» Assignments » Assignment 1: Shapes
In this assignment, you will build a Haskell program that uses the CodeWorld API to draw colourful shapes on the screen, including lines, polygons, rectangles, circles, squares and parallelograms.
This assignment is worth 10% of your final grade.
Deadlines:
Part A: Monday August 23, 2021, at 09:00am Canberra time sharp Part B: Friday September 3, 2021, at 11:00pm Canberra time sharp Part C: Saturday September 4, 2021, at 11:00pm Canberra time sharp
Indicative marks and feedback for Part A will be returned in week 6.
Required Knowledge
If you have finished the week 3 lab, you should be able to complete Part A.
If you have finished the week 4 lab, you should be able to complete the majority of the assignment. Some parts require recursion over lists, which is covered in the week 5 lab.
Overview of Tasks
Task 1: Helper Functions
Task 2: Rendering Shapes
Task 3: Handling Events
Optional Extensions
Technical Report
COMP1100 Marks
20 marks
30 Marks
35 Marks
0 Marks
15 marks
Part A of the assignment requires you to complete task 1. Part B of the assignment requires you to complete tasks 2 and 3. As you complete each task (or even each function within a task), you should commit and push your work with a sensible commit message. Part C of the assignment requires you to write a technical report which documents your program, explains how it was tested, and justifies your design choices. You should work on your report while you work on part B, but it is due separately.
The purpose of Part A is to give you an opportunity to collect feedback on your code and your progress in the course, and for us to give you an indicative mark for your work so far. This will be returned to you before the census date. Part A will be re-marked alongside your Part B and C submissions, giving you a final mark for the assignment.
Getting Started
1. Fork the assignment repository and create a project for it in VSCodium, following the same steps as in Lab 2. The assignment repository is at https://gitlab.cecs.anu.edu.au/comp1100/comp1100-assignment1.
2. Add our version of the repository as a remote called upstream . This allows us (the tutors) to provide additional fixes if they are required. You do this by doing the following:
1. Go to the command palette in VSCode (or VSCodium) by pressing Ctrl + Shift + p
2. Type git remote
3. Click Git: Add Remote…
4. Put the following URL as the remote url: https://gitlab.cecs.anu.edu.au/comp1100/comp1100-assignment1.git 5. Enter upstream into the box for the remote name
OR
In the terminal
1. Make sure you are in the directory
2. Type https://gitlab.cecs.anu.edu.au/comp1100/comp1100-assignment1.git`
Overview of the Repository
Most of your code will be written to Haskell files in the src/ directory. We are using the model-view-controller pattern to structure this
assignment. Each file is called a module, and we use modules to group related code together and separate unrelated code. Model.hs
The model is a data type that describes the state of the running program. The program will move to new states (new values of type Model ) in response to user actions, as defined by the controller.
comp1100-assignment1
git remote add upstream
View.hs
The view turns the model into something that can be shown on the screen; in this project, that is the CodeWorld Picture type. Controller.hs
The controller considers user input (and other events), along with the current model, and uses that to decide what the new model should be. Other Files
tests/ShapesTest.hs contains some unit tests – simple checks that verify small parts of your program are working correctly. You are not required to write tests for this assignment, but you might find it useful to do so. You will be required to write similar tests in assignments 2 and 3.
tests/Testing.hs is a small testing library used by tests/ShapesTest.hs . You are not required to understand it for this assignment.
app/Main.hs ties your functions together into the final program that runs. You are not required to understand it. comp1100-assignment1.cabal tells the cabal build tool how to build your assignment. You are not required to understand this file,
and we will discuss how to use cabal below.
Setup.hs tells cabal that this is a normal package with no unusual build steps. Some complex packages (that we won’t see in this course) need to put more complex code here. You are not required to understand it.
