Building a Compiler with Haskell

A General Guide

4 min read3 days ago

Building a compiler might sound daunting, but it’s an exciting and rewarding project. It involves several stages, like parsing source code, generating machine instructions, and optimizing the output. In this guide, we’ll walk you through how to build a compiler using VS Code and Docker, with a focus on Haskell tools for parsing, working with Abstract Syntax Trees (AST), semantic analysis, error handling, optimization, code generation, and testing.

Setting Up Your Development Environment

To keep things simple and reproducible, we recommend using Docker for your environment and VS Code as your editor. Docker ensures that your environment, dependencies, and configurations stay consistent across different machines.

Tools and Technologies:

Editor: Visual Studio Code (VS Code)
Containerization: Docker
Programming Language: Haskell
Build & Package Management: Cabal, Stack, Nix
Version Control & Deployment: GitHub, GitLab, DockerHub, Nixpkgs

Understanding Compiler Phases

A compiler goes through several phases, each handling a specific task in turning source code into machine-readable instructions. Here’s a quick breakdown:

1. Parsing and Lexical Analysis

Converts raw source code into a structured format using a parser.
Useful Libraries: megaparsec (for combinator-based parsing), alex (for lexical analysis), happy (for generating parsers).

2. Abstract Syntax Tree (AST) Representation

Represents the structure of the program after parsing.
Typically implemented with algebraic data types (ADTs) in Haskell.

3. Semantic Analysis & Type Checking

Ensures the program follows the correct rules — like types and scopes.
Often handled with monads (e.g., State, Reader) or attribute grammars.
Error Handling: Good error messages make debugging easier. You can use structured error types and Megaparsec’s custom error messages to improve clarity.

4. Intermediate Representation (IR) and Code Generation

Turns the AST into an easier-to-analyze Intermediate Representation (IR).
You can use a custom IR or go with frameworks like GHC Core or LLVM IR.
Code Generation:
LLVM: Use llvm-hs to generate LLVM IR and turn it into machine code.
Custom Assembly: Generate assembly code directly for a specific architecture (like x86 or ARM).

5. Optimization Frameworks

Improves performance by removing redundant calculations, simplifying loops, etc.
Common techniques include constant folding, dead code elimination, and loop unrolling.
Haskell-Specific Optimizations:
Use GHC Core for optimizations.
Rewrite rules can help improve performance by changing inefficient expressions.

6. Error Handling and Debugging

Parser Errors: Improve error messages in Megaparsec for better readability.
Semantic Errors: Show clear messages when type checking fails.
Runtime Errors: For compiled languages, you can add debugging features like stack traces.

Testing Your Compiler

To ensure your compiler works correctly, you should use a combination of property-based testing, unit testing, golden testing, and fuzz testing. Haskell offers a variety of frameworks to help:

QuickCheck — Property-based testing for random input validation.
HUnit — A framework for unit testing.
Golden Testing — Compares expected and actual outputs.
Tasty Framework — Combines multiple types of tests.
HPC (Haskell Program Coverage) — Helps ensure you test all parts of your code.
SmallCheck — Tests your program with small inputs.
Fuzz Testing — Generates random inputs to find bugs.
Differential Testing — Compares your compiler’s output to another known working one.

Packaging and Deployment

Once your compiler is working, you’ll want to package it up for distribution. Here are a few tools you can use:

Cabal — A standard package manager for Haskell.
Stack — A tool that simplifies managing dependencies.
Hackage — A repository for Haskell libraries.
Nix — A package manager that helps ensure reproducible builds.
Docker — For containerized deployments.

Deploying Your Compiler

You can share your compiler through:

GitHub or GitLab — For version control and collaboration.
DockerHub — To share prebuilt Docker images.
Nixpkgs — If you want your compiler available via the Nix package system.

Alternative Approaches

Haskell also supports different ways to build a compiler:

Functional Intermediate Representations (FIRs): Use functional constructs as an intermediate step before converting to LLVM IR.
Embedded Domain-Specific Languages (DSLs): You can embed the language within Haskell instead of building a separate compiler (e.g., writing an interpreter).
Using GHC as a Backend: Instead of building your own compiler, you can use GHC plugins to extend Haskell’s compilation process.

Conclusion

Building a compiler involves several stages, each with its own challenges. By using VS Code, Docker, Haskell libraries, and testing tools, you can build a functional and reliable compiler. Whether you’re working on a simple language or something more complex, these tools and practices will help you every step of the way.