introduction

1. Deference between Compilers with Interpreters
   Compiler is off-line, and it’s imput is “program” then compiler it to exec witch can coculate Data to Output.
   Interpreters is on-line, and it’s input is Program and Data, it interpreter the Program line by line, and excute the code.
2. History
   1954 IBM develops the 704. In this time, software is more expensive than hardware.
3. Speedcoding
   1954 John Backus.today’s interperters. very slow.
   than he invented Fortran1(1954-1957). It’s the first compiler.
   （好吧，英语记笔记有点慢）并且编译的核心由此确定为“理论(Theory)+练习(Pratice)”
4. 编译原理分为：lexical analysis, parsing, sematic analysis, optimization, code generation
   lexical analysis和parsing注重句法分析，sematic注重语义，

1.1 编译器的结构

人类是如何理解一段英语的

理解语句	对应编译过程
This is a sentence.	if x == y then z = 1; else z = 2;
理解单词 将句子分割成单词集 {‘This’, ‘is’, ‘a’, ‘sentence’}	词法分析 将独立的程序文本分割成单词或tokens（标记） 可以识别出关键字{‘if’, ‘and’, ‘else’}、变量名{‘x’, ‘y’, ‘z’}、常量{‘1’, ‘2’}、操作符{’==’, ‘’=’, ‘=’}
理解句子结构	语法分析（语法树）
理解句子意思 这是会有歧义的	语义分析 强制规定，避免模糊语言
简化语言表示	自动代码优化 但当Y==NaN时不能这么做
翻译成其他语言	code生成