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# BB.Cldr.Number (bb v0.8.0)

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Formats numbers and currencies based upon CLDR's decimal formats specification.

The format specification is documentated in Unicode TR35. There are several classes of formatting including non-scientific, scientific, rules based (for spelling and ordinal formats), compact formats that display `1k` rather than `1,000` and so on. See `Cldr.Number.to_string/2` for specific formatting options.

### Non-Scientific Notation Formatting

The following description applies to formats that do not use scientific notation or significant digits:

- If the number of actual integer digits exceeds the maximum integer digits, then only the least significant digits are shown. For example, 1997 is formatted as "97" if the maximum integer digits is set to 2.

- If the number of actual integer digits is less than the minimum integer digits, then leading zeros are added. For example, 1997 is formatted as "01997" if the minimum integer digits is set to 5.

- If the number of actual fraction digits exceeds the maximum fraction digits, then half-even rounding it performed to the maximum fraction digits. For example, 0.125 is formatted as "0.12" if the maximum fraction digits is 2. This behavior can be changed by specifying a rounding increment and a rounding mode.

- If the number of actual fraction digits is less than the minimum fraction digits, then trailing zeros are added. For example, 0.125 is formatted as "0.1250" if the minimum fraction digits is set to 4.

- Trailing fractional zeros are not displayed if they occur j positions after the decimal, where j is less than the maximum fraction digits. For example, 0.10004 is formatted as "0.1" if the maximum fraction digits is four or less.

### Scientific Notation Formatting

Numbers in scientific notation are expressed as the product of a mantissa and a power of ten, for example, 1234 can be expressed as 1.234 x 10^3. The mantissa is typically in the half-open interval [1.0, 10.0) or sometimes [0.0, 1.0), but it need not be. In a pattern, the exponent character immediately followed by one or more digit characters indicates scientific notation. Example: "0.###E0" formats the number 1234 as "1.234E3".

- The number of digit characters after the exponent character gives the minimum exponent digit count. There is no maximum. Negative exponents are formatted using the localized minus sign, not the prefix and suffix from the pattern. This allows patterns such as "0.###E0 m/s". To prefix positive exponents with a localized plus sign, specify '+' between the exponent and the digits: "0.###E+0" will produce formats "1E+1", "1E+0", "1E-1", and so on. (In localized patterns, use the localized plus sign rather than '+'.)

- The minimum number of integer digits is achieved by adjusting the exponent. Example: 0.00123 formatted with "00.###E0" yields "12.3E-4". This only happens if there is no maximum number of integer digits. If there is a maximum, then the minimum number of integer digits is fixed at one.

- The maximum number of integer digits, if present, specifies the exponent grouping. The most common use of this is to generate engineering notation, in which the exponent is a multiple of three, for example, "##0.###E0". The number 12345 is formatted using "##0.####E0" as "12.345E3".

- When using scientific notation, the formatter controls the digit counts using significant digits logic. The maximum number of significant digits limits the total number of integer and fraction digits that will be shown in the mantissa; it does not affect parsing. For example, 12345 formatted with "##0.##E0" is "12.3E3". Exponential patterns may not contain grouping separators.

### Significant Digits

There are two ways of controlling how many digits are shows: (a) significant digits counts, or (b) integer and fraction digit counts. Integer and fraction digit counts are described above. When a formatter is using significant digits counts, it uses however many integer and fraction digits are required to display the specified number of significant digits. It may ignore min/max integer/fraction digits, or it may use them to the extent possible.

