Befunge-93 Interpreter

befunge.js

var interpret = (function(){

    var stack = [];
    var sysout = [];
    var dir = '>'
    var strmode = false;
    var skipmode = false;
    var pc = {row:0,col:0};
    var program = [];

    function run(source){
        stack = [], sysout = [], dir = '>';
        strmode = false, skipmode = false;
        pc = {row:0,col:0}, program = source;
        var opcode = program[pc.row][pc.col];
        while(opcode !== '@' || strmode){
            if(skipmode){
                toggleSkipMode();
            }else if(strmode){
                opcode =='"' ? toggleStringMode() : push(opcode);
            }else if(/[<^v>]/.test(opcode)){
                dir = opcode;
            }else if(opcode=='_'){
                dir = (pop() == 0 ? '>' : '<');
            }else if(opcode=='|'){
                dir = (pop() == 0 ? 'v' : '^');
            }else if(opcode=='?'){
                dir = randir();
            }else if(/\d/.test(opcode)){
                push(opcode | 0);
            }else {
                switch(opcode){
                    case '.': printInt(); break;
                    case ',': printChar(); break;
                    case '+': sum(); break;
                    case '-': sub(); break;
                    case '*': mul(); break;
                    case '/': div(); break;
                    case '%': mod(); break;
                    case '!': not(); break;
                    case '`': gt(); break;
                    case '"': toggleStringMode(); break;
                    case "#": toggleSkipMode(); break;
                    case '$': pop(); break;
                    case ':': dup(); break;
                    case '\\': swap(); break;
                    case 'g': get(); break;
                    case 'p': put(); break;
                }
            }
            opcode = move(program);
        }
        return sysout.join('');
    }

    //TODO:deal with empty stack
    function pop(){
        return stack.pop() | 0;
    }

    function push(x){
        if(typeof x == 'string'){
            x = x.charCodeAt(0);
        }
        stack.push(x | 0);
    }

    function toggleStringMode(){
        strmode = !strmode;
    }

    function toggleSkipMode(){
        skipmode = !skipmode;
    }

    function printInt(){
        sysout.push(pop());
    }

    function printChar(){
        sysout.push(String.fromCharCode(pop()));
    }

    function randir(){
        var res = dir;
        switch(Math.round(Math.random() * 4)){
            case 0: res='>'; break;
            case 1: res='<'; break;
            case 2: res='^'; break;
            case 3: res='v'; break;
        }
        return res;
    }

    function dup(){
        if(stack.length==0){
            push(0);
        }else{
            var a = pop();
            push(a);
            push(a);
        }
    }

    function swap(){
        var a=pop(), b=pop();
        push(a);
        push(b);
    }

    function not(){
        push(pop() == 0 ? 1 : 0);
    }

    function gt(){
        var a = pop(), b = pop();
        push(b > a ? 1 : 0);
    }

    function sum(){
        var a = pop(), b = pop();
        push(a + b);
    }

    function sub(){
        var a = pop(), b = pop();
        push(b - a);
    }

    function mul(){
        var a = pop(), b = pop();
        push(a * b);
    }

    function div(){
        var a = pop(), b = pop();
        push(Math.round(b / a));
    }

    function mod(){
        var a = pop(), b = pop();
        push(b % a);
    }

    function get(){
        var y=pop(), x=pop();
        push(program[y][x]);
    }

    function put(){
        var y=pop(), x=pop(), v=pop();
        program[y][x]=v;
    }

    function move(){
        switch(dir){
            case '>': pc.col = next(pc.col+1,program[pc.row].length); break;
            case '<': pc.col = prev(pc.col-1,program[pc.row].length); break;
            case 'v': pc.row = next(pc.row+1,program.length); break;
            case '^': pc.row = prev(pc.row-1,program.length); break;
        }
        return program[pc.row][pc.col];
    }

    function next(p,q){
        return p >= q ? 0 : p;
    }

    function prev(p,q){
        return p < 0 ? q : p;
    }

    return function(code){
        return run(code.split('\n').map(function(s){ return s.split('');}));
    };

})();