Programming · Source Code

C# <3 Ruby

IronRuby allows you to get some of the freedom and expressiveness of Ruby in the .NET biz. world. Recently I’ve been using it as a simple game scripting language.

Warning: This post is a beginner tutorial on how to get started with hosting IronRuby inside your C# application.
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C# loves Ruby
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Step 1
Download the IronRuby binaries from Codeplex: http://ironruby.codeplex.com/ Warning: As of writing this the IronRuby 1.1.3 installer won’t install the binaries.

Step 2
Add references to IronRuby.dll, Microsoft.Csharp.dll and Microsoft.Scripting.dll to your project.
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Step 3
ScriptEngine and ScriptScope are the key classes of the Dynamic Language Runtime that allow us to run Ruby code: (Download Tutorial Source Code – Rename to Zip)

// Tutorial 1:

// Initiate the main object that drives IronRuby:
var engine = IronRuby.Ruby.CreateEngine();

// And here goes the magic:
engine.Execute( "puts 'Meow, from Ruby!'" );
// Tutorial 2:
var engine = IronRuby.Ruby.CreateEngine();

// ScriptScopes allow you to capture variables and methods
// within a specific non-global scope.
ScriptScope scope = engine.CreateScope();

// The ScriptScope API allows us to easily set variables
// from .NET:
scope.SetVariable( "score", 10 );

// You can also use Ruby to set variables:
engine.Execute( "max_score = 10", scope );

// Let us access the variables now. Note the usage of "%Q/ /"
// as a replacement of " " in our Ruby code.
engine.Execute( "puts %Q/Your score is #{score} of #{max_score}!/", scope );

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Step 4 – Domain Specific Languages
We can ‘teach’ our scripts a set of specialized methods that make it easy to interact with the problem domain. With the help of Ruby’s expressiveness our scripts will look more like a custom language that is focused on the target domain. See Teta on github for a text adventure that is build around a Ruby DSL.

# Here's a silly example from my Zelda fangame:
on_time_changed do |time|
  if time == 'DayBegan' then
    if roll_1_in 100 then
      spawn_item 'Ruby1'

      after_seconds 2 do
         fairy_says "Oh, what's that? Lucky!"
      end
    end
  end
end
// Tutorial 3 - how to get started with a Ruby DSL from C#:
var engine = IronRuby.Ruby.CreateEngine();
var scope = engine.CreateScope();

string domain =
    @"
        class Universe
            attr_accessor :underlying_theory
            attr_accessor :groups

            def initialize()
                @groups = []
            end

            def to_s
                %Q/Universe based on #{underlying_theory} is filled with: #{groups}./
            end
        end

        class Group
            attr_accessor :name
            attr_accessor :galaxies

            def initialize()
                @galaxies = []
            end
        end

        class Galaxy
            attr_accessor :name
        end
    ";

// Now teach it about our domain. You could use normal C# classes too.
// But those might be at times be more awkward to access from within Ruby.
engine.Execute( domain, scope );

string dsl =
    @"
        # DSL:
        def universe(hash)
            u = @@current_u = Universe.new()
            u.underlying_theory = hash[:based_on]

            yield if block_given?
            u
        end

        def group(named)
            g = @@currrent_g = Group.new()
            g.name = named

            yield if block_given?
            @@current_u.groups << g
        end

        def galaxy(named)
            g = Galaxy.new()
            g.name = named

            @@currrent_g.galaxies << g
        end
    ";

// 'Enable' our tiny DSL:
engine.Execute( dsl, scope );

// And lets use it to create some universes:
string ruby =
    @"
        mt = universe based_on: 'M-Theory' do
            group 'Local group' do
                galaxy 'Milky Way'
                galaxy 'Andromeda Galaxy'
                galaxy 'Triangulum Galaxy'
            end

            group 'Virgo Cluster'
            group 'Centaurus Supercluster'
        end

        hlt = universe based_on: 'HL-Theory' do
            group 'Black Mesa' do
                galaxy 'On a Rail '
                galaxy 'Questionable Ethics'
                galaxy 'Lambda Core'
                galaxy 'Nihilanth'
            end
        end

        et = universe based_on: 'Empty-World Theory'
        [mt, hlt, et]
    ";

// ScriptEngine.Execute returns our list of universes as the result of the ruby code:
dynamic universes = engine.Execute( ruby, scope );

foreach( dynamic universe in universes )
{
    Console.WriteLine();
    Console.WriteLine( universe );
}

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Step 5 – Miscellaneous Notes
I encourage you to use a Test/Specification Driven Development style when working with your Ruby scripts (It is imho a must with dynamic languages). Personally I can’t yet rate how easy/hard it is to get something like RSpec running with IronRuby and loose scripts.

The outside image of IronRuby looks a bit shady at the moment. The official website doesn’t link to the newest version, and all in all the project is fragmentted over too many different domains. It doesn’t help that the installer and Visual Studio integration (v 1.1.3) is somewhat bugged. From the inside we’ve got a very solid product that can get you some of the Ruby love inside the .NET world. Thanks to the open source community on continuing work on IronRuby and IronPython! <3

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::Edit Step 6 – Tip: Compile from Source ::Edit (30.06.2012)
To get the best experience, until the IronRuby team decides to release a new version, you should compile IronRuby from source for your target framework. This has shown to give me a great performance increase. Great work!

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Step 7 – Additional Resources
IronRuby Tutorial Source Code – Rename to Zip

IronRuby on Codeplex
IronRuby Mailing List
IronRuby Source Code
IronRuby Issue Tracker

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