| OS |
| 1 (Data Constructor) | Distribution.Configuration |
| 2 (Type/Class) | Distribution.System |
| OSX | Distribution.System |
| Other | Distribution.System |
| OtherCompiler | Distribution.Compiler, Distribution.Simple.Compiler, Distribution.Simple.Setup, Distribution.Setup, Distribution.Simple |
| OtherLicense | Distribution.License, Distribution.Make, Distribution.Simple |
| OverlappingInstances | Language.Haskell.Extension, Distribution.Extension, Distribution.Simple |
| OverloadedStrings | Language.Haskell.Extension, Distribution.Extension, Distribution.Simple |
| objExtension | Distribution.Simple.Utils |
| option | Distribution.Compat.ReadP |
| optional | Distribution.Compat.ReadP |
| options | Distribution.PackageDescription |
| orEarlierVersion | Distribution.Version, Distribution.Simple |
| orLaterVersion | Distribution.Version, Distribution.Simple |
| os | Distribution.System |
| otherModules | Distribution.PackageDescription |
