The for loop can also be used to loop through List and Set as well, as follows:

var letters = stringFormatter.csvToList("A,B,C,D,E,F,G,H,I");

if (letters != null) {
    for (letter in letters) {
        var word : String = when(letter) {
            "A" -> "Apple";
            "B" -> "Ball";
            "C" -> "Cat";
            "D" -> "Dog";
            else -> "Don't Know";
        }

        println("$letter for $word");
    }
}

Here, the letters variable is a List of strings objects.