🚀 go-pugleaf

      On Thu, 4 Apr 91 11:59:50, Ole Bjorn Tuftedal <ob@IFI.UIB.NO>, wrote :

>I have read with interest the recent messages about abstract
>data types and generic modules.

>In three following messages I'll post a generic sort by Richard S. Wiener,
>from SIGPLAN Notices, V19 #3, March 1984, pp 66-72.  I have tested it
>on Logitech Modula-2 v. 3.x for MSDOS.


     In the compare procedure you could take advantage of the pointer
compatibility. For example :

      If the compare procedure is defined as :
      TYPE
           CompareProc = PROCEDURE(ADDRESS,ADDRESS) : BOOLEAN;


      In your aplication program your can do this :

      TYPE
           Person =
           RECORD
             Number : CARDINAL;
             Name   : ARRAY 0..19| OF CHAR;
             Age    : CARDINAL
           END (* record *);
           PtrPerson = POINTER TO Person;


       .
       .
       .


      PROCEDURE ComparePerson(p1,p2 : PtrPerson) : BOOLEAN;
      BEGIN
        RETURN p1^.Number > p2^.Number
      END ComaparePerson;

    The procedure ComparePerson is fully compatible with CompareProc.

On the other hand, I think that you could maintain the array manipulation
outsides the sort procedure. I believe that this is another level of
abstraction.

  This is another example of generic sort. This procedure is provided by
  JPI in its module LIB. Its works! :


TYPE
  CompareProc = PROCEDURE(CARDINAL, CARDINAL) : BOOLEAN;
  SwapProc    = PROCEDURE(CARDINAL, CARDINAL);

PROCEDURE QSort(N: CARDINAL; Less: CompareProc; Swap: SwapProc);

  PROCEDURE Sort(l,r: CARDINAL);
  VAR
    i,j:CARDINAL;
  BEGIN
    WHILE r > l DO
      i := l+1;
      j := r;
      WHILE i <= j DO
        WHILE (i <= j) AND NOT Less(l,i) DO INC(i) END;
        WHILE (i <= j) AND Less(l,j) DO DEC(j) END;
        IF i <= j THEN Swap(i,j); INC(i); DEC(j) END;
      END;
      IF j # l THEN Swap(j,l) END;
      IF j+j > r+l THEN
        Sort(j+1,r);
        r := j-1;
      ELSE
        Sort(l,j-1);
        l := j+1;
      END;
    END;
  END Sort;





Instituto Tecnologico y de Estudios Superiores de Monterrey, Campus San Luis
ROberto DOminguez GUtierrez