func (l *Lexer) Next() (string, error) {
	for {
		token, err := (*Tokenizer)(l).Next()
		if err != nil {
			return "", err
		}
		switch token.tokenType {
		case WordToken:
			return token.value, nil
		case CommentToken:
			// skip comments
		default:
			return "", fmt.Errorf("Unknown token type: %v", token.tokenType)
		}
	}
}
func (l *Lexer) Next() (string, error) {
	for {
		token, err := (*Tokenizer)(l).Next()
		if err != nil {
			return "", err
		}
		switch token.tokenType {
		case WordToken:
			return token.value, nil
		case CommentToken:
			// skip comments
		default:
			return "", fmt.Errorf("Unknown token type: %v", token.tokenType)
		}
	}
}
// Next returns the next word, or an error. If there are no more words,
// the error will be io.EOF.