Merge pull request #6906 from fricklerhandwerk/language-overview

add syntax overview from NixOS manual

1 files changed, 548 insertions, 0 deletions

diff --git a/doc/manual/src/language/index.md b/doc/manual/src/language/index.md
index a4b402f8b..f9e9b9781 100644
--- a/doc/manual/src/language/index.md
+++ b/doc/manual/src/language/index.md
@@ -31,3 +31,551 @@ The Nix language is
 
   Type errors are only detected when expressions are evaluated.
 
+# Overview
+
+This is an incomplete overview of language features, by example.
+
+<table>
+ <tr>
+  <th>
+   Example
+  </th>
+  <th>
+   Description
+  </th>
+ </tr>
+ <tr>
+  <td>
+
+
+   *Basic values*
+
+
+  </td>
+  <td>
+
+
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `"hello world"`
+
+  </td>
+  <td>
+
+   A string
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   ```
+   ''
+     multi
+      line
+       string
+   ''
+   ```
+
+  </td>
+  <td>
+
+   A multi-line string. Strips common prefixed whitespace. Evaluates to `"multi\n line\n  string"`.
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `"hello ${ { a = "world" }.a }"`
+
+   `"1 2 ${3}"`
+
+   `"${pkgs.bash}/bin/sh"`
+
+  </td>
+  <td>
+
+   String interpolation (expands to `"hello world"`, `"1 2 3"`, `"/nix/store/<hash>-bash-<version>/bin/sh"`)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `true`, `false`
+
+  </td>
+  <td>
+
+   Booleans
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `null`
+
+  </td>
+  <td>
+
+   Null value
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `123`
+
+  </td>
+  <td>
+
+   An integer
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `3.141`
+
+  </td>
+  <td>
+
+   A floating point number
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `/etc`
+
+  </td>
+  <td>
+
+   An absolute path
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `./foo.png`
+
+  </td>
+  <td>
+
+   A path relative to the file containing this Nix expression
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `~/.config`
+
+  </td>
+  <td>
+
+   A home path. Evaluates to the `"<user's home directory>/.config"`.
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   <nixpkgs>
+
+  </td>
+  <td>
+
+   Search path. Value determined by [`$NIX_PATH` environment variable](../command-ref/env-common.md#env-NIX_PATH).
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   *Compound values*
+
+  </td>
+  <td>
+
+
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ x = 1; y = 2; }`
+
+  </td>
+  <td>
+
+   A set with attributes named `x` and `y`
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ foo.bar = 1; }`
+
+  </td>
+  <td>
+
+   A nested set, equivalent to `{ foo = { bar = 1; }; }`
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `rec { x = "foo"; y = x + "bar"; }`
+
+  </td>
+  <td>
+
+   A recursive set, equivalent to `{ x = "foo"; y = "foobar"; }`
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `[ "foo" "bar" "baz" ]`
+
+   `[ 1 2 3 ]`
+
+   `[ (f 1) { a = 1; b = 2; } [ "c" ] ]`
+
+  </td>
+  <td>
+
+   Lists with three elements.
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   *Operators*
+
+  </td>
+  <td>
+
+
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `"foo" + "bar"`
+
+  </td>
+  <td>
+
+   String concatenation
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `1 + 2`
+
+  </td>
+  <td>
+
+   Integer addition
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `"foo" == "f" + "oo"`
+
+  </td>
+  <td>
+
+   Equality test (evaluates to `true`)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `"foo" != "bar"`
+
+  </td>
+  <td>
+
+   Inequality test (evaluates to `true`)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `!true`
+
+  </td>
+  <td>
+
+   Boolean negation
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ x = 1; y = 2; }.x`
+
+  </td>
+  <td>
+
+   Attribute selection (evaluates to `1`)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ x = 1; y = 2; }.z or 3`
+
+  </td>
+  <td>
+
+   Attribute selection with default (evaluates to `3`)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ x = 1; y = 2; } // { z = 3; }`
+
+  </td>
+  <td>
+
+   Merge two sets (attributes in the right-hand set taking precedence)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   *Control structures*
+
+  </td>
+  <td>
+
+
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `if 1 + 1 == 2 then "yes!" else "no!"`
+
+  </td>
+  <td>
+
+   Conditional expression
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `assert 1 + 1 == 2; "yes!"`
+
+  </td>
+  <td>
+
+   Assertion check (evaluates to `"yes!"`).
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `let x = "foo"; y = "bar"; in x + y`
+
+  </td>
+  <td>
+
+   Variable definition
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `with builtins; head [ 1 2 3 ]`
+
+  </td>
+  <td>
+
+   Add all attributes from the given set to the scope (evaluates to `1`)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   *Functions (lambdas)*
+
+  </td>
+  <td>
+
+
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `x: x + 1`
+
+  </td>
+  <td>
+
+   A function that expects an integer and returns it increased by 1
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `x: y: x + y`
+
+  </td>
+  <td>
+
+   Curried function, equivalent to `x: (y: x + y)`. Can be used like a function that takes two arguments and returns their sum.
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `(x: x + 1) 100`
+
+  </td>
+  <td>
+
+   A function call (evaluates to 101)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `let inc = x: x + 1; in inc (inc (inc 100))`
+
+  </td>
+  <td>
+
+   A function bound to a variable and subsequently called by name (evaluates to 103)
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ x, y }: x + y`
+
+  </td>
+  <td>
+
+   A function that expects a set with required attributes `x` and `y` and concatenates them
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ x, y ? "bar" }: x + y`
+
+  </td>
+  <td>
+
+   A function that expects a set with required attribute `x` and optional `y`, using `"bar"` as default value for `y`
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ x, y, ... }: x + y`
+
+  </td>
+  <td>
+
+   A function that expects a set with required attributes `x` and `y` and ignores any other attributes
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `{ x, y } @ args: x + y`
+
+   `args @ { x, y }: x + y`
+
+  </td>
+  <td>
+
+   A function that expects a set with required attributes `x` and `y`, and binds the whole set to `args`
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   *Built-in functions*
+
+  </td>
+  <td>
+
+
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `import ./foo.nix`
+
+  </td>
+  <td>
+
+   Load and return Nix expression in given file
+
+  </td>
+ </tr>
+ <tr>
+  <td>
+
+   `map (x: x + x) [ 1 2 3 ]`
+
+  </td>
+  <td>
+
+   Apply a function to every element of a list (evaluates to `[ 2 4 6 ]`)
+
+  </td>
+ </tr>
+</table>