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
• Toggle Disabled Code (Ctrl+Shift+/) for switching whole statements off as #[~ … ]# and back on; the graph view shows them greyed out
• 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. PageUp / PageDown scroll vertically by about one screen, except while editing text or using a menu.

Calls and operators place argument expressions in columns by depth. Each column starts at the same top and retains source order. Input groups sit at the right of each call card, with bent definition lines connecting them to the values.

Reassignments and compound assignments use vertical target/value pairs, like let^ / var^, with a definition line for each pair. The heading identifies the operation (Reassignment, Addition Assignment, etc.). All eight compound operators and their nil-checked ? forms are supported; compiler-generated compound-operation trees are displayed using the written RHS only.

Source-backed non-leaf nodes, including calls, operators, index expressions and control structures, can be folded with their arrow button or Toggle Fold/Unfold in the right-click menu. Fold All / Unfold All also covers these nodes. Folding changes only the graph view; input/output slots and layout-only groups do not have independent folds.

if^ statements are labelled Conditional Branch, and if^ expressions Conditional Selection. Their conditions are expression graphs inside independently foldable Condition boxes. Pattern matches use Pattern Matching Branch for statements, with arms arranged horizontally, and Pattern Matching Selection for expressions, with alternatives arranged vertically. Each Pattern box contains an independently foldable expression tree; the default arm has no pattern box. Statement branches without an else show a no-match route around their contents. Completed arms merge below the branch, and execution lines continue to statement addition buttons, including the start-to-add line in an empty document. return^ and panic^ end their execution paths without an outgoing line or a statement append button. Already-written code after an unconditional end remains visible, but is not connected to the execution flow.

For illustrations, use SVG… in the graph toolbar, choose whether to include the background and editing controls, and select Save SVG. The export covers the entire current level, including offscreen nodes, with the current folds, language, colors and graph-only literal edits. Text, node groups and connections remain editable in Inkscape. Editing the SVG does not change the L^ source.

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.

The L^ samples target zero-based indices (lhat commit 5529b14 or later). After rebuilding the runtime, check every repository .lh file and run the indexing regression sample with:

npm run test:lhat -- /path/to/rebuilt/lhat

LHAT_RUNTIME can also select the executable; otherwise it uses lhat from PATH. This includes local, untracked samples and excludes ignored build products. The runtime checks cover dense sequences, inclusive ranges, string positions, variadic arguments, enum numbers and regex capture groups.

testing/ contains the manual Extension Development Host environment and L^ samples. Automated tests and their helpers live in tests/.

npm test includes SVG saving tests. npm run test:svg additionally checks the export in a real browser; set LHAT_TEST_BROWSER to a Chrome/Edge executable if it is not installed in a standard location. This checks offscreen content, editable text, arrows, transparency, folding, drill-down and graph-only edits.

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.