How about

generic
   type Access_Type is private;
   Null_Value : Access_Type;

-CRM

"Rodrigo Garc�a" <rodrigo.garcia.ARROBA.epfl.ch> wrote in message
news:3eb01630@epflnews.epfl.ch...
> Does anybody know why Ada does not have something like:
>
> generic
>     type Access_Type is access (<>);  --  ?
>