SICP問題2.51

上下に並べるペインタ(1つ目が下で2つ目が上)
1. beside に似た実装

(define (below painter1 painter2)
  (let ((split-point (make-vect 0.0 0.5)))
    (let ((paint-bottom
	   (transform-painter painter1
			      (make-vect 0.0 0.0)
			      (make-vect 1.0 0.0)
			      split-point))
	  (paint-top
	   (transform-painter painter2
			      split-point
			      (make-vect 1.0 0.5)
			      (make-vect 0.0 1.0))))
      (lambda (frame)
	(paint-top frame)
	(paint-bottom frame)))))

2. beside + rotation による実装

(define (below painter1 painter2)
  (rotate90 (beside (rotate270 painter1) (rotate270 painter2))))