Index - U
| UndefinedName | FrontEnd.Warning |
| unfoldKind | FrontEnd.Tc.Kind, FrontEnd.Tc.Type |
| UnificationError | FrontEnd.Warning |
| union | Util.SetLike |
| Unionize | Util.SetLike |
| unions | Util.SetLike |
| unionWith | Util.SetLike |
| UniqueProducer | Util.Gen |
| Unit | Grin.Grin |
| Unknown | E.Type |
| UnknownDeriving | FrontEnd.Warning |
| UnknownOption | FrontEnd.Warning |
| UnknownPragma | FrontEnd.Warning |
| UnknownType | Name.Name |
| unpackPS | PackedString |
| unRename | FrontEnd.Rename |
| Unsafe | C.Prims, C.FFI |
| unsafeByteIndex | StringTable.Atom |
| unsafeIntToAtom | StringTable.Atom |
| unsetProperty | Info.Types |
| UnsupportedFeature | FrontEnd.Warning |
| UnVar | FrontEnd.Tc.Type |
| unVar' | FrontEnd.Tc.Type |
| UnVarOpt | |
| 1 (Type/Class) | FrontEnd.Tc.Type |
| 2 (Data Constructor) | FrontEnd.Tc.Type |
| updateChoHo | Ho.Collected |
| updateFuncDefProps | Grin.Grin |
| updateLit | DataConstructors |