I beg to differ, although I am not prepared to quibble. FP means that the primary abstraction mechanism is the function (and I found the xkcd really annoying because it completely missed the point), than which there is no better mechanism for the separation of concerns. TCO is not required (witness CL's DO notation), nor are a statically determined types which are enforced at compile-time (e.g. every Lisp ever). And w/rt TCO, I'm not sure that concept even makes sense for a normal-order reduction system like Haskell. Normal order reduction is closer to a dataflow graph traversal than a stack machine...