C#'s lambda expression tree.

LambdaExpressionTree.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading.Tasks;

namespace LambdaExpressionTree
{
    class Program
    {
        static void Main(string[] args)
        {
            // これはシンプルな式じゃない( {} を含む複数ステートメント構成)ので、Expression<Func<...>> にできない。コンパイラに怒られる。
            // Expression<Func<int, int>> makeDouble = (x) => { return x * 2; };
            
            Expression<Func<int, int>> makeDouble = (x) => x * 2;

            //function makeDouble: x => (x * 2)
            //  .Body: (x * 2)
            //  .TailCall: False
            //  .ReturnType: System.Int32
            //  .Type: System.Func`2[System.Int32,System.Int32]
            //  .CanReduce: False
            //  .NodeType: Lambda
            //  .Parameters: System.Runtime.CompilerServices.TrueReadOnlyCollection`1[System.Linq.Expressions.ParameterExpression]
            //  .Parameters[0]: x
            //  .Parameters[0].Name: x
            //  .Parameters[0].IsByRef: False
            //  .Parameters[0].NodeType: Parameter
            //  .Parameters[0].Type: System.Int32
            DisplayLambdaExpression("function makeDouble", makeDouble);

            //function returnNull: () => null
            //  .Body: null
            //  .TailCall: False
            //  .ReturnType: System.Object
            //  .Type: System.Func`1[System.Object]
            //  .CanReduce: False
            //  .NodeType: Lambda
            //  .Parameters: System.Runtime.CompilerServices.TrueReadOnlyCollection`1[System.Linq.Expressions.ParameterExpression]
            DisplayLambdaExpression("function returnNull", (Expression<Func<object>>)(() => null));

            //function manyParams: (a, b, c, d) => null
            //  .Body: null
            //  .TailCall: False
            //  .ReturnType: System.Object
            //  .Type: System.Func`5[System.Int32,System.Single,System.Char,System.String,System.Object]
            //  .CanReduce: False
            //  .NodeType: Lambda
            //  .Parameters: System.Runtime.CompilerServices.TrueReadOnlyCollection`1[System.Linq.Expressions.ParameterExpression]
            //  .Parameters[0]: a
            //  .Parameters[0].Name: a
            //  .Parameters[0].IsByRef: False
            //  .Parameters[0].NodeType: Parameter
            //  .Parameters[0].Type: System.Int32
            //  .Parameters[1]: b
            //  .Parameters[1].Name: b
            //  .Parameters[1].IsByRef: False
            //  .Parameters[1].NodeType: Parameter
            //  .Parameters[1].Type: System.Single
            //  .Parameters[2]: c
            //  .Parameters[2].Name: c
            //  .Parameters[2].IsByRef: False
            //  .Parameters[2].NodeType: Parameter
            //  .Parameters[2].Type: System.Char
            //  .Parameters[3]: d
            //  .Parameters[3].Name: d
            //  .Parameters[3].IsByRef: False
            //  .Parameters[3].NodeType: Parameter
            //  .Parameters[3].Type: System.String
            DisplayLambdaExpression("function manyParams", (Expression<Func<int, float, char, string, object>>)((a, b, c, d) => null));

            //action givenIntType: x => x.GetType()
            //  .Body: x.GetType()
            //  .TailCall: False
            //  .ReturnType: System.Void
            //  .Type: System.Action`1[System.Int32]
            //  .CanReduce: False
            //  .NodeType: Lambda
            //  .Parameters: System.Runtime.CompilerServices.TrueReadOnlyCollection`1[System.Linq.Expressions.ParameterExpression]
            //  .Parameters[0]: x
            //  .Parameters[0].Name: x
            //  .Parameters[0].IsByRef: False
            //  .Parameters[0].NodeType: Parameter
            //  .Parameters[0].Type: System.Int32
            DisplayLambdaExpression("action givenIntType", (Expression<Action<int>>)((x) => x.GetType()));

            //action stringType: () => "".GetType()
            //  .Body: "".GetType()
            //  .TailCall: False
            //  .ReturnType: System.Void
            //  .Type: System.Action
            //  .CanReduce: False
            //  .NodeType: Lambda
            //  .Parameters: System.Runtime.CompilerServices.TrueReadOnlyCollection`1[System.Linq.Expressions.ParameterExpression]            
            DisplayLambdaExpression("action stringType", (Expression<Action>)(() => "".GetType()));

        }

        private static void DisplayLambdaExpression<T>(string title, Expression<T> makeDouble)
        {
            Debug.WriteLine("{0}: {1}", title, makeDouble);
            Debug.WriteLine("  .Body: {0}", makeDouble.Body);
            Debug.WriteLine("  .TailCall: {0}", makeDouble.TailCall);
            Debug.WriteLine("  .ReturnType: {0}", makeDouble.ReturnType);
            Debug.WriteLine("  .Type: {0}", makeDouble.Type);
            Debug.WriteLine("  .CanReduce: {0}", makeDouble.CanReduce);
            Debug.WriteLine("  .NodeType: {0}", makeDouble.NodeType);
            Debug.WriteLine("  .Parameters: {0}", makeDouble.Parameters);
            var pIdx = 0;
            foreach (var p in makeDouble.Parameters)
            {
                Debug.WriteLine("  .Parameters[{0}]: {1}", pIdx,p);
                Debug.WriteLine("  .Parameters[{0}].Name: {1}", pIdx, p.Name);
                Debug.WriteLine("  .Parameters[{0}].IsByRef: {1}", pIdx,p.IsByRef);
                Debug.WriteLine("  .Parameters[{0}].NodeType: {1}", pIdx,p.NodeType);
                Debug.WriteLine("  .Parameters[{0}].Type: {1}", pIdx,p.Type);
                pIdx++;
            }
        }
    }
}

Compared to Java's lambda expression, C#'s one is able to treated as an expression tree when its form is simple.