This assignment is super easy and super short. We’ll basically complete the whole thing in class on Friday but do not forget to fill out the tutorial team survey.

Part 0. Signing Up for a Tutorial Team

A key part of this class is your Tutorial Team (up to 8 people; no exceptions) with whom you’ll work each week to complete in-class exercises. Think of it as a smaller community within the larger course community. To facilitate building these groups, everyone is required to fill out our 📁 TEAMS SURVEY (note, you must be logged into your NU Gmail account in order to access). This is REQUIRED and if you don't submit it you'll receive a 0 on the entire assignment.

Part 1. Installing DrRacket

Now we need to get DrRacket (and the Racket programming language) installed on your computer.

Download the Installer

1. Go to the Racket download page. You’ll be downloading the latest version that’s available (auto selected) even though in some of my screenshots other versions are shown.
2. Pick the installer that corresponds to your computer’s OS.

Install DrRacket + Racket

Once you’ve downloaded the installer, you’ll need to actually run it. On a Mac, you’ll drag the RACKET folder into your APPLICATIONS folder. On a Windows PC, you’ll run the exe file to install it.

Error: "Windows protected your PC"

You may see the below error if you're installing on a Windows computer with Windows Defender in its default state.



Windows by default protects users from installing "unknown" software on their computers. When a user tries to install a program it doesn't recognize, it "phones home" to Microsoft and asks if this is a common installation that people do. If it gets the response "No" you see this message. You can go around it pretty easily.

1. Press the text that says More info.
2. Press the Run anyway button.
3. Continue the installation as normal.

After enough people do this across the world, Microsoft flags it as "trusted software" so you may not even get this error at all!

Part 2. Setting Up

After installation, you should be able to double click on the DrRacket executable/application to start DrRacket. On a Windows PC, it should be in your Start menu (or whatever they’re calling it these days). On a Mac, it’ll be in your Applications folder.

Screenshot of the open Window (and what to do if you don't see it)

If you don't see this window appear and you're on a Windows machine, you likely saw a blank window appear. That's because you opened the Racket executable rather than DrRacket. Go back to your Racket folder and open DrRacket (not Racket).

Now that DrRacket and Racket are installed and ready to go, we need to do a couple of things:

1. To begin with, we need to tell DrRacket which programming language we intend to use. Select the Language menu –> Choose Language… and choose the option The Racket Language. Hit OK to save your selection. This tells DrRacket that we’ll be specifying what language we’re working in via the first line of each program we write.

2. Now to configure some DrRacket editor features. Open the Preferences menu (on a Mac, first click on the Dr Racket menu then hit Settings)… a. In the Editing tab, choose Racket. Check all four items here. b. Switch to the General tab. i. Check the option Save files whenever switching tabs or windows.

Screenshot Walkthrough

First, the Language Selection!



Then some Editing settings...



Finally the General settings...

Part 3. Selecting our First Language

One of the core tenets of this class is that there is no such thing as a little program. All programs, regardless of their size/length, are powerful in that you have successfully translated an idea from your head to a form that the computer understands. So now, let’s write a POWERFUL program!

The Definitions Window is the top half of the DrRacket app and is where we write our programs. First, we need to tell DrRacket which language we want to use. At the top of the Definitions Window, copy and paste the below line:

#lang htdp/isl+

This tells DrRacket to load the Intermediate Student Language with Lambda, the first programming language we’ll use in this class. Once you’ve selected the language, hit the button at the top of the Window which asks Racket to load the selected language. If everything went well, in the Interactions Window you’ll see a line that says Language: htdp/isl+, with debugging; memory limit: 256 MB. (note: the memory limit might be different on your computer).

Part 4. Writing a Program

Now, we want to write a program! In other words, ask the computer to perform some action with some inputs. We do this with humans all the time:

> Hey what is two plus three?
> Five; no cap.

Human language is often ambiguous and up for interpretation across sociocultural millieus. Computer languages on the other hand must be completely unambiguous and interpreted the same way by many autonomous agents. In the above example, we’ve got a simple action that we’ve asked an agent to perform: add together two numbers and report back the result. But you can imagine asking this in A LOT of different ways and having many different humans still perform the same action.

ISL+ only understands requests written in a very specific syntax:

(action-name input-1 input-2 ...)

Let’s break this down into parts:

1. The open (or left) parenthesis “(” says “please perform…”
2. Then immediately following is the action-name (in CS we call actions functions just like in math class)
3. We terminate the name of the action with a space “ ”
4. Then we give it sensible inputs, in this case 2 and 3 separated by spaces.
5. We indicate the end of the request via a close (or right) parenthesis “)”.

In the Definitions Window type the following below the earlier line that specified the programming langauge:

(+ 2 3)

Now hit RUN. You should see the calculated result now at the bottom in the Interactions Window. If you see a result of 5, congratulations! You’ve officially run your first program.

Screenshot of Result

Note: Never turn in code that you have not tried to RUN! Anytime you add something to your program, you should try running it. Programming is a process of translating what you have in your brain into a form the computer understands. You should be constantly checking to see if that translation process is proceeding as you think it is.

Part 5. Writing a Definition

While (+ 2 3) is a pretty dope program, sometimes we need to teach the computer to remember a particular piece of data to be used later in our programs. We can teach the computer to remember pieces of data using a define special form. Add to your program in the Definitions Window a new line that looks like the following:

(define netid "abc1234")

Make sure to replace the thing in quotation marks with your actual NetID. This tells Racket that from now on, when you give it the symbol netid it will use the value "abc1234".

What should my final program look like?

Notice that you won't see your NetID outputted in the _Interactions Window_. That's because you didn't actually ask Racket to do anything with your NetID–you just asked it to remember it. That's okay for now. We just want to have it store the NetID so that when we run your program, we can tell your program apart from your classmate's.

Part 6. Saving your Program

Okay, now we’ve got a program but we haven’t actually saved it on our computer. To do that, go to the File menu and select Save Definitions as.... This will bring up a prompt on your operating system to save your Racket program (just like you save Microsoft Word documents). We highly recommend setting up a single folder somewhere on your computer (i.e. your Desktop) that will store all of your work for this class.

I like commonsense file names, so go ahead and name your file exercise_0.rkt. Once you hit save, you should be able to go to that folder on your computer and see your new document (it will have the .rkt file extension). Congratulations, you’re officially a Racketeer!

Life Advice: Probably best not to use this term outside of our course community as it has some nasty legal implications.

Double Checking your Work

All of the Exercises in this class will be graded via an autograder – a program, written in Racket, that will run your program and test it to see if it meets all the expectations of the assignment.

This means that you must carefully read each assignment description and follow it exactly. If your assignment does not satisfy the requirements in any way (even if you think it’s small and inconsequential) you will receive points off (or in the worst case, not receive any points at all). For this assignment, because the program is so short, there’s only a few things you should check:

1. Does your program run without any errors?
2. Are you outputting the result of some math calculation?
3. Are you storing your actual netid inside the define statement?
   • Important: Racket is case-sensitive (i.e. capitals matter) so make sure that your define statement actually says (define netid ...) where netid has no spaces and no capitals.
   • Make sure your netid you enter is actually your netid. The autograder will compare the submitter’s netid to the one in your program.

For this assignment, you will upload your exercise_0.rkt file to the assignment on Canvas. DO NOT UPLOAD ANY OTHER FILES.

Once you’ve submitted your file to Canvas, you’re done!

Submission Details