Examples

Explore Roc through small, runnable examples.

Getting started

Hello, World! — Print a greeting with a minimal Roc application.
Multi-line Comments — Write comments across several lines and learn why Roc uses # for each line.
FizzBuzz — Use conditions and arithmetic to solve the classic FizzBuzz exercise.
All Syntax in 1 File — Explore the language syntax in one annotated file.

Tuples — Group values of different types into tuples and access their elements.
Pattern Matching on Lists — Match list shapes and bind their elements to names.
Pattern Aliases — Name an entire matched pattern while binding its individual parts.
Nominal and Opaque Types — Define distinct types and control access to their underlying representation.
Open Records — Accept records with additional fields while requiring the fields a function needs.
Nested Types — Group related types inside a type module.
Recursive Types — Build expression trees with recursive and mutually recursive types.
Polymorphism — Write reusable functions with where constraints and shared constraint aliases.
Custom Inspect — Customize how opaque values appear when inspected, including hiding a secret.
Custom Literals — Create values of your own types from number literals, quoted strings, and interpolated strings.

Basic Dict Usage — Create a dictionary and look up, insert, and remove entries.
Sets — Create sets and combine them with union, intersection, and difference.
Loops — Use for, while, and local variables, and compare loops with fold.
Looping Effectful Functions — Repeat an effectful operation by reading and summing numbers until input ends.
Streams and for! — Consume effectful stream pipelines with for! and create a custom stream for reading file lines.

Error Handling Basic (Try) — Represent success and failure with Try and handle both outcomes.
? Operator Desugaring — See how the ? operator expands into explicit error handling.
Safe Math — Handle arithmetic overflow and other numeric errors explicitly.
Wrapping and Saturating Arithmetic — Choose wrapping or saturating arithmetic when values exceed numeric limits.
Error Handling Real World (Try) — Combine error handling across several operations in a command-line program.

String Capture Patterns — Capture filenames and parse numeric IDs from paths with string patterns.
JSON — Parse JSON data into a typed Roc record.
Advanced Parsing — Parse optional fields, defaults, and camelCase JSON, and work with other formats.
Encoding & Decoding — Define custom encoders and parsers for a nominal type.
Record Builder — Build a date parser by combining field parsers with record builder syntax.

Least Squares — Find the smallest integer whose square exceeds the previous square by more than 1,000.
Towers of Hanoi — Solve the Towers of Hanoi puzzle with recursion.
Graph Traversal — Represent a graph and traverse its connected nodes.

Import Files — Embed text or binary files in an executable at compile time.
Multiple Roc Files — Split an application into modules across multiple files.
Import from Directory — Import a module from a subdirectory.
Import Package from Module — Pass a package dependency from an application to one of its modules.

Paths — Build and inspect file paths with the path package.
Random Numbers — Generate reproducible pseudorandom numbers with the roc-random package.
Unicode Text — Work with graphemes, Unicode scalars, word boundaries, and casing.
Parser — Compose a parser that counts letters using the roc-parser package.

CLI Args Simple — Read arguments passed to a command-line application.
CLI Args File — Open a file named by a command-line argument and read its first line.
Terminal Commands — Run an external command and work with its output.
Snake Game — Build a playable Snake game with an effectful game loop.

Drawing with RocRay — Draw an interactive graphical application with the roc-ray platform.

Each example’s page lists the Roc version used to validate it.