0.4.0-pre-alpha is out now. Since the last build I’ve added two big features: rule frequency and rule symmetry.

Rule frequency is simply the ability to have rules fire at different rates. This is important when authoring rules to move bullets and enemies, for example; you want the bullets to move more quickly than the enemies, and one way of achieving that would be to make the rule for moving bullets fire at higher rate.

Rule symmetry allows rules to be authored with different types of symmetry: horizontal, vertical, four-way, eight-way and infinite. This makes rules much more expressive. For example, to move a monster randomly in one of four different directions, simply author a rule to make the monster move right, and then make that rule four-way symmetrical. The existing routines to resolve conflicts will mean that the monster will move in one of the four directions at random each time the rule fires.

Infinite symmetry may seem weird, but it simply means that the 3x3 neighbourhood of cells can appear in any order, providing that the counts of different cell types match the rule. This makes it easy to author rules for the Conway’s Life, for example.

I’ve updated the demo to showcase these changes: rocks fall every frame, the purple monsters move randomly every second frame, leaving dirt trails as they do so, and Conway’s Life runs every fourth frame, transforming the trails of dirt into familiar patterns. Note that the life rules take account of rocks, trees and monsters, so that a single cell of dirt next to a rock and a tree will continue to survive, as it has two non-empty neighbouts, but new dirt cells are only spawned if at least one of the three neighbours is also dirt.