Oxford Comma

oxford.clj

(defn oxford-comma [phrases]
  (if (> (count phrases) 2)
    (join ", and " [(join ", " (butlast phrases)) (last phrases)])
    (join " and " phrases)))

(oxford-comma []) ;; => ""
(oxford-comma ["one"]) ;; => "one"
(oxford-comma ["one" "two"]) ;; => "one and two"
(oxford-comma ["one" "two" "three"]) ;; => "one, two, and three"
(oxford-comma ["one" "two" "three" "four"]) ;; => "one, two, three, and four"