I first learned about the C## compiler as a service workings way back in 2008 at PDC. At that time, Anders Hejlsberg gave a brief preview of what was to come by showing off a C## Read-Evaluate-Print-Loop (REPL) demo. Since then the project has progressed to include powerful code analysis and compiler APIs as well. In this column I’ll demonstrate how to utilize the C## Roslyn Scripting API to execute expressions , code blocks and classes from a string or file.

Getting Started

The first step is to procure and install the Roslyn CTP bits from bit.ly/rThx5k. Once Roslyn is set up, open up Visual Studio and you should see the Roslyn templates available for both C## and VB.NET, as shown in Figure 1.

Figure 1._ Roslyn Visual Studio Templates._

Figure 1: Roslyn Visual Studio Templates

Next create a new Console Application, open up Program.cs and add the following using statements.

using Roslyn.Scripting;

using Roslyn.Scripting.CSharp;

You’re now set up to run any of the code examples in the remainder of the article.

Executing a C## Expression

One of the most basic scripting needs is the ability to execute a given expression. Accomplishing this task with Roslyn is very similar to using the Dynamic Language Runtime (DLR) . First create a ScriptEngine instance for your target language, in this case C#:

 ScriptEngine  scriptEngine = new ScriptEngine();

Then use the Execute method to run the given expression:

 scriptEngine.Execute("1+1");

The expression above would return an object with a value of 2.

If you know the return type, you can also use the generic Execute method. For example, to get an integer value from a numeric expression, run the following:

 int result =  scriptEngine.Execute<int>("20+22");

#api #csharp #roslyn scripting api