Stumbling on Jim Propp's self-referential aptitude test reminded me that I should really get around to learning Alloy (a "simple structural modeling language based on first-order logic", according to its homepage). The examples in the Alloy tutorial work well enough, but I wanted to know whether will also solve problems not chosen by the author ;-)

My final solution came out surprisingly neatly for a first attempt, following the format of the quiz closely, although it took much experimenting to get the syntax exactly right. The only bit I'm unhappy about is the helper predicates for question 12, as I couldn't find an easy way to test for primes, etc. Any Alloy experts out there want to show me a quicker way?

Wondering why X takes so long to start up (and inspired by the smaller source tree since it went modular ;-), I did a little profiling tonight. Turns out that probing the PCI bus is taking quite a while (Debian/unstable's X.org). The last call to pciFindNext() was taking 1.7 seconds just to report no more devices!

SCons is a rather nice build system written in Python. It compiles many languages, including C and Java. But the problem is that not many people have it, and making your code unnecessarily hard to compile by depending on an uncommon build system is not a good idea. In this article I'll show how you can get your build scripts to automatically download (and cache) SCons as part of the build process...

I've tried installing Klik twice in the past, but the site was down both times. A osnews.com article prompted me to try it again and this time I got it installed.

Klik's main advantage over Zero Install is the large number of packages available for it. Its main disadvantage is that it's totally insecure. However, I've written klik2zero, a little Python script that creates Zero Install packages automatically from Klik ones.

If you compile ROX-Filer on a system with GTK 2.4, it will still work on a system with GTK 2.8. Compile it on a 2.8 system, and it will fail to run with 2.4. This problem isn't specific to ROX-Filer (or to GTK); recent versions of ROX-CLib and programs using it stopped working because they gained a phantom dependency on libglitz. Here's how to avoid these problems...

Federico has written a little Python script to help with profiling Nautilus. I've been wanting something like this for a while so I tried it on ROX-Filer. Turns out that with Zero Install's 0launch command (completely unoptimised Python) parsing a couple of XML files and searching for the best version, plus the filer's initialisation itself, it takes nearly two seconds to start the filer on my machine. Federico's script produced this plot:

I spent a bit of time this weekend hacking on the Xfce panel. The result is that you can now install programs by dragging a URL from a web-browser into the Xfce panel's launcher dialog (much as ROX users do with AddApp). This makes it easy to put ROX applications into your panel; just drag the links from the Zero Install software index to the dialog, as in this screenshot:

My current plans for ROX-CLib are:

• 2.1.8. This was done in March 2006. The major new feature: internationalization support. The messages in ROX-CLib are now translatable, there is a .po file, the .mo files are generated and stored inside the AppDir, and are used when found. Apps get their .mo files loaded if found.
• 2.1.9 was released November 2006. This includes:
  • More support for menus, simplifying the code that needs to be in the app.
  • Extended attribute support.
  • Support for building against GTK 2.4 using Zero Install.
  • 0compile support
• 2.1.10 sometime in the future, including:
  • Improved system tray interface
  • xxmlrpc for communicating with ROX-Session
  • libglade interface similar to that in ROX-Lib.
• 2.2.0, hopefully this will be 2.1.10 deemed stable.

Version 0.18 of 0launch was released yesterday. Notable new features include:

• Signatures in XML comments. This allows us to present feeds nicely in a web-browser, as discussed previously.
• FTP support (not just HTTP).
• Support for extracting from RPMs.
• As an added layer of protection against bugs in tar and cpio, the extraction process is sandboxed using plash, if available.

You can see all these features in action by trying the sample Tgif interface. This interface can be viewed in any web-browser that supports XSLT, and when run it downloads an RPM using FTP, extracts it with plash for sandboxing and then runs it.

I've been spending a bit of time playing with PLASH. Plash is a shell which grants the programs it runs access only to certain files. For example:

$ cat text

Because text appears on the command-line, the cat command is given read access to it (and nothing else). To get write access, you put => before the filename:

$ rm text
/bin/rm: cannot remove `text': Permission denied
$ rm => text
$

You can also give a process access to a file (or directory structure) without also passing its name as an argument. List such files after +, e.g.: