On 4 Apr 2017 13:57, "David Turner" wrote:

It's the currency conversions that will provide the most interesting challenges in that list. If you were only working in a single currency then something based on `Integer` would, I think, be fine. Perhaps `Int` or `Int64` if you needed the extra speed.

There are a number of different ways to implement multiple currencies depending on your desired semantics and applicable accounting rules and regulations. Peter Selinger has a good tutorial covering this at http://www.mathstat.dal.ca/~selinger/accounting/tutorial.html

One thing to watch out for: do you want to be able to do arithmetic on amounts from different currencies? As in, do you want £5 + $5 to have a meaningful result? If you can avoid this, life will be much simpler.

On 4 Apr 2017 12:22, "Saurabh Nanda" wrote:

...

Hi Manuel,

Thank you for your reply. Some clarifications below...

...

It depends on what sort of computation you'll be doing upon those monetary values and on the expectations of your users. It's typical that payment processing applications sacrifice precision and instead prefer to deal in exact quantities

Is there a document which explains common use-cases for monetary values and best-practices for dealing with them? Any guidelines for which **Haskell** data-types to use for what kind of monetary calculations?

Here is what we are doing in our app:

* Powering web-based e-commerce checkout flows * Allowing store owners to input tax rates * Allowing end-customers to see product prices in different currencies (so, currency conversion) * Various reports to see total sales, total receivables, and total payables (basically a **very** small subset of small-business accounting) * Exporting data to full-fledged accounting systems, like Quickbooks and Xero.

Based on this use-case, which Haskell data-type would you suggest?

-- Saurabh.

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