// a demo on OOP

staload "ATS/reference.sats"

//

class ob = {
  super: // no super classes

  method MSGcopy : obj (myclass)
  method MSGprint : unit
}

val supOb : sup (ob) = super {
  super: // none

  method MSGcopy = myself
}

class eq = {
  super: // no super classes

  method MSGeq (obj (myclass)): Bool // binary
  method MSGneq (obj (myclass)): Bool // binary
}

val supEq: sup (eq) = super {
  super: // no super classes

  method MSGeq (other) = not (myself # (MSGneq other))
  method MSGneq (other) = not (myself # (MSGeq other))
}

class ip = { // integer pair
 super: ob, eq

 method MSGgetfst : Int
 method MSGsetfst (Int) : unit
 method MSGgetsnd : Int
 method MSGsetsnd (Int) : unit

}

datatype color = R | B

class cip = { // colored integer pair
 super: ip

 method MSGgetcolor : color
 method MSGsetcolor (color) : unit
}

// obj : cls -> type

fun newIP (x: Int, y: Int): obj (ip) =
  let
     val xref: ref Int = ref x
     and yref: ref Int = ref y
  in
     object {
       super: supOb, supEq
       method MSGgetfst = !xref
       method MSGsetfst (x') = xref := x'
       method MSGgetsnd = !yref
       method MSGsetsnd (y') = yref := y'
       method* MSGcopy = newIP (!xref, !yref) // support no inheritance
       method MSGprint = begin
         print_string "(";
         print_int !xref;
         print_string ", ";
         print_int !yref;
         print_string ")"
       end
     }
  end

fun printIP (O: obj (ip)): unit =
  begin
    print_string "(";
    print_int (O # MSGgetfst);
    print_string ", ";
    print_int (O # MSGgetsnd);
    print_string ")"
  end

fun swapIP (O: obj (ip)): unit =
  let
     val x = O # MSGgetfst
     val y = O # MSGgetsnd
  in
     O # (MSGsetfst y);
     O # (MSGsetsnd x)
  end

// my_ip_1 and my_ip_2 have difference states
val my_ip_1 = newIP (6, 9)
val my_ip_2 = my_ip_1 # MSGcopy

val '() = begin
  my_ip_1 # MSGprint; print_newline ();
  my_ip_2 # MSGprint; print_newline ();
  swapIP my_ip_1;
  my_ip_1 # MSGprint; print_newline ();
  my_ip_2 # MSGprint; print_newline ();
end