This is my worked example from the 32nd meeting of the London Code Dojo. Feel free to play around with it. I've used Clojure, for no particular reason other than that's what I'm currently working in.
The source of the kata is the Diamond Kata, put simply:
Given a letter, print a diamond starting with ‘A’ with the supplied letter at the widest point.
For example: print-diamond ‘C’ prints:
A
B B
C C
B B
A
The earliest mention I could find of it was here [Seb Rose, Nov 2014]
You can find out more about the London Code Dojo at our homepage.