module Weak_memo:The memo class provides an easy way to remember the real class of an object.sig
..end
This module contain the Weak_memo.c
class that contain object that
can be recover latter from the same object with a different type. An
object that is into a Weak_memo.c
object is not prevented from
recolection by the Gc.
class[< .. >]
c :int ->
object
..end