[rplacd]

The sole fact that one has to reach over themselves and make a great deal to invoke it when thinking within Clojure's mechanics - they become neither cheap to mentally fiddle around with, nor actually implement within.

(FWIW, though, Clojure's novelty to me was an STM system that I could get up and running without a night's worth of tweaking, and otherwise fall safely into a great deal of attention if something were to go hilariously wrong - most of the other solutions around "back then" seemed to regard themselves as research curios lagging behind in fit and finish.)