hi - i’m wondering why `Either.catch` is strict in...

# arrow

[Peter]

hi - i’m wondering why Either.catch is strict in evaluating it’s supplied function, is there a way to catch an Exception from an effect? eg

suspend findThing(): Thing {} 

Either.catch { findThing() } // ???

[simon.vergauwen]

It’s inline so you can call a suspending function inside the lambda as long as you’re in another suspending scope

[Peter]

the parameter function passed to catch isn’t inline or suspend?

[Peter]

message has been deleted

[simon.vergauwen]

Is the function suspend?

[Peter]

yes

[Peter]

see context hovering box in the screenshot ^

[simon.vergauwen]

Strange, this works fine for me and I’m also using exposed

[simon.vergauwen]

In production

[Peter]

interesting… are you using exposed with newSuspendedTransaction vs transaction ?

[simon.vergauwen]

Both

[simon.vergauwen]

Both within catch

[simon.vergauwen]

What version are you on?

[Peter]

i definitely understand why the compiler is complaining:

inline fun <R> catch(f: () -> R): Either<Throwable, R> =

f is not marked inline or suspend

[simon.vergauwen]

It doesn’t need to be since the function is marked inline

[Peter]

arrow 0.13.2 exposed: 0.32.1

[simon.vergauwen]

Can you build from cli?

[Peter]

sure, sec

[Peter]

ContractLifecycleTable.kt: (201, 21): Suspension functions can be called only within coroutine body

[simon.vergauwen]

mind blown

[Peter]

actually… i’m sorry this must be something on my side

[Peter]

it’s a lambda inside another block.. if i move it out.. it compiles 😞

[simon.vergauwen]

Oh, no worries. Having function inlined is really powerful for suspension, can be annoying if some libraries hinder it

[simon.vergauwen]

If you own that function marking it inline should fix the issue

[Peter]

btw, i vaguely remembering raul shared a gist you created a while ago for … i think retrying db operations, does that ring any bells?

[simon.vergauwen]

Yes, but it was for SqlDelight

[Peter]

ahhh ok

[simon.vergauwen]

If you’re interested in retrying you can check Schedule docs

[simon.vergauwen]

Or this new one sec

[Peter]

i need to dig into schedule. i’ve ported the haskell retry library to kotlin (though.. it’s not especially effect aware & pure .. yet)

[simon.vergauwen]

https://github.com/arrow-kt/arrow/blob/main/arrow-libs/fx/arrow-fx-coroutines/src/commonMain/kotlin/arrow/fx/coroutines/CircuitBreaker.kt

[simon.vergauwen]

There is a composeable Schedule type in Fx

[Peter]

oooh yea, definitely need to dig into that

[Peter]

do you by any chance have a nice way of retrying transient exceptions thrown by exposed?

[Peter]

eg

[Peter]

org.jetbrains.exposed.exceptions.ExposedSQLException: java.sql.SQLTransientConnectionException: HikariPool-1 - Connection is not available, request timed out after 5004ms.

[Peter]

i just tried cobbling something together quickly but i probably need to take a step back and reevaluate my strategy

[Peter]

private suspend fun <T>runWithContextAndTransaction(block: Transaction.() -> T): Either<Throwable, T> {
        return withContext(<http://Dispatchers.IO|Dispatchers.IO>) {
            retrying(
                defaultRetryPolicy,
                ::eitherDecider,
                onRetry = logRetry(logger, defaultRetryPolicy),
            ) {
                Either.catch {
                    newSuspendedTransaction {
                        block()
                    }
                }
            }
        }
    }

[simon.vergauwen]

Ye, I have something for this. It works based on a predicate for exposed exceptions, and it’s wrapped in schedule and circuit breaker and it comes out Either<Throwable, A> I will share it here tomorrow

[Peter]

sounds perfect, thank you!! 🙏

[simon.vergauwen]

It looks similar to the resilience function in the circuit breaker docs

[CLOVIS]

Is your outside function marked as suspend? If it's not, then the error makes sense

[CLOVIS]

fun foo() {
  // outer function is not suspend
  Either.catch {
    // Therefore ‘catch’, despite being inline, can't suspend (it would be inlined in a non-suspending function)

whatever() // if this function is marked as ‘suspend’, it can't be called here
  }
}