99 Haskell Problems

A comprehensive collection of solutions to the famous 99 Haskell Problems, designed to help developers learn and practice functional programming concepts in Haskell.

About the 99 Haskell Problems

The 99 Haskell Problems are a collection of programming exercises that cover fundamental concepts in functional programming, including:

• List Processing (Problems 1-28): Working with lists, recursion, and basic data manipulation
• Arithmetic (Problems 31-41): Mathematical computations and number theory
• Logic and Codes (Problems 46-50): Boolean logic and binary representations
• Binary Trees (Problems 54-69): Tree data structures and algorithms
• Multiway Trees (Problems 70-73): Complex tree structures
• Graphs (Problems 80-89): Graph theory and algorithms
• Miscellaneous (Problems 90-99): Advanced topics and puzzles

Each problem includes comprehensive test suites with both unit tests and property-based tests using QuickCheck to ensure correctness and robustness of the solutions.

Running Tests

To run all tests:

cabal test

This will:

• Build all problem modules
• Run the comprehensive HSpec test suite
• Execute QuickCheck property tests

Development

The project uses Nix for development environment setup:

nix develop

Code Formatting

To format all Haskell files with ormolu:

./format.sh

Or manually format specific files:

ormolu --mode inplace src/Problem*.hs test/*.hs

The CI checks ensure all code is properly formatted using ormolu.

Pre-commit Hooks

To set up pre-commit hooks that automatically check formatting and linting:

# Install pre-commit (if not already installed)
pip install pre-commit

# Install the hooks
pre-commit install

# Run hooks on all files (optional)
pre-commit run --all-files

The hooks will automatically run ormolu and hlint checks before each commit.

Project Structure

• Problem*.hs - Solution modules for each problem
• test/Problem*Spec.hs - Test specifications for each problem
• test/Spec.hs - Main test runner using hspec-discover