英文:
In haskell, how can I interact with stdin of an `IO ()`?
问题
这显示了我想做的事情的精神，它几乎可以工作（只是不适用于我的当前nix设置）：
```haskell
echo :: IO ()
echo = getLine >>= putStrLn
testEcho :: IO ()
testEcho = do
(Just stdin_hdl, Just stdout_hdl, m_stderr_hdl, p_hdl)
<- createProcess $
(shell "nix run .#echo")
{ std_in = CreatePipe
, std_out = CreatePipe
}
hPutStrLn stdin_hdl "Hello, echo!"
hClose stdin_hdl
!response <- hGetContents stdout_hdl
cleanupProcess (Just stdin_hdl, Just stdout_hdl, m_stderr_hdl, p_hdl)
if response == "Hello, echo!" then
putStrLn "Success!"
else error "Failure"
基本上我想要类似于createProcess的东西，但其类型为createProcess :: IO () -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle)，而不是实际上的类型（createProcess :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) ）。
对于这段代码的精神部分，你需要将echo作为你的nix flake的一个应用，以便nix run .#echo能够正常工作。
关于testEcho不满意的地方在于需要使用一个shell命令（nix run .#echo），而echo可以作为Haskell代码在那里使用。testEcho在我的nix环境中目前也出现了故障，但在从cabal repl调用时运行良好。
<details>
<summary>英文:</summary>
This shows the spirit of what I want to do and it almost works (just not within within my current nix setup):
```haskell
echo :: IO ()
echo = getLine >>= putStrLn
testEcho :: IO ()
testEcho = do
(Just stdin_hdl, Just stdout_hdl, m_stderr_hdl, p_hdl)
<- createProcess $
(shell ("nix run .#echo"))
{ std_in = CreatePipe
, std_out = CreatePipe
}
hPutStrLn stdin_hdl "Hello, echo!"
hClose stdin_hdl
!response <- hGetContents stdout_hdl
cleanupProcess (Just stdin_hdl, Just stdout_hdl, m_stderr_hdl, p_hdl)
if response == "Hello, echo!" then
putStrLn "Success!"
else error "Failure"
basically I want something like createProcess but with a type of createProcess :: IO () -> -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) instead of what it actually is (createProcess :: CreateProcess -> IO (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) )
For the spirit code, you would have to make echo an app of your nix flake for nix run .#echo to work
What is unsatisfactory about testEcho is needing to use a shell command (nix run .#echo) when echo is available there as haskell code. testEcho also currently malfunctions within my nix environment, but works well when called from cabal repl.
答案1
得分: 5
你可以降级到unix包，它提供了forkProcess。它还提供了为通信设置一些新的文件描述符所需的内容。下面是一个完整的示例：
import System.IO
import System.Posix.Process
import System.Posix.IO
import System.Posix.Types
echo :: IO ()
echo = getLine >>= putStrLn
forkWithStandardFds :: IO () -> IO (ProcessID, Handle, Handle, Handle)
forkWithStandardFds act = do
(r0, w0) <- createPipe
(r1, w1) <- createPipe
(r2, w2) <- createPipe
pid <- forkProcess $ do
-- 六个closeFd不是严格必要的，
-- 但它们是良好的卫生习惯
closeFd w0 >> dupTo r0 stdInput
closeFd r1 >> dupTo w1 stdOutput
closeFd r2 >> dupTo w2 stdError
act
hIn <- closeFd r0 >> fdToHandle w0
hOut <- closeFd w1 >> fdToHandle r1
hErr <- closeFd w2 >> fdToHandle r2
pure (pid, hIn, hOut, hErr)
main :: IO ()
main = do
(pid, hIn, hOut, hErr) <- forkWithStandardFds echo
hPutStrLn hIn "Hello, echo!"
hFlush hIn
response <- hGetLine hOut
if response == "Hello, echo!" then putStrLn "Success!" else error "Failure"
getProcessStatus True False pid >>= print
运行时，它会打印：
Success!