# Summary

## Functions

parse(string, options \\ [])

Parse a string locale-aware manner and return a number.

resolve_currencies(list, options \\ [])

Resolve curencies from strings within a list.

resolve_currency(string, options \\ [])

Resolve a currency from a string

resolve_per(string, options \\ [])

Resolve and tokenize percent or permille from the beginning and/or the end of a string

resolve_pers(list, options \\ [])

Resolve and tokenize percent and permille sybols from strings within a list.

scan(string, options \\ [])

Scans a string locale-aware manner and returns a list of strings and numbers.

to_approx_string(number, options \\ [])

Formats a number and applies the `:approximately` format for a locale and number system.

to_at_least_string(number, options \\ [])

Formats a number and applies the `:at_least` format for a locale and number system.

to_at_most_string(number, options \\ [])

Formats a number and applies the `:at_most` format for a locale and number system.

to_range_string(range, options \\ [])

Formats the first and last numbers of a range and applies the `:range` format for a locale and number system.

to_string(number, options \\ default_options())

Returns a number formatted into a string according to a format pattern and options.

to_string!(number, options \\ default_options())

Same as the execution of `to_string/2` but raises an exception if an error would be returned.

validate_number_system(locale, number_system)

Return a valid number system from a provided locale and number system name or type.

# Functions

# parse(string, options \\ [])

Parse a string locale-aware manner and return a number.

## Arguments

- `string` is any `String.t`

- `options` is a keyword list of options

## Options

- `:number` is one of `:integer`, `:float`, `:decimal` or `nil`. The default is `nil` meaning that the type auto-detected as either an `integer` or a `float`.

- `:locale` is any locale returned by `BB.Cldr.known_locale_names/0` or a `Cldr.LanguageTag.t`. The default is `BB.Cldr.get_locale/0`.

## Returns

- A number of the requested or default type or

- `{:error, {exception, error}}` if no number could be determined

## Notes

This function parses a string to return a number but in a locale-aware manner. It will normalise grouping characters and decimal separators, different forms of the `+` and `-` symbols that appear in Unicode and strips any `_` characters that might be used for formatting in a string. It then parses the number using the Elixir standard library functions.

## Examples

    iex> BB.Cldr.Number.parse("＋1.000,34", locale: "de")
    {:ok, 1000.34}

    iex> BB.Cldr.Number.parse("-1_000_000.34")
    {:ok, -1000000.34}

    iex> BB.Cldr.Number.parse("1.000", locale: "de", number: :integer)
    {:ok, 1000}

    iex> BB.Cldr.Number.parse("＋1.000,34", locale: "de", number: :integer)
    {:error,
      {Cldr.Number.ParseError,
       "The string \"＋1.000,34\" could not be parsed as a number"}}

# resolve_currencies(list, options \\ [])

Resolve curencies from strings within a list.

## Arguments

- `list` is any list in which currency names and symbols are expected

- `options` is a keyword list of options

## Options

- `:locale` is any valid locale returned by `Cldr.known_locale_names/1` or a `Cldr.LanguageTag` struct returned by `Cldr.Locale.new!/2` The default is `BB.Cldr.get_locale()`

- `:only` is an `atom` or list of `atoms` representing the currencies or currency types to be considered for a match. The equates to a list of acceptable currencies for parsing. See the notes below for currency types.

- `:except` is an `atom` or list of `atoms` representing the currencies or currency types to be not considered for a match. This equates to a list of unacceptable currencies for parsing. See the notes below for currency types.

- `:fuzzy` is a float greater than `0.0` and less than or equal to `1.0` which is used as input to `String.jaro_distance/2` to determine is the provided currency string is close enough to a known currency string for it to identify definitively a currency code. It is recommended to use numbers greater than `0.8` in order to reduce false positives.

## Notes

The `:only` and `:except` options accept a list of currency codes and/or currency types. The following types are recognised.

If both `:only` and `:except` are specified, the `:except` entries take priority - that means any entries in `:except` are removed from the `:only` entries.

- `:all`, the default, considers all currencies

- `:current` considers those currencies that have a `:to` date of nil and which also is a known ISO4217 currency

- `:historic` is the opposite of `:current`

- `:tender` considers currencies that are legal tender

- `:unannotated` considers currencies that don't have "(some string)" in their names. These are usually financial instruments.

