Caesar.scala

object Caesar extends App {
  
  private lazy val pos2symbol: Vector[Char] = (('A' to 'Z') ++ ('a' to 'z') :+ ' ' ).toVector
  private lazy val symbol2pos: Map[Char, Int] = pos2symbol.zipWithIndex.toMap
  
  def encode(msg: String)(implicit key: Int): String =
    msg collect { case c if symbol2pos contains c => 
      pos2symbol((symbol2pos(c) + key) % symbol2pos.size)
    }
  
  def decode(msg: String)(implicit key: Int): String =
    msg map { c =>
      val s = pos2symbol.size
      pos2symbol((s + symbol2pos(c) - key) % s)
    }
  
}