Index - O
| OS | GHC.Platform |
| OSAIX | GHC.Platform |
| OSDarwin | GHC.Platform |
| OSDragonFly | GHC.Platform |
| osElfTarget | GHC.Platform |
| OSFreeBSD | GHC.Platform |
| OSHaiku | GHC.Platform |
| OSHurd | GHC.Platform |
| OSKFreeBSD | GHC.Platform |
| OSLinux | GHC.Platform |
| osMachOTarget | GHC.Platform |
| OSMinGW32 | GHC.Platform |
| OSNetBSD | GHC.Platform |
| OSOpenBSD | GHC.Platform |
| OSQNXNTO | GHC.Platform |
| OSSolaris2 | GHC.Platform |
| osSubsectionsViaSymbols | GHC.Platform |
| OSUnknown | GHC.Platform |
| OverlappingInstances | GHC.LanguageExtensions |
| OverloadedLabels | GHC.LanguageExtensions |
| OverloadedLists | GHC.LanguageExtensions |
| OverloadedStrings | GHC.LanguageExtensions |