Comment by rho_soul_kg_m3

In general, if it works, leave it alone; but I can think of two reasons to stop using OCaml:

1) You have been ordered to directly interface with some external library that has a complicated C ABI, and you can't isolate it in a separate process and do IPC, and the FFI would be too clunky or slow.

2) You really need to manipulate lots of bits or bytes or floats very fast, or there are lots of them, and speed or memory footprint is becoming an issue. You need to multicore and/or SIMD, you need efficient abstractions, and you do that kind of thing all over the place, not just in a few functions that you separately implement in C or whatever.

As a bonus here's a good reason for NOT leaving OCaml: You can quickly bootstrap the compiler and run it on small embedded machines. I remember using OCaml on a Cyrix 686 with 64 megs I think, it was perfectly fine. Today, the lights dim a bit when I start cargo build.