haskell - 循环文件集？

Question

在 Haskell 中，我尝试将文件列表处理为函数(类似于“for f in file1 file2 file3 file5 do ... in Bash”):

import System.Directory

returnDirectoryContents :: IO [FilePath]
returnDirectoryContents = do
  let path = "."
  filter (isSuffixOf ".txt") <$> getDirectoryContents path

countNumberOfWords :: FilePath -> IO Int
countNumberOfWords path = do ...

countNumberOfWords "file1.txt" 工作正常。但是，我无法将该函数映射到 FilePath 列表:

fmap countNumberOfWords returnDirectoryContents
    • No instance for (Show (IO Int)) arising from a use of ‘print’

将文件列表处理到函数的正确方法是什么？

Answer 1

你想要map的monadic兄弟，mapM。