Generic Formal With Discrim Used As Actual - How?

[Matthew Heaney <matthew_heaney@acm.org>]

I'm having trouble passing generic formal types --one of which has an
access discriminant-- as generic actuals to another generic having an
identical profile.  Something like:

generic
   type T1 (<>) is limited private;
   type T2 (O : access T1) is limited private;
procedure GP;

generic
   type T1 (<>) is limited private;
   type T2 (O : access T1) is limited private;
procedure GQ;

with GQ;
procedure GP is
  procedure Q is new GQ (T1, T2);
begin
   null;
end GP;


When I try to compile the body of GP, I get the following message:

(start of compiler message)
gnatf /home/matt/acl/rings/gp.adb
gp.adb:4:30: types of actual discriminants must match formal
gp.adb:4:30: instantiation abandoned

Compilation exited abnormally with code 1 at Sun Oct 25 01:13:09
(end of compiler message)


Can someone explain what's going on here?  Why doesn't this code compile?

Is there any way to pass a formal type with a discriminant as the actual
type of another instantiation?

Thanks,
Matt