How to use Jane Street's Core with Reason?

Question

I'm new to OCaml and I'm trying to try (:P) Facebook Reason syntax. I cannot find a way to make this compile because if cannot find the Core module (already installed with opam).

I'm trying to compile a sample program from Real World OCaml

open Core.Std;

let rec read_and_accumulate accum => {
  let line = In_channel.input_line In_channel.stdin;
  switch line {
    | None => accum
    | Some x => read_and_accumulate (accum +. Float.of_string x)
  }
};

let () = printf "Total: %F\n" (read_and_accumulate 0.);

This is the command I'm using for compilation: rebuild accum.native.

When I have this in _tags (from the instructions in https://janestreet.github.io/installation.html)

true: package(core,ppx_jane)
true: thread,debug

My error changes but I still don't know what to do:

File "_tags", line 1, characters 6-28:
Warning: tag "package" does not expect a parameter, but is used with parameter "core,ppx_jane"
File "_tags", line 1, characters 6-28:
Warning: the tag "package(core,ppx_jane)" is not used in any flag or dependency declaration, so it will have no effect; it may be a typo. Otherwise you can use `mark_tag_used` in your myocamlbuild.ml to disable this warning.
+ /Users/David/.opam/4.02.3/bin/ocamldep.opt -modules -pp refmt -impl accum2.re | tee accum2.re.depends accum2.ml.depends
accum2.re: Core Float In_channel
+ /Users/David/.opam/4.02.3/bin/ocamlc.opt -c -g -thread -pp '-g -thread' -pp refmt -o accum2.cmo -intf-suffix .rei -impl accum2.re
File "accum2.re", line 1, characters 5-13:
Error: Unbound module Core
Command exited with code 2.
Compilation unsuccessful after building 2 targets (0 cached) in 00:00:00.

What do I have to do to use Core with Reason?

Adopting the syntax is pretty easy and I have only been reading for a couple hours, but there's zero docs about how to use Reason for non OCaml users.

Traherne

Have you achieved compilation since asking this question? I'm currently struggling with the same issue. – Glindaglinka

I'm afraid not. Still stuck with the same step. Without deeper knowledge into OCaml tooling it's impossible. This has something to do with what rebuild that but it's a bash script doing many things around ocamlbuild so I have not idea what most of the output even means. :( – Traherne

Answer 1

Basically the tags indicated in https://janestreet.github.io/installation.html have to be added plus three more flags and values used for this case:

• -linkpkg for static linking I assume
• -pp refmt indicating the ReasonML preprocessor
• -impl file.re to tell what file to read

So if the file's called accum.re it can be compiled to a native binary with:

ocamlfind ocamlc -g -thread -package ppx_jane -package core -pp refmt -linkpkg -o accum.native -impl accum.re

Traherne

Answer 2

It seems there has been a recent bug fix of the issue in the Reason repo. Basically, since rebuild turns out to be a wrapper around reasonbuild it's possible to work around the bug by running reasonbuild directly:

env OCAMLFIND_COMMANDS="ocamlc=$(which reopt)" reasonbuild -use-ocamlfind accum.native

In fact, reasonbuild -use-ocamlfind accum.native also works here.

Intertwine

is this from head? or is this in stable? In 0.6 I think it still doesn't work – Traherne

From the GitHub repo it seems this is currently only in master, it's possible to install reason from this commit with OPAM, e.g. opam pin add -y reason 'https://github.com/facebook/reason.git#44aa9f4695e14c247c29c4fbc98ca10dcf332eab', but as this is not a release this is probably not recommended – Intertwine

Answer 3

I guess rebuild is a wrapper around ocamlbuild. Just call it with the parameter -use-ocamlfind.

Vesperal

That's indeed what I think it's but it's hardly a solution. If you could help with real indications that would be much appreciated. I tried with -pkg core also using -use-ocamlfind without any luck. – Traherne