diff options
Diffstat (limited to 'nixos/doc/manual/configuration/summary.section.md')
| -rw-r--r-- | nixos/doc/manual/configuration/summary.section.md | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/nixos/doc/manual/configuration/summary.section.md b/nixos/doc/manual/configuration/summary.section.md new file mode 100644 index 00000000000..8abbbe257fd --- /dev/null +++ b/nixos/doc/manual/configuration/summary.section.md @@ -0,0 +1,46 @@ +# Syntax Summary {#sec-nix-syntax-summary} + +Below is a summary of the most important syntactic constructs in the Nix +expression language. It's not complete. In particular, there are many +other built-in functions. See the [Nix +manual](https://nixos.org/nix/manual/#chap-writing-nix-expressions) for +the rest. + +| Example | Description | +|-----------------------------------------------|--------------------------------------------------------------------------------------------------------------------| +| *Basic values* | | +| `"Hello world"` | A string | +| `"${pkgs.bash}/bin/sh"` | A string containing an expression (expands to `"/nix/store/hash-bash-version/bin/sh"`) | +| `true`, `false` | Booleans | +| `123` | An integer | +| `./foo.png` | A path (relative to the containing Nix expression) | +| *Compound values* | | +| `{ x = 1; y = 2; }` | A set with attributes named `x` and `y` | +| `{ foo.bar = 1; }` | A nested set, equivalent to `{ foo = { bar = 1; }; }` | +| `rec { x = "foo"; y = x + "bar"; }` | A recursive set, equivalent to `{ x = "foo"; y = "foobar"; }` | +| `[ "foo" "bar" ]` | A list with two elements | +| *Operators* | | +| `"foo" + "bar"` | String concatenation | +| `1 + 2` | Integer addition | +| `"foo" == "f" + "oo"` | Equality test (evaluates to `true`) | +| `"foo" != "bar"` | Inequality test (evaluates to `true`) | +| `!true` | Boolean negation | +| `{ x = 1; y = 2; }.x` | Attribute selection (evaluates to `1`) | +| `{ x = 1; y = 2; }.z or 3` | Attribute selection with default (evaluates to `3`) | +| `{ x = 1; y = 2; } // { z = 3; }` | Merge two sets (attributes in the right-hand set taking precedence) | +| *Control structures* | | +| `if 1 + 1 == 2 then "yes!" else "no!"` | Conditional expression | +| `assert 1 + 1 == 2; "yes!"` | Assertion check (evaluates to `"yes!"`). See [](#sec-assertions) for using assertions in modules | +| `let x = "foo"; y = "bar"; in x + y` | Variable definition | +| `with pkgs.lib; head [ 1 2 3 ]` | Add all attributes from the given set to the scope (evaluates to `1`) | +| *Functions (lambdas)* | | +| `x: x + 1` | A function that expects an integer and returns it increased by 1 | +| `(x: x + 1) 100` | A function call (evaluates to 101) | +| `let inc = x: x + 1; in inc (inc (inc 100))` | A function bound to a variable and subsequently called by name (evaluates to 103) | +| `{ x, y }: x + y` | A function that expects a set with required attributes `x` and `y` and concatenates them | +| `{ x, y ? "bar" }: x + y` | A function that expects a set with required attribute `x` and optional `y`, using `"bar"` as default value for `y` | +| `{ x, y, ... }: x + y` | A function that expects a set with required attributes `x` and `y` and ignores any other attributes | +| `{ x, y } @ args: x + y` | A function that expects a set with required attributes `x` and `y`, and binds the whole set to `args` | +| *Built-in functions* | | +| `import ./foo.nix` | Load and return Nix expression in given file | +| `map (x: x + x) [ 1 2 3 ]` | Apply a function to every element of a list (evaluates to `[ 2 4 6 ]`) | |