SQL> ed
Wrote file afiedt.buf

  1  declare
  2  a varchar2(10):='forward';
  3  o varchar2(10);
  4  b varchar2(10);
  5  begin
  6  for mag in reverse 1..length(a) loop
  7   b:=substr(a,mag,1);
  8   o:=O||b;
  9   end loop;
 10  dbms_output.put_line(o);
 11* end;
SQL> /
drawrof

PL/SQL procedure successfully completed.