Add concpar20final03

.gitlab-ci.yml

@@ -21,4 +21,4 @@ test:
   tags:
     - cs320
   script:
-    - sbt "runMain lecture1.javaThreads; runMain lecture1.scalaThreadWrapper; runMain lecture1.ExampleThread; runMain lecture3.intersectionWrong; runMain lecture3.intersectionCorrect; runMain lecture3.intersectionNoSideEffect; runMain lecture3.parallelGraphContraction; runMain lecture3.parallelGraphContractionCorrect; runMain midterm22.mock1; runMain midterm22.part3; runMain ed.patternMatching; runMain lecture13.askPatternDemo; test; runMain lecture13.becomeDemo; runMain ed.futuresForTranslation; scalafmtCheck; Test / scalafmtCheck"
+    - sbt "runMain lecture1.javaThreads; runMain lecture1.scalaThreadWrapper; runMain lecture1.ExampleThread; runMain lecture3.intersectionWrong; runMain lecture3.intersectionCorrect; runMain lecture3.intersectionNoSideEffect; runMain lecture3.parallelGraphContraction; runMain lecture3.parallelGraphContractionCorrect; runMain midterm22.mock1; runMain midterm22.part3; runMain ed.patternMatching; runMain lecture13.askPatternDemo; test; runMain lecture13.becomeDemo; runMain ed.futuresForTranslation; runMain concpar20final03.concpar20final03; scalafmtCheck; Test / scalafmtCheck"

src/main/scala/concpar20final03/Futures.scala

+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