Tasks to Task of ValidationNel

Flip.scala

import scalaz._, Scalaz._
import scalaz.concurrent.Task

object flip {
  def flip: String = {
    val rnd = new java.util.Random()
    if (rnd.nextInt(2) == 1) {
      "Heads"
    } else {
      throw new RuntimeException("Tails")
    }
  }

  val flips       = List(Task.delay(flip), Task.delay(flip), Task.delay(flip), Task.delay(flip), Task.delay(flip))
  val flipLists   = flips.map(_.map(List(_)))                     // Turn Heads/Tails into List (Monoid)
  val attempts    = flipLists.map(_.attempt)                      // List[Task[Throwable \/ List[String]]]
  val validations = attempts.map(_.map(_.validation))             // List[Task[Validation[Throwable, List[String]]]]
  val vNels       = validations.map(_.map(_.toValidationNel))     // List[Task[ValidationNel[Throwable, List[String]]]]
  val task        = Nondeterminism[Task].aggregate(vNels)         // Task[ValidationNel[Throwable, List[String]]]

/*
    scala> task.unsafePerformSync
    res1: scalaz.ValidationNel[Throwable,List[String]] = Failure(NonEmpty[java.lang.RuntimeException: Tails,java.lang.RuntimeException: Tails,java.lang.RuntimeException: Tails])
 */
}