How to write a simple DLR host in C# using Hosting API

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Let
me start with a (fair) assumption. You reached here by clicking on a link in a
search results page. So, you already have a basic idea of what the DLR is and
that it can be hosted in managed applications. This post addresses
getting you started assuming no prior knowledge of the API that would let you
do this.

Here's
a step by step guide to write a simple DLR host

  1. Currently,
    the DLR is available as part of IronPython. So you can download the
    latest DLR binaries and/or binaries from here. (You can also get it from the IronRuby
    project)
  2. Extract
    the contents of the zip file to disk. The default dir will be 'IronPython-2.0B3'
  3. Fire
    up VS and create a new C# Console application.
  4. In
    VS, choose Project-><project name> Properties... menu itemto bring up project properties.
  5. Use
    the 'Output path' option to set the the project's output path
    to the folder where you unzipped the binaries in step (2).
  6. Make
    sure the folder you set in (5) is the one that has the unzipped binaries
    like ipy.exe, Microsoft.Scripting.Core.dll etc
  7. Add
    a reference to the Scripting dlls. Using Project->Add reference
    menu to bring up the references dialog.Now use the 'Browse' tag to locate 'Microsoft.Scripting.Dll' and 'Microsoft.Scripting.Core.dll'
    in the folder you created in step (2)
  8. Create
    a simple python file. My test python file has just the following line - print
    "hello simple dlr host"
  9. Paste
    the following code in the Program.cs file created in step (3)

using
Microsoft.Scripting.Hosting;

namespace SimpleDLRHost {

   
class Program
{

       
static void
Main(string[] args) {

           
ScriptRuntime runtime = ScriptRuntime.Create();

           
runtime.ExecuteFile(@"D:\test.py");

       
}

   
}

}

  1. Compile and run
  2. You should see the output from the python script in the
    output console of this project

 

By
now, I am sure you are thrilled about being able to write simple programs that
can host a scripting language like IronPython. This sample is the most simplest
DLR host you could write and so doesn't do anything meaningful. The focus of
this post is on setting up the environment correctly to use the API ( the classes
and methods that are part of the Microsoft.Scripting.Hosting namespace)

Using
the Hosting API, You do some very powerful things with the DLR and scripting
languages. For example, you can do things like

  1. Use
    other languages like IronRuby, Managed JScript etc...
  2. Define
    a method in python and invoke from C#
  3. Declare
    a variable in C# and access it from the script (and vice versa)
  4. Add
    user scripting support to your applications.

The
Hosting API spec has some samples that
demonstrate some of the above items. I would also be putting up some more
examples along these lines shortly here.

Further Reading