Scala Code Kata Roman Numerals

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There’s a Scala User Group in Gothenburg that had several meetings during this summer.  In one of the meetings the group solved a Kata named KataRomanNumerals (A Kata is a small problem that you do over and over again to learn)

The KataRomanNumerals says you should write a function to convert from normal numbers to Roman Numerals: e.g.

1 –> I

10 –> X

7 –> VII

Unfortunately I could not attend at this meeting, so I had to do it on my own during a few summer nights when my family finally was asleep :-).

Here’s my solution:

object Program extends Application {

class RomanInt(number: Int) {

def toRomanString() = {

val ones = List(“”, “I”, “II”, “III”, “IV”, “V”, “VI”, “VII”, “VIII”, “IX”);

val tens = List(“”, “X”, “XX”, “XXX”, “XL”, “L”, “LX”, “LXX”, “LXXX”, “XC”);

val hundreds = List(“”, “C”, “CC”, “CCC”, “CD”, “D”, “DC”, “DCC”, “DCCC”, “CM”);

val thousands = List(“”, “M”, “MM”, “MMM”);

thousands(part(1000)) + hundreds(part(100)) + tens(part(10)) + ones(part(1))


def part(digit: Int) = {

number % (digit * 10) / digit



implicit def Int2RomanInt(number: Int) = new RomanInt(number)

println(154.toRomanString()) // prints ‘CLVIII’


Here’s the code with better formatting.

Please comment and correct if I didn’t write idomatic Scala or if you have suggestions for improvements.



  • 1
    Jörgen Lundberg
    2010-08-10 - 09:35 | Permalink

    When scala can figure out the return type you don’t need to specify one. So, in your case you can skip the “:String”, “:Int” and “: RomanInt” from you def’s.

  • 2
    2010-08-12 - 12:00 | Permalink

    Thank you!
    OK, removed. So it got a bit less verbose, but did it really add readability or did it get harder to understand?

    And by the way, I know you have solvd the same problem, where’s your code?


  • 3
    Mats Henricson
    2010-08-10 - 01:44 | Permalink


  • 4
    2015-10-14 - 14:04 | Permalink

    Per your example, if I “println(154.toRomanString())” I had better not get ‘CLVIII’

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