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