Having said that, as the page's problem description stands, it is
straightforward to solve with ML modules:

   signature SHAPE =
   sig
      val draw    : unit -> unit
      val moveTo  : int * int -> unit
      val rMoveTo : int * int -> unit
   end

   functor Shape (val x:int val y:int) =
   struct
      val x = ref x and y = ref y
      fun moveTo (x', y') = (x := x'; y := y')
      fun rMoveTo (dx, dy) = (x := !x+dx; y := !y+dy)
   end

   functor Circle (val x:int val y:int val r:int) =
   struct
      structure Shape = Shape (val x=x val y=y)
      open Shape
      val r = ref r
      fun setRadius r' = r := r'
      fun draw () = ...
   end

   functor Rectangle (val x:int val y:int val w:int val h:int) =
   struct
      structure Shape = Shape (val x=x val y=y)
      open Shape
      val ref w and h = ref h
      fun setWidth w' = w := w'
      fun setHeight h' = h := h'
      fun draw () = ...
   end

   functor DoSomething (S : SHAPE) =
   struct
      val _ = (S.draw (); S.moveTo (100, 100); S.draw ())
   end

   structure R = Rectangle (val x=10 val y=20 val w=5 val h=6)
   structure C = Circle (val x=15 val y=25 val r=8)

   structure _ = DoSomething R
   structure _ = DoSomething C

Note that the problem description does not explicitly require shapes to
be first-class ;-). Also note that I even mimicked inheritance.

Now, if you really need shapes first-class, then you need first-class
modules. In Alice ML you can abuse packages for this, but you loose some
static typing (with static first-class modules like in Moscow ML you
wouldn't):

   signature RECTANGLE =
   sig
      include SHAPE
      val setWidth  : int -> unit
      val setHeight : int -> unit
   end

   signature CIRCLE =
   sig
      include SHAPE
      val setRadius : int -> unit
   end

   val r = pack R : RECTANGLE
   val c = pack C : CIRCLE

   fun doSomething p =
   let
      structure S = unpack p : SHAPE
   in
      S.draw (); S.moveTo (100, 100); S.draw ()
   end

   val _ = List.map doSomething [r, c]

Does that suit you?

Caveat: all code untested.

   - Andreas

--
Andreas Rossberg, rossb...@ps.uni-sb.de