Overview of Cabal
cabal is the build tool for Haskell programs and libraries. It provides several useful commands:
cabal v2-build:Compileyourassignment.Youmaywanttorunthiscommand(orcabalv2-replcomp1100-assignment1`)every time you make a slight change to your code. By doing so, you can check whether your program compiles, and if not you will see a (usually) helpful error message you can use to help fix the problem. If you don’t understand an error message, you are welcome to ask about it on piazza without sharing your code.
cabal v2-run shapes : Build your assignment (if necessary), and run the shapes program. The program will crash if it ever makes a call to a function that is undefined , so you will need to complete a few of the functions before this will be useful.
cabal v2-repl comp1100-assignment1:RuntheGHCiinterpreteroveryourproject.Thisgivesyouthesameghcienvironment you use in labs, but with the assignment code loaded. (Aside: REPL is the name for interactive sessions like GHCi – it stands for read- eval-print loop. Many modern languages have REPLs.) We have done some pattern-matching for you to use in
, and so when you first call cabal v2-repl comp1100-assignment1 , you will probably see some warnings. You do not need to fix these until part B.
cabal v2-test : Build and run the tests. Tests will abort on the first failure, or the first call to a function that is still undefined . You should execute these cabal commands in the top-level directory of your project: ~/comp1100/assignments/assignment1 (i.e.,
the directory you are in when you launch the VSCodium Terminal for your project). Overview of the Program
You use a web browser to interact with the shapes program that you launched with cabal v2-run shapes . Once you have completed the assignment, it will respond to the following actions:
src/Controller.hs
defined but not used
Action
Esc (key) M (key)
C (key)
T (key)
(key)
D (key)
Click-drag-release (mouse)
Click (mouse) Spacebar (key) = / + (key)
– / _ (key)
Effect
Clear the canvas
Display a mystery image
Cycle colour (of shape to draw) Cycle tool (type of shape to draw) Remove the last added shape
Print the current Model to the terminal (useful for testing)
When not drawing polygons, draw a shape between the click-point and release-point.
When drawing polygons, add a point.
When drawing a polygon, finish drawing the polygon, adding it to the canvas. Otherwise, nothing. When drawing parallelograms, increase the area of the next parallelogram to be drawn by 1 unit
When drawing parallelograms, decrease the area of the next parallelogram to be drawn by 1 unit, to no less than 1 unit.
Backspace /
Delete
Task 1: Helper Functions (20 marks)
The easiest way to solve a large problem is often to break it apart into smaller, easier problems. Programming is the same. In this task you
will write some helper functions that will make future tasks easier. You can test your implementations by running cabal v2-test . The functions you need to write for this task are:
Tool
toolToLabel in src/View.hs . This function should return instructions for the user on how to use each Tool , according to the following table:
Label
LineTool
“Line… click-drag-release”
PolygonTool
“Polygon… click 3 or more times then spacebar”
RectangleTool
“Rectangle… click-drag-release between opposite corners”
CircleTool
“Circle… click-drag-release between opposite points on the circumference”
ParallelogramTool
“Parallelogram… +/- to increase/decrease size, then click-drag-release”
SquareTool
“Square… click-drag-release between opposite corners”
Note: At the time this assignment is released, the course will have only briefly covered lists. You do not need to manipulate lists to write toolToLabel ; you can use a blank pattern ( _ ) to ignore them.
nextColour in src/Controller.hs . This function should return the next colour in our set of ColourName s:
Argument Result
Black
Blue
Blue Green
Green
Orange Red
Purple
Purple
Yellow
Yellow
Orange
Red
Black
nextTool in src/Controller.hs . This function implements tool-switching, but should not change Tool if the user is halfway through an operation:
If the tool is not holding a point (that is, a non- PolygonTool tool holding (in all fields) or a holding the empty list [] ), select the next tool in the following sequence: Line -> -> -> ->
Parallelogram -> Square -> Line -> ….
If there is a Point stored in the given tool (because it’s holding a Just value in any Maybe Point field, or the list in
PolygonTool is non-empty), return the argument unchanged.
When switching from the circle tool to the parallelogram tool, set the area field in the parallelogram tool to 1 unit. If any of this is unclear, study the nextToolTests in test/ShapesTest.hs .
Nothing
Polygon
PolygonTool
Note: At the time this assignment is released, the course will have only briefly covered lists. You can write the PolygonTool case for nextTool without using list recursion. Use [] to match an empty list. In a subsequent case, give the entire list a name like points to
match any nonempty list (or find a way to use the blank pattern!).
