interface I
    method foo
        "I#foo"
    method bar
        "I#bar"
    required method quux -> Integer
end

class C {}
    is I
    method foo
        "C#foo"
    method quux -> Integer
        42
end

class Main {}
    class method run: command in: system
        let c = C new.
        system output println: "foo = {c foo}".
        system output println: "bar = {c bar}".
        system output println: "quux = {c quux}".
end