tailcall optimization for javascript by mokrates

// tailcall optimizer for javascript
// written by mokrates

// return new tailresult(func, this, arguments...); // <- mark tailcalls like so.
function tailresult() { //func, this, ...
    this.func = arguments[0];
    this.that = arguments[1];
    this.args = new Array();
    for (i = 2; i<arguments.length; ++i)
        this.args[i-2] = arguments[i];
}

function tailcalling(f) {   // decorator for tailcalling functions
    function decor() {
        res = f.apply(this, arguments);
        while (res instanceof tailresult)
            res = res.func.f.apply(res.that, res.args);

        return res;
    }
    decor.f = f
    return decor;
}

// example
fak = tailcalling(function (acc, still) {
    document.writeln("" + acc + ", " + still);
    if (still == 1) return acc; // no tailcall? just normally return your value
    //else return fak(still*acc, still-1); // unmarked tailcall. 'too much recursion'
    else return new tailresult(fak, this, still*acc, still-1); // marked tailcall. works.
});
document.writeln(fak(1, 100000));