Compute all permutations of a collection in Clojure (non-lazy, iterative)

permutations.clj

(defn permutations [coll]
  (letfn [(rotations [c vs] (reduce (fn [rotations _]
                                        (conj rotations
                                              (let [[head & tail] (peek rotations)]
                                                (conj (vec tail) head))))
                                      [(conj vs c)]
                                      vs))]
    (cond-> (reduce (fn [permutations c] (mapcat (partial rotations c) permutations))
                    [[]]
                    coll)
      (not (or (set? coll) (apply distinct? coll))) distinct)))
;; Examples
;; > (permutations [1 2 3])
;;([1 2 3] [2 3 1] [3 1 2] [2 1 3] [1 3 2] [3 2 1])
;; > (permutations [1 1 3])
;;([1 1 3] [1 3 1] [3 1 1])