Part A ends here.
Submitting Part A
Your submission for Part A should include implementations of toolToLabel , nextColour , and nextTool , that compile without warnings and pass the tests run by cabal v2-test . You are welcome to continue working on Parts B and C of your assignment and committing and pushing changes, so long as the code continues to compile and the tests continue to pass.
Part B begins…
Task 2: Rendering Shapes (30 marks)
In src/View.hs ,
currently does not work, because function to convert the
converts your Model type into a CodeWorld Picture , so that it can be displayed on the screen. It is . In this task you will fill in that missing piece, building up a
from your Model into a . You can test these functions individually by using cabal v2- to show small pictures on the screen. You can also test everything as a whole by
modelToPicture
[ColourShape]
colourShapesToPicture
undefined
Rectangle
Circle
Picture
repl comp1100-assignment1
, using
drawingOf
cabal v2-run shapes
launching the program with and pressing the M key to show the mystery image. The functions you need to write for this task are all in :
colourNameToColour : This function turns your ColourName type from the model into a CodeWorld Colour . You should check the CodeWorld documentation for information on colours.
shapeToPicture : This function turns your Shape type into a CodeWorld Picture . You will need to consider the constructors for Shape individually, and work out the best way to turn each one into a Picture . Here are some hints to help you along:
CodeWorld has no function to draw a single line segment. It does have a function to draw a line made of multiple segments –
polyline .
Polygons, rectangles, squares, circles and parallelograms should be drawn as solid (filled) Picture s.
Rectangles should have two sides parallel to the $x$-axis and two sides parallel to the $y$ axis. The two Point s given are opposite corners.
The two Point s given for squares are opposite corners. Their sides may face any direction.
The two Point s given for circles are opposite points along the circle’s circumference.
Parallelograms should have two sides parallel to the x -axis, and area equal to the given Double . Given this, for any specified pair of opposite corners and given area, there will either be zero, one or two possible parallelograms that can be drawn. In the case where there are two possible parallelograms, draw the one that results in the smaller angles at the given opposite corners, so the other two (unspecified) corners are as close together as possible. This will also be the parallelogram with the smaller perimeter. If there are zero possible parallelograms, you should make a call to error (i.e., error “shapeToPicture: Your Error Message Here” ). This will only happen when both Point s have the same y -coordinates, and so the two parallel horizontal lines will have no space between them.
Most of CodeWorld’s functions draw individual shapes centred on the origin – (0, 0) . You will need to figure out how to slide (translate) the generated Picture so it winds up where it’s supposed to go. Drawing diagrams will help. The abs function will also help – it computes the absolute value of its argument (i.e., abs x == x if x > 0 , and abs x == negate x otherwise).
While CodeWorld has no function for parallelograms, it does have a function that can draw parallelograms.
You do not need to finish this task before moving on to others. If you have written code to render Rectangle s but nothing else, you
can create a drawing out of Rectangle s only, and check that your other functions work, before returning to finish shapeToPicture . : This function should render the Shape and colour it using the Colour that corresponds to the given
.
colourShapesToPicture : This function should turn every ColourShape in a list into a single Picture . You will need to recurse over the input list. If you have not yet completed Lab 5, you may want to work on other parts of the assignment and come back to this.
colourShapeToPicture
ColourName
src/View.hs
Here is an example of the mystery image for you to test yours against:
Task 3: Handling Events (35 marks)
It is now time to tackle handleEvent in src/Controller.hs . CodeWorld calls this function whenever something interesting happens (like a key press, a pointer press, or a pointer release). This function is called with two arguments:
The Event that just happened, and
The current Model at the time the Event happened.
handleEvent then returns a new Model for the program to use moving forward.
(Aside: Elm is a functional programming language that uses a similar pattern to build front-end web applications that are compiled to
JavaScript.)
