Problem with generic parameter

[Jacob Sparre Andersen <sparre@nbi.dk>]

When I try to compile the program included below (cut down version of
a test program) GNAT 3.15p reports:

-----
Compiling: demo.adb (source file time stamp: 2005-06-22 10:10:41)

    16.                               Measurement_Array => Measurement_Array);
                                                           |
        >>> component subtype of actual does not match that of formal "Measurement_Array"
        >>> instantiation abandoned

 20 lines: 2 errors
-----

I can't see _how_ it doesn't match.  Can somebody figure out what I'm
doing wrong?  And maybe even suggest me an elegant solution to the
problem?

The reason I have Measurement_Array as a generic parameter is that I
also use it elsewhere, and that I may want to work with differently
indexed measurement arrays.  Does it - despite that - make more sense
to declare the types "Measurement" and "Measurement_Array" together?

/Jacob

------------------------------------------------------------------------------
--  Source code:

with Generic_Root;
with Generic_Root.Child;

procedure Demo is

   type Scalar is digits 15;

   package Measurements is
      new Generic_Root (Scalar => Scalar);

   type Measurement_Array is array (Positive range <>)
     of Measurements.Measurement;

   package Measurement_Text_IO is
      new Measurements.Child (Indices           => Positive,
                              Measurement_Array => Measurement_Array);

begin
   null;
end Demo;

generic

   type Scalar is digits <>;

package Generic_Root is

   ---------------------------------------------------------------------------
   --  type Limit:

   type Limit is (Below, Exact, Above, Undefined);

   ---------------------------------------------------------------------------
   --  type Measurement:

   type Measurement (As : Limit := Exact) is
      record
         case As is
            when Below | Exact | Above =>
               Value : Scalar;
            when Undefined =>
               null;
         end case;
      end record;

   ---------------------------------------------------------------------------

end Generic_Root;

with Ada.Text_IO;

generic

   type Indices is (<>);

   type Measurement_Array is array (Indices range <>) of Measurement;

package Generic_Root.Child is

end Generic_Root.Child;