ITEC 380 2016fall ibarland

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

hw03
functions for union types
and, images intro

Due:
Sep.21 (Wed) 14:00 (hardcopy and D2L)
Your submitted file should be named “hw03.rkt” as plain-text (which is what DrRacket saves as).

Standard instructions for all homeworks (unless instructed otherwise):

• Your name, the assignment-number, and the URL of this assignment 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.
• Format well (in particular, each open-paren should be preceded by a space or start-of-line, for now).

Open DrRacket (either in labs, or you can download it to your own computer from racket-lang.org). The first time you start DrRacket, it will ask you to choose a language; select Language > Use Language... > Teaching Languages > Beginning Student, for now.

Follow the design recipe, steps 2,3 if using a new data definition; and steps 4,5,7,8.

1. Data definition: A directory-response is one of:

   • a username: a string of lowercase roman letters, whose length is in [1,14) (e.g. "ibarland"), OR
   • #false (indicating no entry), OR
   • 'private (indicating entry exists, but information is non-public).

   (15pts) Write a function which, given a directory-response, returns a string: either

   • a radford email address (e.g. “ibarland@radford.edu”), OR
   • “No such person.”, OR
   • “Information not published.”.
   corresponding to the three cases in our data-definition, respectively.
   (Be sure to give your function a good, descriptive name, of course.)

   You can think of this function as being one part of a larger program which queries a campus-directory, such as radford's, and then has to use the response it gets.

   NOTE: Your function will be given directory-responses: so if you're given a string, you can deduce (from this def'n) that its length is already in [1,14). This is not something you need to check for, or handle. You only need to distinguish between the three variants of a directory-response.

   To think about: As per the design recipe since our data-definition has three different variants, you will have a cond with how many branches? (You don't need to write a template (step 3a) separately from your final code, for this homework.)

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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)

Or, since DrRacket supports image literals (!), I could copy/paste images as the second argument to check-expects:

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2. 
   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).

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

©2016, Ian Barland, Radford University Last modified 2016.Oct.11 (Tue)

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu