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52 lines
1.6 KiB
Markdown
52 lines
1.6 KiB
Markdown
# Identifiers
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An *identifier* is an [ASCII](https://en.wikipedia.org/wiki/ASCII) character sequence that:
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- Starts with a letter (`a-z`, `A-Z`) or underscore (`_`)
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- Can contain any number of:
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- Letters (`a-z`, `A-Z`)
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- Digits (`0-9`)
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- Underscores (`_`)
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- Apostrophes (`'`)
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- Hyphens (`-`)
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- Is not one of the [keywords](#keywords)
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> **Syntax**
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>
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> *identifier* ~ `[A-Za-z_][A-Za-z0-9_'-]*`
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# Names
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A *name* can be written as an [identifier](#identifier) or a [string literal](./string-literals.md).
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> **Syntax**
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>
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> *name* → *identifier* | *string*
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Names are used in [attribute sets](./syntax.md#attrs-literal), [`let` bindings](./syntax.md#let-expressions), and [`inherit`](./syntax.md#inheriting-attributes).
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Two names are the same if they represent the same sequence of characters, regardless of whether they are written as identifiers or strings.
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# Keywords
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These keywords are reserved and cannot be used as [identifiers](#identifiers):
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- [`assert`](./syntax.md#assertions)
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- [`else`][if]
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- [`if`][if]
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- [`in`][let]
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- [`inherit`](./syntax.md#inheriting-attributes)
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- [`let`][let]
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- [`or`](./operators.md#attribute-selection) (see note)
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- [`rec`](./syntax.md#recursive-sets)
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- [`then`][if]
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- [`with`](./syntax.md#with-expressions)
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[if]: ./syntax.md#conditionals
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[let]: ./syntax.md#let-expressions
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> **Note**
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>
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> The Nix language evaluator currently allows `or` to be used as a name in some contexts, for backwards compatibility reasons.
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> Users are advised not to rely on this.
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>
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> There are long-standing issues with how `or` is parsed as a name, which can't be resolved without making a breaking change to the language.
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