__clrtype__ Metaclasses Demo: Silverlight Databinding

I’ve gotten to the point where I can actually demo something interesting with __clrtype__ metaclasses: Silverlight Databinding. This is a trivial sample, data binding a list of Products (aka the sample class I’ve been using all week) to a list box. But according to Jimmy, this is something he gets asked about on a regular basis and there’s a AgDLR bug open for this. The __clrtype__ feature is specific to IronPython but I bet the IronRuby guys could implement something similar if they wanted to.

When you install IronPython 2.6 (or 2.0.1 for that matter), it comes with the AgDLR bits in the Silverlight subfolder. This includes Silverlight compatible versions of the DLR and IronPython as well as the Silverlight DLR host and the development web server Chiron in the Silverlightbin directory. There is also a script in the Silverlightscript directory that will generate a dynamic Silverlight application from a template. I ran “sl.bat python sldemo” in order to build the skeleton project.

In the generated app.xaml file, I removed the default text box and replaced it with this XAML code that I stole nearly-verbatim from my blog post on data binding in WPF with IronPython. The only thing I changed was the binding path for the text block (title became name).

<ListBox x:Name="listbox1" >
      <TextBlock Text="{Binding Path=name}" />

Then in the App class, I set the ItemsSource of the ListBox to a hand-built a list of Products.

class App:
  def __init__(self):
    root = Application.Current.LoadRootVisual(UserControl(), "app.xaml")
    root.listbox1.ItemsSource = [
      Product("Crunchy Frog", 10, 12),
      Product("Rams Bladder Cup", 10, 12),
      Product("Cockroach Cluster", 10, 12),
      Product("Anthrax Ripple", 10, 12),
      Product("Spring Suprise", 10, 12)]

And that’s pretty much it. I used Chiron’s /z command to create a Silverlight XAP file, uploaded it to Silverlight Streaming and embedded it right here in this post. Code is up on my skydrive as well. Uusing Silverlight Streaming for this app was very easy – basically upload the XAP file to their server and embed some iframe code in this post via the source view and that was it. I’m not sure I would use it for a production app, but it rocked for hosting this demo.

The XAP is a big download for such a trivial app – about 1.3MB. The vast majority of that is the DLR and IronPython assemblies. The XAP would only be 2.9kB if it was just the Python, XAML and manifest files. This kinda stinks, but there’s a new transparent platform extensions feature in Silverlight 3 so we can at least break the DLR and IronPython DLLs out into their own separate XAPs. That way they only get downloaded once and cached in the browser instead of being included in every single IronPython Silverlight application anyone creates.

So that’s one scenario down, one to go. In order to be able to build WCF services in IronPython, I have to add a lot more infrastructure – notably emitting CLR methods that can invoke dynamic methods as well as emitting custom attributes. Invoking dynamic methods means understanding DLR binders, so look for more posts on __clrtype__ next week.

AgDLR 0.5


I mentioned yesterday that it looked like a new release of AgDLR was eminent and sure enough here it is. There are some really cool new features including Silverlight 3 Transparent Platform Extension support, In-Browser REPL and In-Browser testing of Silverlight apps. As with IronRuby 0.3, Jimmy has the a summary of the new AgDLR release.

One feature of the new release I did want to highlight was XapHttpHandler because I’m the one who wrote it! 😄

The Silverlight versions of IronPython and IronRuby ship with a tool called Chiron that provides a REPL-esque experience for building dynamic language Silverlight apps. John Lam had a good write-up on Chiron when we first released it last year, but basically the idea is that Chiron is a local web server that will auto-generate a Silverlight XAP from a directory of Python and/or Ruby files on demand. For example, if your HTML page requests a Silverlight app named app.xap, Chiron automatically creates the app.xap file from the files in the app directory. This lets you simply edit your Python and/or Ruby files directly then refresh your browser to get the new version without needing an explicit build step.

The problem is that, unlike IIS and the ASP.NET Development Server, Chiron doesn’t integrate with ASP.NET. So it’s fine for building Silverlight apps that stand alone or talk to 3rd party services. But if you want to build a Silverlight app that talks back to it’s ASP.NET host, you’re out of luck. That’s where XapHttpHandler comes in. XapHttpHandler does the same exact on-demand XAP packaging for dynamic language Silverlight applications that Chiron does, but it’s implemented as an IHttpHandler so it plugs into the standard ASP.NET pipeline. All you have to do is put the Chiron.exe in your web application’s bin directory and add XapHttpHandler to your web.config like so:

  <!--remaining web.config content ommitted for clarity-->
      <add verb="*" path="*.xap" validate="false"

The new AgDLR drop includes a sample website that shows XapHttpHandler in action.

