From Youtube: Arduino Event-Based Programming (Source, etc: github.com/johnnyb/)

// ===================================================================
// demonstrate event driven programming
// (for every event we want a function)
// -------------------------------------------------------------------
//What it does:
// blink LED (on/off) controlled by switch
// -------------------------------------------------------------------
// From: https://www.youtube.com/watch?v=QvQAl-zbiCI
//       Arduino Event-Based Programming
// -------------------------------------------------------------------
// Source code, etc: github.com/johnnyb
// ===================================================================

# include <Eventually.h>

# define LEDPIN    5
# define SWITCHPIN 2

EvtManager mgr;

// -------------------------------------------------------------------
// ---- setup
// -------------------------------------------------------------------

void setup() {
  pinMode(LEDPIN,OUTPUT);
  pinMode(2,OUTPUT);

  // -----------------------------------------------------------------
  // could add listeners here but it is also done in startBlink
  // so just do startBlink
  // add listener to time, every 1000 miliseconds call function
  // add pin listener, start/stop blinking LED
  // mgr.addListener(new EvtTimeListener(1000,true,(EvtAction)BlinkLight));
  // mgr.addListener(new EvtPinListener(SWITCHPIN,(EvtAction)stopBlink));
  // -----------------------------------------------------------------
  startBlink();
}

// -------------------------------------------------------------------
// ---- blink LED
// -------------------------------------------------------------------

bool blinkstate = false;
bool blinkLight() {
  if (blinkstate) {
    blinkstate = false;
    digitalWrite(LEDPIN,LOW);
  } else {
    blinkstate = true;
    digitalWrite(LEDPIN,HIGH);
  }
  return false;
}

// -------------------------------------------------------------------
// ---- stop blinking LED
// -------------------------------------------------------------------

bool stopBlink() {
  mgr.resetContext();           // remove all listeners
  mgr.addListener(new EvtPinListener(2,(EvtAction)startBlink));
  return true;                  // stop event cycle
}

// -------------------------------------------------------------------
// ---- start blinking LED
// -------------------------------------------------------------------

bool startBlink() {
  mgr.resetContext();           // remove all listeners
  // add listener to time, every 1000 miliseconds call function
  // add pin listener, start blinking LED
  mgr.addListener(new EvtTimeListener(1000, true, (EvtAction)blinkLight));
  mgr.addListener(new EvtPinListener(SWITCHPIN, (EvtAction)stopBlink));
  return true;                  // stop event cycle
}


USE_EVENTUALLY_LOOP(mgr)