tail recursion elimination for python by mokrates

# tailrec
# tail-recursion-support by mokrates
# use like this:
#
# @tailrecursive
# def tailrecursive_function(foo, bar): ...
#
# the tail-recursive call
# return tailrecursive_function(foo, bar)
# translates to
# return tailresult(tailrecursive_function, foo, bar)
#
# functions given to tailresult MUST be decorated @tailrecursive

class tailresult:
        def __init__(self, f, *args, **kwargs):
                self.f = f
                self.args = args
                self.kwargs = kwargs

        def __repr__(self):
                return "<tailresult(%s,%s,%s)>" % (repr(self.f), repr(self.args), repr(self.kwargs))

def tailrecursive(f):
        def taildecorator(*args, **kwargs):
                res = f(*args, **kwargs)
                while isinstance(res, tailresult):
                        res = res.f.f(*res.args, **res.kwargs)

                return res

        taildecorator.f = f
        return taildecorator

if __name__ == '__main__':
        def fak(x):
                if (x==1): return 1
                else: return fak(x-1)*x

        @tailrecursive
        def tr_fak(x,y):
                if y==0: return x
                else: return tailresult(tr_fak, x*y, y-1)

        print tr_fak(1,1000)