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Using and Abusing Ruby for Computer Science Great Good

This Talk/Workshop was given at:

You can get the latest slides here (PDF).

This owes a lot to is basically stolen from Chapter 6 of Understanding Computation by Tom Stuart. It's a great book and worthy of your time. It goes into a lot more detail than this talk does, including showing how to add some of the bits that were skipped for this talk, such as recursion.

The Wikipedia page on Church Encoding is also a great companion to this talk, although it contains spoilers for the exercises. It provides some alternative solutions to the problems, and shows you how to derive some of the trickier solutions, like MINUSONE.


You will need a recent version of Ruby installed and to be able to run command on the terminal or Windows prompt. Take a look at the Ruby Quickstart if you're having trouble.

You don't need to know ruby to follow this talk :)

Running irb in your terminal should bring you to a ruby prompt.

If you want to use the unit tests in this repository, you will need to install the dependencies. To do this you will need to have Bundler installed, and run bundle install in the root of the repository. It is recommended that you install the dependencies locally by specifying a path:

➤ bundle install --path vendor/bundle

Using this repository

Once you have the dependencies installed, start an irb session in the root of this project, and load the exercises by running load "./exercises.rb":

irb(main):001:0> load "./exercises.rb"
=> true

Now, just run the test method to run the unit tests. They will guide you through all the exercises.

I have included possible solutions in the solutions branch, but I would highly recommend at least trying to solve the problems yourself before taking a look. The insight gained in figuring out some of these problems on your own – and the feeling of joy when you do – can't be gained by looking at a solution.

The MINUSONE function is tricky, and will take some thinking.