diff --git a/Diagrams.playground/Pages/OffsetTriangleRing.xcplaygroundpage/Contents.swift b/Diagrams.playground/Pages/OffsetTriangleRing.xcplaygroundpage/Contents.swift
index 1dae623..73a8054 100644
--- a/Diagrams.playground/Pages/OffsetTriangleRing.xcplaygroundpage/Contents.swift
+++ b/Diagrams.playground/Pages/OffsetTriangleRing.xcplaygroundpage/Contents.swift
@@ -4,15 +4,15 @@
 import CoreGraphics
 
 extension Diagram {
-  func ring(radius radius: CGFloat, number: Int) -> Diagram {
-    let angles = 0.0.stride(to: 360.0, by: 360.0/Double(number))
+  func ring(radius: CGFloat, number: Int) -> Diagram {
+    let angles = stride(from: 0.0, to: 360.0, by: 360.0/Double(number))
     return diagrams(angles.map {
-      self.translate(x: 0, y: radius).rotate(CGFloat($0))
+      translate(x: 0, y: radius).rotate(CGFloat($0))
       }
     )
   }
   
-  func iterateScale(s: CGFloat, offset: Point = (0,0), iterate: Int) -> Diagram {
+  func iterateScale(_ s: CGFloat, offset: Point = (0,0), iterate: Int) -> Diagram {
     if iterate == 0 { return self }
     return self + scale(s)
       .translate(x: offset.x, y: offset.y)
@@ -26,7 +26,7 @@ let triangleRing = triangle.ring(radius: 220, number: 27)
 let diagram = triangleRing.iterateScale(0.618, offset: (15, 30), iterate: 7)
 
 showCoreGraphicsDiagram(size: CGSize(width: 600, height: 500)) {
-  drawDiagram(diagram)(context: $0)
+  drawDiagram(diagram, context: $0)
 }
 /*:
 To see the result, View>Assistant Editor>Show Assistant Editor (opt-cmd-Return).
diff --git a/Diagrams.playground/Pages/StarRing.xcplaygroundpage/Contents.swift b/Diagrams.playground/Pages/StarRing.xcplaygroundpage/Contents.swift
index 3daed63..fca2936 100644
--- a/Diagrams.playground/Pages/StarRing.xcplaygroundpage/Contents.swift
+++ b/Diagrams.playground/Pages/StarRing.xcplaygroundpage/Contents.swift
@@ -3,15 +3,15 @@
 import CoreGraphics
 
 extension Diagram {
-  func ring(radius radius: CGFloat, number: Int) -> Diagram {
-    let angles = 0.0.stride(to: 360.0, by: 360.0/Double(number))
+  func ring(radius: CGFloat, number: Int) -> Diagram {
+    let angles = stride(from: 0.0, to: 360.0, by: 360.0/Double(number))
     return diagrams(angles.map {
       translate(x: 0, y: radius).rotate(CGFloat($0))
       }
     )
   }
   
-  func iterateScale(s: CGFloat, iterate: Int) -> Diagram {
+  func iterateScale(_ s: CGFloat, iterate: Int) -> Diagram {
     if iterate == 0 { return self }
     return self + scale(s).iterateScale(s, iterate: iterate - 1)
   }
@@ -26,7 +26,7 @@ let starRing = star.ring(radius: 185, number: 16)
 let diagram = starRing.iterateScale(0.74, iterate: 6)
 
 showCoreGraphicsDiagram(size: CGSize(width: 600, height: 500)) {
-  drawDiagram(diagram)(context: $0)
+  drawDiagram(diagram, context: $0)
 }
 /*:
 To see the result, View>Assistant Editor>Show Assistant Editor (opt-cmd-Return).
diff --git a/Diagrams.playground/Pages/Tree - The Larch.xcplaygroundpage/Contents.swift b/Diagrams.playground/Pages/Tree - The Larch.xcplaygroundpage/Contents.swift
index e4ace97..9cdb17f 100644
--- a/Diagrams.playground/Pages/Tree - The Larch.xcplaygroundpage/Contents.swift	
+++ b/Diagrams.playground/Pages/Tree - The Larch.xcplaygroundpage/Contents.swift	
@@ -3,16 +3,8 @@
 
