Sema for Zed

Sema support for Zed — grammar, debugger, and MCP server.

Language support for Sema — a Lisp dialect with first-class LLM primitives — in the Zed editor.

Install

From inside Zed: cmd-shift-P → zed: extensions → search for Sema → Install.

The extension is pending publish to the Zed extension registry. Until it lands there, install it as a dev extension:

1. Clone this repository: git clone https://github.com/sema-lisp/zed-sema.git
2. In Zed, open the command palette (cmd-shift-P) → zed: install dev extension
3. Select the cloned zed-sema directory.

The tree-sitter-sema grammar is fetched automatically by Zed at the commit pinned in extension.toml — no manual grammar setup is required.

Features

• Syntax highlighting — special forms, LLM primitives (llm/chat, defagent, deftool, …), slash-namespaced builtins (string/trim, json/encode), keyword literals (:foo), booleans, nil, numbers, characters, strings, and quote/quasiquote/unquote operators.
• Comments — ; line comments and #| … |# block comments, with TODO/FIXME highlighting injected inside them.
• Auto-pairs & bracket matching — (), [], {}, and "".
• Code outline — top-level define, defun, defn, defmacro, defagent, deftool, define-record-type, lambda/fn, block forms (let, let*, letrec, begin, do, cond, case, when, unless, try), and module/import.
• Auto-indent — 2-space indentation for lists, vectors, and hash maps; outdent on closing delimiters.
• Vim text objects — af/if for function definitions (define, defun, lambda, fn, defmacro), ac/ic for agents and tools (defagent, deftool), plus comment objects.
• Runnables & tasks — a gutter play button (▶) on each top-level form that runs the current file through the sema-run task, backed by the sema CLI.
• Debugging (DAP) — launch-and-debug .sema programs via Sema's debug adapter (sema dap): breakpoints, stepping, and variable inspection. Pick Sema in Zed's debugger, or add a launch config (see below).
• MCP server — the extension registers Sema's MCP context server (sema mcp), exposing Sema's tools (eval, build, notebook, docs) to Zed's agent panel.
• Secret redaction — string arguments to llm/configure, llm/define-provider, and llm/auto-configure are hidden during screen sharing.

Requirements

The syntax queries work on their own, but the run tasks and language server need the sema CLI on your PATH:

cargo install sema-lang

See sema-lang.com for other install options.

Running Sema files

The extension draws a play button (▶) in the gutter next to each top-level form. (Zed only renders runnables anchored to nodes — there's no whole-file ▶ — so it's anchored to each form; clicking any of them runs the file.)

Zed doesn't let an extension bundle the task the ▶ runs, so you add it once, yourself. Run zed: open tasks (a global tasks.json that applies to every project) or create a project .zed/tasks.json, and add:

[
  {
    "label": "sema run",
    "command": "sema",
    "args": ["$ZED_FILE"],
    "tags": ["sema-run"]
  }
]

The tags match the runnable's sema-run tag, so clicking a ▶ runs sema on the current file. Tasks run in your project shell, so sema resolves from your PATH. This is a one-time setup. You can also run it without the gutter via zed: spawn task → sema run.

Language Server (LSP)

The extension registers the language server automatically — no settings needed. Open a .sema file and sema lsp starts (the sema binary is resolved from your PATH). Completions, hover, go-to-definition, references, rename, and semantic tokens work out of the box.

Debugging

Pick Sema when starting a debug session, or add a launch config to .zed/debug.json:

[
  {
    "label": "Debug Sema Program",
    "adapter": "sema",
    "request": "launch",
    "program": "$ZED_FILE",
    "stopOnEntry": false
  }
]

The adapter runs sema dap over stdio (the sema binary is resolved from your PATH, or a per-adapter override).

MCP server

The sema MCP context server is registered automatically; enable it in Zed's agent panel to give the assistant access to Sema's tools (eval, build, notebook, docs). It runs sema mcp.

If the MCP server fails to start (Broken pipe / timeout), it's because Zed launched from the GUI can't find sema on its PATH — the context-server API can't resolve it the way the LSP/debugger can. Point Zed at the full path in your settings:

{
  "context_servers": {
    "sema": { "command": { "path": "/Users/you/.cargo/bin/sema", "arguments": ["mcp"] } }
  }
}

(Find the path with which sema.) The extension honors this override.

Links

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

License

MIT © Helge Sverre