GHC.IO.Device

base-4.6.0.1: Basic libraries

Portability | non-portable
Stability | internal
Maintainer | libraries@haskell.org
Safe Haskell | Trustworthy

GHC.IO.Device

Description

Type classes for I/O providers.

Synopsis

- class RawIO a where
  - read :: a -> Ptr Word8 -> Int -> IO Int
  - readNonBlocking :: a -> Ptr Word8 -> Int -> IO (Maybe Int)
  - write :: a -> Ptr Word8 -> Int -> IO ()
  - writeNonBlocking :: a -> Ptr Word8 -> Int -> IO Int
- class IODevice a where
  - ready :: a -> Bool -> Int -> IO Bool
  - close :: a -> IO ()
  - isTerminal :: a -> IO Bool
  - isSeekable :: a -> IO Bool
  - seek :: a -> SeekMode -> Integer -> IO ()
  - tell :: a -> IO Integer
  - getSize :: a -> IO Integer
  - setSize :: a -> Integer -> IO ()
  - setEcho :: a -> Bool -> IO ()
  - getEcho :: a -> IO Bool
  - setRaw :: a -> Bool -> IO ()
  - devType :: a -> IO IODeviceType
  - dup :: a -> IO a
  - dup2 :: a -> a -> IO a
- data IODeviceType
  - = Directory
  - | Stream
  - | RegularFile
  - | RawDevice
- data SeekMode
  - = AbsoluteSeek
  - | RelativeSeek
  - | SeekFromEnd

# Documentation

class RawIO a where

A low-level I/O provider where the data is bytes in memory.

Methods

read :: a -> Ptr Word8 -> Int -> IO Int

Read up to the specified number of bytes, returning the number of bytes actually read. This function should only block if there is no data available. If there is not enough data available, then the function should just return the available data. A return value of zero indicates that the end of the data stream (e.g. end of file) has been reached.

readNonBlocking :: a -> Ptr Word8 -> Int -> IO (Maybe Int)

Read up to the specified number of bytes, returning the number of bytes actually read, or `Nothing` if the end of the stream has been reached.

write :: a -> Ptr Word8 -> Int -> IO ()

Write the specified number of bytes.

writeNonBlocking :: a -> Ptr Word8 -> Int -> IO Int

Write up to the specified number of bytes without blocking. Returns the actual number of bytes written.

class IODevice a where

I/O operations required for implementing a `Handle`.

Methods

ready :: a -> Bool -> Int -> IO Bool

`ready dev write msecs` returns `True` if the device has data to read (if `write` is `False`) or space to write new data (if `write` is `True`). `msecs` specifies how long to wait, in milliseconds.

close :: a -> IO ()

closes the device. Further operations on the device should produce exceptions.

isTerminal :: a -> IO Bool

returns `True` if the device is a terminal or console.

isSeekable :: a -> IO Bool

returns `True` if the device supports `seek` operations.

seek :: a -> SeekMode -> Integer -> IO ()

seek to the specified position in the data.

tell :: a -> IO Integer

return the current position in the data.

getSize :: a -> IO Integer

return the size of the data.

setSize :: a -> Integer -> IO ()

change the size of the data.

setEcho :: a -> Bool -> IO ()

for terminal devices, changes whether characters are echoed on the device.

getEcho :: a -> IO Bool

returns the current echoing status.

setRaw :: a -> Bool -> IO ()

some devices (e.g. terminals) support a raw mode where characters entered are immediately made available to the program. If available, this operations enables raw mode.

devType :: a -> IO IODeviceType

returns the `IODeviceType` corresponding to this device.

dup :: a -> IO a

duplicates the device, if possible. The new device is expected to share a file pointer with the original device (like Unix `dup`).

dup2 :: a -> a -> IO a

`dup2 source target` replaces the target device with the source device. The target device is closed first, if necessary, and then it is made into a duplicate of the first device (like Unix `dup2`).

data IODeviceType

Type of a device that can be used to back a `Handle` (see also `mkFileHandle`). The standard libraries provide creation of `Handle`s via Posix file operations with file descriptors (see `mkHandleFromFD`) with FD being the underlying `IODevice` instance.

Users may provide custom instances of `IODevice` which are expected to conform the following rules:

Constructors

Directory | The standard libraries do not have direct support for this device type, but a user implementation is expected to provide a list of file names in the directory, in any order, separated by `'\0'` characters, excluding the `.` and `..` names. See also `getDirectoryContents`. Seek operations are not supported on directories (other than to the zero position).
Stream | A duplex communications channel (results in creation of a duplex `Handle`). The standard libraries use this device type when creating `Handle`s for open sockets.
RegularFile | A file that may be read or written, and also may be seekable.
RawDevice | A raw (disk) device which supports block binary read and write operations and may be seekable only to positions of certain granularity (block- aligned).

Instances

Eq IODeviceType |

data SeekMode

A mode that determines the effect of `hSeek` `hdl mode i`.

Constructors

AbsoluteSeek | the position of `hdl` is set to `i`.
RelativeSeek | the position of `hdl` is set to offset `i` from the current position.
SeekFromEnd | the position of `hdl` is set to offset `i` from the end of the file.

Instances

Enum SeekMode |
Eq SeekMode |
Ord SeekMode |
Read SeekMode |
Show SeekMode |
Ix SeekMode |