【SICP练习】79 练习2.51

练习2.51

通过书中前面的内容，我们知道below中来将框架分成上下两部分，而beside将框架分成左右两部分。因此，below定义如下：

(define (below painter1 painter2)

  (let ((split-point (make-vect 0.0 0.5)))

     (let ((paint-top (transform-painter painter2

                                      split-point

                                       (make-vect 1.0 0.5)

                                      (make-vect 0.0 1.0)))

           (paint-down (transform-painterpainter1

                                        (make-vect 0.0 0.0)

                                         (make-vect 1.0 0.0)

                                        split-point)))

       (lambda (frame)

             (paint-top frame)

             (paint-down frame)))))

另一种利用上一题中的rotate270等可以很容易的实现：

(define (below painter1 painter2)

     (lambda (frame)

          ((flip-horiz

               (rotate90

                   (beside

                       (rotate270

                          (flip-horizpainter1))

                       (rotate270

                          (flip-horizpainter2)))))

           frame)))

【SICP练习】79 练习2.51

原文：http://blog.csdn.net/nomasp/article/details/43907459