Index - O
| odd | Prelude |
| openBinaryFile | System.IO |
| openBinaryTempFile | System.IO |
| openBinaryTempFileWithDefaultPermissions | System.IO |
| openFile | System.IO |
| OpenPunctuation | Data.Char |
| openTempFile | System.IO |
| openTempFileWithDefaultPermissions | System.IO |
| or | Prelude |
| Ord | Prelude |
| ord | Data.Char |
| Ordering | Prelude |
| orElse | Control.Concurrent.STM, Control.Monad.STM |
| OtherLetter | Data.Char |
| OtherNumber | Data.Char |
| OtherPunctuation | Data.Char |
| OtherSymbol | Data.Char |
| otherwise | Prelude |
| outputNL | System.IO |