Let’s trace a simple interaction. If the user wants to draw a purple line by clicking on the screen at coordinates
at coordinates . starting at a blank canvas, the state would transition as follows, starting with the initial model:
1. Model [] (LineTool Nothing) Black
2. The user presses “C” to change the colour from black to purple:
Model [] (LineTool Nothing) Purple
3. The user presses the mouse button at changing the state to
Model [] (LineTool (Just (1.0,1.0))) Purple
and releasing the mouse
4. The user releases the mouse button at changing the state to
Model [(Purple, Line (1.0,1.0) (2.0,2.0))] (LineTool Nothing) Purple
)1 ,1(
)2 ,2( )1 ,1(
)2 ,2(
ColourName
Note that the Tool and the do not reset to the default values after a shape has been drawn. However, the s inside the tool reverts to . The size of the next parallelogram to be drawn should not be reset.
Task 3.1: Handling Mouse Input
CodeWorld provides a few different event constructors for mouse input, but the ones we’re interested in here are PointerPress for when the user clicks, and PointerRelease for when the user releases the mouse button.
Maybe Point
Maybe Point
event arrives, you will need to store it in the current Tool . For everything except PolygonTool , you will store it in argument. For PolygonTool , you will add it to the list of vertices.
event arrives, we can ignore it for PolygonTool . We’ll finish polygons using the spacebar in Task 3.2. For will mean the end of a click-drag-release action, so you should construct the appropriate shape and
When a the
Task 3.2: Handling Key Presses
To handle keyboard input, CodeWorld provides a KeyPress event. This case is already present in the assignment skeleton, because we have implemented some keyboard functionality already. In the “Overview of the Program” section, we listed the full set of keyboard commands that your program will respond to. You need to implement the missing functionality for these keys:
Key Effect
C Cycle colour (of shape to draw)
T Cycle tool (type of shape to draw)
Remove the last added shape
Spacebar When applicable, finish drawing a valid polygon, adding it to the canvas.
+/= When applicable, increase the size of the next parallelogram to be drawn by one unit. -/\_ When applicable, decrease the size of the next parallelogram to be drawn by one unit.
If you have made it this far, you should not need to write a lot of code to implement these. A few hints: Think back to Task 1.
with no shapes drawn should not crash the program.
should only add valid polygons to the canvas. Pressing space bar when this is not possible must also not crash the
program.
Nor should any other unexpected input. Try to test all unexpected cases.
Drawing a parallelogram of zero or negative area does not make sense, and so it should not be possible for your parallelogram tool’s area field to go below 1 unit.
Task 4: Optional Extensions (0 Marks)
You are welcome to attempt extensions so long as that does not inhibit the function of tasks 1-4, but will not attract marks for completing them. You are welcome to discuss these extensions in your report, but this is not necessary, even for perfect marks.
If you change the behaviour of tool or colour switching, you may want to adjust the tests in `tests/ShapesTest.hs’ so they continue to pass. They must continue to compile without errors.
Note: Extension functionality must be executed through the codeworld API just like the rest of the assignment. Interactions should be received through the function, which you will need to modify. If you need to add fields to the model, please do so after the existing ones:
Task 4.1
Allow the user to delete multiple shapes using the mouse. The user should enter some kind of ‘‘mouse delete mode’’ and then delete multiple shapes at once by pressing the mouse button and dragging a rectangle around them. When the user releases the mouse, any shape that is wholly within the rectangle should be deleted.
If you wish, you may implement a clipboard (cut, copy and paste) instead of just delete. If you do, make sure to clearly document how this can be used in your report.
Task 4.2
Add a free-hand drawing tool. When using this tool, moving the mouse with the button pressed should draw short lines or curves, as if a pen were being dragged across the screen. When the button is released, the program should stop drawing.
When a
everything else, a
add it to the
too. For the parallelogramTool , if both $y$-cooridinates are the same, you should clear the tool without adding the impossible parallelogram to the list of ColourShapes . (If you have done task 2 correctly, doing so would cause your program to crash!)
in the Model . You should also remove the starting point from the current Tool , so that future shapes draw properly
Task 4.3
PointerPress
PointerRelease
[Shape]
PointerRelease
Backspace /
Delete
Backspace /
handleEvent
Delete
Nothing
Spacebar
data Model = Model [ColourShape] Tool ColourName YourField1 YourField2 …
Add the ability to select and move a shape using the keyboard. How you select shapes, how you move them, and how you enter and leave the ‘‘keyboard movement’’ mode is up to you. But make sure you document how this should be done clearly in your report.
