词法分析程序是独立的一遍，把字符流的源程序变为单词序列，输出到一个中间文件，这个文件作为语法分析程序的输入而继续编译过程。该词法分析程序的功能是输入源程序，按照构词规则分解成一系列的单词符号，包括关键字、标识符、运算符、界符和常量等。(The lexical analysis program is an independent one, which turns the source program of the character stream into a word sequence and outputs it to an intermediate file, which continues to be compiled as the input of the parsing program. The function of the lexical analysis program is the input source program, which is decomposed into a series of word symbols according to the rules of word formation, including keywords, identifiers, operators, bounds and constants.)