PL-specific problem, but: the Rust borrow checker tends to give you a lot of trouble when writing iterative algorithms on nonlinear data structures, because it

PL-specific problem, but: the Rust borrow checker tends to give you a lot of trouble when writing iterative algorithms on nonlinear data structures, because it has trouble reasoning about partial borrows. The upcoming Polonius borrow checker is supposed to solve this, but it's still in alpha...