## Examples

    iex> BB.Cldr.Number.scan("100 US dollars")
    ...> |> BB.Cldr.Number.resolve_currencies
    [100, :USD]

    iex> BB.Cldr.Number.scan("100 eurosports")
    ...> |> BB.Cldr.Number.resolve_currencies(fuzzy: 0.75)
    [100, :EUR]

    iex> BB.Cldr.Number.scan("100 dollars des États-Unis")
    ...> |> BB.Cldr.Number.resolve_currencies(locale: "fr")
    [100, :USD]

# resolve_currency(string, options \\ [])

Resolve a currency from a string

## Arguments

- `list` is any list in which currency names and symbols are expected

- `options` is a keyword list of options

## Options

- `:locale` is any valid locale returned by `Cldr.known_locale_names/1` or a `Cldr.LanguageTag` struct returned by `Cldr.Locale.new!/2` The default is `BB.Cldr.get_locale()`

- `:only` is an `atom` or list of `atoms` representing the currencies or currency types to be considered for a match. The equates to a list of acceptable currencies for parsing. See the notes below for currency types.

- `:except` is an `atom` or list of `atoms` representing the currencies or currency types to be not considered for a match. This equates to a list of unacceptable currencies for parsing. See the notes below for currency types.

- `:fuzzy` is a float greater than `0.0` and less than or equal to `1.0` which is used as input to `String.jaro_distance/2` to determine is the provided currency string is close enough to a known currency string for it to identify definitively a currency code. It is recommended to use numbers greater than `0.8` in order to reduce false positives.

## Returns

- An ISO4217 currency code as an atom or

- `{:error, {exception, message}}`

## Notes

The `:only` and `:except` options accept a list of currency codes and/or currency types. The following types are recognised.

If both `:only` and `:except` are specified, the `:except` entries take priority - that means any entries in `:except` are removed from the `:only` entries.

- `:all`, the default, considers all currencies

- `:current` considers those currencies that have a `:to` date of nil and which also is a known ISO4217 currency

- `:historic` is the opposite of `:current`

- `:tender` considers currencies that are legal tender

- `:unannotated` considers currencies that don't have "(some string)" in their names. These are usually financial instruments.

## Examples

    iex> BB.Cldr.Number.resolve_currency("US dollars")
    [:USD]

    iex> BB.Cldr.Number.resolve_currency("100 eurosports", fuzzy: 0.75)
    [:EUR]

    iex> BB.Cldr.Number.resolve_currency("dollars des États-Unis", locale: "fr")
    [:USD]

    iex> BB.Cldr.Number.resolve_currency("not a known currency", locale: "fr")
    {:error,
     {Cldr.UnknownCurrencyError,
      "The currency \"not a known currency\" is unknown or not supported"}}

# resolve_per(string, options \\ [])

(since 2.22.0)

    @spec resolve_per(String.t(), Keyword.t()) ::
      Cldr.Number.Parser.per()
      | [Cldr.Number.Parser.per() | String.t()]
      | {:error, {module(), String.t()}}

Resolve and tokenize percent or permille from the beginning and/or the end of a string

## Arguments

- `list` is any list in which percent and permille symbols are expected

- `options` is a keyword list of options

## Options

- `:locale` is any valid locale returned by `Cldr.known_locale_names/1` or a `Cldr.LanguageTag` struct returned by `Cldr.Locale.new!/2` The default is `options[:backend].get_locale()`

## Returns

- An `:percent` or `permille` or

- `{:error, {exception, message}}`

## Examples

    iex> BB.Cldr.Number.resolve_per "11%"
    ["11", :percent]

    iex> BB.Cldr.Number.resolve_per "% of linguists"
    [:percent, " of linguists"]

    iex> BB.Cldr.Number.resolve_per "% of linguists %"
    [:percent, " of linguists ", :percent]

# resolve_pers(list, options \\ [])

(since 2.22.0)

    @spec resolve_pers([String.t(), ...], Keyword.t()) :: [
      Cldr.Number.Parser.per() | String.t()
    ]

Resolve and tokenize percent and permille sybols from strings within a list.

Percent and permille symbols can be identified at the beginning and/or the end of a string.

