Lazily remove duplicate members of list, by predicate "hashing" function on members

distinct-p.clj

(defn distinct-p
  ([pred coll]
   (distinct-p pred coll #{}))
  ([pred coll seen]
   (if (empty? coll)
     '()
     (lazy-seq
        (let [next (first coll)
              key (pred next)
              is-dup (contains? seen key)
              recurred (distinct-p pred (rest coll) (if is-dup seen (conj seen key)))]
          (if is-dup
            recurred
            (cons next recurred)))))))

Example:

(distinct-p :id [{:id 1 :v "one"} {:id 2 :v "two"} {:id 1 :v "another 1"}])
;; -> ({:id 1, :v "one"} {:id 2, :v "two"})