Copyright	(c) Tuomas Laakkonen 2016
License	BSD3
Maintainer	pigworts2@gmail.com
Stability	Experimental
Portability	Non-portable (GHC extensions)
Safe Haskell	None
Language	Haskell2010

Data.Currency.Convert

Description

This module allows values of currency to be converted from one currency to another using exchange rates from various sources.

The basic operation for this module is as follows:

First, get a conversion function (with getDefaultConverter or getConverter):

>>> Converter convert <- getDefaultConverter

Then, construct some value of currency using the convenience functions, and convert it using the convert function you just got:

>>> convert (usd 100) :: EUR
90.0 eur

The result type of convert defines what currency the value will be converted into.

Synopsis

Documentation

newtype Converter Source

Converter is a newtype wrapper around the type of conversion functions to avoid ImpredicativeTypes in getConverter

Constructors

Converter (forall a b. (KnownSymbol a, KnownSymbol b) => Currency a -> Currency b)

getConverter :: RateProvider -> IO Converter Source

getConverter takes a rate provider and returns a Converter in the IO monad. It is used like this:

>>> Converter convert <- getConverter provider

convert can then be used to convert between currencies:

>>> convert (usd 100) :: GBP
75.0 gbp

getDefaultConverter :: IO Converter Source

getDefaultConverter is like getConverter except no provider needs to be specified (defaultProvider is used).

unsafeCoerceCurrency :: Currency a -> Currency b Source

unsafeCoerceCurrency can be used to convert between currencies directly without using exchange rates. Only use this if you know the resulting currency is supported by your RateProvider

data Currency s Source

Currency is a wrapper around Double that has a phantom symbol type, allowing different currencies to be distinguished using type level literals.

To extract the value from a Currency value, use toRational from Real.

Instances

Eq (Currency s) Source
Fractional (Currency a) Source
Num (Currency a) Source
Ord (Currency s) Source
Read (Currency a) Source
Real (Currency a) Source
RealFrac (Currency a) Source
KnownSymbol s => Show (Currency s) Source

data RateProvider Source

RateProvider is used by getConverter to provide a conversion rate dictionary to the resulting conversion function. RateProvider has two fields, the name (:: String), and the action (:: IO RateDict). The name is used in error reporting, and the action is used to provide conversion rates when needed.

There are several prebuilt RateProviders - fixerIOProvider, backupProvider, localProvider, dictProvider and defaultProvider.

Constructors

RateProvider String (IO RateDict)

newtype RateDict Source

RateDict is the type provided by a RateProvider. It is a mapping from currency codes to currency-to-euro conversion rates.

Constructors

RateDict [(String, Double)]

defaultProvider :: RateProvider Source

This RateProvider is used by getDefaultConverter it first tries fixer.io and then resorts to the backup dictionary.

backupProvider :: RateProvider Source

This RateProvider has a hardcoded dictionary.

dictProvider :: String -> [(String, Double)] -> RateProvider Source

This RateProvider allows a dictionary to be provided.

localProvider :: FilePath -> RateProvider Source

This RateProvider takes a file path and returns a dictionary of rates from the file. The file must be in the form

    <name1> <rate1>
    <name2> <rate2>
    ...

fixerIOProvider :: RateProvider Source

This RateProvider uses the fixer.io API to return exchange rates updated daily by the European Central Bank.

(<|-|>) :: RateProvider -> RateProvider -> RateProvider infixr 9 Source

'(<|-|>)' combines two RateProviders to create a third. This provider tries to return the first providers result, but if an exception is raised, it returns the second providers result.

aud :: Double -> AUD Source

The Australian Dollar

bgn :: Double -> BGN Source

The Bulgarian Lev

brl :: Double -> BRL Source

The Brazillian Real

cad :: Double -> CAD Source

The Canadian Dollar

chf :: Double -> CHF Source

The Swiss Franc

cny :: Double -> CNY Source

The Yuan