Just checking in…

Wow, so my last post was September? That’s just not good blogging, and for that I apologise… There’s been a lot going on, but this is no time for excuses – I’m just posting this to let you all know that I’m still here, still writing code (lately, not as much as I’d like, but there you go) and I’m soon going to be making a start on the huge list of Open Source stuff that’s been building up over the past few months. Here are a few highlights of what’s in store:

  • Some awesome new stuff will be going into ORMDroid very soon, with some great contributions from Jacob Ferrero including one-to-many support. I can only apologise to Jacob for the time it’s taking to get these reviewed and merged!
  • Speaking or ORMDroid, it must be about time for that 1.0 release…
  • I’m planning to finally finish up Deelang. It still needs the new parser architecture sorting out, and some bug-fixes, plus some decent documentation. It’s been sitting there for too long, it needs to be pushed out the door!
  • I have some new code to put into Mink, including some rudimentary user-mode bootstrap code, along with a basic round-robin scheduler and other basic bits that will allow development to continue. A lot of this code is written, but still shockingly untested and even-more-shockingly out of version control!

Outside of Open Source, I still have to do something with retroify.me, a fact I was reminded of the other day when the domain name came up for renewal. The annoying thing there is that it’s done – I just need a reasonably-priced swag supplier who can print up cool T-shirts and the like for people to buy (any suggestions much appreciated!). We’ve also got an exciting new venture on the verge of private beta, which we hope to be launching as a commercial product later in the year.

So, all in all, exciting times. Now I just have to actually get on and do all this stuff.

Watch this space.

 

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Deelang 0.22 released on GitHub!

So I spent a bit of time today getting together the overdue release of Deelang ready, and finally pushed the 0.22 binary releases to Google Code, with source releases staying on GitHub. The Google Code project has now been fully migrated over to GitHub, and remains only to host binary downloads for those that want to get up and running quickly.

This release of Deelang is largely a maintenance release, with a number of bugfixes to the internals of the Dex compiler, the runtime library and a few other places. It does however include a few new features, notably:

  • Or Blocks are now implemented in the DEX compiler, and are used exactly like as they are in the Dee VM. 
  • Comparison operators are fully implemented.
  • Method chaining on parenthesized expressions works as it always should have!

This release doesn’t yet include the new AST rewriting I previously blogged about (that’s planned for 0.30 at the moment, as it’s a big change) but does address a lot of the issues that will eventually fix in a quick-fix kinda way – mostly as short-term fixups that will go away once the migration to the new AST layout is complete.

 

Deelang & ORMDroid: Moving to GitHub

Image representing GitHub as depicted in Crunc...

After spending all their lives so far on Google Code, I’ve decided it’s time to move both Deelang and ORMDroid over to GitHub. The projects have moved away from the old Subversion VCS and are now using Git, and the actual moving of the wiki pages, issues and everything else is well underway.

Why the move? Well, GitHub makes collaboration much more pleasant (Forks and pull-requests vs. patches isn’t much of a contest), and crucially for an Open Source project, a lot more people are comfortable with Git these days than SVN (in the OSS world, at least). Until fairly recently the whole Git thing had passed me by to an extent, but it’s easy to pick up and I have to say it’s now my preferred VCS.

On top of all that, I just prefer the GitHub interface!

Here are the new links to the projects. Please update your references if you have them.

Rewriting Vs. Rewriting

As previously mentioned, I planned to spend yesterday rewriting Deelang‘s parser with the aim of fixing some long-term issues and revisiting some design decisions that get in the way of the DEX compiler. As it turned out, I didn’t have as much time as I wanted to spend on this (as usual!) but I did get some time to play with it, and it turned out that my decision to rewrite much of the parser was, well, somewhat premature.

The main aim of the rewrite was to change the way the AST is generated, to remove the imaginary CHAIN nodes that proliferate the current AST. CHAIN nodes are used as the LHS in field accesses and method calls, as well as one or two other places, and denote that the receiver is the result of the previous operation. They work great when compiling for a stack machine (such as the JVM or the original Dee VM) – they translate simply as “pop the top object from the stack” – but are less intuitive when compiling for a register architecture, such as Dalvik.

