gistfile1.clj

(ns user)

(def users 
  (ref 
    {:by-name {}
     :by-id {}
     :next-id 0 })
  )

(defn create-user
  "Creates a user"
  [name]
  (dosync
    (let [new-user {:name name :id (@users :next-id)}]
      (alter users (conj @users {:next-id (+ 1 (@users :next-id))}))
      (commute users (conj @users {:by-name (conj (@users :by-name) {name new-user})}))
      (commute users (conj @users {:by-id (conj (@users :by-id) {(new-user :id) new-user})}))
      new-user)))

(def jonas (create-user "Jonas"))