[Haskell-cafe] trying to use unix's openFD ..

Hello, The signature for openFD is openFd: FilePath -> OpenMode -> Maybe FileMode -> OpenFileFlags -> IO Fd I am currently reading http://www.haskell.org/ghc/docs/latest/html/libraries/unix/System-Posix-File... and diving down into links but can't find the definition of data type FileMode. ??? Basically I want to open in O_RDONLY filemode. Kind regards, Vasili