2 files changed, 44 insertions, 1 deletions
diff --git a/src/simulation/lattice_rules.js b/src/simulation/lattice_rules.js
index db027a3..80f3221 100644
--- a/src/simulation/lattice_rules.js
+++ b/src/simulation/lattice_rules.js
@@ -53,7 +53,19 @@ export const lattice_rules = {
     }
   },
 
-  mutable: () => {},
+  mutable: (lattice, x, y) => {
+    const num_active_neighbors = neighbors(lattice, x, y)
+      .map(([x, y, cell]) => cell.type)
+      .filter(type => type === 'active')
+      .length;
+    if (num_active_neighbors > 0) {
+      // become living cell
+      return { world_updates: [{ 
+        x, y, from: 'empty', to: 'active',
+        flags: { emit: [0, 0, 0, 0, 0, 0, 0, 1] },
+      }]};
+    }
+  },
   immutable: () => {},
   flag: () => {},
 
diff --git a/src/simulation/lattice_rules.test.js b/src/simulation/lattice_rules.test.js
index 4b78116..7648a68 100644
--- a/src/simulation/lattice_rules.test.js
+++ b/src/simulation/lattice_rules.test.js
@@ -108,3 +108,34 @@ test("beehive", () => {
   //expect(world_update(world).lattice).toEqual([
   expect(apply(world_update, 1, world).lattice).toEqual(lattice);
 });
+
+
+test("mutables are activated by neighboring actives", () => {
+  const L = { type: 'active', flags: {} };
+  const _ = { type: 'empty', flags: {} };
+  const l = { type: 'active', flags: { emit: [0, 0, 0, 0, 0, 0, 0, 1] } };
+  const d = { type: 'empty', flags: { emit: [0, 0, 0, 0, 0, 0, 0, -1] } };
+  const M = { type: 'mutable', flags: {} };
+
+  const lattice = [
+    [ _, _, _, _, ],
+    [ _, L, M, _, ],
+    [ _, M, M, _, ],
+    [ _, _, _, _, ],
+  ];
+
+  const world = { lattice, lattice_rules, agents: [], senses: [], actions: [], validity: [] };
+
+  expect(apply(world_update, 1, world).lattice).toEqual([
+    [ _, _, _, _, ],
+    [ _, L, l, _, ],
+    [ _, l, l, _, ],
+    [ _, _, _, _, ],
+  ]);
+  expect(apply(world_update, 2, world).lattice).toEqual([
+    [ _, _, _, _, ],
+    [ _, L, L, _, ],
+    [ _, L, L, _, ],
+    [ _, _, _, _, ],
+  ]);
+});