functionsince v1.9.946 clojure.core/swap-vals!Edit
(swap-vals! a f)
(swap-vals! a f x)
(swap-vals! a f x y)
(swap-vals! a f x y & more)

Source docstring:
Atomically swaps the value of atom to be:
(apply f current-value-of-atom args). Note that f may be called
multiple times, and thus should be free of side effects.
Returns [old new], the value of the atom before and after the swap.
Source code @ clojurescript:src/main/cljs/cljs/core.cljs
(defn swap-vals!
  {:added "1.9"}
  ([a f]
   (if (instance? Atom a)
     (reset-vals! a (f (.-state a)))
     [(-deref a) (-swap! a f)]))
  ([a f x]
   (if (instance? Atom a)
     (reset-vals! a (f (.-state a) x))
     [(-deref a) (-swap! a f x)]))
  ([a f x y]
   (if (instance? Atom a)
     (reset-vals! a (f (.-state a) x y))
     [(-deref a) (-swap! a f x y)]))
  ([a f x y & more]
   (if (instance? Atom a)
     (reset-vals! a (apply f (.-state a) x y more))
     [(-deref a) (-swap! a f x y more)])))