ITEC 380 2017fall ibarland

home—lectures—recipe—exams—hws—D2L—breeze (snow day; distance)

func-and-image-intro
defining functions
hw02

Due: Sep.11 (Mon) 15:00, on D2L and hardcopy.
Your submitted file should be named “hw02.rkt” . (To save toner/ink, your hardcopy can omit the images that are already exactly in this assignment, and you may print in black-and-white.)

Standard instructions for all homeworks:

• Your name, the assignment-number, and the URL of this assignment-page must be in a comment at the start of the file.
• Any code which results in syntax errors will generally not earn more than 50% of the points-possible. For grading, I will ignore any commented-out code (including commented-out tests).
• If your hardcopy is more than 1page, it must be stapled.
• Format well. (In particular, each open-paren should be preceded by a space or start-of-line, for now. E.g. (+ 2 (* 3 4 5)), not ( + 2(* 3 4
  5)
  ).)

1. (10pts) Recall from lecture, we demo'd the steps of writing a simple function, pizza-area, which computed the area of a pizza given diameter. We will write a couple of similar functions.

   Of course, Pizzas have topping in the middle, and crust around the edge. (You can think of the full pizza being a disc, with a smaller pure-topping-covered disc inside of it.)

   1. Define a named-constant CRUST-WIDTH, which should be 2 inches.
   2. Some people ignore the crust of a pizza, and just want to know how much topping-covered area they'll be getting when they order a pizza. Write topping-area, which returns the amount of pizza covered in topping (in square-inches), for a given diameter (in inches).
   3. Other people love the crust, and only care about how much crust¹ is on their pizza! Write crust-area, which returns the amount of exposed crust (in square-inches) for a pizza of a given diameter (in inches).

   For now, your code does not need to give a correct answer for pizzas whose diameter is less than twice the CRUST-WIDTH. However, you should still have tests for that situation, which contain the true, expected answer in the check-expect.

   (So, it’s fine if those tests don’t pass. If you really want to get your code working for that case -- again, NOT required -- you can either read about cond, or be clever in using the functions max or min.)

2. (10pts) Write the function has-suffix?, which takes in two strings and returns whether or not the first string ends with (the letters of) the second.

   Note that this is a computer-sciency definition of “suffix”. It has nothing to do with syllables or English. More precisely: we say that string a has b as a suffix, iff: there exists a string x such that (string=? a (string-append x b))².

   hint:You can certainly use cond (or if) if you like, but they're not actually needed; you can instead use a min or max in a clever (but standard) way.

   `if`: We will mention if in class on Friday.

Images in racket

To experiment with functions-which-create-and-handle-images in DrRacket, include (require 2htdp/image) near the top of your file. Then you should be be able to evaluate each of the following:

(rectangle 80 20 'solid 'blue)
(circle 20 'solid 'red)
(ellipse 80 20 'outline 'orange)

(beside (rectangle 80 20 'outline 'blue)
        (circle 20 'solid 'red))
(underlay (rectangle 80 20 'outline 'blue)
         (circle 20 'solid 'red))
; Think of 'underlay' and 'beside' as being "addition for images"

; underlay with an offset:
(underlay/offset (rectangle 80 20 'outline 'blue)
                0
                10
                (circle 20 'solid 'red))


; If you want to explore documentation:
;   In DrRacket, position the caret on a function-name
;   like 'underlay', and hit F1.

Test cases for images

For functions that return an image, your expected-value should either be (a) an expression involving calls to: the image primitives and/or previously-tested functions, OR (b) an image-literal (but, show the expressions you used to create that image-literal).

For example, if the problem were to "create a function that takes in a width, and returns a solid purple rectangle with the given width and a 16:9 aspect ratio", then the "expected result" part of the test cases might involve calling the image-library's functions like rectangle:

(check-expect (screen 32) (rectangle 32 18 'solid 'purple))
(check-expect (screen 16) (rectangle 16 9 'solid 'purple))
(check-expect (screen 0) (rectangle 0 0 'solid 'purple))
  ; Note: for the expected 0x0 rectangle, I could equally well write:
(check-expect (screen 0) empty-image)

3. 
   1. (3pts) Write a function which takes in a size, and returns an image of a brown donut. (Mmmm, doughnut.)
   2. (3pts) Write a function eyes which takes a size and a color, and returns two colored rings side-by-side.
   3. (4pts) As needed, refactor the above functions so that there is little-to-no repeated code. (If the underlying helper function has a solid set of tests, the final function might get by with fewer tests — perhaps even just one.) Only turn in your refactored versions.

   You only need steps 4,5,7,8 of the design recipe (once you decide what how you'll represent "size", which is a straightforward choice), and we're only using existing, simple datatypes (so no steps 1-3 or 6).

4. (10pts) Consider programs that create meme images, such as:

   (check-expect (super-cool-ski-instructor-meme "spend all semester making memes") )

   That expected-result was created from the expression:
   
   This code uses a helper scale-to-width (source); you'll want to open that file in DrRacket then copy/paste it near the top of your own hw02.rkt. (It’s not a hard function — one that I could have required as part of the homework. Just cite the URL, as you do for any code taken from the web.) Note that this code requires internet access.
   1. Give one more test-case for super-cool-ski-instructor-meme.
   2. Write the code for super-cool-ski-instructor-meme.
      (No additional test-cases required.)
   3. Write a test case for futurama-fry-meme in addition to the one shown here:

      (check-expect (futurama-fry-meme "the image-library is easy" "Java's GUI library is hard") )

   4. Write the code for futurama-fry-meme.
      (No additional test-cases required.)
   5. Write one additional meme-making function based on some image from imgflip.com/memetemplates. Include 1-2 test cases.

   6. We notice that there is a lot of repeated code in our functions — very ugly.
      We will refactor it out.

      Task: Write a more general function make-meme, and change your preceding three functions so that they are EACH very-short calls to make-meme. You should not change their behavior at all, nor change any of the existing test cases.

      It is up to you to decide how many parameters (and their type) to provide to make-meme. It should be general enough so that it can create almost all standard memes, though you don't need to worry about having multiple-lines of text at the top or bottom, nor about having the font size work differently than the examples I provided.

      Only submit your refactored versions of the functions for (b),(d),(e) — you don’t need to (and, shouldn’t) keep the original versions around.

conditions/requirements

In addition to the standard instructions for all hws above, here are some requirements for our homeworks:

• For every functions you write, follow the design recipe, steps 4,5,7,8. (You don't need to label each step; just turn in the final result.) When grading, there are points for having a good purpose-statement, good tests, etc. In general, test cases alone can be worth nearly half the points.

• Your programs should be racket’s beginning-student language (for now).
• Don't repeat code!
  For example: If you find yourself repeating similar calculations to what’s already in pizza-area, see if you can avoid the repeated calculations by calling pizza-area as a helper-function (perhaps a couple of times).

home—lectures—recipe—exams—hws—D2L—breeze (snow day; distance)

©2017, Ian Barland, Radford University Last modified 2017.Sep.08 (Fri)

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