10_Modules.md

Modules

Every file is a module Everything is exported from module

let greetings = (~hello="Hello", ~world="World", ()) =>
  Js.log({j|$hello $world|j});

Submodules

module Math = {
  module Tools = {
    let times = (x, y) => x * y;
    let square = x => times(x, x);
  };
};

Interface definitions

module type MathToolsInterface = {
  let times: (int, int) => int;
  let square: (int) => int;
};

module Math: MathToolsInterface = {
  let times = (x, y) => x * y;
  let square = x => times(x, x);
};

We can do that in rei files:

type t = string; /* A */

let make = (): t => "";
let logStr = (str: string, log: t): t => log ++ str ++ "\n";

let print = (log: t) => print_string(log);

Abstract types: hiding internals

We can define abstract type in rei files:

type t;
let make: (unit) => t;
let logStr: (string, t) => t;
let print: (t) => unit;

Using modules

• By qualified names
• Opening them (Belt, Js)
• Opening them locally

let () = Log.(
  make()
    |> logStr("Hello")
    |> logStr("everyone")
    |> print
);

Including modules

module LogWithDate = {
  include Log;
  let logStrWithDate = (str: string, log: t) => {
    let dateStr = Js.Date.toISOString(Js.Date.make());
    logStr("[" ++ dateStr ++ "] " ++ str, log);
  };
};
let () = LogWithDate.(
  make()
    |> logStrWithDate("Hello")
    |> logStrWithDate("everyone")
    |> print
);

Disclaimer: Some examples taken from the following book Exploring ReasonML