fullhouse

(defn n-of-a-kind ;untested
  [n cards]
  (let [ranked (vals (group-by :rank cards)),
        candidates (filter #(>= (count %) n) ranked),
        highest (max-by #(:rank (first c)) candidates)]
    {:cards (take n highest), :remaining candidates}))

;untested
(def pair (partial n-of-a-kind 2))
(def triple (partial n-of-a-kind 2))

(def fullhouse4 ;untested
  [cards]
  (when-let [{t :cards, remaining :remaining} (triple cards)]
    (when-let [{p :cards} (pair remaining)]
      (compose t p))))