2023
vimjoyer - Nix Language Explained of 8:52
    https://www.youtube.com/watch?v=UgrwoAGSPOQ
    ! nix-instantiate --eval "...expr"
JakeHamilton - Nix From Nothing | Let's Learn Nix & NixOS! of 1:06:35
    https://www.youtube.com/watch?v=t8ydCYe9Y3M
    ! $ echo 42 > example.nix
    ! $ nix repl eval --file ./example.nix
    ! 42
    ! // attribute set
    ! { name = val; } 
    ! // lists are space-delimited
    ! [ 1 2 3 ]
    ! let mynumber = 42; in mynumber + 1
    ! let greet = name: "Hello, ${name}"; in greet "Chat"
    ! let greet = greeting: name: "${greeting}, ${name}"; in greet "Hello" "Chat"
    ! let
        makeSecret = { key, value, ... }: {
          mySuperSecretValue = value;
          ${key} = value;
          "user-${key}" = value;
          // value = value
          inherit value;
        };
      in
        makeSecret { key = "my_secret"; value = "super-secret"; }
    ! other-file.nix
    !   { greet = name: "Hello, ${name}!"; }
    ! example.nix
    ! let
        myLibrary = import ./other-file.nix;
      in
        myLibrary.greet "Chat"

    ! We can do the same thing with nix packages
    ! $ nix registry list
    ! $ echo $NIX_PATH
    !   /etc/nix/inputs (with the same stuff)

    ! let
        pkgs = import <nixpkgs>
      in
        pkgs
      ** brings <LAMBDA> **

    ! $cat /etc/nix/inputs/nixpkgs/default.nix

    ! let
        pkgs = import <nixpkgs> {}
      in
        pkgs.lib

    ! $ nix repl
    ! > pkgs = import <nixpkgs> {}
    ! > pkgs.lib
    ! ***
    ! builtins.derivation
    ! ...
    ! pkgs.lib.platform
    ! pkgs.lib.traceCall
    ! ...
    ! > builtins.attrNames pkgs.lib.platform
    ! ["aarch64" ...]

    ! cat example.nix
    ! builtins.derivation {
    !   name = "my-derivation";
    !   system = "x86_64-linux";
    !   builder = "/bin/sh";
    !   args = ["-c" "echo Hello > $out"];
    ! } 

    ! $ nix-instantiate ./example.nix
    ! /nix/store/...-my-derivation.drv
    ! $ cat /nix/store/...-my-derivation.drv
    ! Derive([("out","/nix/store/...-my-derivation","","")],[],[],"x86_64-linux","/bin/sh",["-c","echo Hello > $out"],[("builder")])...
    ! $ nix-store --realise /nix/store/...-my-derivation.drv
    ! ...
    ! /nix/store/...-my-derivation
    ! ** (without .drv suffix)
    ! $cat /nix/store/...-my-derivation
    ! Hello

    ! > :l <nixpkgs>
    ! > :e pkgs.runCommand

    ! cat example.nix
    ! let
    !   pkgs = import <nixpkgs> {};
    ! in
    !   pkgs.runCommand "my-derivation" {} ''
    !     echo Hello > $out
    ! ''
    ! $ nix build --file ./example.nix
    ! $ ls -la
    ! ...
    ! result -> /nix/store/...-my-derivation
    ! $ cat result
    ! Hello

    ! usually nixpkgs use a more fully-form wrapper with phases:
    ! cat example.nix
    ! let
    !   pkgs = import <nixpkgs> {};
    ! in
    !   pkgs.stdenv.mkDerivation {
    !     name = "my-derivation";
    !     src = ./.;
    !     installPhase = ''
    !       echo Hello > $out
    !     '';
    !   }
    !
    ! > modulea = { options.a.enable = lib.mkEnableOption "A"; }
    ! > result = lib.evalModules { modules = [ modulea ]; }
    ! > result
    ! > result.options
    ! > result.options.a
    ! > result.options.a.enable
    ! > moduleb = { options.b.enable = lib.mkEnableOption "B"; }
    ! > result = lib.evalModules { modules = [ modulea moduleb]; }

    ! > module = { options ... config { a.enable=true; }; ... }

    ! > modulec = { options.output = lib.mkOption { type = lib.types.str; }; }
    ! > result = lib.evalModules { modules = [ modulea moduleb modulec ]; }
    ! > moduleb = { config, ... }: { config = { output = "something"; }; }
    ! > result.config
    ! { a = { ... }; output = "something"; }
    ! > moduleb = { config, ... }: { config = lib.mkIf config.a.enabled { output = "something"; }; }
    ! > result.config
    ! ???

    ! cat example.nix
    ! let
    !   pkgs = import <nixpkgs> {};
    !   lib = pkgs.lib;
    ! in

2019
NixCon - Reading Nix Expression Zimbatm
    https://www.youtube.com/watch?v=61MuMY9XFNo
    https://zimbatm.com/talks/reading-nix-expressions/
NixCon - Nix - How and Why it Works
    https://www.youtube.com/watch?v=lxtHH838yko