Task 1 – Creating an Expression Tree using a Lambda Expression

In this task, you declare an expression tree and print a representation of the expression body.

 

1. Add the following using directive to gain access to the types in System.Expressions (at the top of the file):

using System.Linq.Expressions;

 

2. Replace the code in the body of the Main method with the following code:

static void Main(string[] args)

{

Expression<Func<int, bool>> filter = n => (n * 3) < 5;

 

BinaryExpression lt = (BinaryExpression) filter.Body;

BinaryExpression mult = (BinaryExpression) lt.Left;

ParameterExpression en = (ParameterExpression) mult.Left;

ConstantExpression three = (ConstantExpression) mult.Right;

ConstantExpression five = (ConstantExpression) lt.Right;

 

Console.WriteLine("({0} ({1} {2} {3}) {4})", lt.NodeType,
mult.NodeType, en.Name, three.Value, five.Value);

}

 

This code creates an expression tree representation from the lambda expression. It then initializes local variables for each node of the tree. Finally, it outputs a LISP-style representation of the expression, to demonstrate a translation of the lambda expression to the expression tree.

3. Press Ctrl+F5 to run the code and see the following output in the console window:

(LessThan (Multiply n 3) 5)

 

4. Press any key to terminate the application.