TIES341 Functional Programming 2, 1–5 ECTS

This is the course plan drafted on 2019-10-25 and finalized on 2019-11-13.

Introduction

Welcome to an advanced course on functional programming. On this course, we will use the Haskell programming language to explore such things as

• algebraic data types, including their
  • inductive definition,
  • interpretation as a semiring,
  • fixed points and
  • differentiation,
• type classes, featuring
  • categorically motivated classes, like
    • monoids,
    • functors,
    • applicative functors and
    • monads,
  • other useful classes, such as
    • alternative functors,
    • monad transformers,
    • foldable types and
    • traversable types, and
  • the implementation of classes as implicit arguments, and
• some practical use cases, involving
  • text processing with parser combinators and
  • optimizing code with recursion schemes.

This course serves as a guided tour through some of the most interesting parts of the Haskell ecosystem. As such, the goal of this course is not to train you to become a Haskell programmer, but rather to refine your skills in abstract thinking and expose you to new ideas that might be of use elsewhere.

Prerequisites

Completing this course requires a bit of mathematical maturity and a good grasp of the basics of Haskell. Thus, you should be familiar with what the following courses offer.

Familiarity with the following courses is also helpful for being able to appreciate the things we explore in a broader context.

As always, the lack of familiarity can be compensated with time and motivation.

Materials

The main material for this course is handed out by need. If you feel like you need supplementary material, you are free to pick your poison from a plethora of existing Haskell books [1].

Schedule

This course begins with an introductory lecture on 2019-10-28 12:15 (local time, whatever that may be), features three consecutive classroom activities per week and ends by 2019-12-24 00:00. The classroom activities feature the following events.

At the beginning of each week, a set of exercises is assigned. Each set must be done before the next set is assigned, so there is exactly one week of time to do each one.

You may personally negotiate later deadlines, but this is generally not a good idea, because catching up is really difficult. Ideally, we would not have any deadlines at all, but experience suggests that they really improve outcomes.

Classroom Activities

The classroom activities on this course are primarily exercise sessions, where you can do exercises together and get guidance from an instructor. The first activity of the day may turn into a lecture, in case general questions arise or I happen to have some interesting stories to tell, but the remaining time is always reserved for exercises. Participation is voluntary, but strongly encouraged.

The activities should take place in a computer classroom, but it is a good idea to bring your own laptop regardless.

Exercises, Grades and Credits

Exercises are graded from zero to three stars, so that you get

• 0 stars for a poor show,
• 1 star for an good attempt,
• 2 stars for an answer that is correct and
• 3 stars for a correct and tasteful answer.

The scale is obviously nonlinear, but this is balanced out by the fact that there is a limited supply of exercises.

Your grade \(\measuredangle\) is simply determined by feeding the number of stars \(\star\) you have gotten from exercises to the projection function \(\pi\), which is defined according to

\[\begin{eqnarray} {\star} & : & \mathcal U \\ {\star} & = & \{n : \mathbb N \mid n \le 72\} \\ {\measuredangle} & : & \mathcal U \\ {\measuredangle} & = & \{n : \mathbb N \mid n \le 5\} \\ \pi & : & {\star} \to {\measuredangle} \\ \pi (n) & = & \begin{cases} 0, & \phantom 00 \le n \le 36 \\ 1, & 37 \le n \le 43 \\ 2, & 44 \le n \le 50 \\ 3, & 51 \le n \le 57 \\ 4, & 58 \le n \le 64 \\ 5, & 65 \le n \le 72. \end{cases} \end{eqnarray}\]

I reserve the right to transparently hand out extra stars for pointing out mistakes in the material or being helpful in other ways.

Summative and Formative Assessment

I will grade your solutions within one month of you handing them in (see the section on completing the course for details).

Time permitting, I will also look over your solutions and provide feedback. The feedback will not affect your grade, unless your solutions are obviously plagiarized. If you happen to copy someone else’s answer, be honest about it and explain what lead you to do so and what you learned from it. As long as this does not happen too frequently, it will not be considered plagiarism.

Tests or Examinations

There is no written test, but there is a brief oral test at the end of the course. The oral test consists of one question and its sole purpose is to ensure that you did not blindly copy your solutions from the Internet. It is not graded, but it can be failed (with a dedicated lack of effort).

If you have a pressing reason that prevents you from doing the exercises or taking the oral test, you may personally negotiate a written test, but this is not going to be easier for you or the instructors.

