1.输入文件解析
2.正则表达式转化为NFA
3.多个NFA合并
4.NFA转换DFA
5代码生成

关于输入文件格式：
没有考虑对lex输入文件的出错处理，所以输入文件务必严格书写正确。
Lex中的正规表达式使用了以下运算符：
[] |　*　@　( )
并且正规表达式中不能出现其他的子正规表达式。
如果想要在待识别的正则式中使用上述运算符，请使用转义符号，即\。
例如，如果想用*，可以写成\*
,1. Analysis of the input file 2. Regular expressions into NFA 3. More than the combined NFA conversion 4.NFA Code Generation DFA 5 on input file format: There is no consideration of the lex input file error handling, the input file must be written in strict correct. Lex in the regular expression operators used the following: [] |* @ () and regular expressions can not be a subset of other regular expressions. If you want to be identified in the regular-type operator to use the above, please use the escape symbol, that is, \. For example, if you want to use*, can be written in \*