diff --git a/.gitignore b/.gitignore
index c480bf5..b4bd7ce 100644
--- a/.gitignore
+++ b/.gitignore
@@ -28,6 +28,7 @@ lib/
 
 # Dependency directory
 node_modules
+typings/
 
 # Optional npm cache directory
 .npm
diff --git a/package.json b/package.json
index 7d09ff5..bc469b2 100644
--- a/package.json
+++ b/package.json
@@ -6,11 +6,13 @@
   "scripts": {
     "commit": "git-cz",
     "lint": "tslint -c tslint.json src/*.ts",
-    "pretape": "npm run lib",
-    "tape": "ts-node ./node_modules/.bin/tape tests/**/*.ts",
-    "test": "npm run lint && npm run tape",
+    "premocha": "npm run lib",
+    "mocha": "mocha tests/**/*.ts --require ts-node/register",
+    "postmocha": "rm -f tests/**/*.js",
+    "test": "npm run lint && npm run mocha",
     "prelib": "rm -rf lib/ && mkdirp lib/",
     "lib": "tsc",
+    "postinstall": "typings install",
     "predist": "rm -rf dist/ && mkdirp dist/ && npm run lib",
     "dist": "browserify lib/index.js -o dist/xstream.js",
     "postdist": "uglifyjs dist/xstream.js -o dist/xstream.min.js",
@@ -29,15 +31,18 @@
   },
   "homepage": "https://github.com/staltz/xstream#readme",
   "devDependencies": {
+    "assert": "^1.3.0",
     "browserify": "^13.0.0",
     "commitizen": "^2.5.0",
     "conventional-changelog": "^1.1.0",
     "cz-conventional-changelog": "^1.1.5",
     "ghooks": "^1.0.3",
     "mkdirp": "^0.5.1",
+    "mocha": "^2.4.5",
     "ts-node": "^0.5.5",
     "tslint": "^3.5.0",
     "typescript": "^1.8.2",
+    "typings": "^0.6.8",
     "validate-commit-msg": "^2.1.0"
   },
   "config": {
diff --git a/src/index.ts b/src/index.ts
index a36e84a..ba3cce6 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,3 +1,81 @@
-export function Stream(subscribe: () => void) {
-    this.subscribe = subscribe;
+export interface Observer<T> {
+  next: (x: T) => void;
+  error: (err: any) => void;
+  complete: () => void;
 }
+
+export interface Machine<T> {
+  start: (observer: Observer<T>) => void;
+  stop: () => void;
+}
+
+export class Stream<T> implements Observer<T> {
+  public observers: Array<Observer<T>>;
+
+  constructor(public machine: Machine<T>) {
+    this.observers = [];
+  }
+
+  next(x: T): void {
+    const len = this.observers.length;
+    for (let i = len - 1; i >= 0; i--) {
+      this.observers[i].next(x);
+    }
+  }
+
+  error(err: any): void {
+    const len = this.observers.length;
+    for (let i = len - 1; i >= 0; i--) {
+      this.observers[i].error(err);
+    }
+  }
+
+  complete(): void {
+    const len = this.observers.length;
+    for (let i = len - 1; i >= 0; i--) {
+      this.observers[i].complete();
+    }
+  }
+
+  subscribe(observer: Observer<T>): void {
+    this.observers.push(observer);
+    if (this.observers.length === 1) this.machine.start(this);
+  }
+
+  unsubscribe(observer: Observer<T>): void {
+    const i = this.observers.indexOf(observer);
+    if (i > -1) {
+      this.observers.splice(i, 1);
+      if (!this.observers.length) this.machine.stop();
+    }
+  }
+}
+
+class IntervalMachine implements Machine<number> {
+  on: boolean;
+  intervalID: any;
+  i: number;
+
+  constructor(public period: number) {
+    this.intervalID = -1;
+    this.i = 0;
+  }
+
+  start(observer: Observer<number>): void {
+    this.intervalID = setInterval(() => observer.next(this.i++), this.period);
+  }
+
+  stop(): void {
+    this.i = 0;
+    if (this.intervalID !== -1) clearInterval(this.intervalID);
+  }
+}
+
+export function interval(period: number) {
+  const intervalMachine = new IntervalMachine(period);
+  return new Stream<number>(intervalMachine);
+}
+
+export default {
+  interval
+};
diff --git a/tests/stream.js b/tests/stream.js
new file mode 100644
index 0000000..8e6253d
--- /dev/null
+++ b/tests/stream.js
@@ -0,0 +1,22 @@
+"use strict";
+var index_1 = require('../src/index');
+var assert = require('assert');
+describe('Stream', function () {
+    it('can be subscribed and unsubscribed with one observer', function (done) {
+        var stream = index_1.default.interval(100);
+        var i = 0;
+        var observer = {
+            next: function (x) {
+                assert.equal(x, i);
+                i += 1;
+                if (i === 2) {
+                    stream.unsubscribe(observer);
+                    done();
+                }
+            },
+            error: done.fail,
+            complete: done.fail,
+        };
+        stream.subscribe(observer);
+    });
+});
diff --git a/tests/stream.ts b/tests/stream.ts
new file mode 100644
index 0000000..474fbac
--- /dev/null
+++ b/tests/stream.ts
@@ -0,0 +1,22 @@
+import xs from '../src/index';
+import * as assert from 'assert';
+
+describe('Stream', () => {
+  it('can be subscribed and unsubscribed with one observer', (done) => {
+    const stream = xs.interval(100);
+    let i = 0;
+    let observer = {
+      next: (x: number) => {
+        assert.equal(x, i);
+        i += 1;
+        if (i === 2) {
+          stream.unsubscribe(observer);
+          done();
+        }
+      },
+      error: done.fail,
+      complete: done.fail,
+    };
+    stream.subscribe(observer);
+  });
+});
diff --git a/tsconfig.json b/tsconfig.json
index 4c69f81..3948a9c 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -7,6 +7,7 @@
     "noImplicitAny": true,
     "suppressImplicitAnyIndexErrors": true,
     "module": "commonjs",
+    "noEmitHelpers": true,
     "target": "ES5",
     "outDir": "lib/"
   },
@@ -15,6 +16,7 @@
     "tabSize": 2
   },
   "files": [
+    "typings/main.d.ts",
     "src/index.ts"
   ],
   "exclude": [
diff --git a/tslint.json b/tslint.json
index 34fac9b..46c5c3e 100644
--- a/tslint.json
+++ b/tslint.json
@@ -1,6 +1,6 @@
 {
   "rules": {
-    "curly": true,
+    "curly": false,
     "eofline": false,
     "align": [true, "parameters"],
     "class-name": true,
diff --git a/typings.json b/typings.json
new file mode 100644
index 0000000..510b724
--- /dev/null
+++ b/typings.json
@@ -0,0 +1,9 @@
+{
+  "name": "xstream",
+  "dependencies": {},
+  "devDependencies": {},
+  "ambientDevDependencies": {
+    "mocha": "github:DefinitelyTyped/DefinitelyTyped/mocha/mocha.d.ts#d6dd320291705694ba8e1a79497a908e9f5e6617",
+    "node": "github:DefinitelyTyped/DefinitelyTyped/node/node.d.ts#20e1eb9616922d382d918cc5a21870a9dbe255f5"
+  }
+}