Before the lab

Before every lab in this course, you will be given tasks to complete. These will generally be easy tasks like watching videos, but you need to complete them in order to keep up with the class.

Command Line Familiarity Check

1. In an FCS linux lab (remote or locally) log in, and open a terminal.

2. Make a directory *

3. Create a file in that directory using one of the available text editors

4. Now clean up, removing the file and the directory.

If any of this was new to you, then please take the time to go through parts 1 to 5 of the Learning the Shell Tutorial.

Read the course syllabus.

The Course Syllabus is available on line. Please read it, and bring any questions you have about it to the first lab.

Background Reading

For every lab there will be some related reading. I'll point these out as we go through the lab, but I'll also collect them at the start of the lab in case you want to get a head start (or refer back to them later).

• The Frog manual
• Git Basics from Pro Git
• Basic Shell Background

About the course

1. What's similar to other CS courses you've taken?

2. What's different?

3. Key point, how are labs evaluated?

Software Setup

1. Open a terminal.

2. Install frog and the other tools we need via the following command (throughout the course, $ at the beginning of a line will indicate a shell prompt, you don't need to type it.):

     $ raco pkg install --auto unb-cs2613
   

3. Install the python library pygments, used by frog for syntax highlighting

    $ python -m ensurepip --upgrade
    $ python -m pip install pygments
   

There are an unfortunate number of warnings here, but we can ignore them for now.

Getting Started with Frog

We'll be using frog frog to keep a journal of what we learn in this course.

1. Open a terminal.

2. Make a directory called cs2613 that will keep all of your work (note that case and spaces matter in Linux and this is not the same as CS2613 or CS 2613. For the rest of this course we will assume it is directly under your home directory. The shortcut ~/cs2613 will refer to this directory in the lab texts and in the shell.

3. Make a directory journal inside ~/cs2613. Inside ~/cs2613/journal, run

    $ raco frog --init
   

4. Try viewing the newly created blog with

    $ raco frog -bp
   

5. Start a new blog page for today's lab, and delete the fake entry created by the frog setup command. Note that you may have to refresh the browser after running raco frog -bp.

Setting up a git repo

1. Change to ~/cs2613. This directory should have one subdirectory called journal, which has the results of your experiments above with frog.

2. Create the git repository

    $ git init -b main
   

   Git will reply with something like

    Initialized empty Git repository in /home1/ugrads/$username/cs2613/.git/
   

   You’ve now initialized the working directory — you may notice a new directory created, named ".git". You should mentally replace "$username" with whatever the login name is that you use to log into the FCS linux machines.

3. Read the git-quickref page, and follow the initial configuration steps there.

   • note that the "--wait" option for gedit is important here.

4. Next, tell Git to take a snapshot of the contents of all files under the journal, with git add:

   $ git add journal
   

This snapshot is now stored in a temporary staging area which Git calls the "index". You can permanently store the contents of the index in the repository with git commit:

   $ git commit

This will open and editor and prompt you for a commit message. Enter one and exit the editor. You’ve now stored the first version of your project in Git. See §5.2 of Pro Git for some hints about writing good commit messages. As mentioned in the class git policy, you will be marked on your commit messages, so you may as well get started with good habits.

Pushing to a central repo

Since we are using the FCS git repositories there is an existing repository for all students who registered early enough. If it turns out there is no repository for you, you may need to do the last step later.

• First add the remote. This something like a nickname for the URL where the repo will be stored.

    $ git remote add origin https://$username@vcs.cs.unb.ca/git/cs2613-$username
  

  origin is the default name for a remote, but we could have used a different name here. Replace $username with your FCS Linux account name.

• Now upload your local copy of the repo.

    $ git push --all origin
  

  you should see something like

            Counting objects: 388, done.
            Delta compression using up to 8 threads.
            Compressing objects: 100% (350/350), done.
            Writing objects: 100% (388/388), 71.63 KiB | 0 bytes/s, done.
            Total 388 (delta 223), reused 59 (delta 33)
            To https://$username@vcs.cs.unb.ca/git/cs2613-$username
               e7e5311..f1ae959  main -> main
  

• If you have extra time, start L02

Before next lab

Before the lab

Background

• This lab completes our discussion git, and starts our first programming language, namely Racket.

• For learning racket, we will mainly follow Functional Introduction to computer science

• You may also find the BSL reference helpful.

Git Tutorial Continued

Making Changes in git

Having at look at our test post from Lab 1, we can observe the post template adds a bunch of stuff related to social media. Let's suppose that for our cs2613 journal we want a more minimal look.

Start by finding the right files to edit with

$ git grep disqus

git grep is a very useful (and fast!) tool to find occurrences of strings in your git repository. Notice in the output there are some files created by frog; we will clean those up later. Find the template file (under _src) and edit it to remove the undesired social media links. Check the results with

$ raco frog -bp

You might notice one more link to twitter in a different template file. Feel free to remove that one as well.

