My first D module - Critiques welcome.

[Timon Gehr]

On 12/23/2013 10:34 PM, John Carter wrote:
> So I resolved to learn D, and try code as idiomatically as I could.
>
> So here is a trivial module that encodes and decodes roman numerals.
>
> https://bitbucket.org/JohnCarter/roman/src/9ec5b36b9973426f35b0ab9dfd595cb3b305e39e/roman.d?at=default
>
> I also attempted to do it in "Best Practice Test Driven Development"
> form with commits on every change.
>
> So you can see the blow by blow history of how it grew.
>
> I would welcome any critique, advice, flames, recommendations, etc. etc.
>
> Thanks for your help and patience with various stupid newbie questions I
> asked in the process!
>...

What is the intended behaviour? I think that eg. "XIIX" is not a valid 
roman numeral.

pure immutable uint[] romanToDigitArray( in string roman)

'immutable' does not do anything here.