andymatuschak

A composable pattern for pure state machines with effects

State machines are everywhere in interactive systems, but they're rarely defined clearly and explicitly. Given some big blob of code including implicit state machines, which transitions are possible and under what conditions? What effects take place on what transitions?

There are existing design patterns for state machines, but all the patterns I've seen complect side effects with the structure of the state machine itself. Instances of these patterns are difficult to test without mocking, and they end up with more dependencies. Worse, the classic patterns compose poorly: hierarchical state machines are typically not straightforward extensions. The functional programming world has solutions, but they don't transpose neatly enough to be broadly usable in mainstream languages.

Here I present a composable pattern for pure state machiness with effects,

steipete

# The trick is to link the DeviceSupport folder from the beta to the stable version.
# sudo needed if you run the Mac App Store version. Always download the dmg instead... you'll thank me later :)

# Support iOS 15 devices (Xcode 13.0) with Xcode 12.5:
sudo ln -s /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/15.0 /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport

# Then restart Xcode and reconnect your devices. You will need to do that for every beta of future iOS versions

# (A similar approach works for older versions too, just change the version number after DeviceSupport)

paulirish

/* bling.js */

window.$ = document.querySelectorAll.bind(document);

Node.prototype.on = window.on = function (name, fn) {
  this.addEventListener(name, fn);
};

NodeList.prototype.__proto__ = Array.prototype;

gist:bb1e911cc54f0f695821

// by dave @ bees & bombs >:)

int[][] result;
float t;

float ease(float p) {
  return 3*p*p - 2*p*p*p;
}

float ease(float p, float g) {

gist:7225d966e3ffc3eaff1a

// gif by dave whyte >:)

int[][] result;
float t;

float ease(float p) {
  return 3*p*p - 2*p*p*p;
}

float ease(float p, float g) {

gist:e7fbae56ed3dfb2c7834

// by dave @ bees & bombs

int[][] result;
float t;

float ease(float p) {
  return 3*p*p - 2*p*p*p;
}

float ease(float p, float g) {

gist:6bc37347274caf7665ca

// by dave @ bees & bombs >:)

int[][] result;
float t;

float ease(float p) {
  return 3*p*p - 2*p*p*p;
}

float ease(float p, float g) {

gist:3a7a03a119921a969e94

// by david whyte >:)

void setup() {
  setup_();
  result = new int[width*height][3];
  result_ = new int[width*height][3];
}

int[][] result, result_;
float time;

gist:7824bc6f9e06c31992f8

// by dw @ bees & bombs

int[][] result;
float t;

float ease(float p) {
  return 3*p*p - 2*p*p*p;
}

float ease(float p, float g) {

gist:8d2d3c1dcd95a8abf4ba

// by david >:)

int[][] result;
float t;

float ease(float p) {
  return 3*p*p - 2*p*p*p;
}

float ease(float p, float g) {