SASS: concat-list function. Concat nested list or arglist to the flat list.

gistfile1.txt

@function concat-list($nestedList) {
  $list: ();
  @each $elem in $nestedList {
    @if type-of($elem) == list {
      $elem: concat-list($elem);
    }
    $list: join($list, $elem);
  }
  @return $list;
}