/*We define a list of alien species*/
val aliens_species = List[String]("gazorpian","supernova","birdman", "sqanchy")

/*Now we define a function that checks if a string is an alien species*/
def isAlien(maybe_alien:String) = aliens_species.contains(maybe_alien)

/*We pass the function isAlien as a parameter to the filter function*/
var list = List[String]("human","dog","gazorpian","birdman")
val aliens = list.filter(isAlien) //result : List(gazorpian, birdman)