Hi, On 2014-09-02 03:07, David Fox wrote:

I would expect the expression above to finish - but it doesn't. Is this a bug?

Below is a lazier variant of readProcess. If you use this, your example will work as expected. You can also pipe several processes together, e.g. readProcess (shell "yes") "" >>= readProcess (shell "head") -- Thomas H -- | Lazy variant of readProcess module Process(readProcess,shell,proc) where import System.Process hiding (readProcess) import System.IO(hGetContents,hClose,hPutStr) import Control.Concurrent(forkIO) import System.IO.Error(tryIOError) -- | Feed some input to a shell process and read the output lazily readProcess :: CreateProcess -- ^ Process specified with 'shell' or 'proc' -> String -- ^ input to the process -> IO String -- ^ output from the process readProcess proc input = do (Just stdin,Just stdout,Nothing,ph) <- createProcess proc{std_in=CreatePipe,std_out=CreatePipe} forkIO $ do tryIOError $ hPutStr stdin input tryIOError $ hClose stdin waitForProcess ph return () hGetContents stdout