validation.scala

// have

    val params = (
      (postalCode |> notNone("postal code missing")) |@|
      (countryCode |> notNone("country code missing")).flatMap(validIso2CountryCode("country code invalid"))
    )

// would like

    val params = (
      (postalCode |> notNone("postal code missing")) |@|
      (countryCode |> (notNone("country code missing") ==> validIso2CountryCode("country code invalid")))
    )

// ...where  ==> is currently flatMap but that's beyond the idea here