Linked List in Haskell
Implement a doubly linked list
exercism fetch haskell linked-list
Implement a doubly linked list.
Like an array, a linked list is a simple linear data structure. Several common data types can be implemented using linked lists, like queues, stacks, and associative arrays.
A linked list is a collection of data elements called nodes. In a singly linked list each node holds a value and a link to the next node. In a doubly linked list each node also holds a link to the previous node.
You will write an implementation of a doubly linked list. Implement a Node to hold a value and pointers to the next and previous nodes. Then implement a List which holds references to the first and last node and offers an array-like interface for adding and removing items:
push(insert value at back);
pop(remove value at back);
shift(remove value at front).
unshift(insert value at front);
To keep your implementation simple, the tests will not cover error
shift will never be called on an
If you want to know more about linked lists, check Wikipedia.
To complete this exercise, you need to create the data type
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.
For installation and learning resources, refer to the exercism help page.
Running the tests
To run the test suite, execute the following command:
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:
If you want to play with your solution in GHCi, just run the command:
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!
Classic computer science topic
Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.