Enumeration representation

[Alex <busato@newtech.it>]

I've written the following example program for testing enumeration
represetantion clause:

with Ada.Text_IO; use Ada.Text_IO;


procedure MainEnum is

      type Status is (a,b,c,d,e);
      pragma Discard_Names(Status);

      for Status use
       ( a => 0,
         b => 20,
         c => 400,
         d => 800,
         e => 1600);

       S : Status;
begin
      S := b;
      Put(" => " & S'img);
end MainEnum;

I've compiled it with Gnat (the latest version)
the output of program is 1 but I was expecting another value : 20.
Does  Gnat support this clause?
Did I use this clause badly?

Thank you very much,
by
Alessandro Busato
busato@newtech.it