Quick note of caution: by design, XapHttpHandler does not cache the XAP file – it’s generated anew on every request. So I would highly recommend against using XapHttpHandler on a production web server. You’re much better off using Chiron to build a physical XAP file that you then deploy to your production web server.

Afternoon Coffee 174

You know, this gets pretty long when I go a week between morning coffee posts.

Dynamic Language Stuff

Other Stuff

  • Don Syme blogs about an update to the F# CTP, a mere week after the original release. One week? That’s more often than even IPy releases. I can’t wait to see what they ship in next week’s release! 😄 Seriously, I hope they can keep the release sprints short, but every week would be a bit crazy!
  • Speaking of F#, Matt Podwysocki updates FsTest for the F# CTP and posts about Extension Everything in F#. Unlike C#, which only supports extension methods, F# also supports extensions properties, static methods and events, though like Matt I can’t think of a good use for extension events.
  • Still speaking about F#, Andrew Kennedy has a three part series on the new units of measure feature of F#. If you were going to use F# to build the physics engine of a game, I would suspect UoM would be extremely useful. (via Don Syme)
  • Oh look, Chris Smith built an F# version of artillery game that uses Units of Measure for the physics code. I’ll bet UoM was extremely useful. 😄
  • Talking about Live Mesh at TechEd Australia – where much to my surprise frankly they were demoing Live Mesh Apps – I pointed out to Scott Hanselman that Mesh is running an embedded CoreCLR (aka the same CLR from Silverlight 2). Scott went poking around and posted what he discovered. Looking forward to finding out what he digs up on using CoreCLR outside the browser.
  • Speaking of Scott, I need to set up a family video conference solution like Scott’s before my next trip.
  • Congrats to Glenn Block and the MEF team for their initial CodePlex source drop! I’ve been hearing about this possibility since Glenn joined the team, so I’m really excited to see it happen. I need to take a look at it in detail (in my copious spare time) because I want to find out how to make it work with IPy.
  • Bart de Smet has a whole series (starting here) on Dynamic Expression Trees. However, given that he specifically writes “This blog series is not about DLR itself” makes it seem pretty conceptual to me. Why not talk about DLR expression trees instead Bart?
  • I’m sure you noticed ASP.NET MVC preview 5 dropped last week. I really liked Brad Wilson’s discussion of the new view engine design.
  • Tomas Restrepo has started publishing his source code on GitHub. Personally, I haven’t published any source code lately but I am using Git for all of my non IPy core work (which is stored in TFS). Like Tomas, I’m still getting the hang of Git but I’m really digging it’s speed, it’s branching and the fact that there’s zero infrastructure requirements. SVN provides the lightweight svnserve, but Git is even lighter weight than that.
  • I liked Steve Yegge’s post on typing. I am a touch typer, but I doubt I type 70 words a minutes. I do know where the number keys are without looking though, so I guess that’s pretty good. I remember seeing Chris Anderson demo Avalon WPF long before it was public and being impressed at how fast he could type.

Morning Coffee 172

  • I took the kids to see Fly Me To The Moon recently. We had to trek to Monroe (about 30 minutes away) because it’s a special 3D movie, and it was only playing there and in downtown Seattle. The movie’s story is insipid – three flies stow away on Apollo 11 – but all the space shots were actually kinda cool. It sure felt like they wanted to be scientifically and historically accurate about the the actual mission (well, other than the part about the flies). Patrick really liked it (he wants to build a rocket in the back yard) and Riley sat thru the whole thing with a minimum of fussing.
  • I’m a big fan of Joe Biden, so I’m really happy Obama picked him to be his running mate.
  • I know it’s old news but what the frak was John Edwards thinking? I like his policies, but the arrogance it takes to run for president when you know you’ve got that skeleton in your closet is mind-boggling.
  • On the other hand, watching the Sean Hannity and guest’s hypocrisy on Edwards’ affair, only to watch them scramble like cockroaches when Colmes points out McCain had admitted to having an affair was frakking hilarious.

