2 files changed, 78 insertions, 0 deletions
diff --git a/src/simulation/lattice_rules.js b/src/simulation/lattice_rules.js
new file mode 100644
index 0000000..0f46d0d
--- /dev/null
+++ b/src/simulation/lattice_rules.js
@@ -0,0 +1,53 @@
+import { pairs } from '../util.js';
+
+function mod(k, n) {
+  return ((k % n) + n) % n;
+}
+
+function pos_wrap(lattice, x, y) {
+  const height = lattice.length;
+  const width = lattice[0].length;
+  return [mod(x, width), mod(y, height)];
+}
+
+
+function neighbors(lattice, x, y) {
+  const offsets = [-1, 0, 1];
+  const positions = pairs(offsets, offsets)
+    .filter(([dx, dy]) => dx !== 0 || dy !== 0)
+    .map(([dx, dy]) => pos_wrap(lattice, x+dx, y+dy));
+  const neighbors = positions
+    .map(([x, y]) => [x, y, lattice[y][x]]);
+  return neighbors;
+}
+
+
+export const lattice_rules = {
+
+  empty: (lattice, x, y) => {
+    const num_active_neighbors = neighbors(lattice, x, y)
+      .map(([x, y, cell]) => cell.type)
+      .filter(type => type === 'mutable' || type === 'active')
+      .length;
+    if (num_active_neighbors === 3) {
+      return { world_updates: [{ x, y, from: 'empty', to: 'active' }] };
+    }
+  },
+
+  active: (lattice, x, y) => {
+    const num_active_neighbors = neighbors(lattice, x, y)
+      .map(([x, y, cell]) => cell.type)
+      .filter(type => type === 'mutable' || type === 'active')
+      .length;
+    if (num_active_neighbors < 2) {
+      return { world_updates: [{ x, y, from: 'active', to: 'empty' }] };
+    } else if (num_active_neighbors > 3) {
+      return { world_updates: [{ x, y, from: 'active', to: 'empty' }] };
+    }
+  },
+
+  mutable: () => {},
+  immutable: () => {},
+  flag: () => {},
+
+};
diff --git a/src/simulation/lattice_rules.test.js b/src/simulation/lattice_rules.test.js
new file mode 100644
index 0000000..a91400e
--- /dev/null
+++ b/src/simulation/lattice_rules.test.js
@@ -0,0 +1,25 @@
+import { world_update } from '../world/world.js';
+import { lattice_rules } from './lattice_rules.js';
+
+
+test("blinker", () => {
+  const L = { type: 'active', flags: {} };
+  const D = { type: 'empty', flags: {} };
+  const lattice = [
+    [ D, D, D, D, D ],
+    [ D, D, D, D, D ],
+    [ D, L, L, L, D ],
+    [ D, D, D, D, D ],
+    [ D, D, D, D, D ],
+  ];
+
+  const world = { lattice, lattice_rules, agents: [], senses: [], actions: [] };
+  expect(world_update(world).lattice).toEqual([
+    [ D, D, D, D, D ],
+    [ D, D, L, D, D ],
+    [ D, D, L, D, D ],
+    [ D, D, L, D, D ],
+    [ D, D, D, D, D ],
+  ]);
+  expect(world_update(world_update(world)).lattice).toEqual(lattice);
+});