edsger is a web service to evaluate mathematical expressions. On the back end is an implementation of the Shunting-Hall algorithm. It's named edsger because Edsger Dijkstra came up with the algorithm.
Try out a demo here
edsger was written for Python 2.5. Other versions should work alright. For the web component of the application, you'll need mako and bottle. You can install these with easy_install.
Rename config.sample.py to config.py, then run python app.py. You should see the homepage on localhost:8080.
A straightforward implementation of the Shunting-Hall algorithm powers edsger. Expression evaluation is efficient as a result.
Cool stuff
- Unary minuses stack correctly. (Try '5-----6', for example)
- Error messages are lucid, for the most part.
- Operators are abstracted, allowing more to be added in the future. This was nice when I realized that I hadn't implemented negative numbers at the last minute.
- Lots of unit tests. Run them using nosetests, if you like.
Limitations
- Assumes you never want to do integer division.
- Complex numbers aren't included.
- Tokenizing of the input expression relies on string splitting. To handle really long input expressions efficiently, this would have to be changed.
- Overflow is considered an error.
edsger can be deployed as a JSON web service using Bottle. There is a little HTML console included to demonstrate its usage in AJAX, as well.
Bottle exposes the app using WSGI, so it could be plugged into any WSGI compatible multi-threaded Python server (like gunicorn, cherryPy, fapws3, ...)