nicbell

//Primitive Type Comparison
var a = 1;
var b = 1;
var c = a;

console.log(a == b);  //true
console.log(a === b); //true
console.log(a == c);  //true
console.log(a === c); //true

busypeoples

Making Impossible States Impossible in ReasonML

Introduction

If you have already seen Richard Feldman's talk entitled "Making Impossible States Impossible" or have read "Designing with types: Making illegal states unrepresentable" then you can skip the explanations and just head straight to the Reason examples.

This post is intended to display how to model your Reason Application to prevent creating impossible states. The benefits of being able to design a feature in this way include avoiding having to deal with complex test scenarios regarding defined business rules and a clear documentation of what is possible just by looking at the type definition. Long story short, let's see how this all works by implementing an example.

Requirements

lilactown

/**
 * Making promises
 */
let okPromise = Js.Promise.make((~resolve, ~reject as _) => [@bs] resolve("ok"));

/* Simpler promise creation for static values */
Js.Promise.resolve("easy");

Js.Promise.reject(Invalid_argument("too easy"));

Leonidas-from-XIV

module Let_syntax = struct
  let return = Lwt.return
  let (>>=) = Lwt.Infix.(>>=)
  let (>>|) = Lwt.Infix.(>|=)
  module Let_syntax = struct
    let bind m ~f = Lwt.bind m f
  end
end