Clojure: sort by multiple keys with different orderings

by-sorting.clj

;; https://www.reddit.com/r/Clojure/comments/ufa8e0/clojure_sort_by_multiple_keys_with_different/ 

(let [sort-fns-map {:asc (fn [a b] (. clojure.lang.Util compare a b))
                    :desc (fn [a b] (. clojure.lang.Util compare b a))}]
 (defn by [& keys-orderings]
   (fn [a b]
       (loop [[key ordering & keys-orderings] keys-orderings]
         (let [order ((get sort-fns-map ordering ordering) (key a) (key b))]
           (if (and (zero? order) keys-orderings)
             (recur keys-orderings)
             order))))))

(sort (by :birthyear :desc :surname :asc) [{:birthyear 1990 :surname "ertu"}
                                           {:birthyear 1992 :surname "ertu"}])

(sort (by :birthyear :desc :surname (fn [a b] (. clojure.lang.Util compare b a)))
  [{:birthyear 1990 :surname "ertu"}
   {:birthyear 1992 :surname "ertu"}])