For anyone interested in applying functional concepts to Perl, I highly recommend Mark Jason Dominus's Higher Order Perl[1], the full text of which is now available online for free.
It starts by teaching a reader moderately familiar with Perl functional concepts, and then it deep dives into these concepts and iteratively applies them to example programs to make them better.
Functional code isn't just good for concurrency, it also helps when trying to reason about lists and associative containers at a higher level.