Haskell从数据类型中随机 [英] Haskell Random from Datatype

问题描述

对于Haskell来说，我很新。
我有一个数据类型：

  data句子= Prop Int 
 |没有句子
 |和[句子] 
 |或[语句] 
导出Eq 
  

我已经为它写了一个Show实例

然而，无论是否合理，我都希望能够生成一个随机的句子。
如何在Haskell中完成这项工作？

解决方案

随机数生成是不纯操作的典型示例，因为调用一个随机生成器两次当然会产生不同的结果 - Haskell的本性不允许这样做。

因此，您需要使用一个所谓的monad Gen a 代表一个随机生成器，运行时产生一个类型为 a 的值。 >

幸运的是，您可以将这些生成器以相当好的语法组合起来......

所以，你只需要一些库，它实现了这样一个生成器 - 现在我们开始吧。

  randomNo =无< $> randomSentence 
 randomProp = Prop< $>选择（1，10）
 [...] 
 
 randomSentence = oneOf [randomNo，randomProp，...] 
  

Im pretty new to Haskell. I have a datatype:

data Sentence= Prop Int
          | No Sentence
          | And [Sentence]
          | Or [Sentence]
          deriving Eq

I already wrote a Show instance for it

However, whether it makes sense or not, I would like to be able to generate a random Sentence. How can i accomplish this in Haskell?

解决方案

Random number generation is a typical example of an "impure" operation, since calling a random generator twice will of course yield different results - Haskell's nature disallows this.

Therefore, you need to use a so called monad Gen a that represents a random generator, that, when run, yields a value of type a.

Fortunately, you can combine these generators in a quite nice syntax ...

So, you just need some library that implements such a generator - and here we go.

randomNo   = No <$> randomSentence
randomProp = Prop <$> choose (1, 10) 
[...]

randomSentence = oneOf [randomNo, randomProp, ...]

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