Exercism exercises in Haskell

Please see the contributing guide

There are currently two distinct ways to set up an environment to collaborate on the development of the Haskell track:

• Using a global GHC installation.
• Using Stack. (experimental)

The first method is more convenient when you just want to write code without caring too much about which packages are being used. The second one is better to track exercises' dependencies and test them against multiple GHC versions.

If you have a recent Haskell Platform installed, probably most of the packages you need are already installed for you. Otherwise, you can manually install the missing ones.

The following is the list of all packages used in this repository, just don't trust this list to be updated.

These packages come installed with GHC:

• array
• base
• containers
• filepath
• directory
• process
• time
• unix

These are already installed in recent version of the Haskell Platform:

• attoparsec
• HUnit
• text
• parallel
• QuickCheck
• random
• split
• stm
• vector

These you will have to add to your installation:

• lens
• old-locale

$ cabal install lens

This will download and installed the package named lens.

All the tests:

$ ./_test/check-exercises.hs
-- accumulate
Cases: 5  Tried: 5  Errors: 0  Failures: 0
[…]
-- wordy
Cases: 16  Tried: 16  Errors: 0  Failures: 0
-- zipper
Cases: 8  Tried: 8  Errors: 0  Failures: 0
SUCCESS!

Test only specific exercises:

$ ./_test/check-exercises.hs triangle trinary
-- triangle
Cases: 8  Tried: 8  Errors: 0  Failures: 0
-- trinary
+++ OK, passed 100 tests.
+++ OK, passed 100 tests.
+++ OK, passed 100 tests.
+++ OK, passed 100 tests.
SUCCESS!

This is an experimental method tested only on GNU/Linux. It depends on having bash and GNU getopt installed on your system.

Please let us know if you find anything wrong with it.

You can use stack to handle all the dependencies for you. But first, you need to transform the exercises into stack projects.

The _test/stackalize bash script will extract the exercise's dependencies from _test/dependencies.txt and create a stack project for you:

$ _test/stackalize --resolver lts-6.4 exercises/leap

This will transform the exercise leap in a stack project using the resolver lts-6.4. Change it for your favourite Stackage snapshot.

You can make your life easier by adding \_test to your PATH. That way you can simply call stackalize from anywhere without having to provide a path to it.

To download, install the compiler and packages needed, compile and test an exercise, run the following commands:

$ cd exercises/leap
$ stack test

Testing if it compiles without warnings and pass the tests:

$ stack clean
$ stack test --pedantic

Testing with a specific resolver:

$ stack test --resolver lts-2.22           # GHC-7.8.4
$ stack test --resolver lts-6.4            # GHC-7.10.3
$ stack test --resolver nightly-2016-06-21 # GHC-8.0.1
$ stack test --resolver nightly            # Newest compiler and packages.

If you are making major changes to an exercise, it's recommended that you test it against those three versions of GHC with --pedantic, to be sure it will not fail when your pull request is tested on Travis-CI.

If you need to make a commit, you can remove the stack project and change the exercise back to its previous form:

$ stackalize --undo exercises/leap

This command will intentionally leave the .stack-work folder intact, to preserve the cache in case you decide to test it with stack again.

Each exercise in the Haskell track is composed of at least two files:

• name_test.hs # Both filenames must be all lowercase and any deviations
• example.hs # will generate failures in the future.

Optionally, a third file with a stub can also be provided:

• ModuleName.hs # This file must be named exactly as the module.

We also keep track of all the packages used by the examples and test files in _test/dependencies.txt. If you are implementing a new exercise or changing the dependencies of a existing one, please don't forget to update it.

At the moment, we may not detect incorrectly specified dependencies in your pull requests automatically. But soon we expect Travis-CI be able to catch it, so please declare in dependencies.txt all the packages used by the examples and tests.

The MIT License (MIT)

Copyright (c) 2014 Katrina Owen, _@kytrinyx.com