说明：  词法分析是编制一个读单词的过程，从输入的源程序中，识别出各个具有独立意义的单词，即基本保留字、标识符、常数、运算符、分隔符五大类。并依次输出各个单词的内部编码及单词符号自身值。程序语言的单词符号一般分为五种：关键字（保留字/基本字）if、while、begin…；标识符：常量名、变量名…；常数：34、56.78、true、‘a’、…；运算符：+、-、*、/、〈、and、or、….、；界限符：， ； （ ） { } /*…。
(Lexical analysis is the preparation of a process of reading words from the input source program to identify each word has an independent significance, that is the basic retention of the word, identifiers, constants, operators, delimiters five categories. And followed by all the output of the internal code word and the word itself the value of symbols. Programming language the word symbols are generally divided into five: keywords (reserved words/basic word) if, while, begin ... identifier: constant name, variable name ... constants: 34,56.78, true, a, ... Operator: 2B !,-,*,/,<, and, or, ...., boundaries Fu:, () ()/* ....)