diff --git a/lib/co/co.js b/lib/co/co.js
new file mode 100644
index 0000000..aacf6ef
--- /dev/null
+++ b/lib/co/co.js
@@ -0,0 +1,239 @@
+
+/**
+ * slice() reference.
+ */
+
+var slice = Array.prototype.slice;
+
+/**
+ * Expose `co`.
+ */
+
+module.exports = co['default'] = co.co = co;
+
+/**
+ * Wrap the given generator `fn` into a
+ * function that returns a promise.
+ * This is a separate function so that
+ * every `co()` call doesn't create a new,
+ * unnecessary closure.
+ *
+ * @param {GeneratorFunction} fn
+ * @return {Function}
+ * @api public
+ */
+
+co.wrap = function (fn) {
+  createPromise.__generatorFunction__ = fn;
+  return createPromise;
+  function createPromise() {
+    return co.call(this, fn.apply(this, arguments));
+  }
+};
+
+/**
+ * Execute the generator function or a generator
+ * and return a promise.
+ *
+ * @param {Function} fn
+ * @return {Promise}
+ * @api public
+ */
+
+function co(gen) {
+  var ctx = this;
+  var args = slice.call(arguments, 1);
+
+  // we wrap everything in a promise to avoid promise chaining,
+  // which leads to memory leak errors.
+  // see https://github.com/tj/co/issues/180
+  return new Promise(function(resolve, reject) {
+    if (typeof gen === 'function') gen = gen.apply(ctx, args);
+    if (!gen || typeof gen.next !== 'function') return resolve(gen);
+
+    onFulfilled();
+
+    /**
+     * @param {Mixed} res
+     * @return {Promise}
+     * @api private
+     */
+
+    function onFulfilled(res) {
+      var ret;
+      try {
+        ret = gen.next(res);
+      } catch (e) {
+        return reject(e);
+      }
+      next(ret);
+      return null;
+    }
+
+    /**
+     * @param {Error} err
+     * @return {Promise}
+     * @api private
+     */
+
+    function onRejected(err) {
+      var ret;
+      try {
+        ret = gen.throw(err);
+      } catch (e) {
+        return reject(e);
+      }
+      next(ret);
+    }
+
+    /**
+     * Get the next value in the generator,
+     * return a promise.
+     *
+     * @param {Object} ret
+     * @return {Promise}
+     * @api private
+     */
+
+    function next(ret) {
+      if (ret.done) return resolve(ret.value);
+      var value = toPromise.call(ctx, ret.value);
+      if (value && isPromise(value)) return value.then(onFulfilled, onRejected);
+      return onRejected(new TypeError('You may only yield a function, promise, generator, array, or object, '
+        + 'but the following object was passed: "' + String(ret.value) + '"'));
+    }
+  });
+}
+
+/**
+ * Convert a `yield`ed value into a promise.
+ *
+ * @param {Mixed} obj
+ * @return {Promise}
+ * @api private
+ */
+
+function toPromise(obj) {
+  if (!obj) return obj;
+  if (isPromise(obj)) return obj;
+  if (isGeneratorFunction(obj) || isGenerator(obj)) return co.call(this, obj);
+  if ('function' == typeof obj) return thunkToPromise.call(this, obj);
+  if (Array.isArray(obj)) return arrayToPromise.call(this, obj);
+  if (isObject(obj)) return objectToPromise.call(this, obj);
+  return obj;
+}
+
+/**
+ * Convert a thunk to a promise.
+ *
+ * @param {Function}
+ * @return {Promise}
+ * @api private
+ */
+
+function thunkToPromise(fn) {
+  var ctx = this;
+  return new Promise(function (resolve, reject) {
+    fn.call(ctx, function (err, res) {
+      if (err) return reject(err);
+      if (arguments.length > 2) res = slice.call(arguments, 1);
+      resolve(res);
+    });
+  });
+}
+
+/**
+ * Convert an array of "yieldables" to a promise.
+ * Uses `Promise.all()` internally.
+ *
+ * @param {Array} obj
+ * @return {Promise}
+ * @api private
+ */
+
+function arrayToPromise(obj) {
+  return Promise.all(obj.map(toPromise, this));
+}
+
+/**
+ * Convert an object of "yieldables" to a promise.
+ * Uses `Promise.all()` internally.
+ *
+ * @param {Object} obj
+ * @return {Promise}
+ * @api private
+ */
+
+function objectToPromise(obj){
+  var results = new obj.constructor();
+  var keys = Object.keys(obj);
+  var promises = [];
+  for (var i = 0; i < keys.length; i++) {
+    var key = keys[i];
+    var promise = toPromise.call(this, obj[key]);
+    if (promise && isPromise(promise)) defer(promise, key);
+    else results[key] = obj[key];
+  }
+  return Promise.all(promises).then(function () {
+    return results;
+  });
+
+  function defer(promise, key) {
+    // predefine the key in the result
+    results[key] = undefined;
+    promises.push(promise.then(function (res) {
+      results[key] = res;
+    }));
+  }
+}
+
+/**
+ * Check if `obj` is a promise.
