| O | GHC.Base |
| objectName | GHC.ExecutionStack.Internal, GHC.ExecutionStack |
| odd | GHC.Real, Prelude |
| oldGenFactor | GHC.RTS.Flags |
| on | Data.Function |
| oneBits | Data.Bits, Foreign, Foreign.Safe |
| OneLineGCStats | GHC.RTS.Flags |
| OneShot | GHC.Event |
| oneShot | GHC.Base, GHC.Exts |
| onException | |
| 1 (Function) | GHC.IO |
| 2 (Function) | Control.Exception, Control.Exception.Base |
| Op | |
| 1 (Type/Class) | Data.Functor.Contravariant |
| 2 (Data Constructor) | Data.Functor.Contravariant |
| Opaque | GHC.Base |
| openBinaryFile | |
| 1 (Function) | GHC.IO.Handle.FD |
| 2 (Function) | System.IO, GHC.IO.StdHandles |
| openBinaryTempFile | System.IO |
| openBinaryTempFileWithDefaultPermissions | System.IO |
| openFile | |
| 1 (Function) | GHC.IO.FD |
| 2 (Function) | GHC.IO.Handle.FD |
| 3 (Function) | System.IO, GHC.IO.StdHandles |
| openFileBlocking | |
| 1 (Function) | GHC.IO.Handle.FD |
| 2 (Function) | GHC.IO.StdHandles |
| openFileWith | GHC.IO.FD |
| OpenPunctuation | GHC.Unicode, Data.Char |
| openTempFile | System.IO |
| openTempFileWithDefaultPermissions | System.IO |
| openTextEncoding | GHC.IO.Handle.Internals |
| OptArg | System.Console.GetOpt |
| OptDescr | System.Console.GetOpt |
| Option | System.Console.GetOpt |
| option | Text.ParserCombinators.ReadP |
| optional | |
| 1 (Function) | Text.ParserCombinators.ReadP |
| 2 (Function) | Control.Applicative |
| or | |
| 1 (Function) | GHC.List, GHC.OldList |
| 2 (Function) | Data.List, Data.Foldable, Prelude |
| or# | GHC.Base, GHC.Exts |
| Ord | GHC.Base, Data.Ord, Prelude |
| ord | GHC.Base, Data.Char |
| ord# | GHC.Base, GHC.Exts |
| Ord1 | Data.Functor.Classes |
| Ord2 | Data.Functor.Classes |
| OrdCond | Data.Type.Ord |
| Ordering | GHC.Base, Data.Ord, Prelude |
| OrderingI | GHC.TypeLits, Data.Type.Ord |
| orElse | GHC.Conc.Sync, GHC.Conc |
| orI# | GHC.Base, GHC.Exts |
| orInteger | GHC.Integer |
| orNatural | GHC.Natural |
| orWord16# | GHC.Base, GHC.Exts |
| orWord32# | GHC.Base, GHC.Exts |
| orWord8# | GHC.Base, GHC.Exts |
| os | System.Info |
| OtherError | GHC.IO.Exception |
| OtherLetter | GHC.Unicode, Data.Char |
| OtherNumber | GHC.Unicode, Data.Char |
| OtherPunctuation | GHC.Unicode, Data.Char |
| OtherSymbol | GHC.Unicode, Data.Char |
| otherwise | GHC.Base, Data.Bool, Prelude |
| outer | Data.Type.Equality |
| outputNL | System.IO, GHC.IO.Handle.Types, GHC.IO.Handle |
| OutputUnderflow | GHC.IO.Encoding, GHC.IO.Encoding.Types |
| Overflow | GHC.Exception, Control.Exception, Control.Exception.Base, GHC.Exception.Type |
| overflowError | GHC.Real |
| overflowException | GHC.Exception, GHC.Exception.Type |
| o_APPEND | System.Posix.Internals |
| o_BINARY | System.Posix.Internals |
| o_CREAT | System.Posix.Internals |
| o_EXCL | System.Posix.Internals |
| o_NOCTTY | System.Posix.Internals |
| o_NONBLOCK | System.Posix.Internals |
| o_RDONLY | System.Posix.Internals |
| o_RDWR | System.Posix.Internals |
| o_TRUNC | System.Posix.Internals |
| o_WRONLY | System.Posix.Internals |