defmodule Gettext.Plural do
@moduledoc """
Behaviour and default implementation for finding plural forms in given
locales.
This module both defines the `Gettext.Plural` behaviour and provides a default
implementation for it.
## Plural forms
> For a given language, there is a grammatical rule on how to change words
> depending on the number qualifying the word. Different languages can have
> different rules.
[[source]](https://udn.realityripple.com/docs/Mozilla/Localization/Localization_and_Plurals)
Such grammatical rules define a number of **plural forms**. For example,
English has two plural forms: one for when there is just one element (the
*singular*) and another one for when there are zero or more than one elements
(the *plural*). There are languages which only have one plural form and there
are languages which have more than two.
In GNU Gettext (and in Gettext for Elixir), plural forms are represented by
increasing 0-indexed integers. For example, in English `0` means singular and
`1` means plural.
The goal of this module is to determine, given a locale:
* how many plural forms exist in that locale (`nplurals/1`);
* to what plural form a given number of elements belongs to in that locale
(`plural/2`).
## Default implementation
`Gettext.Plural` provides a default implementation of a plural module. Most
languages used on Earth should be covered by this default implementation. If
custom pluralization rules are needed (for example, to add additional
languages) a different plural module can be specified when creating a Gettext
backend. For example, pluralization rules for the Elvish language could be
added as follows:
defmodule MyApp.Plural do
@behaviour Gettext.Plural
def nplurals("elv"), do: 3
def plural("elv", 0), do: 0
def plural("elv", 1), do: 1
def plural("elv", _), do: 2
# Fallback to Gettext.Plural
def nplurals(locale), do: Gettext.Plural.nplurals(locale)
def plural(locale, n), do: Gettext.Plural.plural(locale, n)
end
The mathematical expressions used in this module to determine the plural form
of a given number of elements are taken from [this
page](http://localization-guide.readthedocs.org/en/latest/l10n/pluralforms.html#f2)
as well as from [Mozilla's guide on "Localization and
plurals"](https://udn.realityripple.com/docs/Mozilla/Localization/Localization_and_Plurals).
Now that we have defined our custom plural forms, we can use them
in two ways. You can set it for all `:gettext` backends in your
config files:
config :gettext, :plural_forms, MyApp.Plural
Or to each specific backend:
defmodule MyApp.Gettext do
use Gettext, otp_app: :my_app, plural_forms: MyApp.Plural
end
**Note**: set `:plural_forms` in your `config/config.exs` and
not in `config/runtime.exs`, as this configuration is read when
compiling your backends.
Notice that tasks such as `mix gettext.merge` use the plural
backend configured under the `:gettext` application, so generally
speaking the first format is preferred.
Note some tasks also allow the number of plural forms to be given
explicitly, for example:
mix gettext.merge priv/gettext --locale=gsw_CH --plural-forms=2
### Unknown locales
Trying to call `Gettext.Plural` functions with unknown locales will result in
a `Gettext.Plural.UnknownLocaleError` exception.
### Language and territory
Often, a locale is composed as a language and territory couple, such as
`en_US`. The default implementation for `Gettext.Plural` handles `xx_YY` by
forwarding it to `xx` (except for *just Brazilian Portuguese*, `pt_BR`, which
is not forwarded to `pt` as pluralization rules slightly differ). We treat the
underscore as a separator according to
[ISO 15897](https://en.wikipedia.org/wiki/ISO/IEC_15897). Sometimes, a dash `-` is
used as a separator (for example [BCP47](https://en.wikipedia.org/wiki/IETF_language_tag)
locales use this as in `en-US`): this is not forwarded to `en` in the default
`Gettext.Plural` (and it will raise an `Gettext.Plural.UnknownLocaleError` exception
if there are no translations for `en-US`).
## Examples
An example of the plural form of a given number of elements in the Polish
language:
iex> Plural.plural("pl", 1)
0
iex> Plural.plural("pl", 2)
1
iex> Plural.plural("pl", 5)
2
iex> Plural.plural("pl", 112)
2
As expected, `nplurals/1` returns the possible number of plural forms:
iex> Plural.nplurals("pl")
3
"""
# Behaviour definition.
@doc """
Returns the number of possible plural forms in the given `locale`.
