This is the seventh in a series about locals in OCaml. This episode explains the challenges around tail-call optimization and how to keep local variables from escaping their region. I introduce the [@nontail] annotation to prevent tail-call optimization, which is often needed when writing code with locals. Code used in this video: https://github.com/goldfirere/janestreet-videos/blob/main/locals/07-tails/local.ml View instructions to get the compiler I use in this video: https://github.com/janestreet/opam-repository/tree/with-extensions