 ## The Larch
 */
-import CoreGraphics
-
-func displayDiagram(diagram: Diagram) {
-  showCoreGraphicsDiagram(size: CGSize(width: 600, height: 600)) {
-    drawDiagram(diagram)(context: $0)
-  }
-}
-
 extension Diagram {
-  func tree(n: Int) -> Diagram {
+  func tree(_ n: Int) -> Diagram {
     if n == 0 { return self }
     
     let smallTree = tree(n - 1).scale(x: 0.33, y: 0.45)
diff --git a/Diagrams.playground/Pages/Tree.xcplaygroundpage/Contents.swift b/Diagrams.playground/Pages/Tree.xcplaygroundpage/Contents.swift
index 3b06a19..bdfff62 100644
--- a/Diagrams.playground/Pages/Tree.xcplaygroundpage/Contents.swift
+++ b/Diagrams.playground/Pages/Tree.xcplaygroundpage/Contents.swift
@@ -3,16 +3,8 @@
 
 ## I want to be a tree
 */
-import CoreGraphics
-
-func displayDiagram(diagram: Diagram) {
-  showCoreGraphicsDiagram(size: CGSize(width: 600, height: 600)) {
-    drawDiagram(diagram)(context: $0)
-  }
-}
-
 extension Diagram {
-  func tree(n: Int) -> Diagram {
+  func tree(_ n: Int) -> Diagram {
     if n == 0 { return self }
     
     let smallTree = tree(n - 1).scale(x: 0.6, y: 0.67)
diff --git a/Diagrams.playground/Sources/CGContextExtension.swift b/Diagrams.playground/Sources/CGContextExtension.swift
index 8408c4d..8d9eba8 100644
--- a/Diagrams.playground/Sources/CGContextExtension.swift
+++ b/Diagrams.playground/Sources/CGContextExtension.swift
@@ -1,49 +1,47 @@
 import CoreGraphics
 
 public extension CGContext {
-  func moveTo(position: CGPoint) {
-    CGContextMoveToPoint(self, position.x, position.y)
-  }
-  func lineTo(position: CGPoint) {
-    CGContextAddLineToPoint(self, position.x, position.y)
-  }
-  func drawPath(points: [CGPoint]) {
-    if let p = points.first { moveTo(p) }
-    points.forEach(lineTo)
+  func drawPath(_ points: [CGPoint]) {
+    if let p = points.first {
+      move(to: p)
+      points.forEach { addLine(to: $0) }
+    }
   }
-  func drawPolygon(points: [CGPoint]) {
-    if let p = points.last { moveTo(p) }
-    points.forEach(lineTo)
+  func drawPolygon(_ points: [CGPoint]) {
+    if let p = points.last {
+      move(to: p)
+      points.forEach { addLine(to: $0) }
+    }
   }
   func arc(radius: CGFloat, startAngle: CGFloat, endAngle: CGFloat) {
-    let arc = CGPathCreateMutable()
-    CGPathAddArc(arc, nil, 0, 0, radius, startAngle, endAngle, false)
-    CGContextAddPath(self, arc)
+    let arc = CGMutablePath()
+    arc.addArc(center: .zero, radius: radius, startAngle: startAngle, endAngle: endAngle, clockwise: true)
+    addPath(arc)
   }
   func circle(radius: CGFloat) {
-    arc(radius, startAngle: 0.0, endAngle: twoPi)
+    arc(radius: radius, startAngle: 0.0, endAngle: twoPi)
   }
   func saveContext(operation: () -> ()) {
-    CGContextSaveGState(self)
+    saveGState()
     operation()
-    CGContextRestoreGState(self)
+    restoreGState()
   }
-  func scale(x: CGFloat, _ y: CGFloat, operation: CGContext -> ()) {
+  func scale(x: CGFloat, y: CGFloat, operation: (CGContext) -> ()) {
     saveContext {
-      CGContextScaleCTM(self, x, y)
+      scaleBy(x: x, y: y)
       operation(self)
     }
   }
-  func translate(x: CGFloat, _ y: CGFloat, operation: CGContext -> ()) {
+  func translate(x: CGFloat, y: CGFloat, operation: (CGContext) -> ()) {
     saveContext {
-      CGContextTranslateCTM(self, x, y)
+      translateBy(x: x, y: y)
       operation(self)
     }
   }
-  func rotate(angle: CGFloat, operation: CGContext -> ()) {
+  func rotate(angle: CGFloat, operation: (CGContext) -> ()) {
     saveContext {
-      CGContextRotateCTM(self, angle)
+      rotate(by: angle)
       operation(self)
     }
   }
-}
\ No newline at end of file
+}
diff --git a/Diagrams.playground/Sources/CoreGraphicsDiagramView.swift b/Diagrams.playground/Sources/CoreGraphicsDiagramView.swift
index a1e4e42..3fa7f16 100644
--- a/Diagrams.playground/Sources/CoreGraphicsDiagramView.swift
+++ b/Diagrams.playground/Sources/CoreGraphicsDiagramView.swift
@@ -1,24 +1,24 @@
 import UIKit
-import XCPlayground
+import PlaygroundSupport
 
