Cats-Money

Scala functional library to deal amounts of money. The goal is to provide basic mathematical reasoning to work in money currency and exchange rate.

See the Documentation website https://fabiopinheiro.github.io/cats-money/

Power by cats & shapeless:

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Getting Started with Gitpod

To use the online IDE dondload and install the Visual Studio plugins from the marketplace:

• Scala - https://marketplace.visualstudio.com/items?itemName=scala-lang.scala
• Metals - https://marketplace.visualstudio.com/items?itemName=scalameta.metals

To compile and run you can install scala and sbt: sdk install scala & sdk install sbt

Getting Started locally

You will need to have Git, Java 8, and SBT installed.

We try to have a similar structure to the cats library. Have a look of the Cats Infographic from tpolecat and to the Underscore's Scala Book.

You can also start a Scala console from in SBT (scala> prompt) to play with small snippets of code:

import cats._, implicits._
import shapeless._, record._, union._, syntax.singleton._
import app.fmgp.money.instances.all._

import app.fmgp.money._
import app.fmgp.money.MoneyY._
import app.fmgp.money.CurrencyY._

Have a look on the to Demos for more examples (on the test folder):

• sbt "test:runMain app.fmgp.money.Demo"
• sbt "test:runMain app.fmgp.money.Main"

Adopters

This is still only a draft and experimental library. But I plane to use this on the near future. If anyone else is also looking for a functional approach to work with monetary value, send me a messagem. (I would appreciate example use cases to better reflect over the library.)

Maintainers

The current maintainers (people who can merge pull requests) are:

• Fabio Pinheiro - BitBucket / GitHub

TODO LIST

• implement:
  • Traverse[MoneyTree]
  • Money comparison of different Currency shound NOT compile
    • Try derivation -> https://dotty.epfl.ch/docs/reference/contextual/derivation.html
    • Try multiversal-equality -> https://dotty.epfl.ch/docs/reference/contextual/multiversal-equality.html
  • Add Documentation
    • [WIP] Make a website with https://v2.docusaurus.io/
  • Use dotty Importing Givens - https://dotty.epfl.ch/docs/reference/contextual/given-imports.html
  • Wirte the Demo using mdoc. (Need to wait for better integration with dotty)
• rename classes and draw a UML
  • rename MoneyY and CurrencyY files
  • rename MoneyY to Money.
  • move all the other Money type to other place (like 'experimental' package)
• currency
  • add all currencies from ISO-4217
  • create subset type of currencies
    • [-] try shapeless Union type

      type U = Union.`'a -> EUR, 'b -> USD`.T
      val u1 = Coproduct[U]('a ->> EUR)
      println("u1", u1)

    • try Dotty Union Types =)
  • implement the rates conversion on a subset of currencies
    • [-] try shapeless polymorphic function

      object polymorphicF extends Poly1 {
        implicit def caseEUR = at[EUR.type](i => "sEUR")
        implicit def caseSUSD = at[USD.type](s => "sUSD")
      }
      type CU = EUR.type :+: USD.type :+: CNil
      val cu = Coproduct[CU](USD)
      println("cu", cu, cu map polymorphicF)

• tests:
  • Testing for non-compilation of type unsafe
    • shapeless.test.illTyped
  • Add a code coverage tool (sbt-scoverage)
• demo:
  • [WIP] (+- Done) Demo Main
• to try:
  • Epimorphism, Monomorphism and Isomorphism
  • Rings +-

Copyright and License

cats-money is licensed under the MIT license, available at http://opensource.org/licenses/mit-license.php and also in the LICENSE file.

Copyright the Fabio Pinheiro, 2020.