Learning exercise, writing a code kata to convert roman numerals to arabic numbers. This is simply a reversal of the kata at: https://codingdojo.org/kata/RomanNumerals/

The Romans wrote numbers using letters : I, V, X, L, C, D, M. (notice these letters have lots of straight lines and are hence easy to hack into stone tablets) Part I

The Kata says you should write a function to convert from Roman Numerals to "normal" Arabic numbers: eg

 null --> 0
 I --> 1
 III --> 3
 IV --> 4
 V --> 5
 VI --> 6
 VII --> 7
 VIII --> 8
 IX --> 9
 X --> 10
 XXX --> 30
 XL --> 40
 L --> 50
 C --> 100
 CCC --> 300
 CD --> 400
 D --> 500
 CM --> 900
 M --> 1000
 MCCC --> 1300
 MD --> 1500
 MDCCCXXXII --> 1832
etc.

For a full description of how it works, take a look at this useful reference website.

There is no need to be able to convert numbers larger than 3999. (The Romans themselves didn’t tend to go any higher.)