Haskell Nix dev template

A template for completely reproducile build and development in Haskell using Nix.

UPDATE: 10/11/2020

Since I have created this project, I have now found ways to make Haskell projects that I find more convenient. I think using:

• stack with Nix support enabled
• Haskell Language Server (distributed by Nix, see here)
• VSCode with Nix Env Selector & (new) Haskell extensions

is now the best way to go for the most seemless Haskell experience (yet). I might write about it later.

I am still going to let this repository because:

• it still works
• it is just one out of a million ways to setup a Haskell project

TL;DR: this is outdated but not completly irrelevant

How to use

Dependencies

1. Install Nix

Please find the documentation here: https://nixos.org/nix/manual/#chap-installation

TL;DR

bash <(curl https://nixos.org/nix/install)

2. Install VS Code and some plugins:
   • Nix Environment Selector
   • Haskell Syntax Highlighting
   • Either ghcide for ghcide (default) or Haskell Language Server for HIE (slower but has a bit more tools)

Recommanded steps for faster use

Nix will compile everything that is not in the cache, especially HIE, GHCIDE, etc. In order to build the environment faster, please use Cachix.

2. Install Cachix

nix-env -iA cachix -f https://cachix.org/api/v1/install

3. Add caches for this project

cachix use all-hies
cachix use hercules-ci

Get started

1. Clone this repository

git clone https://github.com/GuillaumeDesforges/haskell-nix-dev-template.git
cd haskell-nix-dev-template

2. Build the environment for the first time
   • Wait for the build to complete. It can be very long but don't worry, it will work almost instantly next time.

nix-shell --run "echo Sucessfully built the environment"

3. Start VS Code

code .

4. Use Nix Environment Selector (bottom left of the VS Code window, in the toolbar) to select shell.nix as the environment.

   • Reload the VS Code window when asked (a notification will pop up at the bottom right of the window).

5. You can now create projects (Cabal packages) in the ./packages directory.

Repeat from step (2) when you add, remove or modify a .cabal file.

Configuration

Some parameters can be configured by editing the file ./nix/confgi.nix.

For now you can:

• Change the GHC version to use
  • Warning: check that this version is supported by nixpkgs and your IDE
• Select the IDE used
  • For now either ghcide (default) or HIE

Extra dependencies

In some cases, you might need to use Haskell packages that are not on Nixpkgs. This goes beyond the scope of this template. However here is some information to achieve that:

0. WARNING: You need to know how to write Nix expressions and how Haskell packages are built on Nixpkgs
1. Look here for a guide on how to write extra dependencies
2. Write those extra dependencies in the ./nix/extra-deps.nix file

Note: don't forget to add those dependencies in your .cabal file or else it won't be added.

Motivations

I found setting up a Haskell project way more complicated than nearly any modern language. I decided to make once and for all a way for beginners such as myself to start playing with Haskell quickly without spending so much time thinking about the IDE.

The philosophy

1. The development can be started after only a few commands in CLI.
2. Use Nix to handle packages (Haskell compiler, development tools).
3. Use Cabal for the Haskell package definition.
4. Use VS Code to write code.

Please note that this is not educational content.

It is not a reference, nor is it readable for a beginner in Nix. It just gets the job done enough in order to spend less time on setting up an environment as a beginner.

Credits

Huge credits to https://github.com/fghibellini/nix-haskell-monorepo/. You must go there if you want to go any futher into Haskell & Nix from this repo.