You lot crack me up. I'm the author of the video, and it's clear to me that you didn't watch much of it. You'll find your Tree at 6.15. Indeed, the external interface of this whole thing consists of "Tree", "insert" and "delete". Is that clear enough for you?
And also bear in mind that this is a screencast, so you can't ask me to scroll around the code while I'm building it in front of you. You can either have descriptive identifiers, or you can have more than 10% of the implementation visible at a time. Not both. And frankly, it's my video, which I spent over 200 hours writing and producing, so I think I get to make that choice.
I indeed didn't watch the video, and the part I've seen I watched with audio muted. That's because I'm not that interested in Haskell and because I've built many BTrees in many different languages already. Because of this my comment was not aimed at you specifically, which I felt was clear in my first post.
I'm not criticizing your work, rather I point out a larger trend in one community. You should stop being that emotionally attached to your work, because there are people out there who will criticize your work directly. I'm not one of them, however.
I'm also not familiar with making screencasts, but I would suppose that there are some tools for displaying outline of the code. For example, the Speedbar extension for Emacs is able to outline the types, variables and function definitions declared in a module. Take a look here: http://cedet.sourceforge.net/speedbar-multi-2.jpg (the left-most one).
Anyway, I'm not in position to criticize your work, and I never did it. So please stop referring to me as "you lot" and save it for when (not if) it will be really necessary.
And also bear in mind that this is a screencast, so you can't ask me to scroll around the code while I'm building it in front of you. You can either have descriptive identifiers, or you can have more than 10% of the implementation visible at a time. Not both. And frankly, it's my video, which I spent over 200 hours writing and producing, so I think I get to make that choice.