Calling a function with named arguments in a hosted application

Question

So I am hosting IronPython in my C# application. IronPhyton is used to implement a DSL for users. The DSL syntax should be something like this:

Ping(Message = "testOne1")

The hosting code looks like:

var engine = Python.CreateEngine();
var scope = engine.CreateScope();

Action<string> ping = (message) => Console.WriteLine(message.ToString());            
scope.SetVariable("Ping", ping);
var script = @"
Ping(Message = ""testOne1"")
";
engine.Execute(script, scope);

But this does not work because Action<string> does not keep name of the argument. Calling it without the parameter name works as expected:

Ping("testOne1")

How do I store a function and call it with named arguments?

Answer 1

To use named arguments you'll have to define the method statically. For example, I'll just put all DSL operations into an Operations static class.

public static class Operations {
  public static void Ping(string Message) {
    Console.WriteLine(Message);
  }
}

Then named arguments will work:

var engine = Python.CreateEngine();
var scope = engine.CreateScope();

// Load the assembly where the operations are defined.
engine.Runtime.LoadAssembly(Assembly.GetExecutingAssembly());

// Import the operations modules, settings their names as desired.
engine.Execute(@"
from Operations import Ping
", scope);

// Now named arguments will work...
var script = @"
Ping(Message = ""Ping!"")
";

engine.Execute(script, scope);

Now if I could give you some advise; I'd prefer to implement the actual Python API in Python, and have that call back into my .NET code as needed. For example, instead of having the "operations" defined in C#, you'd have an Operations.py file which defines your Python DSL:

# Get access to your .NET API
import clr
clr.AddReference("MyAPI")
import MyAPI

# Define the Ping call to call into your .NET API
def Ping(Message):
  MyAPI.Ping(Message)

And your hosting code doesn't need to change at all.

Both are valid solutions, but the last one lets you iterate on your DSL easily.

Good luck!

Answer 2

The name of the parameter is defined by the name provided in the delegate type. In the case of Action<T>, the parameter name is obj.

public delegate void Action<in T>(
    T obj
)

obj should work for you. Are you sure it isn't working? It works for me.

In an IronPython project I have a library:

namespace TestLibrary
{
    public static class Test
    {
        public static readonly Action<string> WriteLine =
            msg => Console.WriteLine(msg);

        // the same works if I do this instead
        //public static readonly Action<string> WriteLine = Console.WriteLine;
    }
}

And this works:

from TestLibrary import Test

#Test.WriteLine(msg='foo') # error 
Test.WriteLine(obj='foo') # works

---

Hosted, same deal:

var engine = Python.CreateEngine();
dynamic scope = engine.CreateScope();

Action<string> writeLine = msg => Console.WriteLine(msg);
// or even
//Action<string> writeLine = Console.WriteLine;
scope.writeLine = writeLine;

//engine.Execute("writeLine(msg='foo')", scope); // error
engine.Execute("writeLine(obj='foo')", scope); // works