I18N::LangTags - functions for dealing with RFC3066-style language tags |
I18N::LangTags - functions for dealing with RFC3066-style language tags
use I18N::LangTags qw(is_language_tag same_language_tag extract_language_tags super_languages similarity_language_tag is_dialect_of locale2language_tag alternate_language_tags encode_language_tag panic_languages );
...or whatever of those functions you want to import. Those are all the exportable functions -- you're free to import only some, or none at all. By default, none are imported. If you say:
use I18N::LangTags qw(:ALL)
...then all are exported. (This saves you from having to use
something less obvious like use I18N::LangTags qw(/./)
.)
If you don't import any of these functions, assume a &I18N::LangTags::
in front of all the function names in the following examples.
Language tags are a formalism, described in RFC 3066 (obsoleting 1766), for declaring what language form (language and possibly dialect) a given chunk of information is in.
This library provides functions for common tasks involving language tags as they are needed in a variety of protocols and applications.
Please see the ``See Also'' references for a thorough explanation of how to correctly use language tags.
is_language_tag($lang1)
is_language_tag("fr") is TRUE is_language_tag("x-jicarilla") is FALSE (Subtags can be 8 chars long at most -- 'jicarilla' is 9)
is_language_tag("sgn-US") is TRUE (That's American Sign Language)
is_language_tag("i-Klikitat") is TRUE (True without regard to the fact noone has actually registered Klikitat -- it's a formally valid tag)
is_language_tag("fr-patois") is TRUE (Formally valid -- altho descriptively weak!)
is_language_tag("Spanish") is FALSE is_language_tag("french-patois") is FALSE (No good -- first subtag has to match /^([xXiI]|[a-zA-Z]{2,3})$/ -- see RFC3066)
is_language_tag("x-borg-prot2532") is TRUE (Yes, subtags can contain digits, as of RFC3066)
extract_language_tags($whatever)
extract_language_tags("fr, fr-ca, i-mingo") returns: ('fr', 'fr-ca', 'i-mingo')
extract_language_tags("It's like this: I'm in fr -- French!") returns: ('It', 'in', 'fr') (So don't just feed it any old thing.)
The output is untainted. If you don't know what tainting is, don't worry about it.
same_language_tag('x-kadara', 'i-kadara') is TRUE (The x/i- alternation doesn't matter) same_language_tag('X-KADARA', 'i-kadara') is TRUE (...and neither does case) same_language_tag('en', 'en-US') is FALSE (all-English is not the SAME as US English) same_language_tag('x-kadara', 'x-kadar') is FALSE (these are totally unrelated tags) same_language_tag('no-bok', 'nb') is TRUE (no-bok is a legacy tag for nb (Norwegian Bokmal))
same_language_tag
works by just seeing whether
encode_language_tag($lang1)
is the same as
encode_language_tag($lang2)
.
(Yes, I know this function is named a bit oddly. Call it historic reasons.)
similarity_language_tag('fr', 'fr-ca') is 1 (one element in common) similarity_language_tag('fr-ca', 'fr-FR') is 1 (one element in common)
similarity_language_tag('fr-CA-joual', 'fr-CA-PEI') is 2 similarity_language_tag('fr-CA-joual', 'fr-CA') is 2 (two elements in common)
similarity_language_tag('x-kadara', 'i-kadara') is 1 (x/i- doesn't matter)
similarity_language_tag('en', 'x-kadar') is 0 similarity_language_tag('x-kadara', 'x-kadar') is 0 (unrelated tags -- no similarity)
similarity_language_tag('i-cree-syllabic', 'i-cherokee-syllabic') is 0 (no B<leftmost> elements in common!)
