chunksOf模拟ByteString？

Question

我需要将字节串拆分为先跳转100个字符的字节串列表。对于列表，我可以使用chunksOf，但不能使用ByteString。

有什么合适的方法吗？

Answer 1

ByteString和Lazy.Bytestring都有splitAt 函数，您可以使用它来表示列表。

import Data.List (unfoldr)
import Data.Int (Int64)

import qualified Data.ByteString as BS
import qualified Data.ByteString.Lazy as Lazy

justWhen :: (a -> Bool) -> (a -> b) -> (a -> Maybe b)
justWhen f g a = if f a then Just (g a) else Nothing

nothingWhen :: (a -> Bool) -> (a -> b) -> (a -> Maybe b)
nothingWhen f = justWhen (not . f)

chunksOf :: Int -> BS.ByteString -> [BS.ByteString]
chunksOf x = unfoldr (nothingWhen BS.null (BS.splitAt x))

chunksOf' :: Int64 -> Lazy.ByteString -> [Lazy.ByteString]
chunksOf' x = unfoldr (nothingWhen Lazy.null (Lazy.splitAt x))

使用OverloadedStrings构建示例的字节串更容易

{-# LANGUAGE OverloadedStrings #-}

main = do
    print $ chunksOf 3 ""
    print $ chunksOf 3 "Hello World!"
    print $ chunksOf' 3 ""
    print $ chunksOf' 3 "Hello, World"