I come from a functional background (significant work in SML and Ocaml) and went into learning Rust excited to implement all my favorite persistent data structu

I come from a functional background (significant work in SML and Ocaml) and went into learning Rust excited to implement all my favorite persistent data structures, only to find myself foiled by borrow and lifetime madness similar to what’s described in the naive implementation in the OP. Where I could define a simple tree in one line of SML, I struggled to define one at all in Rust! (I think my problem actually just came down to the lifetime on the object holding the tree itself and the way I was instantiating nodes; but when those lifetime compiler warnings popped up my eyes would glaze over and I knew it was time to put rust down for the day) I imagine Haskell programmers have a step up because the Monad system is significantly less forgiving than SML’s look-the-other-way approach to side effects, and in this sense Haskell and Rust are more similar than many other functional languages.