# Idris

One of the easiest ways to add new exercises to the Idris track is to translate them from other language tracks on Exercism. This page lists all of the problem specifications in the common pool of exercises which have not yet been implemented in Idris.

The icon links to the language-independent description of the problem.

The icon links to the canonical test data.

We also link to all the implementations of each exercise in other languages, which you can use for inspiration.

Once you've picked an exercise, follow the instructions in this guide and submit your pull request to the Idris track repository on GitHub.

### Bob

Bob is a lackadaisical teenager. In conversation, his responses are very limited.

### Raindrops

Convert a number to a string, the contents of which depend on the number's factors.

### Difference Of Squares

Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.

### Anagram

Given a word and a list of possible anagrams, select the correct sublist.

### Word Count

Given a phrase, count the occurrences of each word in that phrase.

### Atbash Cipher

Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.

### Phone Number

Clean up user-entered phone numbers so that they can be sent SMS messages.

### Roman Numerals

Write a function to convert from normal numbers to Roman Numerals.

### Triangle

Determine if a triangle is equilateral, isosceles, or scalene.

### Nucleotide Count

Given a DNA string, compute how many times each nucleotide occurs in the string.

### Pangram

Determine if a sentence is a pangram.

### Scrabble Score

Given a word, compute the scrabble score for that word.

### Grains

Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.

### Allergies

Given a person's allergy score, determine whether or not they're allergic to a given item, and their full list of allergies.

### Gigasecond

Calculate the moment when someone has lived for 10^9 seconds.

### Etl

We are going to do the `Transform` step of an Extract-Transform-Load.

### Space Age

Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.

### Sum Of Multiples

Given a number, find the sum of all the multiples of particular numbers up to but not including that number.

### Acronym

Convert a long phrase to its acronym

### Beer Song

Produce the lyrics to that beloved classic, that field-trip favorite: 99 Bottles of Beer on the Wall.

### Isogram

Determine if a word or phrase is an isogram.

### Luhn

Given a number determine whether or not it is valid per the Luhn formula.

### Collatz Conjecture

Calculate the number of steps to reach 1 using the Collatz conjecture

### Largest Series Product

Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.

### Pascals Triangle

Compute Pascal's triangle up to a given number of rows.

### Bracket Push

Make sure the brackets and braces all match.

Given students' names along with the grade that they are in, create a roster for the school

### Robot Name

Manage robot factory settings.

### Sieve

Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.

Convert a number, represented as a sequence of digits in one base, to any other base.

### Clock

Implement a clock that handles times without dates.

### Meetup

Calculate the date of meetups.

### Nth Prime

Given a number n, determine what the nth prime is.

### Crypto Square

Implement the classic method for composing secret messages called a square code.

### Perfect Numbers

Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for natural numbers.

### Prime Factors

Compute the prime factors of a given natural number.

### Series

Given a string of digits, output all the contiguous substrings of length `n` in that string.

### Two Fer

Create a sentence of the form "One for X, one for me."

### Binary Search

Implement a binary search algorithm.

### Robot Simulator

Write a robot simulator.

### Run Length Encoding

Implement run-length encoding and decoding.

### Pig Latin

Implement a program that translates from English to Pig Latin

### 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.

### Say

Given a number from 0 to 999,999,999,999, spell out that number in English.

### Secret Handshake

Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.

### Minesweeper

Add the numbers to a minesweeper board

### Diamond

Given a letter, print a diamond starting with 'A' with the supplied letter at the widest point.

### Flatten Array

Take a nested list and return a single list with all values except nil/null

### Sublist

Write a function to determine if a list is a sublist of another list.

### Wordy

Parse and evaluate simple math word problems returning the answer as an integer.

### Binary Search Tree

Insert and search for numbers in a binary tree.

### Custom Set

Create a custom set type.

### List Ops

Implement basic list operations

### Rotational Cipher

Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.

### Bowling

Score a bowling game

### Isbn Verifier

Check if a given string is a valid ISBN-10 number.

### Palindrome Products

Detect palindrome products in a given range.

Detect saddle points in a matrix.

### 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.

### Change

Correctly determine change to be given using the least number of coins

### Ocr Numbers

Given a 3 x 4 grid of pipes, underscores, and spaces, determine which number is represented, or whether it is garbled.

### Transpose

Take input text and output it transposed.

### Armstrong Numbers

Determine if a number is an Armstrong number

### Circular Buffer

A data structure that uses a single, fixed-size buffer as if it were connected end-to-end.

### Kindergarten Garden

Given a diagram, determine which plants each child in the kindergarten class is responsible for.

### Protein Translation

Translate RNA sequences into proteins.

### Pythagorean Triplet

There exists exactly one Pythagorean triplet for which a + b + c = 1000. Find the product a * b * c.

### Simple Cipher

Implement a simple shift cipher like Caesar and a more secure substitution cipher

### Bank Account

Simulate a bank account supporting opening/closing, withdraws, and deposits of money. Watch out for concurrent transactions!

### Complex Numbers

Implement complex numbers.

### Food Chain

Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'

### Matrix

Given a string representing a matrix of numbers, return the rows and columns of that matrix.

Reverse a string

### React

Implement a basic reactive system.

Write a simple linked list implementation that uses Elements and a List

### Spiral Matrix

Given the size, return a square matrix of numbers in spiral order.

### Twelve Days

Output the lyrics to 'The Twelve Days of Christmas'

### Alphametics

Write a function to solve alphametics puzzles.

### Connect

Compute the result for a game of Hex / Polygon

### Dominoes

Make a chain of dominoes.

### Forth

Implement an evaluator for a very simple subset of Forth

### House

Output the nursery rhyme 'This is the House that Jack Built'.

### Proverb

For want of a horseshoe nail, a kingdom was lost, or so the saying goes. Output the full text of this proverbial rhyme.

### Poker

Pick the best hand(s) from a list of poker hands.

### Rail Fence Cipher

Implement encoding and decoding for the rail fence cipher.

### Rectangles

Count the rectangles in an ASCII diagram.

### Tournament

Tally the results of a small football competition.

### Variable Length Quantity

Implement variable length quantity encoding and decoding.

### Zipper

Creating a zipper for a binary tree.

### Book Store

To try and encourage more sales of different books from a popular 5 book series, a bookshop has decided to offer discounts of multiple-book purchases.

### Diffie Hellman

Diffie-Hellman key exchange.

### Parallel Letter Frequency

Count the frequency of letters in texts using parallel computation.

### Two Bucket

Given two buckets of different size, demonstrate how to measure an exact number of liters.

### Markdown

Refactor a Markdown parser

### Grep

Search a file for lines matching a regular expression pattern. Return the line number and contents of each matching line.

### Pov

Reparent a graph on a selected node

### Scale Generator

Generate musical scales, given a starting note and a set of intervals.

### Word Search

Create a program to solve a word search puzzle.

### Error Handling

Implement various kinds of error handling and resource management

### Rational Numbers

Implement rational numbers.

### Zebra Puzzle

Solve the zebra puzzle.

### Go Counting

Count the scored points on a Go board.

### Sgf Parsing

Parsing a Smart Game Format string.

### Dot Dsl

Write a Domain Specific Language similar to the Graphviz dot language

### Tree Building

Refactor a tree building algorithm.

### Yacht

Score a single throw of dice in the game Yacht

### Hangman

Implement the logic of the hangman game using functional reactive programming.

### Ledger

Refactor a ledger printer.

### Lens Person

Use lenses to update nested records (specific to languages with immutable data).

### Paasio

Report network IO statistics