The changes were significant because Heist isn't just an API. It's an inversion of control where you provide routines that get run for various parts of your DO

The changes were significant because Heist isn't just an API. It's an inversion of control where you provide routines that get run for various parts of your DOM. They used to be functions that took a node and returned a list of nodes. In order to do the optimizations that we wanted to do we had to change the type signature of the callbacks that the users write to something that took a node and returned a special data structure. We actually did preserve the old API, so you can actually migrate without making significant changes to your code. Most of those changes are because of the general cleanup. So maybe my statement about big breaking changes was misleading. They're big breaking changes IF you want the performance increase. Otherwise things still work the way they did before. In fact, the process of implementing this refactoring impressed upon me that the old paradigm was even more important that I initially realized. If you're interested in more detail, check out the rest of the docs linked at the end. They describe the concepts in more detail with a focus on how to use them. In January I will also be giving a presentation to the New York Haskell Users Group (http://www.meetup.com/NY-Haskell/ http://www.meetup.com/NY-Haskell/) about some of the things I learned while implementing this new approach and merging it back into the original Heist code base.