Today I Learned

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Compile ReasonML With An OCaml Package Using Dune

In Compile Reason To Native With Dune, I showed how to compile a basic ReasonML file as a native executable using Dune.

Any non-trivial program will likely involve pulling in an OCaml dependency. For example, you may want to pull in Lwt. Assuming this package is available, whether you’ve manually downloaded it via opam or used something like esy, you’ll want to let Dune know that Lwt is an available library.

;; dune
(executable
 (name hello_reason)
 (libraries lwt lwt.unix))

The modules in the Lwt package will now be globally available to your Reason code.

let () = {
  Lwt_main.run(
    Lwt_io.printf("Hello, Reason!\n")
  );
};

When Dune builds your code, it will include and compile Lwt.

See a full example here.