facebook/reason と BuckleScript で JavaScript の関数を呼び出すパターン

とくに新出のトランスパイラだと、バインディングが少ないので、いかにしてFFI叩くかが勝負になる

参考: https://bloomberg.github.io/bucklescript/Manual.html

main.re

let add a b => a + b;
Js.log "this is console.log";
Js.log(add 3 4);

/* function call */
external imul : int => int => int = "Math.imul" [@@bs.val];
Js.log(imul 3 4);

/* function call with unit */
external now : unit => int = "Date.now" [@@bs.val];
Js.log(now());

/* new */
external create_date: unit => string = "Date" [@@bs.new];
Js.log(create_date());

/* value */
external dirname : string = "__dirname" [@@bs.val];
Js.log dirname;

/* require */
external resolve_path : string => string => string = "resolve" [@@bs.val] [@@bs.module "path"];
Js.log(resolve_path "a" "b");

コンパイル後

// Generated by BUCKLESCRIPT VERSION 1.5.2, PLEASE EDIT WITH CARE
'use strict';

var Path = require("path");

function add(a, b) {
  return a + b | 0;
}

console.log("this is console.log");

console.log(7);

console.log(Math.imul(3, 4));

console.log(Date.now());

console.log(new Date());

console.log(__dirname);

console.log(Path.resolve("a", "b"));

exports.add = add;
/*  Not a pure module */