Assignment 4

Due Date : 10/9 @ 11:59pm

Note

For each function that you design you are expected to follow the Design Recipe in the same way as we did in class. Failure to show all your work for each step will cost you points.

Problem 1

The local meteorological society keeps records about the weather each day. They track the following attributes: humidity (as a percentage), zip code, and high and low temperatures for the day.

Design a data definition and provide an interpretation for these records. Design a function that computes the average temperature for the given day.

Problem 2

A movie store sells two kinds of movies: regular and classic. For regular movies, they track the product id (a string, such as "234-87-1DX"), its base price, and the number of years it has been in their collection. For each year a movie is in stock, it is marked down by 3.5% of the base price, but no movie is sold for less than $2. For classic movies, they track the product id (again, represented as a string), and its price, which is never discounted.

Design a data representation for the store's items and a function that computes the current price of an item. (Think of the program in a cash register and how it computes the current price from the price tag.)

Problem 3

Below is a data definition for a class of shapes (See the code at the bottom). Add an interpretation for the Square and Rectangle classes. Both represent shapes whose borders are parallel to the borders of a canvas (window).

Develop the template for functions that consume Shapes.

1. Use the template to design shape-shift-x. The function consumes a Shape, sh, and a number, delta. It produces a shape that is like shbut shifted by deltapixels along the x-axis.
2. Use the template to design shape-in?. The function consumes a Shape, sh, and a Posn, p, and determines whether p is inside (or on the boundary) of sh.
   
   Domain Knowledge: for a point to be within a circle, its distance to the center must be smaller than (or equal to) the radius. For a point to be within a rectangle, its x coordinate must be between the x coordinate of the left line and the x coordinate of the right line. How do you compute the x coordinates of these lines? Naturally something analogous must hold for the y coordinates. Remember that squares are just special rectangles.
   
   
3. Use the template to design shape-draw. The function consumes a Shape, sh and a Scene, sc and adds sh to sc.

Hint: most of the exercises do not depend on each other. If you're stuck with one, try another one.

;; --- copy and paste into DrRacket --- 
;; Shape is one of: 
;; -- Circle 
;; -- Square 
;; -- Rectangle 


(define-struct circl (x y r outline c))
;; A Circle is a
;;  (make-circl Number Number Number Boolean Symbol)
;; interpretation: x and y determine the center of the circle,
;;   r the radius, outline whether it's outlined or solid, 
;;   and c its color

(define-struct squar (x y size outline c))
;; A Square is a
;;  (make-squar Number Number Number Boolean Symbol)
;; interpretation: Supply a good interpretation of Square.

(define-struct recta (x y width height outline c))
;; A Rectangle is a
;;  (make-recta Number Number Number Number Boolean Symbol)
;; interpretation: Supply a good interpretation of Rectangle.

;; ... problem solving steps ... 

;; inspect for expected results:
(define sh (make-squar 100 100 50 true 'red))
(define pt (make-posn  130 130))

(shape-in? sh pt)
(shape-draw (make-circl 130 130 5 true 'red) 
  (shape-draw sh 
     (empty-scene 300 300)))