(also not 100% sure I've wrapped my head around this correctly, so please let me know if I got it wrong and I can fix it)

Nice, thank you!

I think there's a missing space on line 133.

Pure isn't quite right, but I'm not sure how to explain it succinctly without assuming some understanding of the pure function and indexed monads, at which point it mostly speaks for itself.. maybe it'd be better to just remove it, as it isn't used much and can almost always be replaced by adding pure to any non-Render function. Maybe something like "Type alias for Render x x _, used to lift otherwise pure functionality into the Render type. Not commonly used." (I'm abbreviating a little still)

Hook is just a shorthand for Render x (newHook x) _ so it's easier to recognize a function as a hook. I almost called Render itself Hook, but this seemed to leave it a little bit more flexible for future use.

Sorry, that's not very constructive feedback, just a small thought dump. What I really need to get around to is a blog post which introduces concepts alongside relevant code, with a bit more room to explain.

Thank you for the explanation!

I've modified the PR to more closely reflect how you described things. If it still feels iffy, I could maybe drop the annotations on Pure and Hook?

Having a blog post about the library whenever you are able would certainly be awesome. :)