How can i print the element poped from a generic STACK

[jordan <huikeith@hotmail.com>]

Dear all,
i want to ask that how can i print the element poped from a generic
STACK.
i have write the following code:
=====================================================
with TEXT_IO;
use TEXT_IO;

procedure sample is

generic
 SIZE : POSITIVE;
 type ITEM is private;
package STACK is
 procedure PUSH(E : in ITEM);
 procedure POP (E : out ITEM);
end STACK;

package body STACK is
 type TABLE is array (POSITIVE range <>) of ITEM;
 SPACE : TABLE(1..SIZE);
 INDEX : NATURAL := 0;

 procedure PUSH(E : in ITEM) is
 begin
  INDEX := INDEX + 1;
  SPACE(INDEX) := E;
 end PUSH;

 procedure POP(E : out ITEM) is
 begin
  E := SPACE(INDEX);
  INDEX := INDEX - 1;
 end POP;
end STACK;

 package stackOfInt is new STACK(100, INTEGER);
 use stackOfInt;

 package INT_IO is new TEXT_IO.INTEGER_IO(INTEGER);
 use INT_IO;

 i : Integer;

begin


 stackOfInt.push(20);

 Put(stackOfInt.pop(i));            <------------- error!!!

end sample;

==============================================
i want to print the element of integer 20 on the screen, how can i do??
is my implementation wrong???