Hi, what is the replacement for: ```IO { //somet...

# arrow

[dnowak]

Hi, what is the replacement for:

IO {
  //something may throw exception here
}.handleError { t -> 
  //map exception to some result
}

[Patrick Louis]

Hey @dnowak,
one option would be to use

either.runCatching {
    // do something
}.mapLeft {
    // Handle thrown exception
}

[Patrick Louis]

The mapLeft part could also be done with

.fold(
{ // handle exception 
},
{ // handle success 
}
)

[dnowak]

We use Either<E, A almost every where so in the old IO times when I had IO<Either<E, A>> then in handleError I only had to transform Exception into some left value.
Either.catch in that case will return Either<Throwable, Either<E, A>>

[dnowak]

so mapLeft will leave me with Either<E, Either<E, A>>

[dnowak]

OK, I see it now I can write my own handleError for such nested Eithers fold({mapError(it)}, ::identity}

[Patrick Louis]

depending on how it's used, you could also use the mapLeft-version with bind(), so

either<e,a> {
  val successResult = either.runCatching {
    // do something
  }.mapLeft { mapError(it) }.bind()
}

[Patrick Louis]

where mapError has type (Throwable)->E

[dnowak]

Thanks a lot 🙂