics and the library does that for you.
If you’re carious about a plausible reality. I recommend watching this for a few minutes to get the idea

https://youtu.be/VOZZTSuDMFE?t=389▾

[Robert Menke]

Awesome, thank you for the link. I ended up taking everyone’s advice and just sticking to Either in this case. Works great and is much simpler!