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package concpar20final03
import scala.concurrent.{Await, Future}
import scala.concurrent.duration.Duration
import scala.concurrent.ExecutionContext.Implicits.global
import scala.util.{Failure, Success}
def sequence1[A](fs: List[Future[A]]): Future[List[A]] =
fs match
case f :: fs =>
for
x <- f
xs <- sequence1(fs)
yield x :: xs
case Nil =>
Future.successful(Nil)
def sequence2[A](fs: List[Future[A]]): Future[List[A]] =
fs match
case f :: fs =>
f.flatMap(x => sequence2(fs).map(xs => x :: xs))
case Nil =>
Future.successful(Nil)
def sequence3[A](fs: List[Future[A]]): Future[List[A]] =
fs match
case f :: fs =>
f.transformWith {
case Failure(e) => Future.failed(e)
case Success(value) =>
sequence3(fs).transform {
case res: Failure[List[A]] => res
case Success(values) => Success(value :: values)
}
}
case Nil =>
Future.successful(Nil)
def sequence4[A](fs: List[Future[A]]): Future[List[A]] =
fs match
case f :: fs =>
val fsFuture: Future[List[A]] = sequence4(fs)
f.zip(fsFuture).map((fValue, fsValue) => fValue :: fsValue)
case Nil =>
Future.successful(Nil)
@main def concpar20final03 =
val xs = List(Future { 1 }, Future { 2 }, Future { 3 })
val ys = List(Future { 1 }, Future.failed(Error("BOOM")), Future { 3 })
println(Await.result(sequence1(xs), Duration.Inf))
// println(Await.result(sequence1(xs), Duration.Inf)) // Throws exception
println(Await.result(sequence2(xs), Duration.Inf))
// println(Await.result(sequence2(ys), Duration.Inf)) // Throws exception
println(Await.result(sequence3(xs), Duration.Inf))
// println(Await.result(sequence3(ys), Duration.Inf)) // Throws exception
println(Await.result(sequence4(xs), Duration.Inf))
// println(Await.result(sequence4(ys), Duration.Inf)) // Throws exception