"Quit" Command Challenge

I was initially trying to figure out how to use “break” to quit the while loop, but I wasn’t able to figure it out. Turns out, the solution is still simple, just changing the value of a boolean variable upon which the while loop runs:

object Game {
    var whileIsTrue = true
    fun play() {
        while (whileIsTrue) {
            print("> Enter your command: ")
            println(GameInput(readLine()).processCommand())
        }
    }

    private class GameInput(arg: String?) {
        private val input = arg ?: ""
        val command = input.split(" ")[0]
        val argument = input.split(" ").getOrElse(1, { "" })

        fun processCommand() = when (command.toLowerCase()){
            "move" -> move(argument)
            "quit", "exit" -> {whileIsTrue = false; "Quitting..."}
            else -> commandNotFound()
        }

        private fun commandNotFound() = "I'm not quite sure what you're trying to do!"
    }
}