Rewriting this to solve PythonChallenge level 23. It works, but it's not very readable. Suggestions welcome.

gistfile1.scala

val map = {
  type Dict = Map[Char, Char]
  
  val initial = Map[Char, Char]()
  
  (for(c <- List('A', 'a'); i <- 0 until 26) yield {
    ((i + c).toChar, ((i + 13) % 26 + c).toChar)
  }).foldLeft[Dict](initial)({ (map, kv) =>
    val (k, v) = kv
    map.updated(k, v)
  })
}