What is the best scripting language to embed in a C# desktop application?

We are writing a complex rich desktop application and need to offer flexibility in reporting formats so we thought we would just expose our object model to a scripting langauge. Time was when that meant VBA (which is still an option), but the managed code derivative VSTA (I think) seems to have withered on the vine.

What is now the best choice for an embedded scripting language on Windows .NET?

Personally, I'd use C# as the scripting language. The .NET framework (and Mono, thanks Matthew Scharley) actually includes the compilers for each of the .NET languages in the framework itself.

Basically, there's 2 parts to the implementation of this system.

1. Allow the user to compile the code This is relatively easy, and can be done in only a few lines of code (though you might want to add an error dialog, which would probably be a couple dozen more lines of code, depending on how usable you want it to be).

2. Create and use classes contained within the compiled assembly This is a little more difficult than the previous step (requires a tiny bit of reflection). Basically, you should just treat the compiled assembly as a "plug-in" for the program. There are quite a few tutorials on various ways you can create a plug-in system in C# (Google is your friend).

I've implemented a "quick" application to demonstrate how you can implement this system (includes 2 working scripts!). This is the complete code for the application, just create a new one and paste the code in the "program.cs" file. At this point I must apologize for the large chunk of code I'm about to paste (I didn't intend for it to be so large, but got a little carried away with my commenting)

using System;
using System.Windows.Forms;
using System.Reflection;
using System.CodeDom.Compiler;




namespace ScriptingInterface
{
public interface IScriptType1
{
string RunScript(int value);
}
}




namespace ScriptingExample
{
static class Program
{
/// 


/// The main entry point for the application.
/// 
[STAThread]
static void Main()
{



        // Lets compile some code (I'm lazy, so I'll just hardcode it all, i'm sure you can work out how to read from a file/text box instead
        Assembly compiledScript = CompileCode(
            "namespace SimpleScripts" +
            "{" +
            "    public class MyScriptMul5 : ScriptingInterface.IScriptType1" +
            "    {" +
            "        public string RunScript(int value)" +
            "        {" +
            "            return this.ToString() + \" just ran! Result: \" + (value*5).ToString();" +
            "        }" +
            "    }" +
            "    public class MyScriptNegate : ScriptingInterface.IScriptType1" +
            "    {" +
            "        public string RunScript(int value)" +
            "        {" +
            "            return this.ToString() + \" just ran! Result: \" + (-value).ToString();" +
            "        }" +
            "    }" +
            "}");

        if (compiledScript != null)
        {
            RunScript(compiledScript);
        }
    }

    static Assembly CompileCode(string code)
    {
        // Create a code provider
        // This class implements the 'CodeDomProvider' class as its base. All of the current .Net languages (at least Microsoft ones)
        // come with thier own implemtation, thus you can allow the user to use the language of thier choice (though i recommend that
        // you don't allow the use of c++, which is too volatile for scripting use - memory leaks anyone?)
        Microsoft.CSharp.CSharpCodeProvider csProvider = new Microsoft.CSharp.CSharpCodeProvider();

        // Setup our options
        CompilerParameters options = new CompilerParameters();
        options.GenerateExecutable = false; // we want a Dll (or "Class Library" as its called in .Net)
        options.GenerateInMemory = true; // Saves us from deleting the Dll when we are done with it, though you could set this to false and save start-up time by next time by not having to re-compile
        // And set any others you want, there a quite a few, take some time to look through them all and decide which fit your application best!

        // Add any references you want the users to be able to access, be warned that giving them access to some classes can allow
        // harmful code to be written and executed. I recommend that you write your own Class library that is the only reference it allows
        // thus they can only do the things you want them to.
        // (though things like "System.Xml.dll" can be useful, just need to provide a way users can read a file to pass in to it)
        // Just to avoid bloatin this example to much, we will just add THIS program to its references, that way we don't need another
        // project to store the interfaces that both this class and the other uses. Just remember, this will expose ALL public classes to
        // the "script"
        options.ReferencedAssemblies.Add(Assembly.GetExecutingAssembly().Location);

