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    Types: TextFile
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TextFile

generic
    type Element is private;

    pragma Must_Be_Constrained (Yes => Element);

package Queue_Generic is

    pragma Subsystem (Abstract_Types, Private_Part => Open);
    pragma Module_Name (4, 712);

    type Queue is private;

    procedure Initialize (Q : out Queue);

    function  Is_Empty   (Q : Queue) return Boolean;
    procedure Make_Empty (Q : in out Queue);

    procedure Copy (Target : in out Queue; Source : Queue);

    procedure Add    (Q : in out Queue; X : Element);
    procedure Delete (Q : in out Queue);
    function  First  (Q : Queue) return Element;
    -- on calls to delete and first, not is_empty(q) is assumed
    -- constraint error will be raises is is_empty(q)

    type Iterator is private;

    procedure Init  (Iter : out Iterator; Q : Queue);
    procedure Next  (Iter : in out Iterator);
    function  Value (Iter : Iterator) return Element;
    function  Done  (Iter : Iterator) return Boolean;

    ------------------------------------------------------
    -- Implementation Notes and Non-Standard Operations --
    ------------------------------------------------------

    -- variables of type queue are initially empty
    --    therefore, the call to initialize is optional

    -- := and = are meaningless
    --   := implies sharing (introduces an alias) for sub-structures

    -- garbage may be generated

private

    type Node;
    type Pointer is access Node;

    type Node is
        record
            Value : Element;
            Link  : Pointer;
        end record;

    type Queue is
        record
            Head : Pointer;
            Tail : Pointer;
        end record;

    type Iterator is new Queue;

end Queue_Generic