write a pl/sql block to check a string for palindrome

DECLARE
    len number;
    palstr varchar2(20) := '&palstr';
    chkstr varchar2(20);

BEGIN
    len := length(palstr);
    for i in REVERSE 1..len loop
     chkstr := chkstr||substr(palstr,i,1);
    end loop;
    if chkstr = palstr then
     dbms_output.put_line(palstr||' is a PALINDROME');
    else
     dbms_output.put_line(palstr||' is not a PALINDROME');
    end if;
END;