Romans number parser with (some) validation. Not beautiful, not efficient, just small...

SmallRomans.scala

def table(i: Char, v: Char, x: Char) = Seq("", s"$i", s"$i$i", s"$i$i$i", s"$i$v", s"$v",  s"$v$i",  s"$v$i$i",  s"$v$i$i$i",  s"$i$x" )
val x1000 = Seq("", "M", "MM", "MMM", "MMMM")
val x100 = table('C', 'D', 'M')
val x10 = table('X', 'L', 'C')
val x1 = table('I', 'V', 'X')

val lookup: Map[String, Int] = (1 to 4999).foldLeft(Map.empty[String, Int]) {
  case (m, d) => m.updated(x1000(d / 1000) + x100((d % 1000) / 100) + x10((d % 100) / 10) + x1(d % 10), d)
}

override def parsed(roman: String) = lookup.get(roman.trim().toUpperCase()).map(Right(_)).getOrElse(Left("Invalid roman number"))