salanki

import scalaz._
import Scalaz._
import scala.concurrent.Future
import scalaz.contrib.std.scalaFuture._ // typeclass instances for Scala Future
import scala.concurrent.ExecutionContext.Implicits.global // implicit execution context...you probably want a better one for real-world

type ErrorsOrT[M[+_], +A] = EitherT[M, NonEmptyList[String], A] // String could be your error type of choice

for {
  thing1 <- EitherT(Future.successful(1.right))

salanki

def union[A](a: Set[A], b: Set[A]) { 
  var c = b
  for(item <- a) {
   c += item
  }
  c
}

OR: