clojure的快乐,宏

Question

我一直在经历clojure练习的喜悦,并且遇到了这个例子

(defn build-contract [c]
    (let [args (first c)]
      (list
       (into '[f] args) ;; here is where i am confused
       (apply merge
              (for [con (rest c)]
                (cond (= (first con) :require)
                      (assoc {} :pre (vec (rest con)))
                      (= (first con) :ensure)
                      (assoc {} :post (vec (rest con)))
                      :else (throw (Exception. (str "Unkown tag " (first con)))))))
       (list* 'f args)))) ;; and here

  (defn collect-bodies [forms]
    (for [form (partition 3 forms)]
      (build-contract form)))

  (defmacro contract [cg & forms]
    (list* `fn cg (collect-bodies forms)))

我似乎无法理解你为什么要在那个向量中使用一个名为f的符号.符号是对事物的引用,那么将引用什么？为什么我们需要参考它？

Answer 1

宏构建函数文字表达式(fn表单).

(into '[f] args) ;; here is where i am confused

这是参数向量.这里f出现的是正式论证的角色.

(list* 'f args)))) ;; and here

这是功能应用.f是一个函数参数,这里它适用于args.

构建时,生成的定义将如下所示.

(fn name [f arg1 arg2] ... (f arg1 arg2))