| OneShotAction | Std.Data.Builder.Base | 
| oneShotAction | Std.Data.Builder.Base | 
| onException | Std.IO.Exception | 
| or# | Std.Foreign.PrimArray | 
| ord# | Std.Foreign.PrimArray | 
| orI# | Std.Foreign.PrimArray | 
| OtherError |   | 
| 1 (Type/Class) | Std.IO.Exception | 
| 2 (Data Constructor) | Std.IO.Exception | 
| otherLevel | Std.IO.Logger | 
| otherLevelWith | Std.IO.Logger | 
| Output | Std.IO.Buffered | 
| Overflow | Std.IO.Exception | 
| O_APPEND | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_CREAT | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_DIRECT | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_DIRECTORY | Std.IO.UV.FFI | 
| O_DSYNC | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_EXCL | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_EXLOCK | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_NOATIME | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_NOCTTY | Std.IO.UV.FFI | 
| O_NOFOLLOW | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_NONBLOCK | Std.IO.UV.FFI | 
| O_RANDOM | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_RDONLY | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_RDWR | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_SEQUENTIAL | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_SHORT_LIVED | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_SYMLINK | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_SYNC | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_TEMPORARY | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_TRUNC | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem | 
| O_WRONLY | Std.IO.UV.FFI, Std.IO.FileSystemT, Std.IO.FileSystem |