Overview of the Nix Language: Difference between revisions

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 This [[:Category:Discussion|discussion]] article covers the syntax, semantics, typing, compilation, tooling and libraries of the Nix Expression Language.
+== Language Overview ==
+''The Nix expression language is a pure, lazy, functional language. Purity means that operations in the language don't have side-effects (for instance, there is no variable assignment). Laziness means that arguments to functions are evaluated only when they are needed. Functional means that functions are “normal” values that can be passed around and manipulated in interesting ways. The language is not a full-featured, general purpose language. Its main job is to describe packages, compositions of packages, and the variability within packages.'' - From the  [https://nixos.org/nix/manual/#ch-expression-language nix manual].
+The language was designed especially for the [[Nix Package Manager]].
 == Learning the Nix language ==
-The [https://nixos.org/nix/manual/#ch-expression-language manual] provides a reference of the Nix language.
+The [https://nixos.org/nix/manual/#ch-expression-language manual] provides a '''reference''' of the Nix language. All language constructs you may use in nix are defined here, together with code snippets.
 [https://medium.com/@MrJamesFisher/nix-by-example-a0063a1a4c55 Nix By Example] is a step-by-step tutorial.
+The [https://nixos.org/nixos/nix-pills/index.html nix pills] also provide a lot of insight into the language and functional package management in general.
+=== Notable Language Constructs ===
+Nix looks a lot like JSON with functions but also provides a number of very specialized constructs which can help you build clean and easy to read expressions. In this sub-chapter the most notable constructs will be shown by example:
+==== <code>with</code> statement ====
+The <code>with</code> statement introduces the lexical scope of a set into the expression which follows.
+Common usages are:
+===== '''On top of expressions''' =====
+You will see the with statement a lot at the beginning of expression definition. Most of the time it is used to load the lib functions into the namespace for quick access.
+<syntaxHighlight lang=nix>
+{lib, ... }:
+with lib;
+{
+  options = {
+    networking.hosts = mkOption {
+      type = with types; attrsOf ( listOf str);
+      default = {};
+    };
+  };
+  ...
+}
+</syntaxHighlight>
+instead of:
+<syntaxHighlight lang=nix>
+{lib, ... }:
+{
+  options = {
+    networking.hosts = lib.mkOption {
+      type = lib.types.attrsOf ( lib.types.listOf lib.types.str);
+      default = {};
+    };
+  };
+  ...
+}
+</syntaxHighlight>
+===== '''In package input definitions''' =====
+<syntaxHighlight lang=nix>
+{pkgs}:
+{
+  ...
+  buildInputs = with pkgs; [ curl php coreutils procps ffmpeg ];
+}
+</syntaxHighlight>
+Instead of :
+<syntaxHighlight lang=nix>
+{pkgs}:
+{
+  ...
+  buildInputs = [ pkgs.curl pkgs.php pkgs.coreutils pkgs.procps pkgs.ffmpeg ];
+}
+</syntaxHighlight>
+===== '''In the package meta tag''' =====
+<syntaxHighlight lang=nix>
+{stdenv, ...}:
+{
+  ...
+  meta = with stdenv.lib; {
+    license = with licenses; [ lgp3 gpl3 ];
+    maintainers = with maintainers; [ adisbladis lassulus ];
+  };
+}
+</syntaxHighlight>
+Instead of :
+<syntaxHighlight lang=nix>
+{stdenv, ...}:
+{
+  ...
+  meta = {
+    license = [ stdenv.lib.licenses.lgp3 stdenv.lib.licenses.gpl3 ];
+    maintainers = [ stdenv.lib.maintainers.adisbladis stdenv.lib.maintainers.lassulus ];
+  };
+}
+</syntaxHighlight>
+==== <code>let ... in</code> statement ====
+TODO
+==== <code>inherit</code> statement ====
+TODO
+==== <code>rec</code> statement ====
+TODO
 == Syntax Highlighting/IDE Support ==
 Nix language has decent syntax highlighting (SH) support among popular code editors, but refactoring/autocomplete is still rare.
-see: [[Editor Modes for Nix Files]]
+Reference: [[Editor Modes for Nix Files]]
 [[Category:Discussion]]
 [[Category:Nix Language]]
 [[Category:Incomplete]]