MODULE PList;
TYPE Node = RECORD val : INTEGER; next : POINTER TO Node END;
TYPE PNode = POINTER TO Node;
VAR head : PNode; ExitCode : INTEGER;
PROCEDURE Append(v : INTEGER);
VAR q, r : PNode;
BEGIN
  NEW(q);
  q^.val := v;
  q^.next := NIL;
  IF head = NIL THEN
    head := q
  ELSE
    r := head;
    WHILE r^.next # NIL DO
      r := r^.next
    END;
    r^.next := q
  END
END Append;
PROCEDURE Sum(p : PNode) : INTEGER;
BEGIN
  IF p = NIL THEN
    RETURN 0
  ELSE
    RETURN p^.val + Sum(p^.next)
  END
END Sum;
BEGIN
  head := NIL;
  Append(5);
  Append(7);
  Append(9);
  ExitCode := Sum(head)
END PList.