<===> input.scss
@function push($list, $items...) {
  @return join($list, $items, $separator: auto);
}

.test {
  $list: push(1 2 3, 4, 5);
  list: inspect($list);
  value: nth($list, 4);
}
<===> output.css
.test {
  list: 1 2 3 4 5;
  value: 4;
}