一直都知道一个很有趣的语言，Brainfuck，只是一直尚未研究，今天晚上看了一下，竟然不是那么难，而且还撸出来了一个解释器。这是一种极小化的计算机语言，它是由Urban Müller在1993年创建的。

就象它的名字所暗示的，brainfuck程序很难读懂。尽管如此，brainfuck图灵机一样可以完成任何计算任务。虽然brainfuck的计算方式如此与众不同，但它确实能够正确运行。

这种语言基于一个简单的机器模型，除了指令，这个机器还包括：一个以字节为单位、被初始化为零的数组、一个指向该数组的指针（初始时指向数组的第一个字节）、以及用于输入输出的两个字节流。

下面是这八种状态的描述，其中每个状态由一个字符标识：

举个例子，hello world

[ This program prints "Hello World!" and a newline to the screen, its
  length is 106 active command characters [it is not the shortest.]
 
  This loop is a "comment loop", it's a simple way of adding a comment
  to a BF program such that you don't have to worry about any command
  characters. Any ".", ",", "+", "-", "<" and ">" characters are simply
  ignored, the "[" and "]" characters just have to be balanced.
]
+++++ +++               Set Cell #0 to 8
[
    >++++               Add 4 to Cell #1; this will always set Cell #1 to 4
    [                   as the cell will be cleared by the loop
        >++             Add 2 to Cell #2
        >+++            Add 3 to Cell #3
        >+++            Add 3 to Cell #4
        >+              Add 1 to Cell #5
        <<<<-           Decrement the loop counter in Cell #1
    ]                   Loop till Cell #1 is zero; number of iterations is 4
    >+                  Add 1 to Cell #2
    >+                  Add 1 to Cell #3
    >-                  Subtract 1 from Cell #4
    >>+                 Add 1 to Cell #6
    [<]                 Move back to the first zero cell you find; this will
                        be Cell #1 which was cleared by the previous loop
    <-                  Decrement the loop Counter in Cell #0
]                       Loop till Cell #0 is zero; number of iterations is 8
 
The result of this is:
Cell No :   0   1   2   3   4   5   6
Contents:   0   0  72 104  88  32   8
Pointer :   ^
 
>>.                     Cell #2 has value 72 which is 'H'
>---.                   Subtract 3 from Cell #3 to get 101 which is 'e'
+++++++..+++.           Likewise for 'llo' from Cell #3
>>.                     Cell #5 is 32 for the space
<-.                     Subtract 1 from Cell #4 for 87 to give a 'W'
<.                      Cell #3 was set to 'o' from the end of 'Hello'
+++.------.--------.    Cell #3 for 'rl' and 'd'
>>+.                    Add 1 to Cell #5 gives us an exclamation point
>++.                    And finally a newline from Cell #6

自己看下原理并不难，于是自己撸了一个解释器，话不多说直接上代码，用es6写的。

/**
 * Brainfuck Interpreter
 * author: yfgeek
 * https://github.com/yfgeek
 */
'use strict';

class Interpreter{
    constructor(code,input) {
        this.code = code.trim().replace(/ /g, "").replace(/(\r\n|\n|\r)/gm,"").split("");
        this.input = input || [];
        this.pointer = 0;
        this.codePointer = 0 ;
        this.dataset = [];
        this.bracketStack = [];
        this.output = [];
    }

    operation(str){

        switch(str){
            case '+':  {
                this.dataset[this.pointer] = this.dataset[this.pointer] || 0;
                ++this.dataset[this.pointer];
                break;
            }

            case  '-':  {
                this.dataset[this.pointer] = this.dataset[this.pointer] || 0;
                --this.dataset[this.pointer];
                break;
            }

            case  '<':{
                this.pointer = --this.pointer<0 ? 0: this.pointer;
                break;
            }

            case '>': {
                this.pointer++;
                break;
            }

            case '.':{
                this.output.push(String.fromCharCode(this.dataset[this.pointer]));
                break;
            }

            case ',':{
                let c = this.input.shift();
                if (typeof c === "string") {
                    this.dataset[this.pointer] = c.charCodeAt(0);
                }
                break;
            }

            case '[': {
                this.leftBracket();
                break;
            }

            case ']': {
                this.rightBracket();
                break;
            }
        }

    };

    leftBracket(){
        let openBrackets = 1;
        if (this.dataset[this.pointer]) {
            this.bracketStack.push(this.codePointer);
        } else {
            while (openBrackets && this.code[++this.codePointer]) {
                if (this.code[this.codePointer] === ']') {
                    openBrackets--;
                } else if (this.code[this.codePointer] === '[') {
                    openBrackets++;
                }
            }
        }
    }

    rightBracket(){
        this.codePointer =  this.bracketStack.pop() - 1;
    }

    run(){
        let list = ['+','-','<','>','.',',','[',']'];
        do{
           let c = this.code[this.codePointer];
           if(list.indexOf(c) >= 0)  this.operation(c);
        }while(++this.codePointer < this.code.length);
        return this.output;
    }

    toString(){
        return this.run().join('');
    }

}

let code = '++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.';
let i = new Interpreter(code,[]);
console.log(i.toString());