GHC's wasm backend now supports Template Haskell and ghci - Tweag

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2024-11-21 10:00:04

Two years ago I wrote a blog post to announce that the GHC wasm backend had been merged upstream. I’ve been too lazy to write another blog post about the project since then, but rest assured, the project hasn’t stagnated. A lot of improvements have happened after the initial merge, including but not limited to:

Both the Nix and non-Nix installation methods default to GHC HEAD, for which binary artifacts for Linux and macOS hosts, for both x86_64 and aarch64, are provided. The Linux binaries are statically linked so they should work across a wide range of Linux distros.

If you take a look at htop, you’ll notice wasm32-wasi-ghc spawns a node child process. That’s the “external interpreter” process that runs our Template Haskell (TH) splice code as well as ghci bytecode. We’ll get to what this “external interpreter” is about later, just keep in mind that whatever code is typed into this ghci session is executed on the wasm side, not on the native side.

Now let’s run some code. It’s been six years since I published the first blog post when I joined Tweag and worked on a prototype compiler codenamed “Asterius”; the first Haskell program I managed to compile to wasm was fib, time to do that again: