#include <Servo.h>
#include <Toggle.h>

const byte servoPin = 3;
const byte buttonPin = 12;
enum {SERVO_0, SERVO_90} servoPosition = SERVO_0;
Toggle button;
Servo servo;

void moveTo0() {
  servo.write(0);
  servoPosition = SERVO_0;
}

void moveTo90() {
  servo.write(90);
  servoPosition = SERVO_90;
}

void setup() {
  button.begin(buttonPin);
  servo.attach(servoPin);
  moveTo0();
}

void loop() {
  button.poll();
  if (button.onPress()) {               // we got a new button press
    switch (servoPosition) {            // handle the change based on current position
      case SERVO_0:  moveTo90(); break; // we were at 0°, move to 90°
      case SERVO_90: moveTo0();  break; // we were at 90°, move to 0°
    }
  }
}