_sass/vendor/bourbon/helpers/_is-num.scss

//************************************************************************//
// Helper for linear-gradient-parser
//************************************************************************//
@function _is-num($char) {
  $values: '0' '1' '2' '3' '4' '5' '6' '7' '8' '9' 0 1 2 3 4 5 6 7 8 9;
  $index: index($values, $char);
  @return if($index, true, false);
}