Exercise 2.48 · 习题

Exercise 2.48: A directed line segment in the

plane can be represented as a pair of vectors—the vector running from the

origin to the start-point of the segment, and the vector running from the

origin to the end-point of the segment. Use your vector representation from

Exercise 2.46 to define a representation for segments with a constructor

make-segment and selectors start-segment and end-segment.

练习 2.48：平面中的有向线段可以表示为一对向量——从原点到线段起点的向量，以及从原点到线段终点的向量。利用练习 2.46 中的向量表示，定义线段的表示，包括构造函数 make-segment 和选择函数 start-segment、end-segment。