gistfile1.js

function Machine(first, $){
    var cur = {}, next = $[first];
    var self = {
        go : function(to){ next = next ? next : ($[to] || $.undefined); },
        trigger : function(event){ var t = cur.tx && cur.tx[event]; t && self.go(t); }
    };
    return function(){
        if(next){
            cur.exit && cur.exit.call(self);
            cur = next; next = undefined;
            self.__proto__ = cur.data;
            cur.enter && cur.enter.call(self);
        }
        cur.fn && cur.fn.call(self);
    };
};


var str = '12345 + 12345';
var pos = 0;
var stk = [];

function isDigit(num){
    return num >= '0' && num <= '9'
}

var transition = function(self, str, pos){
    if( pos >= str.length){
        self.go("done");
        return
    }
    if( isDigit(str[pos]) ){
        console.log("==> digit");
        self.trigger("digit")
    } else {
        console.log("==> other");
        self.trigger("other")
    }      
}

var mch = Machine('start', {
    start : {
        fn : function(){
            console.log("start");
            transition(this, str, pos);
        },
        tx : {
            digit : "number",
            other : "whitespace"
        }
    },
    undefined : { fn : function(){ console.log("ERROR"); }}, 
    done : { fn : function(){ console.log("DONE"); } },    
    whitespace: {
        fn: function(){
            console.log(pos);
            pos += 1;
            transition(this, str, pos);
        },
        tx : {
            digit : "number",
            other : "whitespace"
        }
    }, 
    number: {
        data : { buf : "" },
        enter : function(){ this.buf = ""; },
        exit : function(){
            stk.push(this.buf);
            console.log("TOKEN Number: " + this.buf);
        },
        fn: function() {
            var cur = str[pos];
            this.buf += cur;
            pos += 1;
            transition(this, str, pos);
        },
        tx : {
            other : "whitespace"
        }
    }
});

for(var i = 0; i < 20; i += 1) 
    mch();