Using the Mono C# compiler as a service (error)

Question

I'm relatively new to Mono and I am trying to add C# scripting capabilities to my application. I found this blog post by Miguel de Icaza. The way to call the C# compiler as a service is to include Mono.CSharp and use the Evaluator class, specifically the Evaluate or Run methods. This is documented here .

So here is my example code (derived from the other blog posts on the internet on this subject, yes I've done my googling)

using System;
using Mono.CSharp;

namespace EvalTest
{
  public class Test
  {
    static void Main(string [] args)
    {
      Mono.CSharp.Evaluator.Evaluate("using System;");
      Mono.CSharp.Evaluator.Run("using System;");
    }
  }
}

And when we try to compile it I get these errors:

eval.cs(10,19): error CS0234: The type or namespace name `Evaluator' does not exist in the namespace `Mono.CSharp'. Are you missing an assembly reference?
eval.cs(11,19): error CS0234: The type or namespace name `Evaluator' does not exist in the namespace `Mono.CSharp'. Are you missing an assembly reference?

The same thing happens on Linux and OSX using all the Mono compilers, I even tried the silverlight one. I have searched stackoverflow for similar questions, everyone references Miguel's blog post and some similar sample code. What am I missing? Is there some compiler flag I need to add? Thanks for your help.

Answer 1

Did you follow this bit of the blog post:

Usage is very simple, you must reference the `gmcs.exe' assembly

? This is what I did with your code (in Test.cs):

c:\Users\Jon\Test>copy "c:\Program Files (x86)\Mono-2.8"\lib\mono\2.0\gmcs.exe .
        1 file(s) copied.

c:\Users\Jon\Test>gmcs /r:gmcs.exe Test.cs

c:\Users\Jon\Test>mono Test.exe

Unhandled Exception: System.ArgumentException:
  The expression did not set a result
  at Mono.CSharp.Evaluator.Evaluate (System.String input) [...]
  at EvalTest.Test.Main (System.String[] args) [...]

It's fair enough that it doesn't give any result - it's only a using directive. This works fine though:

Mono.CSharp.Evaluator.Run("System.Console.WriteLine(5 + 5);");

Answer 2

Are you missing an assembly reference?

It's one of those psychic error messages that tends to be right 95% of the time. Go back to the blog post and note this line:

Usage is very simple, you must reference the `gmcs.exe' assembly