一、　　实验目的与要求

目的：在分析理解一个教学型编译程序（如PL/0）的基础上，对其词法分析程序、语法分析程序和语义处理程序进行部分修改扩充。达到进一步了解程序编译过程的基本原理和基本实现方法的目的。

要求：对PL/0作以下修改扩充

基本内容：

增加单词：保留字 ELSE，FOR，TO，DOWNTO，RETURN

运算符 +=，-=，++，--

修改单词：不等号# 改为 <>

增加条件语句的ELSE子句

-First, the purpose and requirements for experimental purposes: the analysis of a teaching-oriented compiler to understand (such as PL/0), based on its lexical analyzer, parser and semantic processing to expand a partial modification. Compiled to learn more about the process of realization of basic principle and purpose. Requirements: The PL/0 expansion of the basic content of the following modifications: increase the word: reserved word ELSE, FOR, TO, DOWNTO, RETURN operator+=,-=,++,-- modify words: inequality# to < >　to increase The ELSE clause of conditional statement