CQRS

Commands.scala

sealed trait Command

case class CreatePotato(sort: String) extends Command
case class CookPotato() extends Command
case class EatPotato() extends Command


object Command {

  import cats.data.State

  def dispatch(c: Command): State[List[String], Unit] = State( s => {
    c match {
      case EatPotato() => (s.tail, ())
      case CreatePotato(sort) => (sort :: s, ())
      case CookPotato() => (s, ())
    }
  })

}

Main.scala

import cats.data.State

object Main extends App {

  // parse command from json
  val command = CreatePotato("samsø")

  val program = for {
    _ <- Command.dispatch(command)
    _ <- Command.dispatch(command)
    _ <- Command.dispatch(command)
    _ <- Command.dispatch(command)
    _ <- Command.dispatch(command)
    _ <- Command.dispatch(EatPotato())
    potatoes <- Query.list()
  } yield potatoes

  println(program.run(List()).value)
}

Query.scala

import cats.data.State

object Query {

  def list(): State[List[String], List[String]] = State(s => (s,s))

}