Wren

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Wren is a small, fast, class-based concurrent scripting language. Think Smalltalk in a Lua-sized package with a dash of Erlang and wrapped up in a familiar, modern syntax. Small. The VM is under 4,000 semicolons of readable and lovingly-commented C.

Syllabus

Hello World

Exercism's classic introductory exercise. Just say "Hello, World!".

Leap

Determine whether a given year is a leap year.

Two-Fer

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

Armstrong Numbers

Determine if a number is an Armstrong number.

Bank Account

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

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

Collatz Conjecture

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

Darts

Calculate the points scored in a single toss of a Darts game.

Difference of Squares

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

Eliud's Eggs

Help Eliud count the number of eggs in her chicken coop by counting the number of 1 bits in a binary representation.

Hamming

Calculate the Hamming distance between two DNA strands.

Isogram

Determine if a word or phrase is an isogram.

Line Up

Help lining up customers at Yaʻqūb's Deli.

Pangram

Determine if a sentence is a pangram.

Raindrops

Convert a number into its corresponding raindrop sounds - Pling, Plang and Plong.

Resistor Color

Convert a resistor band's color to its numeric representation.

Resistor Color Duo

Convert color codes, as used on resistors, to a numeric value.

Reverse String

Reverse a given string.

RNA Transcription

Given a DNA strand, return its RNA complement.

Scrabble Score

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

Space Age

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

Acronym

Convert a long phrase to its acronym.

Allergies

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

Anagram

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

Binary Search

Implement a binary search algorithm.

Clock

Implement a clock that handles times without dates.

D&D Character

Randomly generate Dungeons & Dragons characters.

Change the data format for scoring a game to more easily add other languages.

Flatten Array

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

Grains

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

High Scores

Manage a player's High Score list.

ISBN Verifier

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

Largest Series Product

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

Luhn

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

Matrix

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

Micro Blog

Given an input string, truncate it to 5 characters.

Nucleotide Count

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

Perfect Numbers

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

Phone Number

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

Prime Factors

Compute the prime factors of a given natural number.

Protein Translation

Translate RNA sequences into proteins.

Proverb

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

Resistor Color Trio

Convert color codes, as used on resistors, to a human-readable label.

Roman Numerals

Convert modern Arabic numbers into Roman numerals.

Rotational Cipher

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

Secret Handshake

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

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.

Square Root

Given a natural radicand, return its square root.

Strain

Implement the `keep` and `discard` operation on collections.

Sum of Multiples

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

Triangle

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

Twelve Days

Output the lyrics to 'The Twelve Days of Christmas'.

All Your Base

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

Atbash Cipher

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

Bottle Song

Produce the lyrics to the popular children's repetitive song: Ten Green Bottles.

Crypto Square

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

Diamond

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

Food Chain

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

House

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

Matching Brackets

Make sure the brackets and braces all match.

Nth Prime

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

Pascal's Triangle

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

Pig Latin

Implement a program that translates from English to Pig Latin.

Pythagorean Triplet

Given an integer N, find all Pythagorean triplets for which a + b + c = N.

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.

Robot Name

Manage robot factory settings.

Robot Simulator

Write a robot simulator.

Run-Length Encoding

Implement run-length encoding and decoding.

Saddle Points

Detect saddle points in a matrix.

Simple Cipher

Implement the Vigenère cipher, a simple substitution cipher.

Simple Linked List

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.

Sublist

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

Word Count

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

Yacht

Score a single throw of dice in the game Yacht.

Affine Cipher

Create an implementation of the Affine cipher, an ancient encryption algorithm from the Middle East.

Binary Search Tree

Insert and search for numbers in a binary tree.

Camicia

Simulate the card game and determine whether the match ends or enters an infinite loop.

Circular Buffer

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

Complex Numbers

Implement complex numbers.

Conway's Game of Life

Implement Conway's Game of Life.

Custom Set

Create a custom set type.

Grade School

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

Killer Sudoku Helper

Write a tool that makes it easier to solve Killer Sudokus

Kindergarten Garden

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

Knapsack

Given a knapsack that can only carry a certain weight, determine which items to put in the knapsack in order to maximize their combined value.

Linked List

Implement a doubly linked list.

List Ops

Implement basic list operations.

OCR Numbers

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

Rational Numbers

Implement rational numbers.

Relative Distance

Given a family tree, calculate the degree of separation.

Split-Second Stopwatch

Keep track of time through a digital stopwatch.

State of Tic-Tac-Toe

Determine the game state of a match of Tic-Tac-Toe.

Tournament

Tally the results of a small football competition.

Transpose

Take input text and output it transposed.

Wordy

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

Flower Field

Mark all the flowers in a garden.

Grep

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

Intergalactic Transmission

Add parity bits to a message for transmission

Palindrome Products

Detect palindrome products in a given range.

Piecing It Together

Fill in missing jigsaw puzzle details from partial data

Rail Fence Cipher

Implement encoding and decoding for the rail fence cipher.

Rectangles

Count the rectangles in an ASCII diagram.

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

Two Bucket

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

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.