#include <Servo.h>

Servo myservo;  

int pos = 0;
int sensor = 2;
int state = LOW;
int val = 0;

void setup() {
  myservo.attach(9);
  pinMode(sensor, INPUT);
  Serial.begin(9600);
}

void loop(){
  val = digitalRead(sensor);
  if (val == HIGH) {
    for (pos = 0; pos <= 90; pos += 1) {
    myservo.write(0);
    delay(10);
  } 
    
    if (state == LOW) {
      state = HIGH;
    }
  } 
  else {
      for (pos = 90; pos >= 0; pos -= 1) {
    myservo.write(90);
    delay(10);
  }
      
      if (state == HIGH){
        state = LOW;
    }
  }
}