But this is fun stuff, so I couldn't help creating a simple gist to demonstrate the concept: https://gist.github.com/sebastiaanvisser/cd6ee46356e3ecc8945...

The trick is to keep all the combinators specific to your data type. In Haskell you can derive your functor (and applicative/foldable/traversable) and have a single cata to rule them all. In Rust you build them specifically for every datatype. Less neat, but could still be totally worth it!