Haskell：如何使用attoparsec从ByteString读取嵌套列表 [英] Haskell: How to use attoparsec in order to read a nested list from a ByteString

问题描述

  [[p>]我有一个带有嵌套列表的文本文件（〜300 MB大） 4，9，11，28，30，45，55，58，61，62，63，69，74，76，77，82，87，92，93，94，95]，[ 28,30,45,55,58,61,62,63,69,74,76,77,82,87,92,93,94]，[4,9,11， 58,61,62,63,69,74,76,77,82,85,87,92,93,94,95]] 
  

这是我的程序，将文件读入haskell Integer 列表：

< pre $ 导入限定的Data.ByteString作为ByteStr

main :: IO（）

- 如何做同样的事情，但使用用于文件访问的ByteStr.readFile？
main = do fContents< - readFile filePath
let numList = readNums fContents
putStrLn（show nums）


这适用于小文本文件，但我想用 ByteString 快速读取文件。我发现ByteString没有 read 函数，而应该在attoparsec中编写自己的解析器，因为它支持解析ByteStrings。

如何使用 attoparsec 解析嵌套列表？

解决方案数据似乎是JSON格式，所以你可以使用 Data.Aeson decode 函数在 ByteString

上运行
$ b

 导入限定的Data.ByteString.Lazy作为BL 
 import Data.Aeson 
 import Data.Maybe 
 
 main = do fContents<  -  BL.readFile filePath 
 let numList = decode fContents :: Maybe [[Int] ] 
 putStrLn（show $ fromJust numList）
  

I have a text file (~ 300 MB large) with a nested list, similar to this one:

[[4, 9, 11, 28, 30, 45, 55, 58, 61, 62, 63, 69, 74, 76, 77, 82, 87, 92, 93, 94, 95], [4, 9, 11, 28, 30, 45, 55, 58, 61, 62, 63, 69, 74, 76, 77, 82, 87, 92, 93, 94],[4, 9, 11, 28, 30, 45, 55, 58, 61, 62, 63, 69, 74, 76, 77, 82, 85, 87, 92, 93, 94, 95]]

Here is my program to read the file into a haskell Integer list:

import qualified Data.ByteString as ByteStr

main :: IO ()

-- HOW to do the same thing but using ByteStr.readFile for file access?
main = do fContents <- readFile filePath 
          let numList = readNums fContents
          putStrLn (show nums)

This works for small text files, but I want to use ByteString to read the file quickly. I found out that there is no read function for ByteString, instead you should write your own parser in attoparsec, since it supports parsing ByteStrings.

How can I use attoparsec to parse the nested list?

解决方案

The data seems to be in JSON format, so you can use Data.Aeson decode function which works on ByteString

import qualified Data.ByteString.Lazy as BL
import Data.Aeson
import Data.Maybe

main = do fContents <- BL.readFile filePath 
          let numList = decode fContents :: Maybe [[Int]]
          putStrLn (show $ fromJust numList)

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