L^ Language Support

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Language support for L^ (lhat) in Visual Studio Code. Open a .lh or .lton file to receive diagnostics and language features from lhatls, L^'s language server.

Install

Install L^ Language Support from the Visual Studio Marketplace, then open an L^ workspace. Marketplace installs the platform-specific extension package for your machine; it already contains the matching lhatls binary. No separate language-server installation or network download at editor startup is needed.

The extension supports VS Code 1.85 and newer.

If you install a generic VSIX or build the extension from source, provide a server yourself with lhat.serverPath, or put lhatls on PATH.

{
  "lhat.serverPath": "/absolute/path/to/lhatls"
}

Use lhatls.exe on Windows. An explicit setting always takes precedence over the bundled server, so it is also the way to try a locally built server.

Features

• Syntax and semantic highlighting for L^ and LTON (.lton) files
• Live type-checking diagnostics
• Completion, hover information, go to definition, find references, and rename
• Document symbols and a graph-specific outline
• Copy Signature for copying the full inferred type of the name at the cursor
• A read-only graph view of an L^ source file
• Debugging through the L^ Debug Adapter Protocol implementation

Open the Command Palette and run L^: Show Graph View to switch a .lh file to its graph view. Run L^: Show Source to switch back. Set lhat.graph.openBeside to true when the graph should open in a split editor.

Debug L^ programs

The language server is included with the extension; the runtime is deliberately not. Running or debugging a program requires the standalone lhat executable from the L^ releases, either on PATH or named by lhat.runtimePath.

{
  "lhat.runtimePath": "C:\\path\\to\\lhat.exe"
}

With a .lh file active, press F5 to run it under the debugger. Breakpoints, stepping, variables, expression evaluation, conditional breakpoints, and program output are available in VS Code's normal debug views. For a repeatable configuration, use a launch.json entry such as:

{
  "type": "lhat",
  "request": "launch",
  "name": "Run current L^ program",
  "program": "${file}",
  "cwd": "${workspaceFolder}",
  "args": [],
  "stopOnEntry": false,
  "relaxed": false
}

Workspace configuration

By default, lhatls checks L^ files in the workspace. Add an lhat-lsp.json file at the workspace root to exclude generated or vendored trees, retain specific generated sources, or show relaxed-only diagnostics as warnings:

{
  "exclude": ["build/", "**/node_modules/"],
  "force_include_files": ["build/generated/api.lh"],
  "strict": false
}

If your embedding host registers its own L^ API, generate lhat-host.json at the workspace root so the language server can type-check against that API:

lhat --dump-host-api lhat-host.json

The generated file describes registrations for analysis only; it does not run host callbacks. Regenerate it whenever the host API changes.

Settings

Development

The extension itself is a TypeScript project. To run it in an Extension Development Host:

npm ci
npm run compile

Open this repository in VS Code and press F5. Build lhatls from the L^ repository and set lhat.serverPath to that executable. While rebuilding a server on Windows, set lhat.serverAutoRestart to false to keep the extension from restarting the old process before the linker can replace it.

To create a local generic VSIX:

npm run package

That generic package intentionally contains no native binary. The release workflow produces the platform-specific packages that bundle lhatls.

License

Apache-2.0. See LICENSE.