IronRuby, Silverlight and executing code dynamically in the browser

I’m toying around with the idea of a simple in-browser “coding
for IronRuby, think JSFiddle but for DLR languages. I’m fairly new to
IronRuby, but have lots of Silverlight experience. I have gotten the
up and running, but have ran into a couple issues.

My initial idea was to use the virtual file system the IronPython
Silverlight Host creates when it downloads files included using
tags. However, turns out this virtual file system is read-only, so I
write new Ruby files after the application is loaded.

My second idea was to simply use the DynamicEngine and simply execute
code. The code I’ve written looks something like this:

        def run_tests
            code = window.eval("codeEditor.getCode()").to_s
            test = window.eval("testEditor.getCode()").to_s

            puts code

                dyneng =
                engine = dyneng.runtime.get_engine("ruby")
                scope = dyneng.create_scope

                errorFormatter =

                resultCode =

resultTest =

                puts resultCode
                puts resultTest
            rescue => ex
                puts ex.to_s

It basically gets two pieces of Ruby code, then creates a new engine,
creates script source, compiles it, and then executes it. If I do this
valid Ruby code everything works as expected. However, if I try to
invalid code I was expecting my error handler to execute. But this does
happen. All I get is an error in the FireBug console saying:

“Error calling method on NPObject!”

So does anyone have suggestions on how to handle errors when executing
code dynamically in the browser. Secondly, does anyone have suggestions
alternative approaches to implementing this - i.e. make the virtual file
system writable (write to isolated storage perhaps?).

Best regards,
Jonas Follesø

Hey Jonas, nice running into here (love your blog)!

You could try writing your own virtual filesystem. Check out my blog
some inspiration:

I’m currently working on just that. My current project (porting RPG
XP to Silverlight - already finished the desktop port) requires such
functionality for enumerating file system entries (think Dir.glob), and
saving game state to “disk”. I’m trying to tease out my VFS into
extensible; you can find my code here:

There’s not much there, but perhaps the PathUtil could be handy:

The more I work on abstracting out the core of the VFS, the more I feel
it’s hard to make a “one-fits-all” sort of solution; the use cases can
a lot. I almost think it would be better to publish some guidance and a
reference implementation, rather than try to create some architecture
is either too abstract or, conversely, not extensible enough to be

Let me know where you go with your project - it sounds cool.


Hi Charles,

And thanks for the comment about my blog - really appreciate it!

I had a look at your blog post for a custom virtual file system - and I
think that is the best long-term approach. This would enable a nice “in
browser” coding experience where you can add files, reference other
etc. all client side running in the browser.

If you look at the code in the,
there is a class called IsolatedStorageVirtualFilesystem that extends
the BrowserVirtualFileSystem. The class overrides the GetFileInternal
method, throwing an not implemented exception, and have a TODO comment.
So I
guess this would be a good starting point.

Alternatively you could extend the HttpVirtualFilesystem, which is the
system used by the standard Browser PAL. The HttpVirtualFileSystem will
the XapVirtualFileSystem to check if a file exists in the XAP, if not it
will try to download it. My suggestion would be to add an extra check -
it doesn’t exist on the server, then check Isolated Storage.

You would probably also have to extend BrowserScriptHost class and
BrowserPAL, which currently expose the BrowserVirtualFileSystem, and
use the IsolatedStorageVirtualFileSystem, as well as changing the
OpenInputFileStream method, which throws an exception if any other file
than Open or Read is passed in. This is the exception that bites you if
dry to use Ruby file APIs to write a file in a standard DLR app today.

It would be nice if someone who worked on the Silverlight hosting
environment for IronRuby could chip in with suggestions on how to best
implement write support in the virtual file system. I would be more than
happy trying to implement this and submit a patch.

As for your blog post on enumerating resources that looks handy - as
enumeration is also something that would be useful (when the app loads
would be nice to check which files have been stored in isolated storage,
that way enabling devs to save their work in isolated storage between

I had a look at your SilverlightVFS code - but I guess the thing I don’t
quite get is the proper way to “blog” a new file system into the

  • Jonas

On Fri, Jul 23, 2010 at 12:16 AM, Charles S. <