递归下降分析程序

说明：  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 starts the PASCAL language subset source program which defines to take the lexical analyaer the data-in. In the lexical analysis, starts from the article article to scan the source program character, once discovered when conforms to "the word" the definition source program character string, translates it the fixed length the word interior to indicate, and looks up fills in the suitable information table. After the lexical analysis, the source program character string (source program exterior expression) is translated has and so on the long information the word string (source program internal expression), and produces two forms: The chart and the identifier table, they have separately contained in source program all constants and all identifiers. )