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https://github.com/system-f/fp-course

Functional Programming Course
https://github.com/system-f/fp-course

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Functional Programming Course

Host: GitHub
URL: https://github.com/system-f/fp-course
Owner: system-f
Created: 2013-01-03T00:13:31.000Z (almost 12 years ago)
Default Branch: master
Last Pushed: 2023-10-05T05:47:27.000Z (about 1 year ago)
Last Synced: 2024-05-23T08:19:58.774Z (7 months ago)
Language: Haskell
Homepage:
Size: 4.05 MB
Stars: 4,050
Watchers: 130
Forks: 1,182
Open Issues: 15
Metadata Files:
- Readme: README.markdown
- Changelog: changelog
- Support: support/Setup.hs

Awesome Lists containing this project

my-awesome - system-f/fp-course - 12 star:4.1k fork:1.2k Functional Programming Course (Haskell)
awesome-functional-studies - fp-course
learn-roc - - course/tree/master/src/Course) (Projects / Courses, etc.)

README

# Functional Programming Course

![System-F](https://system-f.gitlab.io/logo/systemf-450x450.jpg)

### Written by Tony Morris & Mark Hibberd

### With contributions from individuals and organisations (thanks!)

#### Special note 1

If you have arrived here by https://github.com/system-f/fp-course and you are
looking for the *answers* (not the exercises), please go to https://github.com/tonymorris/fp-course

#### Special note 2

As of February 2017, this repository is taking the place of the repository hosted at
[https://github.com/NICTA/course](https://github.com/NICTA/course) which is deprecated.

The new repository is located at [https://github.com/system-f/fp-course](https://github.com/system-f/fp-course).

#### Introduction

The course is structured according to a linear progression and uses the Haskell
programming language to learn programming concepts pertaining to functional
programming.

Exercises are annotated with a comment containing the word "Exercise." The existing code compiles, however answers have
been replaced with a call to the Haskell `error` function and so the code will throw an exception if it is run. Some
exercises contain tips, which are annotated with a preceding "Tip:". It is not necessary to adhere to tips. Tips are
provided for potential guidance, which may be discarded if you prefer a different path to a solution.

The exercises are designed in a way that requires personal guidance, so if you
attempt it on your own and feel a little lost, this is normal. All the
instructions are not contained herein.

### Getting Help

There are two mailing lists for asking questions. All questions are welcome,
however, your first post might be moderated. This is simply to prevent spam.

1. [[nicta-fp]](https://groups.google.com/forum/#!forum/nicta-fp) is a Google
Group for any queries related to functional programming. This mailing list is
owned by System F and is open to the public. Questions relating to this course
are most welcome here.

2. [[haskell-exercises]](https://groups.google.com/forum/#!forum/haskell-exercises)
is a Google Group for queries related specifically to this System F functional
programming course material. This mailing list is not owned by System F, but is
run by others who are keen to share ideas relating to the course.

4. \#bfpg [on Libera.chat](ircs://irc.libera.chat:6697/#bfpg) is the IRC channel of the
Queensland Functional Programming Lab - the team that runs the course in Brisbane.

5. \#scalaz [on Libera.chat](ircs://irc.libera.chat:6697/#scalaz) is an IRC channel that is operated
by others who are keen to share ideas relating to functional programming in
general. Most of the participants of this channel have completed the System F
functional programming course to some extent. They are in various timezones
and share a passion for functional programming, so may be able to provide
relatively quick assistance with questions.

### Getting Started

1. Install the Glasgow Haskell Compiler (GHC) version 8.0 or higher.
[GHCup](https://www.haskell.org/ghcup/) is the recommended way to do that these days

2. Change to the directory containing this document.

3. Execute the command `ghci`, which will compile and load all the source code.
You may need to set permissions on the root directory and the ghci configuration
file, `chmod go-w .ghci ./`.

4. Inspect the introductory modules to get a feel for Haskell's syntax, then move
on to the exercises starting with `Course.Optional`. The
[Progression](#progression) section of this document lists the recommended
order in which to attempt the exercises.

5. Edit a source file to a proposed solution to an exercise. At the `ghci`
prompt, issue the command `:reload`. This will compile your solution and
reload it in the GHC interpreter. You may use `:r` for short.

### Tips after having started

1. Some questions take a particular form. These are called *WTF questions*. WTF
questions are those of this form or similar:
* What does ____ mean?
* What does the ____ function mean?
* What is a ____ ?
* Where did ____ come from ?
* What is the structure of ____ ?

They are all answerable with the `:info` command. For example, suppose you
have the question, "What does the `swiggletwoop` function mean?" You may
answer this at GHCi with:

`> :info swiggletwoop`

You may also use `:i` for short.

