Enumerate paths into a nested map

paths.clj

;; Copyright (c) Alan Dipert. All rights reserved.
;; The use and distribution terms for this software are covered by the
;; Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
;; By using this software in any fashion, you are agreeing to be bound by
;; the terms of this license.
;; You must not remove this notice, or any other, from this software.

(defn paths
  "Enumerate paths into a nested map."
  ([root]
   (when (map? root)
     (paths [] root)))
  ([parent x]
   (if (map? x)
     (mapcat (fn [[k v]] (paths (conj parent k) v)) x)
     [parent])))

(def m
  {:q {:z 1}
   :x {:y {:a 1}
       :b {:b 2}}})

(paths m) ;=> ([:q :z] [:x :y :a] [:x :b :b])

(reduce #(update-in %1 %2 dec) m (paths m))
;=> {:q {:z 0}, :x {:y {:a 0}, :b {:b 1}}}