Clojure 1

(defn
  #^{ :test (fn []
          (assert (= "a=>b" (arr 'a 'b)))
          (assert (= "a=>b" (arr "a" "b"))))}
  arr
  "Delimits an arrow between two values.  Good for autogeneration of
converter functions."
  [a b]
  (str-join "=>" [a b]))