$ cat t
use bigrat;
print 1/3 + 1/4,"\n";                 # produces 7/12
$ perl -d t

Loading DB routines from perl5db.pl version 1.33
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(t:2):	print 1/3 + 1/4,"\n";                 # produces 7/12
                                                                                  DB<1> print 1/3 + 1/4,"\n"
0.583333333333333

                                                                                  DB<2> n
7/12
Debugged program terminated.  Use q to quit or R to restart,
  use o inhibit_exit to avoid stopping after program termination,
  h q, h R or h o to get additional info.  

$ perl -v

This is perl 5, version 14, subversion 2 (v5.14.2) built for x86_64-linux-gnu-thread-multi
(with 75 registered patches, see perl -V for more detail)