OK, onto geek stuff:

  • My new boss Dave Remy has moved to a new blog. If you’re curious what he was up to for the 10 months he was away from Microsoft, he’s happy to share.
  • IPy and IRuby developer Curt Hagenlocher (aka Iron Curt) is blogging. Cue the Ozzy…I AM IRON CURT. Or don’t. Anyway, he dives in the deep end of the pool – no “hello world” lollyblogging for Iron Curt – digging into the stack implications of rethrowing exceptions and debugging emitted IL.
  • Srivatsn writes about static compilation of IPy scripts. Note, we’re not talking about static typing – it’s still the same good-old dynamically typed IronPython, just packaged up as an assembly, rather than as a bunch of .py files. Note, if you’re interested in compiling IronPython, you should check out the PYC sample we published as part of Beta 4.
  • Speaking of IPy Beta 4, Shri Borde posts about the COM dispatch support which is enabled by default as of Beta 4. If you’re driving COM automation clients (like Office) from IPy, this is a huge improvement over the old mechanism.
  • Jeff Hardy has released a new version of NWSGI, a managed version of Python’s Web Service Server Gateway Interface. My understanding is that this would allow any Python web stack written against WSGI to run in IIS with IronPython (subject to IronPython’s compatibility with CPython). Jeff’s been documenting his efforts getting Django running with NWSGI on his blog. Awesome work Jeff! (Thanks for the correction Seo!)
  • I never really bought into the “Attention Economy”, but Chris Anderson’s economic analysis of his DIY Drones site traffic was fascinating.
  • Lutz announces “it is time to move on” from Reflector and there was a collective horrified scream in the .NET community. He’s handing it over to Red Gate, who promised they “will continue to offer the tool for free to the community”.
  • I missed this when he posted it in June, but I really liked Nikhil Kothari use of the DLR in Silverlight to cut down on the XAML verbosity in his ViewModel action binding.
  • Brian McNamara previews the new Add Reference and file ordering support in the upcoming F# CTP. I’m really looking forward to the project-to-project reference support. I can’t tell you how many times I’ve gotten burned because my main project recompiled but my test project didn’t. You just get used to hitting Rebuild All instead of Build. As for file ordering, it’s a bit of a bummer that F# requires it, but the new experience is hella better than editing the project file by hand. I’m really looking forward to the new CTP.

Morning Coffee 171

  • Big news for IronRuby out of OSCON. John and Jim have the details. Congrats to the IronRuby folks on reaching these milestones and paving the way for others (i.e. IPy) to follow some of the same paths.
  • One of those OSCON announcements, is a project my teammate Jimmy Schementi has been working on: Silverline, which “let’s you write Rails code that can run on the client“.
  • Shri Borde – the dev manager for IPy, IRuby and F# – tackles a tricky subject of static compilation of dynamic Python code. This came up on the mailing list recently as one of the outstanding requests for IPy to do is support custom attributes, which requires static compilation. Shri lays out some of the big issues with this approach. However, the community has been fairly clear on this, so it’s obviously something we need to look at.
  • I met someone from MS Research at the MS Product Fair who pointed me to the Institute for Personal Robots in Education, a joint effort between Georgia Tech and Bryn Mawr College and sponsored by Microsoft Research. Their Myro software (myro == my robot) is written in CPython, but there’s an effort underway (aka Miro 3.0) to build a .NET version that uses IronPython. Must investigate.
  • Seshadri shows how easy it is to extend C# types in IronPython. It’s also shows how simple it is to host DLR code in your app – it’s like 6 lines of code!
  • Early reviews of IronPython in Action are good.
  • If you want to run an IronPython IDE in your browser with Silverlight, check out SilverShell from Dan Eloff.
  • The XNA team has announced their business plans for community games. Basically, you set a price point between 200 and 800 points (aka between $2.50 and $10) and receive a “baseline” of 70% of the revenue the game generates. More details are available in the FAQ. This is pretty excited. I’d like to build some co-op kids games.
  • Speaking of XNA, Caligari is now offering TrueSpace 7.6 for free . David Weller and Glenn Wilson provide an XNA viewpoint on the announcement, Chris Pendleton shows how to upload your models to VirtualEarth.
  • Congrats to the CodePlex team on their latest drop, which features that a cool new feature – Mailing Lists! IronPython has had a Mailman mailing list for years, so I’m not sure we’ll use this feature on IPy, but I’ll investigate it
  • Two PDC notes: First, Rick Rashid – VP of MS Research – will be delivering a PDC keynote. Second, the PDC team has put up a video podcast on Producing a Ginormous Conference in 10 Minutes or Less! It’s the “inaugural episode” so watch for more Countdown to PDC video podcast episodes in the future.
  • I recently discovered Chris Smith’s F# blog. He’s got recent posts on Mastering F# Lists and Guidelines for Readable F# code. For the F# novice, check out his F# in 20 Minutes posts (part one, part two)
  • Pat Helland is moving to the SQL team. Good luck Pat!
  • I like Nick Malik’s formal definition of use cases, but I can’t help be reminded of Charlie Alfred’s Value-Driven Architecture article in Architecture Journal 5 where he said use cases were “easy to teach and explain” but that “if simplicity were the only goal that counted, we’d all still be walking or riding horses to get from one place to another.”