2 files changed, 58 insertions, 2 deletions
diff --git a/src/simulation/actions.js b/src/simulation/actions.js
index 8a4e8f0..dd7c4e6 100644
--- a/src/simulation/actions.js
+++ b/src/simulation/actions.js
@@ -97,8 +97,26 @@ const place = {
 };
 
 
+const trigger = {
+  size: 1,
+  propose: (world, agent, head) => {
+  if (head[0] < threshold) { return []; }
+    else {
+      const dx = { n: 0, e: 1, s: 0, w: -1 }[agent.flags.orientation];
+      const dy = { n: -1, e: 0, s: 1, w: 0 }[agent.flags.orientation];
+      return [
+        { lattice_changes: [{
+          x: agent.x + dx, y: agent.y + dy,
+          from: 'mutable', to: 'active',
+          flags: { emit: [1, 0, 0, 0, 0, 0, 0, 0] },
+        }]}
+      ];
+    }
+  },
+};
 
 
 export const actions = [
-  move_forward, move_backward, turn_left, turn_right, place,
+  move_forward, move_backward, turn_left, turn_right, 
+  place, trigger,
 ];
diff --git a/src/simulation/actions.test.js b/src/simulation/actions.test.js
index e94605d..1ebe9a9 100644
--- a/src/simulation/actions.test.js
+++ b/src/simulation/actions.test.js
@@ -6,7 +6,7 @@ import { actions } from './actions.js';
 const [
   move_forward, move_backward, 
   turn_left, turn_right,
-  place,
+  place, trigger,
   ...rest
 ] = actions;
 
@@ -159,3 +159,41 @@ test("place", () => {
   expect(place.propose(null, e, [0])).toEqual([]);
   expect(place.propose(null, w, [-1])).toEqual([]);
 });
+
+
+test("trigger", () => {
+  const n = { id: 0, x: 0, y: 0, flags: { orientation: 'n' } };
+  const s = { id: 0, x: 0, y: 0, flags: { orientation: 's' } };
+  const e = { id: 0, x: 0, y: 0, flags: { orientation: 'e' } };
+  const w = { id: 0, x: 0, y: 0, flags: { orientation: 'w' } };
+
+  expect(trigger.propose(null, n, [1])).toEqual([
+    { lattice_changes: [{
+      x: 0, y: -1, from: 'mutable', to: 'active',
+      flags: { emit: [1, 0, 0, 0, 0, 0, 0, 0] },
+    }]},
+  ]);
+  expect(trigger.propose(null, s, [1])).toEqual([
+    { lattice_changes: [{
+      x: 0, y: 1, from: 'mutable', to: 'active',
+      flags: { emit: [1, 0, 0, 0, 0, 0, 0, 0] },
+    }]},
+  ]);
+  expect(trigger.propose(null, e, [1])).toEqual([
+    { lattice_changes: [{
+      x: 1, y: 0, from: 'mutable', to: 'active',
+      flags: { emit: [1, 0, 0, 0, 0, 0, 0, 0] },
+    }]},
+  ]);
+  expect(trigger.propose(null, w, [1])).toEqual([
+    { lattice_changes: [{
+      x: -1, y: 0, from: 'mutable', to: 'active',
+      flags: { emit: [1, 0, 0, 0, 0, 0, 0, 0] },
+    }]},
+  ]);
+
+  expect(trigger.propose(null, n, [0])).toEqual([]);
+  expect(trigger.propose(null, s, [-1])).toEqual([]);
+  expect(trigger.propose(null, e, [0])).toEqual([]);
+  expect(trigger.propose(null, w, [-1])).toEqual([]);
+ });