@function empty-map() {
  @return map-remove((x:x), x);
}

@function prepend($list, $value) {
  @return join($value, $list);
}

@function list-values($len, $step: 1) {
  $result: ();
  @for $i from 1 to $len + 1 {
    $result: append($result, $i * $step);
  }
  @return $result;
}

@function list-map-values($len, $step: 1, $unit: false, $modify-key: true) {
  $result: empty-map();
  @for $i from 1 to $len + 1 {
    $key: $i;
    $value: $i * $step;
    @if $modify-key {
      $key: $key * $step;
    }
    @if $unit {
      $value: $value + $unit;
    }
    $result: map-merge($result, ($key: $value));
  }
  @return $result;
}