Index - U
| UintLit | Language.ATS |
| UintTok | Language.ATS |
| Unary | Language.ATS |
| Unconsumed | Language.ATS |
| UnderscoreLit | Language.ATS |
| Universal | |
| 1 (Type/Class) | Language.ATS |
| 2 (Data Constructor) | Language.ATS |
| UniversalPattern | Language.ATS |
| Unknown | Language.ATS |
| UnOp | Language.ATS |
| Unqualified | Language.ATS |