sub-list-merge

(ns user)

; The empty room
(def room {:id "room1" :people []})

; People to add to the room
(def p1 {:id 1 :name "john"})
(def p2 {:id 2 :name "sam"})

; Adding people to the room
(defn join-rm [room person]
  (let [people (:people room)]
    (merge room {:people (merge people person)})))

(def room' (join-rm room p1))
(join-rm room' p2)