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docs: add identifiers (#11174)

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* docs: add identifiers

* clarify attribute set notation and add examples

* add definition of names

Co-authored-by: Ryan Hendrickson <ryan.hendrickson@alum.mit.edu>
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Valentin Gagarin 2024-07-25 03:45:34 +02:00 • committed by GitHub
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doc/manual/src/language/syntax.md
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@ -247,37 +247,76 @@ Elements in a list can be accessed using [`builtins.elemAt`](./builtins.md#built
## Attribute Set {#attrs-literal}
An attribute set is a collection of name-value-pairs (called *attributes*) enclosed in curly brackets (`{ }`).
An attribute set is a collection of name-value-pairs called *attributes*.
An attribute name can be an identifier or a [string](#string).
An identifier must start with a letter (`a-z`, `A-Z`) or underscore (`_`), and can otherwise contain letters (`a-z`, `A-Z`), numbers (`0-9`), underscores (`_`), apostrophes (`'`), or dashes (`-`).
Attribute sets are written enclosed in curly brackets (`{ }`).
Attribute names and attribute values are separated by an equal sign (`=`).
Each value can be an arbitrary expression, terminated by a semicolon (`;`)
An attribute name is a string without context, and is denoted by a [name] (an [identifier](./identifiers.md#identifiers) or [string literal](#string-literal)).
[name]: ./identifiers.md#names
> **Syntax**
>
> *name* = *identifier* | *string* \
> *identifier* ~ `[a-zA-Z_][a-zA-Z0-9_'-]*`
Names and values are separated by an equal sign (`=`).
Each value is an arbitrary expression terminated by a semicolon (`;`).
> **Syntax**
>
> *attrset* = `{` [ *name* `=` *expr* `;` ]... `}`
> *attrset* → `{` { *name* `=` *expr* `;` } `}`
Attributes can appear in any order.
An attribute name may only occur once.
An attribute name may only occur once in each attribute set.
Example:
> **Example**
>
> This defines an attribute set with attributes named:
> - `x` with the value `123`, an integer
> - `text` with the value `"Hello"`, a string
> - `y` where the value is the result of applying the function `f` to the attribute set `{ bla = 456; }`
>
> ```nix
> {
> x = 123;
> text = "Hello";
> y = f { bla = 456; };
> }
> ```
```nix
{
x = 123;
text = "Hello";
y = f { bla = 456; };
}
```
Attributes in nested attribute sets can be written using *attribute paths*.
This defines a set with attributes named `x`, `text`, `y`.
> **Syntax**
>
> *attrset* → `{` { *attrpath* `=` *expr* `;` } `}`
An attribute path is a dot-separated list of [names][name].
> **Syntax**
>
> *attrpath* = *name* { `.` *name* }
<!-- -->
> **Example**
>
> ```nix
> { a.b.c = 1; a.b.d = 2; }
> ```
>
> {
> a = {
> b = {
> c = 1;
> d = 2;
> };
> };
> }
Attribute names can also be set implicitly by using the [`inherit` keyword](#inheriting-attributes).
> **Example**
>
> ```nix
> { inherit (builtins) true; }
> ```
>
> { true = true; }
Attributes can be accessed with the [`.` operator](./operators.md#attribute-selection).