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└─⟦a7d1ea751⟧ Bits:30000550 8mm tape, Rational 1000, !users!projects 94_04_11
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TextFile

WITH Messages;

PACKAGE BODY Mailboxes IS

   PROCEDURE Find_Message (Message     :        Sequence_Number;
                           The_Mailbox : IN OUT Mailbox);

   FUNCTION Make RETURN Mailbox IS
   BEGIN
      RETURN Nil;
   END Make;
   PROCEDURE Add (Message : Messages.Message; The_Mailbox : IN OUT Mailbox) IS
      New_Entry : CONSTANT Mailbox := Make ((False, Message), Nil);
      Temp      : Mailbox          := The_Mailbox;
   BEGIN
      IF Is_Empty (Temp) THEN
         The_Mailbox := New_Entry;
      ELSE
         WHILE NOT Is_Empty (Rest (Temp)) LOOP
            Temp := Rest (Temp);
         END LOOP;
         Set_Rest (Temp, New_Entry);
      END IF;
   END Add;

   FUNCTION Last_Message (The_Mailbox : Mailbox) RETURN Sequence_Number IS
   BEGIN
      RETURN Length (The_Mailbox);
   END Last_Message;

   PROCEDURE Find_Message (Message     :        Sequence_Number;
                           The_Mailbox : IN OUT Mailbox) IS
   BEGIN
      IF Message = 0 OR ELSE Length (The_Mailbox) < Message THEN
         RAISE Nonexistent_Sequence_Number;
      END IF;
      FOR I IN 1 .. Message - 1 LOOP
         The_Mailbox := Rest (The_Mailbox);
      END LOOP;
   END Find_Message;

   FUNCTION Get_Message (Message : Sequence_Number; The_Mailbox : Mailbox)
                        RETURN Messages.Message IS
      Temp : Mailbox := The_Mailbox;
   BEGIN
      Find_Message (Message, Temp);
      RETURN First (Temp).Message;
   END Get_Message;

   FUNCTION Get_Read_Flag (Message : Sequence_Number; The_Mailbox : Mailbox)
                          RETURN Boolean IS
      Temp : Mailbox := The_Mailbox;
   BEGIN
      Find_Message (Message, Temp);
      RETURN First (Temp).Read_Flag;
   END Get_Read_Flag;

   PROCEDURE Set_Read_Flag (Message     :        Sequence_Number;
                            New_Value   :        Boolean;
                            The_Mailbox : IN OUT Mailbox) IS
      Temp : Mailbox := The_Mailbox;
   BEGIN
      Find_Message (Message, Temp);
      DECLARE
         New_Entry : CONSTANT Mailbox_Entry :=
            (New_Value, First (Temp).Message);
      BEGIN
         Set_First (Temp, New_Entry);
      END;
   END Set_Read_Flag;
   PROCEDURE Delete_Message (Message     :        Sequence_Number;
                             The_Mailbox : IN OUT Mailbox) IS
      Temp : Mailbox := The_Mailbox;
   BEGIN
      IF Message = 1 THEN
         The_Mailbox := Rest (The_Mailbox);
      ELSE
         Find_Message (Message - 1, Temp);
         Set_Rest (Temp, Rest (Rest (Temp)));
      END IF;
   END Delete_Message;

END Mailboxes;