I wouldn't say Ocaml encourages using mutable data structures. You have to use a ref to have a mutable variable. Most stdlib data structure are not mutable (ope

I wouldn't say Ocaml encourages using mutable data structures. You have to use a ref to have a mutable variable. Most stdlib data structure are not mutable (operations on them return an updated structure.) Perhaps Common Lisp is a better example of a language in that part of the functional purity spectrum ?