How to narrow down ZIO Schedule environment? - scala

Question

There is an example of a simple API that uses ZIO effect to return None or Option[String]. I use ZIO Schedule to run the effect as long the None is returned, but limited to a certain number of times. The example is based on the code from ZIO usecases_scheduling:
import zio._
import zio.random._
import zio.duration._
import zio.console.{Console, putStrLn}
import zio.Schedule
import scala.util.{Random => ScalaUtilRandom}
object RecordAPI {
def randomId(length: Int): String =
LazyList.continually(ScalaUtilRandom.nextPrintableChar).filter(_.isLetterOrDigit).take(length).mkString
def getRecordId: Task[Option[String]] = Task.effect(
if (ScalaUtilRandom.nextInt(10) >= 7) Some(randomId(16)) else None
)
}
object ScheduleUtil {
def schedule[A]: Schedule[Random, Option[String], Option[String]] =
(Schedule.exponential(10.milliseconds) && Schedule.recurs(10)) *> Schedule.recurWhile(_.isEmpty)
}
object RandomScheduler extends scala.App {
implicit val rt: Runtime[zio.ZEnv] = Runtime.default
rt.unsafeRun {
RecordAPI.getRecordId
.repeat(ScheduleUtil.schedule)
.foldM(
ex => putStrLn(s"failed with ${ex.getMessage}"),
success => putStrLn(s"Succeeded with $success")
)
}
}
This effect below has the type ZIO[Random with clock.Clock, Throwable, Option[String]]:
RecordAPI.getRecordId.repeat(ScheduleUtil.schedule)
I would like to remove the ScheduleUtil.schedule dependency on Random by providing the Random env and to receive the effect ZIO[Any with clock.Clock, Throwable, Option[String]]:
RecordAPI.getRecordId.repeat(ScheduleUtil.schedule.provide(Random))
but I get compilation error:
[error] found : zio.random.Random.type
[error] required: zio.random.Random
[error] (which expands to) zio.Has[zio.random.Random.Service]
[error] .repeat(ScheduleUtil.schedule.provide(Random))
[error] ^
[error] one error found
What parameter should be provided to the .provide method?

Answer 1

Error message talks you that you tries to pass to function provide Random.type
in the line:
RecordAPI.getRecordId.repeat(ScheduleUtil.schedule.provide(Random))
Random is passed as type but provide expects instance of Random. So you can make your code compilable just replacing Random type to some it's instance:
val hasRandomService: Random = Has.apply(Random.Service.live)
val randomIdZIO: ZIO[Random, Throwable, Option[String]] =
RecordAPI.getRecordId.repeat(ScheduleUtil.schedule.provide(hasRandomService))
but if you want to get rid of ScheduleUtil.schedule maybe it's better to use Schedule.fromFunction function:
val randomIdZIOFromFunction: ZIO[Random, Throwable, Option[String]] =
RecordAPI.getRecordId.repeat(
Schedule.fromFunction(_ => if (ScalaUtilRandom.nextInt(10) >= 7) Some(randomId(16)) else None)
)