Traversing Cats Effect IOs [Part-3]

extension [A](io: IO[A]) {
  def trace: IO[A] =
    for {
      res <- io
      _ = println(s"[${Thread.currentThread().getName}] " + res)
    } yield res
}

Should read:

extension [A](io: IO[A])
  def trace: IO[A] = for {
    res <- io
    _   <- IO.println(s"[${Thread.currentThread.getName}] " + res)
  } yield res

def example6 =
  val io1 = IO("Scala6")
  val io2 = IO("Cats6")
  val listTraverse = Traverse[List] // a typeclass instance  -> import cats.implicits.toTraverseOps
  
  val ioList: List[IO[String]] = List(io1, io2)
  val insideOutIOs: IO[List[String]] = listTraverse.sequence(ioList)

  // is equal to the sequence-method:
  // val seqAsTraverse: IO[List[String]] = listTraverse.traverse(ioList)(identity)

  val traversedList: IO[List[String]] = listTraverse.traverse(ioList)(io => io.map(_ + "!"))
  traversedList.trace

Due to the import, no typeclass instance is needed anymore!

def example7 =
  import cats.implicits.toTraverseOps
    
  val io1 = IO("Scala7")
  val io2 = IO("Cats7")
  
  val ioList: List[IO[String]] = List(io1, io2)
  val insideOutIOs: IO[List[String]] = ioList.sequence

  val traversedList: IO[List[String]] = ioList.traverse(io => io.map(_ + "!"))
  traversedList.trace