Coderunner is an app for OSX that makes it easy to run quick bits of code in a variety of languages. It is perfect for someone just experimenting with a particular language. For working with Ruby, I like to use RVM not only use different versions of Ruby, but also to create very specific gemsets. Getting this functionality to work with Coderunner proved a bit of challenge as the documentation is lacking, so I thought I would post the steps I took.
In this example, I will go through the setting up of a RVM environment for Ruby 1.8.7-p357 with a gemset called "my-gemset". I have already created the gemset for this example using the rvm 1.8.7@my-gemset --create command. It is important to note that the RVM environment must be configured prior to applying the settings to Coderunner.
With the RVM environment setup, the next thing to do is open up the Coderunner preferences and look at the languages. There are quite a few