`haskell.nix` is infrastructure for building Haskell packages with Nix

haskell.nix can automatically translate your Cabal or Stack project and its dependencies into Nix code.

Documentation

Getting started

a) Using `cabal.project`

Add a default.nix:

let 
  # Fetch the latest haskell.nix and import its default.nix
  haskellNix = import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) {};

  # haskell.nix provides access to the nixpkgs pins which are used by our CI, hence
  # you will be more likely to get cache hits when using these.
  # But you can also just use your own, e.g. '<nixpkgs>'
  nixpkgsSrc = haskellNix.sources.nixpkgs-2003;

  # haskell.nix provides some arguments to be passed to nixpkgs, including some patches
  # and also the haskell.nix functionality itself as an overlay.
  nixpkgsArgs = haskellNix.nixpkgsArgs;
in
{ pkgs ? import nixpkgsSrc nixpkgsArgs
, haskellCompiler ? "ghc865"
}:

# 'cabalProject' generates a package set based on a cabal.project (and the corresponding .cabal files)
pkgs.haskell-nix.cabalProject {
  # 'cleanGit' cleans a source directory based on the files known by git
  src = pkgs.haskell-nix.haskellLib.cleanGit { name = "haskell-nix-project"; src = ./.; };
  compiler-nix-name = haskellCompiler;
}

Note that you'll need to add a comment specifying the expected sha256 output for your source-repository-packages in your cabal.project file:

source-repository-package
  type: git
  location: https://github.com/input-output-hk/iohk-monitoring-framework
  subdir:   plugins/backend-editor
  tag: 4956b32f039579a0e7e4fd10793f65b4c77d9044
  --sha256: 03lyb2m4i6p7rpjqarnhsx21nx48fwk6rzsrx15k6274a4bv0pix

b) Using `stack.yaml`

Add a default.nix:

let 
  haskellNix = import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) {};
  nixpkgsSrc = haskellNix.sources.nixpkgs-2003;
  nixpkgsArgs = haskellNix.nixpkgsArgs;
in
{ pkgs ? import nixpkgsSrc nixpkgsArgs
}:
pkgs.haskell-nix.stackProject {
  src = pkgs.haskell-nix.haskellLib.cleanGit { src = ./.; };
}

To build the library component of a package in the project run:

nix build -f . your-package-name.components.library

To build an executable:

nix build -f . your-package-name.components.exes.your-exe-name

To open a shell for use with cabal run:

nix-shell -A shellFor
cabal new-build your-package-name
cabal new-repl your-package-name:library:your-package-name

Using binary Cache to speed up compilation

To use precompiled binaries you'll need:

to configure a binary cache by following instructions on iohk.cachix.org.
to pin nixpkgs according to nix/sources.json.

Related repos

The haskell.nix repository contains the runtime system for building Haskell packages in Nix. It depends on other repos, which are:

nix-tools — provides the programs for generating Nix expressions from Haskell projects.
hackage.nix — the latest contents of the Hackage databases, converted to Nix expressions.
stackage.nix — all of the Stackage snapshots, converted to Nix expressions.

IRC Channel

Join the #haskell.nix channel on irc.freenode.net to get help or discuss the development of haskell.nix and nix-tools.

felixmulder/haskell.nix

haskell.nix is infrastructure for building Haskell packages with Nix