Interning with Clojure

intern.clj

(defn intern-map
  [m]
  (let [val-set (set (vals m))]
    (into {} 
      (for [[k v] m]
        {k (val-set v)}))))

(defn make-duped-hashmap []
  (into {} 
    (for [k (range 10000000)]
      [k (vec (repeatedly 3 #(rand-int 10)))])))

(def a (make-duped-hashmap));4,939,276,440 bytes used
(def a nil);and do a full GC
(def a (intern-map (make-duped-hashmap)));493,937,040 bytes used