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Supercharge your Haskell experience in neovim!

Neovim Lua Haskell Nix

All Contributors




  • telescope.nvim
  • A local hoogle installation (recommended for better hoogle search performance)
  • fast-tags (for automatic tag generation as a fallback for vim.lsp.tagfunc).


Example using packer.nvim:

use {
  requires = {
    'nvim-telescope/telescope.nvim', -- optional
  -- tag = 'x.y.z' -- [^1]

[^1] It is suggested to use the latest release tag and to update it manually, if you would like to avoid breaking changes.

For NixOS users with flakes enabled, this project provides outputs in the form of a package and an overlay; use it as you wish in your nixos or home-manager configuration. It is also available on nixpkgs.

Quick Setup

This plugin automatically configures the haskell-language-server neovim client.

:warning: Do not call the lspconfig.hls setup or set up the lsp manually, as doing so may cause conflicts.

To get started quickly with the default setup, add the following to your neovim config:

local ht = require('haskell-tools')
local def_opts = { noremap = true, silent = true, }
ht.setup {
  hls = {
    -- See nvim-lspconfig's  suggested configuration for keymaps, etc.
    on_attach = function(client, bufnr)
      local opts = vim.tbl_extend('keep', def_opts, { buffer = bufnr, })
      -- haskell-language-server relies heavily on codeLenses,
      -- so auto-refresh (see advanced configuration) is enabled by default
      vim.keymap.set('n', '<space>ca',, opts)
      vim.keymap.set('n', '<space>hs', ht.hoogle.hoogle_signature, opts)
      -- default_on_attach(client, bufnr)  -- if defined, see nvim-lspconfig
-- Suggested keymaps that do not depend on haskell-language-server
-- Toggle a GHCi repl for the current package
vim.keymap.set('n', '<leader>rr', ht.repl.toggle, def_opts)
-- Toggle a GHCi repl for the current buffer
vim.keymap.set('n', '<leader>rf', function()
end, def_opts)
vim.keymap.set('n', '<leader>rq', ht.repl.quit, def_opts)

If using a local hoogle installation, follow these instructions to generate a database.


  • Basic haskell-language-server functionality on par with nvim-lspconfig.hls

Beyond nvim-lspconfig.hls

  • Clean shutdown of language server on exit to prevent corrupted files (see ghc #14533).
  • Automatically adds capabilities for the following plugins, if loaded:
  • Automatically refreshes code lenses by default, which haskell-language-server heavily relies on. Can be disabled.
  • The following code lenses are currently supported:

Show/Add type signatures for bindings without type signatures

Evaluate code snippets in comments

Make import lists fully explicit

Fix module names that do not match the file path

Beyond haskell-language-server

The below features are not implemented by haskell-language-server.

Hoogle-search for signature

  • Search for the type signature under the cursor.
  • Falls back to the word under the cursor if the type signature cannot be determined.
  • Telescope keymaps:
    • <CR> to copy the selected entry ( :: ) to the clipboard.
    • <C-b> to open the selected entry's Hackage URL in a browser.
    • <C-r> to replace the word under the cursor with the selected entry.

Use Hoogle search to fill holes

With the <C-r> keymap, the Hoogle search telescope integration can be used to fill holes.

GHCi repl

Start a GHCi repl for the current project / buffer.

  • Automagically detects the appropriate command (cabal new-repl, stack ghci or ghci) for your project.
  • Choose between a builtin handler or toggleterm.nvim.
  • Dynamically create a repl command for iron.nvim (see advanced configuration).
  • Interact with the repl from any buffer using a lua API.

Open project/package files for the current buffer

Hover actions

Inspired by rust-tools.nvim, this plugin adds the following hover actions (if available):

  • Hoogle search for signature.
  • Open documentation in browser.
  • Open source in browser.
  • Go to definition.
  • Find references.

Additionally, the default behaviour of stylizing markdown is disabled. And the hover buffer's filetype is set to markdown, so that nvim-treesitter users can benefit from syntax highliting of code snippets.

Automatically generate tags

On attaching, Neovim's LSP client will set up tagfunc (:h tagfunc) to query the language server for locations to jump to. If no location is found, it will fall back to a tags file.

If fast-tags is installed, this plugin will set up autocmds to automatically generate tags:

  • For the whole project, when starting a session.
  • For the current (sub)package, when writing a file.

This feature can be tweaked or disabled in the advanced configuration.


For planned features, refer to the issues.