Continue reading

Biting the bullet – time for a rewrite

In response to a feature request from some of the guys here, my current work on Deelang focusses on implementing proper equality and comparison operators as part of the language. The current release has no support for operators beyond basic arithmetic – equality and comparison have traditionally been implemented as methods hacked on top of the standard library. This results in code such as:

1.eql(2)  => true
5.lt(10)  => true
10.gt(20) => false

Leaving aside for a moment that the above isn’t actually that bad (in my opinion at least), implementing this as operators is actually quite simple for both the dex and deevm compilers. However, while putting it together I ran up against an old elephant that’s been sitting quietly in the corner for some time now – the current parser is a mess, and it might just be time to rewrite the grammar.

The problem is not new, but I’ve ignored it for a while. Basically, it boils down to the fact that the current parser cannot handle code such as:

(1+2).foo()

Not only does this not work, but it fails miserably with nothing more specific than a MismatchedSetException at the terminator, after a lot of backtracking and ultimately ignoring the method call completely. The above code parses to the following tree:

Parse Tree Notice all the abandoned trees (in red), before the (erroneous) final parse, and the MismatchSetException up there on the right. The method call gets parsed at one point, but that tree was then abandoned in favour of a tree in which the call is quietly ignored. This is clearly one confused parser, and all over something as simple as (1+2).foo()! Clearly, this needs fixing.

As I say, I’ve ignored this for a while. It should be relatively simple to fix (and indeed it is) with a bit of rejigging in the grammar. However, this problem is actually symptomatic of something deeper – namely, that the Deelang grammar is a mess. In the past, as problems such as this have cropped up, they’ve been fixed by adding to the grammar. New productions, imaginary tokens, and syntactic predicates have all been added to cope with a specific case, with no real wider plan.As long as the tests still passed at the end, the additions stayed.

The result of all this is that things that should be handled in a unified way are actually handled in a variety of ways. My personal favourite example of this is the way chained method calls are handled – I won’t illustrate it here, but if you’re interested just debug something like “foo().bar().baz().quux()” in ANTLRWorks. Trust me, it’s not pretty. It’s inefficient, it’s inconsistent with other parts of the grammar, and it requires the compiler to jump through some pretty awkward hoops to keep track of who is using what target register. It worked well when the only target was the (stack-based) Dee vm, but as requirements have grown it’s become cumbersome – the only reason it still works this way is inertia.

With all this in mind, I’ve decided that now is the ideal time to rewrite the grammar to get rid of these issues. I’ve never been a big believer in planning to throw one away, but in this case it looks like I will, anyhow. To be fair, I’m not planning a complete rewrite – large parts of the grammar are fine as they are (literals, for example). But the meat of it – from atoms through function calls to method calls – will be rewritten in a way that’s more consistent, cleaner, and hopefully requires a lot less backtracking. I’m also aiming to reduce the lookahead where I can, although some of the actual language design makes this quite difficult.

Unfortunately this grand plan must remain just that for now – I’m very short on time to actually work on this at the moment. Since it’s not an actual key requirement I can’t allocate any actual work time to it (even though it will make things easier and save time down the line). So provisionally, I’ve set aside Sunday for the rewrite.

Now I just need to hope nothing more pressing crops up between now and then. Wish me luck!

Deelang 0.20 released!

After about a month of coding (on and off), The Deelang DEX compiler is now feature complete, and what better way to celebrate than by releasing the code? It’s always been available in Subversion of course, but now you can download all the new stuff from the downloads page as either a source package or ready-made Jar, without all that messing around with Subversion, finding the right branch, or any of that. It’s right there, on the downloads page, just waiting for you to grab and go!

I’ve blogged a bit about the new features in this version (for example, here, here and here), and if you missed all that and are now wondering what on Earth I’m on about, I’ve also blogged generally about Deelang (e.g. here). The short version is that Deelang is a compiled script language designed for embedded devices (especially Android) that allows developers to give their users a simple way to extend their apps by writing small scripts.

Now that there’s a file release available, we’re hoping to get some bug reports and open a discussion about where Deelang could/should go. Other than the DEX compiler (which has been about a month of solid effort in OSS terms) development is a bit haphazard – it works for us, so we leave it. If we need something new, we implement it, then we leave it at that. I really want to get a community going around this thing, to make it more generally useful for everyone…

So why not grab the code, play around with it, file issues if you find any bugs, and come over and join the mailing list?

DEXing Deelang – First steps in SVN

If you’re one of the few who’ve already taken a look at Deelang, you’ll know that it’s a simple scripting language that compiles to a custom bytecode format, which then runs in a simple virtual machine. It can run anywhere, but is targeted mostly for embedded devices, and especially for Android.

