| Unauthorized | |
| 1 (Type/Class) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| 2 (Data Constructor) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| UnprocessableEntity | |
| 1 (Type/Class) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| 2 (Data Constructor) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| UnqualifiedImp | Network.HTTP.Lucu.Implant.Rewrite |
| Unqualify | Network.HTTP.Lucu.Implant.Rewrite |
| unqualify | Network.HTTP.Lucu.Implant.Rewrite |
| unqualifyAll | Network.HTTP.Lucu.Implant.Rewrite |
| unqualifyIn | Network.HTTP.Lucu.Implant.Rewrite |
| UnsupportedMediaType | |
| 1 (Type/Class) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| 2 (Data Constructor) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| UpgradeRequired | |
| 1 (Type/Class) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| 2 (Data Constructor) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| uriCIScheme | Network.HTTP.Lucu.Utils |
| uriHost | Network.HTTP.Lucu.Utils |
| uriPathSegments | Network.HTTP.Lucu.Utils |
| useGZip | Network.HTTP.Lucu.Implant |
| UseProxy | |
| 1 (Type/Class) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| 2 (Data Constructor) | Network.HTTP.Lucu.Response.StatusCode, Network.HTTP.Lucu |
| UserID | Network.HTTP.Lucu.Authentication |