Category: Scala

Scala self-recursive types

Posted: 2015-03-30   |   Categories: Programming, Scala   |   Tags: Self-recursive type, Self-type, Type system

One of the advantages of using a statically typed language is that you can use the type system to enforce some constraints. Scala provides self-recursive types, aka F-bounded polymorphic types that–along with self types–let you put powerful constraint to your type definitions.

Self-recursive type definition

Terminology apart, let me show you one of the use cases where this could be useful. Consider the following example which does not use a self-recursive type:

Scala DSL for currency-related operations

Posted: 2015-02-20   |   Categories: Programming, Scala   |   Tags: DSL, Implicit

A simple internal DSL in Scala for money-related operations

Source code: Scala DSL for money-related operations

This Domain-Specific Language (DSL) lets you perform operations among different currencies, by transparently doing all internal conversions. The conversion map is injected implicitly by the client code.

Usage Example

Here’s a simple usage example:

 
import com.lambdista.money._
import com.lambdista.money.Currency._

object Main {

  def main(args: Array[String]): Unit = {

    val conversion: Conversion = Map(
      (GBP, EUR) -> 1.270,
      (EUR, USD) -> 1.268,
      (GBP, USD) -> 1.611
    )

    implicit val converter = Converter(conversion)

    val sumAndConversion1 = 100.001(USD) + 200(EUR) to GBP
    println(s"sumAndConversion1: $sumAndConversion1")

    val sumAndConversion2: Money = 100(USD) + 210.4(EUR) to EUR
    println(s"sumAndConversion2: $sumAndConversion2")

    val sum = 100.001(USD) + 200(EUR)
    val simpleConversion = sum(GBP)
    println(s"simpleConversion: $simpleConversion")

    val sumWithSimpleNumber = 100(USD) + 23.560
    println(s"sumWithSimpleNumber: $sumWithSimpleNumber")

    val multiplicationWithSimpleNumber = 100(USD) * 23
    println(s"multiplicationWithSimpleNumber: $multiplicationWithSimpleNumber")

    val usd = Currency("USD")

    val multiplication = 100(usd) * 23(EUR)
    println(s"multiplication: $multiplication")

    val divisionWithSimpleNumber = 100(USD) / 23
    println(s"divisionWithSimpleNumber: $divisionWithSimpleNumber")

    val comparison = 100(USD) > 90(EUR)
    println(s"100 USD > 90 EUR? $comparison")

  }

}

As you can see the client code just needs two simple imports and an implicit value of type Converter in order to use the DSL. The operations shown in the previous code are only a few among the available ones. Have a look at the Money class for a complete coverage.