static void Main(string[] args)
        {
            TreeNode bin1 = Postfix.InfixToPostfix(Console.ReadLine()); // e.g "5 * 2 + 1" -> "5 2 * 1 +"

            // Using TreeNode type, not BinOp (Binary Operator) as we cannot guarantee the root node of the abstract syntax tree will be an operator.

            Console.WriteLine("To postfix:");
            foreach (TreeNode node in Traversal.postOrder(bin1))
            {
                Console.Write(node.value + " ");
            }
            Console.WriteLine("\nTo infix:");
            foreach (TreeNode node in Traversal.inOrder(bin1))
            {
                Console.Write(node.value + " ");
            }
            Console.WriteLine("\nTo prefix:");
            foreach (TreeNode node in Traversal.preOrder(bin1))
            {
                Console.Write(node.value + " ");
            }
            Console.WriteLine();

            // Now using reverse polish notation, calculate what the result is. This takes in a postfix-ordered list of TreeNodes.
            Console.WriteLine("Answer: " + RPN.Evaluate(Traversal.postOrder(bin1)));
        }
        public static void Run()
        {
            Tokeniser    tokeniser = new Tokeniser(Console.ReadLine());
            List <Token> tokens    = tokeniser.Tokenise().ToList();

            TreeNode bin1 = TreeBuilder.BuildAST(tokens); // e.g "5 * 2 + 1" -> "5 2 * 1 +"

            // Using TreeNode type, not BinOp (Binary Operator) as we cannot guarantee the root node of the abstract syntax tree will be an operator.

            Console.WriteLine("To postfix:");
            foreach (TreeNode node in Traversal.postOrder(bin1))
            {
                Console.Write(node.value + " ");
            }
            Console.WriteLine("\nTo infix:");
            foreach (TreeNode node in Traversal.inOrder(bin1))
            {
                Console.Write(node.value + " ");
            }
            Console.WriteLine("\nTo prefix:");
            foreach (TreeNode node in Traversal.preOrder(bin1))
            {
                Console.Write(node.value + " ");
            }
            Console.WriteLine();

            // Now using reverse polish notation, calculate what the result is. This takes in a postfix-ordered list of TreeNodes.
            Console.WriteLine("Answer: " + RPN.Evaluate(Traversal.postOrder(bin1)));
        }