| O | GHC.Base |
| objectName | GHC.ExecutionStack, GHC.ExecutionStack.Internal |
| odd | GHC.Real, Prelude |
| oldGenFactor | GHC.RTS.Flags |
| on | Data.Function |
| One | GHC.Base, GHC.Exts |
| oneBits | Data.Bits, Foreign.Safe, Foreign |
| 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) | GHC.IO.StdHandles, System.IO |
| openBinaryTempFile | System.IO |
| openBinaryTempFileWithDefaultPermissions | System.IO |
| openFile | |
| 1 (Function) | GHC.IO.FD |
| 2 (Function) | GHC.IO.Handle.FD |
| 3 (Function) | GHC.IO.StdHandles, System.IO |
| openFileBlocking | |
| 1 (Function) | GHC.IO.Handle.FD |
| 2 (Function) | GHC.IO.StdHandles |
| openFileWith | GHC.IO.FD |
| OpenPunctuation | Data.Char, GHC.Unicode |
| 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.Foldable, Data.List, Prelude |
| or# | GHC.Base, GHC.Exts |
| or64# | GHC.Base, GHC.Exts |
| Ord | Data.Ord, GHC.Base, Prelude |
| ord | Data.Char, GHC.Base |
| ord# | GHC.Base, GHC.Exts |
| Ord1 | Data.Functor.Classes |
| Ord2 | Data.Functor.Classes |
| OrdCond | Data.Type.Ord |
| Ordering | Data.Ord, GHC.Base, GHC.Exts, Prelude |
| OrderingI | Data.Type.Ord, GHC.TypeLits |
| orElse | GHC.Conc, GHC.Conc.Sync |
| 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 | Data.Char, GHC.Unicode |
| OtherNumber | Data.Char, GHC.Unicode |
| OtherPunctuation | Data.Char, GHC.Unicode |
| OtherSymbol | Data.Char, GHC.Unicode |
| otherwise | Data.Bool, GHC.Base, Prelude |
| outer | Data.Type.Equality |
| outputNL | GHC.IO.Handle, GHC.IO.Handle.Types, System.IO |
| OutputUnderflow | GHC.IO.Encoding, GHC.IO.Encoding.Types |
| Overflow | Control.Exception, Control.Exception.Base, GHC.Exception, 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 |