#+Title: How I use nix
#+Author: Yann Esposito
#+Email: yann@esposito.host
#+Date: [2020-06-14 Sun]
#+KEYWORDS: nix, programming
#+DESCRIPTION: In this article I explain how I use nix.
#+DESCRIPTION: As a brew replacement, as home environment manager,
#+DESCRIPTION: to have reproductible dev environment.
#+LANGUAGE: en
#+LANG: en
#+OPTIONS: H:5 auto-id:t toc:nil
#+STARTUP: showeverything

In this article I'll explain how I use nix.
I don't use NixOS nor any Linux as my main desktop environment[fn:desktop].
Still I use [[https://nixos.org/nix][nix]] on a few mac computers.
It has multiple usages.

First, let's start by the bad news.
Recent macOS security policy made nix a bit harder to install on a mac.
See [[https://hydra.nixos.org/build/119559243/download/1/manual/#sect-macos-installation][macOS Installation instructions]].

Once you have nix installed you should update the nix-channel.
Mainly a nix-channels is where are the definitions of all the packages.
See [[https://hydra.nixos.org/build/119559243/download/1/manual/#sec-channels][nixOS documentation]].

** Home Manager
:PROPERTIES:
:CUSTOM_ID: home-manager
:END:

First, I use [[https://github.com/rycee/home-manager][home-manager]], it's first usage it to list a reproductible list
of application I need on all my desktop environments.
So i edit the file =~/.config/nixpkgs/home.nix=.
I provide a list of packages I want to have when I start a new shell.


#+begin_src nix
  home.packages = with pkgs; [
    # nix
    nix-prefetch-git
    lorri
    # emacs
    emacsMacport
    imagemagick
    gnupg
    # vim
    neovim
    # shell
    direnv
    fasd
    fd
    findutils
    fortune
    gawk
    git
    gitAndTools.diff-so-fancy
    graphviz
    htop
    httpie
    jq
    jwt-cli
    libressl
    mustache-go
    pandoc
    ripgrep
    rtv
    wakatime
    xpdf # pdftotext
    yadm
    youtube-dl
    # clojure
    leiningen
    boot
    adoptopenjdk-bin
    joker
    # Haskell
    ghc
    cabal-install
    (all-hies.selection
      { selector = p:
          { inherit (p) ghc865; };})
    # Common LISP
    sbcl
    # mails
    offlineimap
    notmuch
    msmtp
    gmailieer
    # docker
    docker-compose
    # weechat
    rel20weechat
    aspell
    aspellDicts.en
    aspellDicts.fr
  ];
#+end_src

There are a few noticiable artifact here:

The first one is ~rel20weechat~ is a very specify build of weechat with the
plugin I need. So here is the block I use:

#+begin_src nix
rel20 = import (fetchGit {
  name = "nixpkgs20";
  url = "https://github.com/NixOS/nixpkgs";
  # obtained via
  # git ls-remote https://github.com/NixOS/nixpkgs nixpkgs-20.03-darwin
  ref = "refs/heads/nixpkgs-20.03-darwin";
  rev = "58f884cd3d89f47672e649c6edfb2382d4afff6a";
}) {};
rel20weechat = rel20.weechat.override {
    configure = { availablePlugins, ... }: {
      # plugins = with availablePlugins; [ python perl guile ];
      scripts = with pkgs.weechatScripts; [ wee-slack ];
    };
  };
#+end_src

First ~rel20~ pin a nixpkgs some specific commit of nix packages.
Second, I overriden the default packages of the =weechat= package.

Another interresting one is this block:

#+begin_src nix
let
  ...
  rel19 = import (fetchGit {
    name = "nixpkgs19";
    url = "https://github.com/NixOS/nixpkgs";
    ref = "refs/heads/nixpkgs-19.09-darwin";
    rev = "2f9bafaca90acd010cccd0e79e5f27aa7537957e";
  }) {};
  haskellDeps = ps: with ps; [
    base
    protolude
    tidal
    shake
    rel19.haskellPackages.sws
    ];
  ghc = pkgs.haskellPackages.ghcWithPackages haskellDeps;
  ...
in
  home.packages = with pkgs; [
    ...
    ghc
    ...
  ]
#+end_src

So it means I want to install =ghc= the main Haskell compiler.
But also with some specific haskell packages.
The interresting part, is that in most classical OS environment if you want
a package from a specific language platform.
You need to install the package manager for this language (npm, pip,
etc...).
And in =nixpkgs= there are formulae for most of these language specific
packages.
So instead of just installing =cabal-install= and then installing the
packages I need.
Which could also go bad, because they might be upgraded and not be
compatible all at the same time.

I used nix to install the packages I needed.
And one interresting detail.
One package [[https://hackage.haskell.org/package/sws][=sws=]] is broken in 20.03 on darwin.
So I used the older version from 19.09.

[fn:desktop]: I'm using macOS, and I have multiple macs.
A laptop and two desktop machines.
Using the 27" iMac is my ultimate work station.
It really enhance my productivity.
Still the laptop is a superior work environment for more casual tasks.
I guess I might write someday about my full work environment.