[Caml-list] A class that contains instances of itself?

[wrader@OCF.Berkeley.EDU]

Please forgive me if there is an obvious answer to
my question.

I want to have an class that can contain instances
of that same class.  Assume something like this:
(ignore any easy syntax errors - I'm making
up this example right now)

class someClass = 
  object
    var mutable anotherInstanceOfSomeClass ???????

    method talk () =
      print_string("Hello.\n")

    method setInstance x = 
      anotherInstanceOfSomeClass <- x

    method useInstance () =
      if anotherInstanceOfSomeClass is set to a
      usable value, then do
        anotherInstanceOfSomeClass#talk
      else
        do nothing
  end;;


One must call anotherInstanceOfSomeClass#setInstance
before using anotherInstanceOfSomeClass#talk.

What do I put in place of the ?????? to indicate
that the value is not yet usable?  I could create
a "dummy" someClass object to use as the "NULL" value,
let's say called someClassNULL.  someClassNULL must
already be defined if I use it in the body of
someClass, but I can't create it before the
definition of someClass because the compiler doesn't
know what someClass _is_ yet.  Catch-22!!

I've been staring at this problem for hours, so any
help would be fantastic!  (If only I spoke French and
could read the many books available about OCaml...)

Thanks,

Walter Rader
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