#define BUTTON 4
#define LED 2

boolean buttonState = HIGH;

void handleButtonPress() {
  buttonState = digitalRead(BUTTON);
}

void setup() {
  pinMode(BUTTON, INPUT);
  pinMode(LED, OUTPUT);
  attachInterrupt(digitalPinToInterrupt(BUTTON), 
    handleButtonPress, CHANGE);
  digitalWrite(LED, HIGH);
}

void loop() {
  if (buttonState == LOW) {
    digitalWrite(LED, LOW);
  } else {
    digitalWrite(LED, HIGH);
  }
}