## Arguments

- `list` is any list in which percent and permille symbols are expected

- `options` is a keyword list of options

## Options

- `:locale` is any valid locale returned by `Cldr.known_locale_names/1` or a `t:Cldr.LanguageTag` struct returned by `Cldr.Locale.new!/2` The default is `options[:backend].get_locale()`

## Examples

    iex> BB.Cldr.Number.scan("100%")
    ...> |> BB.Cldr.Number.resolve_pers()
    [100, :percent]

# scan(string, options \\ [])

Scans a string locale-aware manner and returns a list of strings and numbers.

## Arguments

- `string` is any `String.t`

- `options` is a keyword list of options

## Options

- `:number` is one of `:integer`, `:float`, `:decimal` or `nil`. The default is `nil` meaning that the type auto-detected as either an `integer` or a `float`.

- `:locale` is any locale returned by `Cldr.known_locale_names/1` or a `Cldr.LanguageTag.t`. The default is `BB.Cldr.get_locale/0`.

## Returns

- A list of strings and numbers

## Notes

Number parsing is performed by `Cldr.Number.Parser.parse/2` and any options provided are passed to that function.

## Examples

    iex> BB.Cldr.Number.scan("£1_000_000.34")
    ["£", 1000000.34]

    iex> BB.Cldr.Number.scan("I want £1_000_000 dollars")
    ["I want £", 1000000, " dollars"]

    iex> BB.Cldr.Number.scan("The prize is 23")
    ["The prize is ", 23]

    iex> BB.Cldr.Number.scan("The lottery number is 23 for the next draw")
    ["The lottery number is ", 23, " for the next draw"]

    iex> BB.Cldr.Number.scan("The loss is -1.000 euros", locale: "de", number: :integer)
    ["The loss is ", -1000, " euros"]

# to_approx_string(number, options \\ [])

    @spec to_approx_string(number() | Decimal.t(), Keyword.t() | Keyword.t() | map()) ::
      {:ok, String.t()} | {:error, {module(), String.t()}}

Formats a number and applies the `:approximately` format for a locale and number system.

## Arguments

- `number` is an integer, float or Decimal to be formatted

- `options` is a keyword list defining how the number is to be formatted. See `Cldr.Number.to_string/3` for a description of the available options.

## Example

    iex> BB.Cldr.Number.to_approx_string 1234
    {:ok, "~1,234"}

# to_at_least_string(number, options \\ [])

    @spec to_at_least_string(number() | Decimal.t(), Keyword.t() | Keyword.t() | map()) ::
      {:ok, String.t()} | {:error, {module(), String.t()}}

Formats a number and applies the `:at_least` format for a locale and number system.

## Arguments

- `number` is an integer, float or Decimal to be formatted

- `options` is a keyword list defining how the number is to be formatted. See `BB.Cldr.Number.to_string/2` for a description of the available options.

## Example

    iex> BB.Cldr.Number.to_at_least_string 1234
    {:ok, "1,234+"}

# to_at_most_string(number, options \\ [])

    @spec to_at_most_string(number() | Decimal.t(), Keyword.t() | Keyword.t() | map()) ::
      {:ok, String.t()} | {:error, {module(), String.t()}}

Formats a number and applies the `:at_most` format for a locale and number system.

## Arguments

- `number` is an integer, float or Decimal to be formatted

- `options` is a keyword list defining how the number is to be formatted. See `Cldr.Number.to_string/3` for a description of the available options.

## Example

    iex> BB.Cldr.Number.to_at_most_string 1234
    {:ok, "≤1,234"}

# to_range_string(range, options \\ [])

    @spec to_range_string(Range.t(), Keyword.t() | Keyword.t() | map()) ::
      {:ok, String.t()} | {:error, {module(), String.t()}}

Formats the first and last numbers of a range and applies the `:range` format for a locale and number system.

## Arguments

- `number` is an integer, float or Decimal to be formatted

- `options` is a keyword list defining how the number is to be formatted. See `Cldr.Number.to_string/3` for a description of the available options.

## Example

    iex> BB.Cldr.Number.to_range_string 1234..5678
    {:ok, "1,234–5,678"}

# to_string(number, options \\ default_options())

    @spec to_string(number() | Decimal.t(), Keyword.t() | map()) ::
      {:ok, String.t()} | {:error, {atom(), String.t()}}

Returns a number formatted into a string according to a format pattern and options.

