base-4.3.1.0: Basic libraries

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

GHC.IO.Encoding

Description

Text codecs for I/O

Synopsis

- data BufferCodec from to state = BufferCodec {
  - encode :: Buffer from -> Buffer to -> IO (Buffer from, Buffer to)
  - close :: IO ()
  - getState :: IO state
  - setState :: state -> IO ()
  }
- data TextEncoding = forall dstate estate . TextEncoding {
  - textEncodingName :: String
  - mkTextDecoder :: IO (TextDecoder dstate)
  - mkTextEncoder :: IO (TextEncoder estate)
  }
- type TextEncoder state = BufferCodec CharBufElem Word8 state
- type TextDecoder state = BufferCodec Word8 CharBufElem state
- latin1 :: TextEncoding
- latin1_encode :: CharBuffer -> Buffer Word8 -> IO (CharBuffer, Buffer Word8)
- latin1_decode :: Buffer Word8 -> CharBuffer -> IO (Buffer Word8, CharBuffer)
- utf8 :: TextEncoding
- utf8_bom :: TextEncoding
- utf16 :: TextEncoding
- utf16le :: TextEncoding
- utf16be :: TextEncoding
- utf32 :: TextEncoding
- utf32le :: TextEncoding
- utf32be :: TextEncoding
- localeEncoding :: TextEncoding
- mkTextEncoding :: String -> IO TextEncoding

# Documentation

data BufferCodec from to state

Constructors

BufferCodec |

Fields

encode :: Buffer from -> Buffer to -> IO (Buffer from, Buffer to)

  The `encode` function translates elements of the buffer `from` to the buffer `to`. It should translate as many elements as possible given the sizes of the buffers, including translating zero elements if there is either not enough room in `to`, or `from` does not contain a complete multibyte sequence.

  `encode` should raise an exception if, and only if, `from` begins with an illegal sequence, or the first element of `from` is not representable in the encoding of `to`. That is, if any elements can be successfully translated before an error is encountered, then `encode` should translate as much as it can and not throw an exception. This behaviour is used by the IO library in order to report translation errors at the point they actually occur, rather than when the buffer is translated.

close :: IO ()

  Resources associated with the encoding may now be released. The `encode` function may not be called again after calling `close`.

getState :: IO state

  Return the current state of the codec.

  Many codecs are not stateful, and in these case the state can be represented as '()'. Other codecs maintain a state. For example, UTF-16 recognises a BOM (byte-order-mark) character at the beginning of the input, and remembers thereafter whether to use big-endian or little-endian mode. In this case, the state of the codec would include two pieces of information: whether we are at the beginning of the stream (the BOM only occurs at the beginning), and if not, whether to use the big or little-endian encoding.

setState :: state -> IO ()

data TextEncoding

A `TextEncoding` is a specification of a conversion scheme between sequences of bytes and sequences of Unicode characters.

For example, UTF-8 is an encoding of Unicode characters into a sequence of bytes. The `TextEncoding` for UTF-8 is `utf8`.

Constructors

forall dstate estate . TextEncoding |

Fields

textEncodingName :: String

  a string that can be passed to `mkTextEncoding` to create an equivalent `TextEncoding`.

mkTextDecoder :: IO (TextDecoder dstate)
mkTextEncoder :: IO (TextEncoder estate)

Instances

Show TextEncoding |

type TextEncoder state = BufferCodec CharBufElem Word8 state

type TextDecoder state = BufferCodec Word8 CharBufElem state

latin1 :: TextEncoding

The Latin1 (ISO8859-1) encoding. This encoding maps bytes directly to the first 256 Unicode code points, and is thus not a complete Unicode encoding. An attempt to write a character greater than '\255' to a `Handle` using the `latin1` encoding will result in an error.

latin1_encode :: CharBuffer -> Buffer Word8 -> IO (CharBuffer, Buffer Word8)

latin1_decode :: Buffer Word8 -> CharBuffer -> IO (Buffer Word8, CharBuffer)

utf8 :: TextEncoding

The UTF-8 Unicode encoding

utf8_bom :: TextEncoding

The UTF-8 Unicode encoding, with a byte-order-mark (BOM; the byte sequence 0xEF 0xBB 0xBF). This encoding behaves like `utf8`, except that on input, the BOM sequence is ignored at the beginning of the stream, and on output, the BOM sequence is prepended.

The byte-order-mark is strictly unnecessary in UTF-8, but is sometimes used to identify the encoding of a file.

utf16 :: TextEncoding

The UTF-16 Unicode encoding (a byte-order-mark should be used to indicate endianness).

utf16le :: TextEncoding

The UTF-16 Unicode encoding (litte-endian)

utf16be :: TextEncoding

The UTF-16 Unicode encoding (big-endian)

utf32 :: TextEncoding

The UTF-32 Unicode encoding (a byte-order-mark should be used to indicate endianness).

utf32le :: TextEncoding

The UTF-32 Unicode encoding (litte-endian)

utf32be :: TextEncoding

The UTF-32 Unicode encoding (big-endian)

localeEncoding :: TextEncoding

The Unicode encoding of the current locale

mkTextEncoding :: String -> IO TextEncoding

Look up the named Unicode encoding. May fail with

- `isDoesNotExistError` if the encoding is unknown

The set of known encodings is system-dependent, but includes at least:

-     UTF-8

- `UTF-16`, `UTF-16BE`, `UTF-16LE`
- `UTF-32`, `UTF-32BE`, `UTF-32LE`

On systems using GNU iconv (e.g. Linux), there is additional notation for specifying how illegal characters are handled:

- a suffix of `//IGNORE`, e.g. `UTF-8//IGNORE`, will cause all illegal sequences on input to be ignored, and on output will drop all code points that have no representation in the target encoding.
- a suffix of `//TRANSLIT` will choose a replacement character for illegal sequences or code points.

On Windows, you can access supported code pages with the prefix `CP`; for example, `"CP1250"`.