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

--                                                                          --

--                      DISPLAY_SOURCE COMPONENTS                           --

--                                                                          --

--                              S T A C K S                                 --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--            Copyright (c) 1995-1999, Free Software Foundation, Inc.       --

--                                                                          --

-- Display_Source is free software; you can redistribute it and/or modify it--

-- under terms of the  GNU General Public License  as published by the Free --

-- Software Foundation;  either version 2,  or  (at your option)  any later --

-- version. Display_Source is distributed in the hope  that it will be use- --

-- ful, but WITHOUT ANY WARRANTY; without even the implied warranty of MER- --

-- CHANTABILITY or  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General  --

-- Public License for more details. You should have received a copy of the  --

-- GNU General Public License distributed with GNAT; see file COPYING. If   --

-- not, write to the Free Software Foundation, 59 Temple Place Suite 330,   --

-- Boston, MA 02111-1307, USA.                                              --

--                                                                          --

-- Display_Source is distributed as a part of the ASIS implementation for   --

-- GNAT (ASIS-for-GNAT).                                                     --

--                                                                          --

-- The   original   version   of  Display_Source  has  been  developed  by  --

-- Jean-Charles  Marteau and Serge Reboul,  ENSIMAG  High School Graduates  --

-- (Computer sciences)  Grenoble,  France  in  Sema Group Grenoble, France. --

--                                                                          --

-- Display_Source is now maintained by Ada Core Technologies Inc            --

-- (http://www.gnat.com).                                                   --

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


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

-- This package is part of the ASIS application display_source --

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

-- It provides an implementation of stacks ...                 --

-- It is used in Source_Trav package .                         --

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

generic

   type T_Elem is private;

   type A_Elem is access all T_Elem;

   Initial_Number : Natural := 50;

package Stacks is

   type Stack is private;
   Empty_Stack : constant Stack;

   Stack_Error : exception;

   --  standard functions for a stack :

   --  Push puts an Elem on the top of the stack

   --  Pop gets the last pushed element of the stack

   procedure Push (St : in out Stack; Elem : in T_Elem);
   procedure Pop (St : in out Stack; Elem : out T_Elem);
   --  Upper lets you have access to the first Elem

   --  on the top of the stack.

   function Upper (St : in Stack) return A_Elem;
   function Size_Of_Stack (St : in Stack) return Natural;
   function Is_Empty (St : in Stack) return Boolean;

private

   type T_Node;

   type Stack is access all T_Node;

   Empty_Stack : constant Stack := null;

end Stacks;