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WebAssembly (Wasm) support

Note: WebAssembly support is currently very preliminary.

For horizontal scalability reasons, we would like to run the primer and primer-api packages in the student's browser, rather than on a backend server. Therefore, we'd like to compile these packages to a wasm32-wasi target and call the (native) Primer API from TypeScript.

Currently, we can compile these two packages to wasm32-wasi, but with the following caveats:

  1. Neither haskell.nix nor nixpkgs.haskellPackages support the wasm32-wasi cross-target at the moment, so we can only build Wasm targets directly via wasm32-wasi-cabal and wasm32-wasi-ghc. For interactive development, we provide a special nix develop shell which provides the necessary tools:

    nix develop .#wasm

    Note that the required tools are currently only available for x86_64-linux Nix systems, so the special wasm Nix shell only exists for that platform.

  2. Once you're in the special Wasm shell, it's advisable to use the special Makefile.wasm32. To build the WebAssembly targets, run:

    make -f Makefile.wasm32

    And to run the tests using the wasmtime runtime, run:

    make -f Makefile.wasm32 test

  3. We now have a very preliminary Wasm frontend for Primer. The goal of this frontend is to eventually replace the existing TypeScript frontend, but it's currently missing quite a bit of that implementation's functionality.

    To run the Wasm frontend, use the following command from the special Wasm shell:

    make -f Makefile.wasm32 serve-frontend

    Then visit http://localhost:8000 in your browser.