rajaraodv

//TODO Write this in Imperative v/s Functional style
const getUrlForUser = (user) => {
//todo
}
//User object
let joeUser = {
    name: 'joe',
    email: '[email protected]',
    prefs: {
        languages: {

rajaraodv

//Showing relevant parts from the Maybe implementation from ramda-fantasy lib
//See https://github.com/ramda/ramda-fantasy/blob/master/src/Maybe.js for full source

function Maybe(x) { //<-- main constructor that returns Maybe of Just or Nothing
  return x == null ? _nothing : Maybe.Just(x);
}

function Just(x) {
  this.value = x;
}

rajaraodv

//Monad - a sample implementation
class Monad {
    constructor(val) {
        this.__value = val;
    }
    static of(val) {//Monad.of is simpler than "new Monad(val)
        return new Monad(val);
    };
    map(f) {//Applies the function but returns another Monad!
        return Monad.of(f(this.__value));

rajaraodv

const add1 = (a) => a + 1;
class MyFunctor { //Custom "Functor"
  constructor(value) {
    this.val = value;
  }
  map(fn) {   //Applies function to this.val + returns new Myfunctor
   return new Myfunctor(fn(this.val));
  }
}
//temp is a Functor instance that's storing value 1

rajaraodv

//Imperative:
//Too many if-else and null checks; relying on global indexURLs; decided that "en" urls are default for any country
const getUrlForUser = (user) => {
  if (user == null) { //not logged in
    return indexURLs['en']; //return default page
  }
  if (user.prefs.languages.primary && user.prefs.languages.primary != 'undefined') {
    if (indexURLs[user.prefs.languages.primary]) {//if translation exists,
      return indexURLs[user.prefs.languages.primary];
    } else {

rajaraodv

//Step 1. Instead of..
if (user == null) { //not logged in
    return indexURLs['en']; //return default page
  }

//Use:
 Maybe(user) //Returns Maybe({userObj}) or Maybe(null). i.e. data wrapped INSIDE "Maybe"

rajaraodv

//The below gist shows how to take care of global variables and also make funcs chainable

//Global indexURLs map for different languages
let indexURLs = {
    'en': 'http://mysite.com/en',  //English
    'sp': 'http://mysite.com/sp', //Spanish
    'jp': 'http://mysite.com/jp'   //Japanese
}

//Imperative

rajaraodv

class Maybe {
  constructor(val) {
    this.val = val;
  }
  ...
  ...
  //"ap" takes another "maybe" and applies the function it's holding in itself.
  //this.val MUST be a function or Nothing (and can't be some string or int)
  ap(differentMayBe) { 

rajaraodv

//imperative
//Returns error or price including tax 
const tax = (tax, price) => {
  if (!_.isNumber(price)) return new Error("Price must be numeric");

  return price + (tax * price);
};

//Returns error or price indluding discount
const discount = (dis, price) => {

rajaraodv

var Either = require('ramda-fantasy').Either;
var Left = Either.Left;
var Right = Either.Right;

const tax = R.curry((tax, price) => {
  if (!_.isNumber(price)) return Left(new Error("Price must be numeric")); //<--Wrap Error in Either.Left

  return  Right(price + (tax * price)); //<--Wrap result in Either.Right
});