[Haskell] Win32 process spawning, POpen and Hugs, revisited

[Graham Klyne]

Further to my previous messages:
   http://www.haskell.org//pipermail/haskell/2004-February/013522.html
   http://www.haskell.org//pipermail/haskell/2004-February/013679.html

I've come back to my stripped-down test case, and recreated the C test 
program SpawnEchoShiftLetters.c [1] in Haskell SpawnEchoShiftLetters.hs 
[2].  I've also added some diagnostic code.  To recap:  the C code 
demonstrates that that the Win32 API used by spawnProc.c [4] is working as 
expected, so the problem appears to be in the Haskell interface to it.

My problem seems to be occurring about here:
[[
spawn cmd =
   withCString cmd $ \ p_cmd ->
    withObject 0 $ \ p_wIn  ->
     withObject 0 $ \ p_rOut ->
      withObject 0 $ \ p_rErr -> do
        rc  <- spawnProc p_cmd p_wIn p_rOut p_rErr
        when (rc /= 0) (ioError (userError ("runProc: unable to spawn " ++ 
show cmd)))
        wIn <- peek p_wIn
(-1-}  trace ("wIn "++show wIn) $ return ()
        {- : -}
(-2-}  hIn <- openFd (fromIntegral wIn) False WriteMode False
(-3-}  trace ("hIn "++show hIn) $ return ()
]]
-- http://www.ninebynine.org/Software/HaskellUtils/Win32/POpen.hs

Specifically:
+ the trace at {-1-} displays the expected value (i.e. the same as a 
similar trace in the C version of the code [1], namely the value 3),
+ the trace at {-3-} is not displayed, indicating...
+ failure of the openFd call at {-2-}, also indicated by a Hugs error 
message, thus:
[[
SpawnEchoShiftLetters> runTest
wIn 3

Program error: openFd: does not exist (file does not exist)

SpawnEchoShiftLetters>
]]


Thus, it would appear that I'm misunderstanding how to use the openFd 
function that is part of the Hugs-supplied library code, declared as a 
primitive:
[[
-- Creating a handle from a file descriptor/socket.
--
primitive openFd    :: Int    -- file descriptor
                     -> Bool   -- True => it's a socket.
                     -> IOMode -- what mode to open the handle in.
                     -> Bool   -- binary?
                     -> IO Handle
]]
-- 
http://cvs.haskell.org/cgi-bin/cvsweb.cgi/hugs98/libraries/Hugs/IO.hs?rev=1.9&content-type=text/x-cvsweb-markup

Can anyone help me out here?

My current experimental code is all visible at [4].

Thanks.

#g
--

[1] 
http://www.ninebynine.org/Software/HaskellUtils/Win32/SpawnEchoShiftLetters.c

[2] 
http://www.ninebynine.org/Software/HaskellUtils/Win32/SpawnEchoShiftLetters.hs

[3] http://www.ninebynine.org/Software/HaskellUtils/Win32/spawnProc.c

[4] http://www.ninebynine.org/Software/HaskellUtils/Win32/



------------
Graham Klyne
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http://www.ninebynine.org/#Contact