Sema for VS Code

Sema support for VS Code — a Lisp with first-class LLM primitives.

Language support for Sema, a Lisp dialect with first-class LLM primitives.

Install

Available on the VS Marketplace (VS Code) and Open VSX (VSCodium, Cursor, Windsurf, Gitpod, …):

ext install sema-lang.sema-lang

Or open the Extensions view (Cmd+Shift+X / Ctrl+Shift+X) and search for Sema Lisp.

Features

• Syntax highlighting for .sema files (special forms, builtins, LLM primitives, keywords, strings, numbers, regex/f-string literals, and more)
• Bracket matching, auto-closing, and surrounding pairs for (), [], {}, and strings
• Comment toggling with Cmd+/ / Ctrl+/
• S-expression-aware indentation
• File icons for .sema and .sema-nb files
• Language server (sema lsp): completions, hover docs, go-to-definition, references, rename, signature help, diagnostics, document symbols, and inline eval results
• Debugging (sema dap): step-through debugging with line/conditional breakpoints, step in/over/out, stack traces, variable and upvalue inspection, evaluate-on-hover, pause/continue, and an "Uncaught Exceptions" filter
• Notebooks: open a .sema-nb file to edit it in the embedded Sema notebook UI with live cell execution
• Command: Sema: Clear Inline Results to clear inline eval decorations

Requirements

The language server, debugger, and notebook features shell out to the sema binary. Install it from sema-lang.com and make sure it's on your PATH, or point the extension at it explicitly:

{
  "sema.path": "/absolute/path/to/sema"
}

Syntax highlighting and bracket/comment editing work without the binary.

Debugging

The extension registers a debug adapter that launches sema dap — the stdio DAP server built into your sema binary. Add a launch configuration to .vscode/launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "sema",
      "request": "launch",
      "name": "Debug Sema Program",
      "program": "${file}",
      "stopOnEntry": false
    }
  ]
}

Then press F5 in a .sema file.

Notebooks

Opening a .sema-nb file launches sema notebook serve for that file and embeds its web UI directly in the editor tab (live cell execution, one server per open notebook, stopped when you close the tab). It uses the same sema.path binary — no extra setup.

Building from source

npm install
npm run compile
npx @vscode/vsce package

This produces sema-<version>.vsix, which you can install with:

code --install-extension sema-<version>.vsix

Development

1. Open this repository in VS Code
2. Run npm install
3. Press F5 to launch an Extension Development Host
4. Open any .sema file to see syntax highlighting and, if sema is installed, the language server

Links

• Website — sema-lang.com
• Playground — sema.run
• Documentation — sema-lang.com/docs
• Grammar — tree-sitter-sema
• Repository — sema-lisp/vscode-sema

License

MIT © Helge Sverre