function Length var aL TDList integer var PElem TPElem integer begin P

function Length(var aL : TDList):integer;
var
  PElem: TPElem;
  L:integer;
begin
  L:=0;
  PElem:=aL.PFirst;
  while PElem<>nil do
    begin
       L:=L+1;
       PElem:=Pelem^.PNext;
    end;
  Length:=L;
end;