ClojureDocs - clojure.contrib.def/name-with-attributes

;; Here I use name-with-attributes to create a macro writing
;; macro defmacro! that accepts the same args as defmacro itself,
;; i.e., an optional docstring and an optional metadata map.
;; (In contrast to defmacro, overloading is not supported.)

;; Only a helper...
(defn bang-symbol?
  "Returns true, if sym is a symbol with name ending in a exclamation
  mark (bang)."
  [sym]
  (and (symbol? sym)
       (= (last (name sym)) \!)))

(defmacro defmacro!
  "Defines a macro name with the given docstring, args, and body.
  All args ending in an exclamation mark (!, bang) will be evaluated
  only once in the expansion, even if they are unquoted at several
  places in body.  This is especially important for args whose
  evaluation has side-effecs or who are expensive to evaluate."
  {:arglists '([name doc-string? attr-map? [params*] body])}
  [name & args]
  (let [[name attrs] (tm/name-with-attributes name args)
        meta-map     (meta name)
        args         (first attrs)
        body         (next attrs)
        bang-syms    (filter bang-symbol? (flatten args))
        rep-map      (apply hash-map
                            (mapcat (fn [s] [s `(quote ~(gensym))])
                                    bang-syms))]
    `(defmacro ~name
       ~@(when (seq meta-map) [meta-map])
       ~args
       `(let ~~(vec (mapcat (fn [[s t]] [t s]) rep-map))
          ~(clojure.walk/prewalk-replace ~rep-map ~@body)))))

(defn name-with-attributes "To be used in macro definitions. Handles optional docstrings and attribute maps for a name to be defined in a list of macro arguments. If the first macro argument is a string, it is added as a docstring to name and removed from the macro argument list. If afterwards the first macro argument is a map, its entries are added to the name's metadata map and the map is removed from the macro argument list. The return value is a vector containing the name with its extended metadata map and the list of unprocessed macro arguments." [name macro-args] (let [[docstring macro-args] (if (string? (first macro-args)) [(first macro-args) (next macro-args)] [nil macro-args]) [attr macro-args] (if (map? (first macro-args)) [(first macro-args) (next macro-args)] [{} macro-args]) attr (if docstring (assoc attr :doc docstring) attr) attr (if (meta name) (conj (meta name) attr) attr)] [(with-meta name attr) macro-args]))

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name-with-attributes

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Source clojure/contrib/def.clj:96 top

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