Language Server & Editor Setup

Keel provides IDE support through the Language Server Protocol (LSP) and tree-sitter grammar for syntax highlighting.

Language Server Features

The Keel Language Server provides:

Tree-Sitter Grammar

The keel-tree-sitter grammar provides syntax highlighting for:

• Keywords, functions, types, constructors
• Operators including pipes (|>) and composition (>>)
• Pattern matching syntax
• Comments (line -- and block {- -})

Editor Setup

VS Code / Positron

The keel-vscode extension provides full IDE support including tree-sitter syntax highlighting, LSP features, code formatting, REPL integration, Jupyter notebooks, and data science features.

See the VS Code & Positron page for installation and configuration.

Helix

Helix has built-in support for tree-sitter grammars. Add the following to ~/.config/helix/languages.toml:

[[language]]
name = "keel"
scope = "source.kl"
injection-regex = "keel"
file-types = ["kl"]
comment-token = "--"
indent = { tab-width = 2, unit = "  " }
language-servers = ["keel-lsp"]
roots = ["keel.toml"]

[language.auto-pairs]
'(' = ')'
'{' = '}'
'[' = ']'
'"' = '"'

[[grammar]]
name = "keel"
source = { git = "https://codeberg.org/Keel/keel-tree-sitter", rev = "main" }

[language-server.kl-lsp]
command = "keel"
args = ["lsp"]

Then fetch and build the grammar:

helix --grammar fetch
helix --grammar build

If using the standalone keel-lsp binary instead of the unified CLI:

[language-server.kl-lsp]
command = "keel-lsp"

Zed

Install the Keel extension from the Zed Extensions panel, or see keel-zed-extension for manual installation.

The extension provides:

• Syntax highlighting via tree-sitter
• Auto-indentation — Smart indent/dedent for functions, modules, case expressions
• Format on save via keel-fmt
• Comment support — Line (--) and block ({- -}) comments
• Symbol navigation — Tags for functions, types, and modules

LSP support is not yet available in the Zed extension.

Neovim

Tree-sitter Setup

Add Keel to your nvim-treesitter configuration:

local parser_config = require("nvim-treesitter.parsers").get_parser_configs()

parser_config.kl = {
  install_info = {
    url = "https://codeberg.org/Keel/keel-tree-sitter",
    files = { "src/parser.c" },
    branch = "main",
  },
  filetype = "keel",
}

vim.filetype.add({
  extension = {
    kl = "keel",
  },
})

Then install the parser:

:TSInstall keel

LSP Setup

Using the unified CLI (recommended):

vim.api.nvim_create_autocmd("FileType", {
  pattern = "keel",
  callback = function()
    vim.lsp.start({ name = "keel-lsp", cmd = { "keel", "lsp" } })
  end,
})

Or using the standalone keel-lsp binary:

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

if not configs.keel_lsp then
  configs.keel_lsp = {
    default_config = {
      cmd = { "keel-lsp" },
      filetypes = { "keel" },
      root_dir = lspconfig.util.root_pattern("keel.toml", ".git"),
      settings = {},
    },
  }
end

lspconfig.keel_lsp.setup({})

Emacs

Emacs support is planned for a future release. Contributions welcome!

Building from Source

Recommended: Unified CLI

git clone https://codeberg.org/Keel/keel-cli
cd keel-cli
cargo install --path .

This provides keel lsp along with the formatter, REPL, and runner.

Standalone Language Server

git clone https://codeberg.org/Keel/keel-lsp
cd keel-lsp
cargo build --release

The binary will be at target/release/keel-lsp. Add it to your PATH.

Tree-sitter Grammar

git clone https://codeberg.org/Keel/keel-tree-sitter
cd keel-tree-sitter
tree-sitter generate

Using with Nix

If you use Nix, keel lsp and tree-sitter support are included in the keel-cli flake:

nix develop git+https://codeberg.org/Keel/keel-cli

This provides a development shell with all tools pre-configured.

Related Projects

• keel-cli — Unified CLI (language server, formatter, REPL, runner)
• keel-lsp — Standalone language server
• keel-vscode — VS Code and Positron extension
• keel-jupyter-kernel — Jupyter kernel for Keel
• keel-tree-sitter — Tree-sitter grammar
• keel-zed-extension — Zed editor extension