调用map-function似乎没有做任何事情

问题描述

我有以下代码：

(defn remove-folder [file]
   (do
      (println "Called with file " (.getName file))
      (if (.isDirectory file)
          (do
           (println (.getName file) " is directory")
           (def children (.listFiles file))
           (println "Number of children " (count children))
           (map remove-folder children)
           (delete-file file)))
          (do
           (println (.getName file) " is file")
           (delete-file file)
          )))

我的问题是行（map remove-folder children）似乎不工作。在我的输出，我希望下来虽然文件夹结构，但它似乎保持在第一级。

My problem is that the line (map remove-folder children) doesn't seem to work. In my output I expect to travel down though the folderstructure but it seems to stay in the first level.

我想我已经犯了一些愚蠢的错误，但我现在花了几个小时，似乎没有更接近的解决方案。

I'll guess I have made some stupid misstake but I spent a few hours on it now and doesn't seem to get closer a solution.

推荐答案

正如@ponzao所说， map 是懒惰的。

As @ponzao said, map is lazy.

但是无论如何，我不认为使用 map 只是为了得到副作用和丢弃的结果是个好主意。我个人会使用 doseq ，因为它给我一个暗示，我期待副作用。

But anyway I don't think it's a good idea to use map just to get side effects and "drop" the result. Personally I would use doseq instead, because it gives a hint that I'm expecting side effects.

(defn remove-folder [file]
   (do
      (println "Called with file " (.getName file))
      (if (.isDirectory file)
          (do
           (println (.getName file) " is directory")
           (def children (.listFiles file))
           (println "Number of children " (count children))
           (doseq [c children]
             (remove-folder c))
           (delete-file file)))
          (do
           (println (.getName file) " is file")
           (delete-file file)
          )))

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