The Developer Experience Shell

This repository contains a nix develop shell for Haskell. Its primary purpose is to help get a development shell for Haskell quickly and across multiple operating systems (and architectures).

It requires nix to be installed.

[!IMPORTANT] The README previously suggested to add your current user to trusted-users, but this is essentially equivalent to giving that user root access to the system.

Getting Started

Once you have nix installed:

• Add experimental-features = nix-command flakes to your $XDG_CONFIG_HOME/nix/nix.conf file to enable Nix flakes.
• You should manually add necessary substituters and trusted public keys to your /etc/nix/nix.conf:

  allow-import-from-derivation = "true";
  extra-substituters = https://cache.iog.io https://cache.zw3rk.com
  extra-trusted-public-keys = "hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=" "loony-tools:pr9m4BkM/5/eSTZlkQyRt57Jz7OMBxNSUiMC4FkcNfk="
  

• Ensure that nix-daemon is running (systemctl status nix-daemon on systemd-based systems).

Then, (on Linux, macOS, windows WSL) you can use:

nix develop github:input-output-hk/devx#ghc96 --no-write-lock-file --refresh

To obtain a Haskell development shell for GHC 9.6 including cabal-install, as well as hls and hlint. If you are on macOS on an Apple Silicon chip (M1, M2, ...), and want to switch between Intel (x86_64) and Apple Silicon (aarch64), you can do this by simply passing the corresponding --system argument:

nix develop github:input-output-hk/devx#ghc96 --no-write-lock-file --refresh --system x86_64-darwin
# ... or:
nix develop github:input-output-hk/devx#ghc96 --no-write-lock-file --refresh --system aarch64-darwin

direnv integration

If you use direnv, you can integrate this shell by creating an .envrc file with the following content:

# https://github.com/nix-community/nix-direnv A fast, persistent use_nix/use_flake implementation for direnv:
if ! has nix_direnv_version || ! nix_direnv_version 2.3.0; then
  source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/2.3.0/direnvrc" "sha256-Dmd+j63L84wuzgyjITIfSxSD57Tx7v51DMxVZOsiUD8="
fi
# https://github.com/input-output-hk/devx Slightly opinionated shared GitHub Action for Cardano-Haskell projects 
use flake "github:input-output-hk/devx#ghc96-iog"

Refer to direnv and devx guide for more information.

VSCode DevContainer / GitHub CodeSpace support

To make this developer shell available in VSCode DevContainer or GitHub CodeSpace, simply add a file named .devcontainer/devcontainer.json with the following content:

{
   "image":"ghcr.io/input-output-hk/devx-devcontainer:x86_64-linux.ghc96-iog",
   "onCreateCommand": "on-create-command",
   "customizations":{
      "vscode":{
         "extensions":[
            "haskell.haskell"
         ]
      }
      // Do not set custom `settings` as they would override devx-container defaults...
   }
}

This configuration will work immediately in GitHub CodeSpace! For local VSCode DevContainer, you need Docker and the VSCode extension. For guidance on this, you can follow the Microsoft tutorial.

It's also advised to enable GitHub CodeSpace prebuilds in your repository settings, follow the instructions provided in the GitHub documentation. This will significantly enhance your development experience by reducing the setup time when opening a new CodeSpace.

List of images available: ghc96-iog, ghc98-iog, ghc910-iog, ghc912-iog, ghc96-js-iog, ghc98-js-iog.

[!NOTE] Windows cross-compilation images are currently disabled pending a nixpkgs-2511 fix for the crossThreadsStdenv bootstrap (mcfgthread/pthreads).

[!TIP] If you wish to utilize the DevContainer as a normal Docker container outside of GitHub or VSCode, remember to prefix your commands with bash -ic. This is necessary because the Nix developer environment is loaded through ~/.bashrc. E.g., docker run -it ghcr.io/input-output-hk/devx-devcontainer:x86_64-linux.ghc96-iog bash -ic "cabal --version"

Compilers and Flavors

There are multiple compilers available, and usually the latest for each series from 9.6 to 9.12 (a slight delay between the official release announcement and the compiler showing up in the devx shell is expected due to integration work necessary). The current available ones are: ghc96, ghc98, ghc910, and ghc912 (these are the same ones as in haskell.nix and may contain patches for defects in the official releases).

Flavors

There are various flavors available as suffixes to the compiler names (e.g. #ghc96-minimal-iog).

Flavor	Description	Example	Included
empty	General Haskell Dev	#ghc96	ghc, cabal-install, hls, hlint
-iog	IOG Haskell Dev	#ghc96-iog	adds sodium-vrf, blst, secp256k1, lmdb
-iog-full	IOG Haskell Dev	#ghc96-iog-full	adds sodium-vrf, blst, secp256k1, lmdb, R, postgresql
-minimal	Only GHC, and Cabal	#ghc96-minimal	drops hls, hlint
-static	Building static binaries	#ghc96-static	Static Haskell Cross-Compiler
-js	JavaScript Cross-Compiler	#ghc96-js	JavaScript Haskell Cross-Compiler
-windows	Windows Cross-Compiler	#ghc96-windows	Windows Haskell Cross-Compiler (currently disabled)
-ghc	GHC Development	#ghc96-ghc	GHC Development Compiler

These can then be combined following this schema:

#ghc<ver>[-js|-windows|-static][-minimal][-iog|-iog-full]

For example:

nix develop github:input-output-hk/devx#ghc96-static-minimal-iog --no-write-lock-file --refresh

... would provide a development shell for building static binaries with cabal and the IOG specific libraries, but no Haskell Language Server (hls), and no HLint.

A full list of all available devShells can be seen with:

nix flake show github:input-output-hk/devx

To Go Further

Customizing with haskell.nix

The devx shell utilizes haskell.nix for a consistent development environment across platforms. Direct use of haskell.nix allows for greater customization by adapting Nix expressions to specific project needs, haskell.nix turn a Cabal or Stack projects into a Nix expression. For more details, see the haskell.nix documentation.

Automating with IOG GitHub Actions

The devx GitHub Action, alongside other IOG-provided actions, supports automated workflows for Haskell projects. More information can be found in the IOG GitHub Actions repository.

[!NOTE] For commercial support, please don't hesitate to reach out at devx@iohk.io