我們先定義一個數據結構 Position

struct Position {
    double x;
    double y;
};

struct Position Position(double x, double y)
{
    struct Position position;
    position.x = x;
    position.y = y;
    
    return position;
}

// 判斷一個 Position 是否在圖形內
typedef BOOL (^region_t)(struct Position p);

// 將原有的 region 平移 offset 之后，生成新的 region_t
region_t shift(region_t region, struct Position offset)
{
    return ^(struct Position position) {
        return region(minus(position, offset));
    };
}