2. Functional Programming techniques rely heavily on types. This reliance may
feel foreign at first, however, it is an important part of this course. If
you wish to know the type of an expression or value, use `:type`. For
example,

`> :type reverse`

`List t -> List t`

This tells you that the `reverse` function takes a list of elements of some
arbitrary type (`t`) and returns a list of elements of that same type. Try
it.

You may also use `:t` for short.

3. GHCi has TAB-completion. For example you might type the following:

`> :type rev`

Now hit the TAB key. If there is only one function in scope that begins with
the characters `rev`, then that name will auto-complete. Try it. This
completion is context-sensitive. For example, it doesn't make sense to ask
for the type of a data type itself, so data type names will not auto-complete
in that context, however, if you ask for `:info`, then they are included in
that context. Be aware of this when you use auto-complete.

This also works for file names:

`> readFile "/etc/pas"`

Now hit the TAB key. If there is only one existing filename on a path that
begins with `/etc/pas`, then that name will auto-complete. Try it.

If there is more than one identifier that can complete, hit TAB twice
quickly. This will present you with your options to complete.

4. Follow the types.

You may find yourself in a position of being unsure how to proceed for a
given exercise. You are encouraged to adopt a different perspective. Instead
of asking how to proceed, ask how you might proceed while adhering to the
guideline provided by the types for the exercise at hand.

It is possible to follow the types without achieving the desired goal,
however, this is reasonably unlikely at the start. As you become more reliant
on following the types, you will develop more trust in the potential paths
that they can take you, including identification of false paths.

Where types fall short, use the tests written in comments above each exercise.
They can be copied and pasted into GHCi. You should also take the first step
of following the types. Do it.

5. Do not use tab characters

Set up your text editor to use space characters rather than tabs.
Using tab characters in Haskell can lead to confusing error messages.
GHC will give you a warning if your program contains a tab character.

### Running the tests

Tests are stored under the `src/Test/` directory. Each module from the course that
has tests has a corresponding `Test.hs` file. Within each test module,
tests for each function are grouped using the `testGroup` function. Within each
test group there are test cases (`testCase` function), and properties
(`testProperty` function).

Tests are run using a built-in test runner that has no requirements
beyond those of the course (a supported version of GHCi). By default,
the full test suite is loaded, and each module's tests are
exported. You can run the tests in GHCi like this:

>> test test_List

#### Specific modules

For convenience, each test module also exports individual tests. To run tests
from a single module, load it, and then run `test `. For example, in
`GHCi`:

>> :l src/Test/ListTest.hs
>> test headOrTest
>> test productTest

#### `:reload` and run tests

There is also a custom `:test` command defined in `.ghci` that will
invoke `:reload` and then `test` in a single action:

>> :test test_List
>> :test headOrTest

#### doctest

The doctest tests are a mirror of the tests that reside in comments alongside
the code. They are not executable, but examples can be copied into GHCI.
Examples begin with `>>>` while properties begin with `prop>`.

### Progression

We recommend you perform some exercises before others. The first step
is to inspect the introduction modules.

* `Course.ExactlyOne`
* `Course.Validation`

They contain examples of data structures and Haskell syntax. They do not contain
exercises and exist to provide a cursory examination of Haskell syntax. The next
step is to complete the exercises in `Course.Optional`.

After this, we recommend the following progression of modules:

* `Course.List`
* `Course.Functor`
* `Course.Applicative`
* `Course.Monad`
* `Course.FileIO`
* `Course.State`
* `Course.StateT`
* `Course.Extend`
* `Course.Comonad`
* `Course.Contravariant`
* `Course.Compose`
* `Course.Traversable`
* `Course.ListZipper`
* `Course.Parser` *(see also `Course.Person` for the parsing rules)*
* `Course.MoreParser`
* `Course.JsonParser`
* `Course.Interactive`
* `Course.Anagrams`
* `Course.FastAnagrams`
* `Course.Cheque`

During this progression, it is often the case that some exercises are abandoned
due to time constraints and the benefit of completing some exercises over
others. For example, in the progression, `Course.Functor` to `Course.Monad`, the
exercises repeat a similar theme. Instead, a participant may wish to do
different exercises, such as `Course.Parser`. In this case, the remaining
answers are filled out, so that progress on to `Course.Parser` can begin
(which depends on correct answers up to `Course.Monad`). It is recommended to
take this deviation if it is felt that there is more reward in doing so.

Answers for the exercises can be found here:
[https://github.com/tonymorris/fp-course](https://github.com/tonymorris/fp-course)

After these are completed, complete the exercises in the `projects` directory.

### Introducing Haskell

This section is a guide for the instructor to introduce Haskell syntax. Each of
these points should be covered before attempting the exercises.

