Sorry, to clarify I mean that by design OCaml = Reason. The only way it would not be possible to link the two would be with artificial restrictions. Though they are very different looking, they share the exact same semantics, type system, module system, compiler pipeline, etc. Past parsing, the two languages become the same. I used necessity to mean that for ReasonML to exist, it must be possible (rather than that all Reason programs must necessarily import native OCaml code).