说明：  PL0编译器源代码 2． 要求的PL/0编译器是个一遍的编译程序，词法分析程序作为子程序，需要的时候被语法分析程序调用，使用语法制导的翻译技术，在语法分析的同时生成中间代码，并保存到文件中。
(PL0 compiler source code 2. Requirements of PL/0 compiler is again compiled program, lexical analysis program as a subroutine, and when required by the syntax analysis program call, use the syntax-guided translation technology, in the middle of parsing the same time generating code, and save to a file .)