Visit https://unsafePerform.IO/retroclash/ for sample chapter, full table of contents, and color hardcover version. Haskell has become the functional programming language of choice for many developers due to its excellent tools for abstraction and principled program design. The Clash hardware description language unlocks these features for FPGA design as well. This book takes the experienced Haskell programmer on a journey into the world of hardware design with Clash. Our approach is based on using Haskell to its fullest potential, using abstractions like monads and lenses in building a library of reusable components. But that wouldn't put the "fun" in "functional programming"! And so we put these components to good use in implementing various retro-computing devices: a desktop calculator; Pong; 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.