Sum of collections

sum_of_collections.scala

for {
    a1 <- Future(Set(1, 2, 3))
    b1 <- Future(Set(1, 2, 3))
} yield {
    for {
        x <- a1
        y <- b1 if y > 2
    } yield {
        x + y
    }
}
//Result: Future[Set(4,5,6)]