clojure - 减少递归搜索的代码行数

Question

减少我用 Lisp/Clojure 编写的代码行数已成为我的痴迷。我正在尝试使以下代码(本质上是深度优先搜索)更短。




(defn find-node [nodeid in-node]
 (if (= nodeid (:id in-node))
 in-node
 (loop [node nil activities (:activities in-node)]
 (if (or (empty? activities) (not (nil? node)))
 node
 (recur (find-node nodeid (first activities)) (rest activities))))))

(defn find-node-in-graph [nodeid node activities]
 (if (empty? activities)
 node
 (recur nodeid (find-node nodeid (first activities)) (rest activities))))

(defrecord Graph [id name activities])
(defrecord Node [id name activities])

“事件”是一个列表

Answer 1

这可能是作弊，尽管它只有一行；)

(def tree {:id 1 :children [{:id 2 :children [{:id 3}]} {:id 4}]})

core> (filter #(= 3 (:id %)) (tree-seq :children :children tree)) 
({:id 3}) 

core> (filter #(= 2 (:id %)) (tree-seq :children :children tree))
({:children [{:id 3}], :id 2})

关于问题初衷的几点:

loop/recer 通常不是最紧凑的形式，它通常写成 map或 doseq

if/recur 通常可以替换为对 filter 的调用

如果您似乎因为某些特定要求而确实需要写这样的东西，通常是 zippers会更优雅地解决问题。