For the development snapshot 6.3.20031201, System.Posix.forkProcess has the type IO () -> IO System.Posix.Types.ProcessID. In 6.0.1 it has type IO () -> IO (Maybe System.Posix.Types.ProcessID). Is this change intentional, and if so how are you supposed to test after the fork if this is the parent or child process?
Yes, this is intentional. It turned out to be far too difficult to implement forkProcess as it was previously defined (problems with what happens when the current thread returns in the child process was one difficulty, IIRC). The previous implementation had some serious bugs. See the docs for the new version here: http://www.haskell.org/ghc/docs/6.2/html/libraries/unix/System.Posix.Pro cess.html#v%3AforkProcess Cheers, Simon