以在下面段落中定义的PASCAL语言子集的源程序作为词法分析程序的输入数据。词法分析器打开该文件后，自文件头开始扫描源程序字符，发现符合“单词”定义的源程序字符串时，将它翻译成固定长度的单词内部表示，并查填适当的信息表，一旦发现不符合“单词”定义的源程序字符串时，给出错误提示。经过词法分析后，源程序字符串（源程序的外部表示）被翻译成具有等长信息的单词串（源程序的内部表示），并产生两个表格：常数表和标识符表，它们分别包含了源程序中的所有常数和所有标识符。-PASCAL language subset of the source defined in the following paragraphs as input data for the lexical analyzer. The lexical analyzer to open the file from the file header, scan the source character and found to comply with the definition of the word "source string, it is translated into fixed-length word internal, said check and fill in appropriate information table, found that does not meet the definition of "words" of the source string, given the error. After lexical analysis, the source string (the external representation of a source) has been translated into the word with a long message string (the internal representation of the source), and produce two forms: the constant table and the identifier table, and they contain all constants in the source and all identifiers.