On Thu, 2008-04-10 at 20:34 -0500, John Goerzen wrote:
I have created the named pipe from Haskell no problem.
But I can't use writeFile to write data to it. Worse, it returns:
*** Exception: /tmp/bakroller.zD0xHj/fifo: openFile: does not exist (No such device or address)
What's going on here? Am I going to have to resort to the System.Posix interface just to be able to write to a named pipe?
Named pipes have broken semantics for non-blocking IO, see google or the man pages on named pipes. GHC's standard Handle IO always sets file descriptor to non-blocking mode. That's the problem. That's why cat works, because it uses blocking IO. You would indeed need to use System.Posix to get a FD in blocking mode. Then you have to worry a bit about blocking other Haskell thread when you block on writing to the pipe. Duncan