function calculateArea(shape: Shape): number {
  switch(shape.__typename) {
    case 'Circle':
      return Math.PI * (shape.radius ^ 2);
    case 'Rectangle':
      return shape.width * shape.height;
    case 'Square':
      return shape.side ^ 2;
    case 'Triangle':
      return (shape.base / 2) * shape.height;
    default:
      const nope: never = shape;
      return nope;
  }
}