Get the order right! It doesn't work the other way around!
is_dialect_of('en-US', 'en') is TRUE (American English IS a dialect of all-English)
is_dialect_of('fr-CA-joual', 'fr-CA') is TRUE is_dialect_of('fr-CA-joual', 'fr') is TRUE (Joual is a dialect of (a dialect of) French)
is_dialect_of('en', 'en-US') is FALSE (all-English is a NOT dialect of American English)
is_dialect_of('fr', 'en-CA') is FALSE
is_dialect_of('en', 'en' ) is TRUE is_dialect_of('en-US', 'en-US') is TRUE (B<Note:> these are degenerate cases)
is_dialect_of('i-mingo-tom', 'x-Mingo') is TRUE (the x/i thing doesn't matter, nor does case)
is_dialect_of('nn', 'no') is TRUE (because 'nn' (New Norse) is aliased to 'no-nyn', as a special legacy case, and 'no-nyn' is a subform of 'no' (Norwegian))
super_languages($lang1)
super_languages("fr-CA-joual") is ("fr-CA", "fr")
super_languages("en-AU") is ("en")
super_languages("en") is empty-list, ()
super_languages("i-cherokee") is empty-list, () ...not ("i"), which would be illegal as well as pointless.
If $lang1 is not a valid language tag, returns empty-list in a list context, undef in a scalar context.
A notable and rather unavoidable problem with this method:
``x-mingo-tom'' has an ``x'' because the whole tag isn't an
IANA-registered tag -- but super_languages('x-mingo-tom')
is
('x-mingo') -- which isn't really right, since 'i-mingo' is
registered. But this module has no way of knowing that. (But note
that same_language_tag('x-mingo', 'i-mingo') is TRUE.)
More importantly, you assume at your peril that superordinates of $lang1 are mutually intelligible with $lang1. Consider this carefully.
locale2language_tag($locale_identifier)
locale2language_tag("en") is "en"
locale2language_tag("en_US") is "en-US"
locale2language_tag("en_US.ISO8859-1") is "en-US"
locale2language_tag("C") is undef or ()
locale2language_tag("POSIX") is undef or ()
locale2language_tag("POSIX") is undef or ()
I'm not totally sure that locale names map satisfactorily to language tags. Think REAL hard about how you use this. YOU HAVE BEEN WARNED.
The output is untainted. If you don't know what tainting is, don't worry about it.
encode_language_tag($lang1)
* tags representing different languages never get the same encoding.
* tags representing the same language always get the same encoding.
* an encoding of a formally valid language tag always is a string value that is defined, has length, and is true if considered as a boolean.
Note that the encoding itself is not a formally valid language tag. Note also that you cannot, currently, go from an encoding back to a language tag that it's an encoding of.
Note also that you must consider the encoded value as atomic; i.e., you should not consider it as anything but an opaque, unanalysable string value. (The internals of the encoding method may change in future versions, as the language tagging standard changes over time.)
encode_language_tag
returns undef if given anything other than a
formally valid language tag.
The reason encode_language_tag
exists is because different language
tags may represent the same language; this is normally treatable with
same_language_tag
, but consider this situation:
You have a data file that expresses greetings in different languages. Its format is ``[language tag]=[how to say 'Hello']'', like:
en-US=Hiho fr=Bonjour i-mingo=Hau'
And suppose you write a program that reads that file and then runs as a daemon, answering client requests that specify a language tag and then expect the string that says how to greet in that language. So an interaction looks like:
greeting-client asks: fr greeting-server answers: Bonjour
So far so good. But suppose the way you're implementing this is:
my %greetings; die unless open(IN, "<in.dat"); while(<IN>) { chomp; next unless /^([^=]+)=(.+)/s; my($lang, $expr) = ($1, $2); $greetings{$lang} = $expr; } close(IN);
at which point %greetings has the contents:
"en-US" => "Hiho" "fr" => "Bonjour" "i-mingo" => "Hau'"
And suppose then that you answer client requests for language $wanted by just looking up $greetings{$wanted}.
If the client asks for ``fr'', that will look up successfully in %greetings, to the value ``Bonjour''. And if the client asks for ``i-mingo'', that will look up successfully in %greetings, to the value ``Hau'''.
But if the client asks for ``i-Mingo'' or ``x-mingo'', or ``Fr'', then the lookup in %greetings fails. That's the Wrong Thing.
