从左至右扫描源程序的字符串，按照词法规则（正则文法规则）识别出一个个正确的单词，并转换成该单词相应的二元式（种别码、属性值）交给语法分析使用。

本程序规定输出用KeyWord代表关键字，Word代表普通标识符，Digit代表阿拉伯数字，SingleWord代表单分界符，DoubleWord代表双分界符，ERROR代表无法识别的字符。-String from left to right scan source, according to lexical rules (regular grammar rules) to identify all the right words, and converted into the corresponding binary word type (species ID, attribute value) to the use of grammatical analysis . This program provides an output representative of keywords KeyWord, Word on behalf of ordinary identifiers, Digit behalf of the Arab figures, SingleWord behalf of a single delimiter, DoubleWord behalf double delimiter, ERROR behalf of unrecognized characters.