All this is fine, and for the most part it doesn’t perform too badly. Unfortunately though it does mean that it’s most common operation (calling out to Java methods) is relatively slow, because under the hood reflection is used everywhere. This has the potential to be a problem since in Dee, everything is a method – you can’t define your own classes, methods or functions in scripts, but instead rely on a (Java-side) API provided by whoever embedded the language in their application. Even arithmetic and conditionals are done with methods. Reflection (especially on Android) is just too slow for this kind of usage.

To address this, I’ve been thinking for some time about a implementing a native (i.e. Dex) compiler for Deelang on Android, and over the past few days I’ve finally made a start. The architecture is pretty well mapped out in a first-cut kind of way (well, in my mind at least) but the implementation is only just taking it’s first baby steps. Hardly anything is supported right now – in fact, the only thing it’s possible to actually compile is literals and simple, direct function calls (what the Dee VM calls SELFCALLs). But it’s a start, and it’s in Subversion on Googlecode now if you feel like taking a look. All the work is being done in a branch, which you can browse or check-out at:

http://deelang.googlecode.com/svn/branches/DEXCOMPILER/deelang

What can it do?

As mentioned above, it’s very limited at the moment. In fact, about the most exciting thing it can do is take code such as:

foo(1,2)

and compile it to native Dex bytecode like:

//class:0000  access:0x0001
public class DexCompiledScript531a8036-8e20-4965-8148-e87dfb51283f extends com.roscopeco.deelang.runtime.CompiledScript

//method:0000  access:0x0001
//LDexCompiledScript531a8036-8e20-4965-8148-e87dfb51283f;.run(Ldee/lang/DeelangObject;Lcom/roscopeco/deelang/runtime/Binding;)V
public V run(dee.lang.DeelangObject,com.roscopeco.deelang.runtime.Binding)
                this:v3   //DexCompiledScript531a8036-8e20-4965-8148-e87dfb51283f
                    :v4   //dee.lang.DeelangObject
                    :v5   //com.roscopeco.deelang.runtime.Binding
CONST               |     |v1=0x00000001  // int:1   float:0.000000
NEW_INSTANCE        |     |v0=NEW Ldee/lang/DeelangInteger;
INVOKE_DIRECT       |     |v0.(v5,v1)  //Ldee/lang/DeelangInteger;.(Lcom/roscopeco/deelang/runtime/Binding;I)V
CONST               |     |v1=0x00000002  // int:2   float:0.000000
NEW_INSTANCE        |     |v2=NEW Ldee/lang/DeelangInteger;
INVOKE_DIRECT       |     |v2.(v5,v1)  //Ldee/lang/DeelangInteger;.(Lcom/roscopeco/deelang/runtime/Binding;I)V
INVOKE_VIRTUAL      |     |v4.foo(v0,v2)  //Lcom/roscopeco/deelang/compiler/dex/CompilerFuncTestBase$Foo;.foo(Ldee/lang/DeelangInteger;Ldee/lang/DeelangInteger;)V
RETURN_VOID         |     |return

Development is moving quite quickly though, so over the next few days expect some support for most of the current (VM-based) capabilities.

Why go native?

As mentioned, the current VM architecture makes heavy use of reflection, which in some cases just doesn’t have the performance we need. Compiling ‘natively’ to Dex bytecode will eliminate all reflection in the generated code and core runtime, and will make compiled scripts fully-fledged members of your application. There won’t be any need to carry around the VM and it’s runtime, and instead you’ll only need a lightweight core runtime package that provides the standard implementations of the arithmetic operators, the if and or operators, and so on.

The trade off is flexibility. In the VM, all binding is done at runtime, with the ability to swap out any bound object (including the self reference) at any time. In the compiler, binding has to be static, so some of that flexibility is lost. But in 90% of cases (at least in our code) this doesn’t matter, as scripts are run against a fixed binding anyway (that’s what provides the ‘API’ for users to script against).

In any event, this isn’t about replacing the current VM setup – the new compiler is actually just a new back-end for the existing com.roscopeco.deelang.compiler.Compiler class. To compile the script above, you use the standard compiler with the new backend, like so:

Compiler c = new Compiler();
byte[] dex = c.compile(new DexCompilationUnit(c, "<no file>", Foo.class),
                 Parser.staticParse("foo(1,2)")).getCode();

You can still use the old (now called DVM) compiler and VM runtime as before (although there have been some slightly incompatible API changes during implementation of the new architecture, notably the moving of the deelang.* namespace to dee.vm.lang.*, so you’ll need to tweak your code a bit) if you feel it fits your needs better. There are currently no plans to drop the VM (although it may stop being the default at some point).