Graphic designer and computer scientist John Maeda explored the artistic possibilities of code in his books Design by Numbers (1999) and Creative Code (2004). In 2001, two of his protgs at Massachusetts Institute of Technology, Casey Reas and Ben Fry, released a beta version of their application Processing. It has been used by a vast array of artists, designers, animators and scientists, and the recent publication of a definitive guide blows the app wide open to everyone.
So, why should you be interested in Processing? What can it do that Flash can't? Thanks to the streamlined nature of the language and shortcuts for common actions, it runs very quickly and efficiently. Go to http://complexification.net/gallery/machines/substrate, run the applet and look at what is happening there: code working very fast to create something extraordinarily beautiful. Could you do that as easily in Flash?