Making a Big Pile of Languages

On November 10, 2011, in King Machine, Technical, by bateleur

It's amusing, looking back twenty or even as few as ten years how peopleStack of books seriously used to debate whether high level languages were a good thing. Programmers – and not just the sort with big beards who wore sandals in winter – would sometimes claim that C was just fine and there was no reason for anyone to use anything else. C++ had rather more advocates, but even they were keen to stress that the overheads introduced by their more expressive language were very small. If you did things "right", you were still in some sense writing assembler code. Allegedly.

But all along there have been people who have been quietly doing different things. Even back in the 90s, Tcl/TK could be used to build a fully functional UI for something in under half an hour. PERL has long been used to do all sorts of text-related things with incredibly short dev times. And ultimately even some of the C++ programmers started to bind Python and Lua to their C++ projects. "Scripting" was the word used for these secondary languages, because to admit that they were being used for programming would be to admit defeat.

Now environments like Flash and Unity take things a bit further. You write essentially your whole program in the local ECMAScript dialect (or something similar) and all the C++ is stuff that someone else has written, somewhere in the library layer. Like a kind of OS. Or, if you prefer, like the CPU's microcode somewhere in that layer you probably never even think about. Not that this is really new either. People have been doing approximately the same – albeit without garbage collection – since the 8-bit era.

But what is new is that programmers are finally realising that this is programming after all. In fact, not only is this programming, it's the bit of programming we really care about. Getting things done!

Guess what I'm doing to King Machine this week? I'm adding another language to the big stack of languages.

KMScript is, despite the obvious sounding name, not really a scripting language. What it actually does is to behave like a little virtual machine inside the game. Does that sound completely insane to you? Particularly for a game that's "almost finished"! (In quotes because of course these projects never are.)

In fact this is not some kind of absurd complexity creep. It's the opposite. King Machine's codebase is a huge, sprawling mass. In order to fully debug it and stabilize it ready for release I have to clean it up. But due to the ad-hoc way it has grown that isn't an easy process. I've spent a long time looking through it, searching for ways to simplify it. My conclusion is that there are very few functions that can be shared further and very little complexity that can be removed. However, most of the game's code I don't need to look at most of the time. When it occurred to me that this was rather like having two layers of functionality, I knew what I needed to do…

Within the game world, things happen like a block is created, aligned with another, activated, rotated by 30 degrees or whatever. These are simple things, but currently they are not simple to work with at the code level. So what I need to do is add a new layer of abstraction. So, for example, instead of having a class for "push beam" blocks that inherits from "block" and implements the push beam effect when used such a block should instead be a block containing a small code fragment in a new language internal to King Machine. In that language, a beam within the King Machine world is a known kind of thing and a "push" is a known action, so the behaviour of this block is very simple to express.

So far so not-very-interesting. But the real payoff here is that things like save files and replays can be encoded in this same language. This unifies all the data in the entire game and means I no longer need to add support in four different places for every feature in the game and keep them carefully synchronized. Even better, testing and debugging becomes so much easier because the level of code sharing will be far higher and all the code will be exercised more often.

OK, I lied, that's not the real payoff. The real payoff is that it's going to be fun! What's the point of being an indie developer if I can't have fun, eh?

Tagged with: