Convert numbers to number words in a number of languages. Each language has its own module. The module name is based on one of the ISO 639 Alpha codes. Each module contains one or more cardinal functions and a struct function. The cardinal functions directly convert cardinal numbers to a string-like representation of their spoken form. The struct functions convert numbers to a polymorphic representation of their grammatical structure. All language modules are implemented using the numerals-base package.

The use of this package is best understood with some examples. Because the results of conversion are polymorphic we need to choose a specific type. For these examples we'll use simple strings. But any type that has instances for Monoid and IsString will work. First some English number names, both British and US variants:

>>> import qualified Text.Numeral.Language.EN as EN
>>> EN.uk_cardinal 123 :: Maybe String
Just "one hundred and twenty-three"
>>> EN.us_cardinal (10^50 + 42) :: Maybe String
Just "one hundred quindecillion forty-two"

French, which contains some traces of a base 20 system:

>>> import qualified Text.Numeral.Language.FR as FR
>>> FR.cardinal (-99) :: Maybe String
Just "moins quatre-vingt-dix-neuf"

Conversions can fail. Alamblak, a language spoken by a few people in Papua New Guinea, has no representation for negative numbers:

>>> import qualified Text.Numeral.Language.AMP as AMP
>>> AMP.cardinal (-3) :: Maybe String
Nothing

Some languages have multiple scripts and methods for writing number names. Take Chinese for example, which can be written using Han characters or transcribed to the Latin script using Pinyin.

Traditional Chinese characters:

>>> import qualified Text.Numeral.Language.ZH as ZH
>>> ZH.trad_cardinal 123456 :: Maybe String
Just "十二萬三千四百五十六"

Simplified characters for use in financial contexts:

>>> ZH.finance_simpl_cardinal 123456 :: Maybe String
Just "拾贰万参仟肆伯伍拾陆"

Transcribed using Pinyin:

>>> ZH.pinyin_cardinal 123456 :: Maybe String
Just "shíèrwàn sānqiān sìbǎi wǔshí liù"

Using the struct functions you can see the grammatical structure of number names. Because the results of these functions are polymorphic you need to specify a specific type.

>>> import qualified Text.Numeral.Language.NL as NL
>>> NL.struct 123 :: Maybe Integer
Just 123
>>> import Text.Numeral
>>> NL.struct 123 :: Maybe Exp
Just (Add (Lit 100) (Add (Lit 3) (Mul (Lit 2) (Lit 10))))

Compare with:

>>> NL.cardinal 123 :: Maybe String
Just "honderddrieëntwintig"

100 (honderd) + (3 (drie) + (ën) 2 (twin) * 10 (tig))

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