jamesward

sealed class Bag<out THING> {
    object Empty: Bag<Nothing>()
    data class NonEmpty<out THING>(val thing: THING): Bag<THING>()

    // Make a Bag with a THUNG in it
    companion object {
        fun <THUNG> make(thung: THUNG): Bag<THUNG> = NonEmpty(thung)
    }

    // Do stuff to the THING in the Bag by providing a thingToBagOfThang