OCaml is not a very good fit for competitive programming, you're better off with a language like Python there.
Writing code in a functional language like OCaml requires a mind switch. This can take quite a while. It took me years to really 'get it' after having programmed for 30 years in imperative languages. Now I prefer writing code in FP for a lot of things, but not for everything.
E.g. for coding some algorithms you have a much easier time when you can use mutable arrays.
A nice advantage of OCaml is, IMO, that it is not so strict about pure FP. E.g. unlike in Haskell, arrays are mutable by default.
> As long as you no longer refer to the old instance, this is as efficient as a mutable array.
On paper this is true, in reality though it probably is not. Immutable Haskell arrays are implemented with pointers, mutable arrays are implemented as contiguous memory allocations, so they have great cache locality.
Writing code in a functional language like OCaml requires a mind switch. This can take quite a while. It took me years to really 'get it' after having programmed for 30 years in imperative languages. Now I prefer writing code in FP for a lot of things, but not for everything. E.g. for coding some algorithms you have a much easier time when you can use mutable arrays.
A nice advantage of OCaml is, IMO, that it is not so strict about pure FP. E.g. unlike in Haskell, arrays are mutable by default.