如何在Clojure中创建一个最多执行N次操作的函数？(How can I make a function that execute another function at most N times

如何在Clojure中创建一个最多执行N次操作的函数？(How can I make a function that execute another function at most N times in Clojure?)

首先，我有一个像这样的Mysql表：

create table t (id int(11) PRIMARY KEY unsigned NOT NULL AUTO_INCREMENT, name varchar(20), age int(10));

我定义了一个在t中创建一行的函数：

(require '[honeysql.core :as sql]) (defn do-something [] (sql/query {:insert-into :t :values [{:name "name1" :age 10}]}) (> 3 (rand-int 5)))

现在我想运行这个函数，直到它返回true但最多N次。

这个take-times代码是错误的，因为重复将eval do-something函数一次，然后构造惰性序列。

(defn take-times [] (some true? (repeat 5 (do-something))))

无论什么do-something回归，这个take-times2将评估5次。

(defn take-times2 [] (some true? (for [i (range 5)] (do-something))))

如果我不使用递归函数和宏，我该怎么办？

First of All, I have a Mysql table like this:

create table t (id int(11) PRIMARY KEY unsigned NOT NULL AUTO_INCREMENT, name varchar(20), age int(10));

I define a funtion that will create a row in t:

(require '[honeysql.core :as sql]) (defn do-something [] (sql/query {:insert-into :t :values [{:name "name1" :age 10}]}) (> 3 (rand-int 5)))

And now I want to run this function until it return true but at most N times.

This take-timescode is wrong because repeat will eval the do-something function one time and then structure the lazy sequence.

(defn take-times [] (some true? (repeat 5 (do-something))))

This take-times2 will eval the do-something 5 times no matter what the do-something return.

(defn take-times2 [] (some true? (for [i (range 5)] (do-something))))

What should I do if i do not use recursion function and macro?

最满意答案

这应该工作：

(->> (repeatedly do-something) (take 5) (some true?))

更新（04.11.2014）：

由于repeatedly实际允许可选的长度参数，这也很好：

(some true? (repeatedly 5 do-something))

---

例

(defn do-something [] ;; 20% chance of true (let [ret (rand-nth [true false false false false])] (prn 'hello ret) ret)) (defn run [] (->> (repeatedly do-something) (take 5) (some true?))) (run) ;; hello false ;; hello false ;; hello true ;; => true (run) ;; hello false ;; hello false ;; hello false ;; hello false ;; hello false ;; => nil

This should work:

(->> (repeatedly do-something) (take 5) (some true?))

Update (04.11.2014):

Since repeatedly actually allows for an optional length parameter, this is also fine:

(some true? (repeatedly 5 do-something))

---

Example

(defn do-something [] ;; 20% chance of true (let [ret (rand-nth [true false false false false])] (prn 'hello ret) ret)) (defn run [] (->> (repeatedly do-something) (take 5) (some true?))) (run) ;; hello false ;; hello false ;; hello true ;; => true (run) ;; hello false ;; hello false ;; hello false ;; hello false ;; hello false ;; => nil