在Clojure中打印树的级别

Question

我已经环顾四周，我无法找到办法做到这一点。 我只想逐层打印一棵树。

所以'[a [b c]]会打印出来：

a
b c

Answer 1

如果我理解正确，这段代码应该有效：

(defn bf
  [root] 
  (if (vector? root)
    (let [roots (filterv (complement vector?) root)
          children (filterv vector? root)]
      (if-not (empty? children)
        (into [roots] (mapcat bf children))
        [roots]))
    root))

它不是懒惰的，它返回包含节点的向量向量，例如

(bf ['a ['b 'c] 'd ['e 'f]]) => [[a d] [b c] [e f]]

打印出来：

(let [xs (bf ['a ['b 'c] 'd ['e 'f]])]
   (doseq [line (map str/join xs)] ; you need to require [clojure.string :as str]
     (println line)))