(* The prime number sieve as a self-cloning, self-modifying object. *)

let sieve =
  {m => 
    meth(s,n)
      let sieve1 = clone(s);
      s.prime := n;
      s.next := sieve1;
      s.m := 
        meth(s1,n1)
          if (n1%n) is 0 then ok else sieve1.m(n1) end
        end
    end,
    prime => -1,
    next => ok,
    };

for i = 2 to 100 do sieve.m(i) end;

sieve.next.next.prime;  (* The third prime. *)