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

Install from the VS Code Marketplace:

ext install helgesverre.sema

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

If the Marketplace listing isn't available yet (publish pending), build and install the .vsix locally — see Building from source.

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 bundles a debug adapter backed by the sema dap server. 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

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

Sema Lisp

Sema Lang