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Roslyn September CTP 2012 Overview – API Changes, Using Modified APIs for C# Script Execution, Embedding C# as a scripting language

imageMicrosoft Roslyn September CTP 2012 is now released. You can download the September CTP here

You could find a quick overview about Roslyn in my previous overview post.

Roslyn CTP previews the upcoming features of C# and VB.NET. Roslyn CTP is a pretty exciting release, and it opens up lot of possibilities for C# and VB.NET programmers. Roslyn provides language services and APIs on top of .NET’s compiler services, and this will enable .NET developers to do a lot more things – including using C# and VB.NET as scripting languages, use compiler as a service in your own applications for code related tasks, develop better language and IDE extensions etc.

What’s Exciting In September CTP (CTP3) release

One of the biggest excitement for me is the support for Expression Trees. This means, now you can include LINQ Queries in your script, and you can dynamically execute LINQ queries. This has lot of interesting aspects, and this is huge. For example, see how I’m executing a very simple Linq query from the C# interactive console.


Along with inclusion of Expression trees, the following language features are also now supported in Roslyn, since CTP2.

  • Collection initializers
  • Extern aliases
  • Multi-dimensional arrays
  • Nullable types
  • Object initializers
  • Type forwarders
  • Unsafe code (except fixed-size buffers)

Scripting API Changes

There are some breaking changes in September CTP release. I thought I’ll quickly re-phrase the Scripting Example I provided in the overview post. Some of the major changes for Scripting API includes,

  • Changes for the ScriptEngine constructor
  • Now you need to use ScriptEngine instance’s Create Method instead of Session.Create(..) you had in earlier version of Roslyn.
  • The Execute method is now part of the Session, instead of Engine. So, instead of Engine’s Execute(code,session) in previous versions, you can directly call your Session’s Execute(code) method.

So, here is the updated code for the Scripting example I provided in the previous post. You could compare this with the previous example, and I’ve listed some of the changes below. Note that the change is only with in the ScriptingHost class

using System;
using System.Collections.Generic;
using System.Linq;
using Roslyn.Scripting.CSharp;
using Roslyn.Scripting;

namespace ScriptingRoslyn
    //Our Dog class so that we can train dogs later
    public class OurDog
        private string _name = string.Empty;
        public OurDog(string name)
            _name = name;

        public string Name
            get { return _name; }

        public void Bite(OurDog other)
            Console.WriteLine("{0} is biting the tail of {1}", _name, other.Name);

        public void Walk()
            Console.WriteLine("{0} is Walking", _name);

        public void Eat()
            Console.WriteLine("{0} is Eating", _name);

//Let us create a Host object, where we'll wrap our session and engine
//The methods in the host class are available directly to the environment
//Now you can create a ScriptEngine, and create a session out of the ScriptEngine

 public class ScriptingHost
        private ScriptEngine engine;
        private Session session;

        //Methods in the Host object can be called directly from the 
        public OurDog CreateDog(string name)
            return new OurDog(name);

        public ScriptingHost()
            //Create the script engine
            //Script engine constructor parameters go changed
            engine=new ScriptEngine();

            //Let us use engine's Addreference for adding the required
                    typeof (Console).Assembly,
                    typeof (ScriptingHost).Assembly,
                    typeof (IEnumerable<>).Assembly,
                    typeof (IQueryable).Assembly,
             }.ToList().ForEach(asm => engine.AddReference(asm));

                   "System", "System.Linq", 

            //Now, you need to create a session using engine's CreateSession method,
            //which can be seeded with a host object
            session = engine.CreateSession(this);

        //Pass the code to the engine, nothing much here
        public object Execute(string code)
            return session.Execute (code);

        public T Execute<T>(string code)
            return session.Execute<T>(code);


    //Main driver
    class Program
        static void Main(string[] args)
            var host = new ScriptingHost();
            Console.WriteLine("Hello Dog Trainer!! Type your code.\n\n");

            string codeLine;
            while ((codeLine = Console.ReadLine()) != "Exit();")
                    //Execute the code
                    var res = host.Execute(codeLine);

                    //Write the result back to console
                    if (res != null)
                        Console.WriteLine(" = " + res.ToString());
                catch (Exception e)
                    Console.WriteLine(" !! " + e.Message);


And now, let us run our little scripting app. And try some LINQ queries as part of your script Smile



Other API Changes

There have been some updates to the Roslyn APIs since the second CTP was released in June of 2012. Below is a summary of some of the most important changes, some of which are breaking.  For example, In compiler APIs,

  • Instead of SyntaxTree.ParseCompilationUnit you can use ParseText or ParseFile instead. 
  • Also SyntaxNode.GetText and SyntaxNode.GetFullText have been replaced with ToString and ToFullString respectively

You can see a full list of API changes here - Happy Hacking with the new Roslyn APIs, Enjoy C#

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