Clojure 如何解析postwalk表单参数

我不知道为什么会打印出下面的内容

>(use 'clojure.walk)
>(def thing {:page/tags [{:tag/category "lslsls"}]})

>(postwalk #(println %) thing)
:page/tags
:tag/category
lslsls
[nil nil]
{}
[nil]
[nil nil]
{}
=> nil

---

因为我是Clojure的新手，也许我错过了什么。任何帮助都将不胜感激

你可能已经预料到了

[nil nil]
{}
[nil]
[nil nil]
{}

由于walks会替换每个子窗体所用函数的返回值，因此在打印子窗体后需要返回该子窗体的副本，如中所示

user=> (clojure.walk/postwalk-demo thing)
Walked: :page/tags
Walked: :tag/category
Walked: "lslsls"
Walked: [:tag/category "lslsls"]
Walked: {:tag/category "lslsls"}
Walked: [{:tag/category "lslsls"}]
Walked: [:page/tags [{:tag/category "lslsls"}]]
Walked: {:page/tags [{:tag/category "lslsls"}]}
{:page/tags [{:tag/category "lslsls"}]}

---

从doc

使用f的返回值代替原始的

，您的f是println，它返回nil

user=> (source clojure.walk/postwalk-demo)
(defn postwalk-demo
  "Demonstrates the behavior of postwalk by printing each form as it is
  walked.  Returns form."
  {:added "1.1"}
  [form]
  (postwalk (fn [x] (print "Walked: ") (prn x) x) form))