1<===> input.scss
2$list: one foo three bar six seven;
3$pos: set-nth($list, 2, two);
4$neg: set-nth($pos, -3, four five);
5
6.test {
7  -positive: $pos;
8  -negative: $neg;
9}
10
11<===> output.css
12.test {
13  -positive: one two three bar six seven;
14  -negative: one two three four five six seven;
15}
16