Manikin

The Scala version of Manikin. See also the Kotlin version.

Bank example

// The Bank example with less boilerplate
object Bank {
  
  import org.jmanikin.core._
  import org.jmanikin.scala.message.ScalaMessage._
  import org.jmanikin.scala.world.EventWorld.EventWorld

  case class AccountId(iban: String) extends Id[Account] { def init = Account() }
  case class Account(balance: Double = 0.0)
  trait AccountMsg extends ScalaMessage[AccountId, Account, Unit]

  case class Open(initial: Double) extends AccountMsg {
    def scala =
      pre { initial > 0.0 }.
      app { obj.copy(balance = initial) }.
      eff { }.
      pst { obj.balance == initial }
  }

  case class Deposit(amount: Double) extends AccountMsg {
    def scala =
      pre { amount > 0.0 }.
      app { obj.copy(balance = obj.balance + amount) }.
      eff { }.
      pst { obj.balance == old.balance + amount }
  }

  case class Withdraw(amount: Double) extends AccountMsg {
    def scala =
      pre { amount > 0.0 && obj.balance > amount }.
      app { obj.copy(balance = obj.balance - amount) }.
      eff { }.
      pst { obj.balance == old.balance - amount }
  }

  case class TransferId(id: Long) extends Id[Transfer] { def init = Transfer() }
  case class Transfer(from: AccountId = null, to: AccountId = null, amount: Double = 0.0)
  trait TransferMsg extends ScalaMessage[TransferId, Transfer, Unit]

  case class Book(from: AccountId, to: AccountId, amount: Double) extends TransferMsg {
    def scala =
      pre { amount > 0.0 && from != to }.
      app { Transfer(from, to, amount) }.
      eff { send(from, Withdraw(amount)); send(to, Deposit(amount)) }.
      pst { obj(from).balance + obj(to).balance == old(from).balance + old(to).balance }
  }

  def main(args: Array[String]): Unit = {
    val a1 = AccountId("A1")
    val a2 = AccountId("A2")
    val t1 = TransferId(1)

    val result = EventWorld().
      send(a1, Open(50)).
      send(a2, Open(80)).
      send(t1, Book(a1, a2, 30))

    println(result.obj(a1).value().balance) // 20.0
    println(result.obj(a2).value().balance) // 110.0
  }
}