I've just dome the Happy Numbers kata in Clojure.
It's a simple kata that can be a lot of fun.
I used a mix of TDD and REPL-driven development to code it.
These are the resulting tests in Midje:
and this is the code:
To document the process I commited the code after every passing test and every refactoring. I also commited the REPL history.
You can find the commits step by step here
and the code in this repository in GitHub.
I used memoize to avoid repeated computations.
In the next days I will try other suggested optimizations based on the properties of happy numbers.