Use git add to stage your changes:

$ git add file1 file2 file3

(where file1, file2 and file3 are actual files you modified). You are now ready to commit. You can see what is about to be committed using git diff with the --cached option:

$ git diff --cached

(Without --cached, git diff will show you any changes that you’ve made but not yet added to the index.) You can also get a brief summary of the situation with git status:

$ git status
# On branch master
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#
#       modified:   file1
#       modified:   file2
#       modified:   file3
#

If you need to make any further adjustments, do so now, and then add any newly modified content to the index. Finally, commit your changes with:

$ git commit

This will again prompt you for a message describing the change, and then record a new version of the project.

Alternatively, instead of running git add beforehand, you can use

$ git commit -a

which will automatically notice any modified (but not new) files, add them to the index, and commit, all in one step. Keep in mind that you will be marked on the logical structure of your git commits, so you are better off using git add to explicitely choose what changes to commit.

Cleaning up generated files

A common phenomenon in software development is the existence of generated files. These files are created by some tool, typically based on some source files. In general it is a bad idea to track generated files in version control because they introduce spurious changes into history. We'll look at this more later, but for now let's try to clean up. We can find out what files are generated .e.g. by consulting the frog docs. Let's first try a shortcut. Run

$ cd ~/cs2613/journal
$ raco frog --clean

To find out what changed, run

$ git diff --stat

All going well, you will see a bunch of deletions. We can tell git to make those deletions permanent in several ways. It turns out that there is a handy option to git add that tells git to stage all of the changes in the working tree. Try to figure out which option it is.

• to see the effect of a git add command, run git diff --cached --stat
• to undo the effect of a git add command, run git reset.

When you are satisfied with the changes, run git commit.

It will turn out that this is not all of the generated files; we can use git rm to clean up further as we find more.

Make sure you run

$ raco frog -bp

To make sure the the blog still works after your deletions.

Viewing project history

1. At any point you can view the history of your changes using

    $ git log
   

   Use this command to verify that all the changes you expected to be pushed to the server really were.

   If you also want to see complete diffs at each step, use

    $ git log -p
   

   Often the overview of the changes is useful to get a feel for each step

    $ git log --stat --summary
   

2. In most projects, you have to share commit messages to (at least) the same people who view your source code. Share your "best commit" message with one or more of your neighbours.

3. Find something positive to say about the other commit messages you are reading.

4. Find a constructive improvement with one of the other messages. Don't be mean, people have varying levels of experience with this.

Getting started with racket

Hello Racket World

• Open a terminal

• Make a directory ~/cs2613/labs/L02 (if it does not already exist) and change there with cd

• Save the following code to ~/cs2613/labs/L02/hello.rkt

#lang htdp/bsl
"hello world"
(* 6 7)

Command Line

• run the program with

    $ racket hello.rkt
  

• What is the difference between the first and second line of output?

DrRacket: A Racket Specific IDE

• Start DrRacket from the activities menu

• Referring to the DrRacket documentation as needed, open and run the hello.rkt program from the previous part.

• What is the meaning of the first line of the file?

Racket Expressions.

• Form groups of 2 or 3.

• Work through Exercise 0: for each of the following lines of code, someone from the group should guess what is wrong before trying it in the Interactions window of DrRacket.

    (* (5) 3)
    (+ (* 2 4)
    (5 * 14)
    (* + 3 5 2)
    (/ 25 0)
  

• Work through Exercise 1. In general where the text asks you to predict the value of an expression, you can also enter into the definitions window something like

    (check-expect (* 6 9) 42)
  

  When you run (e.g. F5), then you will find out if your prediction is correct.

• Work through Exercise 2. You can test your answers by applying the following functions to appropriate arguments. Notice that the value of y does not matter.

#lang htdp/bsl
(define y 18)
(define (t1 x)
  (or (= x 0) (< 0 (/ y x))))
(define (t2 x)
  (or (< 0 (/ y x)) (= x 0)))
(define (t3 x)
  (and (= x 0) (< 0 (/ y x))))
(define (t4 x)
  (or (< 0 (/ y x)) (not (= x 0))))

Racket functions

• Do this part on your own.

• Do Exercise 4

  Here are some tests to help you check your function

(check-expect (middle-of-three 1 2 3) 2)
(check-expect (middle-of-three 2 1 3) 2)
(check-expect (middle-of-three 1 3 2) 2)

• Do these tests suffice? Why or why not?

Before Next Lab

Before the lab

Git Questions

Some questions from before:

• What is a remote?
• What is merging?
• What is a conflict?

Setup

• make a directory labs/L03 inside your ~/cs2613 git repository
• All of your work from today should be committed in that directory (and pushed before you leave).

The DrRacket stepper

• copy arith.rkt, save it as ~/cs2613/labs/L03/arith.rkt and commit it.

• run your arith.rkt in DrRacket; observe that the test fails

• run your arith.rkt in the DrRacket Stepper. Notice that after about 7 steps, we have reduced the test case to multiplication by zero which looks wrong. That means that the problem is with the recursive (reduction) step.