"""
@callback nplurals(locale :: String.t()) :: pos_integer
@doc """
Returns the plural form in the given `locale` for the given `count` of
elements.
"""
@callback plural(locale :: String.t(), count :: integer) :: plural_form :: non_neg_integer
defmodule UnknownLocaleError do
@moduledoc """
Raised when a pluralized module doesn't know how to handle a locale.
## Examples
raise Gettext.Plural.UnknownLocaleError, "en-US"
"""
defexception [:message]
def exception(locale) when is_binary(locale) do
message = """
unknown locale #{inspect(locale)}. If this is a locale you need to handle,
consider using a custom pluralizer module instead of the default
Gettext.Plural. You can read more about this on the Gettext docs at
https://hexdocs.pm/gettext/Gettext.Plural.html
"""
%__MODULE__{message: message}
end
end
# Behaviour implementation.
defmacrop ends_in(n, digits) do
digits = List.wrap(digits)
quote do
rem(unquote(n), 10) in unquote(digits)
end
end
@one_form [
# Aymará
"ay",
# Tibetan
"bo",
# Chiga
"cgg",
# Dzongkha
"dz",
# Persian
"fa",
# Indonesian
"id",
# Japanese
"ja",
# Lojban
"jbo",
# Georgian
"ka",
# Kazakh
"kk",
# Khmer
"km",
# Korean
"ko",
# Kyrgyz
"ky",
# Lao
"lo",
# Malay
"ms",
# Burmese
"my",
# Yakut
"sah",
# Sundanese
"su",
# Thai
"th",
# Tatar
"tt",
# Uyghur
"ug",
# Vietnamese
"vi",
# Wolof
"wo",
# Chinese [2]
"zh"
]
@two_forms_1 [
# Afrikaans
"af",
# Aragonese
"an",
# Angika
"anp",
# Assamese
"as",
# Asturian
"ast",
# Azerbaijani
"az",
# Bulgarian
"bg",
# Bengali
"bn",
# Bodo
"brx",
# Catalan
"ca",
# Danish
"da",
# German
"de",
# Dogri
"doi",
# Greek
"el",
# English
"en",
# Esperanto
"eo",
# Spanish
"es",
# Estonian
"et",
# Basque
"eu",
# Fulah
"ff",
# Finnish
"fi",
# Faroese
"fo",
# Friulian
"fur",
# Frisian
"fy",
# Galician
"gl",
# Gujarati
"gu",
# Hausa
"ha",
# Hebrew
"he",
# Hindi
"hi",
# Chhattisgarhi
"hne",
# Armenian
"hy",
# Hungarian
"hu",
# Interlingua
"ia",
# Italian
"it",
# Greenlandic
"kl",
# Kannada
"kn",
# Kurdish
"ku",
# Letzeburgesch
"lb",
# Maithili
"mai",
# Malayalam
"ml",
# Mongolian
"mn",
# Manipuri
"mni",
# Marathi
"mr",
# Nahuatl
"nah",
# Neapolitan
"nap",
# Norwegian Bokmal
"nb",
# Nepali
"ne",
# Dutch
"nl",
# Northern Sami
"se",
# Norwegian Nynorsk
"nn",
# Norwegian (old code)
"no",
# Northern Sotho
"nso",
# Oriya
"or",
# Pashto
"ps",
# Punjabi
"pa",
# Papiamento
"pap",
# Piemontese
"pms",
# Portuguese
"pt",
# Romansh
"rm",
# Kinyarwanda
"rw",
# Santali
"sat",
# Scots
"sco",
# Sindhi
"sd",
# Sinhala
"si",
# Somali
"so",
# Songhay
"son",
# Albanian
"sq",
# Swahili
"sw",
# Swedish
"sv",
# Tamil
"ta",
# Telugu
"te",
# Turkmen
"tk",
# Urdu
"ur",
# Yoruba
"yo"
]
@two_forms_2 [
# Acholi
"ach",
# Akan
"ak",
# Amharic
"am",
# Mapudungun
"arn",
# Breton
"br",
# Filipino
"fil",
# French
"fr",
# Gun
"gun",
# Lingala
"ln",
# Mauritian Creole
"mfe",
# Malagasy
"mg",
# Maori
"mi",
# Occitan
"oc",
# Tajik
"tg",
# Tigrinya
"ti",
# Tagalog
"tl",
# Turkish
"tr",
# Uzbek
"uz",
# Walloon
"wa"
]
@three_forms_slavic [
# Belarusian
"be",
# Bosnian
"bs",
# Croatian
"hr",
# Serbian
"sr",
# Russian
"ru",
# Ukrainian
"uk"
]
@three_forms_slavic_alt [
# Czech
"cs",
# Slovak
"sk"
]
