(def article-validations [validate-word-count])
(def photo-validations (conj article-validations validate-total-weight validate-copyright))

(def type->validations
  {:base article-validations
   :photo photo-validations})

(defn validate [article]
  (reduce (fn [[article validation-data] validator] (merge validation-data (validator article)))
          [article {}]
          (get type->validations (:type article) article-validations)))