Set

(deftype Set [meta hash-map]
  IWithMeta
  (-with-meta [coll meta] (Set. meta hash-map))

  IMeta
  (-meta [coll] meta)

  ICollection
  (-conj [coll o]
    (Set. meta (assoc hash-map o nil)))

  IEmptyableCollection
  (-empty [coll] (with-meta cljs.core.Set/EMPTY meta))

  IEquiv
  (-equiv [coll other]
    (and
     (set? other)
     (= (count coll) (count other))
     (every? #(contains? coll %)
             other)))

  IHash
  (-hash [coll] (hash-coll coll))

  ISeqable
  (-seq [coll] (keys hash-map))

  ICounted
  (-count [coll] (count (seq coll)))

  ILookup
  (-lookup [coll v]
    (-lookup coll v nil))
  (-lookup [coll v not-found]
    (if (-contains-key? hash-map v)
      v
      not-found))

  ISet
  (-disjoin [coll v]
    (Set. meta (dissoc hash-map v)))

  IFn
  (-invoke [coll k]
    (-lookup coll k))
  (-invoke [coll k not-found]
    (-lookup coll k not-found)))