Merge pull request kodecocodes#365 from JaapWijnen/master

Migrate Shunting Yard to Swift 3

Author: kelvinlauKL

Shunting Yard/README.markdown

@@ -6,7 +6,7 @@ Any mathematics we write is expressed in a notation known as *infix notation*. F
 
 The operator is placed in between the operands, hence the expression is said to be in *infix* form. If you think about it, any expression that you write on a piece of paper will always be in infix form. This is what we humans understand.
 
-Multiplication has higher precedence than addition, so when the above expression is evaluated you would first multiply **B** and **C**, and then add the result to **A**. We humans can easily understand the precedence of operators, but a machine needs to be given instructions about each operator. 
+Multiplication has higher precedence than addition, so when the above expression is evaluated you would first multiply **B** and **C**, and then add the result to **A**. We humans can easily understand the precedence of operators, but a machine needs to be given instructions about each operator.
 
 To change the order of evaluation, we can use parentheses:
 
@@ -108,4 +108,5 @@ We end up with the postfix expression:
 
 [Shunting yard algorithm on Wikipedia](https://en.wikipedia.org/wiki/Shunting-yard_algorithm)
 
-*Written for the Swift Algorithm Club by [Ali Hafizji](http://www.github.com/aliHafizji)*
+*Written for the Swift Algorithm Club by [Ali Hafizji](http://www.github.com/aliHafizji)*
+*Migrated to Swift 3 by Jaap Wijnen*

Shunting Yard/ShuntingYard.playground/Contents.swift

@@ -15,17 +15,17 @@ public enum OperatorType: CustomStringConvertible {
 
   public var description: String {
     switch self {
-      case add:
+      case .add:
         return "+"
-      case subtract:
+      case .subtract:
         return "-"
-      case divide:
+      case .divide:
         return "/"
-      case multiply:
+      case .multiply:
         return "*"
-      case percent:
+      case .percent:
         return "%"
-      case exponent:
+      case .exponent:
         return "^"
     }
   }
@@ -39,13 +39,13 @@ public enum TokenType: CustomStringConvertible {
 
   public var description: String {
     switch self {
-      case openBracket:
+      case .openBracket:
         return "("
-      case closeBracket:
+      case .closeBracket:
         return ")"
-      case Operator(let operatorToken):
+      case .Operator(let operatorToken):
         return operatorToken.description
-      case operand(let value):
+      case .operand(let value):
         return "\(value)"
     }
   }
@@ -141,23 +141,23 @@ public struct Token: CustomStringConvertible {
 public class InfixExpressionBuilder {
   private var expression = [Token]()
 
-  public func addOperator(operatorType: OperatorType) -> InfixExpressionBuilder {
+  public func addOperator(_ operatorType: OperatorType) -> InfixExpressionBuilder {
     expression.append(Token(operatorType: operatorType))
     return self
   }
 
-  public func addOperand(operand: Double) -> InfixExpressionBuilder {
+  public func addOperand(_ operand: Double) -> InfixExpressionBuilder {
     expression.append(Token(operand: operand))
     return self
   }
 
   public func addOpenBracket() -> InfixExpressionBuilder {
-    expression.append(Token(tokenType: .OpenBracket))
+    expression.append(Token(tokenType: .openBracket))
     return self
   }
 
   public func addCloseBracket() -> InfixExpressionBuilder {
-    expression.append(Token(tokenType: .CloseBracket))
+    expression.append(Token(tokenType: .closeBracket))
     return self
   }
 
@@ -168,7 +168,7 @@ public class InfixExpressionBuilder {
 }
 
 // This returns the result of the shunting yard algorithm
-public func reversePolishNotation(expression: [Token]) -> String {
+public func reversePolishNotation(_ expression: [Token]) -> String {
 
   var tokenStack = Stack<Token>()
   var reversePolishNotation = [Token]()
@@ -187,14 +187,14 @@ public func reversePolishNotation(expression: [Token]) -> String {
         }
 
       case .Operator(let operatorToken):
-        for tempToken in tokenStack.generate() {
+        for tempToken in tokenStack.makeIterator() {
           if !tempToken.isOperator {
             break
           }
 
           if let tempOperatorToken = tempToken.operatorToken {
-            if operatorToken.associativity == .LeftAssociative && operatorToken <= tempOperatorToken
-                || operatorToken.associativity == .RightAssociative && operatorToken < tempOperatorToken {
+            if operatorToken.associativity == .leftAssociative && operatorToken <= tempOperatorToken
+                || operatorToken.associativity == .rightAssociative && operatorToken < tempOperatorToken {
               reversePolishNotation.append(tokenStack.pop()!)
             } else {
               break
@@ -209,7 +209,7 @@ public func reversePolishNotation(expression: [Token]) -> String {
     reversePolishNotation.append(tokenStack.pop()!)
   }
 
-  return reversePolishNotation.map({token in token.description}).joinWithSeparator(" ")
+  return reversePolishNotation.map({token in token.description}).joined(separator: " ")
 }
 
 

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

@@ -1,41 +1,37 @@
 import Foundation
 
 public struct Stack<T> {
-    private var array = [T]()
-
+    fileprivate var array = [T]()
+    
     public init() {
-        array = []
+        
     }
-
+    
     public var isEmpty: Bool {
         return array.isEmpty
     }
-
+    
     public var count: Int {
         return array.count
     }
-
-    public mutating func push(element: T) {
+    
+    public mutating func push(_ element: T) {
         array.append(element)
     }
-
+    
     public mutating func pop() -> T? {
-        if isEmpty {
-            return nil
-        } else {
-            return array.removeLast()
-        }
+        return array.popLast()
     }
-
-    public func peek() -> T? {
+    
+    public var top: T? {
         return array.last
     }
 }
 
-extension Stack: SequenceType {
-    public func generate() -> AnyGenerator<T> {
+extension Stack: Sequence {
+    public func makeIterator() -> AnyIterator<T> {
         var curr = self
-        return anyGenerator {
+        return AnyIterator {
             _ -> T? in
             return curr.pop()
         }