这是编译原理的源代码，涉及了编译原理的各个过程：词法分析，LL1语法分析，语义分析，中间代码生成，中间代码优化（常表达式优化，公共表达式优化，循环不变式优化），中间代码生成目标代码，目标代码的解释执行.. -this principle is to compile the source code, the compiler principles involved in various processes : lexical analysis, LL1 syntax analysis, semantic analysis and code generation and code optimization (regular expression optimization, public expression optimization, optimization loop invariant), intermediate code generation target code goal of the interpretation and implementation of code ..