using Microsoft.CSharp.RuntimeBinder;
using System;
using System.Dynamic;
using System.Linq.Expressions;

namespace ConsoleApplication1
{
    public class ExpressionTreeUtils
    {
        private static Expression<Func<dynamic, decimal>> CreateLambdaCastExpression()
        {
            // source
            var sourceParameterExpression = Expression.Parameter(typeof(object), "source");

            var binder = Binder.GetMember(
                CSharpBinderFlags.None, "IntProp", typeof(ExpressionTreeUtils),
                new[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null) });

            // CSharpBinderFlags.ConvertExplicit: explicit cast 
            // (will convert double to decimal)
            // CSharpBinderFlags.None: implicit cast
            // (will convert int to decimal)
            var convert = Binder.Convert(CSharpBinderFlags.ConvertExplicit, typeof(decimal), typeof(ExpressionTreeUtils));

            // source.sourceProperty
            var sourcePropertyExpression = Expression.Dynamic(
                binder, typeof(object), sourceParameterExpression);

            // (decimal) source;
            var castedValueExpression = Expression.Dynamic(
                convert, typeof(decimal), sourcePropertyExpression);

            // () =>  (decimal) source;
            return Expression.Lambda<Func<dynamic, decimal>>(castedValueExpression,
                sourceParameterExpression);
        }

        public static void Test()
        {
            dynamic source = new ExpandoObject();
            source.IntProp = 1.5;
            decimal r = CreateLambdaCastExpression().Compile()(source);
            Console.WriteLine(r);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            ExpressionTreeUtils.Test();
        }
    }
}