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. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+ Example + + Description +
+ + + *Basic values* + + + + + + +
+ + `"hello world"` + + + + A string + +
+ + ``` + '' + multi + line + string + '' + ``` + + + + A multi-line string. Strips common prefixed whitespace. Evaluates to `"multi\n line\n string"`. + +
+ + `"hello ${ { a = "world" }.a }"` + + `"1 2 ${3}"` + + `"${pkgs.bash}/bin/sh"` + + + + String interpolation (expands to `"hello world"`, `"1 2 3"`, `"/nix/store/-bash-/bin/sh"`) + +
+ + `true`, `false` + + + + Booleans + +
+ + `null` + + + + Null value + +
+ + `123` + + + + An integer + +
+ + `3.141` + + + + A floating point number + +
+ + `/etc` + + + + An absolute path + +
+ + `./foo.png` + + + + A path relative to the file containing this Nix expression + +
+ + `~/.config` + + + + A home path. Evaluates to the `"/.config"`. + +
+ + + + + + Search path. Value determined by [`$NIX_PATH` environment variable](../command-ref/env-common.md#env-NIX_PATH). + +
+ + *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" "baz" ]` + + `[ 1 2 3 ]` + + `[ (f 1) { a = 1; b = 2; } [ "c" ] ]` + + + + Lists with three 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!"`). + +
+ + `let x = "foo"; y = "bar"; in x + y` + + + + Variable definition + +
+ + `with builtins; 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: y: x + y` + + + + Curried function, equivalent to `x: (y: x + y)`. Can be used like a function that takes two arguments and returns their sum. + +
+ + `(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` + + `args @ { x, y }: 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 ]`) + +