# Number of plural forms.
def nplurals(locale)
# All the groupable forms.
for l <- @one_form do
def nplurals(unquote(l)), do: 1
end
for l <- @two_forms_1 ++ @two_forms_2 do
def nplurals(unquote(l)), do: 2
end
for l <- @three_forms_slavic ++ @three_forms_slavic_alt do
def nplurals(unquote(l)), do: 3
end
# Then, all other ones.
# Arabic
def nplurals("ar"), do: 6
# Kashubian
def nplurals("csb"), do: 3
# Welsh
def nplurals("cy"), do: 4
# Irish
def nplurals("ga"), do: 5
# Scottish Gaelic
def nplurals("gd"), do: 4
# Icelandic
def nplurals("is"), do: 2
# Javanese
def nplurals("jv"), do: 2
# Cornish
def nplurals("kw"), do: 4
# Lithuanian
def nplurals("lt"), do: 3
# Latvian
def nplurals("lv"), do: 3
# Macedonian
def nplurals("mk"), do: 3
# Mandinka
def nplurals("mnk"), do: 3
# Maltese
def nplurals("mt"), do: 4
# Polish
def nplurals("pl"), do: 3
# Romanian
def nplurals("ro"), do: 3
# Slovenian
def nplurals("sl"), do: 4
# Match-all clause.
def nplurals(locale) do
recall_if_territory_or_raise(locale, &nplurals/1)
end
# Plural form of groupable languages.
def plural(locale, count)
# All the `x_Y` languages that have different pluralization rules than `x`.
def plural("pt_BR", n) when n in [0, 1], do: 0
def plural("pt_BR", _n), do: 1
# Groupable forms.
for l <- @one_form do
def plural(unquote(l), _n), do: 0
end
for l <- @two_forms_1 do
def plural(unquote(l), 1), do: 0
def plural(unquote(l), _n), do: 1
end
for l <- @two_forms_2 do
def plural(unquote(l), n) when n in [0, 1], do: 0
def plural(unquote(l), _n), do: 1
end
for l <- @three_forms_slavic do
def plural(unquote(l), n)
when ends_in(n, 1) and rem(n, 100) != 11,
do: 0
def plural(unquote(l), n)
