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Using Mailboxes in Elm

Max Goldstein | July 30, 2015 | Elm 0.15.1

In Elm, signals always have a data source associated with them. Window.dimensions is exactly what you think it is, and you can't send your own events on it. You can derive your own signals from these primitives using map, filter, and merge, but the timing of events is beyond your control.

This becomes a problem when you try to add UI elements. We want to be able to add checkboxes and dropdown menus, and to receive the current state of these elements as a signal. So how do we do that?

The Bad Old Days

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;; -*- mode: emacs-lisp -*-
;; This file is loaded by Spacemacs at startup.
;; It must be stored in your home directory.

(defun dotspacemacs/layers ()
  "Configuration Layers declaration.
You should not put any user code in this function besides modifying the variable
values."
  (setq-default
   ;; Base distribution to use. This is a layer contained in the directory

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use std::boxed::Box;
use std::option::Option;
use std::result::Result;
use Maybe::*;

#[derive(Debug, PartialEq, Eq)]
enum Maybe<T> {
    Nothing,
    Just(T),
}

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// Reference from: https://play.rust-lang.org/?gist=a571361967dc228330b3&version=stable
trait Shape {
  fn draw(&self);
}

struct Square;
impl Shape for Square {
  fn draw(&self)  { println!("Square drawn."); }
}

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let everythingIsDone = Rx.Observable.fromEvent(em, ‘everythingIsDone’);
let eventSource = Rx.Observable.fromEvent(em, ‘event’).takeUntil(everythingIsDone).toArray().toPromise();

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function multiBy10(n) {
  // Setup a base return
  if (n <= 1)
    return 10
  // Loop recursive here
  else
    return 10 + multiBy10(n-1)
}

/**

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// Provided that `request()` is a promise

function *something() {
  var text1 = yield request('url1')
  var text2 = yield request('url2')
  var text3 = yield request('url3')  

}

var it = something() // Start the something() generator

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// Reference from: https://github.com/Reactive-Extensions/RxJS/blob/master/doc/howdoi/eventemitter.md

var hasOwnProp = {}.hasOwnProperty;

function createName (name) {
    return '$' + name;
}

function Emitter() {
    this.subjects = {};

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The introduction to Reactive Programming you've been missing

(by @andrestaltz)

---

This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

---

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// Functors apply a function to a wrapped value and then return a wrapped value
// Functors are chainable
// Functor::(a -> b) -> f(a) -> f(b)
class Wrapper {
  constructor(val) {
    console.log('Created a wrapped value ' + val);
    this.val = val;
  }
  // Functor's `fmap` in Haskell
  map(func) {