I’ve made NIF’s in C, C++, Rust, OCaml, and Terra (basic ‘hello world’ experiment there). Not hard at all. 
Rustler is a fantastic library for Rust to make building NIF’s easy!
Indeed, make sure it is truly worth it. Calling a NIF and marshaling the data across has overhead as well so just making a NIF that adds 2 numbers will actually be a LOT slower than doing it in per BEAM/Erlang/Elixir.
Hear hear!
Plus you don’t need erlport at all, just use the normal Port interface on the BEAM. Those libraries only help when you are talking with programs that are not Port aware, but if you can make the program yourself and just talk over stdin/stdout as proper then nothing special is needed.
OCaml has a GC but OCaml is designed to be linked safely and securely (and type safe) with C interfaces, and NIF’s are C interfaces, so it works fine. Just you might want to mark your NIF’s as CPU using so they get marshalled to another thread, just in case.
You can communicate with any program from any language that supports standard stdin/stdout communication, no libraries needed. Libraries can help for marshalling data via ETF or JSON or whatever of course, but you could use text just as easily.
That is just a library for reading/writing the ETF format across stdin/stdout (which is pretty easy to write it yourself actually, it is a dead-simple binary format). You could just as easily use JSON or text or whatever you want too.
You’d be surprised, OCaml runs at about the same speed as Rust and would be substantially shorter code (plus significantly faster to compiler, Rust compiles horribly slow). Rust would be the better option if you are doing a lot of low level SIMD work or so though.