        // Compile our code
        CompilerResults result;
        result = csProvider.CompileAssemblyFromSource(options, code);

        if (result.Errors.HasErrors)
        {
            // TODO: report back to the user that the script has errored
            return null;
        }

        if (result.Errors.HasWarnings)
        {
            // TODO: tell the user about the warnings, might want to prompt them if they want to continue
            // runnning the "script"
        }

        return result.CompiledAssembly;
    }

    static void RunScript(Assembly script)
    {
        // Now that we have a compiled script, lets run them
        foreach (Type type in script.GetExportedTypes())
        {
            foreach (Type iface in type.GetInterfaces())
            {
                if (iface == typeof(ScriptingInterface.IScriptType1))
                {
                    // yay, we found a script interface, lets create it and run it!

                    // Get the constructor for the current type
                    // you can also specify what creation parameter types you want to pass to it,
                    // so you could possibly pass in data it might need, or a class that it can use to query the host application
                    ConstructorInfo constructor = type.GetConstructor(System.Type.EmptyTypes);
                    if (constructor != null && constructor.IsPublic)
                    {
                        // lets be friendly and only do things legitimitely by only using valid constructors

                        // we specified that we wanted a constructor that doesn't take parameters, so don't pass parameters
                        ScriptingInterface.IScriptType1 scriptObject = constructor.Invoke(null) as ScriptingInterface.IScriptType1;
                        if (scriptObject != null)
                        {
                            //Lets run our script and display its results
                            MessageBox.Show(scriptObject.RunScript(50));
                        }
                        else
                        {
                            // hmmm, for some reason it didn't create the object
                            // this shouldn't happen, as we have been doing checks all along, but we should
                            // inform the user something bad has happened, and possibly request them to send
                            // you the script so you can debug this problem
                        }
                    }
                    else
                    {
                        // and even more friendly and explain that there was no valid constructor
                        // found and thats why this script object wasn't run
                    }
                }
            }
        }
    }
}




}

}

IronPython. Here's an overview of how to embed it.

I've used CSScript with amazing results. It really cut down on having to do bindings and other low level stuff in my scriptable apps.

The PowerShell engine was designed to be easily embedded in an application to make it scriptable. In fact, the PowerShell CLI is just a text based interface to the engine.

Edit: See https://devblogs.microsoft.com/powershell/making-applications-scriptable-via-powershell/

Boo language.

My scripting language of choice would be Lua these days. It's small, fast, clean, fully documented, well supported, has a great community , it's used by many big companies in the industry (Adobe, Blizzard, EA Games), definetely worth a try.

To use it with .NET languages the LuaInterface project will provide all you need.

Why not try C#? Mono has a great new project especially for dynamically evaluating C# :

http://tirania.org/blog/archive/2008/Sep-10.html

IronRuby as mentioned above. An interesting project to me as a C# programmer is C# Eval support in Mono. But it's not available yet (will be part of Mono 2.2).

Another vote for IronPython. Embedding it is simple, interoperation with .Net classes is straightforward, and, well, it's Python.

I may suggest S# which I currently maintain. It is an open source project, written in C# and designed for .NET applications.

Initially (2007-2009) it was hosted at http://www.codeplex.com/scriptdotnet, but recently it was moved to github.

Try Ela. This is a functional language similar to Haskell and can be embedded into any .Net application. Even it has simple but usable IDE.

I havnt tried this yet but it looks pretty cool:

http://www.codeplex.com/scriptdotnet

I've just created a plugin for a client, allowing them to write C# code in modules that act like VBA does for Office.

I've used Lua before; in a Delphi app but it can be embedded in lots of things. It's used in Adobe's Photoshop Lightroom.

I like scripting with C# itself. Now, in 2013, there's quite good support for C# scripting, more and more libraries for it are becoming available.

Mono has a great support to script C# code, and you can use it with .NET by just including the Mono.CSharp.dll in your application. For C# scripting application that I've made check out CShell

Also check out the `ScriptEngine' in Roslyn which is from Microsoft, but this is only CTP.

As some people already mentioned, CS-Script has been around for quite a while as well.