linedemo程序画一个矩形、一个椭圆、一个圆角矩形和两条线段，不过不是按这一顺序。程序表明了定义封闭区域的函数实际上对这些区域进行了填入，因为在椭圆后面的线被遮住了-procedures linedemo draw a rectangle, an oval, a rounded rectangle and two line segments, but not in that order. Procedures show that the definition in fact a functi