More and more sites offer the ability to log in with Facebook, Twitter, or Github, which can be quite convenient, as it means fewer passwords to keep track of. Adding this kind of capability to a Ring based app is easier than you might think, using the ring-oauth2 library. In this episode we’ll demonstrate how to implement a “Sign in with Google” button. The process is very similar for other providers.

A small macro with a lot of power! We start with a quick recap of Clojure’s looping constructs, and then go over the various features and use cases of for, backed by examples taken directly from popular open source projects.

With the basics of multimethods out of the way it’s time to look at some of the more advanced uses. This episodes explores in depth Clojure’s keyword hierarchy features, some little known aspects of the isa? and type functions, and closes off with some examples that demonstrate the flexibility Clojure provides when modeling data and behavior.

Clojure provides polymorphism through protocols and multimethods. Protocols were covered in depth in episode 24. This episode provides a brief recap, then looks at multimethod basics. If you are already familiar with multimethods then you might want to skip to the second part, which covers some of lesser known aspects.