What is Functional Programming?

If you go back in computer history, you'll find that the second–oldest programming language still in use, LISP, has its bases in Functional Programming. Since then there have been many more functional languages, and FP has been applied more widely. But even so, if you ask around what FP is, you'll probably get two widely dissimilar answers.

Depending on whom you ask, you'll either learn that it's a modern, advanced, enlightened approach to programming that leaves every other paradigm behind, or you'll be told that it's mainly a theoretical thing, with more complications than benefits, practically impossible to implement in the real world. And, as usual, the real answer is not in the extremes, but somewhere within.

For Trivia buffs, the oldest language still in use is FORTRAN, which appeared in 1957, a year before LISP. Quite shortly after LISP came another long–lived language: COBOL, for business–oriented programming.