horribly awful clojure code

permutations.clj

(defn decrement-char-count [char-map character]
  (let [new-char-map (assoc char-map character (dec (get char-map character 0)))]
    [(new-char-map character) new-char-map]))

(defn make-char-map [string]
  (reduce (fn [char-map character] (assoc char-map character (inc (get char-map character 0)))) {} (seq string)))

(defn permutation? [str1 str2]
  "return true if str2 can be formed by some permutation of str1, false otherwise"
  (let [str1-map (make-char-map str1)]
    (loop [characters (seq str2)
           char-map str1-map]
      (if (not (seq characters))
        true
        (let [[char-count new-char-map] (decrement-char-count char-map (first characters))]
          (if (< 0 char-count)
            false
            (recur (rest characters) new-char-map)))))))