The fact that you have to use the sentence : "I would say that map being variadic on the set-of-things-being-mapped, and + being variadic on the set-of-things-

The fact that you have to use the sentence : "I would say that map being variadic on the set-of-things-being-mapped, and + being variadic on the set-of-things-to-add, is more of a "semantic axiom of the language" than plain-old DSL-esque "magic." When you debate about any LISP based language is usually my clue.