listparse.clj

(def defaults {:a ["default-a"]
               :b ["default-b"]
               :c ["default-c"]
               :d ["default-d"]})

(def ex1 [:a 1 2 :b 4 5 :c :d])


(defn kw-ob [hm item]
  (if (keyword? item)
    (assoc hm :key item)
    (update-in hm [:result (:key hm)] conj item)))

(merge
  defaults
  (:result (reduce kw-ob {:key nil :result {}} ex1)))


(def output {:a [1 2]
             :b [4 5]
             :c ["default-c"]
             :d ["default-d"]})