+ *
+ * @param {Object} obj
+ * @return {Boolean}
+ * @api private
+ */
+
+function isPromise(obj) {
+  return 'function' == typeof obj.then;
+}
+
+/**
+ * Check if `obj` is a generator.
+ *
+ * @param {Mixed} obj
+ * @return {Boolean}
+ * @api private
+ */
+
+function isGenerator(obj) {
+  return 'function' == typeof obj.next && 'function' == typeof obj.throw;
+}
+
+/**
+ * Check if `obj` is a generator function.
+ *
+ * @param {Mixed} obj
+ * @return {Boolean}
+ * @api private
+ */
+ 
+function isGeneratorFunction(obj) {
+  var constructor = obj.constructor;
+  if (!constructor) return false;
+  if ('GeneratorFunction' === constructor.name || 'GeneratorFunction' === constructor.displayName) return true;
+  return isGenerator(constructor.prototype);
+}
+
+/**
+ * Check for plain object.
+ *
+ * @param {Mixed} val
+ * @return {Boolean}
+ * @api private
+ */
+
+function isObject(val) {
+  return Object == val.constructor;
+}
diff --git a/lib/co/index.d.ts b/lib/co/index.d.ts
new file mode 100644
index 0000000..cf81ee4
--- /dev/null
+++ b/lib/co/index.d.ts
@@ -0,0 +1,4 @@
+
+declare function co(g: () => Generator<any, void, undefined>): any;
+
+export = co;
diff --git a/lib/co/index.js b/lib/co/index.js
index aacf6ef..8ca7718 100644
--- a/lib/co/index.js
+++ b/lib/co/index.js
@@ -1,239 +1 @@
-
-/**
- * slice() reference.
- */
-
-var slice = Array.prototype.slice;
-
-/**
- * Expose `co`.
- */
-
-module.exports = co['default'] = co.co = co;
-
-/**
- * Wrap the given generator `fn` into a
- * function that returns a promise.
- * This is a separate function so that
- * every `co()` call doesn't create a new,
- * unnecessary closure.
- *
- * @param {GeneratorFunction} fn
- * @return {Function}
- * @api public
- */
-
-co.wrap = function (fn) {
-  createPromise.__generatorFunction__ = fn;
-  return createPromise;
-  function createPromise() {
-    return co.call(this, fn.apply(this, arguments));
-  }
-};
-
-/**
- * Execute the generator function or a generator
- * and return a promise.
- *
- * @param {Function} fn
- * @return {Promise}
- * @api public
- */
-
-function co(gen) {
-  var ctx = this;
-  var args = slice.call(arguments, 1);
-
-  // we wrap everything in a promise to avoid promise chaining,
-  // which leads to memory leak errors.
-  // see https://github.com/tj/co/issues/180
-  return new Promise(function(resolve, reject) {
-    if (typeof gen === 'function') gen = gen.apply(ctx, args);
-    if (!gen || typeof gen.next !== 'function') return resolve(gen);
-
-    onFulfilled();
-
-    /**
-     * @param {Mixed} res
-     * @return {Promise}
-     * @api private
-     */
-
-    function onFulfilled(res) {
-      var ret;
-      try {
-        ret = gen.next(res);
-      } catch (e) {
-        return reject(e);
-      }
-      next(ret);
-      return null;
-    }
-
-    /**
-     * @param {Error} err
-     * @return {Promise}
-     * @api private
-     */
-
-    function onRejected(err) {
-      var ret;
-      try {
-        ret = gen.throw(err);
-      } catch (e) {
-        return reject(e);
-      }
-      next(ret);
-    }
-
-    /**
-     * Get the next value in the generator,
-     * return a promise.
-     *
-     * @param {Object} ret
-     * @return {Promise}
-     * @api private
-     */
-
-    function next(ret) {
-      if (ret.done) return resolve(ret.value);
-      var value = toPromise.call(ctx, ret.value);
-      if (value && isPromise(value)) return value.then(onFulfilled, onRejected);
-      return onRejected(new TypeError('You may only yield a function, promise, generator, array, or object, '
-        + 'but the following object was passed: "' + String(ret.value) + '"'));
-    }
-  });
-}
-
-/**
- * Convert a `yield`ed value into a promise.
