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The interface every language-tag type is expected to satisfy — one role with four required methods — so unrelated internationalisation libraries can accept each other's tags.

Version

0.2 zef:guifa

Depends

nothing outside the core

License

see the source

Its own test suite

3 files, green

Checked

2026-09-15 against Raku++ 3.28.0 and Rakudo 2026.08

Where it lives

raku.land · source

Install it #

$ rakupp install Intl::LanguageTaggish

zef install Intl::LanguageTaggish writes the same store; either installer leaves the module usable by both engines.

What it is for #

Two libraries that both handle language tags will each have their own tag type, and a program using both then has to convert between them at every boundary. The usual fix is for one to depend on the other, which makes the ecosystem a chain. The better fix is a tiny shared distribution that neither owns: a role saying what a language tag must be able to do, which both can compose without either depending on the other.

That is all this is. Forty-four lines, one role, four required methods and one optional. It ships no tag class of its own and parses nothing.

Composing it #

use Intl::LanguageTaggish;

class Tag does LanguageTaggish {
    has Str $.bcp47;
    method language { $!bcp47.split('-')[0] }
    method region   { $!bcp47.split('-')[1] // Str }
    multi method COERCE(LanguageTaggish:D $t --> Tag) { self.new: :bcp47($t.bcp47) }
    multi method COERCE(Str:D $s --> Tag)             { self.new: :bcp47($s) }
    method FALLBACK($name, |) { "<$name not modelled>" }
}

my $t = Tag.new(:bcp47('es-MX'));
say $t.language, ' ', $t.region, ' ', $t.bcp47;
say $t ~~ LanguageTaggish;
say $t.script;

my Tag() $coerced = 'pt-BR';
say $coerced.bcp47, ' ', $coerced.language;

es MX es-MX
True
<script not modelled>
pt-BR pt

language, region, bcp47 and COERCE are required; leave any of them out and the class will not compile. FALLBACK is optional and is the interesting one: it lets a tag type answer questions about subtags it does not model, rather than failing, which is how a minimal implementation can still be handed to a library expecting a richer one.

The Tag() coercion on the last two lines is what COERCE buys — any routine declaring a Tag() parameter now accepts a plain string.

The one thing to know #

use Intl::LanguageTaggish; does not give you a type called Intl::LanguageTaggish. It imports exactly one name, the short LanguageTaggish, and that name is a role rather than something you can instantiate:

use Intl::LanguageTaggish;

say LanguageTaggish.HOW.^name.subst(/^.*'::'/, '');
say LanguageTaggish.^name;
say (try LanguageTaggish.new('en-US')) // 'new: refused';
say (try LanguageTaggish('en-US')) // 'coercion: refused';

ParametricRoleGroupHOW
LanguageTaggish
new: refused
coercion: refused

So there is no tag in this distribution and nothing here parses 'es-MX'. The language and region methods in the first example are three lines I wrote, not the module's. If you want a working language tag, the Intl::LanguageTag family is what composes this role; this distribution is for the author of such a family, or for a library that wants to accept any of them.

One thing to watch when writing your own: the required COERCE must be declared multi with the role's exact signature. The natural-looking method COERCE(Str $s) compiles under Raku++ and is a hard compile error under Rakudo, so a class written and tested only on Raku++ will not build for Rakudo users.