[sfvisser]

Note that deriving Traversable for you own datatypes mean changing the structure to map effect over, the `t` variable. Not the effect `f`, which is generic and the Monad/Applicative in this case.

Besides Maybe/Either `t` could represent anything, like container types Lists/Trees/Hashmaps etc, but also more complicated structures like syntax trees for programming languages or custom DSLs. Or (my favorite use case!) recursive command types for robot control. I'm doing this mostly in Rust, but borrow all the ideas from Haskell.