An example program

This example program implements a generic version of a linked list. Note that in order to demonstrate a generic method, we define a simple identity method, PHelper.Identity.

MODULE GListMod;

TYPE
  IDisplayable = EXTENSIBLE INTERFACE RECORD (ANYIFACE) END;
  PIDisplayable = POINTER TO IDisplayable;

  GList<X:PIDisplayable> = 
    EXTENSIBLE RECORD (ANYREC + IDisplayable)
    head: X;
    tail: PGList<X>;
  END;
  PGList<X:PIDisplayable> = 
    POINTER TO GList<X:PIDisplayable>;

  Integer = EXTENSIBLE RECORD (ANYREC + IDisplayable)
    val: INTEGER;
  END;
  PInteger = POINTER TO Integer;

  Helper = RECORD (ANYREC) END;
  PHelper = POINTER TO Helper;

VAR
  list: PGList<PInteger>;
  helper: PHelper;
  head: PInteger;

PROCEDURE (this: PIDisplayable) Display (), NEW, ABSTRACT;

PROCEDURE (this: PInteger) Display ();
BEGIN
  util.WriteInt(this.val);
END Display;

PROCEDURE (this: PGList<X:PIDisplayable>) Display ();
BEGIN
  IF util.Not(util.PEquals(this.head, NIL)) THEN
    this.head.Display();
  END;
  util.WriteString("\n");
  IF util.Not(util.PEquals(this.tail, NIL)) THEN
    this.tail.Display();
  END;
END Display;

PROCEDURE (this: PGList<X:PIDisplayable>) Insert (elem: X), NEW, EXTENSIBLE;
VAR
  newList: PGList<X>;
BEGIN
  IF util.Not(util.PEquals(this.tail, NIL)) THEN
    this.tail.Insert(elem);
  ELSE
    NEW(newList);
    newList.head := elem;
    this.tail := newList;
  END;
END Insert;

PROCEDURE (this: PGList<X:PIDisplayable>) Head (): X, NEW, EXTENSIBLE;
BEGIN
  RETURN this.head;
END Head;

PROCEDURE (this: PGList<X:PIDisplayable>) Last (): X, NEW, EXTENSIBLE;
VAR
  retVal: X;
BEGIN
  IF util.Not(util.PEquals(this.tail, NIL)) THEN
    retVal := this.tail.Last();
  ELSE
    retVal := this.head;
  END;
  RETURN retVal;
END Last;

PROCEDURE (this: PHelper) NewPInteger (val: INTEGER): PInteger, NEW;
VAR
  p: PInteger;
BEGIN
  NEW(p);
  p.val := val;
  RETURN p;
END NewPInteger;

PROCEDURE (this: PHelper) Identity <X:ANYPTR> (x: X): X, NEW;
BEGIN
  RETURN x;
END Identity;

BEGIN
  util.WriteString("GListMod test program\n");
  NEW(list);
  NEW(helper);
  list.head := helper.NewPInteger(5);
  list.Insert(helper.NewPInteger(10));
  list.Insert(helper.NewPInteger(12));
  list.Display();
  head := list.Head();
  util.WriteInt(head.val);
  util.WriteString("\n");
  head := list.Last();
  util.WriteInt(head.val);
  util.WriteString("\n");
  util.WriteInt(helper.Identity<PInteger>(head).val);
END GListMod.