Lisp Flavoured Erlang (LFE) Lisp Flavoured Erlang (LFE)

Add new exercises to Lisp Flavoured Erlang (LFE)

One of the easiest ways to add new exercises to the Lisp Flavoured Erlang (LFE) track is to translate them from other language tracks on Exercism. This page lists all of the exercises that exist on Exercism, but have not yet been implemented in Lisp Flavoured Erlang (LFE).

The icon links to the generic, language-independent problem description

The icon links to the canonical test data

The language icons link to each existing implementation of the problem.

Once you've picked an exercise, follow the instructions in the Contributing Guide and submit your pull request to the Lisp Flavoured Erlang (LFE) track repository on GitHub.





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

Roman Numerals

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

Scrabble Score

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


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


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

Pascals Triangle

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

Nth Prime

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

All Your Base

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

Bracket Push

Make sure the brackets and braces all match.

Binary Search

Implement a binary search algorithm.

Crypto Square

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


Determine if a word or phrase is an isogram.

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.

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.


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


Add the numbers to a minesweeper board

Secret Handshake

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

Pig Latin

Implement a program that translates from English to Pig Latin


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

Custom Set

Create a custom set type.

Ocr Numbers

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

Run Length Encoding

Implement run-length encoding and decoding.

Binary Search Tree

Insert and search for numbers in a binary tree.

Kindergarten Garden

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

Linked List

Implement a doubly linked list

Palindrome Products

Detect palindrome products in a given range.

List Ops

Implement basic list operations


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

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.

Simple Cipher

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


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

Flatten Array

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

Food Chain

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


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


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


Implement a basic reactive system.


Compute the result for a game of Hex / Polygon


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


Tally the results of a small football competition.


Write a function to solve alphametics puzzles.


Implement an evaluator for a very simple subset of Forth

Protein Translation

Translate RNA sequences into proteins.

Simple Linked List

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


Take input text and output it transposed.

Twelve Days

Output the lyrics to 'The Twelve Days of Christmas'


Make a chain of dominoes.


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

Rotational Cipher

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

Variable Length Quantity

Implement variable length quantity encoding and decoding.

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.

Rail Fence Cipher

Implement encoding and decoding for the rail fence cipher.


Creating a zipper for a binary tree.


Reparent a graph on a selected node


Count the rectangles in an ASCII diagram.

Word Search

Create a program to solve a word search puzzle.


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


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

Scale Generator

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

Two Bucket

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

Zebra Puzzle

Solve the zebra puzzle.

Collatz Conjecture

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

Diffie Hellman

Diffie-Hellman key exchange.


Refactor a Markdown parser

Sgf Parsing

Parsing a Smart Game Format string.

Dot Dsl

Write a Domain Specific Language similar to the Graphviz dot language

Error Handling

Implement various kinds of error handling and resource management

Go Counting

Count the scored points on a Go board.


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


Refactor a ledger printer.

Lens Person

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

Tree Building

Refactor a tree building algorithm.

Two Fer

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


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