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.

 

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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.

Jelly Bean on One X – Finally!

HTC One X

After what seems like an eternity since the announcement that HTC would be updating the One X to Jelly Bean, and after a couple of months seeing it happen in other parts of the world, HTC finally got around yesterday to releasing the update to UK users, myself included.

“Been a long time coming” according to Fudzilla, and I’d tend to agree!

This initial update is for phones that aren’t network locked – it will depend now on network when others get the update (obviously, Orange et al. will need time to add their own software, themes and the like) – and you may have to do a manual update check if you didn’t get the update yet. As usual, the update comes in two parts – a small (1.5mb) pre-update, which is then followed by a bigger (~400mb) OS update.

Initial impressions are unsurprising, given that we’ve seen Jelly Bean on many other devices at this point, but it’s definitely a good progression for the One X. Personally I’ve often felt that the UI experience with ICS has always been a little disappointing on the device, given its powerful processor and RAM profile, and this has been addressed to a reasonable extent in the update. It still lags a little in places (orientation changes still aren’t as smooth as I’d like) but it’s definitely better. Coupled with the myriad small UI updates that Jelly Bean brings, this update has made my One X that little bit better – just in time for Christmas!

Had your update yet? Let me know in the comments!

 

Scratch: Teaching kids to think in blocks

The Scratch Cat
The Scratch Cat

Over the weekend I spent a few very rewarding hours with my ten-year-old son playing with Scratch, MIT’s drag-and-drop educational programming system. I’ve often wanted to “get him into” programming (I was a little younger than he is now when I started, and at ten I was beginning to get really interested in writing code on the old 8-bit machines) but haven’t really known where to begin. It turns out the ideal place was Scratch!

Although I’ve been aware of Scratch for a while (it comes pre-installed on the Raspberry Pi I got a few months ago, which I’ve not really done anything with yet) I only really looked at it properly last week, when a friend of mine asked me for a little help with an introduction to CS course he was doing, in which the first problem set was to create something in Scratch (I helped him make a Space Invaders clone). It was while working on that I realised I really should introduce Jake (that’s my son) to Scratch. After I mentioned it to him, it turned out he’d looked at it a little at school, and so it was decided – we’d spend a bit of time on Sunday playing around with it.

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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.

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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!

Tech Filled Fantasy

So, Nokia have advertised the life out of the new Lumia range and the Windows software it will be running, but now the guys over at HTC have released some specs and pictures of their new HTC 8 range.

Im not going to spend all of this article talking about Windows Phone as I’ve already shown my excitement for it previously and wrote a few articles that concern it, as well as the Lumia 920 article, each of these can be found here ..

http://techfilledfantasy.wordpress.com/2012/09/06/nokia-lumia-920-are-the-boots-of-apple-google-shaking/

http://techfilledfantasy.wordpress.com/2012/08/11/270/

These articles will give you a bit of an overview of Windows Phone 8, and what you can expect from it.

The HTC 8X and HTC 8S will both run the Windows OS. Just like the HTC One X & S, you know more or less what to expect from each of these models that each will have its own selling points.

Taking the…

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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?

Dex vs Dee VM – A microbenchmark

During a recent discussion, I had the need to show some numbers demonstrating why Deelang needs the new DEX compiler. As I said in that thread, it’s all about removing reflection from the compiled classes.

We all know that “reflection is slow” (for some value of slow) and especially on Android, that it isn’t generally a good solution for general use in method invocation. Looking up methods by reflection is slow, as is performing the actual invoke. But how slow? Could I quantify the difference?

Since the Deelang DEX compiler is still being actively developed, I’ve never paid much attention to performance before, and have certainly never benchmarked it. We knew that the Dee VM wasn’t fast enough for some of the things we were using it for, and I knew from experience that it would be faster without reflection, and we left it at that. This discussion got me thinking though, and I decided it would be nice to have some idea of the actual difference between the Dee VM and scripts compiled to DEX.

Despite the fact that microbenchmarks are often a bad idea, and are a bit of a minefield at the best of times, I wrote one in this instance. After all, I only want some idea of the comparative performance for the sake of discussion – I won’t actually be basing any design or implementation decisions on these results.

I expected a decent performance boost in the DEX compiled scripts, but I honestly wasn’t quite prepared for how much of a boost:

09-27 10:45:27.525: I/BENCHMARK(15853): Rehearsal
09-27 10:45:37.665: I/BENCHMARK(15853): DeeVM completed : 10000 runs : 10107ms (10.107 seconds)
09-27 10:45:37.725: I/BENCHMARK(15853): Dex completed   : 10000 runs : 31ms (0.031 seconds)
09-27 10:45:37.725: I/BENCHMARK(15853): Real
09-27 10:45:46.695: I/BENCHMARK(15853): DeeVM completed : 10000 runs : 8938ms (8.938 seconds)
09-27 10:45:46.745: I/BENCHMARK(15853): Dex completed   : 10000 runs : 25ms (0.025 seconds)

(This is logcat from the benchmark running on-device on a HTC One X)

That’s right – almost 9 seconds for the reflection-based Dee VM, compared to 0.025 seconds for the DEX compiled version. The difference is so marked that I at first didn’t believe the results. I changed the script to actually produce some output to logcat, to make sure that it was actually running each implementation properly, and it was. It turns out that, in this case, reflection has a much bigger impact that I expected.

In case you’re interested, you can see the benchmark code at the this page on the project wiki on Google Code.