说明：  词法分析的主要任务是：从左到右逐个字符地扫描源程序，产生一个个单词(Token)，同时检查源程序中的词法错误。执行词法分析的程序称为词法分析程序或扫描程序(Scanner)。
(Lexical analysis of the main tasks are: to scan source code character by character from left to right, resulting in one word (Token), also check the source of lexical errors. Perform lexical analysis program called lexical analyzer or scanner (Scanner).)