Generate deterministic type-4 UUIDs with Clojure's test.check

uuid.clj

(require '[clojure.string :as str])
(require '[clojure.test.check.generators :as gen])

(def gen-hex-char
  (gen/elements (concat (map char (range (int \a) (int \f)))
                        (range 0 9))))

(defn gen-hex-string [len]
  (gen/fmap str/join (gen/vector gen-hex-char len len)))

(def gen-uuid
  (->> (gen/tuple (gen-hex-string 8)
                  (gen/return "-")
                  (gen-hex-string 4)
                  (gen/return "-4")
                  (gen-hex-string 3)
                  (gen/return "-a")
                  (gen-hex-string 3)
                  (gen/return "-")
                  (gen-hex-string 12))
       (gen/fmap str/join)
       (gen/fmap (fn [xs] (java.util.UUID/fromString (apply str xs))))))

I found it easier to do this:

(gen/fmap (fn [[a b]] (UUID. a b)) (gen/resize Long/MAX_VALUE (gen/tuple gen/int gen/int)))

I like the use of least and most significant bytes; that's definitely an improvement over messing around with strings. I need to make a few tweaks to the "easier" version to avoid producing irregular UUIDs:

(def eraserhd-uuid
  (gen/fmap (fn [[a b]] (UUID. a b))
            (gen/resize Long/MAX_VALUE (gen/tuple gen/int gen/int))))

(map #(.version ^java.util.UUID %) (gen/sample eraserhd-uuid))
(9 11 14 13 11 14 6 8 14 12)