Web Development with ReasonML

Hiding Type Information

Consider this short module that defines a “time of day” type as a record with fields for the hour and minute:

miscellanea/misc/src/RegularType.re

/* Interface */
module type Time {
  type t = {
    hour: int,
    minute:int
  };

  let make: (int, int) => t;
  let add: (t, t) => t;
};

/* Implementation */
module Time: Time = {
  type t = {
    hour: int,
    minute:int
  };

  let make = (h:int, m:int): t => {
    {hour: abs(h) mod 24,
     minute: abs(m) mod 60}
  }

  let add = (t1: t, t2: t): t => {
    let total = (t1.hour * 60 + t1.minute) +
      (t2.hour * 60 + t2.minute);
    make(total / 60, ...