cljs.repl/merge-require

(defn merge-require [requires [lib :as spec]]
  (let [[before [match & after]]
        (split-with
          (fn [[lib' & _]]
            (not= lib lib'))
          requires)]
    (if (nil? match)
      ;; no match, append to end
      (concat requires [spec])
      (if (= match spec)
        ;; dupe
        requires
        ;; merge
        (concat before [(merge-spec match spec)] after)))))