macros - 如何使用 `clojure.tools.macro/name-with-attributes` ？

Question

我发现对于任何在 clojure.tools.macro 中编写类似 defn 的宏的人来说，这将是一个很棒的工具。图书馆:name-with-attributes功能。文档字符串说:

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.

但我似乎找不到在任何地方使用此函数的示例。

那么，我如何使用这个函数来定义一个 defn2 宏，它应该是包含所有相同内容的 clojure.core/defn 的克隆功能，包括:

• 文档字符串
• 属性映射
• 先决条件
• 多方面

Answer 1

这是defn2:

(require '[clojure.tools.macro :as ctm])

(defmacro defn2
  "A clone of `defn`."
  [symb & defn-args]
  (let [[symb body] (ctm/name-with-attributes symb defn-args)]
    `(defn ~symb ~@body)))

查看元数据，我们可以看到它已正确附加:

(defn2 ^:private add
       "Docstring"
       ([] :foo)
       ([a b] {:pre [(= 1 1)]} (+ a b)))

(pprint (meta #'add))

...产量:

{:arglists ([] [a b]),
 :ns #<Namespace user>,
 :name add,
 :column 1,
 :private true,
 :doc "Docstring",
 :line 1,
 :file
 "/private/var/folders/30/v73zyld1359d7jb2xtlc_kjm0000gn/T/form-init8938188655190399857.clj"}

使用上面的 defn2 创建了一个 add 函数，其工作方式如下:

(add)     ; => :foo
(add 1 2) ; => 3