straw_man_solved_with_stm.scala

import scala.concurrent.stm._

case class Account(accountNo: String, balance: Int){
  def credit(amount: Int) = this.copy(balance = (balance + amount))
  def debit(amount: Int) = this.copy(balance = (balance - amount))
}

object Bank{
        
  val accountsRef = Ref(Map("from" -> Account("from", 500), "to" -> Account("to", 500) ))

  def transfer(fromNo: String, toNo: String, amount: Int): Unit = {
    atomic{ implicit t => 
      var accounts = accountsRef()
      val (from, to) = (accounts(fromNo), accounts(toNo))
      if(from.balance > amount){
        accounts = accounts + (to.accountNo -> to.credit(amount))
        accounts = accounts + (from.accountNo -> from.debit(amount))
        accountsRef() = accounts
      }
    }
  }
  
  def main(args: Array[String]): Unit = {
    Bank.transfer("to", "from", 50)
  }
}