Completing the Course

The following instructions explain how to complete this course, in as much detail as possible.

• Install version 8.4.4 of GHC.
  • If you are using Stack, this version is available in LTS 12.26, so you can run stack --resolver=lts-12.26 ghci to open up the appropriate interpreter.
  • It is not too important to install this exact version, but it prevents potential compatibility problems with language extensions and libraries.
  • The computer classroom machines have Stack, so not you might not need to install anything yourself.
• Do the assigned exercises by writing each one into its own file.
  • If your solutions depend on each other, you may use the module system to make this explicit.
  • This makes it much easier for me to see which exercises you did and give feedback based on them.
• Hand in your solutions by returning the source files.
  • From best to worst method, you can do this by
    • linking me a single Git repository that tracks the source files,
    • linking me a single Gzip archive that contains the source files,
    • linking me a single ZIP archive that contains the source files,
    • sending me an email with the source files as attachments,
    • sending me an email with a single Gzip archive that contains the source files as an attachment or
    • sending me an email with a single ZIP archive that contains the source files as an attachment.
  • You should learn how to do this by the beginning of the course (see the section on returning files for hints).
• Ask me to schedule an oral test for you and attend it.
  • This should only take a minute.

Returning Files

If you send me an archive, package the files instead of the directories and name the archive according to your university username.

To create a Gzip archive, you can use the following command.

$ tar -czf sapekiis.tar.gz Exercise1.hs Exercise2.hs

Make sure to check that you did not accidentally package your animes, because I do not want to see that garbage.

$ tar -tf sapekiis.tar.gz

To create a ZIP archive, you can use either of the following commands.

$ rm -f sapekiis.zip && zip -9q sapekiis.zip Exercise1.hs Exercise2.hs
$ jar -Mcf sapekiis.zip Exercise1.hs Exercise2.hs

Checking the packaging works analogously.

$ unzip -l sapekiis.zip
$ jar -tf sapekiis.zip

Making a public Git repository is a bit more involved, but can be done on the university network as follows.

Let us first create a remote repository with a random name.

$ ssh sapekiis@charra.it.jyu.fi
$ cd /autowebhome/home/sapekiis/public_html
$ echo "$(echo "$RANDOM" | sha256sum | head -c 6).git"
abcdef
$ mkdir abcdef
$ cd abcdef
$ git init --bare
Initialized empty Git repository in /autowebhome/home/sapekiis/public_html/abcdef/
$ mv hooks/post-update.sample hooks/post-update
$ git update-server-info
$ exit

Let us then create a local counterpart of the same repository.

$ cd
$ mkdir ties341
$ cd ties341
$ git init
Initialized empty Git repository in /home/sapekiis/ties341/.git/
$ mkdir Week1
$ cd Week1
$ touch Exercise1.hs Exercise2.hs
$ cd ..
$ git add Week1
$ git commit -m "Did week 1 exercises 1 and 2."
[master (root-commit) defaced] Did week 1 exercises 1 and 2.
  2 files changed, 0 insertions(+), 0 deletions(-)
  create mode 100644 Week1/Exercise1.hs
  create mode 100644 Week1/Exercise2.hs
$ git push --set-upstream \
  sapekiis@charra.it.jyu.fi:/autowebhome/home/sapekiis/public_html/abcdef.git \
  master
Counting objects: 3, done.
Writing objects: 100% (20/20), 420 bytes | 0 bytes/s, done.
Total 20 (delta 0), reused 0 (delta 0)
To sapekiis@charra.it.jyu.fi:/autowebhome/home/sapekiis/public_html/abcdef.git
  * [new branch]      master -> master
Branch master set up to track remote branch master from
sapekiis@charra.it.jyu.fi:/autowebhome/home/sapekiis/public_html/abcdef.git.

Anyone can now clone the repository as follows.

$ cd /tmp
$ git clone http://users.jyu.fi/~sapekiis/abcdef.git
Cloning into 'abcdef'...
Checking connectivity... done.
$ cd abcdef
$ git ls-files
Week1/Exercise1.hs
Week1/Exercise2.hs

While Git is the best way to do and return your solutions, I would recommend against using it if you do not know how to do so properly.

Transcripts

There exist

• handout of week 1 exercises,
• handout of week 2 exercises,
• handout of week 3 exercises,
• handout of week 4 exercises,
• handout of week 5 exercises,
• handout of week 6 exercises,
• handout of week 7 exercises and
• handout of week 8 exercises,

but expect these links to move in the near future.