| UnboxedTuples | Language.Haskell.Extension, Distribution.Extension, Distribution.Simple |
| UndecidableInstances | Language.Haskell.Extension, Distribution.Extension, Distribution.Simple |
| UnicodeSyntax | Language.Haskell.Extension, Distribution.Extension, Distribution.Simple |
| UnionVersionRanges | Distribution.Version, Distribution.Simple |
| UnliftedFFITypes | Language.Haskell.Extension, Distribution.Extension, Distribution.Simple |
| UnregisterCmd | Distribution.Simple.Setup, Distribution.Setup |
| UserHooks |
| 1 (Type/Class) | Distribution.Simple |
| 2 (Data Constructor) | Distribution.Simple |
| UserPackageDB | Distribution.Simple.Compiler, Distribution.Simple.Setup, Distribution.Setup, Distribution.Simple |
| UserSpecified | Distribution.Simple.Program |
| unlit | Distribution.Simple.PreProcess.Unlit |
| unregHook | Distribution.Simple |
| unregister | Distribution.Simple.Register |
| unsupportedExtensions | Distribution.Simple.Compiler, Distribution.Simple |
| updatePackageDescription | Distribution.PackageDescription |
| updateProgram | Distribution.Simple.Program |
| userMaybeSpecifyPath | Distribution.Simple.Program |
| userSpecifyArgs | Distribution.Simple.Program |
| userSpecifyPath | Distribution.Simple.Program |
