text-icu- Bindings to the ICU library

Safe HaskellSafe-Infered




Character set conversion functions for Unicode, implemented as bindings to the International Components for Unicode (ICU) libraries.


Character set conversion

data Converter Source

Character set converter type. Note: this structure is not thread safe. It is not safe to use value of this type simultaneously from multiple threads.

Basic functions



:: String

Name of the converter to use.

-> Maybe Bool

Whether to use fallback mappings (see usesFallback for details).

-> IO Converter 

Create a Converter with the name of a coded character set specified as a string. The actual name will be resolved with the alias file using a case-insensitive string comparison that ignores leading zeroes and all non-alphanumeric characters. E.g., the names "UTF8", "utf-8", "u*T@f08" and "Utf 8" are all equivalent (see also compareNames). If an empty string is passed for the converter name, it will create one with the getDefaultName return value.

A converter name may contain options like a locale specification to control the specific behavior of the newly instantiated converter. The meaning of the options depends on the particular converter. If an option is not defined for or recognized by a given converter, then it is ignored.

Options are appended to the converter name string, with a comma between the name and the first option and also between adjacent options.

If the alias is ambiguous, then the preferred converter is used.

The conversion behavior and names can vary between platforms. ICU may convert some characters differently from other platforms. Details on this topic are in the ICU User's Guide at http://icu-project.org/userguide/conversion.html. Aliases starting with a "cp" prefix have no specific meaning other than its an alias starting with the letters "cp". Please do not associate any meaning to these aliases.

fromUnicode :: Converter -> Text -> ByteStringSource

Convert the Unicode string into a codepage string using the given converter.

toUnicode :: Converter -> ByteString -> TextSource

Convert the codepage string into a Unicode string using the given converter.

Converter metadata

getName :: Converter -> StringSource

Gets the internal, canonical name of the converter.

usesFallback :: Converter -> BoolSource

Determines whether the converter uses fallback mappings or not. This flag has restrictions. Regardless of this flag, the converter will always use fallbacks from Unicode Private Use code points, as well as reverse fallbacks (to Unicode). For details see ".ucm File Format" in the Conversion Data chapter of the ICU User Guide: http://www.icu-project.org/userguide/conversion-data.html#ucmformat

isAmbiguous :: Converter -> BoolSource

Indicates whether the converter contains ambiguous mappings of the same character or not.

Functions for controlling global behavior

getDefaultName :: IO StringSource

Returns the current default converter name. If you want to open a default converter, you do not need to use this function. It is faster to pass the empty string to open the default converter.

setDefaultName :: String -> IO ()Source

Sets the current default converter name. If this function needs to be called, it should be called during application initialization. Most of the time, the results from getDefaultName or open with an empty string argument is sufficient for your application.

Note: this function is not thread safe. Do not call this function when any ICU function is being used from more than one thread!

Miscellaneous functions

compareNames :: String -> String -> OrderingSource

Do a fuzzy compare of two converter/alias names. The comparison is case-insensitive, ignores leading zeroes if they are not followed by further digits, and ignores all but letters and digits. Thus the strings "UTF-8", "utf_8", "u*T@f08" and "Utf 8" are exactly equivalent. See section 1.4, Charset Alias Matching in Unicode Technical Standard #22 at http://www.unicode.org/reports/tr22/

aliases :: String -> [String]Source

Return the aliases for a given converter or alias name.


converterNames :: [String]Source

A list of the canonical names of all available converters.

standardNames :: [String]Source

The list of supported standard names.