编译原理实战入门：用 JavaScript 写一个简单的四则运算编译器（修订版）（二）

function CpuEmulator(instructions) {
    this.ins = instructions.split('\r\n')
    this.memory = []
    this.re = /^(push)\s\w+/
    this.execute()
}
CpuEmulator.prototype = {
    execute() {
        this.ins.forEach(i => {
            switch (i) {
                case 'add':
                    this.add()
                    break
                case 'sub':
                    this.sub()
                    break
                case 'mul':
                    this.mul()
                    break
                case 'div':
                    this.div()
                    break                
                default:
                    if (this.re.test(i)) {
                        this.push(i.split(' ')[1])
                    }
            }
        })
    },
    add() {
        const b = this.pop()
        const a = this.pop()
        this.memory.push(a + b)
    },
    sub() {
        const b = this.pop()
        const a = this.pop()
        this.memory.push(a - b)
    },
    mul() {
        const b = this.pop()
        const a = this.pop()
        this.memory.push(a * b)
    },
    div() {
        const b = this.pop()
        const a = this.pop()
        // 不支持浮点运算，所以在这要取整
        this.memory.push(Math.floor(a / b))
    },
    push(x) {
        this.memory.push(parseInt(x))
    },
    pop() {
        return this.memory.pop()
    },
    getResult() {
        return this.memory[0]
    }
}
const tokens = lexicalAnalysis('(100+  10)*  10-100/  10      +8*  (4+2)')
const writer = new AssemblyWriter()
const parser = new Parser(tokens, writer)
const instructions = parser.getInstructions()
const emulator = new CpuEmulator(instructions)
console.log(emulator.getResult()) // 1138

function assert(expression, result) {
    const tokens = lexicalAnalysis(expression)
    const writer = new AssemblyWriter()
    const parser = new Parser(tokens, writer)
    const instructions = parser.getInstructions()
    const emulator = new CpuEmulator(instructions)
    return emulator.getResult() == result
}
console.log(assert('1 + 2 + 3', 6)) // true
console.log(assert('1 + 2 * 3', 7)) // true
console.log(assert('10 / 2 * 3', 15)) // true
console.log(assert('(10 + 10) / 2', 10)) // true

class Generate {
    field String str;
    static String str1;
    constructor Generate new(String s) {
        let str = s;
        return this;
    }
    method String getString() {
        return str;
    }
}
class Main {
    function void main() {
        var Generate str;
        let str = Generate.new("this is a test");
        do Output.printString(str.getString());
        return;
    }
}