目的：通过编写简单的YACC程序熟悉YACC词法分析工具的基本用法，及词法分析器的设计思路。编写包括赋值语句、if语句以及含有加合乘运算的表达式等语法结构的pascal子集语言的语法分析器。 功能：程序由两个模块LEX和YACC构成，YACC使用LEX分析后的正规单词输出流-Objective : to prepare a simple procedure with YACC YACC lexical analysis of the basic tools to use, and the lexical analyzer designs. Preparation including assignment if statements containing Addition and multiplication of expressions such as grammatical structure of the pascal subset of the language syntax analyzer. Function : procedures by the two modules constitute LEX and YACC, YACC LEX analysis using the formal word output streams