Index - U
| Underscore | |
| 1 (Data Constructor) | ASCII.Caseless |
| 2 (Data Constructor) | ASCII.Char |
| UnicodeChar | ASCII |
| unicodeStringToByteListMaybe | ASCII |
| unicodeStringToByteStringMaybe | ASCII |
| unicodeStringToCharListMaybe | ASCII |
| unicodeStringToCharListUnsafe | ASCII |
| unicodeToCharMaybe | ASCII |
| unicodeToCharUnsafe | ASCII |
| unicodeToDigitMaybe | ASCII |
| unicodeToDigitUnsafe | ASCII |
| unicodeToHexCharMaybe | ASCII |
| unicodeToHexCharUnsafe | ASCII |
| UnitSeparator | |
| 1 (Data Constructor) | ASCII.Caseless |
| 2 (Data Constructor) | ASCII.Char |
| upper | ASCII, ASCII.QuasiQuoters |
| UpperCase | ASCII, ASCII.Case |
| upperStringExp | ASCII.TemplateHaskell |