when ends_in(n, [2, 3, 4]) and (rem(n, 100) < 10 or rem(n, 100) >= 20),
do: 1
def plural(unquote(l), _n), do: 2
end
for l <- @three_forms_slavic_alt do
def plural(unquote(l), 1), do: 0
def plural(unquote(l), n) when n in 2..4, do: 1
def plural(unquote(l), _n), do: 2
end
# Custom plural forms.
# Arabic
# n==0 ? 0 : n==1 ? 1 : n==2 ? 2 : n%100>=3 && n%100<=10 ? 3 : n%100>=11 ? 4 : 5
def plural("ar", 0), do: 0
def plural("ar", 1), do: 1
def plural("ar", 2), do: 2
def plural("ar", n) when rem(n, 100) >= 3 and rem(n, 100) <= 10, do: 3
def plural("ar", n) when rem(n, 100) >= 11, do: 4
def plural("ar", _n), do: 5
# Kashubian
# (n==1) ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2;
def plural("csb", 1), do: 0
def plural("csb", n)
when ends_in(n, [2, 3, 4]) and (rem(n, 100) < 10 or rem(n, 100) >= 20),
do: 1
def plural("csb", _n), do: 2
# Welsh
# (n==1) ? 0 : (n==2) ? 1 : (n != 8 && n != 11) ? 2 : 3
def plural("cy", 1), do: 0
def plural("cy", 2), do: 1
def plural("cy", n) when n != 8 and n != 11, do: 2
def plural("cy", _n), do: 3
# Irish
# n==1 ? 0 : n==2 ? 1 : (n>2 && n<7) ? 2 :(n>6 && n<11) ? 3 : 4
def plural("ga", 1), do: 0
def plural("ga", 2), do: 1
def plural("ga", n) when n in 3..6, do: 2
def plural("ga", n) when n in 7..10, do: 3
def plural("ga", _n), do: 4
# Scottish Gaelic
# (n==1 || n==11) ? 0 : (n==2 || n==12) ? 1 : (n > 2 && n < 20) ? 2 : 3
def plural("gd", n) when n == 1 or n == 11, do: 0
def plural("gd", n) when n == 2 or n == 12, do: 1
def plural("gd", n) when n > 2 and n < 20, do: 2
def plural("gd", _n), do: 3
# Icelandic
# n%10!=1 || n%100==11
def plural("is", n) when ends_in(n, 1) and rem(n, 100) != 11, do: 0
def plural("is", _n), do: 1
# Javanese
# n != 0
def plural("jv", 0), do: 0
def plural("jv", _), do: 1
# Cornish
# (n==1) ? 0 : (n==2) ? 1 : (n == 3) ? 2 : 3
def plural("kw", 1), do: 0
def plural("kw", 2), do: 1
def plural("kw", 3), do: 2
def plural("kw", _), do: 3
# Lithuanian
# n%10==1 && n%100!=11 ? 0 : n%10>=2 && (n%100<10 || n%100>=20) ? 1 : 2
def plural("lt", n)
when ends_in(n, 1) and rem(n, 100) != 11,
do: 0
def plural("lt", n)
when rem(n, 10) >= 2 and (rem(n, 100) < 10 or rem(n, 100) >= 20),
do: 1
def plural("lt", _), do: 2
# Latvian
# n%10==1 && n%100!=11 ? 0 : n != 0 ? 1 : 2
def plural("lv", n) when ends_in(n, 1) and rem(n, 100) != 11, do: 0
def plural("lv", n) when n != 0, do: 1
def plural("lv", _), do: 2
# Macedonian
# n==1 || n%10==1 ? 0 : 1; Can’t be correct needs a 2 somewhere
def plural("mk", n) when ends_in(n, 1), do: 0
def plural("mk", n) when ends_in(n, 2), do: 1
def plural("mk", _), do: 2
# Mandinka
# n==0 ? 0 : n==1 ? 1 : 2
def plural("mnk", 0), do: 0
def plural("mnk", 1), do: 1
def plural("mnk", _), do: 2
# Maltese
# n==1 ? 0 : n==0 || ( n%100>1 && n%100<11) ? 1 : (n%100>10 && n%100<20 ) ? 2 : 3
def plural("mt", 1), do: 0
def plural("mt", n) when n == 0 or (rem(n, 100) > 1 and rem(n, 100) < 11), do: 1
def plural("mt", n) when rem(n, 100) > 10 and rem(n, 100) < 20, do: 2
def plural("mt", _), do: 3
# Polish
# n==1 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2
def plural("pl", 1), do: 0
def plural("pl", n)
when ends_in(n, [2, 3, 4]) and (rem(n, 100) < 10 or rem(n, 100) >= 20),
do: 1
def plural("pl", _), do: 2
# Romanian
# n==1 ? 0 : (n==0 || (n%100 > 0 && n%100 < 20)) ? 1 : 2
def plural("ro", 1), do: 0
def plural("ro", n) when n == 0 or (rem(n, 100) > 0 and rem(n, 100) < 20), do: 1
def plural("ro", _), do: 2
# Slovenian
# n%100==1 ? 1 : n%100==2 ? 2 : n%100==3 || n%100==4 ? 3 : 0
def plural("sl", n) when rem(n, 100) == 1, do: 1
def plural("sl", n) when rem(n, 100) == 2, do: 2
def plural("sl", n) when rem(n, 100) == 3, do: 3
def plural("sl", _), do: 0
# Match-all clause.
def plural(locale, n) do
recall_if_territory_or_raise(locale, &plural(&1, n))
end
defp recall_if_territory_or_raise(locale, fun) do
case String.split(locale, "_", parts: 2, trim: true) do
[lang, _territory] -> fun.(lang)
_other -> raise UnknownLocaleError, locale
end
end
end
