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112 lines
3.6 KiB
Markdown
112 lines
3.6 KiB
Markdown
# Variables
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## Table of Contents
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* [Syntax](#syntax)
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* [Semantics](#semantics)
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* [Executing a Variable Declaration](#executing-a-variable-declaration)
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* [Evaluating a Variable](#evaluating-a-variable)
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## Syntax
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<!-- Escape the first `$` here due to DavidAnson/markdownlint#1262 -->
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<x><pre>
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**Variable** ::= PlainVariable | NamespacedVariable
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**PlainVariable** ::= '\$' [\<ident-token>]
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**NamespacedVariable** ::= [\<ident-token>] '.$' [PublicIdentifier]
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**VariableDeclaration** ::= Variable ':' Expression ('!global' | '!default')*
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</pre></x>
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[\<ident-token>]: https://drafts.csswg.org/css-syntax-3/#ident-token-diagram
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[PublicIdentifier]: modules.md#syntax
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No whitespace is allowed after the `$` in `PlainVariable` or before or after
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the `.$` in `NamespacedVariable`. Each of `!global` and `!default` is allowed
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at most once in `VariableDeclaration`. As with all statements, a
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`VariableDeclaration` must be separated from other statements with a semicolon.
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## Semantics
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### Executing a Variable Declaration
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To execute a `VariableDeclaration` `declaration`:
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* Let `value` be the result of evaluating `declaration`'s `Expression`.
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* Let `name` be `declaration`'s `Variable`.
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* Let `resolved` be the result of [resolving a variable] named `name`.
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[resolving a variable]: modules.md#resolving-a-member
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* If `name` is a `NamespacedVariable` and `declaration` has a `!global` flag,
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throw an error.
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* Otherwise, if `resolved` is a variable from a built-in module, throw an
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error.
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* Otherwise, if `declaration` is outside of any block of statements, *or*
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`declaration` has a `!global` flag, *or* `name` is a `NamespacedVariable`:
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* If `declaration` has a `!default` flag, `resolved` isn't null, *and*
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`resolved`'s value isn't null, do nothing.
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* Otherwise, if `resolved` is a variable in another module:
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* Evaluate `declaration`'s value and set `resolved`'s value to the result.
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* Otherwise:
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* If `declaration` is outside of any block of statements, it has a
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`!default` flag, *and* `config` contains a variable named `name` whose
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value is not null:
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* Let `value` be the value of `config`'s variable named `name`.
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* Otherwise, let `value` be the result of evaluating `declaration`'s value.
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* If `name` *doesn't* begin with `-` or `_`, add a variable with name `name`
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and value `value` to `module`.
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> This overrides the previous definition, if one exists.
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* Add a variable with name `name` and value `value` to `import`.
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> This also overrides the previous definition.
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* Otherwise, if `declaration` is within one or more blocks associated with
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`@if`, `@each`, `@for`, and/or `@while` rules *and no other blocks*:
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* If `resolved` is not null:
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* If `declaration` has a `!default` flag and `resolved`'s value isn't
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null, do nothing.
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* Otherwise, let `value` be the result of evaluating `declaration`'s value.
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* If `name` *doesn't* begin with `-` or `_`, add a variable with name `name`
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and value `value` to `module`.
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> This overrides the previous definition, if one exists.
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* Add a variable with name `name` and value `value` to `import`.
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> This also overrides the previous definition.
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* Otherwise, if `resolved` is null, set the [current scope]'s variable `name` to
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`value`.
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[current scope]: spec.md#scope
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* Otherwise, set `resolved`'s value to `value`.
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### Evaluating a Variable
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To evaluate a `Variable` `variable`:
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* Let `definition` be the result of [resolving a variable] named `variable`.
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If this returns null, throw an error.
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* Return `definition`'s value.
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