Haskell Horizon Platform

horizon-haskell.net.

Horizon is a haskell package set targetting new builds of GHC.

Getting started

You an can use this package set instead of your haskell packages set in nixpkgs. To see an example you can use the template supplied with this repository.

mkdir myProject
cd myProject
nix flake init -t 'git+https://gitlab.homotopic.tech/horizon/horizon-templates'

Updating the package set

The package set is generated from the horizon.dhall using the following command:

nix run .#horizon-gen-nix

This will generate both the packages folder and the package set file. If you want to regenerate a particular package in the packages folder, delete that file from the packages folder. To regenerate the entire package set from scratch, delete the packages folder.

If you need to do additional manual overrides to the nix code, such as addPkgconfigDepends, edit the configuration.nix overlay, which is applied afterwards.

Programmmatic Updates

The package set will be automatically loaded under the variable hz.

import Horizon.Spec.Utils

let f = L.at "lens" L..~ Just (callHackage "lens" "5.1")

:t f
f :: (L.IxValue t ~ HaskellPackage, L.At t,
      IsString (L.Index t)) =>
     t -> t

let hz' = f hz

H.writeHorizonFile hz'

Then remember to delete pkgs/lens.nix and re-run nix run .#horizon-gen-nix as usual.~

Package Set Policy

This package set has the following policy.

• GHC will advance as often as possible
• Nonversioned locations (git, unversioned tarballs) are permitted to allow GHC to advance.
• The following packages must always build:
  • aeson
  • beam-postgres
  • composite-base
  • dhall
  • haskell-language-server
  • hedgehog
  • pandoc
  • persistent-postgresql
  • polysemy
  • servant
  • sydtest
  • tasty
  • xmonad-contrib
  • xmonad
  • wai-app-static
  • warp
• Tags will be of the form unstable-<yyyy>-<mm>-<dd>-r<N> where any unversioned source is used.
• Tags will be of the form stable-<yyyy>-<mm>-<dd>-r<N> where all stable sources are used.

Commit Policy

• All commits should evaluate with nix flake show.
• All commits should pass all checks with nix flake check.
• All derivations in packages should build.
• Where possible, commits should be atomic, of the form
  • foo: init at
  • foo: ->
• If multiple packages need to be maintained in lockstep, the commit message should contain all changes.

ChangeLog Policy

• ChangeLogs should clearly show source stability changes between versions, of the form:
  • stabilized source: aeson, lens
  • destabilized source: pandoc