Task 4.4
Preview shapes as the user draws them. If the user has started to draw a shape, then you should show the shape currently being drawn using a hollow (not solid) rectangle, polygon, circle, or square. For polygons and paralellograms, you should not give a preview until at least two points have been saved.
Task 4.5
Extend Task 4 so that you can reflect about any line that crosses through the origin ( ). You should give a convinient way to select such a line and to action the reflection. After completing this exercise, you will have created the functionality of task 4 twice, this time more generally. As such, after successfully completing this task, you may remove your task 4 code.
Task 4.6 (Difficult)
Each time a new shape is added to the canvas, check whether its perimeter intersects with that of other shapes. If it does, mark the point(s) of intersection with a small x. When a shape is removed, the x’s at any intersections with that shape should also be removed. You may use appropriate approximations for circles to simplify this task.
Part C: Technical Report (15 marks)
You should write a concise technical report explaining your design choices in implementing your program. The maximum word count is
1000. This is a limit, not a quota; concise presentation is a virtue.
Once again: These are not required word counts. They are the maximum number of words that your marker will read. If you can do it in
fewer words without compromising the presentation, please do so.
Your report must be in PDF format, located at the root of your assignment repository on GitLab and named Report.pdf . Otherwise, it may
not be marked, or will be marked but with a penalty. You should double-check on GitLab that this is typed correctly. The report must have a title page with the following items:
Your name
Your laboratory time and tutor Your university ID
Content and Structure
Your audience is the tutors and lecturers, who are proficient at programming and understand most concepts. Therefore you should not, for example, waste words describing the syntax of Haskell or how recursion works. After reading your technical report, the reader should thoroughly understand what problem your program is trying to solve, the reasons behind major design choices in it, as well as how it was tested. Your report should give a broad overview of your program, but focus on the specifics of what you did and why.
Remember that the tutors have access to the above assignment specification, and if your report only contains details from it then you will only receive minimal marks. Below is an potential outline for the structure of your report and some things you might discuss in it.
Introduction
If you wish to do so you can write an introduction. In it, give: A brief overview of your program:
how it works; and
what it is designed to do.
If you have changed the way the controls work, or added something that may make your program behave unexpectedly then it would be worth making a note of it here.
This section is particularly relevant to more complicated programs.
Content
Talk about why you structured the program the way you did. Below are some questions you could answer: Program design
Describe what each relevant function does conceptually. (i.e. how does it get you closer to solving the problems outlined in this assignment spec?)
How do these functions piece together to make the finished program? Why did you design and implement it this way?
What major design choices did you make regarding the functions that you’ve written and the overall structure of your program?
Assumptions
Describe assumptions you have made about how a user might use the program and how this has influenced your design decisions.
Testing
)0 ,0(
How did you test individual functions?
Be specific about this – the tutors know that you have tested your program, but they want to know how.
Describe the tests that prove individual functions on their own behave as expected (i.e. testing a function with different inputs and doing a calculation by hand to check that the outputs are correct).
How did you test the entire program? What tests did you perform to show that the program behaves as expected in all (even unexpected) cases?
Again, be specific – did you check that you can draw shapes from left to right? What about right to left? A circle and a square are each defined by opposite points on their perimeter – did you check that a circle fits perfectly within a square drawn from the same two input points?
Have you checked edge cases (this is a computer science term that refers to unexpected or unlikely inputs that may cause a program to crash or behave in strange ways)? It is not likely that someone would try to change the tool halfway through drawing a shape, but it is essential that it has behaviour defined for that scenario. Describe similar tests that you have done to ensure the program can handle all inputs.
Inspiration / external content
What resources did you use when writing your program (e.g., published algorithms)?
If you have used resources such as a webpage describing an algorithm, be sure to cite it properly at the end of your report in a ‘References’ section. References do not count to the maximum word limit.
