haskell-lsp

Haskell language server (HLS) for Claude Code, providing code intelligence, diagnostics and navigation for Haskell projects.

Supported Extensions

.hs, .lhs, .cabal

Installation

The plugin only registers the server with Claude Code; haskell-language-server-wrapper must be on your PATH. The wrapper picks the HLS build matching the GHC version your project uses.

Via GHCup (recommended)

ghcup install hls

Via Homebrew (macOS)

brew install haskell-language-server

Via package manager (Linux)

# Arch Linux
sudo pacman -S haskell-language-server

# Nix
nix profile install nixpkgs#haskell-language-server

Verify the install with haskell-language-server-wrapper --version.

Project setup

HLS discovers how to build your project through a cradle: cabal.project, stack.yaml or an hie.yaml are detected automatically. The first request in a project can be slow while HLS builds the cradle and loads dependencies, which is why this plugin sets a 120s startup timeout. The project should build with cabal build or stack build before you rely on HLS.

Known limitations

• Slow first request. HLS loads your project and its dependencies on startup. The first one or two LSP calls in a session can fail with server is starting; retrying a moment later succeeds.
• The project must build. HLS needs a working cradle (cabal build / stack build succeeding at least once), otherwise it reports cradle errors instead of code intelligence.

Install the plugin

/plugin install haskell-lsp --marketplace LaurentRDC/haskell-lsp

More Information

• HLS documentation
• GitHub Repository