Retrocomputing with Clash

Retrocomputing with Clash

Haskell for FPGA Hardware Design

Haskell has become the functional programming language of choice<br>for many developers due to its excellent tools for abstraction<br>and principled program design. The open source Clash hardware description<br>language now brings these features to FPGA development.

Retrocomputing with Clash takes the experienced<br>Haskell programmer on a journey into the world of hardware<br>design with Clash. Our approach is based on using Haskell to its<br>fullest potential, using abstractions like monads and lenses in<br>building a library of reusable components.

But that wouldn't put the fun in functional programming! And so we<br>put these components to good use in implementing various<br>retro-computing devices:

Pocket calculator

Pong (sample chapter)

A simple, but Turing-complete computer that uses Brainfuck as its machine code

An implementation of the CHIP-8 virtual computer specification

Intel 8080 CPU

Space Invaders arcade machine

Compucolor II, a home computer from 1977 complete with keyboard, color video, and a floppy drive

Not part of the book, but demonstrating its approach to<br>developing fun FPGA designs with Clash, is Flappy Square from my Haskell<br>eXchange 2022 talk.

I absolutely love the very Haskell approach to circuit design<br>in this book, as opposed to my own write-Verilog-in-Haskell<br>style. It leverages Haskell's type system in a very<br>natural way to protect against many traps we as circuit<br>designers often fall into.

The book clearly demonstrates the benefits of using a modern<br>programming language for circuit design, where it builds<br>reusable functionality and components at a far finer<br>granularity than what I'm used to in traditional hardware<br>description languages.

Another thing that's absolutely great is the book's use of SDL2 multimedia library to<br>emulate peripherals like monitors which enables you to fully interact with the<br>computers and games that you'll be building without having to go through the sometimes<br>long and painful process of programming an FPGA.

– Christiaan Baaij, Clash lead developer, QBayLogic co-founder

This is the book for functional programmers<br>looking to get into FPGAs and digital logic design. Learn<br>Clash, the "I can’t believe it's not Haskell!" hardware<br>description language, while indulging in nostalgia for the<br>1980s. Take a joyride through a variety of hands-on projects,<br>including Pong, Space Invaders, and the Compucolor II, a<br>personal computer based on the Intel 8080. Recommended.

– Miëtek Bak, mathematician

This book is a fascinating, knowledge-expanding work that leads to exciting domains.<br>It is hard for me to believe that I can learn about low level designs through Haskell<br>because it is a notoriously high-level language.

This language has been such a gift that has kept on giving.

Thanks to the clash-shake tool, I can run Haskell code<br>on real hardware without prior knowledge of the FPGA toolchain.

– Tristan de Cacqueray, principal software developer

Where to buy

Electronic version (PDF, e-book, and HTML) from Leanpub

Print<br>version from Lulu (Color hardcover edition)

Print<br>version from Lulu (B&W paperback edition)

Table of contents

Sample chapters

Chapter 8: Generative Graphics

Chapter 9: Project: Pong

Hardware considerations

My other Clash projects

Advent<br>of Clash 2025: FPGA circuits implementing solutions to the<br>Advent of Code<br>2025 problems. Heavily inspired by Tristan de<br>Cacqueray's great blog post on the same topic.

Clash Course in Solving Sudoku:<br>Functional Pearl from Haskell Symposium 2025. Watch my talk on<br>YouTube or look at the<br>code.

Flappy Square, a<br>minimalistic Flappy Bird

Code from the book

retroclash-lib:<br>Library of code shared between repositories, available from Hackage

retroclash-sim:<br>Library of simulation code shared between repositories, available from Hackage

clash-shake:<br>Shake build system rules for driving hardware synthesis from<br>Clash all the way to FPGA bitfile, supporting Xilinx, Intel<br>and SymbiFlow toolchains

Calculator

Pong

Brainfuck computer

CHIP-8

Intel 8080

Space Invaders

Compucolor II

All the rest:<br>smaller programs

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This<br>page is created by Gergő Érdi.<br>Send your comments to gergo@erdi.hu.