macros - 如何使用 defmacro 简化一些代码

Question

我写了两个这样的函数，但是正如你所看到的，它们的大部分是相同的，所以我想写一个宏来简化它们。

我看懂了教科书上的简单宏示例，但我不知道如何编写自己的示例。

这是我的代码:

 (defn load-dict
       ;  "Load database from a txt file previous saved"
       [fname]
       (with-open [rdr (io/reader fname)]
                  (doseq [line (line-seq rdr)]
                         (println line)
                         (def vvv (clojure.string/split line #"\s"))
                         ;(println (str "count of vvv is " (count vvv)))
                         (if (< 1 (count vvv))
                           (add- dict (gen-word (nth vvv 0) (nth vvv 2) (nth vvv 1))))
                         )))
 (defn load-article
       ;  "Load article from a txt file"
       [fname]
       (with-open [rdr (io/reader fname)]
                  (doseq [line (line-seq rdr)]
                         (println line)
                         (def vvv (clojure.string/split line #"\s"))
                         ;(println (str "count of vvv is " (count vvv)))
                         (if (< 1 (count vvv))
                           (add- article vvv ))
                         )))

我应该写一个像这样的宏吗:

(defmacro load- [target fname &expr)
  `(... 
    (add- ~target expr)))

我其实不知道怎么写这样的宏。我只是讨厌重复的代码。

PS，牵引功能工作正常。我不关心变量，这是代码的一部分。

Answer 1

我会使用 let block 而不是 def。使用 def 将绑定(bind)一个 var 并在您的命名空间中定义 vvv。真的不需要宏。您可以像这样简化代码:

(defn load-from
   "Load database from a txt file previous saved"
   [fname load-fn]
   (with-open [rdr (io/reader fname)]
              (doseq [line (line-seq rdr)]
                     (println line)
                     (let [vvv (clojure.string/split line #"\s")]
                       (when (< 1 (count vvv))
                         (load-fn vvv))))))

然后像这样调用它

(load-from "myfile.txt" #(add- dict (apply gen-word (take 3 %))))
(load-from "myfile.txt" #(add- article %))