--- Another migration question… With IO gone, how ...

# arrow

[jem]

---
Another migration question… With IO gone, how can I replicate this IO retry functionality?

fun <T> IO<T>.retry(
  until: (T) -> Boolean = { true },
  additionalTimes: Int = 4,
  initialDelay: Duration = 500.milliseconds
): IO<T> {
  val schedule = Schedule
    .withMonad(IO.monad()) {
      exponential<Either<Throwable, T>>(initialDelay)
        .untilInput<Either<Throwable, T>> { it.exists(until) }
        .and(recurs(additionalTimes))
        .jittered(IO.monadDefer())
        .zipRight(identity())
    }
  return map<Either<Throwable, T>> { it.right() }
    .handleError { it.left() }
    .repeat(IO.concurrent(dispatchers()), schedule).fix()
    .flatMap {
      it.fold({ throwable -> IO.raiseError(throwable) }, { t -> IO.just(t) })
    }
}

[simon.vergauwen]

Rewritten to Arrow Fx Coroutines with suspend instead of IO this would look like this:

@ExperimentalTime
suspend fun <T> retry(
  fa: suspend () -> T,
  until: (T) -> Boolean = { true },
  additionalTimes: Int = 4,
  initialDelay: Duration = 500.milliseconds
): T {
  val schedule =
    Schedule.exponential<Either<Throwable, T>>(initialDelay)
      .untilInput<Either<Throwable, T>> { it.exists(until) }
      .and(Schedule.recurs(additionalTimes))
      .jittered()
      .zipRight(Schedule.identity())

  return schedule.repeat {
    Either.catch { fa() }
  }.fold({ throwable -> throw throwable }, ::identity)
}

[simon.vergauwen]

Arrow Fx and IO is deprecated in favor of Arrow Fx Coroutines and suspend but you can find all the same functionality such as Schedule there.

val arrowFxCoroutines = "io.arrow-kt:arrow-fx-coroutines:0.12.0"

[jem]

Ah, thanks. I misread this initially.