haskell - 在 Haskell 中列出 TAR 存档

Question

我目前正在尝试弄清楚如何在 Haskell 中列出(gzipped)TAR 存档。 Codec.Archive.Tar 似乎是这项任务的正确选择，但我不知道如何map entryPath超过Entries幺半群。

假设 TAR 包含条目(仅文件)a.txt, b.txt, c.txt并命名为foo.tar.gz 。这是我读取文件的代码:

import qualified Codec.Archive.Tar as Tar
import qualified Data.ByteString.Lazy as BS
import qualified Codec.Compression.GZip as GZip

foldEntryToPath :: Tar.Entry -> [String] -> [String]
foldEntryToPath entry list = list ++ [show $ Tar.entryPath entry]

-- Converts TAR errors to a string.
entryFailMapper :: String -> [String]
entryFailMapper err = [err]

main = do
        fileContent <- fmap GZip.decompress $ BS.readFile "foo.tar.gz"
        entries <- fmap Tar.read fileContent :: Tar.Entries
        -- Here I don't know how to correctly apply fmap
        entryPaths <- Tar.foldEntries foldEntryToPath [] entryFailMapper entries :: [String]
        -- This should print ["a.txt", "b.txt", "c.txt"]
        print entryPaths

这是 runghc 打印的错误:

readtar.hs:14:49:
Expecting one more argument to `Tar.Entries'
In an expression type signature: Tar.Entries
In a stmt of a 'do' block:
  entries <- fmap Tar.read fileContent :: Tar.Entries
In the expression:
  do { fileContent <- fmap GZip.decompress
                      $ BS.readFile "foo.tar.gz";
       entries <- fmap Tar.read fileContent :: Tar.Entries;
       entryPaths <- Tar.foldEntries
                       foldEntryToPath [] (\ x -> [...]) entries ::
                       [String];
       print entryPaths }

到目前为止，我对 Haskell 知之甚少，但通过阅读 the docs不知道为什么Tar.Entries是一个类型类(expecting n more arguments to <type> 是正确的术语吗？)或者正确使用的类型是什么。

任何帮助将不胜感激!

Answer 1

我认为 foldEntryToPath 需要修复:

foldEntryToPath :: Tar.Entry -> [String] -> [String]
foldEntryToPath entry list = (show $ Tar.entryPath entry) : list

在main中:

fileContent <- fmap GZip.decompress $ BS.readFile "foo.tar.gz"
let entries = Tar.read fileContent
let entryPaths = Tar.foldEntries foldEntryToPath [] entryFailMapper entries
print entryPaths