L4 IDE MCP

The L4 VS Code extension installs the language server and provides syntax highlighting, diagnostics, and MCP integration without requiring a manual Haskell build. Install it from the VS Code Marketplace.

# Install from VS Code Marketplace
# Search for: L4 Rules-as-code
# Publisher: Legalese
# Or use the web editor: https://jl4.legalese.com/

For development or advanced usage, build both the Haskell backend and TypeScript frontend from source. Ensure GHC 9.10.2 and Node.js 20+ are installed first.

git clone https://github.com/smucclaw/l4-ide.git
cd l4-ide
cabal build all          # Build Haskell components
npm ci && npm run build  # Build TypeScript components

The L4 trace and ladder diagram tools require GraphViz to be installed on your system.

# macOS
brew install graphviz

# Ubuntu/Debian
apt-get install graphviz

Use the jl4-repl to interactively load and evaluate L4 specification files. The REPL supports :load, :reload, and trace evaluation commands.

cabal run jl4-repl -- path/to/your-rules.l4

Add the L4 MCP server integration to your Claude Desktop or Claude Code configuration. The server connects to the L4 language toolchain over stdio to provide specification analysis capabilities.

{
  "mcpServers": {
    "l4-ide": {
      "command": "cabal",
      "args": ["run", "jl4-mcp-server"],
      "env": {}
    }
  }
}

Export an evaluation trace from an L4 file as an SVG diagram for review in a browser or documentation.

l4 trace myfile.l4 > trace.dot
dot -Tsvg trace.dot > trace.svg

# Or output directly
l4 trace myfile.l4 --format svg -o out/