I got history working in my editor and I like how simple of a structure it is. It was pretty straightforward as I ignore memory issues and just save every version of the document. You can imagine how expensive this can get in just a few minutes of editing. I should really write a better data structure that can keep track of just the changes rather than the entire document. It actually wouldn't be much work as all I'd need to do is keep track of the command that was run and the line it was run on. I already do that for the comments.
https://github.com/Krowemoh/aae