## Arguments

- `number` is an integer, float or Decimal to be formatted

- `options` is a keyword list defining how the number is to be formatted.

## Options

- `format`: the format style or a format string defining how the number is formatted. See `Cldr.Number.Format` for how format strings can be constructed. See `Cldr.Number.Format.format_styles_for/3` to return available format styles for a locale. The default `format` is `:standard`.

- If `:format` is set to `:long` or `:short` then the formatting depends on whether `:currency` is specified. If not specified then the number is formatted as `:decimal_long` or `:decimal_short`. If `:currency` is specified the number is formatted as `:currency_long` or `:currency_short` and `:fractional_digits` is set to 0 as a default.

- `:format` may also be a format defined by CLDR's Rules Based Number Formats (RBNF). Further information is found in the module `Cldr.Rbnf`. The most commonly used formats in this category are to spell out the number in a the locales language. The applicable formats are `:spellout`, `:spellout_year`, `:ordinal`. A number can also be formatted as roman numbers by using the format `:roman` or `:roman_lower`.

- `currency`: is the currency for which the number is formatted. For available currencies see `Cldr.Currency.known_currencies/0`. This option is required if `:format` is set to `:currency`. If `currency` is set and no `:format` is set, `:format` will be set to `:currency` as well.

- `currency_symbol`: Allows overriding a currency symbol. The alternatives are:

  - `:iso` the ISO currency code will be used instead of the default currency symbol.
  - `:narrow` uses the narrow symbol defined for the locale. The same narrow symbol can be defined for more than one currency and therefore this should be used with care. If no narrow symbol is defined, the standard symbol is used.
  - `:symbol` uses the standard symbol defined in CLDR. A symbol is unique for each currency and can be safely used.
  - "string" uses `string` as the currency symbol
  - `:standard` (the default and recommended) uses the CLDR-defined symbol based upon the currency format for the locale.

- `:cash`: a boolean which indicates whether a number being formatted as a `:currency` is to be considered a cash value or not. Currencies can be rounded differently depending on whether `:cash` is `true` or `false`. *This option is deprecated in favour of `currency_digits: :cash`.

- `:currency_digits` indicates which of the rounding and digits should be used. The options are `:accounting` which is the default, `:cash` or `:iso`

- `:rounding_mode`: determines how a number is rounded to meet the precision of the format requested. The available rounding modes are `:down`, :half_up, :half_even, :ceiling, :floor, :half_down, :up. The default is `:half_even`.

- `:number_system`: determines which of the number systems for a locale should be used to define the separators and digits for the formatted number. If `number_system` is an `atom` then `number_system` is interpreted as a number system. If the `:number_system` is `binary` then it is interpreted as a number system name. See `Cldr.Number.System.number_system_names_for/2`. The default is `:default`.

- `:locale`: determines the locale in which the number is formatted. See `Cldr.known_locale_names/0`. The default is`Cldr.get_locale/0` which is the locale currently in affect for this `Process` and which is set by `Cldr.put_locale/1`.

- If `:fractional_digits` is set to a positive integer value then the number will be rounded to that number of digits and displayed accordingly - overriding settings that would be applied by default. For example, currencies have fractional digits defined reflecting each currencies minor unit. Setting `:fractional_digits` will override that setting.

- If `:maximum_integer_digits` is set to a positive integer value then the number is left truncated before formatting. For example if the number `1234` is formatted with the option `maximum_integer_digits: 2`, the number is truncated to `34` and formatted.

- If `:round_nearest` is set to a positive integer value then the number will be rounded to nearest increment of that value - overriding settings that would be applied by default.

- `:minimum_grouping_digits` overrides the CLDR definition of minimum grouping digits. For example in the locale `es` the number `1234` is formatted by default as `1345` because the locale defines the `minimium_grouping_digits` as `2`. If `minimum_grouping_digits: 1` is set as an option the number is formatting as `1.345`. The `:minimum_grouping_digits` is added to the grouping defined by the number format. If the sum of these two digits is greater than the number of digits in the integer (or fractional) part of the number then no grouping is performed.

