exercism fetch haskell custom-set

Custom Set

Create a custom set type.

Sometimes it is necessary to define a custom data structure of some type, like a set. In this exercise you will define your own set. How it works internally doesn't matter, as long as it behaves like a set of unique elements.


To complete this exercise, you need to create the data type CustomSet, with Eq and Show instances, and implement the following functions:

You will find a dummy data declaration and type signatures already in place, but it is up to you to define the functions and create a meaningful data type, newtype or type synonym.

If you're interested in writing an efficient implementation but don't quite know where to start, the best primer I know of is Chris Okasaki's "Purely Functional Data Structures", which you can read a version of here: https://www.cs.cmu.edu/~rwh/theses/okasaki.pdf

Getting Started

For installation and learning resources, refer to the exercism help page.

Running the tests

To run the test suite, execute the following command:

stack test

If you get an error message like this...

No .cabal file found in directory

You are probably running an old stack version and need to upgrade it.

Otherwise, if you get an error message like this...

No compiler found, expected minor version match with...
Try running "stack setup" to install the correct GHC...

Just do as it says and it will download and install the correct compiler version:

stack setup

Running GHCi

If you want to play with your solution in GHCi, just run the command:

stack ghci

Feedback, Issues, Pull Requests

The exercism/haskell repository on GitHub is the home for all of the Haskell exercises.

If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue. We'll do our best to help you!

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.