说明：  词法分析程序的功能： 输入：所给文法的源程序字符串。 输出：二元组（syn,token或sum）构成的序列。 其中：syn为单词种别码； token为存放的单词自身字符串； sum为整型常数。 例如：对源程序begin x:=9: if x>9 then x:=2*x+1/3 end #的源文件，经过词法分析后输出如下序列： (1,begin)(10,x)(18,:=)(11,9)(26, )(2,if)……
(Lexical analyzer function: Input: a grammar of the source string. Output: tuple (syn, token or sum) consisting of sequences. Where: syn is another code word kind token string for storing word itself sum to an integer constant. For example: the source program begin x: = 9: if x> 9 then x: = 2* x+1/3 end# of the source file after the lexical analysis following output sequence: (1, begin) (10, x) ( 18,: =) (11,9) (26, ) (2, if) ......)