class spaceship is entity, positionable, canfire, collidecheck
	func oncollide(entity) {
		if (entity is smashable) {
			entity.smash()
		}
	}
	func fire() // fires a bullet
	func pos() (x, y) // returns the X and Y position of spaceship

class rock is entity, positionable, smashable
	func smash() {
		this.destroy()
	}
	func pos() (x, y) // returns the X and Y position of the bullet