You could instead do lookups on $wanted with:
use I18N::LangTags qw(same_language_tag); my $repsonse = ''; foreach my $l2 (keys %greetings) { if(same_language_tag($wanted, $l2)) { $response = $greetings{$l2}; last; } }
But that's rather inefficient. A better way to do it is to start your program with:
use I18N::LangTags qw(encode_language_tag); my %greetings; die unless open(IN, "<in.dat"); while(<IN>) { chomp; next unless /^([^=]+)=(.+)/s; my($lang, $expr) = ($1, $2); $greetings{ encode_language_tag($lang) } = $expr; } close(IN);
and then just answer client requests for language $wanted by just looking up
$greetings{encode_language_tag($wanted)}
And that does the Right Thing.
alternate_language_tags($lang1)
Note that this function does not try to equate new (and never-used, and unusable) ISO639-2 three-letter tags to old (and still in use) ISO639-1 two-letter equivalents -- like ``ara'' -> ``ar'' -- because ``ara'' has never been in use as an Internet language tag, and RFC 3066 stipulates that it never should be, since a shorter tag (``ar'') exists.
Examples:
alternate_language_tags('no-bok') is ('nb') alternate_language_tags('nb') is ('no-bok') alternate_language_tags('he') is ('iw') alternate_language_tags('iw') is ('he') alternate_language_tags('i-hakka') is ('zh-hakka', 'x-hakka') alternate_language_tags('zh-hakka') is ('i-hakka', 'x-hakka') alternate_language_tags('en') is () alternate_language_tags('x-mingo-tom') is ('i-mingo-tom') alternate_language_tags('x-klikitat') is ('i-klikitat') alternate_language_tags('i-klikitat') is ('x-klikitat')
This function returns empty-list if given anything other than a formally valid language tag.
panic_languages(@accept_languages)
For example, if a user accepts only 'ca' (Catalan) and
'es' (Spanish), and the documents/interfaces you have
available are just in German, Italian, and Chinese, then
the user will most likely want the Italian one (and not
the Chinese or German one!), instead of getting
nothing. So panic_languages('ca', 'es')
returns
a list containing 'it' (Italian).
English ('en') is always in the return list, but whether it's at the very end or not depends on the input languages. This function works by consulting an internal table that stipulates what common languages are ``close'' to each other.
A useful construct you might consider using is:
@fallbacks = super_languages(@accept_languages); push @fallbacks, panic_languages( @accept_languages, @fallbacks, );
I've considered making all the above functions that output language
tags return all those tags strictly in lowercase. Having all your
language tags in lowercase does make some things easier. But you
might as well just lowercase as you like, or call
encode_language_tag($lang1)
where appropriate.
In some future version of I18N::LangTags, I plan to include support for RFC2482-style language tags -- which are basically just normal language tags with their ASCII characters shifted into Plane 14.
* RFC 3066, ftp://ftp.isi.edu/in-notes/rfc3066.txt
, ``Tags for the
Identification of Languages''. (Obsoletes RFC 1766)
* RFC 2277, ftp://ftp.isi.edu/in-notes/rfc2277.txt
, ``IETF Policy on
Character Sets and Languages''.
* RFC 2231, ftp://ftp.isi.edu/in-notes/rfc2231.txt
, ``MIME Parameter
Value and Encoded Word Extensions: Character Sets, Languages, and
Continuations''.
* RFC 2482, ftp://ftp.isi.edu/in-notes/rfc2482.txt
,
``Language Tagging in Unicode Plain Text''.
* Locale::Codes, in
http://www.perl.com/CPAN/modules/by-module/Locale/
* ISO 639, ``Code for the representation of names of languages'',
http://www.indigo.ie/egt/standards/iso639/iso639-1-en.html
* ISO 639-2, ``Codes for the representation of names of languages'',
including three-letter codes,
http://lcweb.loc.gov/standards/iso639-2/bibcodes.html
* The IANA list of registered languages (hopefully up-to-date),
ftp://ftp.isi.edu/in-notes/iana/assignments/languages/
Copyright (c) 1998-2001 Sean M. Burke. All rights reserved.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
The programs and documentation in this dist are distributed in the hope that they will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.
Sean M. Burke sburke@cpan.org
I18N::LangTags - functions for dealing with RFC3066-style language tags |