diff --git a/js/compiler/demo-santa.js b/js/compiler/demo-santa.js
new file mode 100644
index 0000000..52deae3
--- /dev/null
+++ b/js/compiler/demo-santa.js
@@ -0,0 +1,138 @@
+// bin/syndicatec compiler/demo-santa.js | node
+//
+// Santa Claus Problem
+// https://www.schoolofhaskell.com/school/advanced-haskell/beautiful-concurrency/4-the-santa-claus-problem
+// https://arxiv.org/pdf/1810.09613.pdf
+
+var Immutable = require('immutable');
+var Syndicate = require('./src/main.js');
+
+assertion type elfProblem(id);
+assertion type reindeerReturned(id);
+
+assertion type problemResolved(id);
+assertion type deliverToys();
+
+function sleep(milliseconds, continuation) {
+  react {
+    var deadline = +(new Date()) + milliseconds;
+    stop on asserted Syndicate.Timer.timeLaterThan(deadline) {
+      continuation();
+    }
+  }
+}
+
+var elfCount = 0;
+function elf() {
+  var elfId = "elf" + ++elfCount;
+  spawn* named elfId {
+    function workIndustriously() {
+      console.log(elfId, "is working.");
+      sleep(Math.random() * 1000.0, haveAProblem);
+    }
+
+    function haveAProblem() {
+      console.log(elfId, "has a problem!");
+      react {
+        assert elfProblem(elfId);
+        stop on asserted problemResolved(elfId) {
+          console.log(elfId, "'s problem is resolved.");
+          workIndustriously();
+        }
+      }
+    }
+
+    workIndustriously();
+  }
+}
+
+var reindeerCount = 0;
+function reindeer() {
+  var reindeerId = "reindeer" + ++reindeerCount;
+  spawn* named reindeerId {
+    function holiday() {
+      console.log(reindeerId, "is on holiday.");
+      sleep(Math.random() * 9000.0, returnToWork);
+    }
+
+    function returnToWork() {
+      console.log(reindeerId, "has returned from holiday and is ready to deliver toys!");
+      react {
+        assert reindeerReturned(reindeerId);
+        stop on asserted deliverToys() {
+          console.log(reindeerId, "delivers toys with the other reindeer.");
+          react {
+            stop on retracted deliverToys() {
+              console.log(reindeerId, "has been dismissed by Santa.");
+              holiday();
+            }
+          }
+        }
+      }
+    }
+
+    holiday();
+  }
+}
+
+ground dataspace {
+  Syndicate.Timer.spawnTimerDriver();
+
+  var nElves = 20;
+  var elfGroupSize = 3;
+  var nReindeer = 9;
+
+  for (var i = 0; i < nElves; i++) { elf(); }
+  for (var i = 0; i < nReindeer; i++) { reindeer(); }
+
+  spawn* named "Santa" {
+    function waitForWork() {
+      console.log("Santa is waiting for something to do.");
+      react {
+        field this.puzzledElves = Immutable.List();
+        on asserted elfProblem($id) {
+          this.puzzledElves = this.puzzledElves.push(id);
+        }
+
+        field this.readyReindeer = Immutable.List();
+        on asserted reindeerReturned($id) {
+          this.readyReindeer = this.readyReindeer.push(id);
+        }
+
+        stop on (this.puzzledElves.size >= elfGroupSize) {
+          talkToElves(this.puzzledElves.take(elfGroupSize));
+        }
+        stop on (this.readyReindeer.size == nReindeer) {
+          harnessReindeer();
+        }
+      }
+    }
+
+    function talkToElves(elves) {
+      if (elves.isEmpty()) {
+        waitForWork();
+      } else {
+        var elf = elves.first();
+        console.log("Santa resolves the problem of", elf);
+        react {
+          assert problemResolved(elf);
+          stop on retracted elfProblem(elf) {
+            talkToElves(elves.shift());
+          }
+        }
+      }
+    }
+
+    function harnessReindeer() {
+      console.log("Santa does the delivery run!");
+      react {
+        assert deliverToys();
+        stop on retracted reindeerReturned(_) {
+          waitForWork();
+        }
+      }
+    }
+
+    waitForWork()
+  }
+}