fn fix_help[A, B](f: @fn(@fn(&A) -> B , &A) -> B , x: &A) -> B {
    ret f(@bind fix_help(f, _), x);
}

fn fix[A, B](f: @fn(@fn(&A) -> B , &A) -> B ) -> @fn(&A) -> B  {
    ret @bind fix_help(f, _);
}

fn fact_(f: @fn(&int) -> int , n: &int) -> int {
    // fun fact 0 = 1
    ret if n == 0 { 1 } else { n * f(n - 1) };
}

fn main() {
    let fact = fix(@fact_);
    assert (fact(5) == 120);
    assert (fact(2) == 2);
}