Verify the checksum of a Chilean RUT. See http://en.wikipedia.org/wiki/National_identification_number#Chile.

Rut.scala

class Rut(id: String, checksumDigit: String) {
  def checksum: String = {
    val digits = id.map(_.toString.toInt)
    val digitsWithMultipliers = digits.zip(
      Rut.ChecksumMultipliers.drop(Rut.ChecksumMultipliers.size - digits.size)
    )
    val productSum = digitsWithMultipliers.foldLeft(0)(
      (acc, multipliers) => acc + multipliers._1 * multipliers._2
    )

    (11 - productSum % 11) match {
      case 11 => "0"
      case 10 => "K"
      case i => i.toString
    }
  }

  def isValid = checksumDigit == checksum
  override def toString = id + "-" + checksumDigit
}

object Rut {
  val ChecksumMultipliers = Seq(3, 2, 7, 6, 5, 4, 3, 2)
  val invalidRutChars = "[^0-9K]".r

  def apply(id: String) = {
    val strippedId = invalidRutChars.replaceAllIn(id, "")
    new Rut(strippedId.take(strippedId.size - 1), strippedId.last.toString)
  }
}