Haskell 标识符中的撇号 [英] Apostrophe in identifiers in Haskell

问题描述

我发现这段代码在互联网上被截断了:

I found this code snipped on the internet:

digits 0 = [0]
digits n = digits' n []
  where digits' 0 ds = ds
        digits' n ds = let (q,r) = quotRem n 10
                       in digits' q (r:ds)

sumOfDigits = sum . digits

有人能快速解释一下递归函数调用后的'"符号( digits n = digits' n [] )是干什么用的?我在 Haskell(教程)中看到了一些其他的代码示例，但我不明白这个.一个快速的解释表示赞赏.

Can someone quickly explain what the " ' " sign ( digits n = digits' n [] ) after the recursive function call is for? I've seen some other code examples in Haskell (tutorials), but im not understandig this one. A quick explanation is appreciated.

推荐答案

撇号只是名称的一部分.它是 Haskell 中采用的命名约定(惯用语).

The apostrophe is just part of the name. It is a naming convention (idiom) adopted in Haskell.

Haskell 中的约定是，就像在数学中，撇号变量名上的变量表示与先前变量有某种关联或相似的变量.

The convention in Haskell is that, like in math, the apostrophe on a variable name represents a variable that is somehow related, or similar, to a prior variable.

示例:

let x  = 1
    x' = x * 2
in x'

x' 与 x 相关，我们用撇号表示.

x' is related to x, and we indicate that with the apostrophe.

顺便说一下，你可以在 GHCi 中运行它，

You can run this in GHCi, by the way,

Prelude> :{ 
Prelude| let x  = 1
Prelude|     x' = x * 2
Prelude| in x'
Prelude| :}
2

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