.forward(@i: 1) when (@i < 10) {
     forward--@{i}: fore(@i);
    .forward(@i + 1);

    .function-fore(@value) {
        return: @i @value;
    }
}

.backward(@i: 9) when (@i > 0) {
    .backward(@i - 1);
     backward-@{i}: back(@i);

    .function-back(@value) {
        return: @i @value;
    }
}

loop-scope {
    .forward();
    .backward();
}