This appears very similar (my Haskell is a bit rusty) to the problem description in Real World OCaml (https://dev.realworldocaml.org/imperative-programming.html

This appears very similar (my Haskell is a bit rusty) to the problem description in Real World OCaml (https://dev.realworldocaml.org/imperative-programming.html https://dev.realworldocaml.org/imperative-programming.html), although made easier by the use of non-pure functions there.