-- File listg.ads
--  This package implements a generic list, using access types
--  The list is intended to be used as part of lab5, being used
--  to implement a queue

generic

   type Element is private;

package Listg is 

   type List is private;

-- constructors

   procedure Copy (Source: in List;
                   Destination: in out List);

   procedure Clear (AList: in out List);

   procedure Cons (Item: in Element;
                   AndList: in out List);
        -- insert a new node containing Item at the front of the list

   procedure Append (AList: in List;
                     ToList: in out List);
        -- make AList the tail of ToList

-- selectors   

   function Equal (Left: in List;
                   Right: in List) return Boolean;

   function Empty (AList: in List) return Boolean;

   function First (OfList: in List) return Element;
        -- return element stored in first node of list

   function Rest (OfList: in List) return List;
        -- return list following first node

-- exceptions

   Underflow, Overflow: exception;

-- hidden part  
 
private
   type Node;
   type List is access Node;
   type Node is
      record
         Datum: Element;
         Tail: List;
      end record;

end Listg;