CSci 1301: Lab 7

Due: Friday, November 30th at 11:59pm

The lab is done in groups of 2 or 3.
Your goal is to explore abstraction by starting with two or three examples and generalizing to a function that takes another function as a parameter. Use examples on the resources page for similar tasks that we did in class.

Make sure to switch DrRacket language to Intermediate student with lambda (even if you are not using lambda.

Since we haven't spent much time on writing general signatures, you are not required to write them. However, correct signatures for the general functions in tasks 1 and 2 would give you 2 points of extra credit each (and a good attempt would give you partial credit).
Signatures for specific functions (for instance, functions that take a list of numbers) are required.

Task 1: All elements satisfy a condition (10 points).

  1. Write a fucntion takes a list of numbers and returns #true if all elements of the list are odd and #false otherwise. Make sure to test the function well.
  2. Write a helper function take takes a string and returns #true if the string has length of 5 characters or less and #false otherwise.
    Once it's written and passes the tests, write a function that takes a list of strings and returns #true if all elements of the list are of length 5 or less and #false otherwise. You must use your helper function.
  3. Generalize the functions in the previous 2 questions to write the function all? that takes a list and a predicate and returns #true if all the elements on the list satisfy the predicate and #false otherwise.
    Before you start, write check-expects to use all? to perform the tasks in the first two questions. In the first case the predicate that you pass to it is odd?. In the second case it's the helper function in question 2.
  4. Use the general function in question 3 to return #true if all numbers on a list of numbers are negative. Hint: use the predicate negative?.

Note: do not use andmap for this problem. Write your own recursive functions.

Task 2: First element that satisfies a condition (10 points).

  1. Write a function that finds and returns the first odd element in a list of numbers. If there are no odd elements, #false is returned.
  2. Write another function that follows the same pattern (returns the first element that satisfies a condition, or #false if there is no such element), but works on a different data type (such as a list of strings, or images, or structures).
  3. Generalize from the previous two examples, just like you did in Task 1. Write the tests first, then the description, and then function (the signature is optional).
  4. Add two more examples of using the general function with predicates that are different from what's used in questions 1 and 2.

Task 3: Using predefined functions (10 points).

In this task you will be using map and filter general functions given here to perform different tasks. You can use helper functions when the functions that you need you need to pass to map or filter aren't defined in Racket. You may use lambda if you would like (see section 17.1 in the book), but this is by no means required.

Below are a couple of examples for using the predefined functions (without a lambda): 


;; using map to produce square roots of a list of numbers:
(map sqrt (list 0 1 2 4 5))

;; legal? : posn -> boolean
;; The function takes a position structure and returns
;; #true if it's within 400-by-400 scene, and #false
;; otherwise
(define (legal? p)
  (and (>= (posn-x p) 0) (<= (posn-x p) 400)
       (>= (posn-y p) 0) (<= (posn-y p) 400)))

;; using filter and a helper function legal? to select only legal
;; positions in a list of position structures
(filter legal? (list (make-posn 200 0) (make-posn 401 50) (make-posn -10 200) (make-posn 100 300)))

Your task is to use map and filter to do the following:

  1. Given a list of numbers, create a list of red circles of the radiuses given in the list.
  2. Given a list of numbers, create a list of their absolute values.
  3. Given a list of position structures, create a list of positions in which the x and the y coordinates are switched (so a position with x = 10, y = 20 in the given list becomes a position with x = 20, y = 10 in the returned list)
  4. Given a list of colors, return a list of all of the same colors except yellow.
  5. Given a list of numbers, return a list of only exact numbers on the list. For instance, (sqrt 2) is not an exact number.

How to submit

Name your file with the combination of your last names, no spaces, followed by the word "Lab" and the lab number. For instance, if your last names are Smith and Lee, the file name should be SmithLeeLab7.rkt If there are others in the class with the same name as yours, you your initial in addition to your last name: MSmithJLeeLab7.rkt

At least one person in the group must submit it via canvas as a file upload (make sure it's that .rkt file). Make a comment indicating who you worked with. The other person (or people) in the group may submit the same file and also indicate who was in the group or just make a comment listing all your group members (note: if you don't submit a note listing your group members, your work may not be counted, even if your group partners list you as the group member).

CSci 1301 course web site.