GHC 9.6.1 Includes Javascript Backend

Some exciting news this week, as the release of GHC 9.6.1 includes the merger of a couple of different web-based backends - one for Web Assembly and one for Javascript. These features move Haskell in the direction of being a first-class web development language!

From the release notes:

The WebAssembly backend has been merged. This allows GHC to be built as a cross-compiler that targets wasm32-wasi and compiles Haskell code to self-contained WebAssembly modules that can be executed on a variety of different runtimes.

The JavaScript backend has been merged. GHC is now able to be built as a cross-compiler targeting the JavaScript platform.

This is a particularly exciting direction for me, since I’ve been exploring ways to use Haskell in web development for many years, but found a lot of the current approaches require a lot of onboarding work to really get going in a meaningful way. In my Practical Haskell course, I show how to do a basic integration of a Haskell Web Server and an Elm frontend. But I look forward to the day when I can re-do that section of the course entirely with Haskell!

Of course, merging the backends is just a first step - there’s a long way to go. A few caveats mentioned in the release notes as well:

There are a few caveats to be aware of [with the WebAssembly backend]:

To use the WebAssembly backend, one would need to follow the instructions on ghc-wasm-meta. The WebAssembly backend is not included in the GHC release bindists for the time being, nor is it supported by ghcup or stack yet.

The WebAssembly backend is still under active development. It’s presented in this GHC version as a technology preview, bugs and missing features are expected.

The [Javascript] backend should be considered a technology preview. As such it is not ready for use in production, is not distributed in the GHC release bindists and requires the user to manually build GHC as a cross-compiler. See the JavaScript backend wiki page on the GHC wiki for the current status, project roadmap, build instructions and demos.

Both of these backends are technology previews, meaning they’re only ready for the most adventurous Haskellers to start experimenting - a lot of setup work is still required. But it’s certainly an important step in the right direction! Since these are included with GHC 9.6.1, improvements are possible in further minor releases to GHC 9.6, rather than needing to wait for the next major release of GHC 9.8.