News: April 2008

If you're building an application, then your users will get much more out of it if you given them a plugin API. For Sublime Text, I settled on Python as the extension language. In fact, I think you'd be mad to choose anything else.

For a desktop application looking for an extension language, the two most important things to optimize for are the likelihood that your users will create plugins, and the chance they'll actually enjoy it. This gives a few guidelines when choosing an extension language:

• Adoption matters. There should be a reasonable chance that users already know the language, or if they don't, learning it is at least a worthy investment.
• Unicode matters. How much depends on the application, but if users can't even write a script that opens a file in their home directory because of Unicode issues, you won't be winning any friends.
• Libraries matter. File access, date / time, socket programming, subprocesses, etc. If you're writing a general purpose desktop application, then most plugins your users will want to write will involve using APIs other that what you've explicitly exposed.
• Ease matters. Any language requiring a separate compilation step isn't a contender.

There are also several criteria that don't matter for a typical desktop application extension language:

• If you're going to depend on the scripting language having fast runtime performance, then Python may well not be for you: Lua or Scheme are both typically much faster, and have a lower memory footprint.
• If you're depending on the language for security, such as a web browser running untrusted code, or a server running code submitted by users, then you have an entirely different set of considerations.
• If the application is only going to be used in house, then it doesn't matter terribly much what percentage of users are familiar with the language, because they're going to be forced to use it anyway.

At first glance, it appears that desktop application developers are spoiled for choice of extension languages, but caveat programmer:

Scheme, despite having reasonable libraries and Unicode support, is far from mainstream. Using Scheme or another Lisp dialect as an extension language is an effective way to make sure you won't have any extensions. Early versions of Sublime Text used Scheme as an extension language, but it was dropped for this reason. Just because you like a language, doesn't mean your users will.

Lua is another candidate, which has a lot of uptake in games. It has a very small code footprint, and excellent runtime speed. However, its paucity of libraries, weak Unicode support, and small-medium user base make it hard to justify as an extension language for desktop applications.

What about JavaScript? It's an underrated, elegant language, with a huge number of people acquainted with its syntax. Its weakness is that it's not used as a general purpose language, so there's no selection of libraries your users will be able to build on. No libraries and no built-in standard APIs (file system access, I'm looking at you) rule JavaScript out.

We come to Python and Ruby. Which language is better really isn't relevant, both are fine languages with pleasant syntax and semantics. In terms of ecosystems, both are popular and have a good selection of libraries. Python, however, is the bigger gorilla, with a larger user base and more libraries.

Python, however, has a secret weapon: Python has ctypes, and Ruby doesn't ⁽¹⁾. ctypes provides an ad-hoc way to call functions in any shared library in the system. This means that the platform's entire native API is available with no C extensions required. Take, for example, a user who wants to launch another application, then set the input focus back to yours. With Python and ctypes on Windows, it's only a few lines of code to call GetForegroundWindow and SetForegroundWindow. That's pretty awesome.

Summary: Your users will be happiest if you choose Python. It's pretty hard to argue with that.

1. Not strictly true, as pointed out in the comments, Ruby has a similar library called Ruby/DL 2. That's pretty cool.

If you're shopping around for an extension language for your project, it's pretty hard to go past Python. Aside from being a very pleasant language to work with, it has a huge selection of libraries, and a user base that's at least as large. Add projects like Boost.Python into that, and you've got a pretty compelling case. However, it's not all beer and sunshine in Python land - at least, not on Windows.

Lets start with the simplest case: Ship python25.dll, and python25.zip (containing the standard libraries) with your application, and provide some means for users to enter Python code.

Golden, right? Not so much. It'll work fine right up until someone with an international version of Windows tries to install your application to a localized version of "C:\Program Files" that contains a unicode character. Then everything falls over.

Oh, you thought Python supported unicode? Well, it does. Sort of. Provided you don't expect to be able to put unicode paths within sys.path, the list of directories python files may be loaded from. Ouch!

There are still options though: you can set sys.path to load from the current directory, and just set the current directory appropriately before making any calls into Python.

Now, let's take a look at loading user supplied plugins from .py files. You could just place them in the same directory that the application is installed to, but that's not a great solution on Vista, as users generally won't have write access to Program Files. A better location is to place them within the Application Data folder, contained within the user's home directory.

This raises some more problems: It's not uncommon for users to have unicode characters in their username, and hence in their Application Data path. So we can't simply add that to sys.path. We also can't use the current directory trick any longer, as there are now two directories to load things from.

For Sublime Text, I've implemented a half way solution: Do some sys.path_hooks mangling to get modules loading from python25.zip, and use the current directory trick for user supplied modules (Drop me an email if you're interested in the code). It's not pretty, but it does work.

Aside from current directory wrangling, there's another option I've yet to try: short path names. Windows has a notion of short path names, where every file has its full path name, and a short one (see GetShortPathName) in 8.3 format for archaic programs. The noteworthy part is that the 8.3 name uses ASCII characters, so they'll be safe to use as Python module paths. There are a few caveats with this approach:

• Not every file has a short path name. Generation of them may be turned off.
• Some file systems don't support 8.3 file names: They presumably won't exist on Samba shares, for instance.

It's unfortunate that Python has this limitation. My understanding is that it is not going to be fixed for Python 3.0, though there has been some work in this direction. Despite this, I still think you'd be mad to use anything else as an extension language.

Sometimes, you just want to focus on what you're writing. You don't need toolbars, you don't need tabs, hell, you don't even need menus. Using full screen mode in a standard text editor is a good start, but it's generally not as minimalist as it could be, and the text is all bunched over on one side of the screen.

So what options do you have? If you're on a Mac, you can use WriteRoom, and which has a Windows clone called Dark Room. Other options are PyRoom, JDarkRoom and Vroom. These are all great for editing prose, but none support editing LaTeX, let alone code.

If, like Mark Pilgrim, all this makes you wonder why someone would want a text editor with no features, then I do suggest giving one of them a try, it's a pleasant experience.

Prompted by a suggestion on the forums, the current beta supports this very style. In this setup, there's nothing at all on the screen but your text in the center, and a muted scrollbar on the right. The cursor doesn't even blink. You can think of it as WriteRoom for Windows, with regular expressions, Python plugins and code editing.

Here's a screen shot of it in action:

Note the lack of menu, status bar, toolbar, line numbers, rulers etc.

Unlike multi pane editing, the objective here isn't to fit as much information as possible on the screen, but to block out everything that you don't need right now. It also works seamlessly with multiple monitors, with each one able to edit a different file in a similar fashion.

[Edit: this is included by default in the latest versions of Sublime Text. Press Shift+F11 to try it out for yourself]

Enjoy!