The Perl 5 module Smart::Comments provide an easy way to insert debugging and tracking code into a program. They can report the value of a variable, track the progress of a loop, and verify that particular assertions are true. Best of all, when you're finished debugging, you don't have to remove them. Simply commenting out the use Smart::Comments line turns them back into regular comments. Leaving smart comments in your code is smart because if you needed them once, you'll almost certainly need them again later.