An example of for-yield flatmapping in scala.

greets.scala

val inputList = List("hi","hello","Bye");
val salutations = List("guvnor","sir","madame","dude","buddy")

def isFormal(ele:String )= ele match{
  case "guvnor"=>true
  case "sir"=>true
  case "madame"=>true
  case _=>false
}

def isGreeting(ele:String) = ele match{
  case "hi" => true
  case "hello"=> true
  case _ => false
}

def greetEveryone(greetings: List[String], salutations: List[String]){
for{
    greet <- inputList
    sal <- salutations
    if isGreeting(greet)
    if isFormal(sal)
  }yield{
    println(greet+" "+sal)
  }
}

greetEveryone(inputList,salutations)