haskell.nix-cabal

Nix-based Haskell project template using haskell.nix

This template has support for:

• Building the project with Nix
• Entering a dev environment with Nix, which includes
  • GHC and cabal-install for the cabal command
  • All the projects Haskell dependencies
  • Haskell IDE Engine with a working Cabal version
  • An up-to-date local Hoogle database, usable by HIE
• Minimal compilation since most things are cached already

It uses the haskell.nix Haskell infrastructure for this.

Usage

Setting up the caches

To use this, you should first enable the necessary Nix caches so that most things don't have to be compiled. This is done using Cachix. If you don't have it already, you can install cachix with

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

After which you can enable the all-hies and iohk caches, both of which are recommended for this template:

$ cachix use all-hies
$ cachix use iohk

Entering the dev environment

This can be done either using nix-shell:

$ nix-shell
[nix-shell:~/all-hies/templates/haskell.nix-cabal]$

Or automatically when you enter the project directory using direnv or lorri (by running lorri init first). Note that entering the environment the first time will take quite some time due to how haskell.nix works.

After entering the environment you can use the standard cabal commands for interacting with the project. Note that these will use all dependencies from Nix:

$ cabal build   # building the project
$ cabal repl    # Getting a ghci repl
$ cabal run     # Running an executable

In this environment HIE is available, which you can verify works with the hie command:

$ hie
[...]
/home/infinisil/all-hies/templates/haskell.nix-cabal/Main.hs: OK

The easiest way to get your editor to find HIE is to just start it in this environment:

$ vim
$ emacs
$ code
$ sublime
$ atom

Note that you still need to set up the necessary editor extensions yourself. See here for how to do this

A local Hoogle database is also available with all the dependencies of the project, which is used by HIE. You can start a hoogle server using

$ hoogle server
Server started on port 8080
Reading log...0.00s
2020-07-25T01:29:13.173630988 - Server starting on port 8080 and host/IP HostAny

Building the project with Nix

This is done with just a nix-build in the root.

$ nix-build