Roman Numerals to Integer (learning scala) :)

roman_to_arabic.scala

import scala.collection.immutable.HashMap;

val tbl = HashMap[Char, Int](
  'M' -> 1000, 
  'D' -> 500, 
  'C' -> 100, 
  'L' -> 50, 
  'X' -> 10, 
  'V' -> 5, 
  'I' -> 1 
)

def romanToArabic(roman: String) : Int = {
  
  (0 /: ((roman.toCharArray :\ List(List[Char]())) ((c: Char, m: List[List[Char]]) => {

    if ((m.head.size > 0) && (tbl(c) < tbl(m.head.head)))
      List((List(c) ++ m.head)) ++ m.tail

    else
      List(List(c), m.head) ++ m.tail    	
    

  })))((m: Int, l: List[Char]) => {

    if (l.size == 1)
      m + tbl(l.head)

    else if (l.size == 0)
      m

    else
      m + (tbl(l.reverse.head) /: l.reverse.tail)(_ - tbl(_))     
    
  })

}

val test1 = romanToArabic("MCMLXXXV")
println((test1, test1 == 1985))

val test2 = romanToArabic("MCMXC")
println((test2, test2 == 1990))

val test3 = romanToArabic("MDCCCCX")
println((test3, test3 == 1910))

val test4 = romanToArabic("MCMXCII")
println((test4, test4 == 1992))