Editor Support for T

This guide describes how to set up syntax highlighting and language server (LSP) features for the T programming language in various editors.

Language Server Protocol (LSP)

The T language server provides advanced features like Autocompletion (context-aware suggestions), Diagnostics (real-time error checking), Hover Information (tooltips showing signatures/docs), and Go to Definition.

The t-lsp server is implemented in OCaml. When you enter a T project via nix develop, the correctly versioned binary is put in your PATH.

[!IMPORTANT] Launching the LSP: For your editor to find the t-lsp binary, you must either launch your editor from within a nix develop shell, or use a tool like direnv with use flake to automatically load the environment.

Editor Configuration

VS Code / Positron

You can install the T language extension in two ways:

  1. Download the latest release: t-lang-0.51.0.vsix (or download from the repository assets).

  2. Install the extension using the command line:

    code --install-extension /path/to/downloaded/t-lang-0.51.0.vsix

    Alternatively, in VS Code, go to the Extensions view, click the ... menu, and select Install from VSIX…

Option B: From a cloned T repository

If you have already cloned the T repository locally:

code --install-extension editors/vscode/t-lang-0.51.0.vsix

Launching the Editor

Start VS Code or Positron from the same nix shell where you run t:

nix develop
code .

Once VS Code opens, we recommend opening the main entry point for your workspace: - For projects: Open src/pipeline.t - For packages: Open src/main.t

Tip: You can use Cmd+Enter (macOS) or Ctrl+Enter (Linux/Windows) to send the current line or selection to the T REPL, exactly like in RStudio.

Vim / Neovim

1. Syntax Highlighting

Copy the support files into your .vim directory:

# Detect .t files
mkdir -p ~/.vim/ftdetect
cp editors/vim/ftdetect/t.vim ~/.vim/ftdetect/t.vim

# Syntax rules
mkdir -p ~/.vim/syntax
cp editors/vim/syntax/t.vim ~/.vim/syntax/t.vim

2. LSP (via coc.nvim or nvim-lspconfig)

For Vim (coc.nvim), add this to your :CocConfig:

{
  "languageserver": {
    "tlang": {
      "command": "t-lsp",
      "filetypes": ["t"],
      "rootPatterns": ["tproject.toml", ".git"]
    }
  }
}

For Neovim (nvim-lspconfig), add this to your init.lua:

local lspconfig = require('lspconfig')
local configs = require('lspconfig.configs')

if not configs.tlang then
  configs.tlang = {
    default_config = {
      cmd = { "t-lsp" },
      filetypes = {'t'},
      root_dir = lspconfig.util.root_pattern('tproject.toml', '.git'),
      settings = {},
    }
  }
end
lspconfig.tlang.setup{}

Emacs

1. Syntax Highlighting

Add the editors/emacs/ directory to your load-path in init.el:

(add-to-list 'load-path "/path/to/tlang/editors/emacs")
(require 't-mode)

2. LSP (via eglot)

Add the following to your init.el:

(with-eval-after-load 'eglot
  (add-to-list 'eglot-server-programs
               '(t-mode . ("t-lsp"))))

;; Automatically start eglot when opening a .t file
(add-hook 't-mode-hook 'eglot-ensure)

Quarto

For literate programming with executable {t} chunks, add Quarto to your T project tools in tproject.toml:

[additional-tools]
packages = ["quarto"]

Then run t update and enter the project with nix develop. T will provision _extensions/tlang automatically. Enable the tlang filter in your document front matter:

---
filters:
  - tlang
---

Building from Source

If you are developing T itself, you can rebuild the LSP server with:

nix build .#default

The binary will be located at result/bin/t-lsp.