@function __list-join($list, $separator: "") {
  $length: length($list);

  @if ($length == 0) {
    @return "";
  }

  $result: nth($list, 1);

  @if $length > 1 {
    @for $index from 2 through $length {
      $result: $result + $separator + nth($list, $index);
    }
  }

  @return $result;
}

@function __join($list, $separator: "", $guard: null) {
  @if $guard and __is-iteratee-call($list, $separator, $guard) {
    $separator: "";
  }

  @if __is-list-like($separator) {
    @return join($list, $separator);
  }

  @return __list-join($list, $separator);
}

/// Joins a single list into a string,
/// similar to the native JavaScript `Array.prototype.join()`.
///
/// **NOTE:** This is not the same as the native Sass `join()` function.
///
/// @access public
/// @group List
/// @param {List} $list The list containing elements to join.
/// @param {String} $separator [''] The string separator.
/// @returns {String} Returns the joined list as a string.
/// @example scss
/// $foo: _join('a' 'b' 'c', '--');
/// // => 'a--b--c'
@function _join($args...) {
  @return call(get-function("__join"), $args...);
}