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将大问题拆分成小问题3.1 电影院利润问题;; profit : number -> number;; to compute the profit as the difference between revenue and costs;; at some given ticket-price(define (profit ticket-price) ...);; revenue :...

How to Design Programs 第二版作者 Matthias Felleisen, Robert Bruce Findler, Matthew Flatt, Shriram Krishnamurthihttp://www.ccs.neu.edu/home/matthias/HtDP2e/index.html Preface 序言好的专职的程序设计需要系统性的思考，...

(+ 2 2)(* 3 3)(- 4 2)(/ 6 2)字符串> "hello world""hello world"字符串合并> (string-append "hello" "world")"helloworld"> (string-append "hello " "world")"hello wo

Exercise 1. Add the following definitions for x and y to DrRacket’s definitions area:(define x 3)(define y 4)Now imagine that x and y are the coordinates of a Cartesian point. Write down an expressi...