Processamento adicional de dados conforme retornado em determinado dbms_output

declare
  v_last_date date; -- is null
  ...
begin
  ...

  for i in t_data.first .. t_data.last loop
    if v_last_date is null then

      dbms_output.put_line(to_char(t_data(i).englishcalendar,'dd-mm-yyyy')||' 0' ); 
    else
      dbms_output.put_line(to_char(t_data(i).englishcalendar,'dd-mm-yyyy')||' ' 
                          ||to_char(t_data(i).englishcalendar - v_last_date)
                          ||' [' ||to_char(t_data(i).englishcalendar,'dd-mm-yyyy')||'-'
                          || to_char(v_last_date ,'dd-mm-yyyy')||']' ); 
    end if;
    v_last_date := t_data(i).englishcalendar; -- save a date of the iteration   
  end loop;
end;