 /// `CoreGraphicsDiagramView` is a `UIView` that draws itself by calling a
 /// user-supplied function to generate paths in a `CGContext`, then strokes
 /// the context's current path, creating lines in a pleasing shade of blue.
 class CoreGraphicsDiagramView : UIView {
-  override func drawRect(rect: CGRect) {
+  override func draw(_ rect: CGRect) {
     if let context = UIGraphicsGetCurrentContext() {
-      CGContextSaveGState(context)
-      let flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, frame.height)
-      CGContextConcatCTM(context, flipVertical);
-      CGContextTranslateCTM(context, frame.width/2, frame.height/2)
+      context.saveGState()
+      let flipVertical = CGAffineTransform(a: 1, b: 0, c: 0, d: -1, tx: 0, ty: frame.height)
+      context.concatenate(flipVertical)
+      context.translateBy(x: frame.width/2, y: frame.height/2)
       
       draw(context)
       
-      let lightBlue = UIColor(red: 0.222, green: 0.617, blue: 0.976, alpha: 1.0).CGColor
-      CGContextSetStrokeColorWithColor(context, lightBlue)
-      CGContextSetLineWidth(context, 2)
-      CGContextStrokePath(context)
-      CGContextRestoreGState(context)
+      let lightBlue = UIColor(red: 0.222, green: 0.617, blue: 0.976, alpha: 1.0).cgColor
+      context.setStrokeColor(lightBlue)
+      context.setLineWidth(2)
+      context.strokePath()
+      context.restoreGState()
     }
   }
   
@@ -28,9 +28,15 @@ class CoreGraphicsDiagramView : UIView {
 /// Shows a `UIView` in the current playground that draws itself by invoking
 /// `draw` on a `CGContext`, then stroking the context's current path in a
 /// pleasing light blue.
-public func showCoreGraphicsDiagram(size size: CGSize, draw: (CGContext)->()) {
-  let diagramView = CoreGraphicsDiagramView(frame: CGRect(origin: CGPointZero, size: size))
+public func showCoreGraphicsDiagram(size: CGSize, draw: @escaping (CGContext)->()) {
+  let diagramView = CoreGraphicsDiagramView(frame: CGRect(origin: .zero, size: size))
   diagramView.draw = draw
   diagramView.setNeedsDisplay()
-  XCPlaygroundPage.currentPage.liveView = diagramView
+  PlaygroundPage.current.liveView = diagramView
+}
+
+public func displayDiagram(_ diagram: Diagram) {
+  showCoreGraphicsDiagram(size: CGSize(width: 600, height: 600)) {
+    drawDiagram(diagram, context: $0)
+  }
 }
diff --git a/Diagrams.playground/Sources/Diagram.swift b/Diagrams.playground/Sources/Diagram.swift
index 622e255..36b2e13 100644
--- a/Diagrams.playground/Sources/Diagram.swift
+++ b/Diagrams.playground/Sources/Diagram.swift
@@ -5,32 +5,32 @@ let toRadians = { $0 * CGFloat(M_PI / 180) }
 public typealias Point = (x: CGFloat, y: CGFloat)
 
 //: A `Diagram` as a recursive enum
-public indirect enum Diagram {
-  case Polygon(corners: [CGPoint])
-  case Line(points: [CGPoint])
+public enum Diagram {
+  case Polygon([CGPoint])
+  case Line([CGPoint])
   case Arc(radius: CGFloat, startAngle: CGFloat, endAngle: CGFloat)
   case Circle(radius: CGFloat)
-  case Scale(x: CGFloat, y: CGFloat, diagram: Diagram)
-  case Translate(x: CGFloat, y: CGFloat, diagram: Diagram)
-  case Rotate(angle: CGFloat, diagram: Diagram)
+  indirect case Scale(x: CGFloat, y: CGFloat, diagram: Diagram)
+  indirect case Translate(x: CGFloat, y: CGFloat, diagram: Diagram)
+  indirect case Rotate(angle: CGFloat, diagram: Diagram)
   case Diagrams([Diagram])
 }
 
 // convenience methods to allow chaining of transformations
 public extension Diagram {
-  func scale(s: CGFloat) -> Diagram {
+  func scale(_ s: CGFloat) -> Diagram {
     return .Scale(x: s, y: s, diagram: self)
   }
   
