Index - O
| odd | Platform.Prelude |
| on | Platform.Prelude |
| oneBits | Platform.Prelude |
| onException | Platform.Prelude |
| OpenPunctuation | Platform.Prelude |
| optional | Platform.Prelude |
| or | Platform.Prelude |
| Ord | Platform.Prelude |
| ord | Platform.Prelude |
| Ordering | Platform.Prelude |
| OtherLetter | Platform.Prelude |
| OtherNumber | Platform.Prelude |
| OtherPunctuation | Platform.Prelude |
| OtherSymbol | Platform.Prelude |
| otherwise | Platform.Prelude |
| Overflow | Platform.Prelude |