code: func (tkn Token) String() string {
  	if 0 == tkn {
  		return "UNKNOWN"
  	}
  	if tkn < Token(len(token2string)) {
  		return token2string[tkn]
  	}
  	return "token(" + strconv.Itoa(int(tkn)) + ")"
  }
docs: // String returns the string corresponding to the token.
  // For operators, delimiters, and keywords the string is the actual
  // token string (e.g., for the token PLUS, the String() is
  // "+"). For all other tokens the string corresponds to the token
  // name (e.g. for the token IDENTIFIER, the string is "IDENTIFIER").
  //