# tagged literal

Some frequently used value types are afforded a "tagged literal" syntax. It is similar to a constructor, but this special syntax makes it de/serializable and easier to read at the REPL.

Tagged literals start with a # followed by a symbol and a literal:

• #js [...] - JavaScript array literal
• #js {...} - JavaScript object literal
• #inst "..." - JavaScript date literal
• #uuid "..." - UUID literal
• #queue [...] - queue literal

These tagged literals are the "extensible" part of extensible data notation (edn), with ClojureScript being a superset of edn.

(Tagged literals are printed as themselves, just like core syntax literals.)

literal JavaScript object:

#js {:foo 1}
;;=> #js {:foo 1}

(def foo 1)
#js {:foo foo}
;;=> #js {:foo 1}

literal queue:

#queue [1 2 3]
;;=> #queue [1 2 3]

(conj #queue [1 2 3] 4)
;;=> #queue [1 2 3 4]

literal instant of time (date):

#inst "2014-10-13"
;;=> #inst "2014-10-13T00:00:00.000-00:00"

literal UUID:

#uuid "97bda55b-6175-4c39-9e04-7c0205c709dc"
;;=> #uuid "97bda55b-6175-4c39-9e04-7c0205c709dc"

Reader code @ tools.reader:src/main/clojure/clojure/tools/reader.clj

(defn- read-tagged [rdr initch opts pending-forms]
  (let [tag (read* rdr true nil opts pending-forms)]
    (if-not (symbol? tag)
      (err/throw-bad-reader-tag rdr tag))
    (if *suppress-read*
      (tagged-literal tag (read* rdr true nil opts pending-forms))
      (if-let [f (or (*data-readers* tag)
                     (default-data-readers tag))]
        (f (read* rdr true nil opts pending-forms))
        (if (.contains (name tag) ".")
          (read-ctor rdr tag opts pending-forms)
          (if-let [f *default-data-reader-fn*]
            (f tag (read* rdr true nil opts pending-forms))
            (err/throw-unknown-reader-tag rdr tag)))))))