Homework 8🔗

Last updated: Fri, 1 Nov 2024 17:15:23 -0400

Out: Mon Oct 28, 2024, 12pm (noon) EST

Due: Mon Nov 04, 2024, 12pm (noon) EST

Overview🔗

In this assignment, you will practice using accumulators by extending the TextBox from Homework 7 with a mouse handler function.

This hw will be graded accordingly:

Setup🔗

Create a new repository for this assignment by going to the CS450 Fall 2024 GitHub Organization and clicking "New".

Note: The CS450 Fall 2024 GitHub Organization must be the owner of the repository. Do not create the repository in your own account.

When done click "Create repository".

Tasks🔗

Reading

• Review the The Design Recipe section of the course website (topics that will be covered in future lectures are marked as such).

Notes and Reminders

• All code you write must now follow the The Design Recipe. (Just submitting code is no longer sufficient.)

• Signatures should use define/contract and the predicates defined in the Data Design Recipe step. You may need more more sophisticated contract constructors such as listof for this assignment.

• For Examples and Tests, do not use check-expect from the Beginning Student Language (even though the textbook says to). Instead, use check-equal? or other testing forms from rackunit.

• Examples for a function definition should come right after the define. But Tests should be put into the test-suite in tests.rkt. Try to think about corner cases and code coverage.

• Also, remember that Racket Style and The Design Recipe reserves certain language features only for specific scenarios. For example, set! and other "imperative" features are not allowed ever. Conditionals such as cond should only be used with enumeration or itemization Data Definitions.

• The submitted program must be only a series of defines (both constants and function definitions are allowed) and tests/examples. Do not run any other code, i.e., do not automatically start big-bang! Not following this this will result in GradeScope errors and point deductions.

• hw8 starter code may be available here. You may look at prior code and examples to help you but BE CAREFUL. A "COPY-AND-MODIFY" PROGRAMMING STRATEGY WILL NOT WORK IN THIS COURSE (nor in the real world). Your program will be wrong (partially because most of the design recipe steps will be wrong) and will receive a low score. Instead, you should write the code for this homework from scratch using The Design Recipe.

• NEW You may find the "Syntactic Test Coverage" feature in DrRacket useful. At minimum, one-hundred percent of your code should be run (if not tested) before submission.

• The main code should go in a file named hw8.rkt and tests should go in a tests.rkt file of the appropriate format.

  In this assignment, each function should have at minimum of one (meaningful) Example and two Tests (that are not the same as the example).

Programming

In this assignment, you will extend your TextBox from Homework 7 with a mouse handler.

Specifically, when the mouse cursor is inside the TextBox window, a "click" (i.e., "button-down" MouseEvent, see mouse-event?) should reposition the cursor in between the closest characters.

Here is an online demo that approximates what the program might look like.

Note that while we are all familiar with this action because we have all done it many many times, there is a sublety to implementing it correctly because if a click occurs when the cursor is pointing in the middle of a rendered character, the program needs to—based on whether the cursor is closer to the left or right side—determine whether to move the cursor to before or after that character.

Specifically, design and implement the following functions:

• textbox-resplit : takes a TextBox and an "X Coordinate" (as received by mouse-handler, see below) and returns a new TextBox where the "pre" component has the TextBox contents "before" the cursor, and the "post" component has the TextBox contents "after" the cursor.

  This function must use an accumulator and thus should follow the Accumulators Design Recipe.

• mouse-handler : used with big-bang on-mouse clause.

  As usual this function should follow the template for a MouseEvent (mouse-event?). More specifically, if the event key is "button-down", it should call the textbox-resplit function above to update the position of the cursor.

Before Submitting🔗

Testing

Style

All code should follow proper Racket Style.

Also, the repository itself must follow proper style. Specifically, it must have appropriate commit messages. See How to Write a Git Commit Message if you are unsure how to write a commit message.

Files

A submission must have the following files in the repository root:

• hw8.rkt: Contains the hw solution code.

  All defines should use the name specified in the exercise (ask if you are unsure) and should be provided.

  The easiest (but not always the most readable) way to ensure all necessary definitions are provided is to (initially) put as the second line in the file:

  (provide (all-defined-out))

  This automatically provides all definitions in the file. (The first line should be #lang racket)

• tests.rkt: This file should require hw8.rkt and define tests for it.

  Specifically, it should define a rackunit test-suite which contains sufficient rackunit test cases (e.g., check-equal?, etc.) for each defined function.

• README.md: Contains the required README information, including the GitHub repo url.

Submitting🔗

When you are done, submit your work to Gradescope hw8. You must use the "GitHub" Submission Method and select your hw<X>-<LASTNAME>-<FIRSTNAME> repository.

Note that this is the only acceptable way to submit homework in this course. (Do not manually upload files and do not email files to the course staff. Homework submitted via any unapproved methods will not be graded.)