Ceylon: Interfaces and mixin inheritance

	class Coordinate(x, y) {
	shared Integer x;
	shared Integer y;
	shared actual String string => "Coordinate(``x``,``y``)";
	}
	/**
	As you can see interfaces in Ceylon can provide concrete implementation of
	methods, unlike java but comparable to Scala traits.
	**/
	interface Movable {
	shared formal variable Coordinate position;
	shared Coordinate moveUp() => position = Coordinate(position.x, position.y + 1);
	shared Coordinate moveDown() => position = Coordinate(position.x, position.y - 1);
	shared Coordinate moveLeft() => position = Coordinate(position.x - 1, position.y);
	shared Coordinate moveRight() => position = Coordinate(position.x + 1, position.y);
	}
	/**
	Here we define that our class MovableObject satisfies the interface Movable
	We have to provide an actual position and get all the move methods for free
	**/
	class MovableObject(position) satisfies Movable {
	shared actual variable Coordinate position;
	shared actual String string => "Object located at ``position``";
	}
	/**
	You can also provide a position when it's not passed as constructor parameter
	**/
	class MovableObject2(Integer x, Integer y) satisfies Movable {
	shared actual variable Coordinate position = Coordinate(x,y);
	shared actual String string => "Object located at ``position``";
	}
	/**
	This demo prints the following to the console
	Object located at Coordinate(5,10)
	Object located at Coordinate(5,11)
	Object located at Coordinate(4,11)
	**/
	void interface_demo() {
	MovableObject movable = MovableObject(Coordinate(5,10));
	print(movable);
	movable.moveUp();
	print(movable);
	movable.moveLeft();
	print(movable);
	}

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