haskell-template

Haskell project template optimized for a fully reproducible and friendly development environment. Based on:

• Nix + Flakes + GHC 9
• VSCode + HLS
• fourmolu autoformatting
• Relude as Prelude.
  • .hlint.yaml is from relude

Getting Started

First-time setup:

• Install Nix & enable Flakes
• Run nix develop -c haskell-language-server to sanity check your environment
• Open as single-folder workspace in Visual Studio Code
  • When prompted by VSCode, install the workspace recommended extensions
  • Ctrl+Shift+P to run command "Nix-Env: Select Environment" and then select shell.nix.
    • The extension will ask you to reload VSCode at the end. Do it.

To run the program with auto-recompile:

• Press Ctrl+Shift+B in VSCode, or run bin/run in terminal, to launch Ghcid running your program.

Open Main.hs, and expect all HLS IDE features like hover-over tooltip to work out of the box. Try changing the source, and expect Ghcid to re-compile and re-run the app in the terminal below.

---

Renaming the project:

git clone <your-clone-url>
cd your-project
NAME=myproject

git mv haskell-template.cabal ${NAME}.cabal
nix run nixpkgs#sd -- haskell-template ${NAME} * */*
git add . && git commit -m rename

Tips

• Run nix flake update to update all flake inputs. nixpkgs is pinned to a specific a rev in flake.nix, which you can advance to the latest rev reported in status.nixos.org.
• Run treefmt in nix shell to autoformat the project. This uses treefmt, which uses ./treefmt.toml (where fourmolu and nixpkgs-fmt are specified).

Alternatives

• haskell.nix: Getting started with Flakes
• Serokell's Flake template
  • Same, but using haskell.nix