func non_continuous(min, max, subseq=[], has_gap=false) {

    static current = [];

    range(min, max).each { |i|
        current.push(i);
        has_gap && subseq.append([current...]);
        i < max && non_continuous(i.inc, max, subseq, has_gap);
        current.pop;
        has_gap = current.len;
    }

    subseq;
}

say non_continuous(1, 3);
say non_continuous(1, 4);
say non_continuous("a", "d");