Index - O
| OddParity | System.Posix.Terminal.ByteString, System.Posix.Terminal, System.Posix.ByteString, System.Posix | 
| openDirStream | |
| 1 (Function) | System.Posix.Directory.ByteString, System.Posix.ByteString | 
| 2 (Function) | System.Posix.Directory, System.Posix | 
| openEndedPipe | System.Posix.Signals, System.Posix.Signals.Exts, System.Posix.ByteString, System.Posix | 
| openFd | |
| 1 (Function) | System.Posix.IO.ByteString, System.Posix.ByteString | 
| 2 (Function) | System.Posix.IO, System.Posix | 
| OpenFileFlags | |
| 1 (Type/Class) | System.Posix.IO.ByteString, System.Posix.IO, System.Posix.ByteString, System.Posix | 
| 2 (Data Constructor) | System.Posix.IO.ByteString, System.Posix.IO, System.Posix.ByteString, System.Posix | 
| OpenFileLimit | System.Posix.Unistd, System.Posix.ByteString, System.Posix | 
| OpenMode | System.Posix.IO.ByteString, System.Posix.IO, System.Posix.ByteString, System.Posix | 
| openPseudoTerminal | |
| 1 (Function) | System.Posix.Terminal.ByteString, System.Posix.ByteString | 
| 2 (Function) | System.Posix.Terminal, System.Posix | 
| OpenSemFlags | |
| 1 (Type/Class) | System.Posix.Semaphore, System.Posix.ByteString, System.Posix | 
| 2 (Data Constructor) | System.Posix.Semaphore, System.Posix.ByteString, System.Posix | 
| otherExecuteMode | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix | 
| otherModes | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix | 
| otherReadMode | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix | 
| otherWriteMode | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix | 
| OutputQueue | System.Posix.Terminal.ByteString, System.Posix.Terminal, System.Posix.ByteString, System.Posix | 
| outputSpeed | System.Posix.Terminal.ByteString, System.Posix.Terminal, System.Posix.ByteString, System.Posix | 
| ownerExecuteMode | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix | 
| ownerModes | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix | 
| ownerReadMode | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix | 
| ownerWriteMode | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix |