diff --git a/.prettierrc b/.prettierrc
index 3cc6dac..97ef6d6 100644
--- a/.prettierrc
+++ b/.prettierrc
@@ -1,5 +1,6 @@
 {
   "printWidth": 80,
   "semi": false,
-  "singleQuote": true
+  "singleQuote": true,
+  "bracketSpacing": false
 }
\ No newline at end of file
diff --git a/API.md b/API.md
index 57602dc..18d2291 100644
--- a/API.md
+++ b/API.md
@@ -549,8 +549,8 @@ Takes in multiple sources and a sample source and returns a new observable which
 
 ```ts
 O.sample(
-  O.interval(1000),
   (a, b) => [a, b],
+  O.interval(1000),
   [
     O.mapTo('A', O.interval(100)),
     O.mapTo('B', O.interval(200))
diff --git a/benchmarks/bm.concat.ts b/benchmarks/bm.concat.ts
index 59fcf0a..7b4ca32 100644
--- a/benchmarks/bm.concat.ts
+++ b/benchmarks/bm.concat.ts
@@ -13,6 +13,8 @@ export function bm_concat(suite: Suite) {
   return suite.add(
     '(file, file) -> concat',
     (d: IDeferred) => run(concat(fromArray(a), fromArray(b)), d),
-    {defer: true}
+    {
+      defer: true
+    }
   )
 }
diff --git a/benchmarks/bm.mergeMap.ts b/benchmarks/bm.mergeMap.ts
index 2a7719c..80d4fa5 100644
--- a/benchmarks/bm.mergeMap.ts
+++ b/benchmarks/bm.mergeMap.ts
@@ -14,6 +14,8 @@ export function bm_mergeMap(suite: Suite) {
   return suite.add(
     'file -> mergeMap',
     (d: IDeferred) => run(mergeMap(just(1e2), fromArray, fromArray(a)), d),
-    {defer: true}
+    {
+      defer: true
+    }
   )
 }
diff --git a/package.json b/package.json
index 8384601..ae89d75 100644
--- a/package.json
+++ b/package.json
@@ -15,7 +15,7 @@
     "build": "rollup -c ./config/rollup.config.js",
     "lint": "git ls-files | grep '.ts$' | xargs tslint",
     "lint:fix": "git ls-files | grep '.ts$' | xargs tslint --fix",
-    "prettier": "git ls-files | grep '.ts$' | xargs prettier --print-width 80 --write --single-quote --no-semi --no-bracket-spacing",
+    "prettier": "git ls-files | grep '.ts$' | xargs prettier --write --config=.prettierrc",
     "travis-deploy-once": "travis-deploy-once",
     "semantic-release": "semantic-release"
   },
diff --git a/src/lib/Periodic.ts b/src/lib/Periodic.ts
new file mode 100644
index 0000000..c5b641c
--- /dev/null
+++ b/src/lib/Periodic.ts
@@ -0,0 +1,20 @@
+import {ISafeObserver} from './SafeObserver'
+import {ISubscription} from './Subscription'
+
+export class Periodic implements ISubscription {
+  protected sub: ISubscription
+  protected sink: ISafeObserver<void>
+
+  onEvent() {
+    this.sink.next(undefined)
+    if (this.sink.erred) this.unsubscribe()
+  }
+
+  unsubscribe(): void {
+    this.sub.unsubscribe()
+  }
+
+  get closed() {
+    return this.sub.closed
+  }
+}
diff --git a/src/lib/SafeObserver.ts b/src/lib/SafeObserver.ts
index 9b8f235..a9ac2c5 100644
--- a/src/lib/SafeObserver.ts
+++ b/src/lib/SafeObserver.ts
@@ -5,9 +5,13 @@ import {CompleteMixin, ErrorMixin, Virgin} from './Mixins'
 import {IObserver} from './Observer'
 import {ISafeFunction, tryCatch} from './Utils'
 
+export interface ISafeObserver<T> extends IObserver<T> {
+  erred: boolean
+}
 class SafeObserver<T> extends ErrorMixin(CompleteMixin(Virgin))
   implements IObserver<T> {
   private _next: ISafeFunction<void, IObserver<T>>
+  erred = false
 
   constructor(public sink: IObserver<T>) {
     super()
@@ -16,17 +20,14 @@ class SafeObserver<T> extends ErrorMixin(CompleteMixin(Virgin))
 
   next(val: T): void {
     const r = this._next.call(this.sink, val)
-    if (r.isError()) this.sink.error(r.getError())
+    if (r.isError) this.error(r.getError())
   }
 
   error(err: Error): void {
+    this.erred = true
     this.sink.error(err)
   }
-
-  complete(): void {
-    this.sink.complete()
-  }
 }
 
-export const safeObserver = <T>(observer: IObserver<T>): IObserver<T> =>
+export const safeObserver = <T>(observer: IObserver<T>): ISafeObserver<T> =>
   observer instanceof SafeObserver ? observer : new SafeObserver(observer)
diff --git a/src/lib/Scheduler.ts b/src/lib/Scheduler.ts
index 93b3e00..3b805a8 100644
--- a/src/lib/Scheduler.ts
+++ b/src/lib/Scheduler.ts
@@ -5,9 +5,15 @@ import {ISubscription} from './Subscription'
 
 export interface IScheduler {
   delay(task: () => void, relativeTime: number): ISubscription
+
   periodic(task: () => void, interval: number): ISubscription
+
   frame(task: () => void): ISubscription
+
+  frames(task: () => void): ISubscription
+
   asap(task: () => void): ISubscription
+
   now(): number
 }
 
@@ -33,6 +39,7 @@ class Periodic implements ISubscription {
     clearInterval(this.id)
   }
 }
+
 class Delay implements ISubscription {
   closed = false
 
@@ -52,6 +59,7 @@ class Delay implements ISubscription {
     }
   }
 }
+
 class ASAP implements ISubscription {
   closed = false
 
@@ -69,7 +77,8 @@ class ASAP implements ISubscription {
     if (this.closed === false) this.closed = true
   }
 }
-class Frames implements ISubscription {
+
+class Frame implements ISubscription {
   closed = false
   private frame: number
 
@@ -89,8 +98,34 @@ class Frames implements ISubscription {
     cancelAnimationFrame(this.frame)
   }
 }
+
+class Frames implements ISubscription {
+  closed = false
+  private frame: number
+
+  constructor(private task: () => void) {
+    this.onEvent = this.onEvent.bind(this)
+    this.frame = requestAnimationFrame(this.onEvent)
+  }
+
+  onEvent() {
+    this.task()
+    this.frame = requestAnimationFrame(this.onEvent)
+  }
+
+  unsubscribe(): void {
+    if (this.closed) return
+    this.closed = true
+    cancelAnimationFrame(this.frame)
+  }
+}
+
 class Scheduler implements IScheduler {
   frame(task: () => void): ISubscription {
+    return new Frame(task)
+  }
+
+  frames(task: () => void): ISubscription {
     return new Frames(task)
   }
 
@@ -110,4 +145,5 @@ class Scheduler implements IScheduler {
     return Date.now()
   }
 }
+
 export const createScheduler = (): IScheduler => new Scheduler()
diff --git a/src/lib/Utils.ts b/src/lib/Utils.ts
index e345d4b..3ffeeab 100644
--- a/src/lib/Utils.ts
+++ b/src/lib/Utils.ts
@@ -12,7 +12,7 @@ export function curry(f: Function, l: number = f.length): any {
 }
 
 export interface ISafeValue<T> {
-  isError(): boolean
+  isError: boolean
   getValue(): T
   getError(): Error
 }
@@ -22,11 +22,7 @@ export interface ISafeFunction<V, C> {
 }
 
 class Guarded<T> implements ISafeValue<T> {
-  constructor(private value: Error | T) {}
-
-  isError(): boolean {
-    return this.value instanceof Error
-  }
+  constructor(private value: Error | T, readonly isError: boolean) {}
 
   getValue() {
     return this.value as T
@@ -43,9 +39,9 @@ class BaseSafeFunction<T extends Function, V, C>
 
   call(ctx: C, ...t: any[]): ISafeValue<V> {
     try {
-      return new Guarded(this.f.apply(ctx, t))
+      return new Guarded(this.f.apply(ctx, t), false)
     } catch (e) {
-      return new Guarded(e)
+      return new Guarded(e, true)
     }
   }
 }
diff --git a/src/sources/Frames.ts b/src/sources/Frames.ts
index 73a8fd4..4ddd2c0 100644
--- a/src/sources/Frames.ts
+++ b/src/sources/Frames.ts
@@ -3,31 +3,15 @@
  */
 import {IObservable} from '../lib/Observable'
 import {IObserver} from '../lib/Observer'
-import {safeObserver} from '../lib/SafeObserver'
+import {Periodic} from '../lib/Periodic'
+import {ISafeObserver, safeObserver} from '../lib/SafeObserver'
 import {IScheduler} from '../lib/Scheduler'
 import {ISubscription} from '../lib/Subscription'
 
-class RAFSubscription implements ISubscription {
-  observer: IObserver<number>
-  subscription: ISubscription
-  closed = false
-
-  constructor(private sink: IObserver<void>, private scheduler: IScheduler) {
-    this.schedule()
-  }
-
-  private schedule() {
-    this.subscription = this.scheduler.frame(this.onFrame)
-  }
-
-  onFrame = () => {
-    if (this.closed) return
-    this.sink.next(undefined)
-    this.schedule()
-  }
-
-  unsubscribe(): void {
-    this.closed = true
+class RAFSubscription extends Periodic {
+  constructor(readonly sink: ISafeObserver<void>, scheduler: IScheduler) {
+    super()
+    this.sub = scheduler.frames(this.onEvent.bind(this))
   }
 }
 
@@ -36,6 +20,7 @@ class FrameObservable implements IObservable<void> {
     return new RAFSubscription(safeObserver(observer), scheduler)
   }
 }
+
 export function frames(): IObservable<void> {
   return new FrameObservable()
 }
diff --git a/src/sources/FromArray.ts b/src/sources/FromArray.ts
index a99b68d..b569eda 100644
--- a/src/sources/FromArray.ts
+++ b/src/sources/FromArray.ts
@@ -19,9 +19,10 @@ class FromArraySubscription<T> implements ISubscription {
     this.subscription = scheduler.asap(this.executeSafely.bind(this))
   }
 
+  // TODO: use mixins
   private executeSafely() {
     const r = tryCatch(this.execute).call(this)
-    if (r.isError()) this.sink.error(r.getError())
+    if (r.isError) this.sink.error(r.getError())
   }
 
   execute() {
diff --git a/src/sources/Interval.ts b/src/sources/Interval.ts
index 0f89f07..4eabdd2 100644
--- a/src/sources/Interval.ts
+++ b/src/sources/Interval.ts
@@ -3,29 +3,19 @@
  */
 import {IObservable} from '../lib/Observable'
 import {IObserver} from '../lib/Observer'
-import {safeObserver} from '../lib/SafeObserver'
+import {Periodic} from '../lib/Periodic'
+import {ISafeObserver, safeObserver} from '../lib/SafeObserver'
 import {IScheduler} from '../lib/Scheduler'
 import {ISubscription} from '../lib/Subscription'
 
-class TimerSubscription implements ISubscription {
-  closed = false
-  subscription: ISubscription
-
+class TimerSubscription extends Periodic {
   constructor(
-    private sink: IObserver<void>,
+    readonly sink: ISafeObserver<void>,
     scheduler: IScheduler,
     interval: number
   ) {
-    this.subscription = scheduler.periodic(this.onFrame.bind(this), interval)
-  }
-
-  onFrame() {
-    this.sink.next(undefined)
-  }
-
-  unsubscribe(): void {
-    this.closed = true
-    this.subscription.unsubscribe()
+    super()
+    this.sub = scheduler.periodic(this.onEvent.bind(this), interval)
   }
 }
 
diff --git a/src/testing/TestScheduler.ts b/src/testing/TestScheduler.ts
index d40cc38..ca5cec1 100644
--- a/src/testing/TestScheduler.ts
+++ b/src/testing/TestScheduler.ts
@@ -88,6 +88,10 @@ export class TestScheduler implements IScheduler {
     return this.delay(task, this.now() + this.rafTimeout, 0)
   }
 
+  frames(task: () => void): ISubscription {
+    return this.periodic(task, this.rafTimeout)