Reflection
Discuss the reasoning behind your decisions, rather than what the decisions were. You can reflect on not only the decisions you made, but the process through which you developed the final program:
Did you encounter any conceptual or technical issues?
If you solved them, describe the relevant details of what happened and how you overcame them.
Sometimes limitations on time or technical skills can limit how much of the assignment can be completed. If you ran into a problem that you could not solve, then your report is the perfect place to describe them. Try to include details such as:
theories as to what caused the problem;
suggestions of things that might have fixed it; and
discussion about what you did try, and the results of these attempts.
What would you have done differently if you were to do it again
What changes to the design and structure you would make if you wrote the program again from scratch?
Are parts of the program confusing for the reader? You can explain them in the report (in this situation you should also make use of comments in your code).
If you collaborated with others, what was the nature of the collaboration? (Note that you are only allowed to collaborate by sharing ideas, not code.)
Collaborating is any discussion or work done together on planning or writing your assignment. Other info
You may like to briefly discuss details of events which were relevant to your process of design – strange or interesting things that you noticed and fixed along the way.
This is a list of suggestions, not requirements. You should only discuss items from this list if you have something interesting to write. Things to avoid in a technical report
Line by line explanations of large portions of code. (If you want to include a specific line of code, be sure to format as described in the “Format” section below.)
Pictures of code or VSCodium.
Content that is not your own, unless cited.
Grammatical errors or misspellings. Proof-read it before submission.
Informal language – a technical report is a professional document, and as such should avoid things such as:
Unnecessary abbreviations (atm, btw, ps, and so on), emojis, and emoticons; and Stories / recounts of events not relevant to the development of the program.
Irrelevant diagrams, graphs, and charts. Unnecessary elements will distract from the important content. Keep it succinct and focused. If you need additional help with report writing, the academic skills writing centre has a peer writing service and writing coaches.
Format
You are not required to follow any specific style guide (such as APA or Harvard). However, here are some tips which will make your report more pleasant to read, and make more sense to someone with a computer science background.
Colours should be kept minimal. If you need to use colour, make sure it is absolutely necessary.
If you are using graphics, make sure they are vector graphics (that stay sharp even as the reader zooms in on them).
Any code, including type/function/module names or file names, that appears in your document should have a monospaced font (such as Consolas, Courier New, Lucida Console, or Monaco)
Other text should be set in serif fonts (popular choices are Times, Palatino, Sabon, Minion, or Caslon).
When available, automatic ligatures should be activated.
Do not use underscore to highlight your text.
Text should be at least 1.5 spaced.
Communicating
Do not post your code publicly, either on Piazza or via other forums. Posts on Piazza trigger emails to all students, so if by mistake you post your code publicly, others will have access to your code and you may be held responsible for plagiarism.
Once again, and we cannot stress this enough: do not post your code publicly . If you need help with your code, post it privately to the instructors.
When brainstorming with your friends, do not share code. There might be pressure from your friends, but this is for both your and their benefit. Anything that smells of plagiarism will be investigated and there may be serious consequences.
Sharing ideas and sketches is perfectly fine, but sharing should stop at ideas. Course staff will not look at assignment code unless it is posted privately in piazza.
Course staff will typically give assistance by asking questions, directing you to relevant exercises from the labs, or definitions and examples from the lectures.
Before the assignment is due, course staff will not give individual tips on writing functions for the assignment or how your code can be improved. We will help you get unstuck by asking questions and pointing you to relevant lecture and lab material. You will receive feedback on you work when marks are released.
Submission Checklist
Once you have finished your assignment, and preferably 24 hours prior to the deadline, you should make sure that:
You have fully read and understand the entire assignment specification.
Your work has been pushed to GitLab.
Your program compiles and runs, including the cabal v2-test test suite.
Your program works on the lab machines – if the program does not work on the lab machines, it might fail tests used by the instructors. You have proof-read and spell-checked your report.
The report is in PDF format, located at the root of your project on GitLab and named Report.pdf . That capital R is important – Linux uses a case-sensitive file system. Otherwise, it may not be marked.
UPDATED: 29 Aug 2021 / RESPONSIBLE OFFICER: Director, School of Computing / PAGE CONTACT: Course Convenor