Re: TeX and Pascal [was Re: The joy of FORTRAN]

In alt.folklore.computers Stefan Ram <ram@zedat.fu-berlin.de> wrote:

John Ames <commodorejohn@gmail.com> wrote or quoted:

rather than having to remember the distinction between:
void sliceApple(apple * f)
and:
void slicePear(pear * f)
one could simply write:
fruitPile[i++].slice();
and trust that the Right Thing will be done.

 
  Ah! I think this is called "polymorphism".
 
  I wondered whether something like this could
  also be formulated in Pascal.
 
  (Unintentionally, I return to the topic
  of the subject somewhat.)
 
PROGRAM ANIMALSOUNDS( OUTPUT );
 
TYPE
   ANIMALTYPE =( DOG, CAT );
 
   ANIMAL = RECORD
      ANIMALKIND: ANIMALTYPE;
   END;
 
FUNCTION SOUND( ANIMAL: ANIMAL ): STRING;
BEGIN
   CASE ANIMAL.ANIMALKIND OF
      DOG: SOUND := 'WOOF!';
      CAT: SOUND := 'MEOW!';
   END;
END;
 
VAR MYDOG, MYCAT: ANIMAL;
 
BEGIN
   MYDOG.ANIMALKIND := DOG;
   MYCAT.ANIMALKIND := CAT;
   WRITELN( 'IT SAYS: ', SOUND( MYDOG ));
   WRITELN( 'IT SAYS: ', SOUND( MYCAT ));
END.
 
  Output:
 
IT SAYS: WOOF!
IT SAYS: MEOW!

It is well-know anty-pattern.  Theoretically it is equvalent
to OO way and may be the only way to implement given functionality
in a strongly-typed language.  But in practice OO way scales
better and is easier to modify.  In particular, this is toy
example and practical class at the beginning may look similar
to such a toy, but will grow together with the program.

--
                              Waldek Hebisch