: keyword

syntaxsince v0.0-1853 in clojure in ednEdit

A keyword starts with a colon and evaluates to itself. It can include an optional namespace.

  • :bar
  • :foo/bar


Keywords are often used as enums or keys for maps. Keywords should not start with a number.

Keywords can have an optional namespace. For example, :foo/bar. This is useful for functions in a namespace to prevent key collisions on a globally accessible map.


;;=> :foo

;;=> :a/foo

A keyword is also callable for retrieving values from a map:

(def m {:foo 1})
(:foo m)
;;=> 1

(def things [{:foo 1 :bar 2}
             {:foo 3 :bar 4}
             {:foo 5 :bar 6}])
(map :foo things)
;;=> (1 3 5)

See Also:

Reader code @ tools.reader:src/main/clojure/clojure/tools/reader.clj
(defn- read-keyword
  [reader initch opts pending-forms]
  (let [ch (read-char reader)]
    (if-not (whitespace? ch)
      (let [token (read-token reader :keyword ch)
            s (parse-symbol token)]
        (if s
          (let [^String ns (s 0)
                ^String name (s 1)]
            (if (identical? \: (nth token 0))
              (if ns
                (let [ns (resolve-alias (symbol (subs ns 1)))]
                  (if ns
                    (keyword (str ns) name)
                    (err/throw-invalid reader :keyword (str \: token))))
                (keyword (str *ns*) (subs name 1)))
              (keyword ns name)))
          (err/throw-invalid reader :keyword (str \: token))))
      (err/throw-single-colon reader))))

Reader table @ tools.reader:src/main/clojure/clojure/tools/reader.clj
(defn- macros [ch]
  (case ch
    \" read-string*
    \: read-keyword
    \; read-comment
    \' (wrapping-reader 'quote)
    \@ (wrapping-reader 'clojure.core/deref)
    \^ read-meta
    \` read-syntax-quote ;;(wrapping-reader 'syntax-quote)
    \~ read-unquote
    \( read-list
    \) read-unmatched-delimiter
    \[ read-vector
    \] read-unmatched-delimiter
    \{ read-map
    \} read-unmatched-delimiter
    \\ read-char*
    \% read-arg
    \# read-dispatch