为什么在 Clojure 中使用种子时不会重复生成可重复的随机数? [英] Why doesn't repeatedly generate reproducible random numbers when using a seed in Clojure?

问题描述

我有一些需要一系列随机数的函数，所以我采用了一些简单的原语，例如 #(inc (g/uniform 0 n)) 并且我似乎无法生成一系列可重复的随机数，即使我重新绑定 *rnd*，除非我按如下所示生成它们.我无法想象这是最好的方法，所以有人能指出如何做得更好吗?

I have some functions that require a series of random numbers so I've taken some simple primitives such as #(inc (g/uniform 0 n)) and I can't seem to generate a reproducible series of random numbers, even though I'm rebinding *rnd*, unless I generate them as shown below. I can't imagine that's the best way, so can anyone point out how to do it better?

注意:我将下面的每个示例运行三次，如图所示，以产生给定的结果.

Note: I run each example below three times as shown to produce the given results.

(ns example.show
  (:require [clojure.data.generators :as g]))


(binding [g/*rnd* (java.util.Random. 42)]
  (take 10 (repeatedly #(inc (g/uniform 0 n))))

=> (9 4 5 4 4 5 1 8 2 9)

=> (2 1 1 6 3 10 10 4 1 9)

=> (10 4 7 8 9 6 10 1 8 3)


(binding [g/*rnd* (java.util.Random. 42)]
  (g/reps 10 #(inc (g/uniform 0 n)))

=> (3 9 4 6 3 8 6 6 5 4)

=> (7 8 4 7 7 5 7 4 8 7)

=> (2 8 7 8 8 8 9 2 6 5)

;; This seems to work
(binding [g/*rnd* (java.util.Random. 42)]
  (letfn [(roll [n] #(inc (g/uniform 0 n)))]
    [((roll 10)) ((roll 10)) ((roll 10)) ((roll 10)) ((roll 10)) ((roll 10)) ((roll 10)) ((roll 10)) ((roll 10)) ((roll 10))]))

=> [8 7 4 3 7 10 4 3 5 8]

=> [8 7 4 3 7 10 4 3 5 8]

=> [8 7 4 3 7 10 4 3 5 8]

推荐答案

因为懒惰.您在序列实现之前从 binding 返回.因此，惰性序列永远不会看到您设置的绑定.一种解决方案是在绑定内的序列上使用 doall 强制实现.

Because of laziness. You return from binding before the sequence is realized. Therefore, the lazy sequence never sees the bindings you set. One solution would be to force realization with a doall on the sequence inside the binding.

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