| OneLineMode | Language.Haskell.Exts.Pretty, Language.Haskell.Exts |
| onsideIndent | Language.Haskell.Exts.Pretty, Language.Haskell.Exts |
| Op | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| op | Language.Haskell.Exts.Build, Language.Haskell.Exts |
| OPTIONS | Language.Haskell.Exts.Lexer, Language.Haskell.Exts |
| OptionsPragma | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| OrFormula | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| OVERLAP | Language.Haskell.Exts.Lexer, Language.Haskell.Exts |
| Overlap | |
| 1 (Type/Class) | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| 2 (Data Constructor) | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| OVERLAPPABLE | Language.Haskell.Exts.Lexer, Language.Haskell.Exts |
| Overlappable | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| OVERLAPPING | Language.Haskell.Exts.Lexer, Language.Haskell.Exts |
| Overlapping | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| OverlappingInstances | Language.Haskell.Exts.Extension, Language.Haskell.Exts |
| OVERLAPS | Language.Haskell.Exts.Lexer, Language.Haskell.Exts |
| Overlaps | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| OverloadedLabel | Language.Haskell.Exts.Syntax, Language.Haskell.Exts |
| OverloadedLabels | Language.Haskell.Exts.Extension, Language.Haskell.Exts |
| OverloadedStrings | Language.Haskell.Exts.Extension, Language.Haskell.Exts |