Background

• This lab completes our discussion git, and starts our first programming language, namely racket.
• We'll mainly follow Quick: An introduction to Racket with Pictures
• You should be familiar with the fcs-vm-cs2613-dev VM from Lab 1.
• For more detail on the topics covered here we will refer to the Racket Guide, mainly chapter 2.
• We will also refer to specific sections of the Racket Reference in particular
  • printing output.
• For a concise guide to lists and recursion, see Beautiful Racket on Lists

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

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 ~/fcshome/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. You need to work in pairs for this part.

2. 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
   

3. Temporarily trade computers with your partner. Use git log to examine the history of their repo. Consider their commit messages, and the construction of their commits (i.e. what changes are commited together). Discuss how each of your might improve your history.

Racket Tutorial

Hello Racket World

• Form into groups of 2-3 students

• Start the fcs-vm-cs2613-dev VM, and start a terminal

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

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

#lang racket
(display "hello world")

Command Line

• run the program with

    $ racket hello.rkt
  

• There's a kindof obvious bug. Figure how to fix the bug. There's a few options.

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.

Squaring the Circle.

• Follow steps 2-5 of the Quick Tutorial

• Make note of the main new concepts encountered for your journal.

• If you have extra time figure out how to have a default argument of 10 to square, i.e. (square) should be equivalent to (square 10)

Functions, Scope, and Lists

• Do this part on your own.

• Follow steps 7-9 of the Quick Tutorial

• Make note of the main new concepts encountered for your journal.

• If you have extra time

  • start reading Section 2.3 of the Racket Guide
  • read Assignment 1

On your own

In this part of the lab I will give some activities that you should work through on your own after the scheduled lab time. Of course if you finish the rest of the lab early, you can start this part. We will set aside some time for discussion at the beginning of L03.

Working with multiple git repos

Cloning

1. Open a terminal on the FCS Linux session (i.e. not in the fcs-vm-cs2613-dev VM). Make a directory lab2-scratch somewhere outside the cs2613 git repository you created earlier.

2. Now move to the lab2-scratch directory, and make a clone of the central repo.

    $ git clone https://<username>@vcs.cs.unb.ca/git/cs2613-<username> cs2613-clone
   

   This creates a new directory "cs2613-clone" containing a clone of your repository. Notice that in general this is a good way of checking that your work is properly submitted. The TA and Prof will do exactly this cloning step in order to mark your work. The clone is on an equal footing with the original project, possessing its own copy of the original project’s history.

Sharing changes with a central repo

1. Switch to (or open) a terminal in the fcs-vm-cs2613-dev VM.

2. Navigate to the ~/fcshome/lab2-scratch/cs2613-clone/journal directory.

3. create a new blog entry, and commit it.

4. Push your changes back to the central repository.

    $ git push origin master
   

5. Change directory to your original directory ~/fcshome/cs2613. Bring in the changes you made

    $ git pull origin
   

This merges the changes from the central copy of "master" branch into the current. branch. If you made other changes in the meantime, then you may need to manually fix any conflicts.

The "pull" command thus performs two operations: it fetches changes from a remote branch, then merges them into the current branch.

Questions

Here are some questions we will be discussing at the beginning of L03.

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

Git next steps

Congratulations, you now know enough git to finish this course.

There is lots more to learn, particularly about branching and collaboration. If you want to get a big(ger) picture view, a good place to start is Git Concepts Simplified.

Racket development tools

• Start the fcs-vm-cs2613-dev VM, and start a terminal

• change to ~fcshome/cs2613/L02.

Byte compilation

• use the time command

    $ time racket hello.rkt
  

• Now compile the code with

    $ raco make hello.rkt
  

• Time it again. What do you observe?

Debugging racket

• run hello.rkt the program under the debugger in DrRacket

Questions

Here are some questions we will be discussing at the beginning of L03.

• For those familiar with other IDEs, what's similar and what's different about this one?
• What's the difference between a text editor and an IDE?
• What's a REPL?