permutations.clj

(declare permutations)

(defn permute [s x]
  (let [ps (permutations (remove (partial = x) s))]
    (map #(cons x %) ps)))

(defn permutations [s]
  (if (-> s (count) (= 1))
    (list s)
    (mapcat (partial permute s) s)))

;; => (permutations "abc")
;; ((\a \b \c) (\a \c \b) (\b \a \c) (\b \c \a) (\c \a \b) (\c \b \a))