* values, assignment
* type signatures `::` reads as *has the type*
* The `->` in a type signature is *right-associative*
* functions are values
* functions take arguments
* functions take *only one argument* but we approximate with spoken
language
* functions can be declared inline using *lambda expressions*
* the `\` symbol in a lambda expression denotes a Greek lambda
* operators, beginning with non-alpha character, are in infix position by
default
* use in prefix position by surrounding with *(parentheses)*
* regular identifiers, beginning with alpha character, are in prefix position by
default
* use in infix position by surrounding with ``backticks``
* polymorphism
* type variables *always* start with a lower-case character
* data types, declared using the `data` keyword
* following the `data` keyword is the *data type name*
* following the data type name are zero of more type variables
* then `=` sign
* data types have zero or more constructors
* data type constructors start with an upper-case character, or colon `(:)`
* following each constructor is a list of zero or more *constructor arguments*
* between each constructor is a pipe symbol `(|)`
* the `deriving` keyword gives us default implementations for some functions
on that data type
* when constructors appear on the left side of `=` we are *pattern-matching*
* when constructors appear on the right side of `=` we are *constructing*
* type-classes

### Learning the tools

When this course is run in-person, some tools, particularly within Haskell, are
covered first.

* GHCi
* `:type`
* `:info`
* values
* type signatures
* `x :: T` is read as *x is of the type T*
* functions are values
* functions take arguments
* functions take one argument
* lambda expressions
* operators (infix/prefix)
* identifiers starting with `isAlpha` are prefix by default, infix surrounded in backticks (\`)
* other identifiers are infix by default, prefix surrounded in parentheses
* data types
* `data` keyword
* recursive data types
* pattern matching
* `deriving` keyword
* type-classes
* type parameters
* always lower-case 'a'..'z'
* aka generics, templates C++, parametric polymorphism

### Parser grammar assistance

The exercises in `Parser.hs` can be assisted by stating problems in a specific way, with a conversion to code.

| English | Parser library |
|-----------|-----------------------------------|
| and then | `bindParser` `>>=` |
| always | `valueParser` `pure` |
| or | `\|\|\|` |
| 0 or many | `list` |
| 1 or many | `list1` |
| is | `is` |
| exactly n | `thisMany n` |
| call it x | `\x ->` |

### Monad comprehension

##### do-notation

* insert the word `do`
* turn `>>=` into `<-`
* delete `->`
* delete `\`
* swap each side of `<-`

##### LINQ

* write `from` on each line
* turn `>>=` into in
* delete `->`
* delete `\`
* swap each side of `in`
* turn value into `select`

### Demonstrate IO maintains referential transparency

Are these two programs, the same program?

p1 ::
IO ()
p1 =
let file = "/tmp/file"
in do _ <- writeFile file "abcdef"
x <- readFile file
_ <- putStrLn x
_ <- writeFile file "ghijkl"
y <- readFile file
putStrLn (show (x, y))

p2 ::
IO ()
p2 =
let file = "/tmp/file"
expr = readFile file
in do _ <- writeFile file "abcdef"
x <- expr
_ <- putStrLn x
_ <- writeFile file "ghijkl"
y <- expr
putStrLn (show (x, y))

What about these two programs?

def writeFile(filename, contents):
with open(filename, "w") as f:
f.write(contents)

def readFile(filename):
contents = ""
with open(filename, "r") as f:
contents = f.read()
return contents

def p1():
file = "/tmp/file"

writeFile(file, "abcdef")
x = readFile(file)
print(x)
writeFile(file, "ghijkl")
y = readFile(file)
print (x + y)

def p2():
file = "/tmp/file"
expr = readFile(file)

writeFile(file, "abcdef")
x = expr
print(x)
writeFile(file, "ghijkl")
y = expr
print (x + y)

### One-day

Sometimes this course material is condensed into one-day. In these cases, the
following exercises are recommended:

* `Optional`
* `mapOptional`
* `bindOptional`
* `(??)`
* `(<+>)`
* `List`
* `headOr`
* `product`
* `length`
* `map`
* `filter`
* `(++)`
* `flatMap`
* `reverse`
* `Functor`
* `instance Functor List`
* `instance Functor Optional`
* `instance Functor ((->) t)`
* `instance Functor void`
* `Applicative`
* `instance Applicative List`
* `instance Applicative Optional`
* `instance Applicative ((->) t)`
* `lift2`
* `sequence`
* `FileIO`

### What about cabal and stack?

This repository's primary purpose is to support in-person instruction
for people who have potentially not even used development tools at
all. We have therefore designed the course around `ghci` as the
primary tool.

If you are a more experienced developer with tooling set up, and you
need a cabal file, `shell.nix` or `stack.yaml` to have working
development tools, run the `support/copy-tool-files.sh` script from
the root of the repository.

(Windows users, try running `support\copy-tool-files.bat` from the
repository root.)

### References

* [The Haskell `error` function](http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.html#v:error)

* [Glasgow Haskell Compiler](http://haskell.org/ghc)