struct Rec<A> {
  unRec: @fn(Rec<A>) -> A
}

fn fix<A,B>(f: @fn(@fn(A) -> B) -> @fn(A) -> B) -> @fn(A) -> B {
  let k: @fn(r: Rec<@fn(A) -> B>) -> @fn(A) -> B =
    |r| |x| f((r.unRec)(r))(x);
  k(Rec { unRec: k })
}

fn main() {
  let fac = fix (|me|
    |x: int|
      if x == 0 { 1 }
      else      { x * me(x - 1) }
    );
  println(fmt!("%d", fac(5)));
}