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"

<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 &gt;&gt;= putStrLn
testEcho :: IO ()
testEcho = do
  (Just stdin_hdl, Just stdout_hdl, m_stderr_hdl, p_hdl)
    &lt;- createProcess $
         (shell (&quot;nix run .#echo&quot;))
           { std_in = CreatePipe
           , std_out = CreatePipe
           }
  hPutStrLn stdin_hdl &quot;Hello, echo!&quot;
  hClose stdin_hdl
  !response &lt;- hGetContents stdout_hdl
  cleanupProcess (Just stdin_hdl, Just stdout_hdl, m_stderr_hdl, p_hdl)
  if response == &quot;Hello, echo!&quot; then
    putStrLn &quot;Success!&quot;
  else error &quot;Failure&quot;

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

Success!
Just (Exited ExitSuccess)

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)