higher order functions w/ generic collections

iterables.scala

    val setToSet: Set[Int] => Set[String] = { _.map(_.toString + "potato")}
    val listToList: List[Int] => List[String] = { _.map(_.toString + "tomato")}
    val listToIterable: List[Int] => Iterable[String] = { _.map(_.toString + "ristretto")}
    println(setToSet(Set(1,2)))
    println(listToList(List(1,2)))
    println(listToIterable(List(1,2)))
    
    def printer(fn: Iterable[Int] => Iterable[String], inputs: Iterable[Int]) = println(fn(inputs))
    printer(setToSet, Set(1,2)) // doesn't compile
    printer(listToList, List(1,2)) // doesn't compile
    printer(listToIterable, List(1,2)) // doesn't compile