-  func scale(x x: CGFloat, y: CGFloat) -> Diagram {
+  func scale(x: CGFloat, y: CGFloat) -> Diagram {
     return .Scale(x: x, y: y, diagram: self)
   }
   
-  func translate(x x: CGFloat, y: CGFloat) -> Diagram {
+  func translate(x: CGFloat, y: CGFloat) -> Diagram {
     return .Translate(x: x, y: y, diagram: self)
   }
   
-  func rotate(x: CGFloat) -> Diagram {
+  func rotate(_ x: CGFloat) -> Diagram {
     return .Rotate(angle: x, diagram: self)
   }
 }
@@ -38,28 +38,28 @@ public extension Diagram {
 // convenience functions to handle conversion from `Point` to `CGPoint`
 // (defining an Array of `CGpoint`s is really verbose – hence the use of the `tuple` typealias `Point`)
 public func line(ps: [Point]) -> Diagram {
-  return .Line(points: ps.map { x, y in CGPoint(x: x, y: y) })
+  return .Line(ps.map { x, y in CGPoint(x: x, y: y) })
 }
 
-public func polygon(ps: [Point]) -> Diagram {
-  return .Polygon(corners: ps.map { x, y in CGPoint(x: x, y: y) })
+public func polygon(_ ps: [Point]) -> Diagram {
+  return .Polygon(ps.map { x, y in CGPoint(x: x, y: y) })
 }
 
-public func rectanglePath(width: CGFloat, _ height: CGFloat) -> [Point] {
+public func rectanglePath(width: CGFloat, height: CGFloat) -> [Point] {
   let sx = width / 2
   let sy = height / 2
   return [(-sx, -sy), (-sx, sy), (sx, sy), (sx, -sy)]
 }
 
 public func rectangle(x: CGFloat, _ y: CGFloat) -> Diagram {
-  return polygon(rectanglePath(x, y))
+  return polygon(rectanglePath(width: x, height: y))
 }
 
-public func circle(radius: CGFloat) -> Diagram {
+public func circle(_ radius: CGFloat) -> Diagram {
   return .Circle(radius: radius)
 }
 
-public func diagrams(diagrams: [Diagram]) -> Diagram {
+public func diagrams(_ diagrams: [Diagram]) -> Diagram {
   return .Diagrams(diagrams)
 }
 
@@ -97,14 +97,14 @@ public func == (lhs: Diagram, rhs: Diagram) -> Bool {
 }
 
 //: Infix operator for combining Diagrams
-public func + (d1:Diagram, d2:Diagram) -> Diagram {
+public func + (d1: Diagram, d2: Diagram) -> Diagram {
   return diagrams([d1, d2])
 }
 
 //: ## Do some drawing!
 //:
 //: A recursive function responsible for drawing a diagram into a CGContext
-public func drawDiagram(diagram: Diagram)(context: CGContext) -> () {
+public func drawDiagram(_ diagram: Diagram, context: CGContext) -> () {
   switch diagram {
   case let .Polygon(corners):
     context.drawPolygon(corners)
@@ -113,28 +113,27 @@ public func drawDiagram(diagram: Diagram)(context: CGContext) -> () {
     context.drawPath(points)
  
   case let .Arc(r, a1, a2):
-    context.arc(r, startAngle: toRadians(a1), endAngle: toRadians(a2))
+    context.arc(radius: r, startAngle: toRadians(a1), endAngle: toRadians(a2))
     
   case let .Circle(radius):
-    context.circle(radius)
-    
+    context.circle(radius: radius)
+
   case let .Scale(x, y, diagram):
-    context.scale(x, y) {
-      drawDiagram(diagram)(context: $0)
+    context.scale(x: x, y: y) {
+      drawDiagram(diagram, context: $0)
     }
     
   case let .Translate(x, y, diagram):
-    context.translate(x, y) {
-      drawDiagram(diagram)(context: $0)
+    context.translate(x: x, y: y) {
+      drawDiagram(diagram, context: $0)
     }
     
   case let .Rotate(angle, diagram):
-    context.rotate(toRadians(angle)) {
-      drawDiagram(diagram)(context: $0)
+    context.rotate(angle: toRadians(angle)) {
+      drawDiagram(diagram, context: $0)
     }
     
   case let .Diagrams(diagrams):
-    diagrams.forEach { d in drawDiagram(d)(context: context) }
+    diagrams.forEach { d in drawDiagram(d, context: context) }
   }
 }
-