> I'm no OCaml programmer but glancing at the beginning of the Real World OCaml's chapter on FFI, it appears OCaml uses dlsym() to look up functions at runtime, whereas Rust can outright link to them like any C program would
This is not a limitation of OCaml but a deliberate choice of the authors of Real World OCaml to use the ctypes library. The OCaml implementation also supports directly linking with C code. What you need:
* Your ordinary C code
* Some C stubs that do the conversion between regular C types and the C types the OCaml runtime uses. Usually they are quite trivial, just use the few macros that OCaml ships with.
* Some type signatures to tell the type system what types your C stubs expect as that can't be inferred.
Generally I think the system is pretty easy to understand and use. Overall it is pretty neat to have two alternatives on how to do FFI, so you can pick the type of FFI (dynamic/static) exactly as your project requires.
You have to write C stubs? I'm glad it's possible, but that's still quite unfortunate. On Rust's side, you usually have to write wrappers around your C FFI functions in order to do any type translation and to add any necessary safety, but those are at least written in Rust (and are not actually necessary to call C, just necessary to provide a safe idiomatically-correct Rust API; you could just vend the C FFI functions directly if you wanted to).
This is not a limitation of OCaml but a deliberate choice of the authors of Real World OCaml to use the ctypes library. The OCaml implementation also supports directly linking with C code. What you need:
Generally I think the system is pretty easy to understand and use. Overall it is pretty neat to have two alternatives on how to do FFI, so you can pick the type of FFI (dynamic/static) exactly as your project requires.