Clash is a functional hardware description language that borrows both its syntax and semantics from the functional programming language Haskell. The Clash compiler transforms these high-level descriptions to low-level synthesizable VHDL, Verilog, or SystemVerilog.

Features of Clash:

• Strongly typed, but with a very high degree of type inference, enabling both safe and fast prototyping using concise descriptions.

• Interactive REPL: load your designs in an interpreter and easily test all your component without needing to setup a test bench.

• Higher-order functions, with type inference, result in designs that are fully parametric by default.

• Synchronous sequential circuit design based on streams of values, called Signals, lead to natural descriptions of feedback loops.

• Support for multiple clock domains, with type safe clock domain crossing.

Mailing list: for updates and questions join the mailing list clash-language+subscribe@googlegroups.com or read the forum

Slack: functionalprogramming.slack.com#clash (Invite yourself at fpslack.com/).

IRC: libera.chat#clash (webchat access) (or ircs://irc.libera.chat:6697/clash if you want to use a regular IRC client)

Check out clash-lang.org/install to install the latest stable release of Clash, or to setup a Clash project.

Get the source code using Git and enter the cloned directory:

git clone git@github.com:clash-lang/clash-compiler.git

# Alternatively, if you haven't setup SSH keys with GitHub:
# git clone https://github.com/clash-lang/clash-compiler.git

cd clash-compiler

To check out a released version, use:

git checkout v1.2.3

To checkout a release branch use:

git checkout 1.2

Note that release branches might contain non-released patches.

¹ GHC 9.2 contains a regression, rendering Clash error messages indecipherable. This change was reverted in 9.4.

² GHC 9.0.2 on Windows fails to compile clash-cores. We therefore don't run the Clash testsuite on CI for this combination.

³ Clash starts extremely slowly when compiled with 9.6 on Windows. See #2684.

To use Cabal you need both Cabal and GHC installed on your system. We recommend using ghcup. For more information, see https://www.haskell.org/downloads/.

To run clash use:

cabal v2-run -- clash

If this fails, make sure you've got an up-to-date package index:

cabal update

Install Stack and run:

stack run -- clash

Or use Nix to get a shell with the clash and clashi binaries on your PATH:

# Start the default dev shell
nix develop .

# Start a dev shell with a specific GHC version
nix develop .#ghc961

You will need a modern version of nix with support for the new-style nix command and flakes (2.4 or newer). Support for these must still be manually enabled, this can be done by setting

experimental-features = nix-command flakes

in your nix.conf.

To automatically enter and exit the nix environment on directory change, you can install direnv and nix-direnv and write the following to a .envrc file in the root of this repository:

use flake

watch_file nix/*

Upon adding or changing this file you must direnv allow in order for the file to be automatically loaded / reloaded on project changes.

Individual packages / applications can also be built or run using the nix build and nix run commands, i.e.

nix build .#clash-ghc
nix run .#clashi

• Clashilator: tooling to integrate Clash with Verilator. Enables fast, multithreaded simulation by compiling Clash designs to C++.
• Clash Protocols: experimental library for writing Clash circuits with bidirectional communication - such as AXI or Avalon.
• Clash Starters: starter projects to quickly get you up and running.
• Clash WaveDrom: generate wave diagrams from Clash using WaveDrom

• Contranomy: a RISCV implementation verified using the RISC-V Formal Verification Framework.
• Space Invaders: a Clash implementation of the 1978 Space Invaders arcade machine by Taito.