一个极简编译器的实现

一篇文章： https://github.com/jamiebuilds/the-super-tiny-compiler/blob/master/the-super-tiny-compiler.js
文章里实现了一个简单的编译器，将LISP代码编译为C代码：

数学算式	LISP	C
2 + (4 - 2)	(add 2 (subtract 4 2))	add(2, subtract(4, 2))

代码编译通常经过三个阶段：

Parsing
Transformation
Code Generation

Parsing

源码

(add 2 (subtract 4 2))

Lexical Analysis Result

[
   { type: 'paren',  value: '('        },
   { type: 'name',   value: 'add'      },
   { type: 'number', value: '2'        },
   { type: 'paren',  value: '('        },
   { type: 'name',   value: 'subtract' },
   { type: 'number', value: '4'        },
   { type: 'number', value: '2'        },
   { type: 'paren',  value: ')'        },
   { type: 'paren',  value: ')'        },
]

Syntactic Analysis Result

{
   type: 'Program',
   body: [{
      type: 'CallExpression',
      name: 'add',
      params: [{
        type: 'NumberLiteral',
        value: '2',
    }, {
      type: 'CallExpression',
      name: 'subtract',
      params: [{
        type: 'NumberLiteral',
        value: '4',
      }, {
        type: 'NumberLiteral',
         value: '2',
       }]
     }]
    }]
}

Transformation

深度优先遍历旧AST，作出相应的修改，生成新AST

修改

创建Visitor对象，定义遍历经过每一种节点时的行为

遍历

实现深度优先遍历的方法

Code Generation

将AST重新序列化，组成目标代码

JavaScript中的AST

AST Explorer

Babel

https://babel.docschina.org/

babel/babylon

babel/babylon
babel-parser

npm install @babel/parser --save-dev

const code = `const text = 'Hello World';`;

const ast = require("@babel/parser").parse(code);

console.log("ast", ast);

babel/traverse

babel-traverse
babel-core

npm install @babel/traverse --save-dev

const code = `const text = 'Hello World';`;

const ast = require("@babel/parser").parse(code);

require("@babel/traverse").default(ast, {
  enter(path) {
    console.log("path type is ", path.type);
  },
});

//path type is  Program
//path type is  VariableDeclaration
//path type is  VariableDeclarator
//path type is  Identifier
//path type is  StringLiteral

const code = `const text = 'Hello World';`;

const ast = require("@babel/parser").parse(code);

require("@babel/traverse").default(ast, {
  enter(path) {
    if (path.node.type === "StringLiteral" && path.node.value) {
      path.node.value = `${path.node.value} new!`;
    }
  },
});

babel/generator

babel-generator

npm install @babel/traverse --save-dev

const code = `const text = 'Hello World';`;

const ast = require("@babel/parser").parse(code);

require("@babel/traverse").default(ast, {
  enter(path) {
    if (path.node.type === "StringLiteral" && path.node.value) {
      path.node.value = `${path.node.value} new!`;
    }
  },
});

const output = require("@babel/generator").default(ast, {});

console.log(output.code);

参考资料：
https://cloud.tencent.com/developer/doc/1260
https://www.zcfy.cc/article/347

抽象语法树（AST）