    "A type capable of representing the values true and
     false of Boolean logic."
    by ("Gavin")
    shared abstract class Boolean()
            of true | false {}

    "A value representing truth in Boolean logic."
    shared object true extends Boolean() {
        string => "true";
    }

    "A value representing falsity in Boolean logic."
    shared object false extends Boolean() {
        string => "false";
    }