Functional Programming Course
Written by Tony Morris & Mark Hibberd for NICTA
With contributions from individuals (thanks!)
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.
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.
[nicta-fp] is a Google Group for any queries related to functional programming. This mailing list is owned by NICTA and is open to the public. Questions relating to this course are most welcome here.
[haskell-exercises] is a Google Group for queries related specifically to this NICTA funtional programming course material. This mailing list is not owned by NICTA, but is run by others who are keen to share ideas relating to the course.
#scalaz on Freenode 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 NICTA 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.
#nicta-course on Freenode is an IRC channel that is operated by others who are going through this course material on their own time and effort.
Install the Glasgow Haskell Compiler (GHC) version 7.6 or higher.
Change to the directory containing this document.
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 600 .ghci ./.
Inspect the introductory modules to get a feel for Haskell's syntax, then move on to the exercises starting with
Course.List. The Progression section of this document lists the recommended order in which to attempt the exercises.
Edit a source file to a proposed solution to an exercise. At the
ghciprompt, issue the command
:reload. This will compile your solution and reload it in the GHC interpreter. You may use
Tips after having started
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
:infocommand. For example, suppose you have the question, "What does the
swiggletwoopfunction mean?" You may answer this at GHCi with:
> :info swiggletwoop
You may also use
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
reversefunction 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
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.
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.
Your instructor must guide you where types fall short, but you should also take the first step. Do it.
Running the tests
Some exercises include examples and properties, which appear in a comment above
the code for that exercise. Examples begin with
>>> while properties begin
The solution to the exercise must satisfy these tests. You can check if you have satisfied all tests with cabal-install and doctest. From the base directory of this source code:
> cabal update > cabal install cabal-install > cabal install --only-dependencies > cabal configure --enable-tests > cabal build > cabal test
Alternatively, you may run the tests in a single source file by using
explicitly. From the base directory of this source code:
> doctest -isrc -Wall -fno-warn-type-defaults <filename.hs>
Note: There is a bug in GHC 7.4.1 where for some configurations, running the tests will cause an unjustified compiler error.
It is recommended to perform some exercises before others. The first step is to inspect the introduction modules.
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
After this, the following progression of modules is recommended:
Course.Monad(please see this issue)
Course.Personfor the parsing rules)
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,
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/course
After these are completed, complete the exercises in the
If you choose to use the Leksah IDE for Haskell, the following tips are recommended:
- Clone the git repo use Package -> Add to add course.cabal.
- Click on the green tick on the toolbar to include
cabal testin each build and list the failures in the Errors pane.
- Choose Package -> Configure to make sure
--enable-testsis used (just building may cause cabal to configure without).
- Ctrl + B to build (Command + B on OS X).
- The test failures should show up in Panes -> Errors.
- Pane -> Log often has useful error messages.
- Ctrl + J (Command + J on OS X) selects the next item in Errors pane and goes to it in the source (hold down Shift to go to previous item).
- Ctrl + Enter on a line starting "-- >>>" will run the selected expression in GHCi (Ctrl + Enter on OS X too). The output goes to Panes -> Log and Panes -> Output.
- The last GHCi expression is reevaluated after each :reload triggered by changes in the code.
- Uncheck Debug -> GHCi when you are done with GHCi and Leksah will go back to running cabal build and cabal test instead.