TheSeamau5

// HELPER FUNCTIONS
const has = (entity, components) => {
  const exists = (x) => typeof x !== "undefined";
  return components.map((component) => exists(entity[component]))
                   .reduce((x,y) => x && y);
};

const clone = (object) => {
  if (object === null || typeof object !== 'object'){
    return object;

TheSeamau5

import Graphics.Collage (..)
import Graphics.Element (..)
import Graphics.Input (..)
import Color (..)
import Signal (..)

import Text
import List
import Mouse

TheSeamau5

import Html exposing (Html, Attribute)
import Html.Attributes
import Html.Events
import Signal exposing (Address)
import List
import String
import StartApp

------------------
--- HELPER CODE --

TheSeamau5

#Exploring Entity Component Systems in Elm

Entity-Component-System (or ECS) is a pattern for designing programs that is prevalent in the games industry. This pattern consists of three simple parts:

• Entity : A uniquely identifiable object that may contain any number of components
• Component : A property usually representing the raw data of one aspect of the object. (Position is a component, Velocity is a component, Strength is a component, etc...)
• System : A continuous process performing actions on every entity that possesses a component of the same aspect as that system

To understand this, let us try to make a simple example: Boxes that move in space:

TheSeamau5

#include <string>
#include <functional>

using namespace std;

template <typename T>
struct Maybe{
  T just;
  bool isNothing;
};

TheSeamau5

import Svg (Svg, circle, svg, g, line, text)
import Svg.Attributes (cx, cy, r, fill, stroke, strokeWidth, x, y, x1, x2, y1, y2, fontSize, style)
import Html
import Html.Attributes as Html

import Signal (Signal, map, foldp)
import DragAndDrop (mouseEvents, MouseEvent(..))
import List

--------------

TheSeamau5

macro eval_with_params(expr, params...)
    # Put the params before the expression
    expr_with_params = [collect(params)..., expr]
    
    # Wrap the expressions in :block Expressions
    Expr(:block, expr_with_params...)    
end

@eval_with_params(
    x + y, 

TheSeamau5

--------------------------
-- CORE LIBRARY IMPORTS --
--------------------------
import Task         exposing (Task, ThreadID, andThen, sequence, succeed, spawn)
import Json.Decode  exposing (Decoder, list, int, string, (:=), map, object2)
import Signal       exposing (Signal, Mailbox, mailbox, send)
import List

---------------------------------
-- THIRD PARTY LIBRARY IMPORTS --

TheSeamau5

----------------------------
----- TYPE DEFINITIONS -----
----------------------------

Entity : Object

Component : Object

DeltaTime : Component 
  deltaTime : Number

TheSeamau5

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 */
'use strict';

var React = require("react-native");

var {
  AppRegistry,