SalaryWorld.scala

object SalaryWorld extends App {

  val rules = Seq(
    ('allowance, 1.2),
    ('bonus, 1.1),
    ('tax, 0.7),
    ('surcharge, 0.9)
  )

  def salary(config: Set[Symbol], base: Double) =
    rules.foldLeft(base)((prior, rule) => if (config.contains(rule._1)) prior * rule._2 else prior)

  def run = {
    println(salary(Set('surcharge, 'tax, 'bonus, 'allowance), 100000))
    println(salary(Set('allowance, 'tax), 100000))
  }

 run
}