Aria

struct Lyrics {
    type func new(n: Int) {
        assert n > 0;
        return alloc(This) {
            .n = n,
        };
    }

    func prettyprint() {
        val suffix_n = this.n == 1 ? "" : "s";
        val suffix_n_minus_1 = this.n == 2 ? "" : "s";
        return "{0} bottle{2} of beer on the wall, {0} bottle{2} of beer.\nTake one down and pass it around, {1} bottle{3} of beer on the wall.\n".format(this.n, this.n-1, suffix_n, suffix_n_minus_1);
    }
}

struct Song {
    type func new(n: Int) {
        assert n > 0;
        return alloc(This) {
            .n = n,
        };
    }

    func iterator() {
        return this;
    }

    func next() {
        if this.n == 0 {
            return Box(){.done = true};
        }

        val n = this.n;
        this.n -= 1;

        return Box() {
            .done = false,
            .value = Lyrics.new(n),
        };
    }
}

func main() {
    val song = Song.new(99);
    for verse in song {
        println(verse);
    }
}