Haskell：比较NaN值 [英] Haskell: comparing NaN values

问题描述

我写了 quickcheck 测试一个Haskell程序，该程序可以优化和评估函数。 =https://hackage.haskell.org/package/QuickCheck-2.8.1/docs/Test-QuickCheck.html =nofollow> quickcheck 生成表达式，导致 NaN 类似：

 > acos（2）
 NaN 
  

Haskell将以下语句计算为false：

 > acos（2）== acos（2）
 False 
  

所以我 quickcheck 测试通过此比较失败。
是否有任何方法可以比较 NaN 值？

解决方案

否，如 IEEE 754 所定义2 NaN s总是返回false。如果你的值在Haskell中是 NaN ，你可以使用 isNaN 方法或自行编写

  isNaN':: a  - > Bool 
 isNaN'a = a / = a 
  

I wrote quickcheck tests for a Haskell program that optimizes and evaluates a function.

The problem is quickcheck generates expressions resulting in NaN like:

> acos(2)
NaN

Haskell evaluates the following statement as false:

> acos(2)==acos(2)
False

So my quickcheck tests fail with this comparison. Is there any way to compare NaN values?

解决方案

No, as is defined by IEEE 754 comparing 2 NaNs always return false. To chceck if your value is NaN in Haskell you can use isNaN method or write it by yourself

isNaN' :: a -> Bool
isNaN' a = a /= a

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