code: func popInt(m map[string]string, key string) (int64, error) {
  	str, ok := m[key]
  	if !ok {
  		return 0, fmt.Errorf("tokens: bad token, missing %q key", key)
  	}
  	asInt, err := strconv.ParseInt(str, 10, 64)
  	if err != nil {
  		return 0, fmt.Errorf("tokens: bad token, %q is not a number", str)
  	}
  	delete(m, key)
  	return asInt, nil
  }
docs: // extractInt pops integer value from the map.