So what do you do with a Raspberry PI / Arduino ZX81 frankensteinian clone beast, that is other than play copious amounts of games?
In a world full of mobile phone apps, it's easy to forget that effectively computers of the ZX81s ilk only ever really ran what we would now consider apps. Refer to any listing in say, the magazine ZX-Computing, one that isn't a game of some dubious nature for examples. The case being, that really very serious software just wont fit into 16k, let alone 1k of RAM. (With all apologies to the masters of machine code and their associated assembly acolytes, who are at this very moment proving my point entirely incorrect.)
Of course all of the above being the case, the answer to the lead question is of to this post, is write an app.
Thanks to the wonders of the post-modern age, apps can quite easily be developed off on a PC some place, then cross complied for injection back into the plastic doorstop that is a ZX81. To give this all a good go, it was off to Z88dk, the C development tool of choice for targeting Z80 based machines.
I'm not about to bore the world with a run down on the inner most workings of Z88dk, not least because never really having used it before, my 2 cents of input here is not going to help anybody. Suffice to say that it's pretty easy to get to grips with, and really the hardest part about it is that you end up primarily programming in C.
Which leads to the point that there is only one really good reason that explains the existence of C++, and that is the annoyance that is C and specifically Cs' painful handling of Strings. The String and C problem being an extra annoyance as the App I ended up making was a conversion of a Roman Numeral Format checking applet, I'd originally written in Java and then moved to C++, an applet that I'd made the Strings do all the heavy lifting in.
Anyway, regardless of any pet C based grievances, Z88dk is brilliant, and in the end I produced a passable piece of ZX81 software.
Wikipeadia for a better explanation.
Of course there is a correct, strict and socially acceptable way to format Roman Numerals, and this is precisely what my little ZX81 app is designed to do. It will check your dodgy formatting, make an informed guess at what you meant, spits out an Arabic Number and presents you with the Correct Roman formatting.
For the moment I've left the app a little bit on the gamey side, it's up to you to try and format your Roman Numeral correctly, there is no Arabic Numeral input option. The code behind the app would easily allow for it, I've just not implemented that extra code as yet, (and possibly wont).
You can download ZX Roman Numeral-izer and give it a go in your favourite ZX81 emulator.