In the spirit of this article ( http://java.dzone.com/articles/merits-verbosity-and-flaws ) I wanted to re-write the implementation in a more verbose and readable fashion. Even if the result is not a cool one-liner ;-)

toRoman-terse.scala

def toRoman( v:Int ) : String = {
  val romanNumerals = List(1000->"M",900->"CM",500->"D",400->"CD",100->"C",90->"XC",
                           50->"L",40->"XL",10->"X",9->"IX",5->"V",4->"IV",1->"I")	
 
  var n = v                          
  romanNumerals.foldLeft(""){(s,t) => {val c = n/t._1; n = n-t._1*c;  s + (t._2 * c) } }
}

toRoman-verbose.scala

def toRoman(num: Int): String = {
  case class RomanUnit(value: Int, token: String)
  val romanNumerals = List(
    RomanUnit(1000, "M"),
    RomanUnit(900, "CM"),
    RomanUnit(500, "D"),
    RomanUnit(400, "CD"),
    RomanUnit(100, "C"),
    RomanUnit(90, "XC"),
    RomanUnit(50, "L"),
    RomanUnit(40, "XL"),
    RomanUnit(10, "X"),
    RomanUnit(9, "IX"),
    RomanUnit(5, "V"),
    RomanUnit(4, "IV"),
    RomanUnit(1, "I"))
 
  var remainingNumber = num
  romanNumerals.foldLeft("") { (outputStr, romanUnit) =>
    {
      val times = remainingNumber / romanUnit.value
      remainingNumber -= romanUnit.value * times
      outputStr + (romanUnit.token * times)
    }
  }
}