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.

Homepage:
https://metacpan.org/release/Smart-Comments
