/*
**************************************
* MathParser Class v2.0              *
* Autor: Carlos R. L. Rodrigues      *
* http://jsfromhell.com/             *
**************************************
*/
MathParser = function(){
        var o = this, p = o.operator = {};
        p["+"] = function(n, m){return n + m;}
        p["-"] = function(n, m){return n - m;}
        p["*"] = function(n, m){return n * m;}
        p["/"] = function(m, n){return n / m;}
        p["%"] = function(m, n){return n % m;}
        p["^"] = function(m, n){return Math.pow(n, m);}
        p["~"] = function(m, n){return Math.sqrt(n, m);}
        o.custom = {}, p.f = function(s, n){
                if(Math[s]) return Math[s](n);
                else if(o.custom[s]) return o.custom[s].apply(o, n);
                else throw new Error("Function \"" + s + "\" not defined.");
        }, o.add = function(n, f){this.custom[n] = f;}
}
MathParser.prototype.eval = function(e){
        var e = e.split(""), v = [], p = [], a, c = 0, s = 0, x, t, d = 0;
        var n = "0123456789.", o = "+-*/^%~", f = this.operator;
        for(var i = 0, l = e.length; i < l; i++)
        if(o.indexOf(e[i]) > -1)
        e[i] == "-" && (s > 1 || !d) && ++s, !s && d && (p.push(e[i]), s = 2), "+-".indexOf(e[i]) < (d = 0) && (c = 1);
        else if(a = n.indexOf(e[i]) + 1 ? e[i++] : ""){
                while(n.indexOf(e[i]) + 1) a += e[i++];
                v.push(d = (s & 1 ? -1 : 1) * a), c && v.push(f[p.pop()](v.pop(), v.pop())) && (c = 0), --i, s = 0;
        }
        for(c = v[0], i = 0, l = p.length; l--; c = f[p[i]](c, v[++i]));
        return c;
}
MathParser.prototype.parse = function(e){
        var p = [], f = [], ag, n, c, a, o = this, v = "0123456789.+-*/^%~(, )";
        for(var x, i = 0, l = e.length; i < l; i++){
                if(v.indexOf(c = e.charAt(i)) < 0){
                        for(a = c; v.indexOf(c = e.charAt(++i)) < 0; a += c); f.push((--i, a));
                }
                else if(!(c == "(" && p.push(i)) && c == ")"){
                        if(a = e.slice(0, (n = p.pop()) - (x = v.indexOf(e.charAt(n - 1)) < 0 ? y = (c = f.pop()).length : 0)), x)
                        for(var j = (ag = e.slice(n, ++i).split(",")).length; j--; ag[j] = o.eval(ag[j]));
                        l = (e = a + (x ? o.operator.f(c, ag) : o.eval(e.slice(n, ++i))) + e.slice(i)).length, i -= i - n + c.length;
                }
        }
        return o.eval(e);
}

var m = new MathParser();
m.add("userFunction", function(n, m){
        return n + m;
});
var expression = "round((-(userFunction(1, 1))) + 9 * 8 -9 + abs(54 % 3 - 8) + -(-7 / -2.989678 - -98.789 % 4 + (456 / 876)))";
alert(m.parse(expression));