Just (Exited ExitSuccess)
英文:
You can drop down a level to the unix package, which offers forkProcess. It also offers the stuff you need to set up a few fresh fds for comms. Here's a complete worked example:
import System.IO
import System.Posix.Process
import System.Posix.IO
import System.Posix.Types
echo :: IO ()
echo = getLine >>= putStrLn
forkWithStandardFds :: IO () -> IO (ProcessID, Handle, Handle, Handle)
forkWithStandardFds act = do
(r0, w0) <- createPipe
(r1, w1) <- createPipe
(r2, w2) <- createPipe
pid <- forkProcess $ do
-- the six closeFd's aren't strictly speaking necessary,
-- but they're good hygiene
closeFd w0 >> dupTo r0 stdInput
closeFd r1 >> dupTo w1 stdOutput
closeFd r2 >> dupTo w2 stdError
act
hIn <- closeFd r0 >> fdToHandle w0
hOut <- closeFd w1 >> fdToHandle r1
hErr <- closeFd w2 >> fdToHandle r2
pure (pid, hIn, hOut, hErr)
main :: IO ()
main = do
(pid, hIn, hOut, hErr) <- forkWithStandardFds echo
hPutStrLn hIn "Hello, echo!"
hFlush hIn
response <- hGetLine hOut
if response == "Hello, echo!" then putStrLn "Success!" else error "Failure"
getProcessStatus True False pid >>= print
When run, it prints
Success!
Just (Exited ExitSuccess)
答案2
得分: 2
你可以在不创建另一个进程的情况下完成这个操作，通过重定向 stdin 和 stdout。这个方法效果很好：
import Control.Exception (bracket)
import GHC.IO.Handle (hDuplicate, hDuplicateTo)
import System.Directory (getTemporaryDirectory, removeFile)
import Test.Hspec
echo :: IO ()
echo = getLine >>= putStrLn
main :: IO ()
main = hspec $ do
specify "echo" $ do
let line = "Hello, echo!\n"
captureStdout (provideStdin line echo)
`shouldReturn`
line
provideStdin :: String -> IO a -> IO a
provideStdin input action =
withTemporaryFile $ \h -> do
hPutStr h input
hSeek h AbsoluteSeek 0
redirectStdin h action
captureStdout :: IO a -> IO String
captureStdout action =
withTemporaryFile $ \h -> do
redirectStdout h $ action *> hFlush stdout
hSeek h AbsoluteSeek 0
hGetContents' h
redirectStdin :: Handle -> IO a -> IO a
redirectStdin h action =
bracket
(hDuplicate stdin <* hDuplicateTo h stdin)
(\saved -> hDuplicateTo saved stdin *> hClose saved)
(const action)
redirectStdout :: Handle -> IO a -> IO a
redirectStdout h action =
bracket
(hFlush stdout *> hDuplicate stdout <* hDuplicateTo h stdout)
(\saved -> hDuplicateTo saved stdout *> hClose saved)
(const action)
withTemporaryFile :: (Handle -> IO a) -> IO a
withTemporaryFile inner = do
tmp <- getTemporaryDirectory
bracket
(openBinaryTempFile tmp "wtf-")
(\(name, h) -> hClose h >> removeFile name)
(inner . snd)
我相信你可以连续执行多个这样的操作，而不会影响原始的 stdin 和 stdout，但我没有测试过。
英文:
You can do it without creating another process, by redirecting stdin and stdout. This works nicely:
import Control.Exception (bracket)
import GHC.IO.Handle (hDuplicate, hDuplicateTo)
import System.Directory (getTemporaryDirectory, removeFile)
import Test.Hspec
echo :: IO ()
echo = getLine >>= putStrLn
main :: IO ()
main = hspec $ do
specify "echo" $ do
let line = "Hello, echo!\n"
captureStdout (provideStdin line echo)
`shouldReturn`
line
provideStdin :: String -> IO a -> IO a
provideStdin input action =
withTemporaryFile $ \h -> do
hPutStr h input
hSeek h AbsoluteSeek 0
redirectStdin h action
captureStdout :: IO a -> IO String
captureStdout action =
withTemporaryFile $ \h -> do
redirectStdout h $ action *> hFlush stdout
hSeek h AbsoluteSeek 0
hGetContents' h
redirectStdin :: Handle -> IO a -> IO a
redirectStdin h action =
bracket
(hDuplicate stdin <* hDuplicateTo h stdin)
(\saved -> hDuplicateTo saved stdin *> hClose saved)
(const action)
redirectStdout :: Handle -> IO a -> IO a
redirectStdout h action =
bracket
(hFlush stdout *> hDuplicate stdout <* hDuplicateTo h stdout)
(\saved -> hDuplicateTo saved stdout *> hClose saved)
(const action)
withTemporaryFile :: (Handle -> IO a) -> IO a
withTemporaryFile inner = do
tmp <- getTemporaryDirectory
bracket
(openBinaryTempFile tmp "wtf-")
(\(name, h) -> hClose h >> removeFile name)
(inner . snd)
I believe you could do several of these in a row without messing up the original stdin and stdout, but I haven't tested that.
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