defactions.clj

(defmacro defactions
  "Takes a list of function symbols and defines atom-swapping versions of each."
  [& syms]
  `(do ~@(for [sym syms
               :let [bang (-> (name sym) (str "!") symbol)]]
           `(def ~(with-meta bang
                    {:arglists (->> (resolve sym) meta :arglists
                                    (map (fn [xs] (into ['state-atom] xs)))
                                    (cons 'quote))})
              (fn [state# & args#]
                (apply swap! state# ~sym args#))))))