User:MaHuJa/Sandbox

Armascript considered harmful

Cliched title, I know. Armascript is a name I invented to describe the scripting language used in the arma series of games, also known by its file extension sqf, to which the game owes most of its extensibility and power. In short, its power, already back in Operation Flashpoint, is probably the biggest reason for the success of ArmA. I believe BIS are well aware of this.

It's my observation that the rate of armascripters also being professional programmers is unusually high. Statistically speaking I do not have a big enough sample size, anyone have anything better?

One possible factor is that these programmers are drawn to a proper simulation like arma in the first place. (The community overall is also unusually tolerant of bugs.) I'm focusing on another: The language is unsuitable for new/non-professional programmers.

ArmAscript, as per arma2, is a huge improvement over the original ofp script language (known by the file extension sqs). The language has certainly evolved since then, with each iteration (ofp,ofp:resistance,arma1,arma2) we've seen large improvements. However, it occurs to me that these improvements constitute evolution rather than design. Thus each improvement, while an improvement, does not always mesh well with the rest of the developments to the language.

Here's a few fundamental problems:

• Forced multithreaded programming:

We have to program as though we were making multithreaded programs. A different thread can change things at any time. Worse yet, we are also not given proper synchronization primitives. The best we have is an intrusive hack:

code; waituntil { critical_section_code; true}; code;

When I say intrusive, I mean that the code fragment needs to have that final "true" statement. This precludes abstracting it.

Apparently the critical_section_code performs a lot better too when run in this fashion. Primarily because the 0.03ms delay isn't present, and also because it will benefit from hardware cache effects. The cost is probably mainly to the framerate, should you take too long.

If the critical section is too large for instant processing, or simply needs to work over time, you have to grab a lock by

code; waituntil { _l = lockname; lockname = true; _l==false}; critical_section_code; lockname=false; code;

• Distributed programming:

If there's one thing that's harder on programmers than multithreaded programming, it's distributed programming. And once a mission is loaded into multiplayer, the programmer better have it down right. But it gets worse; the "local/global" of many functions are not properly documented. Or depend on the context.

Again, we are provided no synchronization. As for making it ourselves, I've seen a good one: it comes down to putting a string in a variable, publicvariable-ing it (note that these have to happen atomically, see above) and having an EH on the server compile and run it. (Apparently publicvariable on code datatype is horrible on performance, presumably lag-wise. For very small blocks of code.)

Combining the above you can create a session-wide lock, as needed. The fact that you need to, though, speaks for itself. Alternatively, send a string (never code) to be compiled and run at the server, which is really just a way to de-distribute it.

Another issue again, is the locality of game objects, and how this can magically break code; especially combined with JIP. We have neither the means to override it, nor to detect where else it is. (And by the time our sent code arrives, it may have changed.)

• Performance issues

There's one rule above all other rules when it comes to performance in armascript. Don't do it (yourself). Even for relatively simple mathematical tasks, it'll still be better to contort the game engine to do it for you.

This is opposite to most environments where accessing external resources is typically the more expensive way to do something.

One recent example I found, which surprised the original programmer; if you want to know if some position is within a tilted rectangle, creating a trigger and a gamelogic, and for each check just move the gamelogic and check the list for that trigger, it's faster than doing the trigonometry by script.

And don't even think of using trigonometry to measure the distance between two coordinates; the distance command does this better. But wait, you need to create two objects (gamelogic preferred) and setposasl them, or the result will be wrong if that area of terrain isn't flat. (Well, unless they were world coordinates and that was exactly what you wanted.)

• The difficulty of getting things right

Bugs will occur in any program, in any language. However, the nature and rate of bugs will vary depending on the language. While there are clearly languages which are harder to get right (see brainfuck), I find armascript ranks quite low. This is especially true given the complications I noted above. And the lack of debugging tools make this even worse. diag_log was no less than a breakthrough.

• Non-linear syntax

Armascript is an operator-based language. This means that each command is in the form of op B; A op B; This makes a lot of sense for -a, a+b, a=b, and so on. It's also a fairly close match to the usual object-oriented notations, {player setpos somepos} instead of player.setpos(somepos) When a command needs more than two operands, that problem is solved by making an array out of B. It's almost decent, as workarounds go.

However, it's also being used where less appropriate. As a particular example, { ... ... ... } foreach whatever; In order to know the context of the block, you need to read below it. Then you can go back up and understand what it's for. Most languages are, and I dare say for a reason, made such that a human reading it from top to bottom can understand it. As a workaround, I usually copy the foreach to a comment on top of the block, but such comments tend to fall out of sync with their original.

• No static code checking

The only way you can check your code, even for syntax, is to run it. Even the compile command will not catch (all) your syntax errors. Squint is a good attempt, but falls short in several areas; some of which, due to the nature of armascript, it cannot fix. For example the surprisingly plentiful code that, for armascript reasons, must be contained in "strings" rather than {blocks}.

Is armascript, in its current condition, salvageable?

We can live with it as it is; but we will suffer the cost of doing so. (Fewer programmers, each working under bad conditions -> Less added value.) How many projects have not been completed and released because its maker gave up on armascript? At some point, I considered the idea of making a C++ compiler backend, that would accept a rather large subset of C++, and turn it into armascript. We also do not want to switch to an alternative that's just plain worse, even should it have prettier syntax. There's also the issue of how much work implementing it will be for BIS. (The parts they cannot leave to the community, that is.)

There are many minor annoyances with armascript, which can be fixed; the language can evolve further. However, there is a limit to how much you can do without breaking existing code, and the above list are fundamental issues, any fix to which WILL break code. And lots of it.

Thus, to fix it, we will need to deprecate it, such that it will only be used for backward compatibility. Similarly to how sqs was deprecated in favor of sqf.

What features do we need of a replacement? We should consider every feature armascript has, look at WHY that feature is there, and compile a list of those requirements. Only when we have the most fundamental parts down, can we begin looking at what we would replace it with. Points that must be covered: -Multithreading: .03, atomicity/pre-emptive, -Distributed -Events -Localization

Clean upgrade path? If possible, make it viable to have a program do the (bulk) conversion of armascript to the new solution. Recycle as many resources as possible?

What is a realistic timeschedule? Probably ArmA 3. For the beginning of the deprecation. No less than the release of a full expansion.