- `:wrapper` is a 2-arity function that will be called for each number component with parameters `string` and `tag` where `tag` is one of `:number`, `:currency_symbol`, `:currency_space`, `:literal`, `:quote`, `:percent`, `:permille`, `:minus` or `:plus`. The function must return a string. The function can be used to wrap format elements in HTML or other tags.

## Locale extensions affecting formatting

A locale identifier can specify options that affect number formatting. These options are:

- `nu`: defines the number system to be used if none is specified by the `:number_system` option to `to_string/2`

This key is part of the u extension and that document should be consulted for details on how to construct a locale identifier with these extensions.

## Wrapping format elements

Wrapping elements is particularly useful when formatting a number with a currency symbol and the requirement is to have different HTML formatting applied to the symbol than the number. For example:

    iex> Cldr.Number.to_string(100, format: :currency, currency: :USD, wrapper: fn
    ...>   string, :currency_symbol -> "<span class=\"symbol\">" <> string <> "</span>"
    ...>   string, :number -> "<span class=\"number\">" <> string <> "</span>"
    ...>   string, :currency_space -> "<span>" <> string <> "</span>"
    ...>   string, _other -> string
    ...> end)
    {:ok, "<span class=\"symbol\">$</span><span class=\"number\">100.00</span>"}

It is also possible and recommended to use the `Phoenix.HTML.Tag.content_tag/3` function if wrapping HTML tags since these will ensure HTML entities are correctly encoded. For example:

    iex> Cldr.Number.to_string(100, format: :currency, currency: :USD, wrapper: fn
    ...>   string, :currency_symbol -> Phoenix.HTML.Tag.content_tag(:span, string, class: "symbol")
    ...>   string, :number -> Phoenix.HTML.Tag.content_tag(:span, string, class: "number")
    ...>   string, :currency_space -> Phoenix.HTML.Tag.content_tag(:span, string)
    ...>   string, _other -> string
    ...> end)
    {:ok, "<span class=\"symbol\">$</span><span class=\"number\">100.00</span>"}

When formatting a number the format is parsed into format elements that might include a currency symbol, a literal string, inserted text between a currency symbol and the currency amount, a percent sign, the number itself and several other elements. In some cases it is helpful to be apply specific formatting to each element. This can be achieved by specifying a `:wrapper` option. This option takes a 2-arity function as an argument. For each element of the format the wrapper function is called with two parameters: the format element as a string and an atom representing the element type. The wrapper function is required to return a string that is then inserted in the final formatted number.

## Returns

- `{:ok, string}` or

- `{:error, {exception, message}}`

## Examples

    iex> BB.Cldr.Number.to_string 12345
    {:ok, "12,345"}

    iex> BB.Cldr.Number.to_string 12345, locale: "fr"
    {:ok, "12 345"}

    iex> BB.Cldr.Number.to_string 1345.32, currency: :EUR, locale: "es", minimum_grouping_digits: 1
    {:ok, "1.345,32 €"}

    iex> BB.Cldr.Number.to_string 1345.32, currency: :EUR, locale: "es"
    {:ok, "1345,32 €"}

    iex> BB.Cldr.Number.to_string 12345, locale: "fr", currency: "USD"
    {:ok, "12 345,00 $US"}

    iex> BB.Cldr.Number.to_string 12345, format: "#E0"
    {:ok, "1.2345E4"}

    iex> BB.Cldr.Number.to_string 12345, format: :accounting, currency: "THB"
    {:ok, "THB 12,345.00"}

    iex> BB.Cldr.Number.to_string -12345, format: :accounting, currency: "THB"
    {:ok, "(THB 12,345.00)"}

    iex> BB.Cldr.Number.to_string 12345, format: :accounting, currency: "THB",
    ...> locale: "th"
    {:ok, "฿12,345.00"}

    iex> BB.Cldr.Number.to_string 12345, format: :accounting, currency: "THB",
    ...> locale: "th", number_system: :native
    {:ok, "฿๑๒,๓๔๕.๐๐"}

    iex> BB.Cldr.Number.to_string 1244.30, format: :long
    {:ok, "1 thousand"}

    iex> BB.Cldr.Number.to_string 1244.30, format: :long, currency: "USD"
    {:ok, "1,244 US dollars"}

    iex> BB.Cldr.Number.to_string 1244.30, format: :short
    {:ok, "1K"}

    iex> BB.Cldr.Number.to_string 1244.30, format: :short, currency: "EUR"
    {:ok, "€1K"}

    iex> BB.Cldr.Number.to_string 1234, format: :spellout
    {:ok, "one thousand two hundred thirty-four"}

    iex> BB.Cldr.Number.to_string 1234, format: :spellout_verbose
    {:ok, "one thousand two hundred and thirty-four"}

    iex> BB.Cldr.Number.to_string 1989, format: :spellout_year
    {:ok, "nineteen eighty-nine"}

    iex> BB.Cldr.Number.to_string 123, format: :ordinal
    {:ok, "123rd"}

    iex> BB.Cldr.Number.to_string 123, format: :roman
    {:ok, "CXXIII"}

    iex> BB.Cldr.Number.to_string 123, locale: "th-u-nu-thai"
    {:ok, "๑๒๓"}

## Errors

An error tuple `{:error, reason}` will be returned if an error is detected. The two most likely causes of an error return are:

- A format cannot be compiled. In this case the error tuple will look like:

        iex> BB.Cldr.Number.to_string(12345, format: "0#")
        {:error, {Cldr.FormatCompileError,
          "Decimal format compiler: syntax error before: \"#\""}}

- The format style requested is not defined for the `locale` and `number_system`. This happens typically when the number system is `:algorithmic` rather than the more common `:numeric`. In this case the error return looks like:

        iex> BB.Cldr.Number.to_string(1234, locale: "he", number_system: "hebr", format: :percent)
        {:error, {Cldr.UnknownFormatError,
          "The locale :he with number system :hebr does not define a format :percent"}}

# to_string!(number, options \\ default_options())

    @spec to_string!(number() | Decimal.t() | String.t(), Keyword.t() | map()) ::
      String.t() | no_return()

Same as the execution of `to_string/2` but raises an exception if an error would be returned.

## Arguments

- `number` is an integer, float or Decimal to be formatted

- `options` is a keyword list defining how the number is to be formatted. See `BB.Cldr.Number.to_string/2`

## Returns

- a formatted number as a string or

- raises an exception

## Examples

    iex> BB.Cldr.Number.to_string! 12345
    "12,345"

    iex> BB.Cldr.Number.to_string! 12345, locale: "fr"
    "12 345"

# validate_number_system(locale, number_system)

    @spec validate_number_system(
      Cldr.Locale.locale_name() | Cldr.LanguageTag.t(),
      Cldr.Number.System.system_name() | Cldr.Number.System.types()
    ) :: {:ok, Cldr.Number.System.system_name()} | {:error, {module(), String.t()}}

Return a valid number system from a provided locale and number system name or type.

The number system or number system type must be valid for the given locale. If a number system type is provided, the underlying number system is returned.

## Arguments

- `locale` is any valid locale name returned by `Cldr.known_locale_names/1` or a `Cldr.LanguageTag` struct returned by `Cldr.Locale.new!/2`

- `system_name` is any number system name returned by `Cldr.known_number_systems/0` or a number system type returned by `Cldr.known_number_system_types/0`

## Examples

    iex> BB.Cldr.Number.validate_number_system "en", :latn
    {:ok, :latn}

    iex> BB.Cldr.Number.validate_number_system "en", :default
    {:ok, :latn}

    iex> BB.Cldr.Number.validate_number_system "en", :unknown
    {:error,
     {Cldr.UnknownNumberSystemError, "The number system :unknown is unknown"}}

    iex> BB.Cldr.Number.validate_number_system "zz", :default
    {:error, {Cldr.InvalidLanguageError, "The language \"zz\" is invalid"}}