Install

Prerequisites

ghcup — the Haskell toolchain installer. Install it via the official one-liner if you haven't already:
```
curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | sh
```
Node.js 22+ — required at build time (the wasm-iserv host for Template Haskell evaluation runs via node) and for post-link.mjs.
Ubuntu's apt nodejs is too old

Ubuntu noble's apt nodejs package is 18.19.1 — post-link.mjs uses import.meta.filename (added in Node 20.11) and will silently exit without writing the JSFFI glue. On Ubuntu, install Node 22 from NodeSource:
```
curl -fsSL https://deb.nodesource.com/setup_22.x | sudo -E bash -
sudo apt-get install -y --no-install-recommends nodejs
```
python3 — for the make run-web static server in the templates (any static server works; this just uses python3 -m http.server).
wasi-sdk (for the wasm target) — the wasm GHC's C compiler (wasm32-unknown-wasi-clang) lives here. We deliberately don't bundle wasi-sdk in the ghcup channel — its version pinning is ghc-wasm-meta's domain, and we'd rather defer to a single source of truth. Install via the upstream bootstrap script:
```
curl -fsSL https://gitlab.haskell.org/ghc/ghc-wasm-meta/-/raw/master/bootstrap.sh \
  | FLAVOUR=9.12 PREFIX=$HOME/.ghc-wasm sh
export PATH="$HOME/.ghc-wasm/wasi-sdk/bin:$PATH"
```
wasi-sdk prefix bridge

wasi-sdk's binaries are named wasm32-wasi-clang etc., but the wasm GHC was configured with the canonical autoconf triple wasm32-unknown-wasi. After installing wasi-sdk, create the missing prefix-bridge symlinks:
```
WASI_BIN="$HOME/.ghc-wasm/wasi-sdk/bin"
for tool in clang clang++; do
  ln -sf "$WASI_BIN/wasm32-wasi-$tool" "$WASI_BIN/wasm32-unknown-wasi-$tool"
done
for tool in ar nm ranlib strip; do
  ln -sf "$WASI_BIN/llvm-$tool" "$WASI_BIN/wasm32-unknown-wasi-$tool"
done
```
Once we ship a ghc98-minimal-ghc-web devx flavor (see stable-haskell/devx#250), this dance disappears.

emscripten (for the JS target) — the JS backend's C toolchain, the JS analogue of wasi-sdk. Install + activate:

git clone --depth 1 --branch 3.1.74 https://github.com/emscripten-core/emsdk.git
cd emsdk && ./emsdk install 3.1.74 && ./emsdk activate 3.1.74 && source ./emsdk_env.sh

Install the toolchain

ghcup config add-release-channel \
  https://stable-haskell.github.io/ghc/ghcup-multi-target-0.1.0.yaml
ghcup install ghc   multi-9.14.0.stable.2
ghcup set     ghc   multi-9.14.0.stable.2
ghcup install cabal 3.17.0.0.stable.0
ghcup set     cabal 3.17.0.0.stable.0

ghcup set (above) symlinks every per-target binary — ghc (native), wasm32-unknown-wasi-*, and javascript-unknown-ghcjs-* — into ~/.ghcup/bin, which ghcup keeps on your $PATH. If it isn't already there, add it:

export PATH="$HOME/.ghcup/bin:$PATH"

Verify

$ ghc --version                          # native
The Glorious Glasgow Haskell Compilation System, version 9.14.0
$ wasm32-unknown-wasi-ghc --version      # wasm cross
The Glorious Glasgow Haskell Compilation System, version 9.14.0
$ javascript-unknown-ghcjs-ghc --version # JS cross
The Glorious Glasgow Haskell Compilation System, version 9.14.0
$ cabal --version
cabal-install version 3.17.0.0.stable.0

If both commands print versions, you're ready for the hello template.

Host platforms

Host	Status	Tarball
`aarch64-darwin` (Apple Silicon)	✅ shipping	`ghc-multi-target-aarch64-darwin.tar.gz`
`x86_64-linux`	✅ shipping	`ghc-multi-target-x86_64-linux.tar.gz`
`aarch64-linux`	✅ shipping	`ghc-multi-target-aarch64-linux.tar.gz`
`x86_64-darwin`, Windows	follow-up	—

The package-db binary cache (package.cache) is regenerated automatically by ghc-pkg on first read (mtime-based), so no relocate step is required after install — ghcup does the right thing out of the box.

What's installed

$HOME/.ghcup/
├── bin/                        # ghcup symlinks: ghc, wasm32-unknown-wasi-*,
│                               #   javascript-unknown-ghcjs-*, cabal, …
├── ghc/multi-9.14.0.stable.2/
│   ├── bin/                    # one binary, three targets (argv[0] dispatch)
│   ├── lib/                    # native package db + libraries
│   ├── lib/targets/
│   │   ├── wasm32-unknown-wasi/lib/        # wasm libs (+ post-link.mjs, dyld.mjs)
│   │   └── javascript-unknown-ghcjs/lib/   # JS libs
│   └── share/                  # settings, GHCi templates, etc.
└── cabal/3.17.0.0.stable.0/
    └── bin/cabal               # dual-compiler aware cabal-install

Next: build the hello template.