docs: def parse_multiple(s, f, values=None):
      """Parse multiple comma-separated elements, each of which is parsed
         using function f."""
      if values is None: values = []
      values.append(f(s))
      if s.pos < len(s) and s.cur == ',':
          s.pos += 1
          return parse_multiple(s, f, values)
      else:
          return values