what would be the way to log the exception (just l...

# arrow

[stojan]

what would be the way to log the exception (just log, do nothing to recover the failure) in case an IO fails?

[Tesserakt]

Use flatTap . It perform an effect without changing the result.

IO(1).map { it + 2 } 
    .flatTap { 
        IO.effect { log.debug(it) } 
    }

The result of this code is 3 and in console you can see 3

[stojan]

that would also log success 😄

[Tesserakt]

oh

[stojan]

let me try again, this is what I came up with:

fun <A> IO<A>.logError(log: (Throwable, () -> String) -> IO<Unit>, msg: () -> String): IO<A> =
    handleErrorWith { log(it, msg).followedBy(IO.raiseError(it)) }

[stojan]

where log is the function that logs

[stojan]

any thoughts on it

[Tesserakt]

I think this is quite good solution. But I came up with attempt and folding either... Not so clean as your

[pakoito]

handleErrorWith { IO { log(it, msg }.followedBy(IO.raiseError(it)) }

yep

[pakoito]

😄

[Sagar Suri]

EitherT<IO, A, B> this will help.

[stojan]

I'm trying to stay away from MTL 😁

[Sagar Suri]

Oh! Just curious to know, is there any downside of using that?

[stojan]

Code that looks like this: https://github.com/arrow-kt/frdomain.kt/blob/567c886435ee0e410ff09d2ffce83204fb3551fe/src/main/kotlin/io/arrowkt/arrowio/service/Common.kt#L17

and the performance issues on the JVM AFIK 😄

[pakoito]

It’ll be miles better after the compiler plugins refactor happens

[pakoito]

@raulraja has all the magic necessary to make them performant and fast

[Jannis]

Also EitherT on the left side, just as bio will only contain the explicit error but io may contain more. Usually that's enough but for logging you might want both