structure S = 
 struct
   val x = 3;
   fun f(x) = if x=0 then 1 else x*f(x-1)
 end;

- use "struct-simple";
[opening struct-simple]
structure S :
  sig
    val f : int -> int
    val x : int
  end
[closing struct-simple]
val it = () : unit
- x;
Error: unbound variable x
- f;
Error: unbound variable f
- S.x;
val it = 3 : int
- val x = 9;
val x = 9 : int
- S.x;
val it = 3 : int
- S.f S.x;
val it = 6 : int
- x;
val it = 9 : int
- open S;
val x = 3 : int
val f = fn : int -> int
- x;
val it = 3 : int
- f x;
val it = 6 : int