Anyone wants to work on real, used-in-production OCaml code, take a look at the various libguestfs virt tools:

https://github.com/libguestfs/libguestfs/tree/master/v2v

https://github.com/libguestfs/libguestfs/tree/master/builder

https://github.com/libguestfs/libguestfs/tree/master/customi...

https://github.com/libguestfs/libguestfs/tree/master/resize

https://github.com/libguestfs/libguestfs/tree/master/sparsif...

https://github.com/libguestfs/libguestfs/tree/master/sysprep

One great no-nonsense feature of OCaml is that you can just link programs directly to C code, include a tiny C wrapper, and call straight into C with virtually no overhead (literally no overhead for functions that don't need to allocate on the OCaml heap).