I used Merlin pretty extensively, yet this example had me sitting there with an open mouth, staring in awe.

The funniest thing is that in my experience Merlin just seems to work. When I think about how many hoops I need to jump through with the Clojure REPL to connect it to CIDER in Emacs, Merlin just works in the background without me having to think about it at all. Very impressive.