[Haskell-cafe] What does the withProcessHandle_ function do?

I want to learn how to use FFI with Win32, so I'm looking through the GHC source code. I encountered the function terminateProcess :: ProcessHandle -> IO () terminateProcess ph = do withProcessHandle_ ph $ \p_ -> case p_ of ClosedHandle _ -> return p_ OpenHandle h -> do throwErrnoIfMinus1_ "terminateProcess" $ c_terminateProcess h return p_ which uses withProcessHandle_. What does it do? Thanks -John