trait BaseMerchantProtocol {
  protected def doCheck(transaction: BaseTransaction, requestParams: List[String]) = {
    // some common code...
    println(requestParams) // this one is specific-class-dependent
    // ...and here is common code as well
  }

  protected def requestParams(): List[String]
}

class SmsCommerceMerchantProtocol(private val smsCommerceTransaction: SmsCommerceTransaction) extends BaseMerchantProtocol
{
  def check = {
    doCheck(smsCommerceTransaction, requestParams())
  }

  protected def requestParams() = {
    List("result specific for SmsCommerceTransaction class")
  }
}

class TelepayMerchantProtocol(private val telepayTransaction: TelepayTransaction) extends BaseMerchantProtocol
{
  def check = {
    doCheck(telepayTransaction, requestParams())
  }

  protected def requestParams() = {
    List("result specific for TelepayTransaction class")
  }
}


trait BaseTransaction
class SmsCommerceTransaction extends BaseTransaction
class TelepayTransaction extends BaseTransaction