Index - O
| objectName | Base, Protolude |
| odd | Base, Protolude |
| on | Protolude |
| one | Semiring, Protolude |
| onException | Protolude |
| openFile | Protolude |
| optional | Protolude |
| or | Protolude |
| orAlt | Applicative, Protolude |
| Ord | Protolude |
| ord | Base, Protolude |
| Ordering | Base, Protolude |
| ordNub | List, Protolude |
| orElse | Protolude |
| orEmpty | Applicative, Protolude |
| orInteger | Base, Protolude |
| otherwise | Protolude |
| Overflow | Protolude |
| overflowError | Base, Protolude |