ReasonML native compilation with Dune

Index

1. Natively compile ReasonML
2. Use OCaml libraries in your program

Compiler du ReasonML avec Dune. Dune est un outil d’aide à la compilation de grand projets pour OCaml.

Information mostly took from : joshbranchaud.

1. Natively compile ReasonML

Dune is “a composable build system for OCaml” with out-of-the-box support for ReasonML. Dune can be used for a lot of things, but in simplest terms it can be used to compile ReasonML programs into native executables.

Considering the following ReasonML program :

/* hello_reason.re */
print_endline("Hello, Reason!")

We can then create the following Dune build file (named dune) :

;; dune
(executable
 (name hello_reason))

Then running the dune build hello_reason.exe command will compile the hello_reason.re into a hello_reason.exe executable binary that can be found in ./build/default.

We can also run dune exec hello_reason.exe which will firstly build the .exe if needed (if the sources have been updated).

Read more in the Quickstart guide of Dune.

2. Use `OCaml` libraries in your program

For instance, if you need an OCaml library in your ReasonML program, instruct Dune about it :

(executable
 (name hello_reason)
 (libraries yojson)
)

We should really provide the library :

$ eval (opam env)
$ opam install yojson

Now we can use the Yojson library in our code :

// month_nb.re
open Yojson.Basic
open Yojson.Basic.Util
let month_nb_json = from_file ("../../month_nb.json")
let () = print_endline(show(member("comment", month_nb_json)))

$ dune exec month_nb.re
`List ([`String ("Name: month_nb.json");
         `String ("Desc: contains the regexp tree of month number deternimation by month_nb.js");

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