错误数量的参数 (0) 传递给:循环/重复函数上的 PersistentVector [英] Wrong number of args (0) passed to: PersistentVector on loop/recur function

问题描述

尝试定义一个 factors 函数，该函数将使用 loop/recur 返回一个数字的所有因子的向量.

<代码>;;`prime?` 借自 https://swizec.com/blog/comparing-clojure-and-node-js-for-speed/swizec/1593(定义素数?[n](如果(甚至?n)假(让 [root (num (int (Math/sqrt n)))](loop [i 3] (if (> i root) true(如果(零?(mod n i))假(重复 (+ i 2)))))))))(定义因子 [x] ((循环 [n x i 2 acc []](if (prime? n) (conj acc n)(if (zero? (mod n i)) (recur (/n i) 2 (conj acc i))(recur n (inc i) acc))))))

但我一直遇到以下错误:

ArityException 错误数量的 args (0) 传递给:PersistentVector clojure.lang.AFn.throwArity

我一定在这里遗漏了一些明显的东西.非常感谢任何建议！

解决方案

让我移动你代码中的空格，这样你就可以明显看出哪里出了问题:

(定义因子 [x]((循环 [n x i 2 acc []](if (prime? n) (conj acc n)(if (zero? (mod n i)) (recur (/n i) 2 (conj acc i))(recur n (inc i) acc))))))

你在函数的开头看到了奇怪的 (( ?那是什么?记住在 Clojure 中，就像在一般的 lisps 中一样，括号不是分组结构!它们是一个函数调用机制，你不能随便乱加东西.这里，你写的意思如下:

<块引用>

1. 运行这个 loop 来计算一个向量.
2. 将结果值作为函数调用，不传递参数.

Trying to define a factors function that will return a vector of all the factors of a number using loop/recur.

;; `prime?` borrowed from https://swizec.com/blog/comparing-clojure-and-node-js-for-speed/swizec/1593

(defn prime? [n]
  (if (even? n) false
      (let [root (num (int (Math/sqrt n)))]
        (loop [i 3] (if (> i root) true
                        (if (zero? (mod n i)) false
                            (recur (+ i 2))))))))

(defn factors [x] (
  (loop [n x i 2 acc []]
    (if (prime? n) (conj acc n)
        (if (zero? (mod n i)) (recur (/ n i) 2 (conj acc i))
            (recur n (inc i) acc))))))

But I keep running into the following error:

ArityException Wrong number of args (0) passed to: PersistentVector clojure.lang.AFn.throwArity

I must be missing something obvious here. Any suggestions are much appreciated!

解决方案

Let me move the whitespace in your code so it's obvious to you what is wrong:

(defn factors [x] 
  ((loop [n x i 2 acc []]
     (if (prime? n) (conj acc n)
         (if (zero? (mod n i)) (recur (/ n i) 2 (conj acc i))
             (recur n (inc i) acc))))))

You see that weird (( at the start of your function? What's that all about? Remember that in Clojure, as in lisps in general, parentheses are not a grouping construct! They are a function-call mechanism, and you can't just throw extras in for fun. Here, what you wrote has the following meaning:

1. Run this loop that will compute a vector.
2. Call the resulting value as a function, passing it no arguments.

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