Run scalaz Task in sequencial and parallel

TaskPrac.scala

import scalaz._
import scalaz.concurrent.Task

object TaskPrac extends App {
  private def task(i: Int) = Task {
    println(s"sleeping: $i")
    Thread.sleep(i * 100)
    println(s"wakeup: $i")
    i
  }

  {
    println("============")
    (for {
      i <- task(1)
      j <- task(2)
      k <- task(3)
    } yield {i + j + k }).unsafePerformAsync(println)

    Thread.sleep(1000)
  }
  {
    println("============")

    val k = task(3)
    val i = task(1)
    val j = task(2)
    (for {
      _i <- i
      _k <- k
      _j <- j
    } yield {_i + _j + _k }).unsafePerformAsync(println)

    Thread.sleep(1000)
  }
  {
    println("============")
    val k = task(3)
    val i = task(1)
    val j = task(2)
    Task.gatherUnordered(k :: j :: i :: Nil).unsafePerformAsync(println)
    Thread.sleep(1000)
  }
}

実行するとこうなる

============
sleeping: 1
wakeup: 1
sleeping: 2
wakeup: 2
sleeping: 3
wakeup: 3
\/-(6)
============
sleeping: 1
wakeup: 1
sleeping: 3
wakeup: 3
sleeping: 2
wakeup: 2
\/-(6)
============
sleeping: 3
sleeping: 2
sleeping: 1
wakeup: 1
wakeup: 2
wakeup: 3