+  }
+
   periodic(task: () => void, interval: number): ISubscription {
     var closed = false
     const repeatedTask = () => {
@@ -97,7 +101,9 @@ export class TestScheduler implements IScheduler {
     }
     this.delay(repeatedTask, interval)
     return {
-      closed,
+      get closed() {
+        return closed
+      },
       unsubscribe() {
         closed = true
       }
diff --git a/test/test.Frames.ts b/test/test.Frames.ts
index f7358dc..b4fa18b 100644
--- a/test/test.Frames.ts
+++ b/test/test.Frames.ts
@@ -6,6 +6,7 @@ import {scan} from '../src/operators/Scan'
 import {frames} from '../src/sources/Frames'
 import {toMarble} from '../src/testing/Marble'
 import {createTestScheduler} from '../src/testing/TestScheduler'
+import {throwError} from '../src/testing/Thrower'
 
 describe('frames()', () => {
   it('should emit requestAnimationFrame events', () => {
@@ -13,4 +14,14 @@ describe('frames()', () => {
     const {results} = sh.start(() => scan(i => i + 1, -1, frames()), 200, 250)
     t.strictEqual(toMarble(results), '-0123')
   })
+
+  it('should capture internal errors', () => {
+    const sh = createTestScheduler(20)
+    const reduce = (i: number) => {
+      if (i === 5) throwError('Yo Air')
+      return i + 1
+    }
+    const {results} = sh.start(() => scan(reduce, -1, frames()), 200, 500)
+    t.strictEqual(toMarble(results), '--0-1-2-3-4-5-#')
+  })
 })
diff --git a/test/test.FromArray.ts b/test/test.FromArray.ts
index d0a3e41..6fb41f4 100644
--- a/test/test.FromArray.ts
+++ b/test/test.FromArray.ts
@@ -12,6 +12,9 @@ import {ERROR_MESSAGE, throwError} from '../src/testing/Thrower'
 const {next, error} = EVENT
 
 describe('fromArray()', () => {
+  const throwMessage = (message: string) => {
+    throw message
+  }
   it('should emit array values as events', () => {
     const sh = createTestScheduler()
     const testFunction = (x: any) =>
@@ -19,4 +22,12 @@ describe('fromArray()', () => {
     const {results} = sh.start(() => map(testFunction, fromArray([1, 2, 3])))
     t.deepEqual(results, [next(201, 100), error(201, new Error(ERROR_MESSAGE))])
   })
+
+  it('should handle thrown non Error exceptions', () => {
+    const sh = createTestScheduler()
+    const testFunction = (x: any) =>
+      x === 2 ? throwMessage(ERROR_MESSAGE) : x * 100
+    const {results} = sh.start(() => map(testFunction, fromArray([1, 2, 3])))
+    t.deepEqual(results, [next(201, 100), error(201, ERROR_MESSAGE as any)])
+  })
 })
diff --git a/test/test.Interval.ts b/test/test.Interval.ts
index a23e430..a9b44a8 100644
--- a/test/test.Interval.ts
+++ b/test/test.Interval.ts
@@ -8,7 +8,7 @@ import {interval} from '../src/sources/Interval'
 import {EVENT, EventError} from '../src/testing/Events'
 import {toMarble} from '../src/testing/Marble'
 import {createTestScheduler} from '../src/testing/TestScheduler'
-import {ERROR_MESSAGE, thrower} from '../src/testing/Thrower'
+import {ERROR_MESSAGE, thrower, throwError} from '../src/testing/Thrower'
 const {error} = EVENT
 
 describe('interval()', () => {
@@ -32,4 +32,13 @@ describe('interval()', () => {
       ERROR_MESSAGE
     )
   })
+
+  it('should stop after error', () => {
+    const sh = createTestScheduler()
+    const {results} = sh.start(() =>
+      scan(i => (i === 5 ? throwError('Yay!') : i + 1), 0, interval(20))
+    )
+    const expected = '--1-2-3-4-5-#'
+    t.strictEqual(toMarble(results), expected)
+  })
 })