Composing complex behavior from simple visual descriptions

An often-mentioned advantage of rule-based programming languages is that a program can be extended simply by adding a few more rules. In practice however the rules tend to be dependent on each other and instead of just adding rules, existing rules need to be changed. The unique rules in Cartoonist, a rule-based visual programming environment to build simulations, provides a solution to this problem. Cartoonist's rules can be used in a more modular way supporting an iterative mode of programming. Libraries of visual descriptions can be built and reused to compose complex behavior from these descriptions. This makes exploring the space of possible descriptions of simulations easier, which is valuable for intended educational use of Cartoonist. Another advantage of Cartoonist is that its programs tend to have fewer and simpler rules than programs written for comparable systems.