When you're logged in, you can say `exercism fetch haskell` to get the next available exercise on the track.

Every time you submit a solution to an exercise, you will get the next in line the next time you fetch.

If you want to try a specific exercise, you can always fetch it directly (commands are listed below).

The exercises are ordered roughly in order of difficulty.

### Available Exercises

• Hello World The classical introductory exercise. Just say "Hello, World!"
• Leap Given a year, report if it is a leap year.
• Space Age Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.
• Bob Bob is a lackadaisical teenager. In conversation, his responses are very limited.
• Pangram Determine if a sentence is a pangram.
• Collatz Conjecture Calculate the number of steps to reach 1 using the Collatz conjecture
• Rna Transcription Given a DNA strand, return its RNA Complement Transcription.
• Sum Of Multiples Given a number, find the sum of all the multiples of particular numbers up to but not including that number.
• Difference Of Squares Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
• Grains Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.
• Acronym Convert a long phrase to its acronym
• Perfect Numbers Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for natural numbers.
• Hamming Calculate the Hamming difference between two DNA strands.
• Nucleotide Count Given a DNA string, compute how many times each nucleotide occurs in the string.
• Grade School Given students' names along with the grade that they are in, create a roster for the school
• Isogram Determine if a word or phrase is an isogram.
• Diamond Given a letter, print a diamond starting with 'A' with the supplied letter at the widest point.
• Etl We are going to do the `Transform` step of an Extract-Transform-Load.
• Raindrops Convert a number to a string, the contents of which depend on the number's factors.
• Accumulate Implement the `accumulate` operation, which, given a collection and an operation to perform on each element of the collection, returns a new collection containing the result of applying that operation to each element of the input collection.
• Strain Implement the `keep` and `discard` operation on collections. Given a collection and a predicate on the collection's elements, `keep` returns a new collection containing those elements where the predicate is true, while `discard` returns a new collection containing those elements where the predicate is false.
• Phone Number Clean up user-entered phone numbers so that they can be sent SMS messages.
• Twelve Days Output the lyrics to 'The Twelve Days of Christmas'
• Isbn Verifier Check if a given string is a valid ISBN-10 number.
• Run Length Encoding Implement run-length encoding and decoding.
• Beer Song Produce the lyrics to that beloved classic, that field-trip favorite: 99 Bottles of Beer on the Wall.
• Triangle Determine if a triangle is equilateral, isosceles, or scalene.
• Scrabble Score Given a word, compute the scrabble score for that word.
• Kindergarten Garden Given a diagram, determine which plants each child in the kindergarten class is responsible for.
• Complex Numbers Implement complex numbers.
• Robot Simulator Write a robot simulator.
• Secret Handshake Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.
• Protein Translation Translate RNA sequences into proteins.
• Anagram Given a word and a list of possible anagrams, select the correct sublist.
• Simple Linked List Write a simple linked list implementation that uses Elements and a List
• List Ops Implement basic list operations
• Meetup Calculate the date of meetups.
• Roman Numerals Write a function to convert from normal numbers to Roman Numerals.
• Prime Factors Compute the prime factors of a given natural number.
• Allergies Given a person's allergy score, determine whether or not they're allergic to a given item, and their full list of allergies.
• All Your Base Convert a number, represented as a sequence of digits in one base, to any other base.
• Largest Series Product Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.
• Clock Implement a clock that handles times without dates.
• Matrix Given a string representing a matrix of numbers, return the rows and columns of that matrix.
• House Output the nursery rhyme 'This is the House that Jack Built'.
• Pascals Triangle Compute Pascal's triangle up to a given number of rows.
• Pythagorean Triplet There exists exactly one Pythagorean triplet for which a + b + c = 1000. Find the product a * b * c.
• Saddle Points Detect saddle points in a matrix.
• Series Given a string of digits, output all the contiguous substrings of length `n` in that string.
• Sieve Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.
• Atbash Cipher Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
• Bracket Push Make sure the brackets and braces all match.
• Crypto Square Implement the classic method for composing secret messages called a square code.
• Nth Prime Given a number n, determine what the nth prime is.
• Word Count Given a phrase, count the occurrences of each word in that phrase.
• Binary Search Tree Insert and search for numbers in a binary tree.
• Luhn Given a number determine whether or not it is valid per the Luhn formula.
• Queen Attack Given the position of two queens on a chess board, indicate whether or not they are positioned so that they can attack each other.
• Ocr Numbers Given a 3 x 4 grid of pipes, underscores, and spaces, determine which number is represented, or whether it is garbled.
• Food Chain Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'
• Rotational Cipher Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
• Spiral Matrix Given the size, return a square matrix of numbers in spiral order.
• Custom Set Create a custom set type.
• Parallel Letter Frequency Count the frequency of letters in texts using parallel computation.
• Transpose Take input text and output it transposed.
• Simple Cipher Implement a simple shift cipher like Caesar and a more secure substitution cipher
• Palindrome Products Detect palindrome products in a given range.
• Robot Name Manage robot factory settings.
• Pig Latin Implement a program that translates from English to Pig Latin
• Say Given a number from 0 to 999,999,999,999, spell out that number in English.
• Bank Account Simulate a bank account supporting opening/closing, withdraws, and deposits of money. Watch out for concurrent transactions!
• Sublist Write a function to determine if a list is a sublist of another list.
• Rail Fence Cipher Implement encoding and decoding for the rail fence cipher.
• Linked List Implement a doubly linked list
• Zebra Puzzle Solve the zebra puzzle.
• Minesweeper Add the numbers to a minesweeper board
• Wordy Parse and evaluate simple math word problems returning the answer as an integer.
• Change Correctly determine change to be given using the least number of coins
• Alphametics Write a function to solve alphametics puzzles.
• Bowling Score a bowling game
• Poker Pick the best hand(s) from a list of poker hands.
• Connect Compute the result for a game of Hex / Polygon
• Dominoes Make a chain of dominoes.
• Sgf Parsing Parsing a Smart Game Format string.
• Go Counting Count the scored points on a Go board.
• Lens Person Use lenses to update nested records (specific to languages with immutable data).
• Zipper Creating a zipper for a binary tree.
• Forth Implement an evaluator for a very simple subset of Forth
• Pov Reparent a graph on a selected node