My guess is that you didn't seriously learn functional programming in any language.

It is not just about memory management and data structures. It is about functions as first class objects, no side effects, lazy evaluation, closure, monads. The fact that you can basically write a compiler in an hour as a first year student (that was exercise 3 in my course).

I'm not a programmer, I'm a DBA. The code I write is mostly short and ugly scripts in Perl and Bash. I can do very little Java and almost no other language. The one and only time I used Lisp was in my first programming course in the university. Incidentally, it was also the one and only time I enjoyed programming.