Nix Shell for Haskell Development

A ready-to-use Nix shell environment tailored for Haskell, having Haskell Streamly and its ecosystem packages installed out of the box. Easily customizable to include any package from Hackage. Includes:

• Haskell compiler - ghc
• Haskell project build tool - cabal
• Streamly ecosystem libraries
• Hoogle server for documentation
• Haskell language server (HLS)
• A few other Haskell dev tools
• Vi editor nvim
• Visual Studio Code editor codium

Check the nixpkgs version used in the default.nix file.

Please refer to this page for Haskell language server features.

Starting the Shell

There are two ways to start the nix shell.

Directly using github URL

To get a shell with the development environment installed in it, use the following command:

nix-shell https://github.com/composewell/streamly-packages/archive/v0.1.4.tar.gz

By default all optional features are installed. If it takes too long or uses too much disk space, you can pass arguments to the nix expression to customize install, for example:

nix-shell --arg haskell-tools false --arg hoogle false ...

Check out default.nix for all available options.

By cloning the github repo

You can clone the streamly-packages repo and run the nix-shell command from the repo root directory.

git clone https://github.com/composewell/streamly-packages
cd streamly-packages
nix-shell

This is especially useful if you would like to customize the environment before using.

Using the Shell

Once you are in the shell, you can use ghc, cabal, nvim, codium, hoogle, and other tools from the PATH. ghc will have streamly packages installed in its package database, ready to use.

To start with, you can try building and running the examples from the streamly-examples package.

Alternatively, you can start the interactive repl ghci and run Haskell code interactively.

Show installed packages

To show the Haskell packages that are already installed in the shell, run the following command in the nix shell:

ghc-pkg list

Updating package versions

To update the versions of Haskell packages included, edit the nix/haskellPackages.nix file to specify particular git commit ids or package versions from hackage to be used.

Changing a package version may break other packages dependent on the changed package. If you do not need the broken packages you can comment those in default.nix. Otherwise change the versions of the broken packages as well accordingly.

Adding your own packages

If you need any additional packages in this environment just add them to the list of packages in default.nix.

Accessing the documentation

Inside the nix shell, run the following command:

hoogle server --local -p 8080

Open the URL http://127.0.0.1:8080 in your browser.

Using vim editor

Inside the nix shell, run the following command:

nvim

Use ESC :q to quit. Use ,h for help. Use :colorscheme morning if you want a light theme.

Add the following to your $HOME/.config/nvim/coc-settings.json to use the haskell language server with nvim:

{
  "languageserver": {
    "haskell": {
      "command": "haskell-language-server-wrapper",
      "args": ["--lsp"],
      "rootPatterns": ["*.cabal", "stack.yaml", "cabal.project", "package.yaml", "hie.yaml"],
      "filetypes": ["haskell", "lhaskell"],
      "settings": {
        "haskell": {
          "checkParents": "CheckOnSave",
          "checkProject": true,
          "formattingProvider": "fourmolu"
        }
      }
    }
  }
}

Using VSCode editor

To run VSCodium, the open source version of Microsoft VSCode, run the following command in the nix-shell:

codium

If you have started the nix-shell with haskell-tools included, you will have the Haskell Language Server installed in the shell. If you get a pop up saying: "How do you want the extension to manage/discover HLS and the relevant toolchain?" just choose, "Manually via PATH".

You can also set it later in the following section in settings:

• Extensions
  • Haskell
    • Manage HLS
      • PATH

If you wish to use your existing installation of VSCode instead of codium from the nix-shell, you can do that too, just make sure to run it from within the nix-shell so that it is able to use the installed Haskell tools and libraries. For example, on MacOS, if you have your vscode app in Downloads folder:

open ~/Downloads/Visual\ Studio\ Code.app