mbank3.scala

case class AccountState(balance: Int, accountHolder: LastOption[String])

object AccountState {

    implicit def accountStateShow[A] = new Show[AccountState] {
        def show(a: AccountState): String = {
            show"Balance: ${a.balance}\nAccount holder: ${a.accountHolder}"
        }
    }
    implicit val accountMonoid = new Monoid[AccountState] {
        def empty : AccountState = AccountState(0, None)
        def combine(p1: AccountState, p2: AccountState) : AccountState = {
            AccountState(p1.balance |+| p2.balance, p1.accountHolder |+| p2.accountHolder)
        }
    }
}