function AddStr(const Str: string; const AdditionalStr: string; const DelimiterStr: string): string;

begin

  if Str = EmptyStr then

  begin

    Result := AdditionalStr;

  end

  else

  begin

    Result := Str + DelimiterStr + AdditionalStr;

  end;

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

Memo1.Text:=AddStr('123----456----789','8888','----');

//原始数据：

//123----456----789

//处理后

//123----456----789----8888

end;