MODULE PointerBirds;
   IMPORT Out;

   TYPE BirdRec*   = RECORD sound* : ARRAY 10 OF CHAR; END;
        DuckRec*   = RECORD(BirdRec) END;
        CuckooRec* = RECORD(BirdRec) END;

   TYPE Bird   = POINTER TO BirdRec;
        Cuckoo = POINTER TO CuckooRec;
        Duck   = POINTER TO DuckRec;

    VAR pb : Bird;
        pc : Cuckoo;
        pd : Duck;

    PROCEDURE makeDuckSound*( bird : Duck );
    BEGIN COPY("Quack!", bird.sound) END makeDuckSound;

    PROCEDURE makeCuckooSound*( bird : Cuckoo );
    BEGIN COPY("Cuckoo!", bird.sound) END makeCuckooSound;

    PROCEDURE makeSound*( bird : Bird );
    BEGIN
        WITH bird : Cuckoo DO makeCuckooSound(bird);
           | bird : Duck   DO makeDuckSound(bird)
          ELSE
            COPY("Tweet!", bird.sound);
        END;
    END makeSound;

BEGIN
   NEW(pc);
   NEW(pd);

   makeCuckooSound( pc );
   makeDuckSound( pd );

   Out.Ln;Out.String( pc^.sound );Out.Ln;
   Out.Ln;Out.String( pd^.sound );Out.Ln;

   makeSound( pc );
   makeSound( pd );

   Out.Ln;Out.String( pc^.sound );Out.Ln;
   Out.Ln;Out.String( pd^.sound );Out.Ln;
(* -------------------------------------- *)
(* Pass dynamic type to procedure         *)

   pb := pd;

   makeDuckSound( pb(Duck) );
   Out.Ln;Out.String( pb^.sound );Out.Ln;

   pb := pc;

   makeCuckooSound( pb(Cuckoo) );
   Out.Ln;Out.String( pb^.sound );Out.Ln;
(* -------------------------------------- *)

   makeSound(pb);
   Out.Ln;Out.String( pb^.sound );Out.Ln;

   pb := pd;

   makeSound(pb);
   Out.Ln;Out.String( pb^.sound );Out.Ln;
(* -------------------------------------- *)
   NEW(pb);

   makeSound(pb);
   Out.Ln;Out.String( pb^.sound );Out.Ln;

END PointerBirds.