Skip to main content

PyCon: Embedding Little Languages in Python

Little languages embedded in Python can improve the readability of code by allowing the coder to specify what he's trying to do (declarative) rather than how to do it (imperative). First you dream up a syntax for what you're trying to convey by typing some pretend code, and then you try to get Python to conform to something similar to your ideal syntax. The author did not cover using a parser, but instead misused (in a good way) Python syntax. He suggested the following tricks:
  • Make use of function parameter lists, including keywords, *args, and **kargs.
  • Use Python classes to represent states. Use methods for transitions.
  • Use reflection tricks.
  • Put domain specific syntax in docstrings.
  • Use operator overloading by doing things like implementing the __add__ method.
All in all, his tricks were all pretty simple. I'm sure all the RoR coders out there are yawning. However, it was a fun talk anyway. Unfortunately, I got so carried away, I missed two talks while talking with some guy about parsers and various other things.

Comments

Anonymous said…
Hi, Could you please give an example of point two:
Use python objects for state and methods for transitions.

Thanks
Andrew
jjinux said…
The slides are here:
http://us.pycon.org/common/talkdata/PyCon2007/048/little-langs-correct.zip

Blogger will probably trample the indentation, but here's the example in the slides:

class Unassigned(TaskState):
def to_Assigned(self, task):
task.email_assignee("Task has been assigned to you")

class Assigned(TaskState):
def to_Declined(self, task):
task.email_manager("Task has been declined")

def to_Assigned(self, task):
task.email_old_assignee, 'Task has been reassigned')
task.email_new_assignee, 'Task has been assigned')

def to_Accepted(self, task):
task.email_manager("Task has been accepted")

Popular posts from this blog

Drawing Sierpinski's Triangle in Minecraft Using Python

In his keynote at PyCon, Eben Upton, the Executive Director of the Rasberry Pi Foundation, mentioned that not only has Minecraft been ported to the Rasberry Pi, but you can even control it with Python. Since four of my kids are avid Minecraft fans, I figured this might be a good time to teach them to program using Python. So I started yesterday with the goal of programming something cool for Minecraft and then showing it off at the San Francisco Python Meetup in the evening.

The first problem that I faced was that I didn't have a Rasberry Pi. You can't hack Minecraft by just installing the Minecraft client. Speaking of which, I didn't have the Minecraft client installed either ;) My kids always play it on their Nexus 7s. I found an open source Minecraft server called Bukkit that "provides the means to extend the popular Minecraft multiplayer server." Then I found a plugin called RaspberryJuice that implements a subset of the Minecraft Pi modding API for Bukkit s…

Apple: iPad and Emacs

Someone asked my boss's buddy Art Medlar if he was going to buy an iPad. He said, "I figure as soon as it runs Emacs, that will be the sign to buy." I think he was just trying to be funny, but his statement is actually fairly profound.

It's well known that submitting iPhone and iPad applications for sale on Apple's store is a huge pain--even if they're free and open source. Apple is acting as a gatekeeper for what is and isn't allowed on your device. I heard that Apple would never allow a scripting language to be installed on your iPad because it would allow end users to run code that they hadn't verified. (I don't have a reference for this, but if you do, please post it below.) Emacs is mostly written in Emacs Lisp. Per Apple's policy, I don't think it'll ever be possible to run Emacs on the iPad.

Emacs was written by Richard Stallman, and it practically defines the Free Software movement (in a manner of speaking at least). Stal…

JavaScript: Porting from react-css-modules to babel-plugin-react-css-modules (with Less)

I recently found a bug in react-css-modules that prevented me from upgrading react-mobx which prevented us from upgrading to React 16. Then, I found out that react-css-modules is "no longer actively maintained". Hence, whether I wanted to or not, I was kind of forced into moving from react-css-modules to babel-plugin-react-css-modules. Doing the port is mostly straightforward. Once I switched libraries, the rest of the port was basically:
Get ESLint to pass now that react-css-modules is no longer available.Get babel-plugin-react-css-modules working with Less.Get my Karma tests to at least build.Get the Karma tests to pass.Test things thoroughly.Fight off merge conflicts from the rest of engineering every 10 minutes ;) There were a few things that resulted in difficult code changes. That's what the rest of this blog post is about. I don't think you can fix all of these things ahead of time. Just read through them and keep them in mind as you follow the approach above.…