Asterius: A Haskell to WebAssembly compiler

A Haskell to WebAssembly compiler
By tweag

webassembly haskell compiler ghc

Asterius: A Haskell to WebAssembly compiler

Asterius is a Haskell to WebAssembly compiler based on GHC. It compiles
Haskell source files or Cabal executable targets to WebAssembly+JavaScript code
which can be run in Node.js or browsers.
It features seamless JavaScript interop
(lightweight Async FFI with Promise support) and small output code (~600KB
hello.wasm for a Hello
World). A lot of common
Haskell packages like lens are already supported. The project is actively
maintained by Tweag I/O.


Demos of popular Haskell apps, running in your browser:

Quickstart using the prebuilt container image

We host a prebuilt container image on Docker
Hub. The image also ships ~2k
prebuilt packages from a recent
Stackage snapshot for convenience of testing simple programs without needing to
set up a Cabal project.

To use the image, mount the working directory containing the source code as a
shared volume, then use the ahc-link program:

[email protected]:/project$ podman run -it --rm -v $(pwd):/workspace -w /workspace terrorjack/asterius
[email protected]:/workspace#

There are a lot of link-time options available to ahc-link, e.g. targeting
the browser platform instead of node, adding extra GHC options or setting
runtime parameters. Check the documentation for
further details.

It's also possible to use ahc-cabal as a drop-in replacement of cabal to
build a Cabal project. Use ahc-dist with --input-exe on the output
"executable" file to generate actual WebAssembly and JavaScript artifacts. See
the diagrams blog
post for an

Check the documentation section
about the prebuilt image for more information, e.g. versioning policy, how to
use with podman/docker, etc.

Building and using asterius locally

See the Building guide in the
documentation for details.

Hacking on Asterius

We recommend using VSCode Remote
Containers to reproduce
the very same dev environment used by our core team members. See the Hacking
guide in the documentation for


We have documentation and blog posts:

Also checkout the HIW 2018 lightning
and the slides of an introductory talk in 2020

Note that they may be slightly out-of-date as the project evolves. Whenever you
find something in the docs of blog posts which doesn't reflect the status quo,
it's a bug and don't hesitate to open a ticket :)

Project status & roadmap

See the roadmap section in the
documentation for details.




Asterius is maintained by Tweag I/O.

Have questions? Need help? Tweet at @tweagio.