Scala MapN with conditions

Question

Hi I have the following Scala code with cats library

results = patrons.map(p => {
  (verifyCardId(p.cardId), verifyAddress(p.address)).map2(
  (maybeValidCard, maybeValidAddress) => {
    val result = for {
      idCheck <- maybeValidCard
      addressCheck <- maybeValidAddress
    } yield CheckResult(p.name, idCheck, addressCheck)
  }
})

where verifyCardId and verifyAddress is an external API call returning a Future which are somehow very expensive and time consuming.

The question is how do I do the following:

• If one of the patron does not have a card, the code should be able to skip checking the card must still check patron's address
• If the patron has both then, the code should check the card and the address

How can I improve the existing code? Thanks heaps

Edit: Add more information about the preference to skip one of the expensive API calls

Answer 1

• If result of address verification doesn't depend on result of card verification then untie them (flatMap binds monads).
• Model CheckResult should be adjusted to case of missing card.

extended sample

    case class Patron(name: String, cardId: String, address: String)
    case class CheckResult(name: String, idCheck: Option[Boolean], addressCheck: Boolean)
    def verifyCardId(cardId: String) = Future{
      Thread.sleep(5000)
      Some(true)
    }
    def verifyAddress(address: String) = Future{
      Thread.sleep(5000)
      Some(true)
    }

    val patrons = List(Patron("p_name", "1234", "Somewhere St. 42"))

    val start = LocalDateTime.now()
    val results = patrons.map(p => {
      (verifyCardId(p.cardId), verifyAddress(p.address)).map2(
        (maybeValidCard, maybeValidAddress) => {
          for {
            addressCheck <- maybeValidAddress
          } yield CheckResult(p.name, maybeValidCard, addressCheck)
        })
    })
    val headResult = Await.result(results.head, Duration.Inf)
    val end = LocalDateTime.now()
    val duration = ChronoUnit.SECONDS.between(start, end)

short output

    patrons: List[Patron] = List(Patron(p_name,1234,Somewhere St. 42))
    headResult: Option[CheckResult] = Some(CheckResult(p_name,Some(true),true))
    duration: Long = 5