Monadic style order resolution

gistfile1.scala

trait MonadicStyleNewOrderResolver extends NewOrderResolutionErrors {

  val symbolDao: SymbolDao
  val marketTakerDao: MarketTakerDao
  val marketMakerDao: MarketMakerDao

  def resolve(order: NewOrder): Validation[String, ResolvedNewOrder] =
    for {
      symbol <- symbolDao.findByName(order.symbolName)
        .toSuccess(UnknownSymbol)
      marketTaker <- marketTakerDao.findByExternalId(order.marketTakerId)
        .toSuccess(UnknownMarketTakerId)
      account <- marketTaker.accounts.find(_.id == order.accountId)
        .toSuccess(UnauthorizedAccount)
      marketMaker <- marketMakerDao.findByExternalId(order.marketMakerId)
        .toSuccess(UnknownMarketMakerId)
      _ <- marketTaker.symbols.find(_ == symbol)
        .toSuccess(UnauthorizedSymbol)
      _ <- (order.quantity > 0).option(order.quantity)
        .toSuccess(InvalidQuantity)
      _ <- (order.price > 0).option(order.price)
        .toSuccess(InvalidPrice)
    } yield
      ResolvedNewOrder(
        account = account,
        symbol = symbol,
        marketMaker = marketMaker,
        price = order.price,
        quantity = order.quantity,
        side = order.side
      )
}