I'm not sure I see the benefits here unless you are buying completely in to: Emacs, and Java and ignoring performance/overhead. Closure is implemented in Java; and the only apparent way to write it is via Emacs. The zero-eth issue I see: functional programming espouses absolutely no side effects, meaning no capability of handling network of physical I/O errors The implementation being in Java means that it is not possible to use it in embedded environments (which might not be a problem for some users) but it does mean that performance is JVM limited. Personally, I find the requirement of Emacs to be QUITE odious. In my opinion, Emacs is an OS/environment and not an editor. I'll use it if I want to edit a binary, but when an editor includes a psychotherapist mode (Eliza) it is not suitable for software development. I have also seen some quite talented researchers/engineers spend multiple seconds trying to remember the sequence to do X in Emacs, when it would have taken FAR less time in vi or vim. Too many parentheses make the code UNMAINTAINABLE in a production environment.