Copyright	(c) The University of Glasgow, 2008-2009
License	see libraries/base/LICENSE
Maintainer	[email protected]
Stability	internal
Portability	non-portable
Safe Haskell	Trustworthy
Language	Haskell2010

data BufferCodec from to state Source

data TextEncoding Source

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.

type TextEncoder state = BufferCodec CharBufElem Word8 state Source

type TextDecoder state = BufferCodec Word8 CharBufElem state Source

data CodingProgress Source

Since: 4.4.0.0

latin1 :: TextEncoding Source

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) Source

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

utf8 :: TextEncoding Source

The UTF-8 Unicode encoding

utf8_bom :: TextEncoding Source

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 Source

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

utf16le :: TextEncoding Source

The UTF-16 Unicode encoding (litte-endian)

utf16be :: TextEncoding Source

The UTF-16 Unicode encoding (big-endian)

utf32 :: TextEncoding Source

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

utf32le :: TextEncoding Source

The UTF-32 Unicode encoding (litte-endian)

utf32be :: TextEncoding Source

The UTF-32 Unicode encoding (big-endian)

initLocaleEncoding :: TextEncoding Source

Since: 4.5.0.0

getLocaleEncoding :: IO TextEncoding Source

The Unicode encoding of the current locale

Since: 4.5.0.0

getFileSystemEncoding :: IO TextEncoding Source

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

This TextEncoding 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 :: IO TextEncoding Source

The Unicode encoding of the current locale, but where undecodable bytes are replaced with their closest visual match. Used for the CString marshalling functions in Foreign.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 :: TextEncoding Source

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 -> IO TextEncoding Source

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 a String 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 prefix CP; for example, "CP1250".