unbalanced(data s)
{
    integer b, i;

    b = i = 0;
    while (i + ~s && -1 < b) {
        b += s[i -= 1] == '[' ? -1 : 1;
    }

    b;
}

generate(data b, integer d)
{
    if (d) {
        d.times(l_bill, list(), -1, '[', ']').l_rand().ucall(b_append, 1, b);
    }
}

main(void)
{
    integer i;

    i = 0;
    while (i < 10) {
        data s;

        generate(s, i);
        o_(s, " is ", unbalanced(s) ? "un" : "", "balanced\n");

        i += 1;
    }

    0;
}