import scala.collection.mutable
val voted = mutable.Map[String, Boolean]()
def check_voter(name: String): Unit = {
  if(voted.exists(_ == (name,true))){
    println("kick them out!")
  } else{
    voted += (name -> true)
    println("let them vote!")
  }
}
check_voter("tom")
check_voter("mike")
check_voter("mike")