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diff --git a/doc/manual/src/language/index.md b/doc/manual/src/language/index.md index c4b3abf75..6c355d923 100644 --- a/doc/manual/src/language/index.md +++ b/doc/manual/src/language/index.md @@ -11,3 +11,309 @@ packages, compositions of packages, and the variability within packages. This section presents the various features of the language. +# 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. + +<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> + `"${pkgs.bash}/bin/sh"` + </td> + <td> + A string containing an expression (expands to `"/nix/store/hash-bash-version/bin/sh"`) + </td> + </tr> + <tr> + <td> + `true`, `false` + </td> + <td> + Booleans + </td> + </tr> + <tr> + <td> + `123` + </td> + <td> + An integer + </td> + </tr> + <tr> + <td> + `./foo.png` + </td> + <td> + A path (relative to the containing Nix expression) + </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" ]` + </td> + <td> + A list with two 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!"`). See [](#sec-assertions) for using assertions in modules + </td> + </tr> + <tr> + <td> + `let x = "foo"; y = "bar"; in x + y` + </td> + <td> + Variable definition + </td> + </tr> + <tr> + <td> + `with pkgs.lib; 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: 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` + </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> |