- *
- * @param {Mixed} obj
- * @return {Promise}
- * @api private
- */
-
-function toPromise(obj) {
-  if (!obj) return obj;
-  if (isPromise(obj)) return obj;
-  if (isGeneratorFunction(obj) || isGenerator(obj)) return co.call(this, obj);
-  if ('function' == typeof obj) return thunkToPromise.call(this, obj);
-  if (Array.isArray(obj)) return arrayToPromise.call(this, obj);
-  if (isObject(obj)) return objectToPromise.call(this, obj);
-  return obj;
-}
-
-/**
- * Convert a thunk to a promise.
- *
- * @param {Function}
- * @return {Promise}
- * @api private
- */
-
-function thunkToPromise(fn) {
-  var ctx = this;
-  return new Promise(function (resolve, reject) {
-    fn.call(ctx, function (err, res) {
-      if (err) return reject(err);
-      if (arguments.length > 2) res = slice.call(arguments, 1);
-      resolve(res);
-    });
-  });
-}
-
-/**
- * Convert an array of "yieldables" to a promise.
- * Uses `Promise.all()` internally.
- *
- * @param {Array} obj
- * @return {Promise}
- * @api private
- */
-
-function arrayToPromise(obj) {
-  return Promise.all(obj.map(toPromise, this));
-}
-
-/**
- * Convert an object of "yieldables" to a promise.
- * Uses `Promise.all()` internally.
- *
- * @param {Object} obj
- * @return {Promise}
- * @api private
- */
-
-function objectToPromise(obj){
-  var results = new obj.constructor();
-  var keys = Object.keys(obj);
-  var promises = [];
-  for (var i = 0; i < keys.length; i++) {
-    var key = keys[i];
-    var promise = toPromise.call(this, obj[key]);
-    if (promise && isPromise(promise)) defer(promise, key);
-    else results[key] = obj[key];
-  }
-  return Promise.all(promises).then(function () {
-    return results;
-  });
-
-  function defer(promise, key) {
-    // predefine the key in the result
-    results[key] = undefined;
-    promises.push(promise.then(function (res) {
-      results[key] = res;
-    }));
-  }
-}
-
-/**
- * Check if `obj` is a promise.
- *
- * @param {Object} obj
- * @return {Boolean}
- * @api private
- */
-
-function isPromise(obj) {
-  return 'function' == typeof obj.then;
-}
-
-/**
- * Check if `obj` is a generator.
- *
- * @param {Mixed} obj
- * @return {Boolean}
- * @api private
- */
-
-function isGenerator(obj) {
-  return 'function' == typeof obj.next && 'function' == typeof obj.throw;
-}
-
-/**
- * Check if `obj` is a generator function.
- *
- * @param {Mixed} obj
- * @return {Boolean}
- * @api private
- */
- 
-function isGeneratorFunction(obj) {
-  var constructor = obj.constructor;
-  if (!constructor) return false;
-  if ('GeneratorFunction' === constructor.name || 'GeneratorFunction' === constructor.displayName) return true;
-  return isGenerator(constructor.prototype);
-}
-
-/**
- * Check for plain object.
- *
- * @param {Mixed} val
- * @return {Boolean}
- * @api private
- */
-
-function isObject(val) {
-  return Object == val.constructor;
-}
+module.exports = require('./co')
diff --git a/src/interface/debug.ts b/src/interface/debug.ts
index eaca510..5c16c33 100644
--- a/src/interface/debug.ts
+++ b/src/interface/debug.ts
@@ -3,7 +3,8 @@ import { Terminal } from '@xterm/xterm';
 import { FitAddon } from '@xterm/addon-fit';
 import { SerializeAddon } from '@xterm/addon-serialize';
 import JSZM from "../../lib/zork";
-var co = require("../../lib/co/index.js");
+// var co = require("../../lib/co/index.js");
+import co from "../../lib/co";
 
 export class DebugWidget implements FarpatchWidget {
     name: string;
@@ -79,15 +80,15 @@ export class DebugWidget implements FarpatchWidget {
             var debugWidget = this;
             fetch("/zork1.z3").then((response) => {
                 response.arrayBuffer().then((buffer) => {
-                    this.zork = co.co(function* () {
+                    this.zork = co(function* () {
                         var zork = new JSZM(new Uint8Array(buffer));
                         zork.print = function* (str: string) {
                             str = str.replace("\n", "\r\n");
                             zorkTerminal.write(str);
                         };
-                        zork.read =  function* (maxlen: number): Generator  {
+                        zork.read = function* (_maxlen: number): Generator {
                             // console.log("Zork: read " + maxlen);
-                            var val = yield new Promise((resolve, reject) => {
+                            var val = yield new Promise((resolve, _reject) => {
                                 debugWidget.zorkCallback = resolve;
                             });
                             return val;