Hal, I was really hoping that someone would have a pretty answer for you by now. Just this last week, I came up with a similar problem--I need to pass a handle to some foreign code, but in my case, the foreign code can treat the handle as opaque, it just needs to be able to give it back to Haskell when needed. I haven't actually solved my problem in a nice way (though your posted code suggests a way, using the file descriptor).
foreign import ccall "myHFile.h myCFun" c__myCFun :: Ptr CInt -> IO () myCFun :: Handle -> IO () myCFun (FileHandle handleMV) = do h__ <- readMVar handleMV ptr <- malloc poke ptr (toCInt $ haFD h__) c__initVars ptr
Do you mean c__myCFun instead of c__initVars? What is toCInt? Is it doing anything wierd? Anyway, might this work?
foreign import ccall "myHFile.h myCFun_stub" c__myCFun :: CInt -> IO ()
myCFun :: Handle -> IO () myCFun (FileHandle handleMV) = readMVar handleMV >>= c__myCFun . toCInt . haFD
To pass a CInt (no need for Ptr here) to a stub function in C, where the stub function just converts the file descriptor to a FILE * and calls yourCFun (I mean, myCFun): void myCFun_stub(int fd) { FILE *f = fdopen(fd, "w"); myCFun(f); fflush(f); } It worked for writing to a text file in a simple test, and for writing to stdout. I needed to fflush on the C side when writing to the file. ---- Kevin S. Millikin Architecture Technology Corporation Research Scientist Specialists in Computer Architecture (952)829-5864 x162 http://www.atcorp.com