Thanks, this was my initial thought as well! Generally: https://ncatlab.org/nlab/show/recursion+scheme https://ncatlab.org/nlab/show/recursion+scheme (I'm actu

Thanks, this was my initial thought as well! Generally: https://ncatlab.org/nlab/show/recursion+scheme https://ncatlab.org/nlab/show/recursion+scheme (I'm actually kind of surprised ncatlab has this article!)