An introduction to algebraic data types (basics) in Scala...some things need to get cleaned up, but only after you grasp the basics. Part 1

AlgDT.scala

package net.susanpotter.algdt

sealed trait Order {
  def execute: Unit // ignore that Unit return type is not a great idea...
}

case class MarketOrder extends Order {
  def execute {
    println "executing market order"
  }
}
case class LimitOrder extends Order {
  def execute {
    println "executing limit order"
  }
}

// Note that the above are mutually exclusive. An order is either a market or limit order not both.
// This is what is called as a Sum type and MarketOrder and LimitOrder are value constructors for the
// type Order. When defining your interfaces you should never use the value constructors only the type.

// Now a product type
// assumes a type of

sealed trait Currency
case class USD extends Currency
case class CAD extends Currency
case class EUR extends Currency
case class GBP extends Currency

case class Money(currency: Currency, amount: Int)

sealed trait Period
case class Hour extends Period
case class Day extends Period
case class Week extends Period
case class Month extends Period

case class Duty(description: String, skillRequired: String)
case class Project(name: String, description: String, deliverables: Seq[String])

sealed trait Worker
case class Employee(title: String, salary: Money, duties: Seq[Duty]) extends Worker
case class Contractor(rate: Money, period: Period, projects: Seq[Project]) extends Worker

// A small domain but modeled with algebraic data types (mostly).
// Currency is a sum type again
// So is Period and it's case classes
// Worker has multually exclusive sum types that are products