Update 11-nix.qmd

11-nix.qmd

@@ -24,9 +24,10 @@ that Java is required and installs and configures it. It all just happens withou
 of Nix is that it is possible to pin a certain revision of the Nix packages’ repository (called nixpkgs) for our project. Pinning a revision 
 ensures that every package that Nix installs will always be at exactly the same versions, regardless of when in the future the packages get installed.
 
-With Nix, it is essentially possible to replace {renv} and Docker combined. If you need other tools or languages like Python or Julia, 
-this can also be done easily. Nix is available for Linux, macOS and Windows (via WSL2). Important remark: since using Nix on Windows
-must go through WSL, when we refer to "Linux" in the context of Nix, this includes Windows by default as well.
+With Nix, it is essentially possible to replace {renv} and Docker combined, or if you’re using mainly Python, you can replace `conda` or `requirements.txt`
+files. If you need other tools or languages like Python or Julia, this can also be done easily. Nix is available for Linux, macOS and Windows (via WSL2). 
+Important remark: since using Nix on Windows must go through WSL, when we refer to "Linux" in the context of Nix, this includes Windows by default as well.
+It is also possible to build multi-language environments, containing R and Python, a LaTeX distribution and packages and so on.
 
 ## The Nix programming language
 
@@ -53,8 +54,53 @@ For example,
 is the Nix expression that contains the derivation to build `quarto`. As you can see, the derivation uses the the pre-built Quarto binaries
 instead of building it from source. Adding packages to nixpkgs (or updating them) can be done by opening pull requests. For example, 
 [here](https://github.com/NixOS/nixpkgs/pull/259443)^[https://github.com/NixOS/nixpkgs/pull/259443] is a pull request to make Quarto
-available to all platforms (before this PR Quarto was only available for Linux).
+available to all platforms (before this PR Quarto was only available for Linux). PRs get reviewed and approuved by maintainers that also
+have the right to merge the PR into master. Once merged, the new or updated package is available for download.
+Because nixpkgs is a “just” Github repository, it is possible to use a specific commit hash to install the packages as they were at 
+a specific point in time. For example, if you use this commit, 7c9cc5a6e, you’ll get the packages as of the 19th of October 2023, 
+but if you used this one instead: 976fa3369, you’ll get packages from the 19th of August 2023. Using specific hashes is called
+"pinning" and you can read more about it [here](https://nixos.wiki/wiki/FAQ/Pinning_Nixpkgs). We will make extensive use of pinning.
 
-## The NixOS operating system
+## The NixOS operating system, Docker and Github Actions
+
+NixOS is a Linux distribution that uses the Nix package manager as its package manager. I won’t go into detail here, but you should know it 
+exists. What’s perhaps more interesting for our purposes is to use Nix within Docker. Because Nix can be installed as any other tool, you could
+very well build a Docker image that starts by installing Nix, and then uses Nix to install, in a reproducible manner, all the tools you need 
+for your project.
+
+There are also a series of Github Actions that you can use to install Nix on runners and build development environments. We will also look that.
+
+## A first Nix expression
+
+The following expression is the one that defines the development environment to build this book:
+
+```
+let
+ pkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/976fa3369d722e76f37c77493d99829540d43845.tar.gz") {};
+ rpkgs = builtins.attrValues {
+  inherit (pkgs.rPackages) quarto Ecdat devtools janitor plm pwt9 rio targets tarchetypes testthat tidyverse usethis formatR;
+};
+  tex = (pkgs.texlive.combine {
+  inherit (pkgs.texlive) scheme-small amsmath framed fvextra environ fontawesome5 orcidlink pdfcol tcolorbox tikzfill;
+});
+ system_packages = builtins.attrValues {
+  inherit (pkgs) R glibcLocalesUtf8 quarto;
+};
+  in
+  pkgs.mkShell {
+    LOCALE_ARCHIVE = if pkgs.system == "x86_64-linux" then  "${pkgs.glibcLocalesUtf8}/lib/locale/locale-archive" else "";
+    LANG = "en_US.UTF-8";
+    LC_ALL = "en_US.UTF-8";
+    LC_TIME = "en_US.UTF-8";
+    LC_MONETARY = "en_US.UTF-8";
+    LC_PAPER = "en_US.UTF-8";
+    LC_MEASUREMENT = "en_US.UTF-8";
+
+    buildInputs = [  rpkgs tex system_packages  ];
+      
+  }
+```
+
+I won’t go into much detail, but here are some pointers:
 
 ## The {rix} package