[英]how to insert an IO operation into a Pipe
I have a Haskell function which given a directory from which to get recursively all files and writes the filenames into a file.我有一个 Haskell function ,它给出了一个目录,从中递归地获取所有文件并将文件名写入文件。 This is a simple example to start with.
这是一个简单的例子。 In the next step I must replace the mapping from file to a text (the
transf
operation) by an operation using the file content;在下一步中,我必须通过使用文件内容的操作替换从文件到文本的映射(
transf
操作); this is obviously an operation in the IO monad.这显然是 IO monad 中的一个操作。
My understanding of Pipe
is very limited;我对
Pipe
的了解非常有限; I tried with a simplistic operation opex
which I tried to lift
into a pipe.我尝试了一个简单的操作
opex
,我试图将其lift
为 pipe。 I want to remove the current transf我想删除当前的传输
This looks like a simple problem but despite of searching the web, I cannot find a solution.这看起来像一个简单的问题,但尽管搜索了 web,但我找不到解决方案。 Thank you for help!
谢谢你的帮助!
pipedDoIO2 :: Path Abs File -> Path Abs Dir -> (Path Abs File -> IO Text) -> ErrIO ()
pipedDoIO2 file path transf = do
hand <- openFile2handle file WriteMode
Pipe.runEffect $
getRecursiveContents path
>-> PipePrelude.map ( transf) -- some IO type left?
-- >-> lift opex
>-> PipePrelude.toHandle hand
closeFile2 hand
return ()
opex :: (Path Abs File -> IO Text)
opex = return . showT
Some more reading lead me to the simple answer: use mapM
from the Path.Prelude.更多阅读使我得到简单的答案:使用
mapM
中的 mapM。 I hope this solution helps others to find this "obvious" solution not easily detected on the web;我希望这个解决方案可以帮助其他人找到这个在 web 上不容易检测到的“明显”解决方案; I added a
filter
on the file extension as an example how to use filter
.我在文件扩展名上添加了一个
filter
作为如何使用filter
的示例。
Caveat: the toHandle
"Write Strings to a Handle using hPutStrLn", ie it inserts a \n
after each insertion.警告:
toHandle
“使用 hPutStrLn 将字符串写入句柄”,即它在每次插入后插入一个\n
。
-- a convenient function to go through a directory and
-- recursively apply a function to each file or directory
-- filters for extension md
pipedDoIO2 :: Path Abs File -> Path Abs Dir -> (Path Abs File -> ErrIO String) -> ErrIO ()
pipedDoIO2 file path opex = do
hand <- openFile2handle file WriteMode
Pipe.runEffect $
getRecursiveContents path
>-> PipePrelude.filter (hasExtension (Extension "md"))
>-> PipePrelude.mapM opex
>-> PipePrelude.toHandle hand
closeFile2 hand
return ()
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