Thanks to PhiLho for pointing out I can use JavaScript inside Processing, and to John Snyders @ www.hardlikesoftware.com for giving me some ideas (which I didn't use at all, but ideas keep brainjuice pumping).

What I do here is string substitution (is there a more efficient way to do that Processing doesn't seem to have a strsubs() function or similar), and uses JS to evaluate strings as math and logic.

Still needs some work. Currently, it can't process strings with more than one "syllabe" (an atom plus its parameters), and if the rule doesn't match, it will become null (it should test the next rules, and if all fail it should leave the string as-is).

Do you have any suggestions I'm worried about efficiency when the number of rules and the size of the string start to increase. Specially about repeatedly using regexp to explode the string being tested. Perhaps I should pre-process it into syllabes, then test each syllabe against each rule Code is pretty straightforward to check if the rle applies, it just takes longer to process the result in case it does.

http://openprocessing.org/visuals/?visualID=8255

(code just outputs text to the console, unfortunately. Tomorrow I may use text to write it on the applet, but for now you should download it to see it working. Any keypress will iterate the LSystem one generation)

If you are interested in the source code for a pure Java based implementation of context-free L-systems using ANTLR have a look at this page:

web.archive.org/web/20080203202325/http://www.lindenmayer.innercitylife.net/

Unfortunately it's down, but you might still be able to contact Frank.
And in case you know some German - the accompanying paper can be found here:

www.iti.cs.tu-bs.de/~waetjen/Studienarbeiten/Boehmer.pdf

Thanks for the replies, guys.

@ Chrisir: I know about turtle drawing, but I'm planning on representing the system differently (think of http://www.michael-hansmeyer.com/projects/project3w.html Hansmeyer's L-Systems, but 2D and way less complex), so for now I'm not implementing graphics until I get a hold of the engine behind the system. And then it will be more hard work getting the graphic engine to work ;) And for replacing a string, unfortunately that was on a different context: they had the index for the character to be replaced, where I want to replace occurences of a string for a different string.

@bit.craft: Well, I know some german, but not enough for a scientific paper! Well, maybe, for luckily math is universal, and I'm quite good at that.

@martin_p: I also think there are easier ways to deal with Parametric L Systems, unfortunately none that I think of is suitable for Processing, at least not without consuming a whole lot of memory on objects and function stacks and stuff. But then, my approach has a fairly large function stack, so I might try something different. The thing is I really want to keep this in Processing, for it is just the missing piece on a larger project.

Do you suppose having "syllabes" as objects makes things easier while not wasting much memory My main concern is in creating rules. You see, on my code, it's as simple as
Code:

 Rule ruleA = new Rule("F(t):(t>1)->F(t-1)");  

and JS processes the string as code. If I could do something similar purely on Processing, I'd be glad ^_^

I've read about StructureSynth, but I never got around trying it, or even seeing what it can do. As for contextfree, I think someone mentioned it here on the forums on some other topic, but I haven't pursued it.

Now this anar+ seems pretty awesome. The first thing that pops up in the demo video is the external editor with javadoc-like help, highlighting of declared variables, etc. Is it part of the anar+ package, or is it independant

martin_p wrote on Mar 16^th, 2010, 10:39pm:

Yeah, I know. That's one of the reasons I haven't tried doing it yet!

martin_p wrote on Mar 16^th, 2010, 10:39pm:

You know, that's usually true for Iterated Function Fractals, tho that's not what I'm aiming for (tho most IFFs can be written as LSystems, usually of the simple kind)

In any case, I'll check ouy what anar+ and structuresynth can do for me. I'll post again when something new happens, thanks.