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@deckyard/money

@deckyard/money

Currency amounts that are always exact: prices, invoices, payouts, ledgers. A float cannot hold 0.10 and drifts with every sum; this deck keeps an amount as an int of the currency's minor units, cents for EUR, fils for KWD, yen for JPY, and does everything that can land between two minor units through the decimal library, rounding in the mode the caller names.

Conventions

Snippets assume this import:

jennifer
import "@deckyard/money/" as money;

def price as money.Money init money.parse("19.99", "EUR");
io.printf("%s\n", money.format(money.multiply($price, "3", "half-even")));   # 59.97

A Money is two plain fields, amount and currency: 19.99 EUR is Money{amount: 1999, currency: "EUR"}. Store those two wherever the program keeps its data; == compares them. Factors, rates and ratios are decimal strings such as "1.19"; a decimal.Decimal becomes one with decimal.toString.

Errors

Every failure of the deck is Error{kind: "money"}:

  • an unknown currency: money: unknown currency: ABC;
  • amounts of two currencies in one operation: money: different currencies: EUR and USD;
  • text that is not an amount, or has too many places: money: "12.345" has more than 2 decimal places for EUR;
  • a mode that is not one of MODES;
  • a result past the int range: money: amount out of range.

A string the caller passed appears in a message cut to 20 characters, with anything but printable ASCII shown as ?, so a message stays one short line.

Requirements

Jennifer 0.26.0 or newer, jennifer or jennifer-tiny. No capabilities.