这里以开始定义的PASCAL语言子集的源程序作为词法分析程序的输入数据。在词法分析中，自文件头开始扫描源程序字符，一旦发现符合"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。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。-here to start the definition of PASCAL language subset of the source as lexical analysis of the data entry process. The lexical analysis, the first since the paper began scanning source characters, once found with "words" definition of the source string, it will be translated into fixed length of the internal word, and to identify the appropriate information filled table. After lexical analysis, source string (source said external) has been translated into information such as a long string of words (internal source said), and produce two forms : Constant table and table identifier, namely contains the source of all the constants and all identifiers.