termonad-with-packages.nix

# This file produces a wrapper around Termonad that will know where to find a
# GHC with the libraries needed to recompile its config file.
#
# This is not NixOS only; it should work with nix on any system.
#
# There are 4 different ways this file can be used.
#
# 1. build directly with `nix-build`
#
# This method allows you to build termonad from the command line with
# `nix-build`.  This is the easiest method.
#
# You can call `nix-build` like the following:
#
# $ nix-build .nix-helpers/termonad-with-packages.nix
#
# (This is the same as just calling `nix-build` on the `../default.nix` file.)
#
# This produces a `result` directory that contains the `termonad` exectuable as
# `result/bin/termonad`.
#
# By default, you will be able to use the Haskell packages `lens` and `colour`
# in your `~/.config/termonad/termonad.hs` configuration file.
#
# If you want to use alternative Haskell packages, you can specify them on the
# command line:
#
# $ nix-build .nix-helpers/termonad-with-packages.nix \
#     --arg extraHaskellPackages 'haskellPackages: [ haskellPackages.colour haskellPackages.lens haskellPackages.pipes ]'
#
# This will make sure you can also use the Haskell packages `lens`, `colour`, and `pipes` in your
# `~/.config/termonad/termonad.hs` file.  (Actually, if Termonad transitively
# depends on a library, you should be able to use it without having to specify
# it.  Although you shouldn't depend on this.)
#
# 2. install with `nix-env`
#
# `nix-env` can be used to install Termonad into your environment:
#
# $ nix-env --file .nix-helpers/termonad-with-packages.nix --install
#
# If you want to specify extra Haskell packages that you can use in your
# `~/.config/termonad/termonad.hs` file, you can call `nix-env` like the
# following:
#
# $ nix-env --file .nix-helpers/termonad-with-packages.nix --install \
#     --arg extraHaskellPackages 'haskellPackages: [ haskellPackages.colour haskellPackages.lens haskellPackages.pipes ]'
#
# 3. an overlay for your user
#
# Nix makes it easy to create overlays.  First, create the following file at
# `~/.config/nixpkgs/overlays/termonad.nix`:
#
# ```nix
# self: super:
# let extraHaskellPackages = hp: [ hp.colour hp.lens hp.MonadRandom ]; in
# { termonad = import /some/path/to/termonad/.nix-helpers/termonad-with-packages.nix { inherit extraHaskellPackages; };
# }
# ```
#
# Now Termonad can be installed through Nix's standard methods, including `nix-env`:
#
# $ nix-env --file '<nixpkgs>' --install --attr termonad
#
# 4. system-wide in /etc/nixos/configuration.nix
#
# You can set the `nixpkgs.overlays` attribute in your
# `/etc/nixos/configuration.nix` file just like in (3) above.
#
# ```nix
# { config, pkgs, ... }:
# {
#   nixpkgs.overlays = [ (import /home/youruser/.config/nixpkgs/overlays/termonad.nix) ];
# }
# ```
#
# You can also add Termonad directly to your system packages:
#
# ```nix
# { config, pkgs, ... }:
# {
#   environment.systemPackages = with pkgs; [
#     ...
#     (import /some/path/to/termonad/.nix-helpers/termonad-with-packages.nix { })
#     ...
#   ];
# }
# ```

let
  # Default Haskell packages that you can use in your Termonad configuration.
  # This is only used if the user doesn't specify the extraHaskellPackages
  # option.
  defaultPackages = haskellPackages: with haskellPackages; [
    colour
    lens
  ];
in

{ extraHaskellPackages ? defaultPackages
, compiler ? null
, nixpkgs ? null
}:

with (import ./nixpkgs.nix { inherit compiler nixpkgs; });

let
  ghcWithPackages = haskellPackages.ghcWithPackages;
  env = ghcWithPackages (self: [ self.termonad ] ++ extraHaskellPackages self);
in

stdenv.mkDerivation {
  name = "termonad-with-packages-${env.version}";
  nativeBuildInputs = [ makeWrapper ];
  buildCommand = ''
    mkdir -p $out/bin
    makeWrapper ${env}/bin/termonad $out/bin/termonad \
      --set NIX_GHC "${env}/bin/ghc"
  '';
  preferLocalBuild = true;
  allowSubstitutes = false;
}