• Fix the a > 0 case of my-* to match the following formula a * b = (a - 1) * b + b, while still using my-+

• DrRacket should report "The test passed!" when you have it working. Commit this version of your code. Remember that git commit message quality counts in this course, so work on making commit messages.

Semantics

As you read in FICS unit 3, we can understand evaluation ("running") of Racket programs as a sequence of "reductions" or "substitutions". These rules are similar to the reduction steps in the DrRacket stepper.

The stepper uses the following rules for and and or (notice that these rules enforce short circuit evaluation)

(and true exp2 ...) => (and exp2 ...)
(and false exp2 ...) => false
(or true exp2 ...) => true
(or false exp2 ...) => (or exp2 ...)
(and) => true
(or) => false

Following Exercise 7, write a new set of rules that requires at least two arguments for and and or. The rules are for human consumption; you can write them as comments in DrRacket. You can write "exp1 exp2 ..." to mean at least 2 expressions.

Discuss your answers with a your group, and try a couple evaluation small examples by hand using your rules.

Test Coverage

Unit testing is an important part of programming, and has inspired something called test driven development.

• This activity continues arith.rkt from the first half of the lab.

• Under

  Language -> Choose Language -> Show Details -> Dynamic Properties
  

  enable

  ⊙ Syntactic test suite coverage
  

• comment out the given test

• run your code in DrRacket again

• most likely you will have some code highlighted with orange text and black foreground. This means that code is not covered by your test suite. Uncomment the given test, and if needed add tests to cover each piece of uncovered code.

• When you have complete test coverage, commit your code.

  In this course, for all racket assignments you will lose marks if you don't have complete test coverage.

• Push your repo to coursegit.

If you have extra time

• Run the tests on the command line with raco test arith.rkt
• Read the first assignment A1
• Update your journal.

Before Next Lab

Before the lab

Questions from last time

• The programming languages we will study this term are all dynamically typed. This means that not only the value but also the type of variables can change at runtime. Why does this make testing even more important?

• What kind of software problems is testing not well suited to find?

• Why might mutable state (e.g. instance variables in Java) make writing unit tests harder?

Setup

• make a directory labs/L04 inside your ~/cs2613 git repository
• All of your work from today should be committed in that directory (and pushed before you leave).

Simulating Natural Numbers I

Write the times function from Exercise 11 in FICS. You can (and should) use the following code from the linked discussion

#lang htdp/bsl
(define-struct Z ())
(define-struct S (pred))
(define (pred nat)
  (cond
    [(Z? nat) (error "can't apply pred to Z")]
    [(S? nat) (S-pred nat)]))

(define (plus nat1 nat2)
  (cond
    [(Z? nat1) nat2]
    [(S? nat1) (make-S (plus (S-pred nat1) nat2))]))

Here is the template for structural recursion on (simulated) natural numbers. See the linked text (or the plus function just above) for how to add a second "carried-along" parameter.

(define (my-nat-fn nat)
  (cond
    [(Z? nat) ...]
    [(S? nat) ... (my-nat-fn (S-pred nat)) ...]))

Here are some tests to get you started. As always, try to have complete test coverage.

;; 0 * 0 = 0
(check-expect (times (make-Z) (make-Z)) (make-Z))
;; 0 * 1 = 0
(check-expect (times (make-Z) (make-S (make-Z))) (make-Z))
;; 2 * 1 = 2
(check-expect (times (make-S (make-S (make-Z)))
                       (make-S (make-Z)))
              (make-S (make-S (make-Z))))

You may find it helpful to refer back to your solution from L03.

Simulating Natural Numbers II

Write the compare function from Exercise 11 in FICS. Your function compare should use the struct definitions Z and S, and pass the following tests

;; 0 = 0
(check-expect (compare (make-Z) (make-Z)) 'equal)
;; 0 < 1
(check-expect (compare (make-Z) (make-S (make-Z))) 'less)
;; 1 > 0
(check-expect (compare (make-S (make-Z)) (make-Z)) 'greater)
;; 2 > 1
(check-expect (compare (make-S (make-S (make-Z)))
                       (make-S (make-Z))) 'greater)

Structural recursion, on numbers

Use structural (note that structural here is only indirectly related to Racket structs) recursion on natural numbers (not the simulated ones from above, but regular Racket numbers like 1, 42, and 1337) to define a function (sum-factors n max-factor) that sums all factors of n (including 1) no larger than max-factor

Recall the template for structural recursion on natural numbers:

(define (my-nat-fn n)
  (cond
    [(zero? n) ...]
    [(positive? n) ... (my-nat-fn (sub1 n)) ...]))

Try to use only one recursive call to sum-factors like in the template. Keep in mind that the n in the template might be a different parameter of your function. You can use the builtin function remainder to test for divisibility.

The following tests should pass

;; 1+2+3 = 6
(check-expect (sum-factors 6 5) 6)
;; 1+2+4+7+14 = 28
(check-expect (sum-factors 28 27) 28)

Before Next Lab