Assignment 8

Due Date : 12/06 @ 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

Write a function find-string that takes in a Listof[String] and a String and that returns a Boolean, true if and only if the given string was in the list.

Abstract find-string to generic-find-string so that the string comparison operation it uses is a parameter. Then use this abstraction to define find-string-case-sensitive, which should operate the same way as the original find-string, and find-string-case-insensitive, which has the same contract as find-string but which ignores the case of alphabetic characters when comparing strings (i.e. the character a is considered the same as A and so on; non-alphabetic characters must still match exactly).

Problem 2

DrRacket has lots of abstract functions for processing lists (pg. 313, Sect. 21.2, or the online version).

Given the following data definitions: 

;; A Grade is: (make-grade Symbol Number)
(define-struct grade (letter num))

;; The Symbol in a Grade represents

;;    'A  >= 90
;;    'B  >= 80
;;    'C  >= 70
;;    'D  >= 60 
;;    'F  < 60

;; A Listof[Grades] ...
(define grades 
  (list (make-grade 'D 62) (make-grade 'C 79) (make-grade 'A 93) (make-grade 'B 84) 
        (make-grade 'F 57) (make-grade 'F 38) (make-grade 'A 90) (make-grade 'A 95)
        (make-grade 'C 76) (make-grade 'A 90) (make-grade 'F 55) (make-grade 'C 74)
        (make-grade 'A 92) (make-grade 'B 86) (make-grade 'F 43) (make-grade 'C 73)))

Design the requested functions to manipulate Grades. You must use the given list as one of your tests. For each you may use a local function.

Note: if you do not use the DrRacket loop function mentioned, you will not recieve credit for the sub-problem!

  1. Design the function log->lon that converts a Listof[Grade] into a Listof[Number] that contains just the numerical grade, using the Scheme function map.
  2. Using foldr, design the function best-grade that finds the highest Grade in a Listof[Grade].
  3. Design a function just-As that returns a list of only the 'A grades, using filter.
  4. Use andmap to design the function all-pass? that checks to see if all the Grades in a given list are not 'F.
  5. Finally design the function bonus that adds 5 to all of the Grades in a given list, and updates the letter portion of the Grade if it changes. Use map to design your function... it must return a Listof[Grade]!

Problem 3

Use local and "loops" (abstractions such as map, filter, foldr, etc) wherever your functions may benefit from them, especially for the lists of objects in your Space Invaders game.