Runtime system doesn't notice changed file descriptor status

Hi

I'm building a program which converts file names from ISO8859-1 to UTF-8. It 
calls the recode program to do the actual conversion. This part does the 
work:

   pfade <- fmap lines getContents

   pipe_to (unlines pfade)
           (execp "recode" ["-f", "latin1..utf8"]
               -|= (do pfade_utf8 <- fmap lines getContents   --XX error here
                       mapM_ (\(pfad, pfad_utf8) -> do 
                                 ...
                             )
                             (zip pfade pfade_utf8)
                   )
           )

pipe_to and (-|=) fork two processes, connected through a pipe. I get this 
error at the marked point:

In child process, part of a pipe:
IO-Error
   Error type:   illegal operation
   Location:     hGetContents
   Description:  handle is closed
   File name:    "<stdin>"

The problem is, the call of getContents at the beginning closes the main 
process' standard input. It is replaced in the child with the pipe from 
recode, but the runtime system doesn't notice that stdin is open again. The 
openness state seems to be duplicated in stdin's file handle.

It works when replacing the marked line with the following.

   h <- fdToHandle 0  -- from hslibs
   pfade_utf8 <- fmap lines (hGetContents h)

I'm using only functions from the System.Posix library (e.g. dupTo), so I 
think the runtime system should notice.

Apart from that, is there any way to notify the runtime system that the file 
descriptor 0 has changed?

But in the first place, it should be avoided to duplicate the file 
descriptor's state in the handle, if possible.

I'm running Linux and GHC 6.2.2.

Greetings,
V.W.

-- 
http://www.volker-wysk.de