Advanced configuration

To modify the default configs, call

-- defaults
require('haskell-tools').setup {
  tools = { -- haskell-tools options
    codeLens = {
      -- Whether to automatically display/refresh codeLenses
      -- (explicitly set to false to disable)
      autoRefresh = true,
    hoogle = {
      -- 'auto': Choose a mode automatically, based on what is available.
      -- 'telescope-local': Force use of a local installation.
      -- 'telescope-web': The online version (depends on curl).
      -- 'browser': Open hoogle search in the default browser.
      mode = 'auto',
    hover = {
      -- Whether to disable haskell-tools hover and use the builtin lsp's default handler
      disable = false,
      -- Set to nil to disable
      border = {
        { '╭', 'FloatBorder' },
        { '─', 'FloatBorder' },
        { '╮', 'FloatBorder' },
        { '│', 'FloatBorder' },
        { '╯', 'FloatBorder' },
        { '─', 'FloatBorder' },
        { '╰', 'FloatBorder' },
        { '│', 'FloatBorder' },
      -- Stylize markdown (the builtin lsp's default behaviour).
      -- Setting this option to false sets the file type to markdown and enables
      -- Treesitter syntax highligting for Haskell snippets if nvim-treesitter is installed
      stylize_markdown = false,
      -- Whether to automatically switch to the hover window
      auto_focus = false,
    definition = {
      -- Configure vim.lsp.definition to fall back to hoogle search
      -- (does not affect vim.lsp.tagfunc)
      hoogle_signature_fallback = false,
    repl = {
      -- 'builtin': Use the simple builtin repl
      -- 'toggleterm': Use akinsho/toggleterm.nvim
      handler = 'builtin',
      builtin = {
        create_repl_window = function(view)
          -- create_repl_split | create_repl_vsplit | create_repl_tabnew | create_repl_cur_win
          return view.create_repl_split { size = vim.o.lines / 3 }
    -- Set up autocmds to generate tags (using fast-tags)
    -- e.g. so that `vim.lsp.tagfunc` can fall back to Haskell tags
    tags = {
      enable = vim.fn.executable('fast-tags') == 1,
      -- Events to trigger package tag generation
      package_events = { 'BufWritePost' },
  hls = { -- LSP client options
    -- ...
    settings = {
      haskell = { -- haskell-language-server options
        formattingProvider = 'ormolu',
        checkProject = true, -- Setting this to true could have a performance impact on large mono repos.
        -- ...
  • The full list of defaults can be found here.
  • To view all available language server settings (including those not set by this plugin), run haskell-language-server generate-default-config.
  • For detailed descriptions of the configs, look at the haskell-language-server documentation.

How to disable individual code lenses

Some code lenses might be more interesting than others. For example, the importLens could be annoying if you prefer to import everything or use a custom prelude. Individual code lenses can be turned off by disabling them in the respective plugin configurations:

hls = {
  settings = {
    haskell = {
      plugin = {
        class = { -- missing class methods
          codeLensOn = false,
        importLens = { -- make import lists fully explicit
          codeLensOn = false,
        refineImports = { -- refine imports
          codeLensOn = false,
        tactics = { -- wingman
          codeLensOn = false,
        moduleName = { -- fix module names
          globalOn = false,
        eval = { -- evaluate code snippets
          globalOn = false,
        ['ghcide-type-lenses'] = { -- show/add missing type signatures
          globalOn = false,

Set up iron.nvim to use haskell-tools.nvim

Depends on iron.nvim/#300.

local iron = require("iron.core")
iron.setup {
  config = {
    repl_definition = {
      haskell = {
        command = function(meta)
          local file = vim.api.nvim_buf_get_name(meta.current_bufnr)
          -- call `require` in case iron is set up before haskell-tools
          return require('haskell-tools').repl.mk_repl_cmd(file)

Available functions


local ht = require('haskell-tools')
-- Run a hoogle signature search for the value under the cursor


local ht = require('haskell-tools')
-- Toggle a GHCi repl

-- Toggle a GHCi repl for `file`

-- Quit the repl

-- Paste a command to the repl from register `reg`. (`reg` defaults to '"')

-- Query the repl for the type of register `reg`. (`reg` defaults to '"')

-- Query the repl for the type of word under the cursor

-- Query the repl for info on register `reg`. (`reg` defaults to '"')

-- Query the repl for info on the word under the cursor

-- Load a file into the repl

-- Reload the repl


local ht = require('haskell-tools')
-- Open the project file for the current buffer (cabal.project or stack.yaml)

-- Open the package.yaml file for the current buffer

-- Open the *.cabal file for the current buffer

-- Search for files within the current (sub)package
-- `opts`: Optional telescope.nvim find_files options
-- Live grep within the current (sub)package
-- `opts`: Optional telescope.nvim live_grep options


The following functions depend on fast-tags.

local ht = require('haskell-tools')

-- Generate tags for the whole project
-- `path`: An optional file path, defaults to the current buffer
-- `opts`: Optional options:
-- `opts.refresh`: Whether to refresh tags if they have already been generated for a project
ht.tags.generate_project_tags(path, opts)

-- Generate tags for the whole project
-- `path`: An optional file path, defaults to the current buffer

Available commands


  • :HsProjectFile - Open the project file for the current buffer (cabal.project or stack.yaml).
  • :HsPackageYaml - Open the package.yaml file for the current buffer.
  • :HsPackageCabal - Open the *.cabal file for the current buffer.

Telescope extension

If telescope.nvim is installed, haskell-tools.nvim will register the ht extenstion with the following commands:

  • :Telescope ht package_files - Search for files within the current (sub)package.
  • :Telescope ht package_hsfiles - Search for Haskell files within the current (sub)package.
  • :Telescope ht package_grep - Live grep within the current (sub)package.
  • :Telescope ht package_hsgrep - Live grep Haskell files within the current (sub)package.
  • :Telescope ht hoogle_signature - Run a Hoogle search for the type signature under the cursor.

To load the extension, call



LSP features not working

Check which version of GHC you are using (:LspInfo). Sometimes, certain features take some time to be implemented for the latest GHC versions. You can see how well a specific GHC version is supported here.

Minimal config

To troubleshoot this plugin with a minimal config in a temporary directory, use minimal.lua.

With bash or zsh, call:

NVIM_DATA_MINIMAL=$(mktemp -d) nvim -u minimal.lua

With fish, call:

NVIM_DATA_MINIMAL=(mktemp -d) nvim -u minimal.lua


Here are some other plugins I recommend for Haskell (and nix) development in neovim:

Contributors ✨

Thanks goes to these wonderful people (emoji key):

This project follows the all-contributors specification. Contributions of any kind welcome!