structure MyStuff =
struct
  datatype MyNum = MyInt of int | MyReal of real;

  val myZero = MyInt(0);

  fun myAdd(MyInt(x),  MyInt(y))  = MyInt(x+y)
    | myAdd(MyInt(x),  MyReal(y)) = MyReal(real(x) + y)
    | myAdd(MyReal(x), MyInt(y))  = MyReal(x + real(y))
    | myAdd(MyReal(x), MyReal(y)) = MyReal(x + y);
end;


val seal = MyStuff.MyReal(3.14159);

val bear = MyStuff.MyInt(21.0);

val theFreakishSealBear = MyStuff.myAdd(seal, bear);


fun ocean() =
    let
        (* open within this let declaration only *)
        open MyStuff;
        val whale = myAdd(MyInt(5), MyReal(5.0));
    in
        myAdd(whale, MyInt(100))
    end;


(* the following remains illegal *)
val aZero = myZero;