如何强制严格评估一系列ByteString [英] How to force strict evaluation of a sequence of ByteString

问题描述

  import Data.Sequence（Seq，length）
 import Data .ByteString.UTF8（ByteString）
 
 type StringSeq = Seq ByteString 
  

I具有类型 StringSeq 的表达式，我想用 deepseq 强制执行严格的评估。所以我需要定义 NFData 的实例。我做了以下事情：

pre $ import Control.DeepSeq（NFData，deepseq）

实例NFData ByteString

实例NFData a => NFData（Seq a）其中
rnf s = rnf（长度s）


序列的长度来强制评估序列本身。这似乎工作，但这是正确的实施？有更好的吗？计算一个序列的长度是否会引入太多开销？计算长度是不够的，你需要计算正常形式的序列内容。我建议你使用来自 Control.Seq 的seqFoldable ，它允许你强制任何可折叠的结构。然后你可以简单地调用

  mySeq`使用`seqFoldable rdeepseq 
  

或定义

  instance NFData a => NFData（Seq a）其中
 rnf = seqFoldable rdeepseq 
  

I have the following Haskell type definition:

import Data.Sequence(Seq, length)
import Data.ByteString.UTF8(ByteString)

type StringSeq = Seq ByteString

I have expressions of type StringSeq for which I would like to force strict evaluation with deepseq. So I need to define instances of NFData. I did the following:

import Control.DeepSeq(NFData, deepseq)

instance NFData ByteString

instance NFData a => NFData (Seq a) where
  rnf s = rnf (length s)

So I compute the length of a sequence to force evaluation of the sequence itself. This seems to work but is this the correct implementation? Are there better ones? Does computing the length of a sequence introduce too much overhead?

解决方案

Computing length is not enough, you need to compute the normal forms of the content of a sequence. I suggest you to use seqFoldable from Control.Seq which allows you to force any foldable structure. Then you can call simply

mySeq `using` seqFoldable rdeepseq

or define

instance NFData a => NFData (Seq a) where
    rnf = seqFoldable rdeepseq

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