[Swift 4] Update Shunting Yard

Author: remlostime

Shunting Yard/ShuntingYard.playground/Contents.swift

@@ -1,5 +1,10 @@
 //: Playground - noun: a place where people can play
 
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 internal enum OperatorAssociativity {
   case leftAssociative
   case rightAssociative

Shunting Yard/ShuntingYard.playground/Sources/Stack.swift

@@ -1,38 +1,36 @@
 import Foundation
 
 public struct Stack<T> {
-    fileprivate var array = [T]()
-
-    public init() {
-
-    }
-
-    public var isEmpty: Bool {
-        return array.isEmpty
-    }
-
-    public var count: Int {
-        return array.count
-    }
-
-    public mutating func push(_ element: T) {
-        array.append(element)
-    }
-
-    public mutating func pop() -> T? {
-        return array.popLast()
-    }
-
-    public var top: T? {
-        return array.last
-    }
+  fileprivate var array = [T]()
+  
+  public init() {
+    
+  }
+  
+  public var isEmpty: Bool {
+    return array.isEmpty
+  }
+  
+  public var count: Int {
+    return array.count
+  }
+  
+  public mutating func push(_ element: T) {
+    array.append(element)
+  }
+  
+  public mutating func pop() -> T? {
+    return array.popLast()
+  }
+  
+  public var top: T? {
+    return array.last
+  }
 }
 
 extension Stack: Sequence {
-    public func makeIterator() -> AnyIterator<T> {
-        var curr = self
-        return AnyIterator { _ -> T? in
-            return curr.pop()
-        }
-    }
+  public func makeIterator() -> AnyIterator<T> {
+    var curr = self
+    return AnyIterator { curr.pop() }
+  }
 }