Generate all the len length sequences with elements from xs #clojure

selections.clj

(defn selections [xs len]
  (if (zero? len)
      [[]]
      (mapcat (fn [pd] (map #(conj pd %) xs))
              (selections xs (dec len)))))

(defn selections-with-all [xs len]
  (filter #(= (set %) (set xs)) (permu xs len)))