I interactively build a simple B-tree data structure in Haskell, implementing insertion and deletion, using a GADT to ensure that I maintain the structural invariant.
You can download the video as MP4 or WebM, as well as the slides I used for my YLJ13 talk, in PDF or Keynote. There’s some code on GitHub. Sorry, no subtitles yet, but you can read along with this script. You can also find the video on BitCast.