[Haskell-cafe] No handles from createProcess

15 Dec 2014

      L.S.,

I am experimenting with the createProcess function from the package  
"process"; this function does not return any handle, on both Ubuntu and  
Windows. I am doing something wrong, or is this a bug? (I am using GHC  
7.8.3 on both platforms.)

The program I am running:
---✂----------------------------------------------
import System.IO
import System.Process

f =
   do
     (  maybeStdinHandel
      , maybeStdoutHandel
      , maybeStderrHandel
      , processHandle
      ) <- createProcess (proc "cat" ["a.txt"])
     case maybeStdinHandel of
       Just stdinHandel ->
         do
           putStrLn "stdin"
       _ -> putStrLn "No stdin handle"
     case maybeStdoutHandel of
       Just stdoutHandel ->
         do
           putStrLn "stdout"
           putStrLn =<< hGetContents stdoutHandel
       _ -> putStrLn "No stdout handle"
     case maybeStderrHandel of
       Just stderrHandel ->
         do
           putStrLn "stderr"
           putStrLn =<< hGetContents stderrHandel
       _ -> putStrLn "No stderr handle"

main = f
---✂----------------------------------------------

The output:
---✂----------------------------------------------
$ ./ProcessTry
No stdin handle
No stdout handle
No stderr handle
asdf
---✂----------------------------------------------
(asdf is the contents of file a.txt)

Regards,
Henk-Jan van Tuyl

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