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base-4.12.0.0: Basic libraries

Copyright(c) The University of Glasgow 2008-2009
Licensesee libraries/base/LICENSE
Maintainerlibraries@haskell.org
Stabilityinternal
Portabilitynon-portable
Safe HaskellTrustworthy
LanguageHaskell2010

GHC.IO.Encoding

Description

Text codecs for I/O

Synopsis

Documentation

dataBufferCodec from to stateSource#

Constructors

BufferCodec 

Fields

  • encode ::CodeBuffer from to

    Theencode function translates elements of the bufferfrom to the bufferto. 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 into, orfrom does not contain a complete multibyte sequence.

    If multiple CodingProgress returns are possible, OutputUnderflow must be preferred to InvalidSequence. This allows GHC's IO library to assume that if we observe InvalidSequence there is at least a single element available in the output buffer.

    The fact that as many elements as possible are translated 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.

  • recover ::Buffer from ->Buffer to ->IO (Buffer from,Buffer to)

    Therecover function is used to continue decoding in the presence of invalid or unrepresentable sequences. This includes both those detected byencode returningInvalidSequence and those that occur because the input byte sequence appears to be truncated.

    Progress will usually be made by skipping the first element of thefrom buffer. This function should only be called if you are certain that you wish to do this skipping and if theto buffer has at least one element of free space. Because this function deals with decoding failure, it assumes that the from buffer has at least one element.

    recover may raise an exception rather than skipping anything.

    Currently, some implementations ofrecover may mutate the input buffer. In particular, this feature is used to implement transliteration.

    Since: 4.4.0.0

  • close ::IO ()

    Resources associated with the encoding may now be released. Theencode function may not be called again after callingclose.

  • 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 ()
     

dataTextEncodingSource#

ATextEncoding 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. TheTextEncoding for UTF-8 isutf8.

Constructors

TextEncoding 

Fields

  • textEncodingName ::String

    a string that can be passed tomkTextEncoding to create an equivalentTextEncoding.

  • mkTextDecoder ::IO (TextDecoder dstate)

    Creates a means of decoding bytes into characters: the result must not be shared between several byte sequences or simultaneously across threads

  • mkTextEncoder ::IO (TextEncoder estate)

    Creates a means of encode characters into bytes: the result must not be shared between several character sequences or simultaneously across threads

Instances
ShowTextEncodingSource#

Since: 4.3.0.0

Instance details

Defined inGHC.IO.Encoding.Types

typeTextEncoder state =BufferCodecCharBufElemWord8 stateSource#

typeTextDecoder state =BufferCodecWord8CharBufElem stateSource#

dataCodingProgressSource#

Since: 4.4.0.0

Constructors

InputUnderflow

Stopped because the input contains insufficient available elements, or all of the input sequence has been successfully translated.

OutputUnderflow

Stopped because the output contains insufficient free elements

InvalidSequence

Stopped because there are sufficient free elements in the output to output at least one encoded ASCII character, but the input contains an invalid or unrepresentable sequence

Instances
EqCodingProgressSource#

Since: 4.4.0.0

Instance details

Defined inGHC.IO.Encoding.Types

ShowCodingProgressSource#

Since: 4.4.0.0

Instance details

Defined inGHC.IO.Encoding.Types

latin1 ::TextEncodingSource#

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 aHandle using thelatin1 encoding will result in an error.

latin1_encode ::CharBuffer ->BufferWord8 ->IO (CharBuffer,BufferWord8)Source#

latin1_decode ::BufferWord8 ->CharBuffer ->IO (BufferWord8,CharBuffer)Source#

utf8 ::TextEncodingSource#

The UTF-8 Unicode encoding

utf8_bom ::TextEncodingSource#

The UTF-8 Unicode encoding, with a byte-order-mark (BOM; the byte sequence 0xEF 0xBB 0xBF). This encoding behaves likeutf8, 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 ::TextEncodingSource#

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

utf16le ::TextEncodingSource#

The UTF-16 Unicode encoding (litte-endian)

utf16be ::TextEncodingSource#

The UTF-16 Unicode encoding (big-endian)

utf32 ::TextEncodingSource#

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

utf32le ::TextEncodingSource#

The UTF-32 Unicode encoding (litte-endian)

utf32be ::TextEncodingSource#

The UTF-32 Unicode encoding (big-endian)

initLocaleEncoding ::TextEncodingSource#

Since: 4.5.0.0

getLocaleEncoding ::IOTextEncodingSource#

The Unicode encoding of the current locale

Since: 4.5.0.0

getFileSystemEncoding ::IOTextEncodingSource#

The Unicode encoding of the current locale, but allowing arbitrary undecodable bytes to be round-tripped through it.

ThisTextEncoding is used to decode and encode command line arguments and environment variables on non-Windows platforms.

On Windows, this encoding *should not* be used if possible because the use of code pages is deprecated: Strings should be retrieved via the "wide" W-family of UTF-16 APIs instead

Since: 4.5.0.0

getForeignEncoding ::IOTextEncodingSource#

The Unicode encoding of the current locale, but where undecodable bytes are replaced with their closest visual match. Used for theCString marshalling functions inForeign.C.String

Since: 4.5.0.0

setLocaleEncoding ::TextEncoding ->IO ()Source#

Since: 4.5.0.0

setFileSystemEncoding ::TextEncoding ->IO ()Source#

Since: 4.5.0.0

setForeignEncoding ::TextEncoding ->IO ()Source#

Since: 4.5.0.0

char8 ::TextEncodingSource#

An encoding in which Unicode code points are translated to bytes by taking the code point modulo 256. When decoding, bytes are translated directly into the equivalent code point.

This encoding never fails in either direction. However, encoding discards information, so encode followed by decode is not the identity.

Since: 4.4.0.0

mkTextEncoding ::String ->IOTextEncodingSource#

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

There is additional notation (borrowed from GNU iconv) 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.
  • a suffix of//ROUNDTRIP will use a PEP383-style escape mechanism to represent any invalid bytes in the input as Unicode codepoints (specifically, as lone surrogates, which are normally invalid in UTF-32). Upon output, these special codepoints are detected and turned back into the corresponding original byte.

In theory, this mechanism allows arbitrary data to be roundtripped via aString with no loss of data. In practice, there are two limitations to be aware of:

  1. This only stands a chance of working for an encoding which is an ASCII superset, as for security reasons we refuse to escape any bytes smaller than 128. Many encodings of interest are ASCII supersets (in particular, you can assume that the locale encoding is an ASCII superset) but many (such as UTF-16) are not.
  2. If the underlying encoding is not itself roundtrippable, this mechanism can fail. Roundtrippable encodings are those which have an injective mapping into Unicode. Almost all encodings meet this criteria, but some do not. Notably, Shift-JIS (CP932) and Big5 contain several different encodings of the same Unicode codepoint.

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

argvEncoding ::IOTextEncodingSource#

Internal encoding of argv

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