distinct(clojure.core)

Returns a lazy sequence of the elements of coll with duplicates removed

; clojure/core.clj:3010
(defn distinct
  [coll]
    (let [step (fn step [xs seen]
                   (lazy-seq
                    ((fn [[f :as xs] seen]
                      (when-let [s (seq xs)]
                        (if (contains? seen f) 
                          (recur (rest s) seen)
                          (cons f (step (rest s) (conj seen f))))))
                     xs seen)))]
      (step coll #{})))

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